# Advances in Three Dimensional Bioprinting for Wound Healing: A Comprehensive Review
## 4 3D Bioprinting Techniques
### Other Techniques
#### 4.4.5. Microfluidic-Based Techniques  
Microfluidic devices are functional in vitro structures that strive to miniaturize a structure's in vivo physiology. They do so by employing various cell types and ECM while retaining the chemical and mechanical characteristics of micro-level surroundings [226]. During the production, cleanroom technology is essential to prevent dust or particle accumulation in microchannels [132; 227]. Given the valve integrations and time-consuming procedures, these technologies result in intensive resource consumption and time-consuming activities. Microfluidic devices cannot be used due to production constraints and complexity. These constraints, along with the benefits of 3D printers, have piqued researchers' interest in the fabrication of microfluidic devices. A 3D printer comprises bioink and a printed design in a digital file for the creation of microfluidic devices using 3D bioprinting technology. The 3D printer travels in the X, Y, and Z directions, allowing 3D printing to becreated. The X and Y axes reflect the nozzle's lateral motions, while the Z axis represents its vertical movement [228; 229; 230].  
Among the 3D bioprinting technologies of microfluidic devices, laser-based bioprinting, droplet-based bioprinting, and molten deposition modeling are commonly employed. The layers created by fused deposition modeling (FDM) biotechnology have heights ranging from 50 to 400 microns. Low layer length improves accuracy; nevertheless, this approach requires more time and money to develop the bioprinter. In comparison to FDM biotechnology, they are extensively employed in the 3D manufacture of SLA and SLS microfluidic devices because of their benefits such as high sensitivity, rapid production time, and low cost [231; 232; 233; 234]. Owing to the indicated advantages, one study produced a graphene oxide (GO)-mediated photothermal responsive dextran hydrogel scaffold using microfluidic 3D printing technique. According to mechanical and in vitro tests, the storage modulus (G') increased gradually with differing GO concentrations from 2 to 8 mg/mL and the degradation rate was delayed as the concentration was increased. A Live/Dead assay has shown no cytotoxicity towards cells, and normal cell proliferation occurred. After near-infrared (NIR) laser exposure for 5 min, the DEX/GO5 hydrogel exhibited an approximately 100% antibacterial effect against _E. coli_, _S. aureus_ and _C. albicans_, proving the photothermal antibacterial properties of DEX/GO hydrogels. In vivo wound-healing tests were conducted on rats with _S. aureus_-infected wounds and after 11 days, the DEX/GO5/VEGF+NIR group had the smallest wound area at 5.3% \(\pm\) 0.8%. When loaded with VEGF and used as a wound dressing, the scaffold achieved adjustable mechanical, photothermal antibacterial properties, followed by angiogenesis during the wound healing process. According to the study, the GO hybrid hydrogel revealed an evident stiffness decrease, a good photothermal antibacterial performance, as well as effectively stimulating cargo release with NIR light [235].