Stone, J.J.

Abstract An efficient 2-D continuum finite element method (FEM), including the rigid body algorithm and our previously developed contact element, was formulated for the contact stress analysis of articular joints. This FEM can calculate the contact pressure distribution on articular surfaces and stress distribution inside of cartilage. This method can model geometric and material nonlinearities for both the static and dynamic situations. The major advantage of this method is that only the soft cartilage requires finite element (FE) mesh, while the bony structure can be modeled as a rigid body due to its relatively rigid nature. Since much less degrees of freedom are now required in FEM, much faster computing speed can be achieved.

Abstract The methodological procedure for generating three-dimensional (3-D) finite element analysis (FEA) geometry models from CT or MRI medical imaging scan data was developed in this study. Medical images of a human scapula and a fifth proximal phalangeal bone were used to demonstrate the techniques of image processing and generation of 3-D FEA models. The biomedical imaging quality and its effects on the outcome of the FEA geometry model was also studied.

Total joint arthroplasty (TJA) is implemented primarily for the relief of pain, and secondarily for achieving better function by increasing the joint’s strength and motion. In order to keep health costs low, it is desirable that the TJA achieves and maintains a long-term and secure fixation of the implanted components. Unfortunately, clinical follow-up shows that the prosthetic finger implant components have long-term complications including bone resorption, wear, loosening, and failure of the implant components. Although the mechanism of complications is not fully understood, it is well known that the wear and failure of prostheses are highly related to the mechanical forces or stresses of implant components. It is therefore desirable that reliable 3-D computational finite element analysis (FEA) models can be developed and used for the stress analysis of implants. In this study, the finger proximal interphalangeal (PIP) prosthetic components were analyzed using a nonlinear finite element method. Implant components under different joint flexion angles as well as different forces were studied. The stress distribution on the contact surface of the implant component was obtained. The developed FEA models can be used to examine the contact situations (contact stress, contact region, and stress distribution), which are critical to the wear and potential failure of the implant components. Based on FEA results, the design of the current finger PIP implants can be improved for optimum performance and a long-term fixation.

A custom computer-controlled rapid prototyping system was designed and developed in this research. This system for bio-manufacturing of polymer scaffolds included 3D motion control components, a nozzle, a pressure controller, and a temperature-controlled reservoir containing a biomaterial. Heating elements built into the reservoir melted the biomaterial. The pressure line attached to the reservoir provided a controllable force that extruded the polymer biomaterial through the nozzle and deposited the polymer biomaterial onto a platform to fabricate scaffolds. A low pressure (830 KPa) system was designed and fabricated to accommodate different temperatures, motion speeds, and viscosities of polymer biomaterials. The reservoir with the nozzle was mounted to servo motor-controlled linear x-y motion devices along with a third servo motor-controlled device that controlled the z-position of the platform. Poly(ε-caprolactone) [PCL] was used to fabricate scaffolds with designed structure that were used in cell and tissue regeneration studies. 3D computer-aided design (CAD) with Pro-Engineer and computational finite element analysis (FEA) programs with MSC_Patran and MSC_Marc were used to model scaffold designs with appropriate architecture and material selection. The CAD models were used in FEA to develop new methods for determining mechanical properties of tissue scaffolds of desired structure and geometry. FEA models were validated by mechanical testing and other published results. Technology developed in this research has potential for the advancement of bio-manufacturing, and design optimization of scaffolds for tissue engineering.