Electrospun multicomponent and multifunctional nanofibrous tissue engineering scaffolds : fabrication, characteristics and biological performance

Abstract

Electrospinning has attracted great attention in the fields of tissue engineering and controlled release of drugs/biomolecules. The aim of this project was to investigate electrospinning of nanofibers with core-shell structures using emulsion electrospinning, the formation of monolithic and core-shell structured nanofibrous drug/biomolecule delivery vehicles using polymers such as poly(D,L-lactic acid) (PDLLA) and poly(lactic-co-glycolic acid) (PLGA), and the formation of multicomponent bone tissue engineering scaffolds with angiogenic property, osteoinductivity and osteoconductivity. The foundation of this project was laid by investigating monocomponent scaffolds. First, effects of properties of polymer solutions and water-in-oil (w/o) emulsions and electrospinning parameters on the morphology, diameter and structure of fibers were systematically investigated. Second, drugs (vancomycin and rifamycin) and a model protein (bovine serum albumin) were incorporated in monolithic or core-shell nanofibers via blend electrospinning or emulsion electrospinning to form single or dual delivery systems, providing fundamental understandings. Growth factors such as recombinant human bone morphogenetic protein-2 (rhBMP-2) and basic-fibroblast growth factor (b-FGF) were then incorporated in PLGA or PDLLA nanofibrous delivery vehicles. The in vitro release behaviour of drugs and biomolecules was studied. Third, calcium phosphate (Ca-P) nanoparticles were synthesized and used for fabricating Ca-P/PLGA and Ca-P/PDLLA nanocomposite scaffolds. Homogeneous distribution of Ca-P in fibrous scaffolds could be achieved. With the assistance of emulsion electrospinning and nanocomposite electrospinning, bicomponent scaffolds containing rhBMP-2 and Ca-P nanoparticles were fabricated using dual-source dual-power electrospinning. The fibrous component ratio could be varied by using multiple syringes for electrospinning fibers. The structure and properties, including in vitro release behaviour, of mono- and bicomponent scaffolds were studied in detail. Tricomponent scaffolds incorporated with recombinant human vein endothelial growth factor (rhVEGF), rhBMP-2 and Ca-P nanoparticles were subsequently fabricated using multi-source dual-power electrospinning. To achieve a sequential release of firstly rhVEGF and then rhBMP-2, PLGA/polyethylene glycol (PEG) blends and PLGA were used for incorporating rhVEGF and rhBMP-2, respectively. For tricomponent scaffolds with different component ratios, different release amounts but similar release profiles could be achieved for the growth factors. In vitro biological investigations were conducted for mono-, bi- and tricomponent scaffolds. Pre-osteoblast cells (MC3T3-E1) were found to attach, spread, proliferate and express alkaline phosphatase (ALP) activity on rhBMP-2 and Ca-P nanoparticle incorporated bicomponent scaffolds. Calcium deposition was also observed in cells cultured with bicomponent scaffolds. Human umbilical vein endothelial cells (HUVECs) were found to attach, spread, proliferate on tricomponent scaffolds and rhVEGF released from mono-, bi- and tricomponent scaffolds could facilitate cell proliferation and migration, indicating released rhVEGF could promote angiogenesis. C3H10T1/2 cell line and human bone marrow derived mesenchymal stem cells (hBMSCs) were found to attach, spread and proliferate on bi- and tricomponent scaffolds. As compared with cells seeded on monocomponent scaffolds, C3H10T1/2 cells and hBMSCs on bi- and tricomponent scaffolds expressed higher ALP activity. Enhanced mineralization was observed for C3H10T1/2 cells and hBMSCs seeded bicomponent scaffolds comprising rhBMP-2/PLGA and Ca-P/PLGA fibers and also tricomponent scaffolds. hBMSCs seeded on rhBMP-2/PLGA and Ca-P/PLGA monocomponent scaffolds expressed abundant F-actin and vinculin, while bicomponent and tricomponent scaffolds induced much more F-actin and vinculin expression.