M.Sc Thesis

M.Sc StudentSocolovsky Noga
SubjectA Hydrogel-Based Nerve Regeneration Conduit with Nano-Scale
Feature Control
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisor PROF. Shy Shoham


Recent years have seen significant progress in tissue engineering and in research of cellular interactions and responses. To further advance this research it is necessary to develop the ability to perform experiments in fully controllable three-dimensional environments similar to the physiological one. Moreover, these environments should provide the cells with cues that are in the same scale as cellular interactions - the sub-micrometric and nanometric scales. In particular, achieving three-dimensional controlled guidance of nerve regeneration may lead to significant outcome not only in repairing nerve functionality but also to the end of creating artificial neural networks for computational and pharmacological studies.

This research explores the application of femtosecond laser processing for patterning a biosynthetic hydrogel (PEGylated-fibrinogen) with the aim of promoting functional nerve regeneration. Our study approaches the challenge of achieving precise geometrical patterning of the hydrogel material in two ways - photo-polymerization and photo-ablation - and explores the capabilities and limits of each technique.

First, we study multi-photon photo-polymerization in this hydrogel using an Eosin-Y and MDEA photo-initiator system. We demonstrate the formation of polymerized dots and lines. However, we find that the polymerized lines have a wavy morphology, which limits the application and necessitates further research.

Next, we study the formation of channels in the hydrogel using femtosecond laser photo-ablation (these results are compared with related results from a nanosecond laser system). We observe the emergence of localized defects in the hydrogel in laser intensities above 2.3x1012 W/cm2, consistent with theoretical threshold values for the physical process of optical breakdown in water. We use histological sectioning and a custom micro-fluidic approach to characterize the dimensions and properties of the ablated regions, and demonstrate the formation of submicron-scale physical voids under certain conditions. We find that these characterization approaches are, however, limited in dealing with the submicron dimensions of channels formed using femtosecond photo-ablation.

Our results show that cellular processes from chick dorsal root ganglion (DRG) explants are directionally guided by channels inscribed in the hydrogels. Guided growth to distances exceeding 1mm was observed, at rates of up to 100μm per day. The cellular extension into the channels included both neurites and support cells, not relying on the power level that was used to create the channel. A threshold behavior was found here too.

 Calcium imaging experiments were finally used to demonstrate that the DRG neurons used in our experiments are excitable, and we conclude by discussing directions for future research.