Tissue engineering is a relatively new discipline that recently has received significant attention.³ Tissue engineering has provided a fundamental understanding and technology that has permitted the development of structures derived from biological tissues. Bioresorbable collagen matrices are one important example of innovative new devices that resulted from the discipline of tissue engineering.^4,5,6 These collagen matrix materials have many positive features for use in preservation and restoration of meniscus tissue, including a controlled rate of resorption based on the degree of cross-linking. Most noteworthy, processing of the collagen can minimize any immune response, and the extremely complex biochemical composition of the normal meniscus might be recapitulated during the production process.^4,5,6 If such a material could serve successfully as a scaffold for regeneration of new tissue, then many of the previously noted negative effects of losing the meniscus cartilage might be prevented or at least minimized.⁷

We started development of this collagen scaffold, which we refer to as the collagen meniscus implant (CMI), with straightforward goals. We set out to generate or grow new meniscuslike tissue in an effort to restore or preserve the critical functions of the meniscus.^8,9,10 We also hoped to prevent further degenerative joint disease and osteoarthritis that likely would be progressive and lead to multiple surgeries, possibly including total knee replacement. Another goal for this regenerated tissue was to enhance joint stability. And finally, we wanted the implant and the new tissue to have the effect of providing pain relief and precluding the necessity for constant medication. We also focused on several criteria for design of the CMI.^8,9,10 We desired to have a material that would be resorbable over time so that as the collagen of the scaffold was metabolized, the regenerated tissue would have the opportunity to replace it. We also planned for the CMI to maintain its structural integrity in the intra-articular environment for a period that would be adequate to support the new matrix formation and maturation. It was essential that the material be nonimmunogenic to minimize reactions that might cause rejection or destruction of the implant. Consequently, biochemical techniques were developed as part of the processing procedures to minimize such reactions.^4,5,6 We designed the implant to be technically straightforward to implant surgically with a minimum of sizing considerations. We thought that the implant would have to be nonabrasive, not produce any wear particles, and not incite an excessive inflammatory response. And finally, it was extremely critical that the implant be nontoxic to the cells that invaded the scaffold and eventually produced the new matrix.^8,9,10

Hence, it was our hypothesis that if we could provide such an environment, the meniscus fibrochondrocytes, or other progenitor cells as we would learn later, would migrate into the scaffold, divide and populate the scaffold, produce extracellular matrix, and finally lead to the generation of new meniscuslike tissue. This new tissue then would preserve and help restore the damaged meniscus cartilage and would function like the meniscus to be chondroprotective. We affirmed our hypothesis and confirmed that we had met our requirements in various animal studies.^6,8,11