1. PeerJ. 2016; 4: e2661.
On the intrinsic sterility of 3D printing
One of the most important properties of basic labware in the biological sciences is sterility, and one of the most frequent questions laboratory biologists ask when they first learn of 3D printing is, “Can I autoclave these things?” Unfortunately, most thermoplastics that are widely used in biomedical applications, particularly polylactic acid (PLA) and polyglycolic acid (PGA), will not survive a standard autoclave cycle (Rozema et al., 1991). Sterilization with γ-radiation is effective, but causes drastic changes to the biochemical properties of the material (Gilding & Reed, 1979).1 Here we detail our work demonstrating that the 3D printing process itself appears to be sufficient for ensuring sterility.
We note that the fused deposition modeling (FDM) 3D printing process, in which a thermoplastic filament is heated to melting and forced through a narrow tube under high pressure, resembles a sort of extreme pasteurization. Figure 1 compares the FDM 3D printing to several sterilization processes (note that thermal contact time is in log scale). The 3D printing process holds the material at a higher temperature for longer duration than both Ultra-High Temperature (UTH) pasteurization, which is used to produce shelf-stable milk (138 °C for two seconds) and high-temperature, short-time (HTST) pasteurization used for dairy, juice and other beverages and liquid ingredients (71.5 °C–74 °C for 15–30 s). The only legal pasteurization method that exceeds the thermal contact time typical of FDM 3D printing is mentioned in Title 21, Sec. 1240.61 of the Code of Federal Regulations, which permits milk to be treated at 63 °C for 30 min. This is a convenient sanitation regime for milk in non-commercial settings (indicated in Fig. 1 as “stovetop” pasteurization). 3D printing is also both hotter and longer duration than thermization, a process used to extend the shelf life of raw milk that cannot be immediately used, such as at cheese making facilities.
2. J Funct Biomater. 2018 Mar; 9(1): 17.
Novel Biomaterials Used in Medical 3D Printing Techniques
|Fused Deposition Modeling (FDM) ||A thermoplastic material is melted and laid on to the build platform in layer-by-layer fashion, until the object is formed.|
|Materials: acrylonitrile butadiene styrene (ABS), poly-lactic acid (PLA), nylon.|
|Bioprinting ||Biological materials are extruded through a nozzle under pressure to lay down materials in sequential layers till the scaffold is built.|
|Materials: alginate, chitosan, gelatin, collagen, fibrin.|
|Selective Laser Sintering (SLS) ||A high-power laser beam fuses the powdered materials in layer-by-layer pattern to form an object.|
|Materials: nylon, polyamide.|
|Electron Beam Manufacturing (EBM)||EBM is similar to SLS, except for high power electron beam is used to fuse the powdered particles.|
|Materials: titanium, cobalt−chrome alloy.|
|Stereolithography (SLA) ||A UV laser beam selectively hardens the photo-polymer resin in layers.|
|Each layer is solidified and built on top of next until the object is formed.|
|Continuous Liquid Interface Production (CLIP) ||CLIP is similar to SLA, except for UV beam is passed through a transparent window at the bottom of the resin and build platform raises upwards holding the 3D printed object.|
|Binder Jetting/Inkjet ||A liquid binding material is selectively dropped into the powder bed in alternative layers of powder–binding liquid–powder, until the final object is formed.|
|Materials: starch or gypsum (powder bed) and water (binding agent)|
|Polyjet||Polyjet printing is similar to inkjet, but instead of binding agents, photopolymer liquid is sprayed in layers onto the build platform and is instantaneously cured using UV light.|
|Materials: polypropylene, polystyrene, polycarbonate.|
|Laminated Object Manufacturing (LOM)||Layers of adhesive coated material are successively glued together and cut in required shapes using a laser.|
|Materials: thin sheets of paper, polyvinyl caprolactam (PVC) plastic, or metal laminates|