Artificial Organs 27(5):428–431, Blackwell Publishing, Inc. © 2003 International Society for Artificial Organs
Bioreabsorbable Polymer Scaffold as Temporary Meniscal Prosthesis *Ana Paula Testa Pezzin, †Túlio Pereira Cardoso, ‡Maria do Carmo Alberto Rincón, *Cecília Amélia de Carvalho Zavaglia, and ‡Eliana Aparecida de Rezende Duek *State University of Campinas, UNICAMP, Faculty of Mechanical Engineering, Campinas; University of São Paulo (USP), Faculty of Medicine, Clinical Hospital, São Paulo; and ‡Pontificie University Catholic of São Paulo, Faculty of Biological Science (CCMB-PUC-SP), Sorocaba, SP, Brazil
Abstract: Menisci have an important role in load bearing, shock absorption, knee joint stability, and joint lubrication. Meniscal lesions and meniscectomy are followed by osteoarthritis in a high percentage of patients. At present, there is no ideal prosthesis for meniscal substitution. In this work, a bioreabsorbable polymer scaffold made of poly(Llactic acid) (PLLA) and poly(p-dioxanone) (PPD) blend was developed to be used as a temporary meniscal prosthesis to stimulate the formation of an in situ meniscal replication while the scaffold is reabsorbed by the organism. Total meniscectomy of medial meniscus and arthrotomy was
made in both back knees of 34 adult New Zealand white rabbits by medial parapatellar incision. The scaffolds were sutured in one of the knees, and other was used as a control. A meniscal replica was developed, suggesting that this material has great potential to be used as a meniscal prosthesis, especially because the new meniscus promoted a significant protection of cartilage, and cartilage degeneration in the control condyles was observed. Key Words: Meniscal prosthesis—Scaffold—Bioreabsorbable polymer—Blends—Polyt(L-lactic acid)— Poly(p-dioxanone).
Menisci perform important biomechanical functions in the knee. They are recognized as integral components of the knee joint and their presence is important for normal knee function (1). They equalize the incongruence of the articular surfaces of the femur and tibia (2), distribute the load over a large area of the tibia, absorb shocks during dynamic loading, and possibly are responsible for joint lubrication (3). At least 50% of the total load imposed on the knee joint is borne by the menisci (1). Although menisci possess excellent mechanical properties, their exposure to abnormal pressure or tension can exceed their elasticity limit and cause tears. This occurs when the load-bearing joint is submitted to a combined flexion-rotation or extensionmotion. Since sport activities have increased in recent years, there has been a significant rise in the
incidence of meniscal injuries, making partial meniscectomy and suturing procedures one of the most frequently performed orthopedic procedures today. Taking into account its functions, it is not surprising that meniscus cannot easily be removed without consequences. Meniscal lesions and meniscectomy can lead to the development of osteoarthritis (4) and a high percentage of cartilage degeneration (5). It has been shown that the degree of degenerative changes is directly proportional to the amount of meniscal tissue removed, so it is better to preserve as much meniscal tissue as possible. Although partial meniscectomy has been shown to be biomechanically more favorable than total meniscectomy, further degeneration of cartilage is not prevented (6). Possible rejection and potential risks of transmission of infectious diseases are still associated with meniscal replacement with allografts (7). Synthetic prostheses have been studied, but with poor results. A review about meniscal prostheses developed up until now was published in literature (8). Bioabsorbable polymers are gaining increasing importance in tissue engineering and cell transplan-
Received December 2002. Presented in part at the 2nd Latin American Congress for Artificial Organs and Biomaterials, held December 2001, in Brazil. Address correspondence and reprint requests to Dr. Ana Paula Testa Pezzin, State University of Campinas, UNICAMP, Faculty of Mechanical Engineering, CP 6122, 13083-970 SP, Brazil. E-mail:
[email protected]
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BIOREABSORBABLE POLYMER SCAFFOLD tation because they are good templates for cell culture. Freed et al. showed that cartilaginous tissue can be regenerated by culturing chondrocytes on fibrous polyglycolic acid (PGA) scaffold (9). It has been shown that culturing of chondrocytes is only possible when they grow in a three-dimensional matrix; otherwise they differentiate into cells with a fibroblast-like appearance (10). The use of a new meniscus created by cell culture in vitro from the patient’s own cells has been studied to replace the resected menisci, substituting the use of allografts in meniscus transplantation. The tissue-engineered meniscus can be obtained by using biodegradable polymer scaffolds made of polyglycolic acid (PGA) seeded with meniscal fibrochondrocytes in culture (11). Metak et al. developed a meniscal prosthesis made of poly(p-dioxanone)/collagen composite (12). The prosthesis was implanted in sheep, and after one year of implantation a neomeniscal formation was observed, which in comparison with the native meniscus presented a reduction in volume and loss of tensile strength. However, histological analysis was not presented. Regeneration of meniscal fibrochondrocytes across a reabsorbable scaffold will proceed to form a meniscus replica if the degradation rate of the scaffold is controlled to a critical level and the pore size is controlled to optimize the implant-host interface (13). The aim of this research was to develop a bioreabsorbable polymer scaffold made of poly(L-lactic) (PLLA) and poly(p-dioxanone) (PPD) blend to be used as a temporary meniscal prosthesis to stimulate the formation of a meniscal replica in situ while the scaffold is reabsorbed by the organism.
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All operations were performed under intravenous general anesthesia using atropine/ketamine 5%/ xylasin 2% (30/3/0.2 mg/kg). At the end of the procedure, a single dose of intravenous antibiotics was used. Postoperatively, free cage activities were allowed. The animals were sacrificed after 3, 6, 12, and 14 weeks. Tissue samples for histologic examination were removed. The specimens were immersed in Bouin’s solution, paraffin embedded, and stained with Masson’s trichrome. The prosthesis–tissue interaction was evaluated by optical microscopy. RESULTS AND DISCUSSION Porous materials were used for the meniscal prosthesis. Figure 1a shows a scanning electron micrograph of the porous structure of PPD/PLLA blend where the macropores are well interconnected. The porous formation is due to the addition of triethyl citrate in the blend. Figure 1b shows the surgical
MATERIALS AND METHODS Poly(p-dioxanone)/poly(L-lactic acid), PPD/PLLA, (80/20, w/w) blends containing 10 wt% of polymer and 3 wt% of triethyl citrate (plasticizer) were prepared by casting. The blends were analyzed by scanning electron microscopy (SEM). The scaffolds were obtained in the shape and size of the meniscus and sterilized with ethylene oxide before implantation. A total of 34 adult New Zealand white rabbits of both sexes with ages varying between 5 and 7 months were used, each weighing between 2 and 4 kg at the start of experiment. The surgical material was sterilized in autoclave at 120°C. Total meniscectomy of medial meniscus and arthrotomy was made in both back knees of the rabbits by medial parapatellar incision,and the scaffolds were sutured in one of the knees.
FIG. 1. a) Scanning electron micrograph of fracture surface of porous PPD/PLLA blend used for meniscal prosthesis is shown; b) operative procedure for suturing meniscal prosthesis is shown. Artif Organs, Vol. 27, No. 5, 2003
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A. PEZZIN ET AL. with appearance of foreign-body giant cells (macrophages) (Fig. 2a, arrows). An intense degradation of the polymer was verified after 6 weeks (Fig. 2b), and consequently more intense tissue infiltration when compared with 3 weeks (Fig. 2c). Histological examination revealed the presence of fibrocartilagenous tissue at 12 weeks after implantation, with the collagenous fibers not much aligned (Fig. 2c). After 14 weeks, it was possible to observe fibrocartilage with aligned fibers along the fibrochondrocytes. The oriented fiber pattern is very similar to the normal meniscus. Using gross inspection, the cartilage of the control condyles appeared to be less preserved than in the condyles with prostheses. The degenerative changes in the cartilage were statistically confirmed by the frequency of chondrocytes (Anova test). The results showed that the prosthesis promoted a significant protection of cartilage, while it was observed that cartilage degeneration occurs under the control condyles. CONCLUSIONS In this in vivo study, it was possible to conclude that bioreabsorbable scaffold allowed tissue ingrowth and induced fibrocartilage formation after 12 weeks. A meniscal replica was developed, suggesting that this material has great potential to be used as a meniscal prosthesis, especially because the new meniscus promoted a significant protection of cartilage, and cartilage degeneration in the control condyles was observed. Acknowledgments: The authors thank Foundation of Research Support of São Paulo State (FAPESP) for a fellowship (Process No. 97/03587-8). REFERENCES
FIG. 2. Light micrographs of PPD/PLLA implant are shown. Shown are a) 3 weeks after implantation (170x), b) 6 weeks after implantation (170x), and c) 12 weeks after implantation (290x).
procedure, where we can see the prosthesis being sutured. The morphological analysis showed that after 3 weeks, collagenous tissue grew into the porous scaffold while the prosthesis started its degradation process and a moderate reaction was seen Artif Organs, Vol. 27, No. 5, 2003
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BIOREABSORBABLE POLYMER SCAFFOLD tilage in the dog: characterization on the repair tissue and the role of vascularity. Biomaterials 1996;17:1685–91. 7. Messner K. Review: The concept of a permanent synthetic meniscus prothesis: a critical discussion after 5 years of experimental investigations using dacron and teflon implants. Biomaterials 1994:15(4). 8. Pezzin APT, Cardoso TP, Rincón MCA, Duek EAR. Prótese de menisco bioreabsorvível: uma nova alternativa para a substituição de meniscos. Revista Saúde e Ambiente 2002;3(1): 38–44. 9. Freed LE, Marquis JC, Nohria A, Emmanual J, Mikos AG, Langer R. Neocartilage formation in vitro and in vivo using cells cultured on synthetic biodegradable polymers. J Biomed Mater Res 1993;27:11–23.
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10. Archer CW, McDowell J, Bayliss MT, Stephens MD, Bentley G. Phenotypic modulation in sub-populations of human articular chondrocytes in vitro. J Cell Sci 1990;97:361–71. 11. Ibarra C, Jannetta C, Vacanti CA, Cao Y, Kim TH, Upton J, Vacanti JP. Tissue engineered meniscus: a potential new alternative to allogeneic meniscus transplantation. Transplant Proc 1997;29:986–8. 12. Metak G, Heitland A, Nickisch F, Stephan C, Milachowski KA, Scherer MA. Kollagen-Polydioxanon-composite graft als meniskusersatz-eine experimentelle studie am schaf. Langenbecks Arch Chir 1997;1:505–9. 13. Stone KR, Rodkey WG, Webber R, McKinney L, Steadman R. Meniscal regeneration with copolymeric collagen scaffolds. Am J Sports Med 1992;20(2):104–11.
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