Biphasic biomaterials: combining a synthetic bone graft and a polymer membrane

Abstract

Bone grafts are needed to treat bone diseases and injuries if the natural bone regeneration is insufficient. These situations include bone loss caused by disease or trauma or non-union of a fracture. A common problem with bone grafts is the infiltration of soft tissue into the graft, which prevents bone regeneration. Guided bone tissue regeneration (GBR) prevents such event from occurring, by using a membrane that prevents soft tissue from infiltrating the graft. Currently, bone graft and membrane are separate materials, which is why they are placed separately during surgery. To ease and decrease the length of clinical procedures, biphasic biomaterials could be developed so that only one implant would be required. In this thesis, a biphasic biomaterial is made from bioactive glass, which acts as a bone graft substitute, and from a biodegradable synthetic polymer, which acts as a membrane in GBR. The thesis consists of a literature review and an experimental part. First, the literature review introduces existing bone graft and polymer membrane alternatives. Next, the requirements for an optimal bone graft and polymer membrane are presented, as well as methods for making a porous scaffold from bioactive glass and a porous polymer membrane. In the experimental part, the aim is to produce a biphasic biomaterial, in which a porous scaffold with a dense upper surface is first made from bioactive glass by robocasting. After sintering, a porous polymer membrane is deposited onto the scaffold using the breath figure method (BFM). Experimental 13-93B20 borosilicate glass was used as the bioactive glass. Pluronic F127 polymer solution was used as a binder for the robocasting ink. An ink suitable for robocasting was produced with a composition of 30 vol% of 13-93B20 bioactive glass and 70 vol% of 30 wt% Pluronic F127 polymer solution, as this composition produced a uniform ink flow and a continuous filament. With this ink, cylindrical scaffolds with dense upper surfaces were successfully printed. Poly-L/DL-lactide (PLDLA) membrane deposition using the BFM was attempted onto the sintered scaffolds since this has been accomplished with 13-93B20 bioactive glass discs. With the sintered scaffolds, membrane deposition was not successful. While the sintered surface appeared to be dense by optical microscopy, the macro-porosity was such to induce a capillary effect. Therefore, the solution used to produce the membrane flowed into the scaffold structure. To prevent this, the scaffold was immersed for 24 h in TRIS buffer solution, with the aim to promote Ca-P layer formation, thus occluding the macro-porosity. Again, the membrane could not be deposited since the formation of the Ca-P layer was not sufficiently dense to occlude the macro-pores. In the future, sintering parameters of the 13-93B20 bioactive glass scaffold should be optimized to avoid the capillary effect created by macro-pores in the surface layer of the scaffold. This could result in the successful combination of a bioactive glass scaffold and polymer membrane to form a biphasic material. The findings in this thesis contribute to the development of new biphasic materials for bone tissue engineering.