Ph.D Thesis

Ph.D StudentDikovsky Daniel
SubjectPoly(ethylene glycol)-based biosynthetic Scaffolds for
Tissue Engineering
DepartmentDepartment of Biotechnology
Supervisors ASSOCIATE PROF. Dror Seliktar
PROF. Havazelet Bianco-Peled
Full Thesis textFull thesis text - English Version


The need for alternative scaffolds in tissue engineering has motivated the establishment of advanced biomaterial technologies based on biosynthetic polymers. Networks of synthetic and endogenous building blocks are created into a biomimetic environment for enhanced tissue compatibility with precise properties. The current investigation describes a unique biosynthetic scaffold comprised of synthetic polyethylene glycol (PEG) and fibrinogen protein and its interaction with a three-dimensional smooth muscle cells (SMCs) tissue culture.

The effects of conjugating large PEG chains to fibrinogen were examined using rheometry and swelling experiments. The physical properties of both un-cross-linked and UV cross-linked PEGylated fibrinogen (PF) with PEG molecular weights ranging from 6 to 20 kDa were investigated. The PF was cross-linked using photoinitation in the presence of SMCs to form a dense cellularized hydrogel. The structural properties of the scaffold were controlled by modifying the molecular weight of the attached PEG, changing the precursor concentration and by addition of cross-linker. The gels were characterized in terms of cross-linking kinetics, swelling properties and compliance and related to the degradation kinetics of the scaffold.

As expected, the conjugated protein-polymer formed a continuous molecular network upon photopolymerization of the pendent acrylate groups. Accordingly, the cross-linking kinetics and stiffness of the hydrogel were highly influenced by the protein-polymer conjugate architecture and molecular entanglements arising from hydrophobic/hydrophilic interactions and steric hindrances. The proteolytic degradation products of the PF conjugates proved very different than the un-conjugated denatured protein degradation products, indicating that steric hindrances may alter the proteolytic susceptibility of the PF. Experiments using SMCs cultured inside the PEG-fibrinogen scaffold demonstrated a relationship between the molecular architecture of the matrix and the cellular morphology. A quantitative assessment of cellular viability, morphology and migration demonstrated a strong correlation between the extents of ECM remodeling processes and the network structure of the matrix. The initial cell spreading into the hydrogel matrix was dependent on the proteolytic susceptibility of the materials, whereas the extent of cell compaction proved to be more correlated to the modulus of the material.

We concluded that SMCs use proteolysis to form lamellipodia and tractional forces to contract and remodel their surrounding microenvironment. Matrix modulus can therefore be used to control the extent of cellular remodeling and compaction. This should allow manipulating cellular characteristics using straightforward structural modifications to the PF scaffold. Such approach may become a valuable tool in tissue engineering and tissue regeneration.