A biodegradable nanofiber scaffold by electrospinning and its potential for bone tissue engineering

Abstract

Microporous, non-woven poly(ε-caprolactone) (PCL) scaffolds were made by electrostatic fiber spinning. In this process, polymer fibers with diameters down to the nanometer range, or nanofibers, are formed by subjecting a fluid jet to a high electric field. Mesenchymal stem cells (MSCs) derived from the bone marrow of neonatal rats were cultured, expanded and seeded on electrospun PCL scaffolds. The cell-polymer constructs were cultured with osteogenic supplements under dynamic culture conditions for up to 4 weeks. The cell-polymer constructs maintained the size and shape of the original scaffolds. Scanning electron microscopy (SEM), histological and immunohistochemical examinations were performed. Penetration of cells and abundant extracellular matrix were observed in the cell-polymer constructs after 1 week. SEM showed that the surfaces of the cell-polymer constructs were covered with cell multilayers at 4 weeks. In addition, mineralization and type I collagen were observed at 4 weeks. This suggests that electrospun PCL is a potential candidate scaffold for bone tissue engineering.

Introduction

Engineering living tissue for reconstructive surgery requires an appropriate cell source, optimal culture conditions and a biodegradable scaffold as the basic elements. While specialized cells remain an important source, stem cells have emerged as a promising new alternative. Recent advances in stem cell biology have shown that mesenchymal stem cells (MSCs) can differentiate into cells of mesenchymal tissues such as bone, cartilage, muscle, tendon, ligament and fat, and are expected to play an important role in the repair of skeletal defects [1], [2].

It is also a well-accepted paradigm that the culture conditions affect the quality of the engineered tissue, and the development of bioreactors to provide optimal culture conditions remains an active field of research [3]. Recently, a rotational oxygen-permeable bioreactor system (ROBS) has been developed in our laboratory to provide optimal oxygen tension and mechanical stresses to cell-polymer constructs in culture. Osteoblasts derived from MSCs of neonatal rats were cultured on poly(dl-lactide-co-glycolide) (PLGA) foams, and mineralization as well as three-dimensional bone formation was observed [4].

Regarding the scaffold, it is generally agreed that a highly porous microstructure with interconnected pores and a large surface area is conducive to tissue ingrowth. For bone regeneration, pore sizes between 100 and 350 μm and porosities of more than 90% are preferred, and a variety of different scaffold fabrication techniques has been reported [5].

This study assesses the potential of electrostatic fiber spinning, or electrospinning, as an alternative scaffold fabrication technique to engineer bone in vitro using ROBS. Electrospinning produces highly porous non-woven fabrics consisting of ultrafine fibers. A wide variety of polymers have been electrospun and several applications have been proposed in recent years based on the small fiber diameters and high porosities, e.g. Refs. [6], [7]. Poly (ε-caprolactone) PCL was chosen as a model polymer due to its lack of toxicity, low cost and slow degradation [8]. MSCs were harvested from the bone marrow of neonatal rats and seeded on electrospun (PCL) scaffolds. The cell-polymer constructs were cultured with osteogenic supplements under dynamic culture conditions for 4 weeks. Cell behavior was observed using scanning electron microscopy (SEM), histological and immunohistochemical analyses.