organ printing organ printing organ printing utilizes techniques similar to conventional 3d printing where a computer model is fed into a printer that lays down successive layers of plastics or wax until a 3d object is produced. in the case of organ printing, the material being used by the printer is a biocompatible plastic. the biocompatible plastic forms a scaffold that acts as the skeleton for the organ that is being printed. as the plastic is being laid down, it is also seeded with human cells from the patient's organ that is being printed for. after printing, the organ is transferred to an incubation chamber to give the cells time to grow. after a sufficient amount of time, the organ is implanted into the patient. a cellink 3d bioprinter total artificial heart developed at eth zurich the ultimate goal of organ printing is to create organs that can fully integrate into the human body as if they had been there all along. successful organ printing has the potential to impact several industries. these include artificial organs organ transplants, pharmaceutical research, and the training of physicians and surgeons. history the field of organ printing stemmed from research in the area of stereolithography, the basis for the practice of 3d printing that was invented in 1984. in this early era of 3d printing, it was not possible to create lasting objects because the materials that were being used were not very sturdy. therefore, in the early days, 3d printing was simply used a way to model potential end products that would eventually be made from different materials under more traditional techniques. in the beginning of the 1990s, nanocomposites were developed that allowed 3d printed objects to be more durable, permitting 3d printed objects to be used for more than just models. it was around this time that those in the medical field began considering 3d printing as an avenue for generating artificial organs. by the late 1990s, medical researchers were searching for biocompatible materialss that could be used in 3d printing. the concept of bioprinting was first demonstrated in 1988. at this time, a researcher used a modified hp inkjet printer to deposit cells using cytoscribing technology. progress continued in 1999 when the first artificial organ made using bioprinting was printed by a team of scientist leads by dr. anthony atala at the wake forest institute for regenerative medicine. the scientists at wake forest printed an artificial scaffold for a human bladder and then seeded the scaffold with cells from their patient. using this method, they were able to grow a functioning organ and ten years after implantation the patient had no serious complications. after the bladder at wake forest, strides were taken towards printing other organs. in 2002, a miniature, fully functional kidney was printed. in 2003, dr. thomas boland from clemson university patented the use of inkjet printing for cells. this process utilized a modified spotting system for the deposition of cells into organized 3d matrices placed on a substrate. this printer allowed for extensive research into bioprinting and suitable biomaterials. for instance, since these initial findings, the 3d printing of biological structures has been further developed to encompass the production of tissue and organ structures, as opposed to cell matrices. additionally, more techniques for printing, such as extrusion bioprinting, have been researched and subsequently introduced as a means of production. in 2004, the field of bioprinting was drastically changed by yet another new bioprinter. this new printer was able to use live human cells without having to build an artificial scaffold first. in 2009, organovo used this novel technology to create the first commercially available bioprinter. soon after, organovo's bioprinter was used to develop a biodegradable blood vessel, the first of its kind, without a cell scaffold. in the 2010s and beyond, further research has been put forth into producing other organs, such as the liver and heart valves, and tissues, such as a blood-borne network, via 3d printing. in 2019, scientists in israel made a major breakthrough when they were able to print a rabbit-sized heart with a network of blood vessels that were capable of contracting like natural blood vessels. the printed heart had the correct anatomical structure and function compared to real hearts. this breakthrough represented a real possibility of printing fully functioning human organs. in fact, scientists at the warsaw foundation for research and development of science in poland have been working on creating a fully artificial pancreas using bioprinting technology. as of today, these scientists have been able to develop a functioning prototype. this is a growing field and much research is still being conducted. 3d printing techniques 3d printing for the manufacturing of artificial organs has been a major topic of study in biological engineering. as the rapid manufacturing techniques entailed by 3d printing become increasingly efficient, their applicability in artificial organ synthesis has grown more evident. some of the primary benefits of 3d printing lie in its capability of mass-producing scaffold structures, as well as the high degree of anatomical precision in scaffold products. this allows for the creation of constructs that more effectively resemble the microstructure of a natural organ or tissue structure. organ printing using 3d printing can be conducted using a variety of techniques, each of which confers specific advantages that can be suited to particular types of organ production. sacrificial writing into functional tissue (swift) sacrificial writing into function tissue (swift) is a method of organ printing where living cells are packed tightly to mimic the density that occurs in the human body. while packing, tunnels are carved to mimic blood vessels and oxygen and essential nutrients are delivered via these tunnels. this technique pieces together other methods that only packed cells or created vasculature. swift combines both and is an improvement that brings researchers closer to creating functional artificial organs. stereolithographic (sla) 3d bioprinting this method of organ printing uses spatially controlled light or laser to create a 2d pattern that is layered through a selective photopolymerization in the bio-ink reservoir. a 3d structure can then be built in layers using the 2d pattern. afterwards the bio-ink is removed from the final product. sla bioprinting allows for the creation of complex shapes and internal structures. the feature resolution for this method is extremely high and the only disadvantage is the scarcity of resins that are biocompatible. drop-based bioprinting (inkjet) drop-based bioprinting makes cellular developments utilizing droplets of an assigned material, which has oftentimes been combined with a cell line. cells themselves can also be deposited in this manner with or without polymer. when printing polymer scaffolds using these methods, each drop starts to polymerize upon contact with the substrate surface and merge into a larger structure as droplets start to coalesce. polymerization can happen through a variety of methods depending on the polymer used. for instance, alginate polymerization is started by calcium ions in the substrate, which diffuse into the liquified bioink and permit for the arrangement of a strong gel. drop-based bioprinting is commonly utilized due to its productive speed. however, this may make it less appropriate for more complicated organ structures. extrusion bioprinting extrusion bioprinting includes the consistent statement of a specific printing fabric and cell line from an extruder, a sort of portable print head. this tends to be a more controlled and gentler handle for fabric or cell statement, and permits for more noteworthy cell densities to be utilized within the development of 3d tissue or organ structures. in any case, such benefits are set back by the slower printing speeds involved by this procedure. extrusion bioprinting is frequently coupled with uv light, which photopolymerizes the printed fabric to create a more steady, coordinated construct. fused deposition modeling fused deposition modeling (fdm) is more common and inexpensive compared to selective laser sintering. this printer uses a printhead that is similar in structure to an inkjet printer; however, ink is not used. plastic beads are heated at high temperature and released from the printhead as it moves, building the object in thin layers. a variety of plastics can be used with fdm printers. additionally, most of the parts printed by fdm are typically composed from the same thermoplastics that are utilized in tradition injection molding or machining techniques. due to this, these parts have analogous durability, mechanical properties, and stability characteristics. precision control allows for a consistent release amount and specific location deposition for each layer contributing to the shape. as the heated plastic is deposited from the printhead, it fuses or bonds to the layers below. as each layer cools, they harden and gradually take hold of the solid shape intended to be created as more layers are contributed to the structure. selective laser sintering selective laser sintering (sls) uses powdered material as the substrate for printing new objects. sls can be used to create metal, plastic, and ceramic objects. this technique uses a laser controlled by a computer as the power source to sinter powdered material. the laser traces a cross-section of the shape of the desired object in the powder, which fuses it together into a solid form. a new layer of powder is then laid down and the process repeats itself, building each layer with every new application of powder, one by one, to form the entirety of the object. one of the advantages of sls printing is that it requires very little additional tooling, i.e. sanding, once the object is printed. recent advances in organ printing using sls include 3d constructs of craniofacial implants as well as scaffolds for cardiac tissue engineering. printing materials printing materials must fit a broad spectrum of criteria, one of the foremost being biocompatibility. the resulting scaffolds formed by 3d printed materials should be physically and chemically appropriate for cell proliferation. biodegradability is another important factor, and insures that the artificially formed structure can be broken down upon successful transplantation, to be replaced by a completely natural cellular structure. due to the nature of 3d printing, materials used must be customizable and adaptable, being suited to wide array of cell types and structural conformations. natural polymers materials for 3d printing usually consist of alginate or fibrin polymers that have been integrated with cellular adhesion molecules, which support the physical attachment of cells. such polymers are specifically designed to maintain structural stability and be receptive to cellular integration. the term bio-ink has been used as a broad classification of materials that are compatible with 3d bioprinting. hydrogel alginates have emerged as one of the most commonly used materials in organ printing research, as they are highly customizable, and can be fine-tuned to simulate certain mechanical and biological properties characteristic of natural tissue. the ability of hydrogels to be tailored to specific needs allows them to be used as an adaptable scaffold material, that are suited for a variety of tissue or organ structures and physiological conditions. a major challenge in the use of alginate is its stability and slow degradation, which makes it difficult for the artificial gel scaffolding to be broken down and replaced with the implanted cells' own extracellular matrix. alginate hydrogel that is suitable for extrusion printing is also often less structurally and mechanically sound; however, this issue can be mediated by the incorporation of other biopolymers, such as nanocellulose, to provide greater stability. the properties of the alginate or mixed-polymer bioink are tunable and can be altered for different applications and types of organs. other natural polymers that have been used for tissue and 3d organ printing include chitosan, hydroxyapatite (ha), collagen, and gelatin. gelatin is a thermosensitive polymer with properties exhibiting excellent wear solubility, biodegradability, biocompatibility, as well as a low immunologic rejection. these qualities are advantageous and result in high acceptance of the 3d bioprinted organ when implanted in vivo. synthetic polymers synthetic polymers are human made through chemical reactions of monomers. their mechanical properties are favorable in that their molecular weights can be regulated from low to high based on differing requirements. however, their lack of functional groups and structural complexity has limited their usage in organ printing. current synthetic polymers with excellent 3d printability and in vivo tissue compatibility, include polyethylene glycol (peg), poly(lactic-glycolic acid) (plga), and polyurethane (pu). peg is a biocompatible, nonimmunogenic synthetic polyether that has tunable mechanical properties for use in 3d