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Electrospinning of water-soluble polymers and retaining their mechanical strength and bioactivity remain challenging. Volatile organic solvent soluble polymers and their derivatives are preferred for fabricating electrospun nanofibers. We report the synthesis and characterization of 2-nitrobenzyl-gelatin (N-Gelatin)--a novel gelatin Schiff base derivative--and the resulting electrospun nanofiber matrices. The 2-nitrobenzyl group is a photoactivatable-caged compound and can be cleaved from the gelatin nanofiber matrices following UV exposure. Such hydrophobic modification allowed the fabrication of gelatin and blend nanofibers with poly(caprolactone) (PCL) having significantly improved tensile properties. Neat gelatin and their PCL blend nanofiber matrices showed a modulus of 9.08 ± 1.5 MPa and 27.61 ± 4.3 MPa, respectively while the modified gelatin and their blends showed 15.63 ± 2.8 MPa and 24.47 ± 8.7 MPa, respectively. The characteristic infrared spectroscopy band for gelatin Schiff base derivative at 1560 cm(-1) disappeared following exposure to UV light indicating the regeneration of free NH2 group and gelatin. These nanofiber matrices supported cell attachment and proliferation with a well spread morphology as evidenced through cell proliferation assay and microscopic techniques. Modified gelatin fiber matrices showed a 73% enhanced cell attachment and proliferation rate compared to pure gelatin. This polymer modification methodology may offer a promising way to fabricate electrospun nanofiber matrices using a variety of proteins and peptides without loss of bioactivity and mechanical strength.

Cartilage degeneration is the major cause of disability and poses several challenges to repair and regenerate. Conventional surgical treatments often induce fibrous tissues and compromise its function. Alternative tissue engineering strategies utilized scaffolds, factors and cells alone or in combination with some degree of success. This study reports the use of nanostructured biomimetic scaffold system in regulating the rat bone marrow stem cells (rBMSCs) differentiation into chondrogenic lineage in vitro. The biometric scaffold is essentially a micro-porous polycaprolactone (PCL) spiral structure decorated with sparsely spaced bioactive PCL nanofibers. The bioactivity stems from the use of two major components of hyaline cartilage extracellular matrix (ECM) namely chondroitin sulfate (CS) and hyaluronic acid (HYA). The PCL spiral structure was surface functionalized with PCL nanofibers encapsulated with CS (20% (w/w)) and HYA (0.2% (w/w)). In order to retain and sustain the release of CS and HYA nanofibers were cross-linked using carbodiimide chemistry. This study also evaluated the effect of nanofiber alignment on rBMSCs differentiation and evaluated the production of characteristic hyaline cartilage proteins namely collagen type II and aggrecan in vitro up to 28 days. Rat bone marrow derived stem cells cultured on the aligned nanofibers expressed significantly elevated levels of collagen type II and aggrecan secretions (western blots) as compared to scaffolds decorated with random fibers and tissue culture polystyrene (TCPS). This fiber alignment dependent expression of collagen type II and aggrecan secretion were further confirmed through immunofluorescence staining. This biomimetic and bioactive scaffold may serve as a serve as an efficient scaffold system for cartilage regeneration.

Scaffold architecture, surface topography, biochemical and mechanical cues have been shown to significantly improve cellular events and in vivo tissue regeneration. Specifically electrospun nanofiber matrices have gained tremendous interest due to their intrinsic structural resemblance to native tissue extracellular matrix (ECM). The present study reports on the electrospun nanofiber matrices of polycaprolactone (PCL)-chitosan (CS) blends and effect of type I collagen surface functionalization in regulating rat bone marrow derived stromal cells (rBMSCs) differentiation into osteogenic lineage. Collagen was covalently attached to blend nanofibers via carbodiimide (EDC) coupling. Bead-free smooth nanofibers (diameter-700-850 nm) obtained at the optimized conditions of polymer concentration and electrospinning parameters were used for the study. EDC collagen coupling resulted in 0.120+/-0.016 micro g of collagen immobilization onto a 1 cm2 area of the PCL/CS nanofibers, which was 2.6-folds higher than the amount of collagen that can be retained by physical adsorption. Significantly improved rBMSCs adhesion, spreading, proliferation and osteogenic differentiation was observed on the collagen functionalized COL-PCULCS nanofiber matrices as compared to control groups. Osteogenic phenotypic markers such as alkaline phosphatase (ALP) activity and mineralization were found to be significantly higher on COL-PCL/CS nanofiber matrices as compared to controls. Elevated gene expression profiles of osteogenic markers such as osteocalcin (0CN), osteopontin (OPN) and ALP further corroborate the osteoinductive nature of the collagen functionalized PCL/CS nanofiber matrices. These fiber matrices and modification techniques could be extended to other scaffold systems for tissue engineering applications.

Scaffold based bone tissue engineering (BTE) has made great progress in regenerating lost bone tissue. Materials of natural and synthetic origin have been used for scaffold fabrication. Scaffolds derived from natural polymers offer greater bioactivity and biocompatibility with mammalian tissues to favor tissue healing, due to their similarity to native extracellular matrix (ECM) components. Often it is a challenge to fabricate natural polymer based scaffolds for BTE applications without compromising their bioactivity, while maintaining adequate mechanical properties. In this work, we report the fabrication and characterization of cellulose and collagen based micro-nano structured scaffolds using human osteoblasts (HOB) for BTE applications. These porous micro-nano structured scaffolds (average pore diameter 190 +/- 10 microm) exhibited mechanical properties in the mid range of human trabecular bone (compressive modulus 266.75 +/- 33.22 MPa and strength 12.15 3 +/- 2.23 MPa). These scaffolds supported the greater adhesion and phenotype maintenance of cultured HOB as reflected by higher levels of osteogenic enzyme alkaline phosphatase and mineral deposition compared to control polyester micro-nano structured scaffolds of identical pore properties. These natural polymer based micro-nano structured scaffolds may serve as alternatives to polyester based scaffolds for BTE applications.

Nanotechnology and nanoscience are relatively new technological endeavors that encompass the study, control, manipulation, and assembly of multifarious nanoscale components into materials, systems and devices to serve human interest and needs. Among the various currently used nanostructures for high technology applications polymeric nanofibers have received immense interest due to the ease of fabrication, controllable size/shape, and properties. Polymeric nanofibers have been extensively investigated for diversified applications, including filtration, barrier fabrics, wipes, personal care, biomedical, and pharmaceutical applications. This review mainly focuses on the fabrication of therapeutic agent loaded polymeric nanofibers and their controlled/sustained release behavior for the delivery of these active agents for various therapeutic applications. The nonwoven biodegradable polymeric nanofiber matrices are currently being reported as topical/local therapeutic agent delivery systems and as resorbable/biodegradable gauze for wound healing applications.