Antifibrotic properties of hyaluronic acid crosslinked polyisocyanide hydrogels

Tissue-Level Effects of Autologous Fat Grafting in Hypertrophic Scars-A Case Series Study

INTRODUCTION

Fat grafting has antifibrotic effects and it improves scar quality. However, the biological mechanisms of fat grafts on scar healing are poorly understood.

METHODS

This was a prospective study to identify differences in the epidermal and dermal structure, macrophage infiltration, or inflammatory and fibrotic markers in hypertrophic scars before and after fat grafting surgery compared to normal skin. Seven patients with hypertrophic scar completed the study. Biopsies from hypertrophic scars and normal skin were taken at the time of fat grafting surgery and follow-up biopsies 6 mo postoperatively. A clinical Patient and Observer Scar Assessment Scale was used to monitor the clinical aspects of the scars. Immunohistochemical stainings were performed to analyze the changes occurring in the hypertrophic scar tissue after fat grafting.

RESULTS

Hypertrophic scars demonstrated decreased presence of rete ridges and increased levels of the profibrotic transforming growth factor beta-1 (TGF-β1) (P < 0.05) compared to normal skin. Fat grafting significantly increased the presence of rete ridges to the level of normal skin and reduced TGF-β1 expression (hypertrophic scars + fat) (P < 0.05). Fat grafting also increased the total macrophage count (CD68 pan-macrophage marker) (P < 0.05) and M1 macrophage count (inducible nitric oxide synthase M1 macrophage marker) (P < 0.05). The clinical evaluation of the scars (Patient and Observer Scar Assessment Scale) by the observer and patients improved after fat grafting (P < 0.05).

CONCLUSIONS

Our findings indicate that fat grafting promotes normalization of skin by improving epidermal structure and reducing TGF-β1 levels and favors less fibrotic healing by regulating macrophages levels.

Nonlinear Elastic Bottlebrush Polymer Hydrogels Modulate Actomyosin Mediated Protrusion Formation in Mesenchymal Stromal Cells

The nonlinear elasticity of many tissue-specific extracellular matrices is difficult to recapitulate without the use of fibrous architectures, which couple strain-stiffening with stress relaxation. Herein, bottlebrush polymers are synthesized and crosslinked to form poly(ethylene glycol)-based hydrogels and used to study how strain-stiffening behavior affects human mesenchymal stromal cells (hMSCs). By tailoring the bottlebrush polymer length, the critical stress associated with the onset of network stiffening is systematically varied, and a unique protrusion-rich hMSC morphology emerges only at critical stresses within a biologically accessible stress regime. Local cell-matrix interactions are quantified using 3D traction force microscopy and small molecule inhibitors are used to identify cellular machinery that plays a critical role in hMSC mechanosensing of the engineered, strain-stiffening microenvironment. Collectively, this study demonstrates how covalently crosslinked bottlebrush polymer hydrogels can recapitulate strain-stiffening biomechanical cues at biologically relevant stresses and be used to probe how nonlinear elastic matrix properties regulate cellular processes.

Conductive Polyisocyanide Hydrogels Inhibit Fibrosis and Promote Myogenesis

Reliable in vitro models closely resembling native tissue are urgently needed for disease modeling and drug screening applications. Recently, conductive biomaterials have received increasing attention in the development of in vitro models as they permit exogenous electrical signals to guide cells toward a desired cellular response. Interestingly, they have demonstrated that they promote cellular proliferation and adhesion even without external electrical stimulation. This paper describes the development of a conductive, fully synthetic hydrogel based on hybrids of the peptide-modified polyisocyanide (PIC-RGD) and the relatively conductive poly(aniline-co-N-(4-sulfophenyl)aniline) (PASA) and its suitability as the in vitro matrix. We demonstrate that incorporating PASA enhances the PIC-RGD hydrogel's electroactive nature without significantly altering the fibrous architecture and nonlinear mechanics of the PIC-RGD network. The biocompatibility of our model was assessed through phenotyping cultured human foreskin fibroblasts (HFF) and murine C2C12 myoblasts. Immunofluorescence analysis revealed that PIC-PASA hydrogels inhibit the fibrotic behavior of HFFs while promoting myogenesis in C2C12 cells without electrical stimulation. The composite PIC-PASA hydrogel can actively change the cell fate of different cell types, providing an attractive tool to improve skin and muscle repair.