TABLE 1.
Stimuli-responsive materials with their applications.
| Stimulus | Bioinks used for 4DP | Stimuli | Application | References |
|---|---|---|---|---|
| Chemical stimuli-responsive materials | ||||
| Ion-sensitive | Poly (acrylonitrile) | Crosslinked with multivalent ions (Zn2+ and Ca2+) | Fabrication of cell-loaded, shape-changing objects for tissue engineering | Bai et al. (2012) |
| pH-responsive | Poly (N-isopropylacrylamide) | Shape transition in pH range (pH 2–10) | Controlled release of drugs, cell encapsulation, tissue engineering | Nadgorny and Ameli (2018) |
| Chitosan/TPP | Shape transition in pH range (pH 4–7) | Regenerative bone medicine | Xu et al. (2018) | |
| Physical stimuli-responsive materials | ||||
| Temperature-responsive | Poly (caprolactone) (PCL) | Change in hydrogel shape due to thermal activation at 37°C | Bone defects | Zarek et al. (2017) |
| Magnetic Responsive | Poly (lactic acid) | Change in hydrogel shape due to magnetic field (30 kHz) | Tissue engineering, drug delivery devices, and actuators | Wei et al. (2017) |
| Electro-responsive | Poly (thiophene), poly (aniline), and poly (pyrrole) | Electrical conduction causes hydrogel to change shape | Neuro-prosthetic devices and bioelectronic designs | Fantino et al. (2018) |
| Photo-responsive | Poly (lactic acid) | Change in shape using a UV cross-linking agent | Soft robotics, flexible electronics, minimally invasive medicine | Wei et al. (2017) |
| Urethane diacrylate and a linear semicrystalline polymer | Soft actuators, deployable smart medical devices, and flexible electronics | Kuang et al. (2018) | ||
| Water-responsive | PCL, PEG, and cellulose nanocrystals (CNCs) | Water absorption leads to shape change | Self-tightening sutures and self-retractable smart stents | Li et al. (2015) |
| Biological stimuli-responsive materials | ||||
| Enzyme | Hyaluronic acid | Activation of shape memory capabilities of hydrogels | Tissue engineering by improving tissue defect regeneration and tissue remodelling | Wang (2018) |