Silk scaffolds for neural tissue engineering.
Abstract: There is a
critical need for therapies that promote neural regeneration and target disease
mechanisms of the nervous system. Neural tissue engineering (TE) is in the early stages
of development with research focusing on several aspects of therapeutics including
peripheral nerve repair, image processing analysis techniques, and in vitro tissue
systems. TE functional neural systems pr... read moreesent unique challenges including low tissue
stiffness, high cell density, and complex neural network functions still being
elucidated in vivo. Silk biomaterials are attractive candidates for TE applications due
to their biocompatibility, aqueous-based processing, and robust and tunable mechanical
and degradation properties. The present work evaluated two silk scaffold platforms for
neural TE applications: (1) silk hydrogels, and (2) silk sponges. Mechanical stiffness
and biochemical functionalization of silk hydrogels were examined for promotion of
neurite extension for peripheral nerve guidance. One to 8% silk hydrogels exhibited low
stiffness of 4-33kPa as measured by atomic force microscopy. The structural integrity of
the silk gels was maintained throughout cell culture whereas fibrin and collagen gels
decreased in mass over time. Neurite extension was greatest on 2 and 4% silk hydrogels
as compared to softer or stiffer gels and gels loaded with neurotrophin-3 exhibited low
release of <5% and remained bioactive over 2 weeks. Functionalization of silk
hydrogels with fibronectin and laminin led to observations of differences in axonal
bundling. Due to the lack of quantitative image processing methods for analysis of
fasciculation events, silk hydrogels were employed for development of a semi-automated
neurite directional distribution analysis (NDDA) program, which quantifies fasciculation
based on tortuosity of neurite extension. Finally, a compartmentalized silk sponge
scaffold with arrays of hollow channels was characterized for development of 3D neuron
cell culture systems. The silk sponge scaffold allowed for localized, long-term
co-cultures of vascular and neuronal cells and resembled the 3D architecture of the
neurovascular unit (NVU). The 3D NVU culture system has potential for supplementing 2D
cultures and animal models for CNS therapeutic development. Collectively, this work
exemplifies several neural TE applications with silk biomaterial scaffolds offering
promising in vitro systems for understanding nervous system mechanisms and therapeutic
Thesis (Ph.D.)--Tufts University, 2013.
Submitted to the Dept. of Biomedical Engineering.
Advisor: David Kaplan.
Committee: Fiorenzo Omenetto, Barry Trimmer, Michael Whalen, and Cristian Staii.
Keyword: Biomedical engineering.read less