Design, Develop and Characterization of a DLP Printer for Biomedical Applications

Digital light processing (DLP) based 3D printers have become popular for higher surface quality and faster processing. However functionality and process optimization of the CLIP printer heavily depends on the accuracy and precision of the mechanical actuation system. Mechanical actuation system coordinates and ensures optical requirement, curing time and processing speed of the CLIP printer. This project examines the design and manufacture of a low cost but highly efficient DLP 3D printer for making biomedical devices. Mechanical actuation system was developed using steeper motor mounted in a lead screw to provide a linear slide for the platform, flexible resin container, digital light projection (DLP) projector holder and resizable build platform. The individual parts in AutoCAD modeling were converted into STL file/G-codes and printed using ObjetPro 30 3D printer, lathe machine and CNC. The actuation system was then assembled with the in-house manufactured parts and tested. The developed system was able to produce linear motion with at demand and variable speeds without mechanical noise and vibration.The electrical control unit consists of various components including sensors, microcontrollers, motors, and switches. A raspberry Pi 4, a microcontroller, was programmed to control NanoDLP, an open source platform for slicing and image processing, as well as mechanical actuation system. The developed control unit was tested and optimized to synchronize the exporting and slicing of 3D STL files of parts into a projector and monitor process parameters such as temperature of the unit, exposure time, z-axis range and emergency shut off. The test demonstration shows that the developed control unit can successfully perform the specified job with accuracy and precision. The performance of the printer was characterized by making a dog bone model using Cyanate Ester, a candidate photosensitive flexible resin material. It is found that 7s is optimum curing time for a millimeter thickness of dog bone shape. Mechanical testing of the fabricated sample was conducted for various curing time. Biodegradation and biocompatibility study of the Cyanate Ester were also conducted. For degradation experiment, 1 cm long and 5 mm diameter of a dog bone specimen of Cyanate Ester was fabricated using the developed DLP printer. The specimen was submerged in PBS buffer with pH of 7.5. Specimen were weighted before submerging in PBS and then for 2, 4 and 8 weeks. Human dermal fibroblasts cells were cultured with cured cyanate ester speciment. Cell performance and interactions with Cyanate Ester plate were evaluated by quantifying various cellular functions such as proliferation, differentiation, and adhesion. Results show that degradation rate is much slower than common biomaterial such as Polyethylene glycol diacrylate (PEGDA) hydrogel. Slower degradation rate may be helpful for certain biomedical application such as bioresorbable stent for cardiovascular diseases. On the other hand, biocompatibility studies show that cell performance in Cyanate Ester was reduced compared to a control group without specimen. However, more studies are being conducted to verify this finding. Overall, the developed DLP printer can print biomedical device with faster processing time and desired surface quality.