Cotton-wool-like bioactive glasses for bone regeneration

G Poologasundarampillai,D Wang,S Li,J Nakamura,R Bradley,P.D Lee,M.M Stevens,D.S Mcphail,T Kasuga,J.R Jones

doi:10.1016/j.actbio.2014.05.020

Abstract

Inorganic sol–gel solutions were electrospun to produce the first bioactive three-dimensional (3-D) scaffolds for bone tissue regeneration with a structure like cotton-wool (or cotton candy). This flexible 3-D fibrous structure is ideal for packing into complex defects. It also has large inter-fiber spaces to promote vascularization, penetration of cells and transport of nutrients throughout the scaffold. The 3-D fibrous structure was obtained by electrospinning, where the applied electric field and the instabilities exert tremendous force on the spinning jet, which is required to be viscoelastic to prevent jet break up. Previously, polymer binding agents were used with inorganic solutions to produce electrospun composite two-dimensional fibermats, requiring calcination to remove the polymer. This study presents novel reaction and processing conditions for producing a viscoelastic inorganic sol–gel solution that results in fibers by the entanglement of the intermolecularly overlapped nanosilica species in the solution, eliminating the need for a binder. Three-dimensional cotton-wool-like structures were only produced when solutions containing calcium nitrate were used, suggesting that the charge of the Ca2+ ions had a significant effect. The resulting bioactive silica fibers had a narrow diameter range of 0.5–2μm and were nanoporous. A hydroxycarbonate apatite layer was formed on the fibers within the first 12h of soaking in simulated body fluid. MC3T3-E1 preosteoblast cells cultured on the fibers showed no adverse cytotoxic effect and they were observed to attach to and spread in the material.

Highlights

Bone tissue regeneration strategies aim to use synthetic temporary templates to aid the natural healing of bone defects
The low viscosity (0.03 and 0.04 PaÁs for 100 mol.% SiO2 (100S) and 70 mol.% SiO2 and mol.% CaO (70S30C), respectively) of the precursor solution led to spraying, which resulted in the production of whiskers
Standard a-MEM did not contain Si species and, 70S30C cotton-wool-like fibrous scaffolds produced the increase in the Si species level of the media. These findings suggest that Si dissolution products from the fibers have a more profound stimulatory effect on the formation of extracellular matrix (ECM)

Summary

Introduction

Bone tissue regeneration strategies aim to use synthetic temporary templates (scaffolds) to aid the natural healing of bone defects. Osteoblasts secrete bone extracellular matrix (ECM), which is composed of collagen fibrous structure, with mineralized calcium phosphate [1,2]. In defects where load-bearing materials are not needed, an ideal biomaterial scaffold for bone regeneration might have a three-dimensional (3-D) fibrous structure that mimics the ECM [3,4,5] and can be pushed into position by a surgeon or dentist. The scaffolds are required to be biocompatible, bioactive (bond with bone) and bioresorbable [6]. Bioactive glasses can form a rapid bond with bone through formation of a hydroxycarbonate apatite (HCA) surface layer on contact with body fluid, and through release of soluble silica and calcium ions that can stimulate osteoprogenitor cells to produce more bone [7].

Methods

Results

Conclusion