Table 2. Overview of Water-Soluble Base Polymers Used in the Formulation of Bioinks in Bioprinting, With Key Characteristicsa.
| bioactivity |
cross-link
type |
gelation
trigger |
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| polymer | adhesive | cleavable | instructive | covalent | electrostatic | hydrophobic interaction | temperature | ions | enzymes | mix components | ref |
| Natural | |||||||||||
| proteins | |||||||||||
| collagen | x | x | x | x | irrev | (180) | |||||
| elastin (and -like peptides) | x | x | x | LCST | mTG | x | (181−183) | ||||
| fibrin | x | x | x | x | thrombin | (72) | |||||
| gelatin | x | x | x | x | x | UCST | mTG | (156,184) | |||
| Matrigel | x | x | x | x | irrev | (185) | |||||
| silk fibroin | x | x | x | x | x | HRP | x | (186,187) | |||
| polysaccharides | |||||||||||
| agar(ose) | x | UCST | (18,188) | ||||||||
| alginate | (x)1 | x | ≥divalent | (158) | |||||||
| cellulose | x | (189) | |||||||||
| dextran | (190) | ||||||||||
| gellan gum | x | x | UCST | ≥monovalent | (191−194) | ||||||
| pectin | x | Ca2+ | (195,196) | ||||||||
| xanthan gum | (197) | ||||||||||
| glycosaminoglycans | |||||||||||
| chitosan | x | x | x | pH change | (165,198) | ||||||
| chondroitin sulfate | x | x | (199) | ||||||||
| hyaluronic acid | x | x | (200) | ||||||||
| Synthetic | |||||||||||
| PHPMA | LCST | (201) | |||||||||
| poloxamer 407 | LCST | (202−204) | |||||||||
| poly(ethylene glycol) | (57,103) | ||||||||||
| poly(2-oxazoline/oxazine) | x | LCST | (205) | ||||||||
| PNIPAAm | LCST | (206) | |||||||||
| poly(vinyl alcohol) | (138,207) | ||||||||||
| synthetic polypeptides | x | x | x | x | x | ≥monovalent | x | (67,178,208) | |||
a
The references are to reviews on a particular polymer and its use in the field where available, or to key original research articles. PHPMA = poly(hydroxypropyl methacrylamide), PNIPAAm = poly(N-isopropylacrylamide), irrev = irreversible, UCST = upper critical solution temperature, LCST = lower critical solution temperature, mTG = microbial transglutaminase, HRP = horseradish peroxidase.1 Alginate is cleavable through alginate lyases, which are not normally expressed by mammalian cells.