▼ Drop foot is a neuromuscular disorder causing a loss of use of the muscles that lift the foot. Drop foot can primarily be caused by stroke, cerebral palsy, multiple sclerosis, or neurological trauma. The two major complications of drop foot are slapping of the foot after heel strike (foot slap) and dragging of the toe during swing (toe drag). The current treatment options like Ankle Foot Orthosis (AFO) and Functional Electrical Stimulation, while offering some biomechanical benefits, do not adapt to different walking conditions and fail to eliminate significant gait complications. This study proposes a novel Active Ankle Foot Orthosis design which combines an AFO and combinations of shape memory alloy (SMA) wires. The key feature of SMA is its ability to undergo seemingly large plastic strains and subsequently recover these strains when a load is removed or the material is heated. Because of this distinct thermomechanical behavior, SMA can potentially resolve some of the gait complications associated with use of an AFO. To provide a basis for the design of an AAFO, gait analysis is performed on healthy subjects along with drop foot patients to establish the deficiency in ankle stiffness characteristics. The initial verification of the thermomechanical behavior of SMA in the form of stiffness variation is carried out by testing SMA wire combinations. Based on these experiments a COMSOL model is verified which is used for simulating the combinations of SMA wires. Through simulations and experiments it has been shown that changing the combination of SMA wires result in variable stiffness pattern. The performance of different types and combinations of SMA wires are tested successfully on an AFO. The preliminary results demonstrate that SMA wires provide controlled plantarflexion during stance phase, and active dorsiflexion in the swing phase by using stiffness variations of shape memory alloy wires. In particular, the AAFO helps to avoid major complications of drop foot gait. Thus, with the development of a control strategy, and using the inherent stiffness variation of SMA wires it is possible to produce close-to-normal stiffness profiles in the ankle motion of drop-foot patients who are wearing the AAFO. Advisors/Committee Members: Elahinia, Mohammad.

▼ Natural bone is a complex composite mainly constituted of inorganic minerals and organic collagen molecules. Calcium phosphate (CaP) based materials have been proposed as the predominant bone substitute for bone tissue engineering applications due to their chemical similarity to bone mineral. Amorphous carbonated calcium deficient hydroxyapatite (CDHA) is an important compound among CaP materials because of the amorphous crystallite structure. The presence of extra ions in its lattice structure not only influences cell attachment and proliferation of osteoblasts, but also helps in bone metabolism. Biomimetic coating approach is the most widely used approach to produce CDHA coatings to implant. It is a process using simulated body fluid (SBF) to deposit bone-like CDHA coating to various material surfaces. The CDHA formation mechanism, SBF compositions and reacting conditions of biomimetic coating have already been sufficiently studied and compared in the past 20 years. It is an attempt in this thesis to explore new applications of SBF in biomedical research, focusing on different biomaterial applications: 1) based on the low temperature reaction condition of SBF, bisphosphonate incorporated CDHA coatings were deposited onto Ti6Al4V surface for the treatment of osteoporosis; 2) amorphous calcium phosphate nanospheres with extra elements in the lattice structure were prepared by a novel microwave assisted approach, providing a new potential of CaP materials production; 3) CDHA particles formed in SBF can be used as great fillers with biopolymers for preparing biocomposites for biomedical applications; 4) based on the high activity of CDHA amorphous structure and the stabilization ability of ethanol, yttrium and europium doped calcium phosphates were prepared using CDHA as a sacrificing template. In the end, future work based on these observations in the thesis is addressed, including areas of drug delivery, biocomposite fabrication and preparation of functionalized calcium phosphate materials. Advisors/Committee Members: Bhaduri, Sarit.