To combat this difficultyâEUR"one among manyâEUR"Wittemore says bioengineers must turn to biomaterials in combination with stem cells to find successful implants. Fiber and channel-based guidance, as well as incorporating ligands, can help regulate cell interactions as well as control differentiation and function of transplanted cells. Wittemore works at the Kentucky Spinal Cord Injury Research Center and Departments of Neurological Surgery and Anatomical Sciences and Neurobiology at the University of Louisville School of Medicine.