neural prostheses neuroprosthetics are devices capable of supplementing or replacing missing functions of the nervous system by stimulating the nervous system and recording its activity. electrodes that measure firing of nerves can integrate with prosthetic devices and signal them to perform the function intended by the transmitted signal. sensory prostheses use artificial sensors to replace neural input that might be missing from biological sources (he 2005). engineers researching these devices are charged with providing a chronic, safe, artificial interface with neuronal tissue. perhaps the most successful of these sensory prostheses is the cochlear implant which has restored hearing abilities to the deaf. visual prosthesis for restoring visual capabilities of blind persons is still in more elementary stages of development. motor prosthetics are devices involved with electrical stimulation of biological neural muscular system that can substitute for control mechanisms of the brain or spinal cord. smart prostheses can be designed to replace missing limbs controlled by neural signals by transplanting nerves from the stump of an amputee to muscles. sensory prosthetics provide sensory feedback by transforming mechanical stimuli from the periphery into encoded information accessible by the nervous system. electrodes placed on the skin can interpret signals and then control the prosthetic limb. these prosthetics have been very successful. functional electrical stimulation (fes) is a system aimed at restoring motor processes such as standing, walking, and hand grasp. neurorobotics neurorobotics is the study of how neural systems can be embodied and movements emulated in mechanical machines. neurorobots are typically used to study motor control and locomotion, learning and memory selection, and value systems and action selection. by studying neurorobots in real-world environments, they are more easily observed and assessed to describe heuristics of robot function in terms of its embedded neural systems and the reactions of these systems to its environment (krichmar 2008). for instance, making use of a computational model of epilectic spike-wave dynamics, it has been already proven the effectiveness of a method to simulate seizure abatement through a pseudospectral protocol. the computational model emulates the brain connectivity by using a magnetic imaging resonance from a patient with idiopathic generalized epilepsy. the method was able to generate stimuli able to lessen the seizures. neural tissue regeneration neural tissue regeneration, or neuroregeneration looks to restore function to those neurons that have been damaged in small injuries and larger injuries like those caused by traumatic brain injury. functional restoration of damaged nerves involves re-establishment of a continuous pathway for regenerating axons to the site of innervation. researchers like dr. laplaca at georgia institute of technology are looking to help find treatment for repair and regeneration after traumatic brain injury and spinal cord injuries by applying tissue engineering strategies. dr. laplaca is looking into methods combining neural stem cells with an extracellular matrix protein based scaffold for minimally invasive delivery into the irregular shaped lesions that form after a traumatic insult. by studying the neural stem cells in vitro and exploring alternative cell sources, engineering novel biopolymers that could be utilized in a scaffold, and investigating cell or tissue engineered construct transplants in vivo in models of traumatic brain and spinal cord injury, dr. laplaca's lab aims to identify optimal strategies for nerve regeneration post injury. current approaches to clinical treatment end to end surgical suture of damaged nerve ends can repair small gaps with autologous nerve grafts. for larger injuries, an autologous nerve graft that has been harvested from another site in the body might be used, though this process is time-consuming, costly and requires two surgeries (schmidt & leach 2003). clinical treatment for cns is minimally available and focuses mostly on reducing collateral damage caused by bone fragments near the site of injury or inflammation. after swelling surrounding injury lessens, patients undergo rehabilitation so that remaining nerves can be trained to compensate for the lack of nerve function in injured nerves. no treatment currently exists to restore nerve function of cns nerves that have been damaged (schmidt & leach 2003). engineering strategies for repair engineering strategies for the repair of spinal cord injury are focused on creating a friendly environment for nerve regeneration. only pns nerve damage has been clinically possible so far, but advances in research of genetic techniques and biomaterials demonstrate the potential for sc nerves to regenerate in permissible environments. grafts advantages of autologous tissue grafts are that they come from natural materials which have a high likelihood of biocompatibility while providing structural support to nerves that encourage cell adhesion and migration (schmidt & leach 2003). nonautologous tissue, acellular grafts, and extracellular matrix based materials are all options that may also provide ideal scaffolding for nerve regeneration. some come from allogenic or xenogenic tissues that must be combined with immunosuppressants. while others include small intestinal submucosa and amniotic tissue grafts (schmidt & leach 2003). synthetic materials are attractive options because their physical and chemical properties can typically be controlled. a challenge that remains with synthetic materials is biocompatibility (schmidt & leach 2003). methylcellulose-based constructs have been shown to be a biocompatible option serving this purpose (tate et al. 2001). axogen uses a cell graft technology avance to mimic a human nerve. it has been shown to achieve meaningful recovery in 87 percent of patients with peripheral nerve injuries. nerve guidance channels nerve guidance channels, nerve guidance conduit are innovative strategies focusing on larger defects that provide a conduit for sprouting axons directing growth and reducing growth inhibition from scar tissue. nerve guidance channels must be readily formed into a conduit with the desired dimensions, sterilizable, tear resistant, and easy to handle and suture (schmidt & leach 2003). ideally they would degrade over time with nerve regeneration, be pliable, semipermeable, maintain their shape, and have a smooth inner wall that mimics that of a real nerve (schmidt & leach 2003). biomolecular therapies highly controlled delivery systems are needed to promote neural regeneration. neurotrophic factors can influence development, survival, outgrowth, and branching. neurotrophins include nerve growth factor (ngf), brain derived neurotrophic factor (bdnf), neurotrophin-3 (nt-3) and neurotrophin-4/5 (nt-4/5). other factors are ciliary neurotrophic factor (cntf), glial cell line-derived growth factor (gdnf) and acidic and basic fibroblast growth factor (afgf, bfgf) that promote a range of neural responses.(schmidt & leach 2003) fibronectin has also been shown to support nerve regeneration following tbi in rats (tate et al. 2002). other therapies are looking into regeneration of nerves by upregulating regeneration associated genes (rags), neuronal cytoskeletal components, and antiapoptosis factors. rags include gap-43 and cap-23, adhesion molecules such as l1 family, ncam, and n-cadherin (schmidt & leach 2003). there is also the potential for blocking inhibitory biomolecules in the cns due to glial scarring. some currently being studied are treatments with chondroitinase abc and blocking ngr, adp-ribose (schmidt & leach 2003). delivery techniques delivery devices must be biocompatible and stable in vivo. some examples include osmotic pumps, silicone reservoirs, polymer matrices, and microspheres. gene therapy techniques have also been studied to provide long-term production of growth factors and could be delivered with viral or non-viral vectors such as lipoplexes. cells are also effective delivery vehicles for ecm components, neurotrophic factors and cell adhesion molecules. olfactory ensheathing cells (oecs) and stem cells as well as genetically modified cells have been used as transplants to support nerve regeneration (laplaca et al. 2005, schmidt & leach 2003, tate et al. 2002). advanced therapies advanced therapies combine complex guidance channels and multiple stimuli that focus on internal structures that mimic the nerve architecture containing internal matrices of longitudinally aligned fibers or channels. fabrication of these structures can use a number of technologies: magnetic polymer fiber alignment, injection molding, phase separation, solid free-form fabrication, and ink jet polymer printing (schmidt & leach 2003). neural enhancement augmentation of human neural systems, or human enhancement using engineering techniques is another possible application of neuroengineering. deep brain stimulation has already been shown to enhance memory recall as noted by patients currently using this treatment for neurological disorders. brain stimulation techniques are postulated to be able to sculpt emotions and personalities as well as enhance motivation, reduce inhibitions, etc. as requested by the individual. ethical issues with this sort of human augmentation are a new set of questions that neural engineers have to grapple with as these studies develop.