Date of Award

6-2013

Degree Name

MS in Biomedical Engineering

Department

Biomedical and General Engineering

Advisor

Scott Hazelwood

Abstract

Introduction: Articular cartilage (AC) is a low friction load bearing material found in synovial joints. The natural repair of damaged tissue is difficult and often requires surgical intervention. With large defects it becomes necessary to match the original tissue geometry. We hypothesized that localized collagen (COL) and/or proteoglycan (PG) remodeling occurs during AC spherical reshaping. The objective of this study was to determine the presence, magnitude and depth dependence of COL and PG remodeling that accompanies AC reshaping. Methods: Full thickness AC blocks (7x7 mm2 surface area) were harvested from the ridges of the patellofemoral groove of immature (1-3 week old) bovine knees. The top 0-1 mm with intact articular surface was sliced off with a vibrating microtome. A 6 mm diameter disk was punched out of the slice and the most anterior edge was notched to mark directionality. The final sample was a 1 mm thick, 6 mm diameter disk with a notch on the most anterior edge. Samples were either not treated (day 0; D0) or allowed to free swell overnight in 20% FBS. Then cultured samples were placed in culture with 20% FBS in either free swelling (FS), static bending with the articular surface concave (concave) or in static bending with the articular surface convex (convex). Wet-weight and opening angle were measured before and 2 hours after removal from culture. Following culture, samples were cut in half in the anterior posterior direction. One half of each sample was frozen and later analyzed for PG, COL and cell content. The other half was fixed for 24-48 hours in 4% paraformaldehyde; samples were then transferred to 20% Hexabrix for 24 hours before imaging by micro-computed tomography (μCT) to assess PG distribution. Following μCT, samples were again placed in 4% paraformaldehyde for 24-48 hours and then prepared for qPLM to assess collagen orientation (α), parallelism index (PI), and area fraction of non-birefringent tissue (AFNBR). Variations were assessed by ANOVA with post hoc tests for significant ANOVA (pResults: Four days of spherical bending significantly changed (pDiscussion: Spherical bending reshapes AC into a cup shape. Trends of decreasing α standard deviation (αSD) with depth in concave samples and increasing αSD with depth in convex samples indicate that COL matrix disorganization is associated with regions of compressive strain. Consequently, further evaluation on the disorganization of the collagen network should be studied to elucidate mechanisms of cartilage reshaping.

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