467 A PHYSIOLOGIC ROBOT REACTOR SYSTEM TO SIMULATE IN VIVO CONDITIONS

Abstract

Purpose: Success in cartilage tissue engineering and cartilage repair strategies depends on the formation of a hyaline cartilage tissue. In any circumstances, the interaction of at least the four components cells, scaffold/ matrix, biochemical, and biomechanical factors, is of utmost importance to induce or maintain the cells in a chondrocytic phenotype, which is a prerequisite to form hyaline cartilage tissue. Any significant in vitro evaluation, such as testing different cell-scaffold constructs, has to be performed under the harsh conditions encountered in vivo within synovial joints. Therefore, many different bioreactor systems have been developed with the aim to simulate these conditions. However, two main shortcomings have been identified in these systems: (i) the mechanical stimulation units do not operate within a physiological stress range and are limited in the applicable motion pattern, and (ii) most systems lack an ambient control and therefore no hypoxic environment is generated as encountered in synovial joints. We have addressed these shortcomings by designing a fully autonomic modular Physiologic Robot Reactor System (PRRS). Methods: We have engineered a reactor system that comprises a mechanical stimulation unit (MSU), an automatic sample changer (ASC), and an environmental control box (ECB) (Figure 1). The MSU is designed with three linear (orthogonal axes) and one rotational degree of freedom (around z-axis; a rotational component around y-axis is pending). The load generated by the MSU is transferred via an exchangeable plunger on a sample tissue placed in a sample holder (Figure 2). Highly accurate force-feedback and motion systems are controlled by ultrafast Field Programmable Gate Array (FPGA) and real-time components which continuously monitor all system parameters. The ASC is designed as a carrousel providing space for 24 sample holders, which allows for individual piloting of the samples with their own stimulation pattern. The ASC and the MSU are integrated in the ECB in which humidity, temperature, gas composition (O2, CO2), and pressure are actively controlled. In addition, an automated media exchange is also implemented in the system, which enables a prolonged uninterrupted cultivation of sample tissues. Results: The complex physiological motion and load pattern of a knee joint were closely simulated by combining sinusoidal and linear motions. Loading forces of up to 500 N in z-axis were achieved, closely matching the physiological forces encountered in the knee. Within the ECB, the climate is accurately controlled and maintained (deviations of less than 0.1% and 0.1°C from given gas concentrations and temperature, respectively) within the range of the detectors.