Novel multifunctional scaffolds and structures with controlled cell release for tissue engineering

Abstract

Controlled release of live cells is an important strategy in tissue engineering when cells can be encapsulated to maintain normal cellular physiology and then released at targeted sites with well-designed cell density and distribution that mimick the native tissues. The aim of this project is to investigate suitable vehicles for controlled cell release and integrate the cell-encapsulated vehicles into scaffolds/structures to enhance human tissue regeneration. Therefore, cell-laden hydrogel fibers (“cell fibers”) and cell-encapsulated bicontinuous interfacially jammed emulsion gels (“bijels”)-derived bicontinuous structures were developed in this project.

Cell encapsulation in fibers for their subsequent delivery has been attractive in tissue engineering since many types of fiber-shaped cellular structures exist in human bodies. In this investigation, micro-size cell fibers consisting of calcium alginate hydrogel with desired controlled cell release property were fabricated continuously using either wet spinning or cell-electrospinning. The wetspun fibers were also used as drug carriers and the in vitro release behaviors of encapsulated fluorouracil and vancomycin were studied. The cell fibers encapsulated with mesenchymal stem cells (MSCs) or human dermal fibroblasts (HDFs) were prepared by cell-electrospinning and then incorporated in poly(lactic-co-glycolic acid) (PLGA) electrospun nanofibrous scaffolds for potential tendon and ligament regeneration. The PLGA nanofibrous scaffolds were also encapsulated with bFGF to further regulate tissue regrowth. Enhanced proliferation and cytoskeleton development of released MSCs and HDFs and fibroblast-like differentiation of released MSCs were achieved by released bFGF. Epidermal growth factor (EGF)-encapsulated gelatin-chitosan nanofibrous scaffolds were also fabricated in this project for corneal tissue engineering.

The unique bicontinuous structure makes bijels and bijels-derived structures attractive for tissue engineering applications. A new facile phase separation-based fabrication technique that can generate bijels, bijels-derived polymer porous structures, and bijels-derived bicontinuous polymer-hydrogel hybrid structures with good bicontinuous structure and adjustable domain/channel sizes was developed in this project. The structure and properties of fabricated bijels and bijels-derived structures were studied and bijels-derived polymer-hydrogel hybrid structures exhibited good biocompatibility and biodegradability. The effects of pore sizes of bijels-derived porous polymer structures on the migration of seeded cells were studied. Growth factors including vascular endothelial growth factor (VEGF) and platelet-derived growth factors (PDGF) were encapsulated in the hydrogel phase of bijels-derived polymer-hydrogel hybrid structures and their in vitro release behavior and the influence of PDGF on the cell behavior of loaded HDFs were studied. Bijels-derived polymer-hydrogel hybrid structures were used as vehicles for the controlled release of several cell types, including mouse osteoblastic cells (MC3T3 cells), HDFs, and MSCs. The cell release rate could be regulated by varying the crosslinking degree of hydrogel. The encapsulated cells could be released from the hydrogel phase and exhibited good cell proliferation and cytoskeleton development. MSC-encapsulated bijels-derived polymer-hydrogel hybrid structures were fabricated for bone tissue engineering, and the osteogenic differentiation of released MSC, which was evidenced by different biomarkers, could be achieved. MSC-encapsulated and bFGF-incorporated bijels-derived polymer-hydrogel hybrid structures were fabricated for skin tissue engineering. The released MSCs exhibited enhanced fibroblast-specific protein 1 (FSP1) expression.