Gelatin Methacryloyl (GelMA) Hydrogel Scaffolds: Predicting Physical Properties Using an Experimental Design Approach

There is a growing interest for complex in vitro environments that closely mimic the extracellular matrix and allow cells to grow in microenvironments that are closer to the one in vivo. Protein-based matrices and especially hydrogels can answer this need, thanks to their similarity with the cell microenvironment and their ease of customization. In this study, an experimental design was conducted to study the influence of synthesis parameters on the physical properties of gelatin methacryloyl (GelMA). Temperature, ratio of methacrylic anhydride over gelatin, rate of addition, and stirring speed of the reaction were studied using a Doehlert matrix. Their impact on the following parameters was analyzed: degree of substitution, mass swelling ratio, storage modulus (log(G')), and compression modulus. This study highlights that the most impactful parameter was the ratio of methacrylic anhydride over gelatin. Although, temperature affected the degree of substitution, and methacrylic anhydride addition flow rate impacted the gel's physical properties, namely, its storage modulus and compression modulus. Moreover, this experimental design proposed a theoretical model that described the variation of GelMA's physical characteristics as a function of synthesis conditions.

Nonlinear Model for Viscoelastic Behavior of Achilles Tendon

Although the mechanical properties of ligament and tendon are well documented in research literature, very few unified mechanical formulations can describe a wide range of different loadings. The aim of this study was to propose a new model, which can describe tendon responses to various solicitations such as cycles of loading, unloading, and reloading or successive relaxations at different strain levels. In this work, experiments with cycles of loading and reloading at increasing strain level and sequences of relaxation were performed on white New Zealand rabbit Achilles tendons. We presented a local formulation of thermodynamic evolution outside equilibrium at a representative element volume scale to describe the tendon’s macroscopic behavior based on the notion of relaxed stress. It was shown that the model corresponds quite well to the experimental data. This work concludes with the complexity of tendons’ mechanical properties due to various microphysical mechanisms of deformation involved in loading such as the recruitment of collagen fibers, the rearrangement of the microstructure (i.e., collagens type I and III, proteoglycans, and water), and the evolution of relaxed stress linked to these mechanisms.

Adequacy of hospital discharge data for determining trauma morbidity patterns

To determine the adequacy of hospital discharge data for describing the nature and severity of multiple trauma, injury data coded from full hospital records were compared with injury data coded from discharge summaries for 83 plane crash survivors admitted to 14 different hospitals. Full hospital records indicated that 33% sustained intracranial, 39% thoracic, and 27% abdominal/pelvic injuries. Thirty-five percent had spinal fractures, 40% upper limb fractures, and 70% lower limb fractures. Discharge summary data missed 52% of the intracranial injuries, 28% of the thoracic injuries, and 30% of the spinal fractures, yet only missed 5% of the lower limb and 15% of the skull, pelvic, and upper limb fractures. These differences point to concerns regarding the use of discharge data for determining the nature, severity, and sequelae of injuries. The observed underreporting of neurological injury suggests a need to re-evaluate discharge data systems for measuring brain and spinal cord injury patterns, particularly given the increasing reliance on these systems for health policy and programmatic decision making.