All ETDs from UAB

Advisory Committee Chair

Susan L Bellis

Advisory Committee Members

Alan W Eberhardt

Jack E Lemons

Selvarangan Ponnazhagan

Timothy M Wick

Document Type

Dissertation

Date of Award

2013

Degree Name by School

Doctor of Philosophy (PhD) School of Engineering

Abstract

Hydroxyapatite (HA) makes up the mineral component of bone, and synthetic HA is commonly used to coat metal implants for use in dentistry and orthopedics. Additionally, allograft and synthetic HA are common alternatives to autograft bone, to circumvent the complications associated with a second surgery site. While both HA and allograft are known to be osteoconductive, osteoinductivity is limited. In this work, we developed methods for anchoring osteoinductive factors onto multiple types of HA biomaterials and human allograft bone, with the goal of enhancing their osteoregenerative potential. Specifically, a HA-binding domain, heptaglutamate (E7), modeled on bone-binding domains within native proteins, was attached to peptides derived from osteoinductive proteins, collagen I and Bone Morphogenic Protein-2 (BMP-2). Addition of the E7 domain to osteoinductive peptides resulted in greater peptide loading and retention in vitro; importantly, E7-peptides were retained on implanted allograft for at least 1 month. While long-term coupling is likely the optimal presentation for extracellular matrix molecules, growth factors and chemoattractants are expected to be more effective if released from the substrate to form a gradient. We hypothesized that by manipulating the length of the polyglutamate-binding domain, release kinetics of peptides from HA substrates could be finely tuned. We found that a greater number of glutamates present in the binding domain resulted in slower release from the substrate, and as expected, fewer glutamate domains resulted in a faster release. These studies are significant because they extend the previously established anchoring technology to include finely tuned release of molecules from both synthetic HA and allograft. Additionally, we exploited the polyglutamate-HA interaction as a mechanism to enhance binding of protein delivery nanocages to HA substrates. Incorporation of polyglutamate domains into the capsid of P22 nanocages significantly increased the number of nanocages initially bound to synthetic HA materials and allograft, potentially enhancing local delivery of a wide range of molecules. In sum, the polyglutamate-HA delivery mechanism is broadly applicable for enhancing the delivery of many types of bioactive peptides, as well as vehicles for cargo delivery, on a multitude of clinically relevant bone graft materials to improve osteoregeneration.

Included in

Engineering Commons

Share

COinS