Table 2.

Significant advancements of 4D printing in orthopaedics.

S No	Advancements	Description	References
1	Self-assembled orthopaedics implants	•4D printing can provide exciting changes by creating self-assembled smart orthopaedics implants using smart materials •These implants may have a lower risk of infection after implanting in the patient body •Having precise, accurate and customised approach with modified surface properties •Smart orthopaedics implants can also be monitored for deformation or other changes	Piedade et al., 20197; Tan et al., 201942; Sinha, 202043
2	Knee prostheses	•Knee prosthetic printed by this technology can improve patient comfort •These smart prosthetics have the capability to handle the movement of the knee in the desired manner •Revolutionised the orthopaedics field to manufacture various other smart prosthetics which can adopt/grow as per the patient body •This technology can effectively create on-demand dynamically controllable shapes with the time dimensions	Teoh et al., 201844; Grinberg et al., 201945
3	Spinal implants	•Surgeons can use this technology for the printing of spinal implants which is helpful to treat deformity and strengthen the spine •Smart spinal implants could be used for the treatment of fracture, degenerative disc disease and scoliosis •This technology is efficient for the treatment of tumour in the patient neck •Customised perfect fitted spinal implants can successfully restore the stability of the spine for a patient	Schwartz et al., 201946; Grinberg et al., 201945
4	Acetabular cups	•4D printing has the capability of manufacturing acetabular cups that can successfully be placed in the hip socket •Revolutionised for massive bone defect treatment of pelvis with better performance •Acetabular cups printed by this technology can be used for long term clinical outcomes •Having design freedom which enables the production of complex porous structure with required features	Wong et al., 201547; Manganaro et al., 201748
5	Smart scaffolds	•4D printing is an emerging technology used to manufacture scaffolds with smart materials which imitate the dynamic responses of tissues •This adapts to the changes in the properties with respect to the environment •This technology uses smart nano bioink to create scaffolds efficiently •Provide feasibility for the stimulation of neural stem cell behaviours •Capability to create complex microarchitecture having a 4D transformation	Shin et al., 201749; Ahadian and Khademhosseini, 201850
6	Tissue engineering	•4D printing can successfully be used in tissue engineering due to its extensive capability of temperature change in a controlled manner •Used for organs and tissue regeneration using self-healing hydrogels •These tissues have a great ability to fold and controlled with the effect of light •Used for replacement of damaged tissues during surgery and drug delivery	Tamay et al., 201910; Miao et al., 201951
7	Living cells	•4D printing could also be used for the printing of cells for bone tissue engineering •These cells are used to support the growth of human bones •Helpful for the bone-implant to increase reliability and functions •A structure created living cells could successfully replace human tissue	Gao et al., 201652; Miao et al., 202053
8	Smart stents	•Stents having complex geometry and these also required the flexibility which can quickly fulfil by this technology •This can change the diameter, shape after implanting in the patient body concerning patient temperature •Useful to print stents rapidly to perform successful surgery •Increase success rate after the insertion of stents during operation	Zhang et al., 20196; Shie et al., 201954
9	Surgical implantation	•4D printed external airway splints can be used effectively for surgical implantation •This splint can design in a way which can be grown and resolved the required issues •It enhanced the critical properties and also useful for nerve tissue regeneration	Haleem and Javaid, 201955; González-Henríquez et al., 201956
10	Bone graft	•This technology is used to create bone graft using biocompatible hydrogels •Used to develop a nervous and microvascular system to create bone graft substitute •Also applicable for the generation of 3D printed structure of cell-laden and functionalisation of cells and tissue concerning the time	Zarek et al., 201757; Qasim et al., 201958
11	Development of biomedical splints	•Easily print biomedical splint which can adopt changes in the environment •Potential to print programmed biological materials used for personalised medical and treatment of various other diseases •Printed splint could absorb and hold open airway in newborn babies for their good health	Ge et al., 201659; Bodaghi et al., 201760
12	A better solution for children	•Provide innovative solution which still growing by creating smart implants of required body parts •Researchers have applied 4D printing for facial reconstructions and rebuilding ears using smart biomaterials •Provide a flexible solution to adopt the natural growth of children	Miao et al., 201761; Melocchi et al., 201962