Three-Dimensional-Construct Bioreactor Conditioning in Human Tendon Tissue Engineering

Human tendon tissue engineering attempts to address the shortage of autologous tendon material arising from mutilating injuries and diseases of the hand and forearm. It is important to maximize the tissue-engineered construct's (TEC's) biomechanical properties to ensure that the construct is in its strongest possible state before reimplantation. In this study, we sought to determine the bioreactor treatment parameters that affect these properties. Using small-and large-chamber three-dimensional-construct bioreactors (SCB and LCB, respectively), we applied cyclic axial load to TECs comprising reseeded human flexor and extensor tendons of the hand. First, small-sample pilot studies using the LCB were performed on matched-paired full-length flexor tendons to establish proof of concept. Next, large-sample studies using the SCB were performed on matched-paired extensor tendon segments to determine how reseeding, load duty cycle, load magnitude, conditioning duration, and testing delay affected ultimate tensile stress (UTS) and elastic modulus (EM). We found that compared with reseeded matched-paired controls under dynamic-loading at 1.25N per TEC for 5 days, (1) acellular TECs had lower UTS (p = 0.04) and EM (p < 0.01), (2) unloaded TECs had lower UTS (p = 0.01) and EM (p = 0.02), (3) static-loaded TECs had lower UTS (p = 0.01) and EM (p < 0.01), (4) TECs conditioned for 3 days had lower UTS (p = 0.03) and EM (p = 0.04), and (5) TECs conditioned for 8 days had higher UTS (p = 0.04) and EM (p = 0.01). However, TECs conditioned at higher loads (2.5N per TEC) and lower loads (0.625N per TEC) possessed similar UTS (p = 0.83 and p = 0.89, respectively) and EM (p = 0.48 and p = 0.89, respectively) as controls stimulated with 1.25N per TEC. After cycle completion, there is attrition of UTS (p = 0.03) and EM (p = 0.04) over a 2-day period. Our study showed that the material properties of human allograft TECs can be enhanced by reseeding and dynamic-conditioning. While conditioning duration has a significant effect on material properties, the load magnitude does not. The issue of attrition in biomechanical properties with time following cycle completion must be addressed before bioreactor preconditioning can be successfully introduced as a step in the processing of these constructs for clinical application.