# Current Biomedical Applications of 3D Printing and Additive Manufacturing
## 2 Types of 3D Printing for Biomedical Applications
### Nanofabrication  
Nanofabrication is the process of constructing structures less than 100 nm in size, making the suitable for use in a variety of fields including electronics and medicine. Despite not being recognized as a conventional AM technique, nanofabrication methods can employ many of the same principles. The manufacturing process for nanofabrication can be divided into two categories [29]. A \"top-down\" approach revolves around deconstructing a larger material to form the desired nanostructure, akin to carving a statue out of a block of stone and other traditional machining methods [29]. This principle requires complicated and expensive steps, offering little flexibility for modification. There is limited reproducibility of the nanostructures created through the \"top-down\" approach due to uncontrollable variability in the manufacturing process [29]. The second category of nanofabrication involves a \"bottom-up\" approach, where building blocks such as atoms or molecules either self-assemble or are \"printed\" to create a nanostructure [29]. This in turn can lead to structures with atomic resolution. The \"bottom-up\" approach is additive in nature, similar to most other AM techniques. There are endless applications of nanofabrication in biomedicine and tissue engineering, including (but not limited to): preserving immunogenicity of compounds in vaccines; minimizing transplant rejection through immuno-isolation; creation of biomaterials with unique mechanical and biological properties; drug sequestration and delivery; and circulating toxin and waste binders [30].  
Figure 1: Types of additive manufacturing (AM). (**A**) Binder jetting—a liquid binder is jetted over a precise region of powder, additional powder is placed on top and the process repeats. (**B**) Directed energy deposition—a laser is used to melt metal as it is extruded from a nozzle. (**C**) Material extrusion—molten thermoplastics are dispended through a nozzle and cooled quickly on the print bed. (**D**) Sheet lamination—a sheet of material is cut to size with a blade or laser, the next sheet with adhesive is then added and heat is applied to adhere the layers before the second layer is cut to shape (**E**) Material jetting (MJ)—a layer of liquid resin is sprayed and then cured (often with UV light) before proceeding to the next layer. (**F**) Stereolithography—the print bed is lowered by a one-layer distance into a vat of liquid resin, which is then UV-cured; the print bed continues to move through the resin one layer at a time. (**G**) Powder bed fusion—a layer of powder (often metal) is spread over the print bed before being molten using a laser and formed into a layer. The print bed moves down, the next layer of powder is spread over the solidified layer and the process repeats. (**H**) Extrusion bioprinting (left)—similar to material extrusion, a bioink (mixture of cells and carrier material) is extruded from a nozzle or needle layer-by-layer before crosslinking or curing. Inkjet bioprinting (center)—picoliter-sized droplets of bioink are deposited onto the print bed and allowed to coalesce into fibers. Laser-assisted bioprinting (right)—a laser pulse causes small droplets of bioink to be dropped from a surface into defined geometries. *All figures are designed and created by the authors.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Printing Technique** & **Material** & **Resolution** & **Biomedical Applications** & **Advantage** & **Disadvantage** \\ \hline \multirow{2}{*}{Binder Jetting} & Sand & \multirow{2}{*}{50–400 μm} & Dysbridable (Fe-based Alloys) & Low cost, fast, color printing, no & Low strength, requires post-processing, \\  & Metal powder & multi impulse impulse [11]. Generally & support software needed, large & powders pose a regulatory hazard \\  & Metal & & & & \\  & Nylon &