Investigation and enhancement of lateral integration of tissue engineered articular cartilage under dynamic mechanical stimulation

Abstract

Scaffolds were characterized as having little innate impact on chondrocyte phenotype, and exhibited little to no degradation after 6 weeks of culture. Optimization of the mechanical properties of the hybrid scaffolding material was performed by direct comparison with arthritic human articular cartilage tissue. Reformulated scaffolds possessed a high mean porosity of ~80% and a Poisson's ratio of 0.34.

The research contained herein pertains to the development and implementation of methods to investigate properties relevant to the lateral integration between a tissue engineered chondral implant and surrounding articular hyaline cartilage under static and physiologically relevant dynamic mechanical loading conditions. Previous attempts at translating tissue engineered cartilage implants to the clinical setting have yet to gain widespread acceptance and FDA approval. One of the primary reasons for this is inadequate integration between the implant and surrounding cartilage tissue, especially under mechanical loading, where the border region between implants and surrounding tissue often contains gaps and areas of mechanically inferior fibrocartilageneous tissue. Although in vitro models for the study of lateral integration in a controlled environment have been developed, models to study the effects of the application of mechanical loading have not yet been formulated, and standard protocols for stimulation and testing have yet to be developed. This thesis describes the development of a novel biphasic poly(ε-caprolactone) and hyaluronic acid hydrogel scaffold for use in cartilage tissue engineering, and an ex vivo dynamic loading experiment designed to act as a new gold standard for determining the effect of physiologically relevant levels of mechanical stimulation on biomaterial and tissue integration with human tissue.

The ring integration model, consisting of an outer ring of human articular cartilage and a central plug of either hybrid scaffold material or articular cartilage, was incorporated into a dynamic culture experiment utilizing a bioreactor operating at 1Hz and 10% strain. Significant bridging was observed via histology for scaffold and tissue groups in static culture, while dynamic culture samples lacked significant nascent growth in the defect space. RT-PCR data indicated possible differences between arthritic chondrocyte gene regulation under dynamic culture conditions observed in the study and changes that occur in normal cells under similar conditions in previous studies.