Table 1.

Common biomaterials and their solution preparation/gelation methods, along with their merits/demerits and applications.

Biomaterials	Water soluble or non-soluble	Typical preparation conditions	Gelation or crosslinked methods	Merits	Demerits	Applications	References
Alginate	Water soluble	Dissolves within hours in water or water-based solutions at room temperature [41,129]	Ionic and pH crosslinking [22,32,41,[130], [131], [132]]	•Low price •Easy to fabricate 3D structures •Good biocompatibility •Easy gelation •High biodegradability and low immunological stimulation •Retains cell viability and osmolar requirements of cells •A suitable material for 3D printing due to crosslinkable features •Shear-thinning behavior	•Bioinert •Limited long-term stability •Rapid loss of mechanical properties during in-vitro culture •Limited 3D shape-ability •Low degradation	•Bone •Cartilage •Cardiovascular •Liver •Muscle •Nerve •Wound •Drug delivery	[[133], [134], [135], [136], [137], [138], [139], [140], [141], [142]]
Chitosan	Water soluble	Dissolves within hours in weak acid at room temperature [47]	Thermal crosslinking [143]	•Ingredients resemble ECM components of native tissue •Non-toxic by-products •Induces cell adhesion proliferation, differentiation, and viability •Antimicrobial •Partially osteoconductive	•Slow gelation rate •Poor mechanical properties •Can conflict with printing of cells and pH-sensitive molecules •Slow gelation	•Drug delivery and gene therapy •Bone •Skin •Bioadhesives •Cartilage •Blood vessels •Neural •Cornea	[[144], [145], [146], [147], [148], [149]]
Agarose	Water soluble	Easily dissolves in near-boiling water or water-based solutions [150]	Thermal and chemical crosslinking [151]	•Responsive to temperature •Rapid gelation •Gelation at physiological temperature •Mechanically robust	•Poor cell attachment •Excessive water uptake	•Cartilage •Bone •Targeted drug delivery •Spinal cord •Pancreas •Skin •Wound •Neural •Cardiac	[[152], [153], [154], [155], [156], [157], [158], [159]]
Hyaluronic acid (HA)	Water soluble	Dissolves within hours in weak acid at room temperature [160,161]	Physical crosslinking (controlling pH, temperature and ions) and chemical crosslinking [162]	•Good biocompatibility •Non-toxic degradation by-products •Visco-elastic properties •Highly hydrophilic •Anti-microbial properties •Good shear thinning properties	•Poor mechanical strength •Fast degradation rate •Required modification for stable cross-linking	•Cartilage •Drug and gene delivery •Wound healing •Odontology •Wound treatment •Ophthalmology •Urethra	[158,[163], [164], [165], [166], [167], [168], [169]]
Collagen	Water soluble	Dissolves in weak acid at room temperature and gels at neutral pH at 37 °C [170]	Photo crosslinking [171]	•Low immunogenicity •Good biocompatibility •Biodegradability •Regulates cell adhesion and differentiation	•Poor mechanical properties •Loses shape and consistency •Low viscosity and slow gelation	•Spinal repair •Vascular •Dental •Cartilage •Bone •Corneal •Oral mucosa •Wound healing •Heart tissue repair	[[172], [173], [174], [175], [176]]
Gelatin	Water soluble	Dissolves in water or water-based solutions at ≥ 40 °C and gradually gels as temperature drops [177]	Physical, chemical, and enzymatic crosslinking [178]	•Derivative of collagen •Accelerates gelation time •Capable of reversible thermal gelation •Biocompatible •Biodegradable	•Poor mechanical properties •High degradation rate	•Cartilage •Wound healing •Heart tissue repair •Cornea •Neovascularization •Bone •Muscle •Ligament [179] •Drug delivery	[[180], [181], [182], [183], [184]]
Fibrin	Water soluble	Dissolves within minutes in water or water-based solutions at room temperature [185]	Enzymatic crosslinking [186]	•ECM functional protein •Highly bioactive •High cell adhesion	•Rapid degradation •Poor mechanical properties	•Wound healing •Drug and growth factor delivery •Regeneration of stem cells, bone, peripheral nerves, and other injured tissues •Hemostasis	[78,[187], [188], [189], [190], [191]]
Poly(ethylene glycol) (PEG)	Water soluble	Dissolves in water or water-based solutions at room temperature and polar solvents such as acetone [192]	Physical crosslinking [193]	•Chemically well-defined •Allows for versatile chemical modifications •Highly water-soluble •High capacity for chemical modification	•Poor biodegradability •Poor cell attachment	•Wound healing •Drug delivery •Bone •Cartilage	[[194], [195], [196], [197], [198], [199]]
Poly(ethylene oxide) (PEO)	Water soluble	Dissolves in water or water-based solutions at room temperature and polar solvents such as acetone [200]	Physical crosslinking [201]	•Hydrophilic •biocompatible and biodegradable •non-immunogenic	•Lack of cell specific adhesion •Poor mechanical properties for hard tissue engineering	•Wound healing •Bone	[[202], [203], [204], [205], [206]]
Polyvinyl alcohol (PVA)	Water soluble	Dissolves within minutes in water or water-based solutions over 40 °C [207]	Chemical and physical crosslinking [208,209]	•Good biocompatibility •Suitable mechanical strength •Highly hydrophilic	•Inability to support cell attachment •Fast degradation	•Bone •Cartilage •Wound dressing •Vascular grafts •Nervous •Corneal •Kidney •Artificial meniscus •Artificial Pancreas	[[210], [211], [212], [213], [214], [215]]
Decellularized matrix (dECM)	Water soluble	Dissolves in acetic solutions in low temperature [84]	Chemical and physical crosslinking [84]	•Great biocompatibility •Support cell growth and viability •Source of bioactive molecules •	•Poor mechanical properties •Hard to print without modification	•Skin •Bone •Nerve •Heart •Lung •Liver •Kidney •Urethra •Corneal •Muscle	[83,84,213]
Polycaprolactone (PCL)	Non-soluble	Dissolves in organic solvent such as chloroform; melts at 60 °C [216,217]	Physical crosslinking [94]	•Low cost •Tunable degradation •Excellent rheological and viscoelastic properties upon heating •high mechanical toughness at physiological temperature	•Hard tissue engineering •Long-term degradation •Lack of biofunctional groups •Adheres poorly to cells	•Bone •Cartilage •Wound healing •Heart	[[218], [219], [220], [221], [222], [223], [224]]
Polylactic acid (PLA)	Non-soluble	Dissolves in organic solvents such as propanol; melts at 170 °C [225,226]	Physical crosslinking [227]	•Biocompatible •Controllable degradation rates in vivo •High elastic modulus	•Low cell adhesion •Biological inertness •Low degradation rate •Acid degradation by-products	•Bladder •Cartilage •Liver •Adipose •Bone •drug encapsulation and delivery systems •Wound healing •Vascular grafts •	[[228], [229], [230], [231], [232], [233]]
Polyglycolic acid (PGA)	Non-soluble	Dissolves in solvents such as hexafluoroisopropanol; melts at 225 °C [234,235]	Physical crosslinking [236,237]	•Biodegradable •Biocompatible •High strength •Tunable mechanical properties •Erosion resistant •Hydrophil •Possibly antibacterial	•Fast degradation •Expensive	•Drug delivery career •Bone •Cartilage •Tooth •Tendon •Spinal regeneration	[[238], [239], [240], [241], [242]]