@article{nalband_sarker_khan_freytes_2023, title={Characterization and biological evaluation of a novel flavonoid-collagen antioxidant hydrogel with cytoprotective properties}, volume={9}, ISSN={["1552-4981"]}, DOI={10.1002/jbm.b.35321}, abstractNote={AbstractReactive oxygen species (ROS) play a critical and important role during wound healing but excess ROS at the wound site can lead to cellular damage and sub‐optimal healing. Minimizing oxidative damage to the wound site and any supplemental therapeutic cells can be achieved by delivering exogenous antioxidants. Collagen hydrogels are ideal wound care materials due to their biocompatibility, high water content, and porous, three‐dimensional architecture. Yet, they lack the inherent antioxidant activity that could help mitigate excess ROS at a wound site. This work formulates and evaluates the in vitro biocompatibility and antioxidant capabilities of collagen‐fibroblast hydrogels combined with the polyphenolic antioxidant luteolin. Collagen solutions mixed with luteolin readily assembled into robust hydrogels with increasing gel strength due to increasing concentrations of luteolin. SEM images confirmed a mean pore size of 2.2 μm and a drastically different macromolecular ultrastructure with extensive fine crosslinking relative to collagen. Adequate cell viability and metabolic activity of dermal fibroblasts cultured within the gels were measured across all formulations, resulting in higher antioxidant activity and more than double the protection to cells from oxidative damage than traditional collagen hydrogels. Given these results, luteolin‐collagen hydrogels demonstrate the potential for superior wound‐healing properties when compared to collagen alone.}, journal={JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART B-APPLIED BIOMATERIALS}, author={Nalband, Danielle M. and Sarker, Prottasha and Khan, Saad A. and Freytes, Donald O.}, year={2023}, month={Sep} }
 @article{biehl_colmon_timofeeva_gracioso martins_dion_peters_freytes_2023, title={Scalable and High-Throughput In Vitro Vibratory Platform for Vocal Fold Tissue Engineering Applications}, volume={10}, ISSN={["2306-5354"]}, url={https://www.mdpi.com/2306-5354/10/5/602}, DOI={10.3390/bioengineering10050602}, abstractNote={The vocal folds (VFs) are constantly exposed to mechanical stimulation leading to changes in biomechanical properties, structure, and composition. The development of long-term strategies for VF treatment depends on the characterization of related cells, biomaterials, or engineered tissues in a controlled mechanical environment. Our aim was to design, develop, and characterize a scalable and high-throughput platform that mimics the mechanical microenvironment of the VFs in vitro. The platform consists of a 24-well plate fitted with a flexible membrane atop a waveguide equipped with piezoelectric speakers which allows for cells to be exposed to various phonatory stimuli. The displacements of the flexible membrane were characterized via Laser Doppler Vibrometry (LDV). Human VF fibroblasts and mesenchymal stem cells were seeded, exposed to various vibratory regimes, and the expression of pro-fibrotic and pro-inflammatory genes was analyzed. Compared to current bioreactor designs, the platform developed in this study can incorporate commercial assay formats ranging from 6- to 96-well plates which represents a significant improvement in scalability. This platform is modular and allows for tunable frequency regimes.}, number={5}, journal={BIOENGINEERING-BASEL}, author={Biehl, Andreea and Colmon, Ramair and Timofeeva, Anastasia and Gracioso Martins, Ana Maria and Dion, Gregory R. and Peters, Kara and Freytes, Donald O.}, year={2023}, month={May} }
 @article{gaffney_fisher_freytes_2023, title={Tendon Extracellular Matrix Promotes Myotendinous Junction Protein Expression in Engineered Muscle Tissue under Both Static and Mechanically Stimulated Culture Conditions}, volume={2023}, ISSN={["1932-7005"]}, DOI={10.1155/2023/6658543}, abstractNote={Studying the crosstalk between the muscle and tendon tissue is an important yet understudied area in musculoskeletal research. In vitro models can help elucidate the function and repair of the myotendinous junction (MTJ) under static and dynamic culture conditions using engineered muscle tissues. The goal of this study was to culture engineered muscle tissues in a novel bioreactor in both static and mechanically stimulated cultures and evaluate the expression of MTJ-specific proteins within the muscle-tendon unit(paxillin and type XXII collagen). C2C12 myoblasts were seeded in hydrogels made from type I collagen ortendon-derived extracellular matrix (tECM) and allowed to form around movable anchors. Engineered tissues were allowed to form and stabilize for 10 days. After 10 days in the culture, stimulated cultures were cyclically stimulated for 3 hours per day for 2 and 4 weeks alongside static cultures. Strain values at the maximum displacement of the anchors averaged about 0.10, a target that has been shown to induce myogenic phenotype in C2C12s. Protein expression of paxillin after 2 weeks did not differ between hydrogel materials in static cultures but increased by 62% in tECM when mechanically stimulated. These differences continued after 4 weeks, with 31% and 57% increases in tECM tissues relative to type I collagen. Expression of type XXII collagen was similarly influenced by hydrogel material and culture conditions. Overall, this research combined a relevant microenvironment to study muscle and tendon interactions with a novel bioreactor to apply mechanical strain, an important regulator of the formation and maintenance of the native MTJ.}, journal={JOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE}, author={Gaffney, Lewis S. and Fisher, Matthew B. and Freytes, Donald O.}, year={2023}, month={Aug} }
 @article{biehl_martins_davis_sze_collins_mora-navarro_fisher_freytes_2022, title={Towards a standardized multi-tissue decellularization protocol for the derivation of extracellular matrix materials}, volume={12}, ISSN={["2047-4849"]}, DOI={10.1039/d2bm01012g}, abstractNote={This study represents the first proof-of-concept standardized automated multi-tissue decellularization protocol for the derivation of ECM biomaterials.}, journal={BIOMATERIALS SCIENCE}, author={Biehl, Andreea and Martins, Ana M. Gracioso M. and Davis, Zachary G. G. and Sze, Daphne and Collins, Leonard and Mora-Navarro, Camilo and Fisher, Matthew B. B. and Freytes, Donald O. O.}, year={2022}, month={Dec} }
 @article{detwiler_polkoff_gaffney_freytes_piedrahita_2022, title={Donor Age and Time in Culture Affect Dermal Fibroblast Contraction in an In Vitro Hydrogel Model}, volume={8}, ISSN={["1937-335X"]}, DOI={10.1089/ten.tea.2021.0217}, abstractNote={Current cellular hydrogel-based skin grafts composed of human dermal fibroblasts and a hydrogel scaffold tend to minimize contraction of full-thickness skin wounds and support skin regeneration. However, there has been no comparison between the sources of the dermal fibroblast used. Products using human adult or neonatal foreskin dermal fibroblasts are often expanded in vitro and used after multiple passages without a clear understanding of the effects of this initial production step on the quality and reproducibility of the cellular behavior. Based on the known effects of 2D tissue culture expansion on cellular proliferation and gene expression, we hypothesized that differences in donor age and time in culture may influence cellular properties and contractile behavior in a fibroblast-populated collagen matrix. Using porcine skin as a model based on its similarity to human skin in structure and wound healing properties, we isolated porcine dermal fibroblasts of three different donor ages for use in a 2D proliferation assay and in a 3D cell-populated collagen matrix contractility assay. In 2D cell culture, doubling time remained relatively consistent between all age groups from passage 1 to 6. In the contractility assays, fetal and neonatal groups contracted faster and generated more contractile force than the adult group at passage 1 in vitro. However, after five passages in culture, there was no difference in contractility between ages. These results show how cellular responses in a hydrogel scaffold differ based on donor age and time in culture in vitro, and suggest that consistency in the cellular component of bioengineered skin products could be beneficial in the biomanufacturing of consistent, reliable skin grafts and graft in vivo models. Future research and therapies using bioengineered skin grafts should consider how results may vary based on donor age and time in culture before seeding.}, journal={TISSUE ENGINEERING PART A}, author={Detwiler, Amber and Polkoff, Kathryn and Gaffney, Lewis and Freytes, Donald O. and Piedrahita, Jorge A.}, year={2022}, month={Aug} }
 @article{sarker_nalband_freytes_rojas_khan_2022, title={High-Axial-Aspect Tannic Acid Microparticles Facilitate Gelation and Injectability of Collagen-Based Hydrogels}, volume={10}, ISSN={["1526-4602"]}, url={https://doi.org/10.1021/acs.biomac.2c00916}, DOI={10.1021/acs.biomac.2c00916}, abstractNote={Injectable collagen-based hydrogels offer great promise for tissue engineering and regeneration, but their use is limited by poor mechanical strength. Herein, we incorporate tannic acid (TA) to tailor the rheology of the corresponding hydrogels while simultaneously adding the therapeutic benefits inherent to this polyphenolic component. TA in the solution form and needle-shaped TA microparticles are combined with collagen and the respective systems studied for their time-dependent sol-gel transitions (from storage to body temperatures, 4-37 °C) as a function of TA concentration. Compared to systems incorporating TA microparticles, those with dissolved TA, applied at a similar concentration, generate a less significant enhancement of the elastic modulus. Premature gelation at a low temperature and associated colloidal arrest of the system are proposed as a main factor explaining this limited performance. A higher yield stress (elastic stress method) is determined for systems loaded with TA microparticles compared to the system with dissolved TA. These results are interpreted in terms of the underlying interactions of TA with collagen, as probed by spectroscopy and isothermal titration calorimetry. Importantly, hydrogels containing TA microparticles show high cell viability (human dermal fibroblasts) and comparative cellular activity relative to the collagen-only hydrogel. Overall, composite hydrogels incorporating TA microparticles demonstrate a new, simple, and better-performance alternative to cell culturing and difficult implantation scenarios.}, journal={BIOMACROMOLECULES}, author={Sarker, Prottasha and Nalband, Danielle M. and Freytes, Donald O. and Rojas, Orlando J. and Khan, Saad A.}, year={2022}, month={Oct} }
 @article{gracioso martins_biehl_sze_freytes_2022, title={Bioreactors for Vocal Fold Tissue Engineering}, volume={28}, ISSN={["1937-3376"]}, DOI={10.1089/ten.teb.2020.0285}, abstractNote={It is estimated that almost one-third of the US population will be affected by a vocal fold (VF) disorder during their lifespan. Promising therapies to treat VF injury and scarring are mostly centered on VF tissue engineering strategies such as the injection of engineered biomaterials and cell therapy. VF tissue engineering, however, is a challenging field as the biomechanical properties, structure, and composition of the VF tissue change upon exposure to mechanical stimulation. As a result, the development of long-term VF treatment strategies relies on the characterization of engineered tissues under a controlled mechanical environment. In this review, we highlight the importance of bioreactors as a powerful tool for VF tissue engineering with a focus on the current state of the art of bioreactors designed to mimic phonation in vitro. We discuss the influence of the phonatory environment on the development, function, injury, and healing of the VF tissue and its importance for the development of efficient therapeutic strategies. A concise and comprehensive overview of bioreactor designs, principles, operating parameters, and scalability is presented. An in-depth analysis of VF bioreactor data to date reveals that mechanical stimulation significantly influences cell viability and the expression of pro-inflammatory and pro-fibrotic genes in vitro. Although the precision and accuracy of bioreactors contributes to generating reliable results, diverse gene expression profiles across the literature suggest that future efforts should focus on the standardization of bioreactor parameters to enable direct comparisons between studies.}, number={1}, journal={TISSUE ENGINEERING PART B-REVIEWS}, author={Gracioso Martins, Ana M. and Biehl, Andreea and Sze, Daphne and Freytes, Donald O.}, year={2022}, month={Feb}, pages={182–205} }
 @article{ozpinar_frey_arthur_mora-navarro_biehl_snider_cruse_freytes_2021, title={Dermal Extracellular Matrix-Derived Hydrogels as an In Vitro Substrate to Study Mast Cell Maturation}, volume={27}, ISSN={["1937-335X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85110277858&partnerID=MN8TOARS}, DOI={10.1089/ten.tea.2020.0142}, abstractNote={Mast cells (MCs) are pro-inflammatory tissue-resident immune cells that play a key role in inflammation. MCs circulate in peripheral blood as progenitors and undergo terminal differentiation in the tissue microenvironment where they can remain for many years. This in situ maturation results in tissue- and species-specific MC phenotypes, culminating in significant variability in response to environmental stimuli. There are many challenges associated with studying mature tissue-derived MCs, particularly in humans. In cases where cultured MCs are able to differentiate in two-dimensional in vitro cultures, there remains an inability for full maturation. Extracellular matrix (ECM) scaffolds provide for a more physiologically relevant environment for cells in vitro and have been shown to modulate the response of other immune cells such as T cells, monocytes, and macrophages. To improve current in vitro testing platforms of MCs and to assess future use of ECM scaffolds for MC regulation, we studied the in vitro response of human MCs cultured on decellularized porcine dermis hydrogels (dermis extracellular matrix hydrogel [dECM-H]). This study investigated the effect of dECM-H on cellular metabolic activity, cell viability, and receptor expression compared to collagen type I hydrogel (Collagen-H). Human MCs showed different metabolic activity when cultured in the dECM-H and also upregulated immunoglobulin E (IgE) receptors associated with MC maturation/activation compared to collagen type I. These results suggest an overall benefit in the long-term culture of human MCs in the dECM-H compared to Collagen-H providing important steps toward a model that is more representative of in vivo conditions. Mast cells (MCs) are difficult to culture in vitro as current culture conditions and substrates fail to promote similar phenotypic features observed in vivo. Extracellular matrix (ECM)-based biomaterials offer three-dimensional, tissue-specific environments that more closely resemble in vivo conditions. Our study explores the use of dermal ECM hydrogels for MC culture and shows significant upregulation of metabolic activity, cell viability, and gene expression of markers associated with MC maturation or activation compared to collagen type I-hydrogel and tissue culture plastic controls at 7 days. These results are among the first to describe MC behavior in response to ECM hydrogels.}, number={15-16}, journal={TISSUE ENGINEERING PART A}, author={Ozpinar, Emily W. and Frey, Ariana L. and Arthur, Greer K. and Mora-Navarro, Camilo and Biehl, Andreea and Snider, Douglas B. and Cruse, Glenn and Freytes, Donald O.}, year={2021}, month={Aug}, pages={1008–1022} }
 @article{gaffney_davis_mora-navarro_fisher_freytes_2021, title={Extracellular Matrix Hydrogels Promote Expression of Muscle-Tendon Junction Proteins}, volume={11}, ISSN={["1937-335X"]}, DOI={10.1089/ten.tea.2021.0070}, abstractNote={Muscle and tendon injuries are prevalent and range from minor sprains and strains to traumatic, debilitating injuries. However, the interactions between these tissues during injury and recovery remain unclear. Three-dimensional tissue models that incorporate both tissues and a physiologically relevant junction between muscle and tendon may help understand how the two tissues interact. Here, we use tissue specific extracellular matrix (ECM) derived from muscle and tendon to determine how cells of each tissue interact with the microenvironment of the opposite tissue, resulting in junction-specific features. The ECM materials were derived from the Achilles tendon and gastrocnemius muscle, decellularized, and processed to form tissue-specific pre-hydrogel digests. The ECM materials were unique in respect to protein composition and included many types of ECM proteins, not just collagens. After digestion and gelation, ECM hydrogels had similar complex viscosities that were less than type I collagen hydrogels at the same concentration. C2C12 myoblasts and tendon fibroblasts were cultured in tissue-specific ECM conditioned media or encapsulated in tissue-specific ECM hydrogels to determine cell–matrix interactions and the effects on a muscle–tendon junction marker, paxillin. The ECM conditioned media had only a minor effect on the upregulation of paxillin in cells cultured in monolayer. However, cells cultured within ECM hydrogels had 50–70% higher paxillin expression than cells cultured in type I collagen hydrogels. Contraction of the ECM hydrogels varied by the type of ECM used. Subsequent experiments with a varying density of type I collagen (and thus contraction) showed no correlation between paxillin expression and the amount of gel contraction, suggesting that a constituent of the ECM was the driver of paxillin expression in the ECM hydrogels. In addition, another junction marker, type XXII collagen, had similar expression patterns as paxillin, with smaller effect sizes. Using tissue-specific ECM allowed for the de-construction of the cell–matrix interactions similar to muscle–tendon junctions to study the expression of myotendinous junction-specific proteins. The muscle–tendon junction is an important feature of muscle–tendon units; however, despite crosstalk between the two tissue types, the junction is often overlooked in current research. Deconstructing the cell–matrix interactions will provide the opportunity to study significant junction-specific features and markers that should be included in tissue models of the muscle–tendon unit, while gaining a deeper understanding of the natural junction. This research aims at informing future methods to engineer a more relevant multi-tissue platform to study the muscle–tendon unit.}, journal={TISSUE ENGINEERING PART A}, author={Gaffney, Lewis S. and Davis, Zachary G. and Mora-Navarro, Camilo and Fisher, Matthew B. and Freytes, Donald O.}, year={2021}, month={Nov} }
 @article{martins_wilkins_ligler_daniele_freytes_2021, title={Microphysiological System for High-Throughput Computer Vision Measurement of Microtissue Contraction}, volume={6}, ISSN={["2379-3694"]}, DOI={10.1021/acssensors.0c02172}, abstractNote={The ability to measure microtissue contraction in vitro can provide important information when modeling cardiac, cardiovascular, respiratory, digestive, dermal, and skeletal tissues. However, measuring tissue contraction in vitro often requires the use of high number of cells per tissue construct along with time-consuming microscopy and image analysis. Here, we present an inexpensive, versatile, high-throughput platform to measure microtissue contraction in a 96-well plate configuration using one-step batch imaging. More specifically, optical fiber microprobes are embedded in microtissues, and contraction is measured as a function of the deflection of optical signals emitted from the end of the fibers. Signals can be measured from all the filled wells on the plate simultaneously using a digital camera. An algorithm uses pixel-based image analysis and computer vision techniques for the accurate multiwell quantification of positional changes in the optical microprobes caused by the contraction of the microtissues. Microtissue constructs containing 20,000-100,000 human ventricular cardiac fibroblasts (NHCF-V) in 6 mg/mL collagen type I showed contractile displacements ranging from 20-200 μm. This highly sensitive and versatile platform can be used for the high-throughput screening of microtissues in disease modeling, drug screening for therapeutics, physiology research, and safety pharmacology.}, number={3}, journal={ACS SENSORS}, author={Martins, Ana Maria Gracioso and Wilkins, Michael D. and Ligler, Frances S. and Daniele, Michael A. and Freytes, Donald O.}, year={2021}, month={Mar}, pages={985–994} }
 @article{mora-navarro_garcia_sarker_ozpinar_enders_khan_branski_freytes_2022, title={Monitoring decellularization via absorbance spectroscopy during the derivation of extracellular matrix scaffolds}, volume={17}, ISSN={["1748-605X"]}, url={https://doi.org/10.1088/1748-605X/ac361f}, DOI={10.1088/1748-605X/ac361f}, abstractNote={Abstract
               Extracellular matrix (ECM) is a complex structure composed of bioactive molecules representative of the local tissue microenvironment. Decellularized ECM biomaterials harness these biomolecules for regenerative medicine applications. One potential therapeutic application is the use of vocal fold (VF) specific ECM to restore the VFs after injury. ECM scaffolds are derived through a process of decellularization, which aims to remove unwanted immunogenic biomolecules (e.g. DNA) while preserving the composition of the ECM. The effectiveness of the decellularization is typically assessed at the end by quantifying ECM attributes such as final dsDNA content. However, batch-to-batch variability in ECM manufacturing remains a significant challenge for the standardization, cost-effectiveness, and scale-up process. The limited number of tools available for in-process control heavily restricts the uncovering of the correlations between decellularization process parameters and ECM attributes. In this study, we developed a technique applicable to both the classical batch method and semi-continuous decellularization systems to trace the decellularization of two laryngeal tissues in real-time. We hypothesize that monitoring the bioreactor’s effluent absorbance at 260 nm as a function of time will provide a representative DNA release profile from the tissue and thus allow for process optimization. The DNA release profiles were obtained for laryngeal tissues and were successfully used to optimize the derivation of VF lamina propria-ECM (auVF-ECM) hydrogels. This hydrogel had comparable rheological properties to commonly used biomaterials to treat VF injuries. Also, the auVF-ECM hydrogel promoted the down-regulation of CCR7 by THP-1 macrophages upon lipopolysaccharide stimulation in vitro suggesting some anti-inflammatory properties. The results show that absorbance profiles are a good representation of DNA removal during the decellularization process thus providing an important tool to optimize future protocols.}, number={1}, journal={BIOMEDICAL MATERIALS}, publisher={IOP Publishing}, author={Mora-Navarro, Camilo and Garcia, Mario E. and Sarker, Prottasha and Ozpinar, Emily W. and Enders, Jeffrey R. and Khan, Saad and Branski, Ryan C. and Freytes, Donald O.}, year={2022}, month={Jan} }
 @article{mora-navarro_ozpinar_sze_martin_freytes_2021, title={Transcriptome-targeted analysis of human peripheral blood-derived macrophages when cultured on biomaterial meshes}, volume={16}, ISSN={["1748-605X"]}, url={http://dx.doi.org/10.1088/1748-605x/abdbdb}, DOI={10.1088/1748-605X/abdbdb}, abstractNote={Abstract
               Surgical meshes are commonly used to repair defects and support soft tissues. Macrophages (Mφs) are critical cells in the wound healing process and are involved in the host response upon foreign biomaterials. There are various commercially available permanent and absorbable meshes used by surgeons for surgical interventions. Polypropylene (PP) meshes represent a permanent biomaterial that can elicit both inflammatory and anti-inflammatory responses. In contrast, poly-4-hydroxybutyrate (P4HB) based meshes are absorbable and linked to positive clinical outcomes but have a poorly characterized immune response. This study evaluated the in vitro targeted transcriptomic response of human Mφs seeded for 48 h on PP and P4HB surgical meshes. The in vitro measured response from human Mφs cultured on P4HB exhibited inflammatory and anti-inflammatory gene expression profiles typically associated with wound healing, which aligns with in vivo animal studies from literature. The work herein provides in vitro evidence for the early transcriptomic targeted signature of human Mφs upon two commonly used surgical meshes. The findings suggest a transition from an inflammatory to a non-inflammatory phenotype by P4HB as well as an upregulation of genes annotated under the pathogen response pathway.}, number={2}, journal={BIOMEDICAL MATERIALS}, publisher={IOP Publishing}, author={Mora-Navarro, Camilo and Ozpinar, Emily W. and Sze, Daphne and Martin, David P. and Freytes, Donald O.}, year={2021}, month={Mar} }
 @article{ozpinar_frey_cruse_freytes_2021, title={Mast Cell-Biomaterial Interactions and Tissue Repair}, volume={27}, ISSN={["1937-3376"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85122126010&partnerID=MN8TOARS}, DOI={10.1089/ten.teb.2020.0275}, abstractNote={Tissue engineers often use biomaterials to provide structural support along with mechanical and chemical signals to modulate the wound healing process. Biomaterials that are implanted into the body interact with a heterogeneous and dynamic inflammatory environment that is present at the site of injury. Whether synthetically-derived, naturally-derived, or a combination of both, it is important to assess biomaterials for their ability to modulate inflammation in order to understand their potential clinical use. One important, but under-explored cell in the context of biomaterials is the mast cell (MC). MCs are granulocytic leukocytes that engage in a variety of events in both the innate and adaptive immune systems. Though highly recognized for their roles in allergic reactions, MCs play an important role in wound healing by recognizing antigens through pattern recognition receptors and the high-affinity immunoglobulin E (IgE) receptor, FcεRI, and releasing granules that affect cell recruitment, fibrosis, extracellular matrix deposition, angiogenesis, and vasculogenesis. MCs also mediate the foreign body response, contributing to the incorporation or rejection of implants. Studies of MC-biomaterial interactions can aid in the elucidation of MC roles during the host tissue response. This review is designed for those in the tissue engineering and biomaterials fields who are interested in exploring the role MCs may play in wound-biomaterial interactions and wound healing. With this review, we hope to inspire more research in the MC-biomaterial space in order to accelerate the design and construction of optimized implants.}, number={6}, journal={TISSUE ENGINEERING PART B-REVIEWS}, author={Ozpinar, Emily W. and Frey, Ariana L. and Cruse, Glenn and Freytes, Donald O.}, year={2021}, month={Dec}, pages={590–603} }
 @article{day_schneible_young_pozdin_driessche_gaffney_prodromou_freytes_fourches_daniele_et al._2020, title={Photoinduced reconfiguration to control the protein-binding affinity of azobenzene-cyclized peptides}, volume={8}, ISSN={["2050-7518"]}, DOI={10.1039/d0tb01189d}, abstractNote={Light-controlled switching of cell-binding activity of fluorescently-labeled peptides for on-demand cell labeling.}, number={33}, journal={JOURNAL OF MATERIALS CHEMISTRY B}, author={Day, Kevin and Schneible, John D. and Young, Ashlyn T. and Pozdin, Vladimir A. and Driessche, George and Gaffney, Lewis A. and Prodromou, Raphael and Freytes, Donald O. and Fourches, Denis and Daniele, Michael and et al.}, year={2020}, month={Sep}, pages={7413–7427} }
 @article{nandi_sommerville_nellenbach_mihalko_erb_freytes_hoffman_monroe_brown_2020, title={Platelet-like particles improve fibrin network properties in a hemophilic model of provisional matrix structural defects}, volume={577}, ISSN={0021-9797}, url={http://dx.doi.org/10.1016/j.jcis.2020.05.088}, DOI={10.1016/j.jcis.2020.05.088}, abstractNote={Following injury, a fibrin-rich provisional matrix is formed to stem blood loss and provide a scaffold for infiltrating cells, which rebuild the damaged tissue. Defects in fibrin network formation contribute to impaired healing outcomes, as evidenced in hemophilia. Platelet-fibrin interactions greatly influence fibrin network structure via clot contraction, which increases fibrin density over time. Previously developed hemostatic platelet-like particles (PLPs) are capable of mimicking platelet functions including binding to fibrin fibers, augmenting clotting, and inducing clot retraction. In this study, we aimed to apply PLPs within a plasma-based in vitro hemophilia B model of deficient fibrin network structure to determine the ability of PLPs to improve fibrin structure and wound healing responses within hemophilia-like abnormal fibrin network formation. PLP impact on structurally deficient clot networks was assessed via confocal microscopy, a micropost deflection model, atomic force microscopy and an in vitro wound healing model of early cell migration within a provisional fibrin matrix. PLPs improved clot network density, force generation, and stiffness, and promoted fibroblast migration within an in vitro model of early wound healing under hemophilic conditions, indicating that PLPs could provide a biomimetic platform for improving wound healing events in disease conditions that cause deficient fibrin network formation.}, journal={Journal of Colloid and Interface Science}, publisher={Elsevier BV}, author={Nandi, Seema and Sommerville, Laura and Nellenbach, Kimberly and Mihalko, Emily and Erb, Mary and Freytes, Donald O. and Hoffman, Maureane and Monroe, Dougald and Brown, Ashley C.}, year={2020}, month={Oct}, pages={406–418} }
 @article{liang_huang_su_li_hu_dinh_wrona_shao_qiao_vandergriff_et al._2018, title={Mesenchymal Stem Cell/Red Blood Cell-Inspired Nanoparticle Therapy in Mice with Carbon Tetrachloride-Induced Acute Liver Failure}, volume={12}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/ACSNANO.8B00553}, DOI={10.1021/ACSNANO.8B00553}, abstractNote={Acute liver failure is a critical condition characterized by global hepatocyte death and often time needs a liver transplantation. Such treatment is largely limited by donor organ shortage. Stem cell therapy offers a promising option to patients with acute liver failure. Yet, therapeutic efficacy and feasibility are hindered by delivery route and storage instability of live cell products. We fabricated a nanoparticle that carries the beneficial regenerative factors from mesenchymal stem cells and further coated it with the membranes of red blood cells to increase blood stability. Unlike uncoated nanoparticles, these particles promote liver cell proliferation in vitro and have lower internalization by macrophage cells. After intravenous delivery, these artificial stem cell analogs are able to remain in the liver and mitigate carbon tetrachloride-induced liver failure in a mouse model, as gauged by histology and liver function test. Our technology provides an innovative and off-the-shelf strategy to treat liver failure.}, number={7}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Liang, Hongxia and Huang, Ke and Su, Teng and Li, Zhenhua and Hu, Shiqi and Dinh, Phuong-Uyen and Wrona, Emily A. and Shao, Chen and Qiao, Li and Vandergriff, Adam C. and et al.}, year={2018}, month={Jun}, pages={6536–6544} }
 @article{nandi_sproul_nellenbach_erb_gaffney_freytes_brown_2019, title={Platelet-like particles dynamically stiffen fibrin matrices and improve wound healing outcomes}, volume={7}, ISSN={2047-4830 2047-4849}, url={http://dx.doi.org/10.1039/C8BM01201F}, DOI={10.1039/c8bm01201f}, abstractNote={PLPs increase fibrin stiffness, promote cell migration, and improve healing outcomes.}, number={2}, journal={Biomaterials Science}, publisher={Royal Society of Chemistry (RSC)}, author={Nandi, Seema and Sproul, Erin P. and Nellenbach, Kimberly and Erb, Mary and Gaffney, Lewis and Freytes, Donald O. and Brown, Ashley C.}, year={2019}, pages={669–682} }
 @article{douvaras_sun_wang_kruglikov_lallos_zimmer_terrenoire_zhang_gandy_schadt_et al._2017, title={Directed Differentiation of Human Pluripotent Stem Cells to Microglia}, volume={8}, ISSN={["2213-6711"]}, DOI={10.1016/j.stemcr.2017.04.023}, abstractNote={<h2>Summary</h2> Microglia, the immune cells of the brain, are crucial to proper development and maintenance of the CNS, and their involvement in numerous neurological disorders is increasingly being recognized. To improve our understanding of human microglial biology, we devised a chemically defined protocol to generate human microglia from pluripotent stem cells. Myeloid progenitors expressing CD14/CX3CR1 were generated within 30 days of differentiation from both embryonic and induced pluripotent stem cells (iPSCs). Further differentiation of the progenitors resulted in ramified microglia with highly motile processes, expressing typical microglial markers. Analyses of gene expression and cytokine release showed close similarities between iPSC-derived (iPSC-MG) and human primary microglia as well as clear distinctions from macrophages. iPSC-MG were able to phagocytose and responded to ADP by producing intracellular Ca<sup>2+</sup> transients, whereas macrophages lacked such response. The differentiation protocol was highly reproducible across several pluripotent stem cell lines.}, number={6}, journal={STEM CELL REPORTS}, author={Douvaras, Panagiotis and Sun, Bruce and Wang, Minghui and Kruglikov, Ilya and Lallos, Gregory and Zimmer, Matthew and Terrenoire, Cecile and Zhang, Bin and Gandy, Sam and Schadt, Eric and et al.}, year={2017}, month={Jun}, pages={1516–1524} }
 @article{choi_an_shin_kim_lim_2018, title={Enhanced tissue remodelling efficacy of adipose-derived mesenchymal stem cells using injectable matrices in radiation-damaged salivary gland model}, volume={12}, ISSN={["1932-7005"]}, DOI={10.1002/term.2460}, abstractNote={One of the main efforts in myocardial tissue engineering is towards designing cardiac tissues able to rescue the reduction in heart function once implanted at the site of myocardial infarction. To date, the efficiency of this approach in preclinical applications is limited in part by our incomplete understanding of the inflammatory environment known to be present at the site of myocardial infarct and by poor vascularization. It was recently reported that polarized macrophages known to be present at the site of myocardial infarction secrete bone morphogenetic proteins (BMPs)‐2 and ‐4 causing changes in the expression of cardiac proteins in a 2D in vitro model. Here, these findings were extended towards cardiac tissues composed of human embryonic stem cell derived cardiomyocytes embedded in collagen gel. By preconditioning cardiac tissues with BMPs, constructs were obtained with enhanced expression of cardiac markers. Additionally, after BMP preconditioning, the resulting cardiac‐tissues were able to sustain diffusion of the BMPs with the added benefit of supporting human umbilical vein endothelial cell tube formation. Here, a model is proposed of cardiac tissues preconditioned with BMPs that results in stimulation of cardiomyocyte function and diffusion of BMPs able to support angiogenesis. This platform represents a step towards the validation of more complex bioengineered constructs for in vivo applications.}, number={2}, journal={JOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE}, author={Choi, Jeong-Seok and An, Hye-Young and Shin, Hyun-Soo and Kim, Young-Mo and Lim, Jae-Yol}, year={2018}, month={Feb}, pages={E695–E706} }
 @article{gaffney_warren_wrona_fisher_freytes_2017, title={Macrophages' role in tissue disease and regeneration}, volume={62}, journal={Macrophages: origin, functions and biointervention}, author={Gaffney, L. and Warren, P. and Wrona, E. A. and Fisher, M. B. and Freytes, D. O.}, year={2017}, pages={245–271} }
 @misc{gaffney_wrona_freytes_2018, title={Potential Synergistic Effects of Stem Cells and Extracellular Matrix Scaffolds}, volume={4}, ISSN={["2373-9878"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85045213284&partnerID=MN8TOARS}, DOI={10.1021/acsbiomaterials.7b00083}, abstractNote={In recent years, extracellular matrix (ECM)-derived biomaterials have been used as scaffolds to help regenerate diseased or damaged tissues. These biomaterials are prepared by decellularization of a tissue of interest by chemical or physical removal of the cellular components. The goal of the decellularization process is to remove cells without disturbing tissue-specific composition, growth factor content, and, in some cases, the mechanical properties. As decellularization can be achieved without significantly affecting the native architecture of the tissue or organ of interest, it provides a scaffold material with native-like composition and structure. ECM scaffolds promote constructive remodeling through several mechanisms that include chemotactic properties, growth factor release, and modulation of the immune response. Constructive remodeling by ECM scaffolds relies, in part, on the recruitment of neighboring or circulating cells to the wound site. However, this is a relatively lengthy process, and the...}, number={4}, journal={ACS BIOMATERIALS SCIENCE & ENGINEERING}, author={Gaffney, Lewis and Wrona, Emily A. and Freytes, Donald O.}, year={2018}, month={Apr}, pages={1208–1222} }
 @misc{wrona_peng_amin_branski_freytes_2016, title={Extracellular Matrix for Vocal Fold Lamina Propria Replacement: A Review}, volume={22}, ISSN={["1937-3376"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85020490144&partnerID=MN8TOARS}, DOI={10.1089/ten.teb.2016.0015}, abstractNote={The vocal folds (VFs) are exposed to a number of injurious stimuli that frequently lead to aberrant structural alterations and altered biomechanical properties that clinically manifest as voice disorders. Therapies to restore both structure and function of this delicate tissue are ideal. However, such methods have not been adequately developed. Our group and others hypothesize that tissue engineering and regenerative medicine approaches, previously described for other tissue systems, hold significant promise for the VFs. In this review, we explore the concept of tissue engineering as it relates to the VFs, as well as recent studies employing both naturally and synthetically derived biomaterials, including those from laryngeal and nonlaryngeal sources, in combination with stem cells for a tissue-engineered approach to VF repair.}, number={6}, journal={TISSUE ENGINEERING PART B-REVIEWS}, author={Wrona, Emily A. and Peng, Robert and Amin, Milan R. and Branski, Ryan C. and Freytes, Donald O.}, year={2016}, month={Dec}, pages={421–429} }
 @article{witherel_graney_freytes_weingarten_spiller_2016, title={Response of human macrophages to wound matrices in vitro}, volume={24}, ISSN={["1524-475X"]}, DOI={10.1111/wrr.12423}, abstractNote={AbstractChronic wounds remain a major burden to the global healthcare system. Myriad wound matrices are commercially available but their mechanisms of action are poorly understood. Recent studies have shown that macrophages are highly influenced by their microenvironment, but it is not known how different biomaterials affect this interaction. Here, it was hypothesized that human macrophages respond differently to changes in biomaterial properties in vitro with respect to phenotype, including pro‐inflammatory M1, anti‐inflammatory M2a, known for facilitating extracellular matrix deposition and proliferation, and M2c, which has recently been associated with tissue remodeling. Using multiple donors, it was found that collagen scaffolds cross‐linked with 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide and N‐hydroxysuccinimide (EDC/NHS) promoted the least inflammatory phenotype in primary human macrophages compared with scaffolds cross‐linked with formaldehyde or glutaraldehyde. Importantly, gene expression analysis trends were largely conserved between donors, especially TNFa (M1), CCL22 (M2a), and MRC1 (M2a). Then the response of primary and THP1 monocyte‐derived macrophages to four commercially available wound matrices were compared—Integra Dermal Regeneration Template (Integra), PriMatrix Dermal Repair Scaffold (PriMatrix), AlloMend Acellular Dermal Matrix (AlloMend), and Oasis Wound Matrix (Oasis). Gene expression trends were different between primary and THP1 monocyte‐derived macrophages for all six genes analyzed in this study. Finally, the behavior of primary macrophages cultured onto the wound matrices over time was analyzed. Integra and Oasis caused down‐regulation of M2a markers CCL22 and TIMP3. PriMatrix caused up‐regulation of TNFa (M1) and CD163 (M2c) and down‐regulation of CCL22 and TIMP3 (both M2a). AlloMend caused up‐regulation in CD163 (M2c). Lastly, Oasis promoted the largest increase in the combinatorial M1/M2 score, defined as the sum of M1 genes divided by the sum of M2 genes. This preliminary study suggested that biomaterials influenced the wound microenvironment to affect macrophage phenotype.}, number={3}, journal={WOUND REPAIR AND REGENERATION}, author={Witherel, Claire E. and Graney, Pamela L. and Freytes, Donald O. and Weingarten, Michael S. and Spiller, Kara L.}, year={2016}, pages={514–524} }
 @article{pallotta_sun_wrona_freytes_2017, title={BMP protein-mediated crosstalk between inflammatory cells and human pluripotent stem cell-derived cardiomyocytes}, volume={11}, ISSN={1932-6254}, url={http://dx.doi.org/10.1002/TERM.2045}, DOI={10.1002/TERM.2045}, abstractNote={Following cardiac injury, the ischaemic heart tissue is characterized by the invasion of pro‐inflammatory (M1) and pro‐healing (M2) macrophages. Any engineered cardiac tissue will inevitably interact with the inflammatory environment found at the site of myocardial infarction at the time of implantation. However, the interactions between the inflammatory and the cardiac repair cells remain poorly understood. Here we recapitulated in vitro some of the important cellular events found at the site of myocardial injury, such as macrophage recruitment and their effect on cardiac differentiation and maturation, by taking into account the involvement of paracrine‐mediated signalling. By using a 3D inverted invasion assay, we found that cardiomyocyte (CM) conditioned medium can trigger the recruitment of pro‐inflammatory (M1) macrophages, through a mechanism that involves, in part, CM‐derived BMP4. Pro‐inflammatory (M1) macrophages were also found to affect CM proliferation and differentiation potential, in part due to BMP molecules secreted by macrophages. These effects involved the activation of the canonical outside‐in signalling pathways, such as SMAD1,5,8, which are known to be activated during myocardial injury in vivo. In the present study we propose a new role for CM‐ and macrophage‐derived BMP proteins during the recruitment of macrophage subtypes and the maturation of repair cells, representing an important step towards creating a functional cardiac patch with superior therapeutic properties. Copyright © 2015 John Wiley & Sons, Ltd.}, number={5}, journal={Journal of Tissue Engineering and Regenerative Medicine}, publisher={Wiley}, author={Pallotta, Isabella and Sun, Bruce and Wrona, Emily A. and Freytes, Donald O.}, year={2017}, month={May}, pages={1466–1478} }
 @article{reeves_spiller_freytes_vunjak-novakovic_kaplan_2015, title={Controlled release of cytokines using silk-biomaterials for macrophage polarization}, volume={73}, ISSN={0142-9612}, url={http://dx.doi.org/10.1016/J.BIOMATERIALS.2015.09.027}, DOI={10.1016/J.BIOMATERIALS.2015.09.027}, abstractNote={Polarization of macrophages into an inflammatory (M1) or anti-inflammatory (M2) phenotype is important for clearing pathogens and wound repair, however chronic activation of either type of macrophage has been implicated in several diseases. Methods to locally control the polarization of macrophages is of great interest for biomedical implants and tissue engineering. To that end, silk protein was used to form biopolymer films that release either IFN-γ or IL-4 to control the polarization of macrophages. Modulation of the solubility of the silk films through regulation of β-sheet (crystalline) content enabled a short-term release (4–8 h) of either cytokine, with smaller amounts released out to 24 h. Altering the solubility of the films was accomplished by varying the time that the films were exposed to water vapor. The released IFN-γ or IL-4 induced polarization of THP-1 derived macrophages into the M1 or M2 phenotypes, respectively. The silk biomaterials were able to release enough IFN-γ or IL-4 to repolarize the macrophage from M1 to M2 and vice versa, demonstrating the well-established plasticity of macrophages. High β-sheet content films that are not soluble and do not release the trapped cytokines were also able to polarize macrophages that adhered to the surface through degradation of the silk protein. Chemically conjugating IFN-γ to silk films through disulfide bonds allowed for longer-term release to 10 days. The release of covalently attached IFN-γ from the films was also able to polarize M1 macrophages in vitro. Thus, the strategy described here offers new approaches to utilizing biomaterials for directing the polarization of macrophages.}, journal={Biomaterials}, publisher={Elsevier BV}, author={Reeves, Andrew R.D. and Spiller, Kara L. and Freytes, Donald O. and Vunjak-Novakovic, Gordana and Kaplan, David L.}, year={2015}, month={Dec}, pages={272–283} }
 @article{wrona_peng_born_amin_branski_freytes_2015, title={Derivation and characterization of porcine vocal fold extracellular matrix scaffold}, volume={126}, ISSN={0023-852X}, url={http://dx.doi.org/10.1002/LARY.25640}, DOI={10.1002/LARY.25640}, abstractNote={Objectives/HypothesisTo optimize decellularization of porcine vocal folds (VF) and quantify human bone marrow‐derived mesenchymal stem cell (BM‐MSC) interactions with this matrix to provide a foundation for regenerative approaches to VF repair.Study Design and MethodsVocal folds were dissected from porcine larynges and three decellularization protocols were compared, each consisting of washes and mechanical agitations with different combinations of reagents. DNA content was analyzed via Quant‐iT Picogreen assay and hematoxylin and eosin staining. Bone marrow‐derived MSCs were then seeded onto the decellularized VF matrices. Morphology, metabolic activity, DNA content, and gene expression were assessed using LIVE/DEAD Cell Viability, alamarBlue Cell Viability Assay, Quant‐iT Picogreen assay, and quantitative polymerase chain reaction, respectively.ResultsThe most successful decellularization protocol removed 95% DNA content within 1 day, compared to several days required for previously described protocols. Histology confirmed the retention of extracellular matrix (ECM) and its components, including glycosaminoglycans, collagen, and fibrin, while void of nuclear/cellular content. Decellularized scaffolds were then seeded with BM‐MSCs. Similar DNA quantities were observed after 24 hours of seeding within the VF‐ECM scaffold when compared to cells on tissue culture plastic (TCP). LIVE/DEAD staining of the seeded VF‐ECM confirmed excellent cell viability, and the metabolic activity of BM‐MSCs increased significantly on VF‐ECM compared to TCP. Endoglin gene expression decreased, suggestive of differentiation.ConclusionPorcine VFs can be efficiently decellularized within 5 hours using a combination of sodium deoxycholate and peracetic acid. Decellularized VF‐ECM supported attachment and growth of human BM‐MSCs, with evidence of differentiation.Level of EvidenceN/A Laryngoscope, 126:928–935, 2016}, number={4}, journal={The Laryngoscope}, publisher={Wiley}, author={Wrona, Emily A. and Peng, Robert and Born, Hayley and Amin, Milan R. and Branski, Ryan C. and Freytes, Donald O.}, year={2015}, month={Sep}, pages={928–935} }
 @article{spiller_wrona_romero-torres_pallotta_graney_witherel_panicker_feldman_urbanska_santambrogio_et al._2016, title={Differential gene expression in human, murine, and cell line-derived macrophages upon polarization}, volume={347}, ISSN={0014-4827}, url={http://dx.doi.org/10.1016/J.YEXCR.2015.10.017}, DOI={10.1016/J.YEXCR.2015.10.017}, abstractNote={The mechanisms by which macrophages control the inflammatory response, wound healing, biomaterial-interactions, and tissue regeneration appear to be related to their activation/differentiation states. Studies of macrophage behavior in vitro can be useful for elucidating their mechanisms of action, but it is not clear to what extent the source of macrophages affects their apparent behavior, potentially affecting interpretation of results. Although comparative studies of macrophage behavior with respect to cell source have been conducted, there has been no direct comparison of the three most commonly used cell sources: murine bone marrow, human monocytes from peripheral blood (PB), and the human leukemic monocytic cell line THP-1, across multiple macrophage phenotypes. In this study, we used multivariate discriminant analysis to compare the in vitro expression of genes commonly chosen to assess macrophage phenotype across all three sources of macrophages, as well as those derived from induced pluripotent stem cells (iPSCs), that were polarized towards four distinct phenotypes using the same differentiation protocols: M(LPS,IFN) (aka M1), M(IL4,IL13) (aka M2a), M(IL10) (aka M2c), and M(-) (aka M0) used as control. Several differences in gene expression trends were found among the sources of macrophages, especially between murine bone marrow-derived and human blood-derived M(LPS,IFN) and M(IL4,IL13) macrophages with respect to commonly used phenotype markers like CCR7 and genes associated with angiogenesis and tissue regeneration like FGF2 and MMP9. We found that the genes with the most similar patterns of expression among all sources were CXCL-10 and CXCL-11 for M(LPS,IFN) and CCL17 and CCL22 for M(IL4,IL13). Human PB-derived macrophages and human iPSC-derived macrophages showed similar gene expression patterns among the groups and genes studied here, suggesting that iPSC-derived monocytes have the potential to be used as a reliable cell source of human macrophages for in vitro studies. These findings could help select appropriate markers when testing macrophage behavior in vitro and highlight those markers that may confuse interpretation of results from experiments employing macrophages from different sources.}, number={1}, journal={Experimental Cell Research}, publisher={Elsevier BV}, author={Spiller, Kara L. and Wrona, Emily A. and Romero-Torres, Saly and Pallotta, Isabella and Graney, Pamela L. and Witherel, Claire E. and Panicker, Leelamma M. and Feldman, Ricardo A. and Urbanska, Aleksandra M. and Santambrogio, Laura and et al.}, year={2016}, month={Sep}, pages={1–13} }
 @article{badylak_freytes_gilbert_2015, title={Reprint of: Extracellular matrix as a biological scaffold material: Structure and function}, volume={23}, ISSN={1742-7061}, url={http://dx.doi.org/10.1016/J.ACTBIO.2015.07.016}, DOI={10.1016/J.ACTBIO.2015.07.016}, abstractNote={Biological scaffold materials derived from the extracellular matrix (ECM) of intact mammalian tissues have been successfully used in a variety of tissue engineering/regenerative medicine applications both in preclinical studies and in clinical applications. Although it is recognized that the materials have constructive remodeling properties, the mechanisms by which functional tissue restoration is achieved are not well understood. There is evidence to support essential roles for both the structural and functional characteristics of the biological scaffold materials. This paper provides an overview of the composition and structure of selected ECM scaffold materials, the effects of manufacturing methods upon the structural properties and resulting mechanical behavior of the scaffold materials, and the in vivo degradation and remodeling of ECM scaffolds with an emphasis on tissue function.}, journal={Acta Biomaterialia}, publisher={Elsevier BV}, author={Badylak, Stephen F. and Freytes, Donald O. and Gilbert, Thomas W.}, year={2015}, month={Sep}, pages={S17–S26} }
 @article{spiller_freytes_vunjak-novakovic_2014, title={Macrophages Modulate Engineered Human Tissues for Enhanced Vascularization and Healing}, volume={43}, ISSN={0090-6964 1573-9686}, url={http://dx.doi.org/10.1007/S10439-014-1156-8}, DOI={10.1007/S10439-014-1156-8}, abstractNote={Tissue engineering is increasingly based on recapitulating human physiology, through integration of biological principles into engineering designs. In spite of all progress in engineering functional human tissues, we are just beginning to develop effective methods for establishing blood perfusion and controlling the inflammatory factors following implantation into the host. Functional vasculature largely determines tissue survival and function in vivo. The inflammatory response is a major regulator of vascularization and overall functionality of engineered tissues, through the activity of different types of macrophages and the cytokines they secrete. We discuss here the cell–scaffold–bioreactor systems for harnessing the inflammatory response for enhanced tissue vascularization and healing. To this end, inert scaffolds that have been considered for many decades a "gold standard" in regenerative medicine are beginning to be replaced by a new generation of "smart" tissue engineering systems designed to actively mediate tissue survival and function.}, number={3}, journal={Annals of Biomedical Engineering}, publisher={Springer Science and Business Media LLC}, author={Spiller, Kara L. and Freytes, Donald O. and Vunjak-Novakovic, Gordana}, year={2014}, month={Oct}, pages={616–627} }
 @article{o'neill_anfang_anandappa_costa_javidfar_wobma_singh_freytes_bacchetta_sonett_et al._2013, title={Decellularization of Human and Porcine Lung Tissues for Pulmonary Tissue Engineering}, volume={96}, ISSN={0003-4975}, url={http://dx.doi.org/10.1016/J.ATHORACSUR.2013.04.022}, DOI={10.1016/J.ATHORACSUR.2013.04.022}, abstractNote={<h3>Background</h3> The only definitive treatment for end-stage organ failure is orthotopic transplantation. Lung extracellular matrix (LECM) holds great potential as a scaffold for lung tissue engineering because it retains the complex architecture, biomechanics, and topologic specificity of the lung. Decellularization of human lungs rejected from transplantation could provide "ideal" biologic scaffolds for lung tissue engineering, but the availability of such lungs remains limited. The present study was designed to determine whether porcine lung could serve as a suitable substitute for human lung to study tissue engineering therapies. <h3>Methods</h3> Human and porcine lungs were procured, sliced into sheets, and decellularized by three different methods. Compositional, ultrastructural, and biomechanical changes to the LECM were characterized. The suitability of LECM for cellular repopulation was evaluated by assessing the viability, growth, and metabolic activity of human lung fibroblasts, human small airway epithelial cells, and human adipose-derived mesenchymal stem cells over a period of 7 days. <h3>Results</h3> Decellularization with 3-[(3-Cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) showed the best maintenance of both human and porcine LECM, with similar retention of LECM proteins except for elastin. Human and porcine LECM supported the cultivation of pulmonary cells in a similar way, except that the human LECM was stiffer and resulted in higher metabolic activity of the cells than porcine LECM. <h3>Conclusions</h3> Porcine lungs can be decellularized with CHAPS to produce LECM scaffolds with properties resembling those of human lungs, for pulmonary tissue engineering. We propose that porcine LECM can be an excellent screening platform for the envisioned human tissue engineering applications of decellularized lungs.}, number={3}, journal={The Annals of Thoracic Surgery}, publisher={Elsevier BV}, author={O'Neill, John D. and Anfang, Rachel and Anandappa, Annabelle and Costa, Joseph and Javidfar, Jeffrey and Wobma, Holly M. and Singh, Gopal and Freytes, Donald O. and Bacchetta, Matthew D. and Sonett, Joshua R. and et al.}, year={2013}, month={Sep}, pages={1046–1056} }
 @article{o'neill_freytes_anandappa_oliver_vunjak-novakovic_2013, title={The regulation of growth and metabolism of kidney stem cells with regional specificity using extracellular matrix derived from kidney}, volume={34}, ISSN={0142-9612}, url={http://dx.doi.org/10.1016/J.BIOMATERIALS.2013.09.022}, DOI={10.1016/J.BIOMATERIALS.2013.09.022}, abstractNote={Native extracellular matrix (ECM) that is secreted and maintained by resident cells is of great interest for cell culture and cell delivery. We hypothesized that specialized bioengineered niches for stem cells can be established using ECM-derived scaffolding materials. Kidney was selected as a model system because of the high regional diversification of renal tissue matrix. By preparing the ECM from three specialized regions of the kidney (cortex, medulla, and papilla; whole kidney, heart, and bladder as controls) in three forms: (i) intact sheets of decellularized ECM, (ii) ECM hydrogels, and (iii) solubilized ECM, we investigated how the structure and composition of ECM affect the function of kidney stem cells (with mesenchymal stem cells, MSCs, as controls). All three forms of the ECM regulated KSC function, with differential structural and compositional effects. KSCs cultured on papilla ECM consistently displayed lower proliferation, higher metabolic activity, and differences in cell morphology, alignment, and structure formation as compared to KSCs on cortex and medulla ECM, effects not observed in corresponding MSC cultures. These data suggest that tissue- and region-specific ECM can provide an effective substrate for in vitro studies of therapeutic stem cells.}, number={38}, journal={Biomaterials}, publisher={Elsevier BV}, author={O'Neill, John D. and Freytes, Donald O. and Anandappa, Annabelle J. and Oliver, Juan A. and Vunjak-Novakovic, Gordana V.}, year={2013}, month={Dec}, pages={9830–9841} }
 @article{freytes_kang_marcos-campos_vunjak-novakovic_2012, title={Macrophages modulate the viability and growth of human mesenchymal stem cells}, volume={114}, ISSN={0730-2312}, url={http://dx.doi.org/10.1002/jcb.24357}, DOI={10.1002/jcb.24357}, abstractNote={AbstractFollowing myocardial infarction, tissue repair is mediated by the recruitment of monocytes and their subsequent differentiation into macrophages. Recent findings have revealed the dynamic changes in the presence of polarized macrophages with pro‐inflammatory (M1) and anti‐inflammatory (M2) properties during the early (acute) and late (chronic) stages of cardiac ischemia. Mesenchymal stem cells (MSCs) delivered into the injured myocardium as reparative cells are subjected to the effects of polarized macrophages and the inflammatory milieu. The present study investigated how cytokines and polarized macrophages associated with pro‐inflammatory (M1) and anti‐inflammatory (M2) responses affect the survival of MSCs. Human MSCs were studied using an in vitro platform with individual and combined M1 and M2 cytokines: IL‐1β, IL‐6, TNF‐α, and IFN‐γ (for M1), and IL‐10, TGF‐β1, TGF‐β3, and VEGF (for M2). In addition, polarization molecules (M1: LPS and IFN‐γ; M2: IL‐4 and IL‐13) and common chemokines (SDF‐1 and MCP‐1) found during inflammation were also studied. Indirect and direct co‐cultures were conducted using M1 and M2 polarized human THP‐1 monocytes. M2 macrophages and their associated cytokines supported the growth of hMSCs, while M1 macrophages and their associated cytokines inhibited the growth of hMSCs in vitro under certain conditions. These data imply that an anti‐inflammatory (M2) environment is more accommodating to the therapeutic hMSCs than a pro‐inflammatory (M1) environment at specific concentrations. J. Cell. Biochem. 114: 220–229, 2012. © 2012 Wiley Periodicals, Inc.}, number={1}, journal={Journal of Cellular Biochemistry}, publisher={Wiley}, author={Freytes, Donald O. and Kang, Jung W. and Marcos-Campos, Ivan and Vunjak-Novakovic, Gordana}, year={2012}, month={Nov}, pages={220–229} }
 @article{singh_javidfar_costa_guarrera_miller_henry_jallerat_freytes_vunjak-novakovic_sonett_et al._2011, title={549 Perfusion/Decellularization of Large Animal Lungs}, volume={30}, ISSN={1053-2498}, url={http://dx.doi.org/10.1016/j.healun.2011.01.560}, DOI={10.1016/j.healun.2011.01.560}, abstractNote={Lung transplantation for end-stage disease is limited secondary to the need for chronic immunosuppression, rejection and shortage of organs. Regenerative medicine has emerged as a potential alternative to tissue or organ transplantation. A functional lung engineered on demand would permit de novo generation of an organ graft that could be transplanted similarly to a donor lung,with possibilities to alleviate organ shortages and rejection. We present early work in a large animal model demonstrating techniques toward regenerative lung transplantation.}, number={4}, journal={The Journal of Heart and Lung Transplantation}, publisher={Elsevier BV}, author={Singh, G. and Javidfar, J. and Costa, J. and Guarrera, J.V. and Miller, J. and Henry, S. and Jallerat, Q. and Freytes, D.O. and Vunjak-Novakovic, G. and Sonett, J.R. and et al.}, year={2011}, month={Apr}, pages={S184–S185} }
 @article{duan_liu_o’neill_wan_freytes_vunjak-novakovic_2011, title={Hybrid Gel Composed of Native Heart Matrix and Collagen Induces Cardiac Differentiation of Human Embryonic Stem Cells without Supplemental Growth Factors}, volume={4}, ISSN={1937-5387 1937-5395}, url={http://dx.doi.org/10.1007/S12265-011-9304-0}, DOI={10.1007/S12265-011-9304-0}, abstractNote={Our goal was to assess the ability of native heart extracellular matrix (ECM) to direct cardiac differentiation of human embryonic stem cells (hESCs) in vitro. In order to probe the effects of cardiac matrix on hESC differentiation, a series of hydrogels was prepared from decellularized ECM from porcine hearts by mixing ECM and collagen type I at varying ratios. Maturation of cardiac function in embryoid bodies formed from hESCs was documented in terms of spontaneous contractile behavior and the mRNA and protein expression of cardiac markers. Hydrogel with high ECM content (75% ECM, 25% collagen, no supplemental soluble factors) increased the fraction of cells expressing cardiac marker troponin T, when compared with either hydrogel with low ECM content (25% ECM, 75% collagen, no supplemental soluble factors) or collagen hydrogel (100% collagen, with supplemental soluble factors). Furthermore, cardiac maturation was promoted in high-ECM content hydrogels, as evidenced by the striation patterns of cardiac troponin I and by upregulation of Cx43 gene. Consistently, high-ECM content hydrogels improved the contractile function of cardiac cells, as evidenced by increased numbers of contracting cells and increased contraction amplitudes. The ability of native ECM hydrogel to induce cardiac differentiation of hESCs without the addition of soluble factors makes it an attractive biomaterial system for basic studies of cardiac development and potentially for the delivery of therapeutic cells into the heart.}, number={5}, journal={Journal of Cardiovascular Translational Research}, publisher={Springer Science and Business Media LLC}, author={Duan, Yi and Liu, Zen and O’Neill, John and Wan, Leo Q. and Freytes, Donald O. and Vunjak-Novakovic, Gordana}, year={2011}, month={Jul}, pages={605–615} }
 @article{badylak_freytes_gilbert_2009, title={Extracellular matrix as a biological scaffold material: Structure and function}, volume={5}, ISSN={1742-7061}, url={http://dx.doi.org/10.1016/j.actbio.2008.09.013}, DOI={10.1016/j.actbio.2008.09.013}, abstractNote={Biological scaffold materials derived from the extracellular matrix (ECM) of intact mammalian tissues have been successfully used in a variety of tissue engineering/regenerative medicine applications both in preclinical studies and in clinical applications. Although it is recognized that the materials have constructive remodeling properties, the mechanisms by which functional tissue restoration is achieved are not well understood. There is evidence to support essential roles for both the structural and functional characteristics of the biological scaffold materials. This paper provides an overview of the composition and structure of selected ECM scaffold materials, the effects of manufacturing methods upon the structural properties and resulting mechanical behavior of the scaffold materials, and the in vivo degradation and remodeling of ECM scaffolds with an emphasis on tissue function.}, number={1}, journal={Acta Biomaterialia}, publisher={Elsevier BV}, author={Badylak, S and Freytes, D and Gilbert, T}, year={2009}, month={Jan}, pages={1–13} }
 @article{freytes_wan_vunjak-novakovic_2009, title={Geometry and force control of cell function}, volume={108}, ISSN={0730-2312 1097-4644}, url={http://dx.doi.org/10.1002/jcb.22355}, DOI={10.1002/jcb.22355}, abstractNote={AbstractTissue engineering is becoming increasingly ambitious in its efforts to create functional human tissues, and to provide stem cell scientists with culture systems of high biological fidelity. Novel engineering designs are being guided by biological principles, in an attempt to recapitulate more faithfully the complexities of native cellular milieu. Three‐dimensional (3D) scaffolds are being designed to mimic native‐like cell environments and thereby elicit native‐like cell responses. Also, the traditional focus on molecular regulatory factors is shifting towards the combined application of molecular and physical factors. Finally, methods are becoming available for the coordinated presentation of molecular and physical factors in the form of controllable spatial and temporal gradients. Taken together, these recent developments enable the interrogation of cellular behavior within dynamic culture settings designed to mimic some aspects of native tissue development, disease, or regeneration. We discuss here these advanced cell culture environments, with emphasis on the derivation of design principles from the development (the biomimetic paradigm) and the geometry‐force control of cell function (the biophysical regulation paradigm). J. Cell. Biochem. 108: 1047–1058, 2009. © 2009 Wiley‐Liss, Inc.}, number={5}, journal={Journal of Cellular Biochemistry}, publisher={Wiley}, author={Freytes, Donald O. and Wan, Leo Q. and Vunjak-Novakovic, Gordana}, year={2009}, month={Dec}, pages={1047–1058} }
 @article{gilbert_wognum_joyce_freytes_sacks_badylak_2008, title={Collagen fiber alignment and biaxial mechanical behavior of porcine urinary bladder derived extracellular matrix}, volume={29}, ISSN={0142-9612}, url={http://dx.doi.org/10.1016/j.biomaterials.2008.08.022}, DOI={10.1016/j.biomaterials.2008.08.022}, abstractNote={The collagen fiber alignment and biomechanical behavior of naturally occurring extracellular matrix (ECM) scaffolds are important considerations for the design of medical devices from these materials. Both should be considered in order to produce a device to meet tissue specific mechanical requirements (e.g., tendon vs. urinary bladder), and could ultimately affect the remodeling response in vivo. The present study evaluated the collagen fiber alignment and biaxial mechanical behavior of ECM scaffold material harvested from porcine urinary bladder tunica mucosa and basement membrane (together referred to as urinary bladder matrix (UBM)) and ECM harvested from urinary bladder submucosa (UBS). Since the preparation of UBM allows for control of the direction of delamination, the effect of the delamination method on the mechanical behavior of UBM was determined by delaminating the submucosa and other abluminal layers by scraping along the longitudinal axis of the bladder (apex to neck) (UBML) or along the circumferential direction (UBMC). The processing of UBS does not allow for similar directional control. UBML and UBS had similar collagen fiber distributions, with a preferred collagen fiber alignment along the longitudinal direction. UBMC showed a more homogenous collagen fiber orientation. All samples showed a stiffer mechanical behavior in the longitudinal direction. Despite similar collagen fiber distributions, UBML and UBS showed quite different mechanical behavior for the applied loading patterns with UBS showing a much more pronounced toe region. The mechanical behavior for UBMC in both directions was similar to the mechanical behavior of UBML. There are distinct differences in the mechanical behavior of different layers of ECM from the porcine urinary bladder, and the processing methods can substantially alter the mechanical behavior observed.}, number={36}, journal={Biomaterials}, publisher={Elsevier BV}, author={Gilbert, Thomas W. and Wognum, Silvia and Joyce, Erinn M. and Freytes, Donald O. and Sacks, Michael S. and Badylak, Stephen F.}, year={2008}, month={Dec}, pages={4775–4782} }
 @article{freytes_tullius_valentin_stewart-akers_badylak_2008, title={Hydrated versus lyophilized forms of porcine extracellular matrix derived from the urinary bladder}, volume={87A}, ISSN={1549-3296 1552-4965}, url={http://dx.doi.org/10.1002/jbm.a.31821}, DOI={10.1002/jbm.a.31821}, abstractNote={AbstractBiologic scaffolds composed of naturally occurring extracellular matrix (ECM) are currently in clinical use for the repair and reconstruction of damaged or missing tissues. The material and structural properties of the ECM scaffold are important determinants of the potential clinical applications and these properties may be affected by manufacturing steps, processing steps, and storage conditions. The present study compared the structural properties of hydrated and lyophilized forms of a biologic scaffold derived from the porcine urinary bladder (urinary bladder matrix or UBM). The structural properties evaluated include: maximum load and elongation, maximum tangential stiffness, energy absorbed, suture retention strength, ball‐burst strength, and the hydrostatic permeability index. Other properties that were investigated include changes in the water content, structural morphology, and thickness and the ability to support in vitro growth of NIH 3T3 cells. Lyophilization caused no changes in the structural properties evaluated with the exception of a decrease in maximum elongation. NIH 3T3 cells showed invasion of the scaffold when seeded on the abluminal side of both hydrated and lyophilized UBM, and there were more cells present on lyophilized UBM when compared to hydrated UBM devices after the 7‐days culture period. Irreversible changes were observed in the microstructure and ultrastructure of lyophilized UBM devices. We conclude that lyophilization affects the overall in vitro cell growth of NIH 3T3 cells and the ultrastructural morphology of UBM devices, but does not result in significant changes in structural properties. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2008}, number={4}, journal={Journal of Biomedical Materials Research Part A}, publisher={Wiley}, author={Freytes, Donald O. and Tullius, Robert S. and Valentin, Jolene E. and Stewart-Akers, Ann M. and Badylak, Stephen F.}, year={2008}, month={Dec}, pages={862–872} }
 @article{valentin_freytes_grasman_pesyna_freund_gilbert_badylak_2009, title={Oxygen diffusivity of biologic and synthetic scaffold materials for tissue engineering}, volume={91A}, ISSN={1549-3296 1552-4965}, url={http://dx.doi.org/10.1002/jbm.a.32328}, DOI={10.1002/jbm.a.32328}, abstractNote={AbstractScaffolds for tissue engineering and regenerative medicine applications are commonly manufactured from synthetic materials, intact or isolated components of extracellular matrix (ECM), or a combination of such materials. After surgical implantation, the metabolic requirements of cells that populate the scaffold depend upon adequate gas and nutrient exchange with the surrounding microenvironment. The present study measured the oxygen transfer through three biologic scaffold materials composed of ECM including small intestinal submucosa (SIS), urinary bladder submucosa (UBS), and urinary bladder matrix (UBM), and one synthetic biomaterial, Dacron™. The oxygen diffusivity was calculated from Fick's first law of diffusion. Each material permitted measurable oxygen diffusion. The diffusivity of SIS was found to be dependent on the direction of oxygen transfer; the oxygen transfer in the abluminal‐to‐luminal direction was significantly greater than the luminal‐to‐abluminal direction. The oxygen diffusivity of UBM and UBS were similar despite the presence of an intact basement membrane on the luminal surface of UBM. Dacron showed oxygen diffusivity values seven times greater than the ECM biomaterials. The current study showed that each material has unique oxygen diffusivity values, and these values may be dependent on the scaffold's ultrastructure. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009}, number={4}, journal={Journal of Biomedical Materials Research Part A}, publisher={Wiley}, author={Valentin, Jolene E. and Freytes, Donald O. and Grasman, Jonathan M. and Pesyna, Colin and Freund, John and Gilbert, Thomas W. and Badylak, Stephen F.}, year={2009}, month={Dec}, pages={1010–1017} }
 @article{freytes_martin_velankar_lee_badylak_2008, title={Preparation and rheological characterization of a gel form of the porcine urinary bladder matrix}, volume={29}, ISSN={0142-9612}, url={http://dx.doi.org/10.1016/j.biomaterials.2007.12.014}, DOI={10.1016/j.biomaterials.2007.12.014}, abstractNote={Biologic scaffolds composed of extracellular matrix (ECM) have been used to facilitate the repair and reconstruction of a variety of tissues in clinical and pre-clinical studies. The clinical utility of such scaffolds can be limited by the geometric and mechanical properties of the tissue or organ from which the ECM is harvested. An injectable gel form of ECM could potentially conform to any three-dimensional shape and could be delivered to sites of interest by minimally invasive techniques. The objectives of the present study were to prepare a gel form of ECM harvested from the urinary bladder (urinary bladder matrix or UBM), to characterize the rheological properties of the gel, and finally to evaluate the ability of the gel to support in vitro growth of smooth muscle cells. Following enzymatic solubilization with pepsin, UBM was induced to self-assemble into a gel when brought to physiological conditions. The UBM gel supported the adhesion and growth of rat aortic smooth muscle cells when cultured under static in vitro conditions. The present study showed that an intact form of UBM can be successfully solubilized without purification steps and induced to repolymerize into a gel form of the UBM biologic scaffold material.}, number={11}, journal={Biomaterials}, publisher={Elsevier BV}, author={Freytes, Donald O. and Martin, Jeffrey and Velankar, Sachin S. and Lee, Annie S. and Badylak, Stephen F.}, year={2008}, month={Apr}, pages={1630–1637} }
 @article{freytes_stoner_badylak_2008, title={Uniaxial and biaxial properties of terminally sterilized porcine urinary bladder matrix scaffolds}, volume={84B}, ISSN={1552-4973 1552-4981}, url={http://dx.doi.org/10.1002/jbm.b.30885}, DOI={10.1002/jbm.b.30885}, abstractNote={AbstractScaffolds composed of extracellular matrix have been successfully used to support the reconstruction of a variety of tissues in preclinical studies and in clinical applications. As an off‐the‐shelf product, extracellular matrix (ECM) scaffolds must be subjected to terminal sterilization before use. The choice of sterilization method may alter the integrity of the ECM's composition and structure such that the mechanical and material properties are adversely affected. The present study evaluated selected structural properties of an ECM scaffold derived from the urinary bladder termed urinary bladder matrix after being sterilized by three different methods: ethylene oxide (ETO) (750 mg/h for 16 h), gamma irradiation (2.0 Mrads), or electron beam irradiation (e‐beam) (2.2 Mrads). The structural properties that were evaluated include maximum force, maximum elongation, maximum tangential stiffness, energy dissipation, and ball‐burst strength. All sterilization methods affected at least two of the measured properties. ETO was shown to have the least detrimental effect upon the measured properties. Gamma and e‐beam irradiation were shown to decrease the uniaxial and biaxial strength, maximum tangential stiffness, and the energy dissipation of the ECM scaffolds. The present study showed that the choice of terminal sterilization method affects the structural properties of scaffolds composed of extracellular matrix. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2008}, number={2}, journal={Journal of Biomedical Materials Research Part B: Applied Biomaterials}, publisher={Wiley}, author={Freytes, Donald O. and Stoner, Richard M. and Badylak, Stephen F.}, year={2008}, pages={408–414} }
 @article{gilbert_freytes_willment_sacks_badylak_2006, title={Fiber architecture and biaxial mechanical behavior of porcine urinary bladder extracellular matrix}, volume={39}, ISSN={0021-9290}, url={http://dx.doi.org/10.1016/S0021-9290(06)84582-3}, DOI={10.1016/S0021-9290(06)84582-3}, journal={Journal of Biomechanics}, publisher={Elsevier BV}, author={Gilbert, T.W. and Freytes, D.O. and Willment, A.R. and Sacks, M.S. and Badylak, S.F.}, year={2006}, month={Jan}, pages={S391} }
 @article{freytes_rundell_vandegeest_vorp_webster_badylak_2005, title={Analytically derived material properties of multilaminated extracellular matrix devices using the ball-burst test}, volume={26}, ISSN={0142-9612}, url={http://dx.doi.org/10.1016/j.biomaterials.2005.01.070}, DOI={10.1016/j.biomaterials.2005.01.070}, abstractNote={Xenogeneic extracellular matrices (ECMs) have been shown to be effective as naturally occurring scaffolds for soft-tissue repair. As acellular tissue substitutes at the time of surgical implantation, ECMs are subjected to the mechanical forces and micro-environmental conditions representative of the anatomical location in which they are placed. Ideally such natural scaffolds would possess mechanical properties that allow for normal tissue function in and around the implant site. The ball-burst test was used to simulate biaxial forces and to determine the strength of the ECM scaffold under a relevant physiological loading condition. The ball-burst test, in itself, does not quantify intrinsic mechanical properties and therefore a methodology was developed to determine the maximum stress resultant tangent modulus (MSRTM) or the maximum stress tangent modulus (MSTM), stress to failure (σf), failure stress resultant (Nf), ball-burst pressure (P), and maximum elongation (λmax) from the raw ball-burst data obtained at a constant-rate of transverse. The analytical methodology was compared to finite element simulations and showed good correlation with the analytical solution presented. The proposed approximations were used to compute biaxial failure properties for a variety of multilaminate ECM devices with varying number of layers, disinfection and sterilization, and organ origin.}, number={27}, journal={Biomaterials}, publisher={Elsevier BV}, author={Freytes, D and Rundell, A and Vandegeest, J and Vorp, D and Webster, T and Badylak, S}, year={2005}, month={Sep}, pages={5518–5531} }
 @article{freytes_tullius_badylak_2006, title={Effect of storage upon material properties of lyophilized porcine extracellular matrix derived from the urinary bladder}, volume={78B}, ISSN={1552-4973 1552-4981}, url={http://dx.doi.org/10.1002/jbm.b.30491}, DOI={10.1002/jbm.b.30491}, abstractNote={AbstractXenogeneic extracellular matrices (ECMs) have been developed as off‐the‐shelf biologic scaffolds that have been effectively used in preclinical and clinical applications for tissue reconstruction. Such materials must be suitable for terminal sterilization and capable of storage for extended periods of time without significant changes in material properties and bioactivity. Material properties of interest for ECM scaffolds include hydrostatic permeability index (PI), uniaxial maximum load and elongation, maximum tangential stiffness (MTS), suture retention strength (SRS), and ball‐burst strength (BBS). The present study evaluated these material properties for lyophilized forms of an ECM scaffold derived from the porcine urinary bladder, termed urinary bladder matrix (UBM), that was terminally sterilized by e‐beam irradiation at 22 kGy and stored at room temperature (RT; 20–24°C) or refrigerated temperature (REFT; 4–8°C) for up to 12 months. UBM devices showed no change in SRS, BBS, and hydrostatic PI after the evaluation period. Lyophilized devices stored at RT showed an increase in maximum load and MTS while devices stored at REFT showed an increase in maximum elongation after 1 year of storage (p < 0.05). These results indicate that structural changes in the UBM device may slowly occur as a function of prolonged storage and storage temperature. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006}, number={2}, journal={Journal of Biomedical Materials Research Part B: Applied Biomaterials}, publisher={Wiley}, author={Freytes, Donald O. and Tullius, Robert S. and Badylak, Stephen F.}, year={2006}, month={Aug}, pages={327–333} }
 @article{badylak_vorp_spievack_simmons-byrd_hanke_freytes_thapa_gilbert_nieponice_2005, title={Esophageal Reconstruction with ECM and Muscle Tissue in a Dog Model}, volume={128}, ISSN={0022-4804}, url={http://dx.doi.org/10.1016/j.jss.2005.03.002}, DOI={10.1016/j.jss.2005.03.002}, abstractNote={An in vivo study was conducted to determine if an extracellular matrix (ECM) scaffold co-localized with autologous muscle tissue could achieve constructive remodeling of esophageal tissue without stricture. ECM derived from the porcine urinary bladder was processed, decellularized, configured into a tube shape, and terminally sterilized for use as a bioscaffold for esophageal reconstruction in a dog model. Twenty-two dogs were divided into four groups, three groups of five and one group of seven. Groups 1 and 2 were repaired with either ECM alone or muscle tissue alone, respectively. Groups 3 and 4 were repaired with ECM plus either a partial (30%) covering with muscle tissue or a complete (100%) covering with muscle tissue, respectively. Animals in groups 1 and 2 were sacrificed within approximately 3 weeks because of the formation of intractable esophageal stricture. Four of five dogs in group 3 and six of seven dogs in group 4 were survived for 26 days to 230 days and showed constructive remodeling of esophageal tissue with the formation of well organized esophageal tissue layers, minimal stricture, esophageal motility, and a normal clinical outcome. Mechanical testing of a subset of the remodeled esophageal tissue from animals in groups 3 and 4 showed progressive remodeling from a relatively stiff, non-compliant ECM tube structure toward a tissue with near normal biomechanical properties. We conclude that ECM bioscaffolds plus autologous muscle tissue, but not ECM scaffolds or muscle tissue alone, can facilitate the in situ reconstitution of structurally and functionally acceptable esophageal tissue.}, number={1}, journal={Journal of Surgical Research}, publisher={Elsevier BV}, author={Badylak, Stephen F. and Vorp, David A. and Spievack, Alan R. and Simmons-Byrd, Abby and Hanke, Joseph and Freytes, Donald O. and Thapa, Anil and Gilbert, Thomas W. and Nieponice, Alejandro}, year={2005}, month={Sep}, pages={87–97} }
 @article{freytes_badylak_webster_geddes_rundell_2004, title={Biaxial strength of multilaminated extracellular matrix scaffolds}, volume={25}, ISSN={0142-9612}, url={http://dx.doi.org/10.1016/j.biomaterials.2003.09.015}, DOI={10.1016/j.biomaterials.2003.09.015}, abstractNote={Xenogeneic extracellular matrix (ECM) can be harvested and configured to function as a bioscaffold for tissue and organ reconstruction. The mechanical properties of the ECM vary depending upon the tissue from which it is harvested. Likewise, the manufacturing steps required to develop ECMs into medical grade devices will affect the surface morphology and the mechanical properties of the bioscaffold; important properties for constructive tissue remodeling. The present study compared the ball-burst strength of five different ECM scaffolds before and after treatment with peracetic acid (PAA): porcine small intestinal submucosa (SIS), porcine urinary bladder submucosa (UBS), porcine urinary bladder matrix (UBM), a composite of UBS+UBM, and canine stomach submucosa (SS). This study also compared the mechanical properties of 2- and 4-layer ECM scaffolds. Results showed 2-layer SS devices had the highest ball-burst value of all 2-layer ECM devices. Moreover, all 4-layer ECM devices had similar ball-burst strength except for 4-layer UBM devices which was the weakest. PAA-treatment decreased the ball-burst strength of SS and increased the ball-burst strength of UBS 2-layer devices. This study showed the material properties of the ECM scaffolds could be engineered to mimic those of native soft tissues (i.e. vascular, musculotendinous, etc) by varying the number of layers and modifying the disinfection/sterilization treatments used for manufacturing.}, number={12}, journal={Biomaterials}, publisher={Elsevier BV}, author={Freytes, Donald O and Badylak, Stephen F and Webster, Thomas J and Geddes, Leslie A and Rundell, Ann E}, year={2004}, month={May}, pages={2353–2361} }