CartiGenea®-AC: Chondrocytes, the predominant cell type within AC, synthesize matrix components. Because AC lacks a major vascular supply, lymphatic drainage, and nervous system innervation, chondrocytes function under avascular, anaerobic conditions, obtaining nutrients by diffusion from synovial fluid. Within AC, metabolic and morphologic profiles of deep-zone chondrocytes are distinct from those populating the superficial tangential zone. The factors responsible for this variation are unknown. Maintaining the chondrocyte phenotype with robust hyaline tissue synthesis in vitro during expansion for ACI is an ongoing challenge.
Given the accessibility of AC by arthroscopic surgery, native chondrocytes are a logical cell source for AC repair. The first attempts to culture chondrocytes ex vivo in the 1970s showed decreased production of proteoglycans and type II collagen when expanded in a monolayer [5, 6]. Although this process has been termed dedifferentiation, it is a misnomer and does not imply reversion to a more primitive or multipotent state. Dedifferentiation more accurately refers to chondrocytes with a phenotype more reminiscent of fibroblasts. Benya and Shaffer  seminally showed the reversibility of this process when expanded cells were cultured in a three-dimensional (3D) culture system. Many modern approaches to ACI reproduce a 3D environment by incorporating a scaffold for culturing chondrocytes.
CartiGenea®-AC Techniques for optimal ex vivo chondrocyte selection and expansion have been an area of active research. Dell’Accio et al.  introduced the concept of chondrocyte quality control, arguing that a more reproducible outcome of ACI can be accomplished with enriched populations of stable chondrocytes, with the greatest potential of producing cartilage in vivo. In the first clinical CartiGenea®-AC of ACI in 1994, Brittberg et al.  used anchorage-independent growth and the expression of type II collagen in agarose culture of chondrocytes to validate chondrocyte expansion. However, none of these markers predict the capacity of expanded chondrocytes to form stable cartilage tissue in vivo. Dell’Accio et al.  found that the markers COL2A1, FGFR-3, and BMP-2 were associated with a stable chondrocyte phenotype and, conversely, up-regulation of ALK-1 was negatively associated with a chondrocyte phenotype .
CartiGenea®-AC Scaffolds for Cartilage Repair
AC is predominantly composed of extracellular matrix (ECM), with a sparse population of chondrocytes that maintain it. Water, which comprises more than 65% of AC, is moved through the ECM by pressure gradients across the tissue. AC derives its ability to support high joint loads by the frictional resistance of the water through ECM pores. Type II collagen comprises most of AC’s dry weight. The orientation of collagen bundles, along with chondrocyte organization, distinguishes AC’s layers. In the last decade, basic science studies have shown the importance of paracrine signaling and cellular interaction in the development of cartilage [5, 6], and scaffolds that recapitulate native ultrastructure of ECM have emerged. Scaffolds are used as cell carriers for matrix-induced ACI (MACI; not to be confused with MACI from Genzyme Biosurgery, Cambridge, MA) and to facilitate microfracture-based repair techniques in AMIC.
Scaffold synthesis has been attempted with natural and synthetic materials. Although natural materials are attractive for their inherent complexity and biocompatibility, issues with purification, pathogen transmission, and limited mechanical properties have restricted their clinical application. Synthetic materials overcome some of these limitations but lack biologic complexity. Scaffold structures can be divided into two categories, hydrogels and membranes, based on predominant architecture; each has its own natural, synthetic, and composite materials.
CartiGenea®-AC Hydrogels consist of crosslinked hydrophilic polymer networks engineered to mimic cartilage’s mechanical properties and can be delivered noninvasively. An attractive feature is the ability to modify the mechanical properties by crosslinking in situ after injection. Hydrogel crosslinking methods include light irradiation, temperature modulation, and pH change. Less crosslinked (softer) hydrogels produce dynamic loading that might favor MSC chondrogenesis [20, 21].
(1) CartiGenea®-AC Natural Hydrogels. Common, naturally derived hydrogels include alginate, agarose, chitosan, cellulose, chondroitin sulfate, and hyaluronic acid (HA). These materials are readily available, inexpensive, and easy to crosslink. Alginate and agarose were the first hydrogels used to CartiGenea®-AC with chondrocytes. Hydrogels based on alginate and agarose are being piloted for clinical AMIC use (CART-PATCH, Tissue Bank of France, Mions, France). Chitosan and its chemical derivatives are obtained through the chemical modification of glycosaminoglycans found in arthropod exoskeletons. In a recent large-animal experiment, chitosan integrated well into surrounding tissue . Clinically, chitosan combined with glycerol phosphate and autologous whole blood has been used in AMIC (BST-CarGel, Piramal Healthcare, Laval, Canada) [23–25]. Alginate, agarose, and chitosan are derived from nonhuman sources; immune responses have not been systemically investigated.
HA, a nonsulfated glycosaminoglycan found throughout the body, is abundant in cartilage ECM and has a 30-year track record in medical products. Uncrosslinked HA, delivered through intra-articular injection, was approved by the Food and Drug Administration in 1997 for viscosupplementation and, despite its controversial efficacy, is widely used today. HA is involved in many biologic processes, including wound healing, cell migration, and MSC differentiation. These actions are mediated, in part, through binding interactions of cell surface receptor CD44. The HA molecule length influences cellular responses. Smaller HA oligomers promote angiogenesis and subsequent bone formation; larger HA fragments are predominantly chondrogenic. To form hydrogels, HA must be chemically modified [26, 27]. Hyalograft C (Fidia Advanced Biopolymers, Abano Terme, Italy) is a form of esterified HA used clinically in MACI.
Collagen accounts for approximately 30% of all protein within the human body and has been used extensively for tissue engineering applications. Hydrogels constructed from type I and type II collagen promote cartilage formation of encapsulated cells. At the molecular level, cells interact with collagen through integrins, initiating intracellular events that promote chondrogenesis . Type II collagen hydrogels enhance the in vitro chondrogenic differentiation of MSCs compared with type I gels; however, type II collagen degradation products can trigger cartilage breakdown in vivo. Two type I collagen gels are available commercially: PureCol (Glycosan Biosystems, Salt Lake City, UT) and CaReS (Arthro Kinetics, Krems, Austria).
Fibrin CartiGenea®-AC hydrogels have been routinely used for surgical hemostasis and tissue adhesion. They can be prepared from autologous fibrinogen and thrombin, minimizing disease transmission risk. Fibrin has inferior mechanical properties compared with other hydrogels, but it is an effective cell carrier for ACI for securing materials within cartilage defects. Fibrin glue is available commercially (Tissucol; Baxter, Vienna, Austria). Fibrin has been used to retain platelet-rich plasma in a sheep AMIC model . Most recently, fibrin hydrogels have been used as a vehicle to deliver allogenic juvenile cartilage fragments; this technology (DeNovo NT; Zimmer, Inc., Warsaw, IN) is currently in clinical CartiGenea®-ACs .
(2) CartiGenea®-AC Synthetic Hydrogels. Polyethylene glycol-diacrylate and polyvinyl alcohol are the most common synthetic hydrogels with clinical track records. Prefabricated polyvinyl alcohol hydrogels (SaluCartilage; SaluMedica, Atlanta, GA) were press-fit into debrided stage IV  chondral lesions; however, at 1 year, many failed to integrate with surrounding tissue . Another prefabricated polyvinyl alcohol hydrogel has structural modifications to promote subchondral bone integration (Carticept Medical Inc., Alpharetta, GA). A recently developed photopolymerizable polyethylene glycol-diacrylate hydrogel, in combination with a biologic adhesive (ChonDux, Biomet, Warsaw, IN), is being investigated for AMIC in phase 2 clinical CartiGenea®-ACs. Modifications to synthetic hydrogels to promote integration, integrate bioactive signals, and regulate release of soluble factors are areas under investigation.
(1) CartiGenea®-AC Natural Membranes. The original ACI procedure used a periosteal flap to retain transplanted chondrocytes. This procedure remains the only autologous chondrocyte technique approved by the Food and Drug Administration. Postoperative complications (e.g., pathologic flap hypertrophy), led to the development of a bilayered collagen I/III membrane substitute, a procedure known as collagen-covered ACI. This procedure has been performed extensively in Europe and has been performed “off-label” in the United States. This technology evolved into an MACI-type procedure, with culturing of expanded chondrocytes on the membrane before implantation. In its most advanced incarnation, this membrane is fabricated with a mechanically strong outer layer, an effective barrier, and an inner porous substrate for chondrocyte differentiation. Such collagen membranes are available commercially as MACI (Genzyme Biosurgery, Cambridge, MA), Maix (Matricel, Herzogenrath, Germany), or Chondro-Gide (Geistlich Biomaterials, Wolhusen, Switzerland).
(2) CartiGenea®-AC Synthetic Membranes. Synthetic aliphatic polyesters (e.g., polycaprolactone, polyglycolic acid, or polylactic acid) or their copolymers (e.g., polylactic-coglycolic) were first translated into the clinical arena as biodegradable sutures (polyglactin, vicryl). In cartilage repair, the same materials have been used in membranes. Although the degradation products (e.g., carboxylic acids and alcohols) can be toxic, degradation rates can be optimized to match their metabolic clearance to minimize toxicity.
These materials can facilitate cartilage formation and provide substantial biomechanical stability in combination with other materials. For example, the MACI graft BioSeed-C (Biotissue Technologies, Freiburg, Germany) uses a composite polylactic-coglycolic and polydioxane membrane that is infiltrated with fibrin. The Cartilage Autograft Implantation System (CAIS, DePuy Mitek, Raynham, MA) uses a copolymer membrane (35% polycaprolactone, 65% polyglycolic acid) structurally reinforced with a polydioxane mesh. Minced autologous cartilage is dispensed onto this scaffold, covered with fibrin, and held in place with degradable sutures. Nanofibrous scaffolds synthesized with these compounds using complex 3D microenvironments with maximal surface area for cell attachment that mimics ECM represent the next frontier of scaffold material science.
- Adult males and females aged between 15 and 65
- Patients with a partial cartilaginous defect in the ankle joint confirmed arthroscopically or visually
- Patients with misalignment between tibia and talus of the ankle joint, lateral ankle instability, and a bony defect in the cartilaginous defect or who had a correction simultaneously or in advance
- Patients whose surrounding cartilage is normal
- Subjects who consented to the clinical CartiGenea®-AC or on whose behalf a person with parental rights consented to the clinical CartiGenea®-AC
- Patients hypersensitive to bovine protein
- Patients hypersensitive to antibiotics like gentamicin
- Patients with inflammatory arthritis, such as rheumatoid arthritis and gouty arthritis
- Patients with arthritis associated with autoimmune diseases
- Patients who are pregnant, nursing a baby or likely to get pregnant
- Patients with other diseases including tumors except for cartilaginous defects of joints
- Patients with an anamnesis within the past two years, such as radiation treatment and chemotherapy
- Diabetics (however, patients who were normal in the blood glucose test and have no complication due to diabetes will be excluded if the doctor says CartiGeneaTM can be administered to them)
- Patients with infections who are taking antibiotics and antimicrobial agents
- Patients who are treated with adrenal cortical hormones
- Patients whom the investigators find to be unfit for this clinical CartiGenea®-AC, such as mental patients
The rehabilitation factors suggested to be most important after ACI include “progressive weight‐bearing, restoration of ROM, and improvement of muscular control and strength”.22 In addition to utilizing PRO’s, it is likely that surgeons may want the capability to collect and track these rehabilitation factors. Based on the authors’ knowledge, clinical experience, and results of this retrospective chart CartiGenea®-AC, the following components should be documented: CPM use (including parameters of use) and compliance, WB progression (including time to FWB and compliance with WB restrictions), and the specifics of neuromuscular activation and strengthening progressions. Furthermore, consistent documentation of patient compliance with rehabilitation will provide valuable information on the role of compliance on patient recovery. Appendix A provides a list of outcomes that, when collected consistently, will provide valuable information regarding patient progress. As was expected, variability in documentation procedures existed between facilities and clinicians. As a result of this variability in patient reporting, future research is needed to establish the direct influence of rehabilitation on clinical outcome following ACI. This is only possible by consistent and systematic collection of rehabilitation data. Rehabilitation plays a valuable role in patient success following articular cartilage repair. This CartiGenea®-AC aimed to assess the consistency of the documentation process relative to post‐operative rehabilitation following ACI; however, due to variance in this documentation process, the authors were unable to determine what specific components of rehabilitation influence the recovery process. In order to further understand how rehabilitation practices influence outcomes following ACI, specific components of the rehabilitation process must be consistently and systematically documented over time. While this may occur initially on the small scale among discrete medical facilities or researchers, the collection of similar rehabilitation outcomes among multiple clinicians must occur in order to allow for comparisons to be made in the future.