@article{sarker_su_rojas_khan_2024, title={Colloidal interactions between nanochitin and surfactants: Connecting micro- and macroscopic properties by isothermal titration calorimetry and rheology}, volume={341}, ISSN={["1879-1344"]}, DOI={10.1016/j.carbpol.2024.122341}, abstractNote={This study elucidates the intricate interactions between chitin nanocrystals (ChNC) and surfactants of same hydrophobic tail (C12) but different head groups types (anionic, cationic, nonionic): sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and polyoxyethylene(23)lauryl ether (Brij-35). Isothermal Titration Calorimetry (ITC) and rheology are used to study the complex ChNC-surfactant interactions in aqueous media, affected by adsorption, self-assembly and micellization. The ITC results demonstrate that the surfactant head group significantly influences the dynamics and nature of the involved phenomena. Cationic DTAB's reveal minimal interaction with ChNC, non-ionic Brij-25's interact moderately at low concentrations driven by hydrophobic effects while SDS's interacts strongly and show complex interaction patterns that fall across four distinct regimes with SDS addition. We attribute such behavior to initiate through electrostatic attraction and terminate in surfactant micelle formation on ChNC surfaces. ITC also elucidates the impact of ChNC concentration on key parameters including critical aggregation concentration (CAC) and saturation concentration (C2). Dynamic rheological analysis indicates the molecular interactions translate to non-linear variations in the elastic modulus (G') upon SDS addition mirroring that observed in ITC experiments. Such a direct correlation between molecular interactions and macroscopic rheological properties provides insights to aid in the creation of nanocomposites with tailored properties.}, journal={CARBOHYDRATE POLYMERS}, author={Sarker, Prottasha and Su, Xiaoya and Rojas, Orlando J. and Khan, Saad A.}, year={2024}, month={Oct} }
 @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{sarker_jani_hsiao_rojas_khan_2023, title={Interacting collagen and tannic acid Particles: Uncovering pH-dependent rheological and thermodynamic behaviors}, volume={650}, ISSN={0021-9797}, url={http://dx.doi.org/10.1016/j.jcis.2023.06.209}, DOI={10.1016/j.jcis.2023.06.209}, abstractNote={Biomaterials such as collagen and tannic acid (TA) particles are of interest in the development of advanced hybrid biobased systems due to their beneficial therapeutic functionalities and distinctive structural properties. The presence of numerous functional groups makes both TA and collagen pH responsive, enabling them to interact via non-covalent interactions and offer tunable macroscopic properties.The effect of pH on the interactions between collagen and TA particles is explored by adding TA particles at physiological pH to collagen at both acidic and neutral pH. Rheology, isothermal titration calorimetry (ITC), turbidimetric analysis and quartz crystal microbalance with dissipation monitoring (QCM-D) are used to study the effects.Rheology results show significant increase in elastic modulus with an increase in collagen concentration. However, TA particles at physiological pH provide stronger mechanical reinforcement to collagen at pH 4 than collagen at pH 7 due to the formation of a higher extent of electrostatic interaction and hydrogen bonding. ITC results confirm this hypothesis, with larger changes in enthalpy, |ΔH|, observed when collagen is at acidic pH and |ΔH| > |TΔS| indicating enthalpy-driven collagen-TA interactions. Turbidimetric analysis and QCM-D help to identify structural differences of the collagen-TA complexes and their formation at both pH conditions.}, journal={Journal of Colloid and Interface Science}, publisher={Elsevier BV}, author={Sarker, Prottasha and Jani, Pallav K. and Hsiao, Lilian C. and Rojas, Orlando J. and Khan, Saad A.}, year={2023}, month={Nov}, pages={541–552} }
 @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{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} }