Suppressing the Step Effect of 3D Printing for Constructing Contact Lenses

Recent innovations in interfacial strategies for DLP 3D printing process optimization

Three-dimensional (3D) printing, also known as additive manufacturing, is capable of transforming computer-aided designs into intricate structures directly and on demand. This technology has garnered significant attention in recent years. Among the various approaches, digital light processing (DLP) 3D printing, which utilizes polymers or prepolymers as the ink, has emerged as the leading new technology, driven by high demand across diverse fields such as customized production, healthcare, education, and art design. DLP 3D printing technology employs cured slices as molding units and is recognized for its potential to achieve both high printing speed and resolution. Recent insights into the DLP printing process highlight its inherent interface transformations between liquid and solid states. This review summarizes key aspects of the printing process, speed, precision, and material diversity optimization, from the view of interfacial interactions between solid and liquid phases which are influenced by resin formation, curing surfaces and light source properties. These interactions include those at the liquid resin-UV pattern interface, the cured structure-curing surface interface, the liquid resin-curing surface interface, and the liquid resin-cured structure interface, each contributing to the unique characteristics of the printed results. Finally, this review addresses the current challenges and limitations of DLP 3D printing, providing valuable insights for future improvements and guiding potential innovations in the field.

Vat photopolymerization printing of functionalized hydrogels on commercial contact lenses

Contact lenses are widely used for vision correction and cosmetic purposes. Smart contact lenses offer further opportunities as functionalized non-invasive devices capable of simultaneous vision correction, real-time health monitoring and patient specific drug delivery. Herein, a low-cost vat photopolymerization technique is developed for directly 3D printing functionalized structures on commercially available contact lenses. The process enables controlled deposition of functionalized hydrogels, in customizable patterns, on the commercial contact lens surface with negligible optical losses. Multi-functional contact lenses can also be 3D printed with multiple materials deposited at different regions of the contact lens. Herein, the functionalities of colour blindness correction and real-time UV monitoring are demonstrated, by employing three suitable dyes incorporated into 2-hydroxyethyl methacrylate (HEMA) hydrogel structures printed on contact lenses. The results suggest that 3D printing can pave the way towards simple production of low-cost patient specific smart contact lenses.

Direct-Ink-Writing 3D-Printed Bioelectronics

The development of wearable and implantable bioelectronics has garnered significant momentum in recent years, driven by the ever-increasing demand for personalized health monitoring, remote patient management, and real-time physiological data collection. The elevated sophistication and advancement of these devices have thus led to the use of many new and unconventional materials which cannot be fulfilled through traditional manufacturing techniques. Three-dimension (3D) printing, also known as additive manufacturing, is an emerging technology that opens new opportunities to fabricate next-generation bioelectronic devices. Some significant advantages include its capacity for material versatility and design freedom, rapid prototyping, and manufacturing efficiency with enhanced capabilities. This review provides an overview of the recent advances in 3D printing of bioelectronics, particularly direct ink writing (DIW), encompassing the methodologies, materials, and applications that have emerged in this rapidly evolving field. This review showcases the broad range of bioelectronic devices fabricated through 3D printing including wearable biophysical sensors, biochemical sensors, electrophysiological sensors, energy devices, multimodal systems, implantable devices, and soft robots. This review will also discuss the advantages, existing challenges, and outlook of applying DIW 3D printing for the development of bioelectronic devices toward healthcare applications.

Whole Model Path Planning-Guided Multi-Axis and Multi-Material Printing of High-Performance Intestinal Implantable Stent

The problems of step effects, supporting material waste, and conflict between flexibility and toughness for 3D printed intestinal fistula stents are not yet resolved. Herein, the fabrication of a support-free segmental stent with two types of thermoplastic polyurethane (TPU) using a homemade multi-axis and multi-material conformal printer guided with advanced whole model path planning is demonstrated. One type of TPU segment is soft to increase elasticity, and the other is used to achieve toughness. Owing to advancements in stent design and printing, the obtained stents present three unprecedented properties compared to previous three-axis printed stents: i) Overcoming step effects; ii) Presenting comparable axial flexibility to a stent made of a single soft TPU 87A material, thus increasing the feasibility of implantation; and iii) Showing equivalent radial toughness to a stent made of a single hard TPU 95A material. Hence, the stent can resist the intestinal contractive force and maintain intestinal continuity and patency. Through implanting such stents to the rabbit intestinal fistula models, therapeutic mechanisms of reducing fistula output and improving nutritional states and intestinal flora abundance are revealed. Overall, this study develops a creative and versatile method to improve the poor quality and mechanical properties of medical stents.

Continuous Vat Photopolymerization for Optical Lens Fabrication

Optical lenses require feature resolution and surface roughness that are beyond most (3D) printing methods. A new continuous projection-based vat photopolymerization process is reported that can directly shape polymer materials into optical lenses with microscale dimensional accuracy (< 14.7 µm) and nanoscale surface roughness (< 20 nm) without post-processing. The main idea is to utilize frustum layer stacking, instead of the conventional 2.5D layer stacking, to eliminate staircase aliasing. A continuous change of mask images is achieved using a zooming-focused projection system to generate the desired frustum layer stacking with controlled slant angles. The dynamic control of image size, objective and imaging distances, and light intensity involved in the zooming-focused continuous vat photopolymerization are systematically investigated. The experimental results reveal the effectiveness of the proposed process. The 3D-printed optical lenses with various designs, including parabolic lenses, fisheye lenses, and a laser beam expander, are fabricated with a surface roughness of 3.4 nm without post-processing. The dimensional accuracy and optical performance of the 3D-printed compound parabolic concentrators and fisheye lenses within a few millimeters are investiagted. These results highlight the rapid and precise nature of this novel manufacturing process, demonstrating a promising avenue for future optical component and device fabrication.

3D Printing-Enabled Design and Manufacturing Strategies for Batteries: A Review

Lithium-ion batteries (LIBs) have significantly impacted the daily lives, finding broad applications in various industries such as consumer electronics, electric vehicles, medical devices, aerospace, and power tools. However, they still face issues (i.e., safety due to dendrite propagation, manufacturing cost, random porosities, and basic & planar geometries) that hinder their widespread applications as the demand for LIBs rapidly increases in all sectors due to their high energy and power density values compared to other batteries. Additive manufacturing (AM) is a promising technique for creating precise and programmable structures in energy storage devices. This review first summarizes light, filament, powder, and jetting-based 3D printing methods with the status on current trends and limitations for each AM technology. The paper also delves into 3D printing-enabled electrodes (both anodes and cathodes) and solid-state electrolytes for LIBs, emphasizing the current state-of-the-art materials, manufacturing methods, and properties/performance. Additionally, the current challenges in the AM for electrochemical energy storage (EES) applications, including limited materials, low processing precision, codesign/comanufacturing concepts for complete battery printing, machine learning (ML)/artificial intelligence (AI) for processing optimization and data analysis, environmental risks, and the potential of 4D printing in advanced battery applications, are also presented.

3D-printed tortuous vessels with Photodissociable and morphology-controllable ink

Acute ischemic stroke (AIS) is a high mortality cerebrovascular disease associated with vessel curvature. However, the relevant mechanism remains unclear due to a lack of appropriate tortuous vascular models to investigate and validate. This study explores the combination of projection-based 3D bioprinting (PBP) with photo-stimulus-responsive techniques to fabricate a sodium alginate (SA)/acrylamide (AAM) hydrogel vascular scaffold capable of bending deformation. The coordination of Fe³⁺ ions with carboxylate groups in the alginate chains of the vascular scaffold acts as a molecular switch, which can be dissociated through photoreduction to enable the deformation response. Fourier Transform Infrared (FTIR) and X-ray Photoelectron Spectroscopy (XPS) results verified the deformation principle. By subjecting the scaffold to UV light exposure, Fe³⁺ is reduced to Fe²⁺ in spatially selected regions, resulting in the release of strain and subsequent deformation. Furthermore, it also controlled the degree and direction of curvature of the vessels. The cell seeding experiment verified that the vascular scaffold showed excellent biocompatibility. Overall, our approach could be used to generate an in vitro model of curved vascular pathology to investigate the pathogenesis and provide new directions for the diagnosis and treatment of vascular diseases in the future.

A volatile microemulsion method of preparing water-soluble photo-absorbers for 3D printing of high-resolution, high-water-content hydrogel structures

Digital light processing (DLP)-based three-dimensional (3D) printing is an ideal tool to manufacture hydrogel structures in complex 3D forms. Using DLP to print hydrogel structures with high resolution requires the addition of water-soluble photo-absorbers to absorb excess light and confine photopolymerization to the desired area. However, the current photo-absorbers for hydrogel printing are neither efficient to absorb the excess light nor water-soluble. Herein, we report a volatile microemulsion template method that converts a wide range of commercial non-water-soluble photo-absorbers including Sudan orange G, quercetin, and many others to water-soluble nanoparticles with solubility above 1.0 g mL^-1. After using these water-soluble photo-absorber nanoparticles, the highest lateral and vertical resolutions of printing high-water-content (70-80 wt%) hydrogels can be improved to 5 μm and 20 μm, respectively. Moreover, the quercetin nanoparticle can be easily washed out so that we achieve colorless and transparent printed hydrogel structures with excellent mechanical deformability and biocompatibility as well as thermally controllable variations on transparency and actuation. The proposed methods pave a new efficient way to develop water-soluble photo-absorbers, which helps to greatly improve the printing resolution of the high-water-content hydrogel structure and would be beneficial to extend the application scope of hydrogels.

Interfacial Regulation for 3D Printing based on Slice-Based Photopolymerization

3D printing, also known as additive manufacturing, can turn computer-aided designs into delicate structures directly and on demand by eliminating expensive molds, dies, or lithographic masks. Among the various technical forms, light-based 3D printing mainly involved the control of polymer-based matter fabrication and realized a field of manufacturing with high tunability of printing format, speed, and precision. Emerging slice- and light-based 3D-printing methods have prosperously advanced in recent years but still present challenges to the versatility of printing continuity, printing process, and printing details control. Herein, the field of slice- and light-based 3D printing is discussed and summarized from the view of interfacial regulation strategies to improve the printing continuity, printing process control, and the character of printed results, and several potential strategies to construct complex 3D structures of distinct characteristics with extra external fields, which are favorable for the further improvement and development of 3D printing, are proposed.

3D Printing a Low-Cost Miniature Accommodating Optical Microscope

This decade has witnessed the tremendous progress in miniaturizing optical imaging systems. Despite the advancements in 3D printing optical lenses at increasingly smaller dimensions, challenges remain in precisely manufacturing the dimensionally compatible optomechanical components and assembling them into a functional imaging system. To tackle this issue, the use of 3D printing to enable digitalized optomechanical component manufacturing, part-count-reduction design, and the inclusion of passive alignment features is reported here, all for the ease of system assembly. The key optomechanical components of a penny-sized accommodating optical microscope are 3D printed in 50 min at a significantly reduced unit cost near $4. By actuating a built-in voice-coil motor, its accommodating capability is validated to focus on specimens located at different distances, and a focus-stacking function is further utilized to greatly extend depth of field. The microscope can be readily customized and rapidly manufactured to respond to task-specific needs in form factor and optical characteristics.

Overflow Control for Sustainable Development by Superwetting Surface with Biomimetic Structure

Liquid flowing around a solid edge, i.e., overflow, is a commonly observed flow behavior. Recent research into surface wetting properties and microstructure-controlled overflow behavior has attracted much attention. Achieving controllable macroscale liquid dynamics by manipulating the micro-nanoscale liquid overflow has stimulated diverse scientific interest and fostered widespread use in practical applications. In this review, we outline the evolution of overflow and present a critical survey of the mechanism of surface wetting properties and microstructure-controlled liquid overflow in multilength scales ranging from centimeter to micro and even nanoscale. We summarize the latest progress in utilizing the mechanisms to manipulate liquid overflow and achieve macroscale liquid dynamics and in emerging applications to manipulate overflow for sustainable development in various fields, along with challenges and perspectives.

Progress in the application of 3D printing technology in ophthalmology

Three-dimensional printing (3DP) technology is a rapid prototyping technology that is widely used in the medical field. It can be combined with computer-aided design, material manufacturing, and other technologies to construct medical-related appliances, human implants and even cell-based models or biological tissues. In the field of ophthalmology, the technology can be used to manufacture ocular anatomical models, glasses, intraocular implants, microsurgical instruments, drugs, etc. It can also enable future 'bioprinting', involving the refractive and nervous systems of the eyeball, with excellent development prospects in the field. This review introduces the development of 3DP technology in ophthalmology and discusses its application and potential.

Photopolymerized 3D Printing Scaffolds with Pt(IV) Prodrug Initiator for Postsurgical Tumor Treatment

Biomedical scaffolds have shown great success in postsurgical tumor treatment; their current efforts are focusing on eradicating residual tumor cells and circulating tumor cells and simultaneously repairing postoperative tissue defects. Herein, we report a novel photopolymerized 3D scaffold with Pt(IV) prodrug initiator to achieve the desired features for tumor comprehensive therapy. The Pt-GelMA scaffold was fabricated from the microfluidic 3D printing of methacrylate gelatin (GelMA) bioinks through a Pt(IV)-induced photocrosslinked process without any other additional photoinitiator and chemotherapeutic drug. Thus, the resultant scaffold displayed efficient cell killing ability against breast cancer cells in vitro and significantly inhibited the local tumor growth and distant metastases on an orthotopic postoperative breast cancer model in vivo. Besides, benefiting from their ordered porous structures and favorable biocompatibility, the scaffolds supported the cell attachment, spreading, and proliferation of normal cells in vitro; could facilitate the nutrient transportation; and induced new tissue ingrowth for repairing tissue defects caused by surgery. These properties indicate that such 3D printing scaffold is a promising candidate for efficient postoperative tumor treatment in the practical application.