Scaffolds & Hydrogels

Tissue Engineering Exam 1 Group 2

Natural scaffold materials

proteins (collagens, fibrin), polysaccharides (glycosaminoglycans, alginate, chitosan)

collagen role

strengthen matrix

elastin role

gives fibers resilience

fibrin role

natural wound healing matrix, controlled by calcium ions

polysaccharides role

form hydrogels that resist compressive forces, permit diffusion of nutrients & signals

Glycosaminoglycans (GAG) gels

fill extracellular space, high negative charge density attract water & therefore volume, give mechanical support

Chitosan

biocompatible, cross-linked in films & fibers, used for encapsulation, membrane barriers

Alginate

biocompatible, FDA approved, sponge scaffold, used for injectable cell-delivery vehicle or wound dressing

Decellulariation techniques (chemical/enzymatical)

ionic SDS and non-ionic detergents (Triton), acid/alkaline treatments, metal chelating (EDTA), proteases (trypsin), nucleases

Decellulariation techniques (Physical)

freeze-thaw cycles, high pressure, osmotic shock

Advantages of acellular scaffolds

reduced immunogenicity, removal of alpha-gal structure, retains matrix structure & composition, elastin doesn’t need to regenerate, preserves vascularization

Hydrogel Definition

cross-linked polymer networks with quickly absorbed water

Hydrogel Chemical cross-linking

free radical initiation (PEGDA), condensatoin (genipin)

Hydrogel physical cross-linking

hyrophobic interactions & ionic interactions

Hydrogel structural behaviours

Mc= molecular weight between cross-links (=pore size), SEM tells real pore size

hydrogel swelling

counterbalance swelling w/elastic retractive force, equilibrium swell volume - Vgel/Vdrypolymer

hydrogel mechanical properties

weak, yield stress important, shear stress determines ease of injection. compression modulus of elasticity = mechanical stability, match viscoelastic properties w/intended tissue

smart hydrogels

thermo responsive (gelation at temp), pH responsive (gelation by pH)

advantages of using hydrogels in tissue engineering

encapsulated cells keep unaltered shape, allow for diffusion and mass transport thru pores, can incorporate bioactive molecules, can be injected for in situ polymerization.