Figure 1: Images of a) Discontinuous bioactive fibers; and b) Continuous bioactive fibers. (SB = 2cm)
The regeneration and regrowth of new bone is one of numerous fields encompassed within the broader spectrum of tissue engineering. Current trends in bone tissue engineering are shifting away from the use of auto- and allograft bone and beginning to focus on the use of synthetic materials. Synthetics offer the advantages of mass production, lower sterilization costs, and elimination of donor morbidity, disease transmission or immune rejection. A tailoring of the chemical, physical, and mechanical properties of the synthetic material can thus be used to create a suitable scaffold for the growth of new bone. Ideally, the scaffold should consist of a porous, three-dimensional structure capable of maintaining structural integrity and allow for cellular influx, growth, and ECM deposition as well as metabolic exchanges. The degradation rate, degree of porosity, and mechanical strength should all be adjusted in order to closely match that of the host tissue. The scaffold material must also avoid stimulating an adverse immunological response through chemical species present at the implant surface or through possible degradation byproducts (i.e. act as a biocompatible or bioactive material).
Figure 2: SEM Images of 77S BG fibers; a) Collection of fibers (1300x), b) Single fiber (500x), and c) Fiber submerged in SBF for 20 days (3000x).
In an effort to achieve the regeneration of new bone via synthetic scaffolds, we have been investigating the use of bioactive glass fibers. From this we are able to obtain desired chemical and physical properties. These materials provide the necessary chemistry that results in the precipitation of hydroxyapatite (HA), or bone mineral, on their surface. These glasses also provide a suitable substrate for the colonization of cells and are known to be both osteoconductive and osteoinductive. Fabrication of the glass into fibrous for provide favorable physical properties by allowing for the construction of highly porous, 3 dimensional constructs. These fibrous constructs therefore allow for the infiltration of cells and the exchange of nutrients. The bioactive fibers can also be used as a means of directing cell growth along their axis, and the spanning of cells between fibers may serve to generate tensions necessary for differentiation and mature bone formation.
In our lab we have produced both discontinuous and continuous bioactive fibers following a sol gel technique. We have developed a method in which polymeric additives have been used to modify fiber production and create composite structures. These fibers have been shown to exhibit in vitro bioactivity resulting in the precipitation of a HA layer on their surface following submersion in a simulated body fluid (SBF) solution. We have also shown that these fibers can influence the proliferation rates of rat mesenchymal stem cells in culture when arranged into 3D constructs.
Figure. 3: a) 5000x SEM image of cells present inrat bone marrow (SB = 10μm); b) 200x Light micrograph of mesenchmal stem cells isolated from bone marrow 3 days after primary culture (crystal violet); c) 1500x SEM image of same MSCs in b (SB = 20μm).