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BACKGROUND: Lower extremity wounds in patients with diabetes are difficult to heal due to an overabundance of pro-inflammatory M1 macrophages, reduced phagocytosis of necrosed cells, and circulatory issues. Keratin biomaterials have been shown to address some of these concerns by encouraging the proliferation of anti-inflammatory M2 macrophages, thereby creating more favorable conditions for wound healing resembling those of patients without diabetes. OBJECTIVE: To investigate the effect of a novel human keratin matrix (HKM) on wound healing. MATERIALS AND METHODS: Ten patients with diabetes with lower extremity wounds at risk for delayed healing underwent wound debridement and application of HKM. Patients received weekly follow-up care and reapplication of HKM until healing occurred; wound size at each visit was used to calculate healing rate. RESULTS: Increased healing rates were noted with HKM compared with standard of care (SOC), including debridement and collagen treatment in all 8 patients who had received SOC prior to HKM treatment. When HKM treatment was alternated with SOC in 2 patients due to other medical conditions, healing rates decreased with SOC and then increased after reintroduction of HKM applications. CONCLUSIONS: These results suggest that HKM may help regulate the pathological processes that contribute to wound chronicity to "kick-start" wound healing. This case series demonstrates that HKM is a promising technology to improve healing rates in nonhealing lower extremity wounds in patients with diabetes.

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A wide variety of biomaterials has been developed to assist in wound healing, including acellular animal and human-derived protein matrices. However, millions of patients worldwide still suffer from non-healing chronic wounds, demonstrating a need for further innovation in wound care. To address this need, a novel biomaterial, the human keratin matrix (HKM), was developed, characterised, and tested in vitro and in vivo. HKM was found to be degradation-resistant, and a proteomics analysis showed it to be greater than 99% human keratin proteins. PCR revealed adult human epidermal keratinocytes (HEKa) grown in contact with HKM showed increased gene expression of keratinocyte activations markers such as Epidermal Growth Factor (EGF). Additionally, a cytokine microarray demonstrated culture on HKM increased the release of cytokines involved in wound inflammatory modulation by both HEKa cells and adult human dermal fibroblasts (HDFa). Finally, in a murine chronic wound model, full-thickness wounds treated weekly with HKM were smaller through the healing process than those treated with human amniotic membrane (AM), bovine dermis (BD), or porcine decellularized small intestinal submucosa (SIS). HKM-treated wounds also closed significantly faster than AM- and SIS-treated wounds. These data suggest that HKM is an effective novel treatment for chronic wounds.

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Cells exist in the body in mechanically dynamic environments, yet the vast majority of in vitro cell culture is conducted on static materials such as plastic dishes and gels. To address this limitation, we report an approach to transition widely used hydrogels into mechanically active substrates by doping optomechanical actuator (OMA) nanoparticles within the polymer matrix. OMAs are composed of gold nanorods surrounded by a thermoresponsive polymer shell that rapidly collapses upon near-infrared (NIR) illumination. As a proof of concept, we crosslinked OMAs into laminin-gelatin hydrogels, generating up to 5 µm deformations triggered by NIR pulsing. This response was tunable by NIR intensity and OMA density within the gel and is generalizable to other hydrogel materials. Hydrogel mechanical stimulation enhanced myogenesis in C2C12 myoblasts as evidenced by ERK signaling, myocyte fusion, and sarcomeric myosin expression. We also demonstrate rescued differentiation in a chronic inflammation model as a result of mechanical stimulation. This work establishes OMA-actuated biomaterials as a powerful tool for in vitro mechanical manipulation with broad applications in the field of mechanobiology.

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Programmable mechanically active materials (MAMs) are defined as materials that can sense and transduce external stimuli into mechanical outputs or conversely that can detect mechanical stimuli and respond through an optical change or other change in the appearance of the material. Programmable MAMs are a subset of responsive materials and offer potential in next generation robotics and smart systems. This review specifically focuses on hydrogel-based MAMs because of their mechanical compliance, programmability, biocompatibility, and cost-efficiency. First, the composition of hydrogel MAMs along with the top-down and bottom-up approaches used for programming these materials are discussed. Next, the fundamental principles for engineering responsivity in MAMS, which includes optical, thermal, magnetic, electrical, chemical, and mechanical stimuli, are considered. Some advantages and disadvantages of different responsivities are compared. Then, to conclude, the emerging applications of hydrogel-based MAMs from recently published literature, as well as the future outlook of MAM studies, are summarized.

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The application of cyclic strain is known to enhance myoblast differentiation and muscle growth in vitro and in vivo. However, current techniques apply strain to full tissues or cell monolayers, making it difficult to evaluate whether mechanical stimulation at the subcellular or single-cell scales would drive myoblast differentiation. Here, we report the use of optomechanical actuator (OMA) particles, comprised of a ∼0.6 µm responsive hydrogel coating a gold nanorod (100 × 20 nm) core, to mechanically stimulate the integrin receptors in myoblasts. When illuminated with near-infrared (NIR) light, OMA nanoparticles rapidly collapse, exerting mechanical forces to cell receptors bound to immobilized particles. Using a pulsed illumination pattern, we applied cyclic integrin forces to C2C12 myoblasts cultured on a monolayer of OMA particles and then measured the cellular response. We found that 20 min of OMA actuation resulted in cellular elongation in the direction of the stimulus and enhancement of nuclear YAP1 accumulation, an effector of ERK phosphorylation. Cellular response was dependent on direct conjugation of RGD peptides to the OMA particles. Repeated OMA mechanical stimulation for 5 days led to enhanced myogenesis as quantified using cell alignment, fusion, and sarcomeric myosin expression in myotubes. OMA-mediated myogenesis was sensitive to the geometry of stimulation but not to MEK1/2 inhibition. Finally, we found that OMA stimulation in regions proximal to the nucleus resulted in localization of the transcription activator YAP-1 to the nucleus, further suggesting the role of YAP1 in mechanotransduction in C2C12 cells. These findings demonstrate OMAs as a novel tool for studying the role of spatially localized forces in influencing myogenesis.

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