Sculpting with light: light/matter interactions in biocompatible polymers
Abstract: When light
interacts with matter either the light or the material can be changed. This dissertation
focuses on light/matter interaction in silk fibroin and its utility for biomedical
applications. Silk, a natural biocompatible, biodegradable polymer, has a large 3-photon
absorption cross-section which allows modest peak intensity light to cause significant
multiphoton absorption. ... read moreThis absorption allows voids to be formed with three dimensional
control within soft, transparent silk hydrogels. A theoretical model of the void
formation process is developed to allow the size of the voids to be predicted for a
range of laser and sample parameters. Arbitrary 3D patterns are created in silk gels
that allow cells to penetrate into the bulk of the gel both in vitro and in vivo. To
explore how silk can be used to alter light, the creation of step-index optical
waveguides, formed by encapsulating a silk film within a silk hydrogel, is described.
These waveguides allow light to be delivered to targets through several centimeters of
highly scattering biological tissue. Finally, the interaction of light with riboflavin
is used to photocrosslink silk to form solid structures, rather than voids. The
mechanism of crosslinking to be driven by radicalized tyrosine residues resulting in the
formation of dityrosine bonds which lead to the gelation of a liquid silk solution.
Riboflavin is a versatile photoinitiator and can be used to crosslink collagen as well
as silk, which allows silk to be crosslinked directly to corneal collagen. When applied
to the eye, an artificial corneal layer is formed which has the potential to treat
various corneal diseases and allow for risk-free laser vision correction. These studies
show the versatility of light-based processing of silk for a wide variety of medical
Thesis (Ph.D.)--Tufts University, 2016.
Submitted to the Dept. of Biomedical Engineering.
Advisor: Fiorenzo Omenetto.
Committee: David Kaplan, Irene Georgakoudi, David Walt, and Christopher Schaffer.
Keywords: Biomedical engineering, Optics, and Materials Science.read less