|Ph.D Thesis||Department of Chemical Engineering|
|Supervisor:||Assoc. Prof. Bianco-Peled Havazelet|
|Full Thesis text|
This research focused on poly (ethylene glycole)-Fibrinogen (PF) hybrid scaffold prepared by the cross-linking of PEGylated fibrinogen precursors molecules. We hypothesized that nanostructuring of PF scaffold would provide an additional means to control both their physical properties and their interaction with cells. To examine this hypothesis we suggested utilizing the self-assembly tendency of the biocompatible amphiphilic block-copolymers poly(ethylene oxide)/poly(propylene oxide) (Pluronic?). The overall objective of this research was to study the structure-property relations in nanostructured PF hydrogels in order to gain an additional mean to control their properties. Two methods of utilizing Pluronic? were explored: (1) embedding Pluronic? F127 micelles in the hydrogels (2) conjugating modified Pluronic? F127 molecules to fibrinogen to create a “smart” precursor molecule which can be further cross-linked. The formation of partially ordered micellar structures, surrounded by PEG-fibrinopeptide network was verified and characterized using a combination small angle x-ray scattering and transmission electron microscopy. The mechanical properties were evaluated using rheology measurements. The embedded block-co-polymer micelles increased the storage modulus of the as-prepared hydrogels, however their release, evaluated by swelling and Pluronic? release experiments, resulted in a dramatic decreased of the storage modulus over time. Cell behavior was investigated using cell seeding and outgrowth studies. Following preliminary results demonstrating that Pluronic? addition influences morphology, further studies used image analysis to quantify the interaction with cells. These experiments revealed that cell development depends in a non-linear fashion on the percentage of the added Pluronic? F127.
Nanostructured scaffolds based on “smart” conjugated Pluronic? F127- fibrinopeptide (FF127) molecules were extensively studied. Previous studies have shown that the temperature at which the chemical cross-linking of F127-fibrinopeptide conjugates was initiated had a drastic influence on the mechanical properties of the thermo-responsive hydrogel. The strength of the hydrogel at body temperature was higher as the temperature at the preparation was decreased. In this study we investigated the mechanism for hydrogel formation via reversible (physical cross-linked) and irreversible (chemically cross-linked) routs. Small angle X-ray scattering and transmission electron microscopy were employed and model describing the network structure was suggested. It was found that the mesh size of the hydrogel was lower when the gel was cross-linked at low temperature, and as a result the hydrogel had high storage modulus at body temperature.
The proposed research leads to a better understanding of the influence of structural modification on the cell activity to improved properties of PF scaffolds.