Both endogenous lubricin and injectable hyaluronic acid reduced cartilage friction coefficients, but by distinct mechanisms. Lubricin operated in boundary mode and hyaluronic acid shifted lubrication to mixed or hydrodynamic mode. Intra-articular injections of viscous agents and boundary lubricants have been presented as options to mitigate the progression of articular cartilage damage after the onset of osteoarthritis1,2. Mechanically, these injections are predicted to lower the friction coefficient within a load bearing joint and consequently slow the propagation of damage at the articular surface. Tribologically, boundary lubricants and viscous agents are hypothesised to be effective through different mechanisms affecting boundary-mode lubrication and transition to mixed-mode lubrication, respectively. By normalizing sliding speeds on a Stribeck curve, this study evaluated the efficacy of injectable hyaluronic acid (HA) supplements and endogenous lubricin to alter tribological properties.Summary
Introduction
The purpose of this study was to assess the physical, biochemical and biomechanical properties of a cartilage matrix-chondrocyte-fibrin glue composite as biological tool for cartilage repair. Chondrocytes were enzymatically isolated from pig joints and resuspended in fibrinogen solution. Articular cartilage was harvested from pig joints, chopped into small chips and lyophiliaed. Cartilage chips were rehydrated and mixed with the cell/fibrinogen solution and with thrombin, in order to form a fibrin glue gel composite with cells and chips (group A). Control composites were made from lyophilised cartilage chips assembled with fibrin glue, but not containing chondrocytes (group B). Other control groups included fibrin glue/chondrocyte specimens without cartilage chips (group C) and specimens made of the fibrin glue alone (group D). All samples were weighed and implanted into subcutaneous pouches of nude mice. Animals were sacrificed at 2 and 9 weeks. Samples were evaluated grossly and the final/initial mass ratio was calculated. Samples were evaluated histologically, biomechanically, and biochemically. Upon retrieval, only the samples in experimental group A retained their original pre-implantation mass. Histological analysis showed newly formed cartilage matrix in the specimens from group A and C. Biomechanical analysis showed significantly higher modulus in experimental samples, with respect to the other groups at the latest time point. Analysis of hydraulic permeability showed significantly decreasing values for all groups throughout the experimental times and lowest values for the experimental samples of group A in the latest time point, although there was no statistically significant difference among the groups. Biochemical analysis demonstrated higher values in the latest time point for samples prepared with cells for water and GAG content, whereas highest values for hydroxyproline were recorded for samples assembled with cartilage chips. DNA analysis showed higher values of samples prepared with chondrocytes and fibrin glue and also an important increase in values of the samples made of fibrin glue only, indicating a possible host fibroblast growth inside the samples over time. This tissue-engineered composite presents cartilaginous appearance and biomechanical integrity after 9 weeks in vivo.
