Magnetic-driven micro-robotic devices have shown promising potential in enabling applications in micromanipulation, biosensing, targeted drug delivery, and minimally invasive surgery. However, the fabrication of miniaturized magnetic structures with complex geometries has remained the major technical obstacle. In this study, we report the development of a new magnetically-active photopolymerizable resin comprises poly (ethylene glycol) diacrylate monomer, Fe3O4 magnetic nanoparticles, photoinitiator, and other functional additives. Micro-continuous liquid interface production (micro-CLIP) 3D printing process was employed to realize high-resolution and high-speed fabrication of complex structures. The key characteristic properties of resin along with the matching process conditions were investigated experimentally, which allows for establishing the set of optimal fabrication conditions in fabricating magnetic microactuators towards potential applications.
Recent development of high-resolution micro-Continuous Liquid Interface Production (microCLIP, continuous projection microstereolithography) process has enabled 3D printing of biomedical devices with 10 micron-scale precision. 3D bioresorbable vascular scaffolds (BVS) were printed using an antioxidant, photopolymerizable citric acid-based material (B-InkTM). Despite demonstrating BVS fabrication feasibility, challenges remained. According to literature, a vascular stent when placed in the body must be able to sustain a pressure loading between 10.67kPa and 13.34kPa of pressure loading. To be clinically relevant, struts for vascular scaffolds need to possess very small thickness, 100um or below. Specifically, to improve our material strength/stiffness of our 3D printed BVSs, a dissolved PLLA nanophase (10%, wt./vol in Tetrahydrofuran) and secondary temperature-sensitive initiators (V70, 1wt.%) were added to the photopolymer resin. Through temperature-induced phase separation and solvent exchange, fibrous networks were incorporated through the B-Ink 3D matrix. Secondary initiators allowed for further crosslinkage of the matrix material. Introduction of PLLA nanophase/secondary initiators greatly improved bulk stiffness and yielded BVSs with 100um strut thickness that could sustain the necessary biological radial pressure loadings. This technology and photopolymerizable material is a large step forward toward on-the-spot and on-demand fabrication of patient specific BVSs.
Recently, 3D printing has gone beyond being an industrial prototyping process and has gradually evolved as the tool to manufacture production-quality parts that are otherwise challenging by using traditional methods. Especially, translating 3D printing technique into the optical realm would dramatically improve the time- and cost-efficiency of customized optical elements, while conventional methods such as multiaxial lathes polishing, magnetorheological finishing, molding techniques are relatively expensive and time consuming. However, 3D printing also suffers from the inherent drawback: the reduced surface quality associated with the stair-stepping effect as a direct result of the layered deposition of the material. In this paper, we have demonstrated a time- and cost-effective single photon micro-stereolithography based 3D printing method to eliminate the layer stair-stepping effect. This method supports not only sub-voxel accuracy (~ 2 μm) of the surface in the range of 2 mm diameter, but also features deep sub-wavelength roughness (< 10 nm) of the surfaces and extremely good reproducibility. Furthermore, we designed and rapidly prototyped the aspherical lenses which not only feature low distortion, but also show remarkable optical quality in a broadband wavelength range from 400 nm to 800 nm.
We present in this work the development and experimental validation of a new piezoelectric material (V-Ink) designed for compatibility with projection stereolithography additive manufacturing techniques. Piezoelectric materials generate a voltage output when a stress is applied to the material, and also can be actuated by using an external voltage and power source. This new material opens up new opportunities for functional devices to be developed and rapidly produced at low cost using emerging 3D printing techniques. The new piezoelectric material was able to generate 115mV under 1N of strain after being polled at 80°C for 40 minutes and the optimal results had a piezoelectric coefficient of 105x10^(-3)V.m/N. The current iteration of the material is a suspension, although further work is ongoing to make the resin a true solution. The nature of the suspension was characterized by a time-lapse monitoring and through viscosity testing. The potential exists to further increase the piezoelectric properties of this material by integrating a mechanical to electrical enhancer such as carbon nanotubes or barium titanate into the material. Such materials need to be functionalized to be integrated within the material, which is currently being explored. Printing with this material on a “continuous SLA” printer that we have developed will reduce build times by an order of magnitude to allow for mass manufacturing. Pairing those two advancements will enable faster printing and enhanced piezoelectric properties.
The recent development of “continuous projection microstereolithography” also known as CLIP technology has successfully alleviated the main obstacles surrounding 3D printing technologies: production speed and part quality. Following the same working principle, we further developed the μCLIP process to address the needs for high-resolution 3D printing of biomedical devices with micron-scale precision. Compared to standard stereolithography (SLA) process, μCLIP fabrication can reduce fabrication time from several hours to as little as a few minutes. μCLIP can also produce better surface finish and more uniform mechanical properties than conventional SLA, as each individual “fabrication layer” continuously polymerizes into the subsequent layer. In this study, we report the process development in manufacturing high-resolution bioresorbable stents using our own μCLIP system. The bioresorbable photopolymerizable biomaterial (B-ink) used in this study is methacrylated poly(1, 12 dodecamethylene citrate) (mPDC). Through optimization of our μCLIP process and concentration of B-ink components, we have created a customizable bioresorbable stent with similar mechanical properties exhibited by nitinol stents. Upon optimization, fabricating a 2 cm tall vascular stent that comprises 4000 layers was accomplished in 26.5 minutes.