|
Polymer substrates | + advantages/− disadvantages | Examples | Method to vary elasticity | Reference |
|
Natural polymers |
| + good adhesion capabilities + mimicking of natural ECM | Collagen-I gel (1 wt.%) and collagen-hyaluronic acid mixture | By the concentration of water soluble carbodiimide (EDC) as a crosslinking agent to produce matrices of 1–10 kPa with pore sizes about 50 μm | [49] |
| | | | |
Collagen-based gels | | Collagen-I gel (1 wt.%) | By thickness of solution before polymerization: 500 µm for soft, few microns for stiff | [78] |
| | | | |
| + injectable, for brain repair + biodegradable | Gelatin-hydroxyphenylpropionic acid (Gtn-HPA) hydrogel | By chemical cross-linking by an enzyme-mediated oxidation reaction | [12, 22] |
| | | | |
Hyaluronic acid (HA) gel | + mimicking of natural ECM − pure HA does not permit cells to adhere; must be coated by cell-adhesion proteins predominantly elastic, with very low viscous component | Thiol modified HA (HA-S) gel coated with gelatin | By concentration of PEG-diacrylate as a cross linker | [50] |
Hyaluronic acid (HA) 1 wt.% | By the concentration of water soluble carbodiimide (EDC) as a crosslinking agent, pore size 80 μm | [87] |
|
Synthetic polymers |
Polyacrylamide (PAA) gel | pure PAA is fully elastic material but can be used to produce viscoelastic gel + plenty of methods to tune its stiffness without changing porosity or even pore size − pure PAA do not permit cells to adhere; must be coated by cell-adhesion protein | PAA gel coated with type 1 collagen | By different ratios of acrylamide/bisacrylamide concentrations in a mixture | [55, 62] |
PAA matrices of varying pore sizes but the same stiffness |
—//— | [59] |
PAA gels coated with covalently bound tissue-specific ECM proteins (collagen I, collagen IV, laminin, or fibronectin) | By different ratios of acrylamide to cross-linking agents bisacrylamide, ammonium persulfate, and tetramethylethylenediamine (TEMED) | [52, 57] |
Viscoelastic PAA gels in which the loss modulus is varied whilst the storage modulus is kept constant | —//— | [55] |
| | | | |
Polyethylene glycol- (PEG-) based gels | + high elasticity + cytocompatibility + ability to be photopolymerized | Polyethylene glycol-(PEG) | By percentage of PEG polymer in the precursor solution | [10] |
3D thixotropic polyethylene glycol-silica gel (turns liquid under certain stress) | By weight percentage of fumed silica particles incorporated into the gel | [54] |
Polyethylene glycol diacrylate (PEGDA) | By altering the duration of the photopolymerization process | [68] |
Mixture of PEG-dimethacrylate (PEGDMA) and PEG-methacrylate | By different ratios of PEG-dimethacrylate (PEGDMA) and PEG-methacrylate in a mixture | [51, 132] |
| | | | |
Polyvinyl alcohol (PVA) | + stiffness gradient formation | Polyvinyl alcohol (PVA) hydrogel produced by the hydrolysis of polyvinyl acetate | By gradual freezing | [53] |
| | | | |
Poly dimethylsiloxane (PDMS) | + biocompatibility viscoelastic material used for micropatterned islands formation | Polydimethylsiloxane (PDMS) | By mixing base and cross-linker at different ratios by using temperature gradient to create a gradient in the crosslinking density of siloxane | [56, 58, 58, 64, 89] |
| | | | |
Electrosrun fibers: micro- or nanofibres drawn from a polymer solution using an electric charge | + ECM-mimicking nanofiber structure, allowing control over fiber diameter + allowing achieving high porosities or large pores + ability to be photopolymerized + useful to form 3D matrix + useful to create substrates of different topology | Polyethylene glycol dimethacrylate PEGdma and poly(ethylene oxide) (PEO) | By adjusting the photopolymerization time | [61] |
Poly(ε-caprolactone) (PCL) | By different ratios of solvents | [65] |
Biodegradable polyurethane (PU) synthesized with using poly(ε-caprolactone) (PCL) as the soft segment | By different ratios of solvents (2,2,2-trifluoroethanol and N,N-dimethylacetamide) | [60] |
|