@article{guha_danilov_berkowitz_oluwajire_grace_2023, title={Consequences of Humidity Cycling on the Moisture Absorption Characteristics of Epoxy Resins with Different Network Architectures}, volume={1}, ISSN={["2637-6105"]}, url={https://doi.org/10.1021/acsapm.2c01570}, DOI={10.1021/acsapm.2c01570}, abstractNote={Absorbed moisture is a perpetual contributor to the steady loss of performance for in-service epoxy-based polymer materials. On the atomistic scale, the state of individual water molecules in a crosslinked epoxy is dependent on the strength of the secondary bonding interactions they engage in and their local physical environment. However, these chemical and physical variables can be tailored on the macroscopic scale through changes in the experimental curing schedule. In this study, crosslinked epoxy matrices with different network architectures were cured by varying the stoichiometric mixing ratios of the epoxy: hardener combination. The samples were subsequently subjected to fluctuating humidity conditions which comprises repeating cycles of high (∼95% RH) and ambient humidity. Both infrared (IR) spectroscopy and dielectric readings were successful in establishing a strong correlation between moisture absorption, network morphology, and dielectric properties. An anomalous behavior observed during the spectral peak analysis helped us understand how absorption history can redistribute the concentrations of water species at the same moisture concentrations. The results from this study elucidate how the phenomenon of absorption itself can act as a damage initiation event, and they also indicate that the spatial quantification of the different water species across a sample can allow us to map damage sites, nanopores, and areas with an overall higher void content.}, journal={ACS APPLIED POLYMER MATERIALS}, author={Guha, Rishabh D. and Danilov, Evgeny O. and Berkowitz, Katherine and Oluwajire, Oluwatimilehin and Grace, Landon R.}, year={2023}, month={Jan} }
 @article{guha_danilov_berkowitz_oluwajire_grace_2023, title={Suppressing Hydrogen Evolution in Aqueous Lithium-Ion Batteries with Double-Site Hydrogen Bonding}, volume={5}, ISSN={["2637-6105"]}, DOI={10.1021/acsapm.2c01570400}, number={1}, journal={ACS APPLIED POLYMER MATERIALS}, author={Guha, Rishabh D. and Danilov, Evgeny O. and Berkowitz, Katherine and Oluwajire, Oluwatimilehin and Grace, Landon R.}, year={2023}, month={Jan}, pages={400–411} }
 @article{kaskar_wells-gray_fleischman_grace_2022, title={Evaluating machine learning classifiers for glaucoma referral decision support in primary care settings}, volume={12}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-022-12270-w}, abstractNote={Abstract}, number={1}, journal={SCIENTIFIC REPORTS}, author={Kaskar, Omkar G. and Wells-Gray, Elaine and Fleischman, David and Grace, Landon}, year={2022}, month={May} }
 @article{idolor_berkowitz_guha_grace_2022, title={Nondestructive examination of polymer composites by analysis of polymer-water interactions and damage-dependent hysteresis}, volume={287}, ISSN={["1879-1085"]}, DOI={10.1016/j.compstruct.2022.115377}, abstractNote={Polymer composites are currently replacing metals in applications requiring design flexibility, high strength-to-weight ratio, and corrosion resistance. However, the damage modes in these materials are very different from metals and require specialized techniques to detect internal flaws which may exist even in the absence of visible surface damage. This study proposes a technique for damage detection in polymer composites which uses naturally absorbed moisture as an ‘imaging’ agent. The locally higher concentration of water in the ‘free’ state at damaged regions and the tendency of such water to quickly migrate to and from damage sites—exhibiting damage-dependent hysteresis—is leveraged for damage detection. To identify damaged regions, a machine learning approach is adopted using logistic regression to classify local regions as ‘undamaged’ or ‘damaged’. New possibilities resulting from higher sensitivity levels achievable by damage-dependent hysteresis are highlighted, providing a pathway to field deployment of the novel damage detection technique.}, journal={COMPOSITE STRUCTURES}, author={Idolor, Ogheneovo and Berkowitz, Katherine and Guha, Rishabh Debraj and Grace, Landon}, year={2022}, month={May} }
 @article{guha_rahmani_berkowitz_pasquinelli_grace_2022, title={Temporal evolution of the behavior of absorbed moisture in a damaged polymer-quartz composite: A molecular dynamics study}, volume={214}, ISSN={["1879-0801"]}, DOI={10.1016/j.commatsci.2022.111690}, abstractNote={• Interfacial Debonding was simulated on a nanoscale using an atomistic model of a quartz-fiber composite. • The temporal behavior of absorbed moisture was analyzed near the damage site. • Irrespective of the initial state of moisture in the composite, they eventually agglomerate near the damage location. • Spatial confinement near the interface bolsters previous experiments which hypothesize that absorbed moisture behaves like bulk water when clustered at microcracks. Exposure of a composite structure to mechanical or environmental stressors often leads to the formation of damage sites which contain rupture mechanisms such as matrix cracking and interfacial debonding. Continued accumulation of this type of small-scale damage can cause sudden and catastrophic large-scale failure. A novel damage characterization technique which leverages the altered physical and chemical states of naturally absorbed moisture in response to sub-micron scale damage has recently shown promise for early detection of damage. In this work, molecular dynamics simulations are used to better understand the differences in the behavior of absorbed water molecules near a damage site. The results show that, irrespective of the initial distribution of molecular water throughout the composite, or the presence of polar atoms in the polymer matrix, water tends to preferentially cluster near the damage location. It was also found that spatial confinement near the polymer-fiber interface hinders diffusion of the water molecules into the polymer matrix. These molecular level insights bolster the hypothesis formulated in previous experimental studies that absorbed moisture behaves like free water in terms of its dielectric activity when the water molecules agglomerate at the damage location. Consequently, this locally distinct permittivity can be leveraged for damage detection and quantification.}, journal={COMPUTATIONAL MATERIALS SCIENCE}, author={Guha, Rishabh D. and Rahmani, Farzin and Berkowitz, Katherine and Pasquinelli, Melissa and Grace, Landon R.}, year={2022}, month={Nov} }
 @article{casimir_pavone_faircloth_khan_khawaja_grace_fransen_mclaughlin_2021, title={A Human Factors Evaluation of a Screening System for Diabetic Retinopathy Centered in Psychological Theory}, ISSN={["2169-5083"]}, DOI={10.1177/10648046211039911}, abstractNote={ People with diabetes are at risk for diabetic retinopathy (DR), a leading cause of blindness. Early treatment can preserve sight; however, screening rates are low. We utilized psychological theories of motivation in tandem with human factors tools such as heuristic evaluation and task analysis to develop interventions to improve screening rates at a single clinic. Interventions addressed the system of screening, from the patients and their choices to clinic workers, device usability, and the clinic environment. Findings showed potential solutions to the screening issue situated within the theory of planned behavior. Future steps are to refine interventions and measure effectiveness. }, journal={ERGONOMICS IN DESIGN}, author={Casimir, Alexander T. and Pavone, Adrian M. and Faircloth, Abby and Khan, Amina and Khawaja, Ommar and Grace, Landon and Fransen, Stephen and McLaughlin, Anne Collins}, year={2021}, month={Aug} }
 @article{idolor_guha_berkowitz_grace_2021, title={An experimental study of the dynamic molecular state of transient moisture in damaged polymer composites}, volume={42}, ISSN={["1548-0569"]}, url={https://doi.org/10.1002/pc.26066}, DOI={10.1002/pc.26066}, abstractNote={Abstract}, number={7}, journal={POLYMER COMPOSITES}, publisher={Wiley}, author={Idolor, Ogheneovo and Guha, Rishabh Debraj and Berkowitz, Katherine and Grace, Landon}, year={2021}, month={Jul}, pages={3391–3403} }
 @article{guha_idolor_berkowitz_pasquinelli_grace_2021, title={Exploring secondary interactions and the role of temperature in moisture-contaminated polymer networks through molecular simulations}, volume={17}, ISSN={["1744-6848"]}, url={https://doi.org/10.1039/D0SM02009E}, DOI={10.1039/d0sm02009e}, abstractNote={We investigated the effect of temperature variation on the secondary bonding interactions between absorbed moisture and epoxies with different morphologies using molecular dynamics simulations.}, number={10}, journal={SOFT MATTER}, publisher={Royal Society of Chemistry (RSC)}, author={Guha, Rishabh D. and Idolor, Ogheneovo and Berkowitz, Katherine and Pasquinelli, Melissa and Grace, Landon R.}, year={2021}, month={Mar}, pages={2942–2956} }
 @article{guha_idolor_berkowitz_pasquinelli_grace_2021, title={Exploring secondary interactions and the role of temperature in moisture-contaminated polymer networks through molecular simulations (vol 17, pg 2942, 2021)}, volume={5}, ISSN={["1744-6848"]}, DOI={10.1039/d1sm90100a}, abstractNote={Correction for ‘Exploring secondary interactions and the role of temperature in moisture-contaminated polymer networks through molecular simulations’ by Rishabh D. Guha et al., Soft Matter, 2021, 17, 2942–2956, DOI: 10.1039/D0SM02009E.}, journal={SOFT MATTER}, author={Guha, Rishabh D. and Idolor, Ogheneovo and Berkowitz, Katherine and Pasquinelli, Melissa and Grace, Landon R.}, year={2021}, month={May} }
 @article{ju_kim_li_knowles_mills_grace_jur_2021, title={Inkjet Printed Textile Force Sensitive Resistors for Wearable and Healthcare Devices}, volume={7}, ISSN={["2192-2659"]}, url={https://doi.org/10.1002/adhm.202100893}, DOI={10.1002/adhm.202100893}, abstractNote={Abstract}, journal={ADVANCED HEALTHCARE MATERIALS}, author={Ju, Beomjun and Kim, Inhwan and Li, Braden M. and Knowles, Caitlin G. and Mills, Amanda and Grace, Landon and Jur, Jesse S.}, year={2021}, month={Jul} }
 @article{idolor_guha_berkowitz_geiger_davenport_grace_2021, title={Polymer-water interactions and damage detection in polymer matrix composites}, volume={211}, ISSN={["1879-1069"]}, url={https://doi.org/10.1016/j.compositesb.2021.108637}, DOI={10.1016/j.compositesb.2021.108637}, abstractNote={Polymer matrix composites have a tendency to absorb measurable moisture in nearly all operating environments. This absorbed moisture either becomes bound to the polymer network via secondary bonding interactions or exists as free water with negligible interactions. Damage creates new internal free volume where water molecules can exist in the latter state. This study introduces a novel basis for non-destructive examination in polymer matrix composites which leverages locally-higher concentration of free water in damaged areas. Experiments involved impact-induced sub-surface damage in a laminate prior to moisture exposure. Polymer-water interaction—determining the free or bound state of water—was characterized by near-infrared spectroscopy and microwave-range relative permittivity. Results show a direct correlation between the extent of local damage and higher relative levels of free water at damage sites.}, journal={COMPOSITES PART B-ENGINEERING}, publisher={Elsevier BV}, author={Idolor, Ogheneovo and Guha, Rishabh Debraj and Berkowitz, Katherine and Geiger, Carl and Davenport, Matthew and Grace, Landon}, year={2021}, month={Apr} }
 @article{guha_idolor_grace_2020, title={An atomistic simulation study investigating the effect of varying network structure and polarity in a moisture contaminated epoxy network}, volume={179}, ISSN={["1879-0801"]}, DOI={10.1016/j.commatsci.2020.109683}, abstractNote={Absorbed moisture is a frequent contributor to performance loss in polymer-based composite structures operating in nearly all environments. However, the fundamental mechanisms that govern water-polymer interaction remain poorly understood. In this molecular dynamics study, the polarity and internal structure of an epoxy-based composite matrix was varied through manipulation of crosslink density. A commonly used epoxy-hardener combination (DGEBA- DETA) was chosen and four different models were created with crosslinking density of 20%, 51%, 65% and 81% respectively. The results indicate that the increase in crosslinking leads to a greater availability of polar sites with a concomitant rise in available free volume. The rise in network polarity aids the hydrogen bonding interactions between the absorbed water and the composite matrix, but the greater availability of free volume also allows water molecules to cluster together through mutual hydrogen bonding activity. This results in a subsequent decrease in moisture interaction with polar sites at very high crosslink densities. It was also found that the diffusivity and average dipole moment of the absorbed moisture are correlated with the state of water molecules and that a greater percentage of network-bonded molecules tends to lower both of these quantities. These results are consistent with previously published experimental results which have contemplated the dual nature of water molecules in an epoxy network. The results also highlight the potential of leveraging this phenomenon for non-destructive inspection of the physical and chemical state of a polymer network.}, journal={COMPUTATIONAL MATERIALS SCIENCE}, author={Guha, Rishabh Debraj and Idolor, Ogheneovo and Grace, Landon}, year={2020}, month={Jun} }
 @article{weisson_fittipaldi_concepcion_pelaez_grace_tse_2020, title={Automated Noncontact Facial Topography Mapping, 3-Dimensional Printing, and Silicone Casting of Orbital Prosthesis}, volume={220}, ISSN={["1879-1891"]}, DOI={10.1016/j.ajo.2020.06.032}, abstractNote={A proof-of-concept workflow study for the fabrication of custom orbital exenteration prostheses via automated noncontact scanning, 3D printing, and silicone casting.Noncomparative, interventional case series.Setting: Single-center institutional study. StudyPopulation: Three patients who have discontinued wearing of the ocularist-made exenteration prosthesis due to altered fit, discoloration, or material degradation. InterventionProcedure: A digital representation of the exenteration socket and contralateral periocular region was captured through noncontact facial topography mapping. Digital construction of the anterior prosthesis surface was based on the mirrored image of the contralateral side, and the posterior surface contour was based on orbital cavity geometry. The anterior and posterior surface details were digitally merged. A 2-piece mold was designed and produced in a 3D printer. Colorimetry was used to create a custom blend of pigments for incorporation into the Shore 40 silicone elastomer to generate a prosthesis that approximates the patient's skin tone. MainOutcomeMeasures: Prosthesis symmetry, skin tone match, comfort of wear, and appearance.The first copy of every 3D-printed orbital prosthesis using this fabrication workflow produced good symmetry, color match, and prosthesis fit. In one case, the recontoured second copy with improved prosthesis edge-to-skin interface was made without the patient present.A noncontact 3D scanning, computer-aided design, 3D printing, and silicone casting for fabrication of orbital prosthesis was developed and validated. This production workflow has the potential to provide an efficient, standardized, reproducible exenteration prosthesis and to overcome the principal barriers to an affordable custom prosthesis worldwide: access and cost.}, journal={AMERICAN JOURNAL OF OPHTHALMOLOGY}, author={Weisson, Ernesto H. and Fittipaldi, Mauro and Concepcion, Carlos A. and Pelaez, Daniel and Grace, Landon and Tse, David T.}, year={2020}, month={Dec}, pages={27–36} }
 @article{fleischman_kaskar_shams_zhang_olson_zdanski_thorp_kuznetsov_grace_lee_2019, title={A Novel Porcine Model for the Study of Cerebrospinal Fluid Dynamics: Development and Preliminary Results}, volume={10}, ISSN={["1664-2295"]}, DOI={10.3389/fneur.2019.01137}, abstractNote={Idiopathic intracranial hypertension, space-flight associated neuro-ocular syndrome (SANS), and glaucoma are conditions that are among a spectrum of cerebrospinal fluid (CSF)-related ophthalmologic disease. This implies that local CSF pressures at the level of the optic nerve are involved to variable extent in these disease processes. However, CSF pressure measurements are problematic due to invasiveness and interpretation. The pressure measured by a lumbar puncture is likely not the same as the orbital CSF pressure. It is believed this is at least in part due to the flow restrictive properties of the optic canal. To investigate CSF flow within the orbit, a model for CSF dynamics was created using three medium-sized pigs. Contrast was administered through a lumbar subarachnoid space access. The contrast front was imaged with repeated computed tomographic (CT) imaging. Once contrast entered the orbit, rapid, sequential CT imaging was performed until the contrast reached the posterior globe. Head tilting was performed to highlight the role of gravitational dependence within the subarachnoid space.}, journal={FRONTIERS IN NEUROLOGY}, author={Fleischman, David and Kaskar, Omkar and Shams, Rayad and Zhang, Xinxin and Olson, Daniel and Zdanski, Carlton and Thorp, Brian D. and Kuznetsov, Andrey V and Grace, Landon and Lee, Yueh Z.}, year={2019}, month={Oct} }
 @article{kaskar_fleischman_lee_thorp_kuznetsov_grace_2019, title={Identifying the Critical Factors Governing Translaminar Pressure Differential Through a Compartmental Model}, volume={60}, ISSN={["1552-5783"]}, DOI={10.1167/iovs.18-26200}, abstractNote={Purpose The effective management of glaucoma is hindered by an incomplete understanding of its pathologic mechanism. While important, intraocular pressure (IOP) alone is inadequate in explaining glaucoma. Non-IOP–mediated risk factors such as cerebrospinal fluid (CSF) pressure have been reported to contribute to glaucomatous optic neuropathy. Due to the difficulty associated with experimental measurement of the salient variables, such as the retrobulbar CSF pressure, porosity of the subarachnoid space (SAS), and especially those concerned with the perioptic SAS, there remains a limited understanding of the CSF behavior contributing to the translaminar pressure gradient (TLPG), hypothesized to be a critical factor in the development of glaucoma. Method An integrated compartmental model describing the intracranial and orbital CSF dynamics, coupled with intraocular dynamics, is developed based on first principles of fluid mechanics. A sensitivity analysis is performed to identify anatomic characteristics that significantly affect the retrobulbar subarachnoid space (RSAS) pressure and, consequently, the TLPG. Results Of the 28 parameters considered, the RSAS pressure is most sensitive to CSF flow resistance in the optic nerve SAS and the potential lymphatic outflow from the optic nerve SAS into the orbital space. A parametric study demonstrates that a combination of resistance in the range of 1.600 × 1012 − 1.930 × 1012 Pa s/m3 (200.0 − 241.3 mm Hg min/mL) with 5% to 10% lymphatic CSF outflow yields RSAS pressures that are consistent with the limited number of studies in the literature. Conclusions The results suggest that a small percentage of lymphatic CSF outflow through the optic nerve SAS is likely. In addition, flow resistance in the orbital CSF space, hypothesized to be a function of patient-specific optic nerve SAS architecture and optic canal geometry, is a critical parameter in regulating the RSAS pressure and TLPG.}, number={8}, journal={INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE}, author={Kaskar, Omkar G. and Fleischman, David and Lee, Yueh Z. and Thorp, Brian D. and Kuznetsov, Andrey V. and Grace, Landon}, year={2019}, month={Jul}, pages={3204–3214} }
 @article{rodriguez_damley-strnad_grace_2019, title={Temperature and anisotropy effects in the application of the hindered diffusion model to composite laminates}, volume={38}, ISSN={["1530-7964"]}, DOI={10.1177/0731684419839220}, abstractNote={The one-dimensional hindered diffusion model was applied to gravimetric moisture uptake data for a six-ply high-temperature quartz-fiber-reinforced bismaleimide laminate. Diffusion behavior was evaluated as a function of specimen geometry and temperature to determine the effect on both diffusivity and the binding and unbinding probabilities of diffusing water molecules predicted by the model. Pre-equilibrium experimental uptake data were used to recover model parameters, including equilibrium moisture content, for specimens designed with intentionally-low planar surface-to-edge area ratios of 20, 12.5, and 5. Gravimetric uptake data for fully-immersed laminates at 25°C, 37°C, and 50°C was used to determine diffusion parameters and characterize the temperature and geometry-dependent behavior of the laminate. A parameter recovery method employing least-squares regression was used to determine best-fit parameters of the hindered diffusion model, including diffusivity (DZ), equilibrium moisture content ( M ∞ ), and molecular binding ( γ ) and unbinding ( β ) probabilities. Results indicate that binding and unbinding probabilities are independent of specimen geometry and material anisotropy. Further, while molecular binding and unbinding probabilities were both directly correlated with immersion temperature, the hindrance coefficient was modestly lower at 50°C, indicating increased bound-phase molecules at high temperatures.}, number={13}, journal={JOURNAL OF REINFORCED PLASTICS AND COMPOSITES}, author={Rodriguez, Luis A. and Damley-Strnad, Alexandra and Grace, Landon R.}, year={2019}, month={Jul}, pages={628–639} }
 @article{morales_kaskar_grace_2018, title={Design and processing of an elastomeric nanocomposite for biomedical pressure sensing applications}, volume={17}, ISSN={["2352-4928"]}, DOI={10.1016/j.mtcomm.2018.09.019}, abstractNote={Taguchi Method is used to identify parameter effects and interactions to inform the design and processing of a carbon black (CB) and poly(styrene-isobutylene-styrene) (SIBS) nanocomposite. Potential uses include stick-to-skin pressure sensors and other applications for which targeted mechanical properties and pressure sensitivity derived from the tailorability of SIBS/CB are required. Specimens ranging from 10% to 20% CB content by weight were fabricated by high-shear mixing, ultrasonication, and solvent casting. The relationship between pressure-sensing capability and tensile strength of SIBS/CB nanocomposites is complex and dependent upon nanoparticle dispersion (represented by high-shear mixing time), CB content, and casting temperature. By using an L8 3-Factor 2-Level Taguchi orthogonal array and screening analysis, design and processing parameters to achieve targeted mechanical and electrical performance of SIBS/CB nanocomposites can be determined through a relatively small number of experiments. Main effects and interactions of the processing parameters were identified. Analysis indicates that mechanical strength is highly dependent on CB content and dispersion (mixing time), whereas pressure-dependent electrical resistance is highly dependent on CB content and casting temperature. The predictive models derived from these efforts will enable preliminary design of processing parameters for SIBS/CB nanocomposites to targeted, application-specific mechanical and pressure-sensing properties.}, journal={MATERIALS TODAY COMMUNICATIONS}, author={Morales, Brigitte and Kaskar, Omkar and Grace, Landon R.}, year={2018}, month={Dec}, pages={278–288} }
 @article{rodriguez_garcia_grace_2018, title={Long-term durability of a water-contaminated quartz-reinforced bismaleimide laminate}, volume={39}, ISSN={["1548-0569"]}, DOI={10.1002/pc.24255}, abstractNote={The long‐term structural viability of a six‐ply water‐contaminated quartz fiber‐reinforced bismaleimide laminate is investigated via dynamic mechanical analysis and flexural strength assessment over a four‐year experimental time frame. Water contamination is achieved via immersion in water at 25°C for short‐term (2 weeks and 1 month), long‐term (6 months), and very long‐term (4 years) duration. Long‐term moisture uptake exhibits distinctly non‐Fickian behavior. Maximum moisture content exceeds 1.5% by weight after four years of immersion. Laminates exhibit a remarkable resistance to degradation for all exposure durations. Flexural strength decreased by roughly 5% in the worst case. Further, no significant change in glass transition temperature was observed. Scanning electron microscopy revealed no micro‐crack formation and a relatively low incidence of fiber–matrix debond. Experimental evidence suggests that quartz fiber‐reinforced bismaleimide is a viable option for long‐term moisture‐prone structural applications at moderate temperatures. POLYM. COMPOS., 39:2643–2649, 2018. © 2016 Society of Plastics Engineers}, number={8}, journal={POLYMER COMPOSITES}, author={Rodriguez, L. A. and Garcia, C. and Grace, L. R.}, year={2018}, month={Aug}, pages={2643–2649} }
 @article{fittipaldi_grace_2018, title={Modeling the effects of lipid contamination in poly(styrene-isobutylene-styrene) (SIBS)}, volume={80}, ISSN={["1878-0180"]}, DOI={10.1016/j.jmbbm.2018.01.030}, abstractNote={Lipid uptake and subsequent degradation was characterized as a function of molecular weight and styrene content in four different formulations of poly(styrene-block-Isobutylene-block-styrene) (SIBS). Mechanical testing in uniaxial tension at varying lipid concentrations showed a consistent decrease in tensile strength for all specimens due to lipid contamination. Higher styrene content was associated with an improved resistance to lipid intrusion. A decrease in elongation at break was observed for low molecular weight formulations only; an expected result of the stiffer network and local chain motion restriction due to increased entanglements in high molecular weight SIBS. A new, coupled diffusion/finite element method was used to recover the swelling coefficient of the four different SIBS formulations. The Ogden strain-density energy function recovered from unidirectional tensile testing and diffusion properties from gravimetric analysis were used to construct the finite element model. The predicted swelling behavior matched experimental data and the swelling coefficients were recovered for all formulations tested. Results indicate that the higher lipid affinity of the isobutylene phase contributed to increased swelling, as expected. This novel method to calculate swelling coefficient effectively circumvents the inability of commonly-used thermal deswelling methods to characterize lipid and oil-induced swelling behavior; enabling better prediction of long-term in vivo performance of polymer-based biomedical devices and more accurate evaluation of lipid-induced degradation and swelling.}, journal={JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS}, author={Fittipaldi, Mauro and Grace, Landon R.}, year={2018}, month={Apr}, pages={97–103} }
 @article{fittipaldi_grace_2017, title={Lipid-induced degradation in biocompatible poly(Styrene-Isobutylene-Styrene) (SIBS) thermoplastic elastomer}, volume={68}, ISSN={["1878-0180"]}, DOI={10.1016/j.jmbbm.2017.01.031}, abstractNote={The thermoplastic elastomer Poly(Styrene-block-Isobutylene-block-Styrene) (SIBS) is highly biocompatible, which has led to its use in several commercially-available implants. However, lipid-induced degradation has been previously identified as a primary cause of failure in long-term SIBS implants subject to mechanical loading. Thus, understanding the mechanisms and extent of lipid-induced damage and the role of styrene-isobutylene ratio and molecular weight is critical to improving longevity of SIBS-based implants in order to fully exploit the biocompatibility advantages. Samples of four different SIBS formulations were fabricated via compression molding, immersed to lipid saturation contents from 5 to 80% by weight, and tested in uniaxial tension, stress relaxation, and dynamic creep modes. Degradation mechanisms were investigated via infrared spectroscopy, chromatography, and microscopy. No evidence of lipid-induced chemical interactions or chain scissoring was observed. However, a decrease in tensile strength, loss of dynamic creep performance and faster relaxation with increasing lipid content is attributed to strong internal straining. The magnitude of these losses is inversely proportional to both molecular weight and styrene content, suggesting that selection of these variables during the design phase should be based not only on the mechanical requirements of the application, but the expected degree of lipid exposure.}, journal={JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS}, author={Fittipaldi, Mauro and Grace, Landon R.}, year={2017}, month={Apr}, pages={80–87} }
 @inproceedings{damley-strnad_fittipaldi_morales_grace_2017, title={The effect of lipid absorption on the mechanical properties of poly(styrene-block-isobutylene-block-styrene) for use in biomedical applications}, url={http://dx.doi.org/10.1063/1.5016760}, DOI={10.1063/1.5016760}, abstractNote={The decrease in tensile strength and increase in specimen weight due to lipid diffusion in a biocompatible thermoplastic elastomer was studied and quantified. Mechanical and viscoelastic properties of poly(styrene-isobutylene-styrene) (SIBS) block copolymer are critical to determine feasibility of certain load bearing in vivo applications. Moreover, changes of these properties due to the presence of lipids must be well understood for long-term bio implantation. Dumbbell specimens were thermoformed via injection molding and weights were recorded. Lipid uptake in the body was simulated by specimen immersion in palm and castor oils at 25 °C and 37 °C. After only 96 hours of immersion at body temperature (37 °C), dumbbell weight increased by 6% and 0.3% for palm oil and castor oil, respectively. These values correspond to a reduction in ultimate tensile strength of approximately 30% and 10%, respectively. These results restrict the use of this biocompatible polymer in certain critical components due to the high concentration of lipids in vivo. Based on these significant and rapid reductions in tensile strength in the presence of lipids, it is of vital importance to fully understand the bio-durability and lipid uptake characteristics of SIBS for future design and performance prediction of implantable devices. Further, the results highlight the necessity of improving lipid resistance in order to fully exploit the biocompatibility of SIBS.}, publisher={Author(s)}, author={Damley-Strnad, Alexandra and Fittipaldi, Mauro and Morales, Brigitte and Grace, Landon R.}, year={2017} }
 @article{fittipaldi_grace_2016, title={Lipid diffusion and swelling in a phase separated biocompatible thermoplastic elastomer}, volume={64}, ISSN={1751-6161}, url={http://dx.doi.org/10.1016/J.JMBBM.2016.07.016}, DOI={10.1016/J.JMBBM.2016.07.016}, abstractNote={Lipid uptake was analyzed via gravimetric measurements in a biocompatible poly(styrene-block-isobutylene-block-styrene) (SIBS) copolymer. Absorption followed Fickian diffusion behavior very closely, although some deviation was noticed once saturation was reached. Diffusion parameters of three different SIBS formulations were calculated and used to predict the behavior of a fourth type based on molecular weight and relative polystyrene content. SIBS with lower polystyrene content and molecular weight showed lower physical stability and developed surface cracks that propagated with exposure to the lipid medium. Saturation lipid content varied from 45% to 63% by weight and was inversely related to polystyrene content, suggesting most of the plasticization is occurring in the isobutylene phase of SIBS. Moreover, swelling of specimens was monitored throughout the immersion in the lipid medium and ranged from 32% to 58%. Swelling in formulations with lower hard phase (polystyrene) was significantly higher than the swelling in SIBS with higher hard phase content. This is consistent with lipid-induced plasticization occurring in the soft (polyisobutylene) segments, relaxing the polymer network and leading to increased swelling and lipid uptake. The biocompatibility and tailorability of SIBS through control of hard/soft phase ratio offer significant advantages for in vivo applications. However, the lipophilic nature of the material and the associated degradation may render the polymer unusable in certain applications. The predictive model of lipid uptake introduced here will allow more accurate evaluation of lipid susceptibility during the preliminary design phase of SIBS-based in vivo structures.}, journal={Journal of the Mechanical Behavior of Biomedical Materials}, publisher={Elsevier BV}, author={Fittipaldi, Mauro and Grace, Landon R.}, year={2016}, month={Dec}, pages={1–9} }
 @inproceedings{fittipaldi_garcia_rodriguez_grace_2016, title={Optimization of injection molding parameters for poly(styrene-isobutylene-styrene) block copolymer}, url={http://dx.doi.org/10.1063/1.4942269}, DOI={10.1063/1.4942269}, abstractNote={Poly(styrene-isobutylene-styrene) (SIBS) is a widely used thermoplastic elastomer in bioimplantable devices due to its inherent stability in vivo. However, the properties of the material are highly dependent on the fabrication conditions, molecular weight, and styrene content. An optimization method for injection molding is herein proposed which can be applied to varying SIBS formulations in order to maximize ultimate tensile strength, which is critical to certain load-bearing implantable applications. The number of injection molded samples required to ascertain the optimum conditions for maximum ultimate tensile strength is limited in order to minimize experimental time and effort. Injection molding parameters including nozzle temperature (three levels: 218, 246, and 274 °C), mold temperature (three levels: 50, 85, and 120 °C), injection speed (three levels: slow, medium and fast) and holding pressure time (three levels: 2, 6, and 10 seconds) were varied to fabricate dumbbell specimens for tensile testin...}, publisher={AIP Publishing LLC}, author={Fittipaldi, Mauro and Garcia, Carla and Rodriguez, Luis A. and Grace, Landon R.}, year={2016} }
 @article{grace_2016, title={Projecting long-term non-Fickian diffusion behavior in polymeric composites based on short-term data: a 5-year validation study}, volume={51}, ISSN={0022-2461 1573-4803}, url={http://dx.doi.org/10.1007/S10853-015-9407-0}, DOI={10.1007/S10853-015-9407-0}, number={2}, journal={Journal of Materials Science}, publisher={Springer Science and Business Media LLC}, author={Grace, Landon R.}, year={2016}, month={Jan}, pages={845–853} }
 @inproceedings{rodriguez_garcía_fittipaldi_grace_2016, title={Reversible dielectric property degradation in moisture-contaminated fiber-reinforced laminates}, url={http://dx.doi.org/10.1063/1.4942332}, DOI={10.1063/1.4942332}, abstractNote={The potential for recovery of dielectric properties of three water-contaminated fiber-reinforced laminates is investigated using a split-post dielectric resonant technique at X-band (10 GHz). The three material systems investigated are bismaleimide (BMI) reinforced with an eight-harness satin weave quartz fabric, an epoxy resin reinforced with an eight- harness satin weave glass fabric (style 7781), and the same epoxy reinforced with a four-harness woven glass fabric (style 4180). A direct correlation between moisture content, dielectric constant, and loss tangent was observed during moisture absorption by immersion in distilled water at 25 °C for five equivalent samples of each material system. This trend is observed through at least 0.72% water content by weight for all three systems. The absorption of water into the BMI, 7781 epoxy, and 4180 epoxy laminates resulted in a 4.66%, 3.35%, and 4.01% increase in dielectric constant for a 0.679%, 0.608%, and 0.719% increase in water content by weight, respectively. Likewise, a significant increase was noticed in loss tangent for each material. The same water content is responsible for a 228%, 71.4%, and 64.1% increase in loss tangent, respectively. Subsequent to full desorption through drying at elevated temperature, the dielectric constant and loss tangent of each laminate exhibited minimal change from the dry, pre-absorption state. The dielectric constant and loss tangent change after the absorption and desorption cycle, relative to the initial state, was 0.144 % and 2.63% in the BMI, 0.084% and 1.71% in the style 7781 epoxy, and 0.003% and 4.51% in the style 4180 epoxy at near-zero moisture content. The similarity of dielectric constant and loss tangent in samples prior to absorption and after desorption suggests that any chemical or morphological changes induced by the presence of water have not caused irreversible changes in the dielectric properties of the laminates.}, publisher={AIP Publishing LLC}, author={Rodriguez, Luis A. and García, Carla and Fittipaldi, Mauro and Grace, Landon R.}, year={2016} }
 @inproceedings{garcia_fittipaldi_grace_2015, title={Effect of nanoclay reinforcement on the X-band dielectric properties of epoxy resins for use in radome applications}, url={http://dx.doi.org/10.1063/1.4918450}, DOI={10.1063/1.4918450}, abstractNote={The suitability of nanoclay reinforcement for improvement of structural and electrical properties of thermosetting epoxy systems at 10 GHz is investigated via a resonant technique. The potential of nanoclay reinforcement to improve mechanical properties and mitigate moisture diffusion in polymer materials has been well-documented in recent years. Further, evidence has shown that the presence of moisture in polymer systems has a profoundly deleterious effect on relative permittivity and loss tangent of the material. This is particularly important for construction or coating of radar protecting structures (radome), in which low relative permittivity and loss tangent are critical to radar transparency. Therefore, the addition of nanoclay reinforcement to polymer composites used in radome applications may prove a viable method for dielectric and structural performance improvement and moisture absorption minimization. The relative permittivity and loss tangent of two epoxy resin systems are evaluated as a func...}, publisher={AIP Publishing LLC}, author={Garcia, Carla and Fittipaldi, Mauro and Grace, Landon R.}, year={2015} }
 @article{garcía_fittipaldi_grace_2015, title={Epoxy/montmorillonite nanocomposites for improving aircraft radome longevity}, volume={132}, ISSN={0021-8995}, url={http://dx.doi.org/10.1002/APP.42691}, DOI={10.1002/APP.42691}, abstractNote={ABSTRACT}, number={43}, journal={Journal of Applied Polymer Science}, publisher={Wiley}, author={García, Carla and Fittipaldi, Mauro and Grace, Landon R.}, year={2015}, month={Jul}, pages={n/a-n/a} }
 @article{fittipaldi_rodriguez_damley-strnad_grace_2015, title={Improving tensile strength of an injection-molded biocompatible thermoplastic elastomer}, volume={86}, ISSN={0264-1275}, url={http://dx.doi.org/10.1016/J.MATDES.2015.07.070}, DOI={10.1016/J.MATDES.2015.07.070}, abstractNote={Poly(styrene-block-isobutylene-block-styrene) (SIBS) is a thermoplastic elastomer often used in implantable structures due to its exceptional biocompatibility. However, because overall performance is extremely sensitive to fabrication conditions, optimal processing of the raw material remains a challenge. In this study, the Taguchi method is proposed for characterization of the effect of injection molding parameters on the ultimate tensile strength of a SIBS block copolymer. An L9 orthogonal array is used with three factor levels for nozzle temperature, mold temperature, packing time and injection speed. Analysis indicates that mold temperature has the least effect on tensile strength, and injection speed the greatest effect. A response surface methodology (RSM) design and an artificial neural network (ANN) were used to model tensile strength based on processing parameters. Both methods proved successful in predicting tensile strength with errors of 3% and 2.55% for RSM and ANN, respectively. Optimized validation samples showed ultimate tensile strengths of 17.7 MPa, which is an improvement of almost 40% over reported strengths for the same material. The results presented here are expected to expand the use of SIBS into new applications requiring improved mechanical properties, without sacrificing biocompatibility via the addition of fiber or particle reinforcement.}, journal={Materials & Design}, publisher={Elsevier BV}, author={Fittipaldi, Mauro and Rodriguez, Luis A. and Damley-Strnad, Alexandra and Grace, Landon R.}, year={2015}, month={Dec}, pages={6–13} }
 @inproceedings{rodriguez_garcía_grace_2015, title={The effect of in-service aerospace contaminants on X-band dielectric properties of a bismaleimide/quartz composite}, url={http://dx.doi.org/10.1063/1.4918423}, DOI={10.1063/1.4918423}, abstractNote={The impact of three common aerospace in-service liquid contaminants on the X-band dielectric properties of a polymer composite radar protecting structure (radome) is investigated and quantified. The dielectric properties of the composite laminate are critical to radar transparency, and thus performance, of the radome structure. Further, polymer composites are highly susceptible to absorption of liquids. As such, the effect of common aerospace contaminants on the dielectric properties of composite laminates is crucial. Measurement of relative permittivity and loss tangent via a split-post dielectric resonant technique at 10 GHz is used to determine the effect of water, deicing fluid, and propylene glycol absorption in a three-ply quartz-reinforced bismaleimide laminate. Additionally, fluid uptake kinetics are investigated as a function of liquid type. An approximately linear relationship between fluid content and relative permittivity is observed for all three contaminant types. A 1% increase in contaminant content by weight results in a 7.8%, 4.5%, and 2.5% increase in relative permittivity of the material due to water, deicing fluid, and propylene glycol, respectively. A more significant impact is seen in material loss tangent, where a 1% increase in contaminant content by weight is responsible for a 378.5%, 593.0%, and 441.5% increase in loss tangent due to the aforementioned fluids, respectively. A fluid uptake weight content of 1.31%, 3.41%, and 4.28% is achieved for water, deicing fluid, and propylene glycol respectively, at approximately 1300 hours exposure. Based on the reported observations, the dielectric property degradation of composite laminates due to these commonly used fluids is of significant concern for in-service aircraft radar systems routinely exposed to these contaminants.}, publisher={AIP Publishing LLC}, author={Rodriguez, Luis A. and García, Carla and Grace, Landon R.}, year={2015} }
 @article{grace_2015, title={The effect of moisture contamination on the relative permittivity of polymeric composite radar-protecting structures at X-band}, volume={128}, ISSN={0263-8223}, url={http://dx.doi.org/10.1016/J.COMPSTRUCT.2015.03.070}, DOI={10.1016/J.COMPSTRUCT.2015.03.070}, abstractNote={The impact of absorbed moisture on the X-band relative permittivity of three composite materials used in aircraft radar-protecting structures (radomes) is investigated, quantified, and analyzed with respect to existing effective medium theories. Two glass-fiber-reinforced epoxy laminates and a quartz-fiber reinforced bismaleimide laminate are fabricated, contaminated with water, and analyzed with a split-post dielectric resonator in order to determine moisture-induced relative permittivity changes at 10 GHz. In the most significant case, a 3.7% increase in water content by weight resulted in a 43% increase in relative permittivity for BMI/quartz laminates. Such an increase may be a root cause of radome-induced radar performance loss for long-service-life aircraft. The relationship between absorbed water volume and relative permittivity is not well described by the existing effective medium theories considered. Support is given to the existence of conditions which lead to restricted molecular dipole rotation of water within a polymer network and a resulting “effective” relative permittivity of water based on polymer chemistry and morphology. A simple power-law expression predicated upon this assumption successfully describes the relative permittivity increase as a result of absorbed water prior to equilibrium moisture condition.}, journal={Composite Structures}, publisher={Elsevier BV}, author={Grace, Landon R.}, year={2015}, month={Sep}, pages={305–312} }
 @inproceedings{fittipaldi_rodriguez_grace_2015, title={The effect of water absorption on the viscoelastic properties of poly(styrene-block-isobutylene-block-styrene) for use in biomedical applications}, url={http://dx.doi.org/10.1063/1.4918393}, DOI={10.1063/1.4918393}, abstractNote={The decrease in glass transition temperature and change in creep compliance due to water diffusion in a biocompatible thermoplastic elastomer was studied and quantified. Knowledge of the mechanical and viscoelastic performance of the styrene-isobutylene-styrene block (SIBS) copolymer is important to determine the feasibility of certain in-vivo applications. Furthermore, the deterioration in these types of properties due to the plasticizing effect of water must be well understood for long term usage. Samples were formed with an injection molding press and fully dried prior to immersion in distilled water at 37°C. Water diffusion kinetics were studied for four different SIBS copolymers of varying molecular weight and styrene content by measuring weight changes as a function of time. These gravimetric diffusion studies showed an inverse relationship between diffusivity and styrene content and molecular weight for the first thousand hours of immersion. Measurements of storage modulus, loss modulus, tangent de...}, publisher={AIP Publishing LLC}, author={Fittipaldi, Mauro and Rodriguez, Luis A. and Grace, Landon R.}, year={2015} }
 @article{grace_altan_2014, title={Three-dimensional anisotropic moisture absorption in quartz-reinforced bismaleimide laminates}, volume={54}, ISSN={0032-3888}, url={http://dx.doi.org/10.1002/PEN.23549}, DOI={10.1002/PEN.23549}, abstractNote={The three-dimensional anisotropic moisture absorption behavior of quartz-fiber-reinforced bismaleimide (BMI) laminates is investigated by collecting 21 months of experimental gravimetric data. Laminates of six, twelve, and forty plies and various planar aspect ratios are used to determine the three-dimensional anisotropic diffusion behavior when exposed to full immersion in distilled water at 25°C. The long-term moisture absorption behavior deviates from the widely used Fickian model, but can be accurately captured by the three-dimensional, anisotropic hindered diffusion model (3D HDM). Excellent agreement is achieved between experimental gravimetric data and the 3D HDM for all laminate thicknesses. Recovered model parameters are shown to slightly vary with laminate thickness due to the small changes in the cured-ply thickness. However, model parameters identified for a given laminate thickness are observed to accurately predict the absorption behavior of samples with different planar dimensions. Equilibrium moisture content of 1.72, 1.69, and 1.84% and corresponding diffusion hindrance coefficients of 0.807, 0.844, and 0.671 are recovered for six, twelve, and forty-ply laminates, respectively, thus confirming strong non-Fickian behavior. Moisture absorption parameters may be determined successfully at 16.5 months of immersion, before reaching approximately 85% of the equilibrium moisture content at 21 months. Subsequent gravimetric measurements up to 21 months are consistent with the predicted long-term behavior. POLYM. ENG. SCI., 54:137–146, 2014. © 2013 Society of Plastics Engineers}, number={1}, journal={Polymer Engineering & Science}, publisher={Wiley}, author={Grace, L.R. and Altan, M.C.}, year={2014}, month={Jan}, pages={137–146} }
 @article{grace_altan_2013, title={Non-fickian three-dimensional hindered moisture absorption in polymeric composites: Model development and validation}, volume={34}, ISSN={0272-8397}, url={http://dx.doi.org/10.1002/PC.22523}, DOI={10.1002/PC.22523}, abstractNote={A new, three-dimensional, anisotropic non-Fickian diffusion model is developed to characterize moisture absorption in polymeric composites. The new hindered diffusion model extends the classical Fickian theory to include the effects of the interaction of diffusing molecules with the chemical and physical structure of polymeric composites. The numerical solution of the hindered diffusion model is obtained for a three-dimensional, anisotropic domain by using a forward-time, centered-space finite difference technique. The moisture weight gain over time predicted by the model is shown to mimic a wide variety of anomalous absorption behavior, often exhibited by anisotropic composite laminates. The accuracy of the numerical solutions is verified by comparing the results to known analytical solutions of a one-dimensional, “Langmuir-type” diffusion model and for the limiting case of the three-dimensional Fickian model. The utility of the proposed hindered diffusion model is demonstrated by accurately recovering the absorption behavior of three different material systems reported in literature. First, it is shown that the hindered diffusion model can accurately predict the moisture absorption data for unidirectional glass-reinforced epoxy plates of varying dimensions exposed to a relative humidity of 80%. Second, the one-dimensional version of the model is applied to experimental moisture absorption data for isotropic epoxy resin samples of different thicknesses. Anomalous effects due to sample thickness reported in the original article are accurately captured. Third, the proposed model is shown to be more accurate than a two-stage diffusion model applied to moisture absorption data obtained from a woven 3-ply carbon fiber reinforced bismaleimide composite. POLYM. COMPOS., 34:1144–1157, 2013. © 2013 Society of Plastics Engineers}, number={7}, journal={Polymer Composites}, publisher={Wiley}, author={Grace, L.R. and Altan, M.C.}, year={2013}, month={Jun}, pages={1144–1157} }
 @article{grace_altan_2012, title={Characterization of anisotropic moisture absorption in polymeric composites using hindered diffusion model}, volume={43}, ISSN={1359-835X}, url={http://dx.doi.org/10.1016/j.compositesa.2012.03.016}, DOI={10.1016/j.compositesa.2012.03.016}, abstractNote={A new method to characterize three-dimensional, anisotropic moisture absorption in polymeric composites using experimental gravimetric absorption data is presented. This is achieved by using the three-dimensional hindered diffusion model to recover the moisture absorption properties of composites which may exhibit Fickian or non-Fickian behavior. Effectiveness of the recovery of absorption properties is assessed using artificially generated experimental data. Anisotropic diffusivities, equilibrium moisture content (M∞), and molecular binding (γ) and unbinding (β) probabilities that govern absorption dynamics are recovered by minimizing the difference between model predictions and experimental data. Using artificial moisture absorption data, diffusivities and M∞ are recovered with less than 1% error, whereas γ and β are recovered with less than 3% error in the non-Fickian diffusion case. Equilibrium moisture content is shown to be accurately determined much earlier by using partial gravimetric data obtained from the initial phases of absorption, even in the presence of considerable measurement error.}, number={8}, journal={Composites Part A: Applied Science and Manufacturing}, publisher={Elsevier BV}, author={Grace, L.R. and Altan, M.C.}, year={2012}, month={Aug}, pages={1187–1196} }