M.Sc Thesis


M.Sc StudentYael Lupu
SubjectDevelopment and Characterization of a Bioactive Ceramic
Scaffold Conjugated with PLAG Particles for Bone
Tissue Engineering
DepartmentDepartment of Biotechnology and Food Engineering
Supervisor Full Professors Machluf Marcelle
Full Thesis textFull thesis text - English Version


Abstract

Loss of bone tissue results in slow healing or large non-healing fractures and often require bone grafting procedures. Bone tissue engineering, is an alternative approach which combines three-dimensional scaffolds with cells and essential growth factors. Composite scaffolds for bone tissue engineering made of a ceramic and a polymeric component are ideal as they combine osteoinductive properties with the ability of growth factors delivery.

In our study we aimed to develop a composite of PLGA and ZrO2 scaffold for bone tissue engineering. PLGA particles have been devised to release bone morphogenetic protein-2 (BMP-2), as this is an expensive growth factor that is crucial for bone formation. First, we focused on optimizing the encapsulation process and found that by changing the polymer's molecular weight and monomer ratio, we can control parameters such as loading, release and size of the microspheres. After the optimization studies, BMP-2 was encapsulated in PLGA with a monomer ratio of 50:50 and medium molecular weight (0.55-0.75dL/gr). We found that the encapsulation efficiency of BMP-2 in a capped PLGA (94%) was higher than in the uncapped PLGA (25%).

Our next aim was incorporating the PLGA microspheres into the ZrO2 scaffold. In the first approach capped polymer microspheres were absorbed using vapors of an organic solvent. However, by this approach the microspheres were not firmly attached to the scaffold and were washed out. Therefore, we assessed a different approach in which uncapped PLGA particles were conjugated using carbodiimide chemistry. This led to attachment of high numbers of microspheres to the scaffold. Once achieving this aim, we have addressed the potential of this composite to be pre-seeded with hMSCs that are known to differentiate to the bone cell linage when exposed to BMP-2. Our results demonstrated that ZrO2 scaffolds support hMSCs growth and proliferation. Also our results demonstrated that the BMP-2 released from the PLGA microspheres retained its biological activity and increased osteoblastic marker expression in hMSCs.

Finally, we aimed to prevascularive the ZrO2 scaffold by seeding endothelial cells. Prevascularization is essential as it helps overcome the nutrient and oxygen diffusion limit. Our results showed that co-culturing the ZrO2 scaffolds with hMSCs and HUVECs enabled cell adhesion and proliferation of both cell types.

To conclude, we successfully developed a delivery system of PLGA microspheres for biologically active BMP-2 that was incorporated into a ZrO2 scaffold. This composite scaffold could serve as a bone substitute for bone grafting applications.