Altering cells used in tissue engineering so as to obtain a better result is a very viable prospect, as demonstrated in a recent investigation of tendon regeneration: "The basic function of tendon is to transmit force from muscle to bone, which makes limb and joint movement possible. Therefore tendons must be capable of resisting high tensile forces with limited elongation. ... the mechanical properties of tendons are related to the fibril diameter distribution, large fibrils could withstand higher tensile forces. ... In the healing tendon, a uniform distribution of small diameter collagen fibrils has been found with poorer mechanical properties than native tissue and shows no improvement of mechanical properties with time ... The present study for the first time demonstrated the use of a scaffold-free tissue engineered tendon model for investigating the biological function of collagen V in tendon fibrillogenesis. ... Conclusively, it was demonstrated that Col V siRNA engineered tenocytes improved tendon tissue regeneration. ... These findings present a good example of in vitro tissue engineering model for tendon biology investigation and may provide basis for future development of cell or gene therapy for tendon repair."