Impacts of Prosthetic Innovation in Ecuador Study Abroad Course.

Biomedical engineering (BME) students typically have a schedule filled with specific course requirements, leaving little room for spending a semester studying abroad. We established a new short-term BME study abroad course, partnering with a non-profit healthcare organization that provides high-quality prosthetic care to underserved populations. This innovative study abroad course was met with great student demand. The impact of this short-term study abroad course is increased by developing year-long BME senior capstone design projects based on the needs identified throughout the experience in Ecuador. Shortly after the conclusion of spring semester, students and two BME faculty/staff traveled to Ecuador. During the work week, the students participated in small teams in patient evaluations, castings, fabrication of prosthetics, device fittings, rapid prototyping-testing iterations, and post-prosthesis gait training with physical therapy. Weekends included guided cultural activities. Each student maintained a journal that reflected observations and insights from these experiences. Upon return to the US, students that registered for an additional course credit created video reflection presentations and wrote project proposal reports based on the needs identified in Ecuador. The project proposal reports were used to develop a BME senior capstone design project. Pre and post course self-assessment surveys showed significant increases in five ABET learning outcomes, three BME learning outcomes, and four course-specific learning outcomes. Students who took the two-credit course reported significant increases in four more learning outcomes than students who took the one-credit course. Many students described the experience as inspiring and life-changing, and the program continues to run each summer.

Macrophage-like U937 cells recognize collagen fibrils with strain-induced discrete plasticity damage.

At its essence, biomechanical injury to soft tissues or tissue products means damage to collagen fibrils. To restore function, damaged collagen must be identified, then repaired or replaced. It is unclear at present what the kernel features of fibrillar damage are, how phagocytic or synthetic cells identify that damage, and how they respond. We recently identified a nanostructural motif characteristic of overloaded collagen fibrils that we have termed discrete plasticity. In this study, we have demonstrated that U937 macrophage-like cells respond specifically to overload-damaged collagen fibrils. Tendons from steer tails were bisected, one half undergoing 15 cycles of subrupture mechanical overload and the other serving as an unloaded control. Both halves were decellularized, producing sterile collagen scaffolds that contained either undamaged collagen fibrils, or fibrils with discrete plasticity damage. Matched-pairs were cultured with U937 cells differentiated to a macrophage-like form directly on the substrate. Morphological responses of the U937 cells to the two substrates-and evidence of collagenolysis by the cells-were assessed using scanning electron microscopy. Enzyme release into medium was quantified for prototypic matrix metalloproteinase-1 (MMP-1) collagenase, and MMP-9 gelatinase. When adherent to damaged collagen fibrils, the cells clustered less, showed ruffled membranes, and frequently spread: increasing their contact area with the damaged substrate. There was clear structural evidence of pericellular enzymolysis of damaged collagen-but not of control collagen. Cells on damaged collagen also released significantly less MMP-9. These results show that U937 macrophage-like cells recognize strain-induced discrete plasticity damage in collagen fibrils: an ability that may be important to their removal or repair.

Riboflavin-sensitized photo-crosslinking of collagen using a dental curing light.

BACKGROUND: Photo-crosslinking of biomolecules such as collagen and fibrinogen is an emerging area of research interest. The use of a small dental curing light with a non-toxic photosensitizer represents a novel, practical approach to periodontal wound treatment. OBJECTIVE: This study evaluated the effects of riboflavin-sensitized photo-oxidation using a dental curing light on two collagenous biomaterials, as a preliminary step towards developing a medical technology for wound closure/healing. METHODS: A collagenous biomaterial (DBP) and type I collagen gels were treated by this photo-oxidative technique and characterized by hydrothermal isometric tension (HIT) analysis, amino acid analysis, SDS-PAGE, and rheology. RESULTS: HIT analysis suggested that dental curing light exposure for 300 s with riboflavin produced heavily crosslinked DBP. Dental curing light exposure for 300 s with riboflavin also showed a reduction in lysine concentration of DBP. SDS-PAGE showed that dental curing light exposure for 30 or 300 s with riboflavin resulted in crosslinked collagen gels. Dental curing light exposure for 30 s with riboflavin yielded a collagen gel with the strongest rheological characteristics. CONCLUSIONS: This novel approach to wound treatment has potential for wide adoption and clinical use, particularly because dental curing lights, riboflavin, and collagen biomaterials are all used clinically, but not yet combined together as one technology for broad application.

Interactions of U937 macrophage-like cells with decellularized pericardial matrix materials: influence of crosslinking treatment.

While macrophages have been implicated in the failure of bioprosthetic heart valves, the macrophage response to crosslinked native pericardial collagen has not been previously investigated. Using decellularized bovine pericardium (DBP) as a model for native collagen, this study investigated the response of macrophage-like cells (U937s) to DBP, either: (i) untreated, or (ii) exogenously crosslinked with glutaraldehyde or 1-ethyl-3-(3-dimethyl-aminopropyl)-carbodiimide (EDC). We have previously validated the use of U937 cells as models for the response of human monocyte-derived macrophages to decellularized pericardial materials and, per our previous work, differentiated the U937 cells directly on the three material surfaces. After 72h in culture, the cells and medium were analyzed for DNA content, acid phosphatase activity, and cytokine and matrix metalloproteinase release. As well, cell/substrate samples were fixed for SEM. Fewer cells attached to or survived on the glutaraldehyde-treated substrate, and some showed an abnormal morphology compared to cells cultured on the other surfaces. Further, cells on glutaraldehyde-treated surfaces released more pro-inflammatory cytokines, more MMP-1 and less MMP-2 and MMP-9. The poor performance of the U937 macrophage-like cells on the glutaraldehyde-treated surfaces appears to be due to surface characteristics rather than to soluble aldehyde or other components leaching from the crosslinked material. These results provide evidence that crosslinking with glutaraldehyde is cytotoxic to macrophage-like cells, and that crosslinking with a zero-length crosslinker like EDC can be an acceptable alternative crosslinking treatment for biomaterials.

A hydrogel derived from decellularized dermal extracellular matrix.

The ECM of mammalian tissues has been used as a scaffold to facilitate the repair and reconstruction of numerous tissues. Such scaffolds are prepared in many forms including sheets, powders, and hydrogels. ECM hydrogels provide advantages such as injectability, the ability to fill an irregularly shaped space, and the inherent bioactivity of native matrix. However, material properties of ECM hydrogels and the effect of these properties upon cell behavior are neither well understood nor controlled. The objective of this study was to prepare and determine the structure, mechanics, and the cell response in vitro and in vivo of ECM hydrogels prepared from decellularized porcine dermis and urinary bladder tissues. Dermal ECM hydrogels were characterized by a more dense fiber architecture and greater mechanical integrity than urinary bladder ECM hydrogels, and showed a dose dependent increase in mechanical properties with ECM concentration. In vitro, dermal ECM hydrogels supported greater C2C12 myoblast fusion, and less fibroblast infiltration and less fibroblast mediated hydrogel contraction than urinary bladder ECM hydrogels. Both hydrogels were rapidly infiltrated by host cells, primarily macrophages, when implanted in a rat abdominal wall defect. Both ECM hydrogels degraded by 35 days in vivo, but UBM hydrogels degraded more quickly, and with greater amounts of myogenesis than dermal ECM. These results show that ECM hydrogel properties can be varied and partially controlled by the scaffold tissue source, and that these properties can markedly affect cell behavior.

An elastomeric patch electrospun from a blended solution of dermal extracellular matrix and biodegradable polyurethane for rat abdominal wall repair.

A biodegradable elastomeric scaffold was created by electrospinning a mixed solution of poly(ester urethane)urea (PEUU) and porcine dermal extracellular matrix (dECM) digest, with PEUU included to provide elasticity, flexibility, and mechanical support and dECM used to enhance bioactivity and biocompatibility. Micrographs and differential scanning calorimetry demonstrated partial miscibility between PEUU and dECM. With greater dECM content, scaffolds were found to possess lower breaking strains and suture retention strength, although initial modulus was greater with higher dECM concentrations. The hybrid scaffolds containing 0% to 50% dECM had tensile strengths of 5 to 7 MPa, breaking strains of 138% to 611%, initial moduli of 3 to 11 Mpa, and suture retention strengths of 35 to 59 MPa. When hydrated, scaffolds were found to contract markedly with 50% dECM content. When used in a rat full-thickness abdominal wall replacement model, no herniation, infection, or tissue adhesion was observed after 4 and 8 weeks with a scaffold containing 25% dECM or a control 100% PEUU scaffold. Scaffolds incorporating dECM were significantly thicker at the time of explant, with greater numbers of associated smooth muscle actin-positive staining cells than in the control, but minimal cellular infiltration and remodeling of the scaffold were detected regardless of dECM addition. The processing of dECM and PEUU from a mixed solution thus provided a scaffold with evidence of better bioactivity and with mechanical properties not achievable with digested dECM alone.