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Discussion. Flexor tendon tissue engineering: acellularized and reseeded tendon constructs.

R surgeons routinely transfer tissues such as skin, bone, muscle, tendon, and nerve when required to restore form and function. Tissue engineering has emerged as an attractive option for complex cases in which we run out of these “raw materials.” In 2006, Drs. Chong and Chang reviewed the current state of this field and set out many goals for the future regarding tissue engineering in the hand.1 It appears that their laboratory has been quite busy trying to achieve some of these objectives. In this study, the authors set out to prove that their tissue-engineered prototype tendon would retain biomechanical properties (ultimate tensile strength and elastic modulus) similar to those of healthy fresh tendon. Because of the proven advantages of intrasynovial tendons over extrasynovial tendons with regard to tendon grafting,2 this has been the area of focus in their laboratory. Intrasynovial tendons were harvested, acellularized, and reseeded with tenocytes obtained from other intrasynovial tendon specimens. They theorize that this construct represents a model of what might be possible in the future of clinical tendon surgery: an acellularized “shelf” allograft that can be reseeded with the recipient’s tenocytes before implantation as a tendon graft for reconstruction. Although the sample size is relatively small, this engineering concept is well designed and the control used is appropriate. The experiment examined freshly harvested tendon, tendon that had been frozen for a short time, acellularized tendon, and acellularized tendon that had been reseeded with tenocytes. Their results showed that there is little difference in biomechanical properties between “fresh” tendons and tendons frozen for a short time or acellularized tendons. Their reseeded tendon construct also had properties similar to those of native tendon, with the exception being the small but significant decrease in ultimate tensile strength. Although a trend was seen toward a decreasing elastic modulus, this was not significant. Although there were some limitations to this study, within its narrow focus, the authors have achieved their intended goal. They have nicely demonstrated that neither short-term freezing nor acellularizing their tendon construct changes the mechanical properties significantly. Furthermore, the addition of an incubation period associated with reseeding was shown to weaken the tendon by only a small amount, which they theorized may be overcome by subjecting this construct to physiologic strain as in a bioreactor during this period. Their laboratory has already demonstrated that such a bioreactor can help facilitate changes in cellular architecture, alignment, and collagen I production.3 It should not be long before the bioreactor can be used to improve on the results of this study. Many unanswered questions remain before this model can be used in the clinical arena. Of course, the antigenicity of this construct and the potential for disease transmission will need to be tested extensively before the technique can be introduced into human subjects. On a more practical front, in vivo testing will be required to compare this construct to extrasynovial tendon grafts to determine whether the reseeded tenocytes confer the same benefit as intrasynovial grafts. Will the outer tenocyte “coating” on these otherwise acellular tendons be sufficient to induce a more “intrinsic” pattern of healing and avoid the more prominent adhesions associated with “extrinsic” healing? If these questions can be