Ultrasonic Machining And Inspection Technology Tissue Engineering Scaffold

Tissue engineering applies the principles of engineering and life science to replace the diseased or damaged organs and to restore the functionality of these organs without retrieving the scaffold. Tissue engineering scaffold is the most important part in realizing the clinical practice of tissue engineering. However, most methods to fabricate tissue engineering scaffold need either the use of organic solvent, which could reduce the biocompatibility of tissue regeneration because of the residual solvent. And the biocompatibility is uncontrollable.According to the solvent residual toxic problems during the Chemical foaming process, by use of the solvent free solid-state foaming technique, cell size from550to20μm of the PLA foam was fabricated under the saturation pressure from1to5MPa. The relationship between cell size and saturation pressure, foaming temperature and pressure time was analyzed. The thermal properties of the PLA foams with respect to the cell sizes were measured using thermal gravimetric analysis in nitrogen atmosphere, and the parameters of activation energy and pre-exponential factor were derived to perform kinetic performance evaluation and lifetime estimation. It is proved that small cell size can be achieved under high saturation pressure and the thermal stability decreases after the fabrication process. The cell size-dependent thermal stability and degradation rate indicate that the PLA foam with larger cell size has shorter degradation time at low temperature of37℃, which is even a few tenth that of the PLA raw material.In addition, aiming to the disadvantages of the poor permeability, the slower metabolism velocity and the uncontrollable degradation time, power ultrasound was applied to improve the permeability of the solid-state fabricated PLA foams with different cell sizes. First, basic principles of the ultrasonic cavitation, the ultrasound micro jet and the permeability enhancement of PLA foams were studied. And then, it is experimentally proved that cell interconnection and the permeability can be improved with the increasing of power ultrasound radiation intensity. Furthermore, the acoustic wave propagation characteristics in the PLA foams were studied, and an insert-substitution testing approach was put forward to perform acoustic measurement and property characterization for the PLA foams before and after ultrasound radiation. The experimental results indicate that the attenuation coefficient of the close-celled PLA foams decreases exponentially with respect to the saturation pressure and it shows linear behavior with respect to the ultrasound radiation intensity. When the ultrasound radiation intensity exceeds80%Pmax for the2.5-MPa PLA foams, water can go into the damaged cells through the big cell cracks, which might be considered as a possible explanation for the rapid decline of the acoustic attenuation coefficient.Results suggest the feasibility of fabrication parameter optimization to satisfy the application requirements for organs with appropriate cell size and lifetime. This study provides the basis of precise scaffold design and quantitative analysis for PLA foams in tissue engineering. The new technologies of the ultrasound enhancement and ultrasound measurement were put forward, which played important role in the development of the performance improving and measurement for the tissue engineering scaffold.