Table III.

Polymers Used in 3D Organ Printing: Chemical and Biological Significance

Polymers	Biological significance	Chemical significance	Limitation	Application
Alginate	Good biocompatibility including low toxicity, non-immunogenicity, rapid biodegradability, and chemical gelling	Alginic acid salts composed of β-d-mannuronic acid (M block) and α-l-glucuronic acid	Potential to cause stem cell death due to their extreme variance from a true physiological ECM	Vascular cartilage and bone tissue printing (40)
Polylactic acid (PLA)	Biodegradable, biocompatible, no toxic fumes	Aliphatic polyester formed from ring-opening polymerization of lactide or polycondensation of lactic acid monomer	Lowers glass transition temperature	Tracheal graft (41)
Polyhydroxy alkenoate (PHA)	High biodegradability, high biocompatibility, brittle, and tough nature	Thermoplastic polyester of hydroxy alkanoic acid	Nano thermal processing window	Fabrication of heart valve, bone scaffolds (42)
Polycaprolactone (PCL)	Biocompatible, non-toxic polymer	Semicrystalline and biodegradable polyester	Hydrophobic causes low bioactivity, slow cell growth tissue adhesion	Tracheal graft joint, cartilage, and trabecular bone (44)
Polyethylene glycol	Nonbiodegradable, poor mechanical strength	Hydrophilic polymer, linear, or branched structure contains asymmetric and dissymmetric hydroxyl ion as its tail group	Hydrolytic and enzymatic degradation easily degrades the PEG	Formation of keratin layers (45)
Polyether ketone (PEEK)	Superior biocompatibility, strength, and elasticity comparable to cortical bone used in prototyping craniofacial implants and bone refreshment	High performance, temperature resistance semicrystalline polymer, biologically inert, radiolucent	Bio-inertness causes reduced osteo-integrative properties, can catalyze reactions such as dislodging, encapsulation, and extrusion in the body	Prosthetics, artificial bone, heart and its parts, and other human parts (46)
Polyglycolic acid	Good biocompatibility, PGA biodegradation produces glycolic acid monomer, which is further metabolized to CO and water, both of which are nontoxic. The use of copolymer enhances their mechanical strength	Chemically versatile, linear polyester which upon degradation produces nontoxic metabolites	Susceptible to erosion resulting in scaffold collapse	3D scaffold architecture, used in bone internal fixation devices, preparation of resorbable sutures (46)
Polylactic co-glycolic acid (PLGA)	Cytocompatibility and biodegradable	Hydrophobic nature, linear structure	Hydrophobicity, usage limited to scaffold material, increase inflammatory reaction	Bone regeneration animal models and other tissue restoring systems (42)
Polyvinyl-alcohol	Biocompatible biodegradable, semicrystalline structure allows efficient oxygen and nutrient passage to cells	Bioinert, semicrystalline nature, hydrophilic, chemical stability in extreme pH and temperature	Hydrophilicity causes uncontrolled swelling	SLS bioprinting, bone cell ingrowth, used in craniofacial treatment, bone tissue engineering (46)
Polyurethane	Excellent biocompatibility and mechanical strength, good cytocompatibility	Multiblock polymers with either aromatic or aliphatic isocyanates	Poor thermal capability, poor weatherability	SLA and DLP printing technique, high printing resolution. Chondrocyte manufacture in cartilage tissue engineering, bone fabrication, construction of muscle and nerve scaffold (44)