M.Sc Thesis

M.Sc StudentFrisman Ilya
SubjectMicrostructural Characterization of Composite Scaffolds for
Tissue Engineering
DepartmentDepartment of Chemical Engineering
Supervisor PROF. Havazelet Bianco-Peled


During the last decade, tissue engineering has become one of the most significant fields of research in medical and biological sciences. The most common approach in tissue engineering is based on the preparation of a scaffold into which the biological supplements (cells, proteins, etc.) are incorporated­­. The scaffold is usually made from synthetic or natural polymers that have a limited ability to degrade in an enzymatic environment. This research deals with a novel class of hybrid scaffold for tissue engineering, invented by Dr. Dror Seliktar from the Department of Biomedical Engineering at the Technion. This scaffold combines fibrinopeptide, a natural polymer, and polyethylene-glycol (PEG), a synthetic polymer. Variations in the molecular weight of the PEG and the PEG/Fibrinopeptide weight ratios were shown to have an influence on the physical properties of the hydrogel, its enzymatic degradability and interactions with cells. Our objective was to characterize the influence of the preparation conditions (polymer concentration, PEG/fibrin ratio, molecular weight of the PEG etc.) on the nano-structure of the gel, on the one hand, and on its physical properties such as rate of proteolytical degradation, on the other.

Characterization of the hydrogel structure was performed using several scattering techniques: light, X-ray and neutron scattering. Light scattering experiments were aimed at determination of the molecular weight of the precursor molecules. These experiments showed that the calculated molecular weights of molecules in aqueous buffer were higher then the ones calculated from a mass balance. We hypothesized that this observation is due to aggregates formation in the precursor solutions. Small angle scattering analysis provided structural information on a single precursor molecule. From X-ray scattering experiments we concluded that the PEG-fibrinopeptide precursors have a cylindrical structure. We also assumed that the X-ray curves only reflect the contribution from the fibrinopeptide backbone. Therefore, neutron scattering experiments were also performed. The experimental data was fitted with a model of a long cylindrical particle with Gaussian chains attached. Base on the results from light and small angle scattering, we provided a schematic drawings that present the approximate position of the precursor molecules in the aggregates, while considering their size.

In the second part of our research, a characterization of enzyme diffusion inside the gel and the kinetics of the enzymatic reaction were performed using diffusion and cleavage reaction experiments, respectively. Combining these results suggested that during the enzymatic penetration the hydrogel experiences mostly surface degradation process.