Synthesis and evaluation of injectable thermosensitive penta‐block copolymer hydrogel (PNIPAAm‐PCL‐PEG‐PCL‐PNIPAAm) and star‐shaped poly(CL─CO─LA)‐b‐PEG for wound healing applications

Abstract

Background Loss of skin integrity due to injury, burning, or illness makes the development of new treatment options necessary. Skin tissue engineering provides some solutions for these problems. Objective The potential of a biodegradable star‐shaped copolymer [Poly(CL─CO─LA)‐b‐PEG] and penta‐block copolymer hydrogel (PNIPAAm‐PCL‐PEG‐PCL‐PNIPAAm) was assessed for skin tissue engineering applications. Methods Two copolymers were synthesized for cellular culture scaffolds and their mechanical properties were compared. The resulting star‐shaped copolymer and thermosensitive penta‐block copolymer were characterized using Fourier transform infrared and nuclear magnetic resonance spectroscopy. The crystallizability of the two copolymers was analyzed using X‐ray diffraction. The resulting thermosensitive penta‐block copolymer was evaluated by differential thermal analysis, differential scanning calorimetry and thermogravimetric analysis. Scanning electron microscopy and in vitro degradation of the polymer network in phosphate buffer solutions (pH 7.4) at 37°C were also examined. The pore size of the gels was calculated with Image Analyzer software. Finally, the cytotoxic, morphological, and gene expression effects of copolymers on the skin fibroblast were evaluated. Results The experiments showed that the PNIPAAm‐PCL‐PEG‐PCL‐PNIPAAm polymer with the right composition and the expected molecular weight was achieved. The hydrogel had less crystallizability compared with its precursors. The resulting thermosensitive hydrogel had a three‐dimensional structure with interconnected pores that mimicked the extracellular matrix. The control of the degradability rate can be possible by weight percent changes. The pore size correlated with the polymer concentration in aqueous solution and the pore sizes of the 20 wt% hydrogel were better for fibroblast cultivation than those of the 10 wt% hydrogel. Cell proliferation on the 20% gel was more than that of the 10% gel. The hydrogel not only preserved the viability and phenotypical morphology of the entrapped cells but also stimulated the initial cell‐cell interactions and proliferation of fibroblasts. The hydrogel did not influence cell conformation and this property of the polymer underlined its safety. Cells seeded on this copolymer showed a normal and spear shape and formed a focal adhesion with the hydrogel surface. Notably, the hydrogel increased collagen I α1 and collagen III mRNAs expression. Conclusion Due to the low molecular weight and poor mechanical strength of the star‐shaped copolymer, it was not considered for fabrication of the scaffolds for wound healing. The biodegradable, biocompatible, injectable and thermosensitive PNIPAAm‐PCL‐PEG‐PCL‐PNIPAAm hydrogel in 20 wt% demonstrated a desirable potential for future application as a cell scaffold in skin tissue engineering and wound healing.

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