Massachusetts Institute of Technology Harvard Medical School Brigham and Women’s/Massachusetts General Hosp. VA Boston Healthcare System 2.79J/3.96J/BE.441/HST522J BIOMATERIALS FOR JOINT REGENERATION-II M. Spector, Ph.D. and I.V. Yannas, Ph.D. TISSUES COMPRISING JOINTS Permanent Regeneration Prosthesis Scaffold Bone Yes Yes Articular cartilage No Yes* Meniscus No Yes* Ligaments No Yes* Synovium No No * In the process of being developed INTRAARTICULAR JOINT TISSUES ? What are the unique characteristics of the joint environment? ? Why don’t these tissues heal? ? How are such diverse functions met by only one structural protein - collagen? INTRAARTICULAR ENVIRONMENT ? Synovial fluid ? High mechanical loads ? Low vascularity JOINT TISSUES Limitations to Healing ? Absence of a fibrin clot – Absent or low vascularity – Dissolution of clot in synovial fluid ? Cell migration restricted by matrix ? Low cell density ? Low mitotic activity ? Mechanical loading disrupts reparative tissue JOINT TISSUES REPARATIVE PROCEDURES Art. Cart. Microfracture, osteochondral plugs, articular chondrocyte implantation [Tiss. engr. cart.; Collagen matrices] ACL Tendon autografts Meniscus Suture, meniscal allografts [Collagen matrices] JOINT TISSUES Tissue Cell Round/ Loading Type Type Lac. Coll. PG Vasc.Heal. Art. Cart. Comp. Hyal. Chond.Yes II +++ 0 0 Cart. Meniscus C/T Fibro- Fibro- Yes I 0/+ 0* 0 Cart. Chond. ACL Tens. Fibrous Fibro- No I 0 0** 0 Tissue blast * Inner third ** Mid-substance ARTICULAR CARTILAGE Chondrocytes Extracellular matrix Water 66-78% Organic material 22-34% Proteoglycan 22-38% Collagen type II 48-62% Fibronectin & Other matrix proteins 05-15% Human Knee from Patient with Rheumatoid Arthritis Image removed due to copyright considerations. Arthroscopic Debridement “Microfracture” Total Knee Replacement Current Clinical Practice Image removed due to copyright considerations Image removed due to copyright considerations Image removed due to copyright considerations Image removed due to copyright considerations Osteochondral Plug Autograft (“Mosaicplasty”) Autologous chondrocytes injected under a periosteal flap (Genzyme; “Carticel”) 30 years Image source: OCW Image removed due to copyright considerations. Image removed due to copyright considerations. Future Clinical Practice Implementing Tissue Engineering Implantation of the matrix alone, or supplemented with growth factors or genes for the GFs Stem cells from bone marrow infiltrate the defect Implantation of a cell-seeded matrix Microfracture Image source: OCW ELEMENTS FOR TISSUE ENGINEERING Tissue Engineering Triad* ? CELLS ? MATRIX (INSOLUBLE REGULATOR) – Porous, absorbable biomaterials ? SOLUBLE REGULATORS – Cytokines (Growth Factors) Environmental Factors ? Mechanical loading * Used individually or in combination, but probably always best with a matrix (i.e., with a biomaterial) ARTICULAR CARTILAGE Limits to Regeneration ? Avascular (and aneural) ? Relatively low cell density ? Cells of low mitotic activity ? Cells cannot freely migrate TISSUE ENGINEERING Cells ? Autologous, allogeneic, or xenogeneic ? Differentiated cell of the same tissue type or another tissue type, or stem cell Autologous Chondrocyte Implantation Image removed due to copyright considerations. This process has been commercialized by Genzyme (for USD$11,500). M Brittberg, et al., NEJM 33:889 (1994) Untreated defects Cells harvested Cells isolated * Cells suspended * Periosteum harvest site Cells cultured * Cells injected under periosteum * by Genzyme Biosurgery Canine Study Autologous Chondrocyte Implantation CELL-SEEDED COLLAGEN MATRICES ? Chondral defects (to the tidemark) Images removed due to copyright considerations ? Type II (porcine) collagen scaffold ? Seeded with cultured autologous chondrocytes (CAC) AUTOLOGOUS CHONDROCYTE- SEEDED COLLAGEN MATRIX 4 mm Chondrocyte- seeded type II collagen implant* * Cells seeded into the matrix 24 hours* and 4 weeks prior to implantation * HA Breinan, et al. J . Orthop. Res. 2000;18:781-789 and C.R. Lee, et al. Seeding of Collagen Matrices with CAC Images removed due to copyright considerations Collagen discs 9 mm diam x 3 mm thick CR Lee, et al, Biomat. 2001;22:3145. Chondral defect immediately postoperative. Arrow shows perforation of calcified cartilage and subchondral bone (SCB) Image removed due to copyright considerations Defects treated by autologous chondrocyte implantation, 6 months postoperative Image removed due to copyright considerations H. Breinan, et al. J. Orthop. Res. 2001;19:282-292 1.5 mo. Fibrous tissue Images removed due to copyright considerations 3 mo. Hyaline cartilage (some articular cartilage), fibrocartilage, and fibrous tissue 6 mo. Articular cartilage and fibrocartilage Images removed due to copyright considerations 12 mo. Degraded tissue, fibrocartilage and fibrous tissue H. Breinan, et al. J. Orthop. Res. 2001;19:282-292 Summary of Results: Canine Model 15 Wks Post-op, Mean, n=6 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Untreated Control CAC Alone CAC/ Collagen II 24 hr CAC/ Collagen II 4 wk % Original Defect Area Cultured Autologous Chondrocytes Hyaline Fibrocartilage Fibrous Image removed due to copyright considerations. Image removed due to copyright considerations. Future Clinical Practice Implementing Tissue Engineering Implantation of the matrix alone, (or supplemented with growth factors or genes for the GFs) “Microfracture”: Stem cells from bone marrow infiltrate the defect Implantation of a cell-seeded matrix Image source: OCW Canine Model Microfracture Images removed due to copyright considerations HA Breinan, et al. J . Orthop. Res. 2000;18:781-789 CANINE MICROFRACTURE STUDY TREATMENT GROUPS 4 mm Collagen (II) film Microfracture Microfracture + Collagen Implant AC Bone Collagen (II) sponge 15 Wks Post-op, Mean, n=6 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Untreated Control CAC Alone CAC/ Collagen II 24 hr CAC/ Collagen II 4 wk % Original Defect Area Hyaline Fibrocartilage Fibrous Cultured Autologous Chondrocytes μfx Alone μfx/ Collagen II Microfracture Procedures currently used Summary of Results: Canine Model JOINT TISSUES Tissue Cell Round/ Loading Type Type Lac. Coll. PG Vasc. Heal. Art. Cart. Comp. Hyal. Chond. Yes II +++ 0 0 Cart. Meniscus C/T Fibro- Fibro- Yes I 0/+ 0* 0 Cart. Chond. ACL Tens. Fibrous Fibro- No I 0 0** 0 Tissue blast * Inner third ** Mid-substance