Lawrence J. Bonassar

This study evaluated the biomechanical characteristics of newly formed cartilaginous tissue synthesized from isolated chondrocytes and seeded onto devitalized cartilage in an extended study in vivo. Cartilage from porcine articular joints was cut into regular discs and devitalized by multiple freeze‐thaw cycles. Articular chondrocytes were enzymatically isolated and incubated in suspension culture in the presence of devitalized cartilage discs for 21 days. This procedure allowed the isolated chondrocytes to adhere to the devitalized matrix surfaces. Chondrocyte‐matrix constructs were assembled with fibrin glue and implanted in dorsal subcutaneous pockets in nude mice for up to 8 months. Histological evaluation and biomechanical testing were performed to quantify the integration of cartilage pieces and the mechanical properties of the constructs over time. Histological analysis indicated that chondrocytes grown on devitalized cartilage discs produced new matrix that bonded and integrated individual cartilage elements with mechanically functional tissue. Biomechanical testing demonstrated a time dependent increase in tensile strength, failure strain, failure energy, and tensile modulus to values 5–30% of normal articular cartilage by 8 months in vivo. The values recorded at 4 months were not statistically different from those collected at the latest time point, indicating that the limits of the biomechanical property values were reached after four months from implantation. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 64A: 517–524, 2003

Over one million patients per year undergo some type of procedure involving cartilage reconstruction. Polymer hydrogels, such as alginate, have been shown to be effective carriers for chondrocytes in subcutaneous cartilage formation. The goal of our current study was to develop a method to create complex structures (nose bridge, chin, etc.) with good dimensional tolerance to form cartilage in specific shapes. Molds of facial implants were prepared using Silastic ERTV. Suspensions of chondrocytes in 2% alginate were gelled by mixing with CaSO₄ (0.2 g/mL) and injected into the molds. Constructs of various cell concentrations (10, 25, and 50 million/mL) were implanted in the dorsal aspect of nude mice and harvested at times up to 30 weeks. Analysis of implanted constructs indicated progressive cartilage formation with time. Proteoglycan and collagen constructs increased with time to approximately 60% that of native tissue. Equilibrium modulus likewise increased with time to 15% that of normal tissue, whereas hydraulic permeability decreased to 20 times that of native tissue. Implants seeded with greater concentrations of cells increased proteoglycan content and collagen content and equilibrium and decreased permeability. Production of shaped cartilage implants by this technique presents several advantages, including good dimensional tolerance, high sample‐to‐sample reproducibility, and high cell viability. This system may be useful in the large‐scale production of precisely shaped cartilage implants. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 55: 503–511, 2001

As a result of the low yield of cartilage from primary patient harvests and a high demand for autologous cartilage for reconstructive surgery and structural repair, primary explant cartilage must be augmented by tissue engineering techniques. In this study, chondrocytes seeded on PLLA/PGA scaffolds in static culture and a direct perfusion bioreactor were biochemically and histologically analyzed to determine the effects of fluid flow and media pH on matrix assembly. A gradual media pH change was maintained in the bioreactor within 7.4−6.96 over 2 weeks compared to a more rapid decrease from 7.4 to 6.58 in static culture over 3 days. Seeded scaffolds subjected to 1 μm/s flow demonstrated a 118% increase (p < 0.05) in DNA content, a 184% increase (p < 0.05) in GAG content, and a 155% (p< 0.05) increase in hydroxyproline content compared to static culture. Distinct differences were noted in tissue morphology, including more intense staining for proteoglycans by safranin‐O and alignment of cells in the direction of media flow. Culture of chondrocyte seeded matrices thus offers the possibility of rapid in vitro expansion of donor cartilage for the repair of structural defects, tracheal injury, and vascularized tissue damage.

In osteoarthritis (OA), the combination of altered cartilage matrix composition and mechanical wear from joint motion can result in erosion of cartilage down to the bone surface [1]. In its degenerated state, OA cartilage exhibits dramatically different biochemical, physicochemical, mechanical, and electromechanical properties from normal tissue, including a distinct loss of proteoglycan [2,3], marked collagen network fibrillation [4], increases in tissue hydration [5], and loss of compressive stiffness [6]. The role of enzymatic degradation in OA has been studied extensively, but is not completely understood. It has been suggested [7] that families of enzymes, including matrix metalloproteinases (MMPs) [8,9], serine proteinases [10], and a novel “aggrecanase” [11] contribute to cartilage degradation in OA. It seems likely that the enzymatic component of OA involves a cascade of activities which work in tandem to degrade the tissue.