Continuous Liquid Interface Research Articles

Comparison of accuracy and precision of various types of photo-curing printing technology

Light-cured 3D printing technology has always had a series of advantages such as high precision, fast forming speed and low cost compared with other printing technologies. Since the invention of Stereo lithography Appearance(SLA) printing technology in 1986, light-cured 3D printing has been developing rapidly, and has been derived into Digital Light Processing (DLP), Laser cladding deposition (LCD), Continuous Liquid Interface Production (CLIP), etc. Object: The roughness of the printed products of various photocurable printers was evaluated by the surface morphology of the printed products on the micro level, Compared with the original digital file model, the dimensional accuracy of printed products of various types of photo-curing printers is evaluated. Materials and Methods: A digital 3D model was obtained by scanning the adult maxillary teeth with a 3shape mouth scanner. Save the upper digital three-dimensional model as an STL file and print it as a physical model using three different 3D printers(UNIZ (LCD), Han’s laser SLA 6000 (SLA) and Han’s laser DLP (DLP)). Again, use 3shape to scan the physical model into a 3D digital model and use the Dental Cad to compare the accuracy. Test blocks (20mm*10mm*5mm) were printed using three different printers, and the surface topography was observed using a KEYENCE optical microscope, and data comparison was performed using DANTAL CAD for file fitting. Results and Conclusion: On the Z direction, the surface bump SLA was 185.1 micron mum, the LCD 105.4 mum, and the DLP 95.2 mum. SLA<LCD<DLP. The model fit DLP was 0.07 mm, the LCD was 0.10 mm, and the SLA was 0.14 mm. In terms of print accuracy, DLP > LCD > SLA. The surface roughness of the test block was DLP>SLA>LCD. Conclusion: DLP performs well in all aspects.

Influence of micro-feature parameters of a constrained substrate on mass transfer of photopolymerization inhibition gas in continuous liquid interface production

<p indent=0mm>The continuous liquid interface production (CLIP) process has dramatically improved the fabrication speed of 3D printing technology, which makes it possible for Stereolithography to be used for direct manufacturing of functional parts. The effect of the CLIP process is significant owing to the skillful application of the photopolymerization inhibition effect of oxygen; therefore, the mass transfer behavior of the oxygen across the substrate is the key factor affecting the thickness and stability of the inhibition zone. In this paper, a low-cost scheme for a constrained substrate with good oxygen permeability that is made of PDMS membrane has been proposed, and the paper focuses on the effect of PDMS membrane and microscopic pore characteristics on the oxygen mass transfer behavior in the substrate. Based on the calculation result of the oxygen-diffusion coefficient in the PDMS membrane through molecular dynamics simulation, the influencing factors and laws of oxygen permeability of substrate are numerically studied using COMSOL software. The substrates with oxygen permeability that was measured based on the constructed experiment device were fabricated. The results show that the PDMS membrane possesses good oxygen content and the diffusion coefficient of the content in the PDMS film is 4.018 ×10⁻⁵ cm²/s. The thickness of the PDMS film and the area ratio and diameter of the micro-pores in the supporting glass substrate affect the oxygen permeability. Reducing the thickness of the PDMS film, increasing the pore-area ratio, and reducing the micro-pore diameter facilitate the oxygen permeability improvement under the premise of meeting the strength requirements. The research results can provide process improvement direction and theoretical basis for the preparation of constrained substrates.

A Simplified 2D Numerical Simulation of Photopolymerization Kinetics and Oxygen Diffusion-Reaction for the Continuous Liquid Interface Production (CLIP) System.

Additive manufacturing is a versatile technology for producing customized 3D products. In 2015, the Continuous Liquid Interface Production (CLIP) system was developed as a part of projection-type, UV-curable resin 3D printers. The CLIP system utilized the dead zone where oxygen inhibition occurs and prevents the UV-cured product from adhering to the UV illumination window. The CLIP system successfully produced complex shapes in a short time. This study investigated how the relationship between the photopolymerization rate, oxygen inhibition rate, and oxygen diffusion rate affects the shape of the product by means of a numerical simulation of the photopolymerization kinetics with oxygen diffusion and reaction. The results indicate that the vertical production speed and transmittance of UV light are crucial to controlling the conversion and shape precision of products.

Thermal curing kinetics optimization of epoxy resin in Digital Light Synthesis

A new class of high-performance resins are available for additive manufacturing with the introduction of Digital Light Synthesis (DLS) technology. In combination with Continuous Liquid Interface Production (CLIP), DLS uses ultraviolet light and oxygen to continuously grow objects from a pool of resin instead of printing them layer-by-layer, subsequently increasing the printing speed and the mechanical performance. For many DLS resin systems, a secondary thermal curing step is required in order to reach the final material properties after printing. This step is a major limiting factor in the production time of the DLS process, as materials may require several hours of thermal post curing. The aim of this study is to optimize this secondary curing cycle for the epoxy-based resin EPX 82 by reducing the thermal curing time while avoiding a negative influence on the final mechanical properties. Differential scanning calorimetry (DSC) was used with different heating rates and a chemical reaction model was developed. The Di Benedetto relationship was used to include diffusion control for high degrees of cure. Based on the kinetics study, an optimized curing cycle was generated using different maximum conversion rates and heating rates. The results show that it is possible to reduce the thermal curing cycle time by more than 9 h (73 percent) compared to the supplier recommendation while maintaining the mechanical properties of the final part.

Towards the integration of additively manufactured photopolymer dies in the polymer profile extrusion process chain

In the context of Industry 4.0, the integration of digital technologies in manufacturing process chains is in progress in several industrial sectors. In this study, additive manufactured polymer extrusion dies were fabricated by continuous liquid interface production and tested in an extrusion production line. The possibility to integrate direct soft tooling manufacturing along with a digital twin environment in the process chain was conceived with great potential time and production cost reductions compared to the conventional process. The dies successfully withstood the demanding process conditions, yielding up to 1000 m of products with process conditions comparable to the conventional process.

Continuous liquid interface production of alginate/polyacrylamide hydrogels with supramolecular shape memory properties

A recently developed three-dimensional (3D) gel-printing technology, namely continuous liquid interface production (CLIP), was utilized to fabricate supramolecular shape memory hydrogels with high resolutions and complex 3D geometries. The UV-curable ink for CLIP was composed of hydrogel precursors (alginate and acrylamide) and a photo-initiator (ammonium persulfate). As expected, the double network formed from ionically crosslinked alginate and covalently crosslinked polyacrylamide endowed the printed hydrogels with excellent mechanical properties. Meanwhile, due to the reversible metal-ligand coordination interaction, the hydrogel could be temporarily immobilized into an optional shape after introducing calcium ions and return to its original shapes upon ion removal, exhibiting ion-triggered shape memory effect. Moreover, the presence of ions greatly improved the conductivity of the resultant hydrogels. Such 3D printed versatile hydrogels with complex geometries demonstrated the potential for selected applications, particularly in load-bearing materials and flexible electronic devices.

Additive Manufacturing of Bovine Serum Albumin-Based Hydrogels and Bioplastics.

Biosourced and biodegradable polymers for additive manufacturing could enable the rapid fabrication of parts for a broad spectrum of applications ranging from healthcare to aerospace. However, a limited number of these materials are suitable for vat photopolymerization processes. Herein, we report a two-step additive manufacturing process to fabricate robust protein-based constructs using a commercially available laser-based stereolithography printer. Methacrylated bovine serum albumin (MA-BSA) was synthesized and formulated into aqueous resins that were used to print complex three-dimensional (3D) objects with a resolution comparable to a commercially available resin. The MA-BSA resins were characterized by rheometry to determine the viscosity and the cure rate, as both parameters can ultimately be used to predict the printability of the resin. In the first step of patterning these materials, the MA-BSA resin was 3D printed, and in the second step, the printed construct was thermally cured to denature the globular protein and increase the intermolecular noncovalent interactions. Thus, the final 3D printed part was comprised of both chemical and physical cross-links. Compression studies of hydrated and dehydrated constructs demonstrated a broad range of compressive strengths and Young's moduli that could be further modulated by adjusting the type and amount of co-monomer. The printed hydrogel constructs demonstrated good cell viability (>95%) after a 21 day culture period. These MA-BSA resins are expected to be compatible with other vat photopolymerization techniques including digital light projection and continuous liquid interface production.

Accuracy of 3D Printed Models Created by Two Technologies of Printers with Different Designs of Model Base

To evaluate the accuracy of three-dimensional (3D) printed models manufactured using two different printer technologies with different model base designs. A maxillary typodont was scanned using a desktop scanner to generate the Standard Tessellation Language (STL) file as a reference scan. After the scanning procedure, the STL file was exported to Model Builder™ for designing the following two types of the model bases: a solid base design and a hollow base design with a 2.0 mm thickness of the external shell. Each design was printed to produce 10 models using a Continuous Liquid Interface Production (CLIP) printer and a Digital Light Processing (DLP) printer. The following four groups were tested: CLIP with solid base (CS); CLIP with hollow base (CH); DLP with solid base (DS); and DLP with hollow base (DH). A total of 40 models were scanned using the same desktop scanner to generate the STL files for evaluation of the accuracy by evaluation of trueness and precision. All STL files were superimposed with the control STL file via surface matching software and a comparison was performed using the 3D color mapping function and a 2D comparison of 48 points selected on the tested model. The data were collected by measuring the deviation between the tested model and the reference scan. Trueness was calculated by using the comparison among four tested groups. The Kruskal-Wallis analysis was conducted to assess the overall statistical significance of differences among the tested groups (α = 0.05). For precision measurement, the evaluation was conducted using Intraclass Correlation Coefficient (ICC) value at 95% confident interval to determine the deviation within the same tested groups. The median values for the deviated distance of the four tested groups were 0.045 (CH), 0.035 (CS), 0.077 (DH), and 0.077 mm (DS). There were no statistically significant differences between the trueness of the two groups when using the same printers regardless of the designs of model base (p>0.05). However, when comparing the two printers using the same model base design and the two different designs of model base, there were statistically significant differences in trueness (p<0.05). The 3D printed models created using CLIP technology had higher trueness than the DLP technology printer. Precision of the 3D printed model was displayed in ICC value. The ICC values of four tested groups were 0.968 (CH), 0.981 (CS), 0.969 (DH), and 0.983 (DS). All tested groups were classified as exhibiting an excellent level of precision based on 95% confident interval of the ICC estimation. The accuracy of 3D printed models was affected by the printer technology regardless of whether the model base was solid or hollow. The CLIP technology printer produced significantly less variation from the reference model than the DLP printer. However, all of the 3D printed models were determined to exhibit a clinically acceptable level of accuracy based on the recorded dimensions being less than 100µm different than the reference model.

Method for Attaining Dimensionally Accurate Conditions for High-Resolution Three-Dimensional Printing Ceramic Composite Structures Using MicroCLIP Process.

Continuous liquid interface production (CLIP) utilizes projection ultraviolet (UV) light and oxygen inhibition to transform the sequential layered three-dimensional (3D) manufacturing into a continuous fabrication flow with tremendous improved fabrication speed and structure integrity. Incorporating ceramic particles to the photo-curable polymers allows for additive manufacturing of ceramic parts featuring sophisticated geometries, mitigating the difficulties associated with traditional manufacturing processes. The presence of ceramic particles within the ink, however, strongly scatters the incident UV light. In the high-resolution CLIP (microCLIP) process, the scattering effect can significantly alter the process characteristics, resulting in broadening of lateral feature dimensions alongside curing depth reduction. Varying exposure conditions to accommodate scattering additionally affects the oxygen deadzone thickness (DZ), which is dependent on power of incident light. This introduces a systematic defocusing error for large deadzone thickness to further complicate process control, such as the unwanted narrowing of part features. In this work, we developed a systematic framework for process optimization by balancing those effects via experimental characterization. We showed that the reported method can provide a set of optimal process parameters (UV power and stage speed) for high-resolution 3D fabrication in accommodating the distinct characteristics of given photo-curable ceramic ink. The method to optimize process parameter was validated experimentally via fabricating a gradient index Luneburg lens comprising densely packed woodpile building-blocks with a strut width of 100 μm and a layer thickness of 60 μm using microCLIP at dimensionally accurate exposure conditions.

Accelerated refilling speed in rapid stereolithography based on nano-textured functional release film

Nowadays, along with the demand for new technologies and new materials, a revolution in 3D printing technology is emerging. In recent years, stereolithography 3D printing has been widely used in both academia and industry, due to its fast forming speed, high precision, and low-cost advantages. The continuous liquid interface production technology has made the printing speed even faster. However, the process of resin refilling constrains the printing speed and the printing capabilities of such technologies, since only hollow structures can be fabricated. In this study, a nano-textured hydrophobic PDMS contacting layer and an oxygen-permeable membrane were bonded together as the functional release film. The oxygen inhibition layer was successfully maintained by the molecular oxygen permeated through the composite release film, achieving rapid stereolithography, and key factors that affecting resin refilling are selectively studied by the orthogonal experiment. Crucially, according to the simulation and experimental results, the adoption of the hydrophobic nano-texture not only increased the refilling speed of the resin by two times and reduced the printing time by nearly 25%, but also improved the printing reliability by reducing the vacuum (negative pressure) caused by the original slow refilling speed. Additionally, optical simulations also demonstrated that the nano-texture would not influence the curing effect of the resin. This work proposed a promising strategy for rapid stereolithography of 3D models containing larger cross-sectional areas.

3466 Innovative 3D Printed Intravaginal Rings: Developing AnelleO PRO, the First Intravaginal Ring for Infertility

OBJECTIVES/SPECIFIC AIMS: The study aims to develop and test a biocompatible 3D-printed IVRs for the mechanical and release properties of a model drug, β-estradiol, then translate these methods to the target drug, progesterone. The goals include demonstrating decoupling of mechanical and release properties of the rings, release profiles driven by geometry and efficacy in sheep animal models to evaluate device safety. METHODS/STUDY POPULATION: A novel 3D-printing platform, continuous liquid interface production (CLIP), pioneered by Carbon, enables the fabrication of complex designs on a timescale that is amenable to manufacturing. The process utilizes computational-aided design (CAD), specifying shape and geometry, which is recreated via a photopolymerization process. IVRs are fabricated with CLIP using a biocompatible resin at a rate of approximately 15 min. per ring. Rings were fabricated and assessed for the release of a model drug, β-estradiol. The process was then translated to the target drug, progesterone. Rings were evaluated for radial compression and in vitro release in simulated vaginal fluid (SVF). RESULTS/ANTICIPATED RESULTS: Intravaginal rings (IVRs) were designed and fabricated to be geometrically complex in an effort to control release. Ring geometry and subsequent pore size was achieved through the use of unit cells. Several design parameters were explored including unit cell type, size, and band presence in two resins of differing mechanical properties. Through design, a wide range of radial compressive properties were achieved which spanned values covered by commercially available rings. The release of β-estradiol in SVF was found to span 57 – 115 days and resulted in near or complete release of the total loaded drug. Changing the internal geometric design of the ring was found to have minimal influence on the compression properties, thus the mechanical and release characteristics of the rings were largely decoupled. DISCUSSION/SIGNIFICANCE OF IMPACT: This is a novel approach to the design and fabrication of intravaginal rings for the treatment of infertility. The use of CAD and the decoupling of release from mechanical properties allows for us to move away from the one-size one-dose fits all approach to IVRs.

Enhanced continuous liquid interface production with track-etched membrane

PurposeThe purpose of this paper is to explore the possibility of an enhanced continuous liquid interface production (CLIP) with a porous track-etched membrane as the oxygen-permeable window, which is prepared by irradiating polyethylene terephthalate membranes with accelerated heavy ions. Design/methodology/approachExperimental approaches are carried out to characterize printing parameters of resins with different photo-initiator concentrations by a photo-polymerization matrix, to experimentally observe and theoretically fit the oxygen inhibition layer thickness during printing under conditions of pure oxygen and air, respectively, and to demonstrate the enhanced CLIP processes by using pure oxygen and air, respectively. FindingsOwing to the high permeability of track-etched membrane, CLIP process is demonstrated with printing speed up to 800 mm/h in the condition of pure oxygen, which matches well with the theoretically predicted maximum printing speed at difference light expose. Making a trade-off between printing speed and surface quality, maximum printing speed of 470 mm/h is also obtained even using air. As the oxygen inhibition layer created by air is thinner than that by pure oxygen, maximum speed cannot be simply increased by intensifying the light exposure as the case with pure oxygen. Originality/valueCLIP process is capable of building objects continuously instead of the traditional layer-by-layer manner, which enables tens of times improvement in printing speed. This work presents an enhanced CLIP process by first using a porous track-etched membrane to serve as the oxygen permeable window, in which a record printing speed up to 800 mm/h using pure oxygen is demonstrated. Owing to the high permeability of track-etched membrane, continuous process at a speed of 470 mm/h is also achieved even using air instead of pure oxygen, which is of significance for a compact robust high-speed 3D printer.

Machine learning for continuous liquid interface production: Printing speed modelling

Continuous Liquid Interface Production (CLIP), a variant of vat photopolymerization additive manufacturing, can achieve build speeds an order of magnitude faster than conventional layer-by-layer stereolithography process. However, identification of the proper continuous printing speed remains a grand challenge in the process planning. To successfully print a part continuously, the printing speed needs to be carefully adjusted and calibrated for the given geometry. In this paper, we investigate machine learning techniques for modeling and predicting the proper printing speed in the CLIP process. The synthetic dataset is generated by physics-based simulations. An experimental dataset is constructed for training the machine learning models to find the appropriate speed range and the optimum speed. Conventional machine learning techniques including Decision Tree, Naïve Bayes, K Nearest Neighbors, and Support Vector Machine (SVM), ensemble methods including Random Forest, Gradient Boosting, and Adaboosting, and the deep learning approach Siamese Network are tested and compared. Experimental results validate the effectiveness of these machine learning models and show that the Siamese Network model gives the highest accuracy.

CFD analysis and prediction of suction force during the pulling-up stage of the continuous liquid interface production process

Continuous liquid interface production (CLIP) is a novel constrained-surface curing approach that, due to its surprisingly fast fabrication speed, is shown to have the potential to revolutionize manufacturing. However, until now, it has not been possible to reliably fabricate parts with large cross-sectional area due to the large stress generated in the cured layer that results from the suction force of the liquid resin during the pulling-up stage. In this work, a systematic computational fluid dynamics (CFD) analysis was performed to investigate the resin flow behaviour in the micro-gap between the new cured layer and the resin tank during the pulling-up stage of the CLIP process, under various operational conditions. COMSOL software package was used to calculate hydrodynamic balance during the pulling-up stage using the so-called ‘deformed geometry’ technique along with the boundary condition of a moving wall and transient analysis. Using the numerical method, local instantaneous negative pressures in the resin flow field under various operational conditions were obtained. The results show that the magnitude of the negative pressure varies with the stage hoisting speed and acceleration, thickness of the oxygen-inhibited zone, cross-sectional area, and the slip at the interface between liquid resin and the bottom of the resin tank, and that the transient vacuum effect is significant enough to possibly damage the fabricated parts. Based on the simulation conclusions, some suggestions for optimizing operational conditions to reduce the suction force and thus improve the reliability of the CLIP process have been proposed.

Synthesis of photocurable cellulose acetate butyrate resin for continuous liquid interface production of three-dimensional objects with excellent mechanical and chemical-resistant properties

Three-dimensional (3D) printing parts with excellent resolution and high performance are of great significance for scientific and engineering applications. In this study, a novel photocurable cellulose acetate butyrate (PC-CAB) resin was synthesized for continuous liquid interface production (CLIP) to construct 3D objects with high resolution, tailored mechanical properties, excellent chemical resistance and thermal stability. Particularly, the tensile and flexural strength of the CLIP 3D printed specimen could reach 44.67 and 64.53 MPa, respectively. Their solvent resistance against various organic solvents and strong acidic/basic solutions was evaluated. As expected, the 3D prints could well maintain their structural integrity and exhibited very low swelling ratios owing to the photo-induced chemical crosslinking structure. Notably, even after immersion in methylene chloride or 1.0 M acid/alkali for 3 h, the 3D prints still showed excellent mechanical and thermal properties. Further study demonstrated that when PC-CAB in the CLIP ink was optimized to 20 wt% while the photoinitiator (PI) was 0.5 wt%, complex-structured 3D printed objects with high surface quality could be obtained under specific printing parameters.

Infused configurations induced by structures influence stability and antifouling performance of biomimetic lubricant-infused surfaces

Biomimetic lubricant-infused surfaces are developed as an effective approach to solve the problem of biofouling. Herein, lubricant-infused surfaces were fabricated on various structured surfaces with polished, nanostructured, microstructured, and micro/nanostructured features. The influences of surface topographies on their infused configurations, stability and antifouling performance were studied in detail. The results indicated that the structures played a decisive role in the formation of lubricant-infused surfaces. Infused configurations of lubricant were various responded to the different structures, including floated on polished surfaces, encapsulated on nanostructured surfaces, impregnated with emergent features on microstructured surfaces and impregnated/encapsulated on micro/nanostructured surfaces. Stability and antifouling performance were decided by the infused configurations. The encapsulated lubricant entrapped by a capillary force in nanostructures can form a continuous liquid interface to retain stability and provide antifouling performance. The results would show great potential for the construction of antifouling coatings by lubricant-infused techniques.

Mechanical properties of hexagonal lattice structures fabricated using continuous liquid interface production additive manufacturing

Additive manufacturing (AM) is a key enabler for architectured lattice materials, because of the geometric complexity of parts that can be produced. Recent advancements in AM have enabled rapid production speeds, high spatial resolution, and a variety of engineering polymers. An open question remains whether production grade AM can accurately and repeatably produce lattice parts. This study presents design, production, and mechanical property testing of hexagonal lattice parts manufactured using continuous liquid interface production (CLIP) based AM. We printed and tested 84 parts, in three polymer materials having relative density ranging from 0.06 to 0.23. Lattice wall structures were reliably printed when truss aspect ratio was in the range 5 to 20 and wall thicknesses were 0.35 or 0.5 mm. The printed lattice parts, each comprising hundreds of slender walls, were measured using high resolution optical scanning. The images were analyzed to evaluate the difference between the printed parts and their designs, and the effect of geometric deviations on the mechanical behavior. The measured elastic moduli of the printed parts are close to the values expected from the materials specifications. The measured strength of the printed parts deviates by 7% from the behavior predicted from the scanned geometry. The failure mode of the printed structures depends upon the material and part geometry. To our knowledge, this is the largest study on the accuracy and performance of AM lattice parts, and the first study of its type for lattice parts made using CLIP.

Spatially controlled coating of continuous liquid interface production microneedles for transdermal protein delivery

Microneedle patches, arrays of micron-scale projections that penetrate skin in a minimally invasive manner, are a promising tool for transdermally delivering therapeutic proteins. However, current microneedle fabrication techniques are limited in their ability to fabricate microneedles rapidly and with a high degree of control over microneedle design parameters. We have previously demonstrated the ability to fabricate microneedle patches with a range of compositions and geometries using the novel additive manufacturing technique Continuous Liquid Interface Production (CLIP). Here, we establish a method for dip coating CLIP microneedles with protein cargo in a spatially controlled manner. Microneedle coating mask devices were fabricated with CLIP and utilized to coat polyethylene glycol-based CLIP microneedles with model proteins bovine serum albumin, ovalbumin, and lysozyme. The design of the coating mask device was used to control spatial deposition and loading of coated protein cargo on the microneedles. CLIP microneedles rapidly released coated protein cargo both in solution and upon insertion into porcine skin. The model enzyme lysozyme was shown to retain its activity throughout the CLIP microneedle coating process, and permeation of bovine serum albumin across full thickness porcine skin was observed after application with coated CLIP microneedles. Protein-coated CLIP microneedles were applied to live mice and showed sustained retention of protein cargo in the skin over 72 h. These results demonstrate the utility of a versatile coating platform for preparation of precisely coated microneedles for transdermal therapeutic delivery.

Continuous liquid interface production (CLIP) method for rapid prototyping

Additive Manufacturing (AM) processes such as three- dimensional (3D) printing are one of most important technologies of our century. Additive manufacturing is a manufacturing process in which 3D solid objects are created. It enables the creation of physical 3D models of objects using a series of an additive or layered development framework, where layers are laid down in succession to create a complete 3D object. Additive manufacturing is also known as 3D printing. The strongest reasons for the use of rapid prototypes in manufacturing are the production of parts with a small quantity or a complex shape, the obtaining of lighter parts, the prevention of waste of raw materials, a wider availability of testing and design and further personalization. Continuous liquid interface production (CLIP) is an alternative approach to AM by exploiting the basic principle of oxygen-impaired photopolymerization to create a continuous fluid interface of uncured resin between the growing section and the exposure window.

Air-Diffusion-Channel Constrained Surface Based Stereolithography for Three-Dimensional Printing of Objects With Wide Solid Cross Sections

Oxygen inhibition has been proved capable of reducing the separation force and enabling successful prints in constrained surface vat photopolymerization (CSVP) based three-dimensional (3D) printing processes. It has also been demonstrated as a key factor that determines the feasibility of the newly developed CSVP-based continuous 3D printing systems, such as the continuous liquid interface production. Despite its well-known importance, it is still largely unknown regarding how to control and enhance the oxygen inhibition in CSVP. To close this knowledge gap, this paper investigates the constrained surface design, which allows for continuous and sufficient air permeation to enhance the oxygen inhibition in CSVP systems. In this paper, a novel constrained surface with air-diffusion-channel is proposed. The influences of the air-diffusion-channel design parameters on the robustness of the constrained surface, the light transmission rate, and light intensity uniformity are studied. The thickness of the oxygen inhibition layer associated with the proposed constrained surface is studied analytically and experimentally. Experimental results show that the proposed air-diffusion-channel design is effective in maintaining and enhancing the oxygen-inhibition effect, and thus can increase the solid cross section size of printable parts.