M.Sc Thesis

M.Sc StudentYom-Tov Ortal
SubjectCharacterization of PEG-Fibrinogen Nano-Structured for
Tissue Engineering
DepartmentDepartment of Chemical Engineering
Supervisor PROF. Havazelet Bianco-Peled
Full Thesis textFull thesis text - English Version


Tissue engineering is a science of creating new tissues in order to regenerate an organ's functionality or to replace damaged organ parts. A common approach in tissue engineering is based on seeding cells in a polymeric scaffold that can mimic the Extra Cellular Matrix (ECM).  The current research focuses on a biosynthetic hydrogel scaffold composed of polyethylene glycol (PEG) and fibrinogen. The use of Pluronic? F127 as an additive to such hydrogel scaffolds has been recently suggested as a means to entrap micelles in the hydrogel, resulting in nanostructuring of the scaffold and enabling for cell development. The goal of the current research was to understand whether the positive effect of the nanostructuring was due to the presence of entrapped micelles, or did it result from an improved ability of the cells to develop within the cavities formed after micelles release. To distinguish between these two possibilities we suggested limiting the ability of the micelles to diffuse out of the hydrogel by using Pluronic? F127-DA as additives. 

Cell assays demonstrated that cell viability and morphology were enhanced in the presence of Pluronic? F127-DA in comparison to the control group. In order to interpret this outcome, characterization of the nanostructure of PEG- fibrinogen solutions and hydrogels via small angle x-ray scattering and cryo - transmission electron microscopy was performed. The experiments reveal the existence of spherical micelles entrapped within the hydrogels. Moreover, an alteration in the nanostructure of the scaffolds after polymerization occurs which depends on Pluronic? F127-DA concentration. Hydrogels submerged in water have lost weight over time, most likely due to migration of both Pluronic? F127 molecules and unbound Pluronic? F127-DA out of the hydrogel. This could result in cavities which are formed within the scaffold causing favorable cell growth in hydrogels which contain Pluronic? F127.

In addition, we investigate the influence of modification with Pluronic? F127-DA on the mechanical and physical properties of PEG-fibrinogen scaffolds through compression tests and swelling experiments. These tests have revealed that crosslinking the hydrogel (either by adding PEG-DA or Pluronic? F127-DA) increased its mechanical strength thus resulting in diminished cell development. However, the cavities formed in the scaffold compensate for the increase in modulus thus the hydrogels still allowed cell spreading and development. This observation further clarifies that the positive effect on cell growth is due to the cavities, and not the presence of micelles.