טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentGonen-Wadmany Maya
SubjectTissue Engineering a Hybrid Material Scaffold for Regulating
the Functionality of Resident Cells
DepartmentDepartment of Biomedical Engineering
Supervisor Professor Dror Seliktar
Full Thesis textFull thesis text - English Version


Abstract

The need for alternative scaffolds in tissue engineering has motivated the establishment of advanced biomaterial technologies based on biosynthetic polymers. The current investigation describes hybrid materials made of a synthetic polymer and endogenous protein precursors including collagen, fibrinogen, and albumin. The proteins were conjugated to two different synthetic polymers poly(ethylene glycol) and Pluronic®F127. These materials exhibit a unique ability to control cellular behavior by changing factors such as density, stiffness and proteolytic susceptibility through the versatile synthetic component. The overall objective of this research was to gain a more complete understanding of the interaction between cells and the cell-signaling domains on the backbone of the hybrid biomaterial so that we can learn how to use the scaffold to regulate cell function. Our first goal was to investigate the effect of the PEGylation on the scaffold's biological properties. For this purpose we examined pure fibrin and PEGylated fibrinogen and studied the effects of the PEG conjugation on the material's biomechanical properties and cellular response. The PEGylated fibrinogen showed reduced mechanical properties and induced degradation kinetics in comparison to the fibrin. The PEG-fibrinogen enabled cell spreading and actin expression indicating the biofunctionality of the PEGylated protein. Lower levels of MMP-2 and MMP-9 were detected in the PEG-fibrinogen cellularized hydrogels which could explain the longer period it took the cells to remodel the PEG-fibrinogen matrix. In order to decouple the matrix stiffness and biodegradation rate in the protein-polymer materials we took advantage of another synthetic polymer, Pluronic®F127, at its unique capabilities to undergo reverse thermal gelation. The biofunctionality of the F127-fibrinogen was thoroughly investigated using 3-D cell culture assays, which demonstrated that the conjugation reaction did not compromise the ability of the material to support the cultivation of encapsulated cells. Studies with the F127-fibrinogen revealed the importance of the matrix modulus in controlling cell spreading in a 3-D hydrogel milieu (independently of proteolysis).

Finally, in order to gain an understanding of how alterations in the protein backbone are interpreted by the resident cells, we established two new PEGylated protein hydrogels; PEGylated collagen and PEGylated albumin.  The differences in rheology and swelling characteristics of the three hydrogel materials underscore the importance of the molecular relationship between the PEG and the protein constituent in this protein-polymer arrangement. The biofunctionality of the PEGylated collagen and fibrinogen hydrogels sustained both cell adhesion and proteolytic degradation that enabled 3-D cell spreading and migration within the hydrogel network.