FRG: Organoapatite-Coated Titanium Foam: A Biohybrid for Skeletal Repair

Northwestern University, Evanston IL

Investigators

Abstract

This is a Focused Research Group(FRG) award co-funded by the Polymers, Ceramics and Metals Programs in the Division of Materials Research. Effective, rapid and permanent skeletal repair is one of the grand challenges of bioengineering and biomaterials research. Load-bearing bone repair is critical in cases of aging-related surgery, accident, disease, and trauma. Current metallic implant technology usually relies on solid implants with a porous coating to enhance cell attachment. Difficulties with stress-shielding and interface failure as well as prolonged recovery times however persist. Here, this Focused Research Group proposes to make a significant contribution in this area by creating a novel biohybrid implant material for bone repair. The biohybrid will consist of a biocompatible titanium foam with pores coated with bioactive organoapatite, in which a biological phase will be grown to provide a biomimetic system with improved strength, stiffness and attachment to the skeleton. %%% In the first stage, a fully porous titanium scaffold will be fabricated by a novel process based on the superplastic expansion of argon bubbles in a titanium matrix. In the second step, the inner and outer surfaces of the titanium scaffold will be coated with organoapatite, containing small quantities of organic molecules. Self-assembling molecules and supramolecular clusters will be used to bind the organoapatite to the metal surface. In the third step, bone growth will be induced by rotating the implant in an aqueous solution containing rat calvaria cells. In-vitro testing will assess ability to fully integrate bone into coated Ti foam and the influence of microstructure on mechanical properties and cell ingrowth will carefully studied. Each of the processing steps will be studied in detail, from which models will be developed to predict biologically and mechanically optimal biohybrids. The microstructure of the implant will be studied at each step with particular emphasis on (i) pores in the foamed materials (pore, size, volume fraction, shape and connectivity), (ii) coating morphology and microstructure in the biohybrid, and (iii) cell characteristics in the complete biohybrid. The mechanical properties of the implant will also be studied at each step, with emphasis on both the macroscopic scale (overall strength, stiffness, fatigue resistance) and the microscopic scale (metal/ceramic/bone interfaces). The experimental results will be validated using analytical and numerical mechanics models. The processing, microstructural and mechanical models will be integrate to allow for the design of an optimal biohybrid.