# 4D Printing of Origami Structures for Minimally Invasive Surgeries Using Functional Scaffold
###### Abstract
In binder jetting, the powder is bound by spraying binder droplets from a jet on top of a layer of powder, then the powder platform is lowered to apply another layer on top of the first layer [23; 24; 25]. Sheet lamination (SL) cuts and glues layers of materials by using a laser or ultrasonic beam to bond the stacked layers. Additional machining and surface finishing are typically used after 3D printing [26; 27]. In material jetting (MJ), droplets of the materials are deposited and dried or cured layer by layer. There are different ways to deposit the material such as in continuous inkjet, in which the material is deposited with the aid of continuous pressure [28; 29], and drop on demand (DOD), which uses discrete pressure instead of continuous pressure [30]. Additive manufacturing has the ability to process a wide range of materials such as metals [31], polymers [32], and ceramics [4]. The technology has been adopted in many industries, such as aerospace [33; 34], biomedical [35], defence [36], and energy [37]. Four-dimensional (4D) printing is an emerging technology that refers to the additive manufacture of material that responds to changes in its immediate environment, therefore enabling engineered solutions to be recovered without direct human or computer interaction. The technology was first introduced in 2013 and since then has attracted great attention in many biomedical applications. Four-dimensional printing offers several benefits, such as the ability to produce smart products from smart material, change of product geometry when required, and adding innovation in the design and development stage [36]. These benefits enabled the penetration of this technology to broad applications in engineering, dentistry, medicine,, and material sciences. Shape-memory polymers are stimuli-responsive polymers that can change their shape from one to another by the use of heat, light, or electricity. The thermally induced shape-memory effect present in specific polymers is due to shape recovery of polymers when subject to heat. The chains in the amorphous polymers are completely dispersed randomly in the matrix without the restriction of crystallites in semicrystalline polymers. On the other hand, movements of the polymer segments are frozen in the case of the glassy state. The rubber-elastic state starts when increasing the activation energy, which initiates the rotation around the segment bonds. This enables the polymer chains to take up energetically equivalent shapes with compact random macromolecules. The rubbery state occurs above the glass transition temperature (Tg), and the polymer becomes flexible. The original shape of the polymer can be recovered when it is plastically deformed only upon heating to above Tg. In this case, physical or chemical cross-link works to store the elastic energy during shape programming and the driving recovery force [38]. The presence of shape-switching part nodes or shape-fixing parts in polylactic acid polymers (PLAs) is behind the shape recovery. Both physical cross-links and the crystallisation of PLAs act as net points and therefore have shape-memory ability. However, the shape-memory effect of PLA polymers is often restricted to minor deformations since breaks occur when programming PLA with more than 10% deformation. This limits the potential for using PLA in minimally invasive surgeries [39]. This communication introduces a design and manufacturing approach to develop deployable scaffolds using 4D printing of shape-memory polymer (SMP) that will be inserted into a cavity in the body through minimally invasive surgery. Once in position, the scaffold will be recovered, causing it to increase in size and fill the cavity where it will substitute as the tissue's extracellular matrix (ECM). The ECM coordinates how cells coordinate with each other as well as providing overall structure to a tissue. An engineered tissue scaffold replicates a diseased or damaged tissue's ECM temporarily when a native ECM is not present.