The Role of Focal Adhesion Kinase in Keratinocyte Fibrogenic Gene Expression.

Abnormal skin scarring causes functional impairment, psychological stress, and high socioeconomic cost. Evidence shows that altered mechanotransduction pathways have been linked to both inflammation and fibrosis, and that focal adhesion kinase (FAK) is a key mediator of these processes. We investigated the importance of keratinocyte FAK at the single cell level in key fibrogenic pathways critical for scar formation. Keratinocytes were isolated from wildtype and keratinocyte-specific FAK-deleted mice, cultured, and sorted into single cells. Keratinocytes were evaluated using a microfluidic-based platform for high-resolution transcriptional analysis. Partitive clustering, gene enrichment analysis, and network modeling were applied to characterize the significance of FAK on regulating keratinocyte subpopulations and fibrogenic pathways important for scar formation. Considerable transcriptional heterogeneity was observed within the keratinocyte populations. FAK-deleted keratinocytes demonstrated increased expression of genes integral to mechanotransduction and extracellular matrix production, including Igtbl, Mmpla, and Col4a1. Transcriptional activities upon FAK deletion were not identical across all single keratinocytes, resulting in higher frequency of a minor subpopulation characterized by a matrix-remodeling profile compared to wildtype keratinocyte population. The importance of keratinocyte FAK signaling gene expression was revealed. A minor subpopulation of keratinocytes characterized by a matrix-modulating profile may be a keratinocyte subset important for mechanotransduction and scar formation.

Empirical validation of the Operative Entrustability Assessment using resident performance in autologous breast reconstruction and hand surgery.

BACKGROUND: In 2013, we developed the Operative Entrustability Assessment (OEA) to facilitate evaluation and documentation of resident operative skills. This web-based tool provides real-time, transparent feedback to residents on operative performance. This study evaluated the construct validity of the OEA, assessing its association with operative time. METHODS: We used simple and multiple linear regression to estimate associations between OEA scores and operative time in selected procedures performed. RESULTS: OEAs were completed for 93 autologous breast reconstructions and 185 hand procedures. Self-assessed OEA was associated with shorter operative time in breast (p = 0.008) and hand (p = 0.036) cases. Evaluator OEA was associated with shorter operative time in breast (p = 0.018), but not hand cases (p = 0.377). Post-graduate year was not associated. CONCLUSIONS: The OEA demonstrates construct validity: increasing scores are associated with shorter operative time and are better predictors of operative time than post-graduate year, making it an option for documenting competence prior to graduation.

Nonoperative Management of Acute Upper Limb Ischemia.

BACKGROUND: Acute upper limb ischemia (AULI) is an uncommon emergency warranting immediate evaluation and treatment. The role of nonsurgical therapies including endovascular techniques, thrombolytics, and anticoagulation remains undefined. The authors systematically reviewed the current literature on the nonsurgical treatment of acute ischemia of the upper extremity. METHODS: A PubMed and Embase search was conducted, and articles were screened using predetermined criteria. Data collected included patient demographics, cause of upper limb ischemia, type of nonsurgical treatment used, treatment outcomes, and complications. Patients were divided into 4 treatment groups: catheter embolectomy, catheter-directed thrombolysis, endovascular stenting, and anticoagulation/medical therapy alone. RESULTS: Twenty-three retrospective studies met the search criteria. Of 1326 reported occlusions, 92% (1221) were attributed to thromboembolic disease. The second most common cause was iatrogenic (1.5%). Overall limb salvage rates were excellent with catheter embolectomy (862 of 882 cases, 97.7%) and catheter-directed thrombolysis (110 of 114 cases, 96.5%). Limb salvage rates were also high with anticoagulation/medical therapy (158 of 165 cases, 95.8%), but poor functional outcomes were more often reported. CONCLUSIONS: High-quality evidence to guide the nonsurgical treatment of AULI is lacking. Retrospective studies support the utility of catheter-based embolectomy and thrombolysis for distal ischemia. Whether a surgical or nonsurgical approach is taken, anticoagulation therapy remains a mainstay of both treatment and prevention of AULI. Because AULI patients often have underlying cardiac and/or systemic disease, a multidisciplinary approach is essential to minimize complications and prevent future occurrences.

The foreign body response: at the interface of surgery and bioengineering.

BACKGROUND: The surgical implantation of materials and devices has dramatically increased over the past decade. This trend is expected to continue with the broadening application of biomaterials and rapid expansion of aging populations. One major factor that limits the potential of implantable materials and devices is the foreign body response, an immunologic reaction characterized by chronic inflammation, foreign body giant cell formation, and fibrotic capsule formation. METHODS: The English literature on the foreign body response to implanted materials and devices is reviewed. RESULTS: Fibrotic encapsulation can cause device malfunction and dramatically limit the function of an implanted medical device or material. Basic science studies suggest a role for immune and inflammatory pathways at the implant-host interface that drive the foreign body response. Current strategies that aim to modulate the host response and improve construct biocompatibility appear promising. CONCLUSIONS: This review article summarizes recent basic science, preclinical, and clinicopathologic studies examining the mechanisms driving the foreign body response, with particular focus on breast implants and synthetic meshes. Understanding these molecular and cellular mechanisms will be critical for achieving the full potential of implanted biomaterials to restore human tissues and organs.

Enhancement of mesenchymal stem cell angiogenic capacity and stemness by a biomimetic hydrogel scaffold.

In this study, we examined the capacity of a biomimetic pullulan-collagen hydrogel to create a functional biomaterial-based stem cell niche for the delivery of mesenchymal stem cells (MSCs) into wounds. Murine bone marrow-derived MSCs were seeded into hydrogels and compared to MSCs grown in standard culture conditions. Hydrogels induced MSC secretion of angiogenic cytokines and expression of transcription factors associated with maintenance of pluripotency and self-renewal (Oct4, Sox2, Klf4) when compared to MSCs grown in standard conditions. An excisonal wound healing model was used to compare the ability of MSC-hydrogel constructs versus MSC injection alone to accelerate wound healing. Injection of MSCs did not significantly improve time to wound closure. In contrast, wounds treated with MSC-seeded hydrogels showed significantly accelerated healing and a return of skin appendages. Bioluminescence imaging and FACS analysis of luciferase+/GFP+ MSCs indicated that stem cells delivered within the hydrogel remained viable longer and demonstrated enhanced engraftment efficiency than those delivered via injection. Engrafted MSCs were found to differentiate into fibroblasts, pericytes and endothelial cells but did not contribute to the epidermis. Wounds treated with MSC-seeded hydrogels demonstrated significantly enhanced angiogenesis, which was associated with increased levels of VEGF and other angiogenic cytokines within the wounds. Our data suggest that biomimetic hydrogels provide a functional niche capable of augmenting MSC regenerative potential and enhancing wound healing.

Pullulan hydrogels improve mesenchymal stem cell delivery into high-oxidative-stress wounds.

Cell-based therapies for wound repair are limited by inefficient delivery systems that fail to protect cells from the acute inflammatory environment. Here, a biomimetic hydrogel system is described that is based on the polymer pullulan, a carbohydrate glucan known to exhibit potent antioxidant capabilities. It is shown that pullulan hydrogels are an effective cell delivery system and improve mesenchymal stem cell survival and engraftment in high-oxidative-stress environments. The results suggest that glucan hydrogel systems may prove beneficial for progenitor-cell-based approaches to skin regeneration.

Engineered pullulan-collagen composite dermal hydrogels improve early cutaneous wound healing.

New strategies for skin regeneration are needed to address the significant medical burden caused by cutaneous wounds and disease. In this study, pullulan-collagen composite hydrogel matrices were fabricated using a salt-induced phase inversion technique, resulting in a structured yet soft scaffold for skin engineering. Salt crystallization induced interconnected pore formation, and modification of collagen concentration permitted regulation of scaffold pore size. Hydrogel architecture recapitulated the reticular distribution of human dermal matrix while maintaining flexible properties essential for skin applications. In vitro, collagen hydrogel scaffolds retained their open porous architecture and viably sustained human fibroblasts and murine mesenchymal stem cells and endothelial cells. In vivo, hydrogel-treated murine excisional wounds demonstrated improved wound closure, which was associated with increased recruitment of stromal cells and formation of vascularized granulation tissue. In conclusion, salt-induced phase inversion techniques can be used to create modifiable pullulan-collagen composite dermal scaffolds that augment early wound healing. These novel biomatrices can potentially serve as a structured delivery template for cells and biomolecules in regenerative skin applications.