# 4D Printing of Origami Structures for Minimally Invasive Surgeries Using Functional Scaffold
###### Abstract  
Origami structures have attracted attention in biomedical applications due to their ability to develop surgical tools that can be expanded from a minimal volume to a larger and functional device. On the other hand, four-dimensional (4D) printing is an emerging technology, which involves 3D printing of smart materials that can respond to external stimuli such as heat. This short communication introduces the proof of concept of merging origami and 4D printing technologies to develop minimally invasive delivery of functional biomedical scaffolds with high shape recovery. The shape-memory effect (SME) of the PLA filament and the origami designs were also assessed in terms of deformability and recovery rate. The results showed that herringbone tessellation origami structure combined with internal natural cancellous bone core satisfies the design requirement of foldable scaffolds. The substantial and consistent SME of the 4D printed herringbone tessellation origami, which exhibited 96% recovery compared to 61% for PLA filament, was the most significant discovery of this paper. The experiments demonstrated how the use of 4D printing in situ with origami structures could achieve reliable and repeatable results, therefore conclusively proving how 4D printing of origami structures can be applied to biomedical scaffolds. origami; additive manufacturing; 4D printing; scaffolds; shape-memory polymer 11332202028 December 2  
where it is being placed. Minimally invasive surgery is associated with fewer complications, less pain, shorter hospital stay, as well as the cosmetic benefit of reducing post-surgery scars. Implementing minimally invasive surgery in bone scaffold treatment requires smart scaffolds that can be deformed before insertion and then recover once in position so that smaller points of incision would be required. Additive manufacturing (AM) or 3D printing is the manufacturing of a 3D object layer by layer from a digital design. There are several categories of AM technologies, such as powder bed fusion, material extrusion, direct energy deposition, vat photo polymerisation, binder jetting, sheet lamination, and material jetting. Material extrusion is a low cost, easy to use technique and available in many commercial forms [5; 6]. In material extrusion, the material is extruded under pressure through a nozzle according to a digital design. The extruded material is deposited on top of each layer and solidifies. Fused deposition modelling (FDM) is a technique of material extrusion where a thermoplastic filament is softened by heaters and extruded from a nozzle, whereas pneumatic or syringe extrusion (PE/SE) techniques extrude paste materials such as ceramic clays. The vat polymerisation (VP) technique uses UV to initiate the cross-linking of a layer of photosensitive resin to cure it into a solid polymer. Afterwards, another layer of the polymer is deposited and cured onto the past layers until the part is completed. VP techniques include stereolithography (SLA), continuous liquid interface production (CLIP), digital light processing (DLP), and photon polymerisation [7; 8; 9; 10]. The technique has been adopted to fabricate polymer and ceramic micro parts for MEMS applications as it outperformed the conventional soft lithography processes that are limited to fabricate 2.5 D parts and not real 3D components [11; 12; 13; 14; 15; 16; 17]. Powder bed fusion (PBF) is an approach in which a laser beam selectively scans a layer of the powder according to a digital design to build components in the typical layer-wise way [18; 19]. In direct energy deposition (DED), a laser or electron beam is focused on melting metal powder. The molten droplets are then deposited on the top of a substrate. Laser energy net shaping (LENS), laser deposition welding (LDW), and wire and arc AM (WAAM) are widely used techniques of DED [20; 21; 22].