In this study, polyurethane (TPU) scaffolds were fabricated using freeze-drying technique and gelatin macromolecules immobilized on the activated surface by oxygen plasma treatment. Scanning electron microscopy (SEM) micrographs indicated an interconnected porous microstructure with randomly oriented pores. According to the results, the diameter of pores increased after plasma treatment and gelatin grafting. Fourier transform infrared spectroscopy illustrated that there is no inappropriate interaction between materials during processing; furthermore, attenuated total reflection Fourier transform infrared spectroscopy confirmed the immobilization of gelatin molecules on the surface of the plasma-treated polymeric scaffolds. Waterdrop contact angle analysis presented that wettability and hydrophilicity of constructs increased after grafting gelatin on the activated surface. Phosphate-buffered saline absorption and hydrolytic biodegradation enhanced after surface modification of the polymeric samples. Cellular behavior demonstrated better adhesion and spreading after grafting gelatin of oxygen plasma-treated constructs. No evidence of toxicity was observed for 7 days. DNA content determined that the number of viable cells increased in TPU-gelatin matrixes after 1 day in contrast with TPU scaffolds. Based on results, oxygen plasma treatment can create an activated surface to graft gelatin macromolecules and achieve optimum physicochemical, mechanical, and biological features for the neo-tissue formation.

In this study, retinoic acid loaded-PLGA-gelatin matrixes were prepared with both freeze-casting and freeze-drying techniques. Herein, the effect of unidirectional microstructure with tunable pores on release profile, cellular adhesion, migration, and differentiation was compared. Morphological observation determined that highly interconnected porous structure can be formed, but lamellar pore channels were observed in freeze-casting prepared constructs. The absorption ratio was increased, and the biodegradation rate was decreased as a function of the orientation of microstructure. The in-vitro release study illustrated non-Fickian release mechanism in both methods, so that erosion has predominated over diffusion. Accordingly, PLGA-gelatin scaffolds prepared with freeze-drying technique showed no adequate erosion due to the rigid structure, while freeze-casting one presented more favorable erosion. Microscopic observations of adhered P19 embryonic cells on the scaffolds showed that the freeze-casting matrixes with unidirectional pores provide a more compatible microenvironment for cell attachments and spreading. Besides, it facilitated cell migration and penetration inside the structure and may act as guidance for neuron growth. Improvement in the expression of neural genes in unidirectionally oriented pores proved the decisive role of contact guidance for nerve healing. It seems that the freeze-cast PLGA-gelatin-retinoic acid scaffolds have initial features for nerve tissue regeneration studies.