Clopidogrel-loaded vascular grafts prepared using digital light processing 3D printing

The leading cause of death worldwide and a significant factor in decreased quality of life are the cardiovascular diseases. Endovascular operations like angioplasty, stent placement, or atherectomy are often used in vascular surgery to either dilate a narrowed blood artery or remove a blockage. As an alternative, a vascular transplant may be utilised to replace or bypass a dysfunctional or blocked blood vessel. Despite the advancements in endovascular surgery and its popularisation over the past few decades, vascular bypass grafting remains prevalent and is considered the best option for patients in need of long-term revascularisation treatments. Consequently, the demand for synthetic vascular grafts composed of biocompatible materials persists. To address this need, biodegradable clopidogrel (CLOP)-loaded vascular grafts have been fabricated using the digital light processing (DLP) 3D printing technique. A mixture of polylactic acid-polyurethane acrylate (PLA-PUA), low molecular weight polycaprolactone (L-PCL), and CLOP was used to achieve the required mechanical and biological properties for vascular grafts. The 3D printing technology provides precise detail in terms of shape and size, which lead to the fabrication of customised vascular grafts. The fabricated vascular grafts were fully characterised using different techniques, and finally, the drug release was evaluated. Results suggested that the performed 3D-printed small-diameter vascular grafts containing the highest CLOP cargo (20% w/w) were able to provide a sustained drug release for up to 27 days. Furthermore, all the CLOP-loaded 3D-printed materials resulted in a substantial reduction of the platelet deposition across their surface compared to the blank materials containing no drug. Haemolysis percentage for all the 3D-printed samples was lower than 5%. Moreover, 3D-printed materials were able to provide a supportive environment for cellular attachment, viability, and growth. A substantial increase in cell growth was detected between the blank and drug-loaded grafts.

Chemistry matters: A side-by-side comparison of two chemically distinct methacryloylated dECM bioresins for vat photopolymerization

Decellularized extracellular matrix (dECM) is an excellent natural source for 3D bioprinting materials due to its inherent cell compatibility. In vat photopolymerization, the use of dECM-based bioresins is just emerging, and extensive research is needed to fully exploit their potential. In this study, two distinct methacryloyl-functionalized, photocrosslinkable dECM-based bioresins were prepared from digested porcine liver dECM through functionalization with glycidyl methacrylate (GMA) or conventional methacrylic anhydride (MA) under mild conditions for systematic comparison. Although the chemical modifications did not significantly affect the structural integrity of the dECM proteins, mammalian cells encapsulated in the respective hydrogels performed differently in long-term culture. In either case, photocrosslinking during 3D (bio)printing resulted in transparent, highly swollen, and soft hydrogels with good shape fidelity, excellent biomimetic properties and tunable mechanical properties (~ 0.2-2.5 kPa). Interestingly, at a similar degree of functionalization (DOF ~ 81.5-83.5 %), the dECM-GMA resin showed faster photocrosslinking kinetics in photorheology resulting in lower final stiffness and faster enzymatic biodegradation compared to the dECM-MA gels, yet comparable network homogeneity as assessed via Brillouin imaging. While human hepatic HepaRG cells exhibited comparable cell viability directly after 3D bioprinting within both materials, cell proliferation and spreading were clearly enhanced in the softer dECM-GMA hydrogels at a comparable degree of crosslinking. These differences were attributed to the additional hydrophilicity introduced to dECM via methacryloylation through GMA compared to MA. Due to its excellent printability and cytocompatibility, the functional porcine liver dECM-GMA biomaterial enables the advanced biofabrication of soft 3D tissue analogs using vat photopolymerization-based bioprinting.

Accuracy of the intaglio surface of 3D-printed hybrid resin-ceramic crowns, veneers and table-tops: An in vitro study

OBJECTIVES

The present study aims to examine the influence of the build angle on the accuracy (trueness and precision) of 3D printed crowns, table-tops and veneers with a hybrid resin-ceramic material.

METHODS

One crown, on table-top and one veneer were printed in five different build angles (0°, 30°, 45°, 60°, 90°) (n = 50) with the digital light processing (DLP) system (Varseo XS, Bego) using hybrid resin (Varseo Smile Crownplus A3, Bego). All printed restorations were scanned using the laboratory scanner (D2000, 3Shape) and matched onto the initial reference design in metrology software (Geomagic Control X, 3D Systems). The root mean square error (RMSE) was calculated between the scanned and reference data. The data was statistically analyzed using the Tukey multiple comparison test and Wilcoxon multiple comparison test.

RESULTS

The crown group showed higher trueness at 30° (0.021 ± 0.002) and 45° (0.020 ± 0.002), and table-tops at 0° (0.015 ± 0.001) and 30° (0.014 ± 0.001) (p < 0.0001). Veneers demonstrated higher trueness at 30° (0.016 ± 0.002) (p < 0.0001). All three restoration types demonstrated the lowest trueness at a 90° build angle and portrayed deviations along the z axis. The veneer and table-top groups showed the lowest precision at 90° (veneers: 0.021 ± 0.008; table-tops: 0.013 ± 0.003). The crown group portrayed the lowest precision at 45° (0.017 ± 0.005) (p < 0.0001).

CONCLUSION

The build angle of DLP-printed hybrid resin-ceramic restorations influences their accuracy.

CLINICAL SIGNIFICANCE

Considering the build angle is important to achieve a better accuracy of 3D-printed resin-ceramic hybrid restorations. This may help predict or avoid the interference points between a restoration and a die and minimize the clinical adjustments.

The importance of mechanical and biological cues of tympanic membrane grafts to ensure optimal regeneration

Chronic suppurative otitis media (CSOM) is often associated with permanent tympanic membrane (TM) perforation and conductive hearing loss. The current clinical gold standard, using autografts and allografts, suffers from several drawbacks. Artificial replacement materials can help to overcome these drawbacks. Therefore, scaffolds fabricated through digital light processing (DLP) were herein created to support TM regeneration. Various UV-curable printing inks, including gelatin methacryloyl (GelMA), gelatin-norbornene-norbornene (GelNBNB) (crosslinked with thiolated gelatin (GelSH)) and alkene-functionalized poly-ε-caprolactone (E-PCL) (crosslinked with pentaerythritol tetrakis(3-mercaptopropionate) (PETA4SH)) were optimized regarding photo-initiator (PI) and photo-absorber (PA) concentrations through viscosity characterization, photo-rheology and the establishment of working curves for DLP. Our material platform enabled the development of constructs with a range of mechanical properties (plateau storage modulus varying between 15 and 119 kPa). Excellent network connectivity for the GelNBNB and E-PCL constructs was demonstrated (gel fractions >95 %) whereas a post-crosslinking step was required for the GelMA constructs. All samples showed excellent biocompatibility (viability >93 % and metabolic activity >88 %). Finally, in vivo and ex vivo assessments, including histology, vibration and deformation responses measured through laser doppler vibrometry and digital image correlation respectively, were performed to investigate the effects of the scaffolds on the anatomical and physiological regeneration of acute TM perforations in rabbits. The data showed that the most efficient healing with the best functional quality was obtained when both mechanical (obtained with the PCL-based resin) and biological (obtained with the gelatin-based resins) material properties were taken into account.

Calcium silicate/gelatin composite scaffolds with controllable degradation behavior: Fabrication and evaluation

Calcium silicate can be used as an excellent material for biodegradable bone scaffolds because it can provide bioactive ions to promote bone regeneration. However, the brittleness and rapid degradation of calcium silicate scaffolds have significantly limited their clinical application. In this work, the calcium silicate scaffolds printed by DLP technology were immersed in a gelatin solution under high vacuum condition to obtain calcium silicate/gelatin composite scaffolds with good mechanical and biological properties. Then, genipin was used as a cross-linker for gelatin to control the degradation properties of the composite scaffolds. The initial compressive strength and toughness of the composite scaffolds were 5.0 times and one order of magnitude higher than those of the pure calcium silicate scaffolds, respectively. The gelatin on the surface of the scaffolds could effectively act as a protective layer to regulate the degradation behaviors of the calcium silicate substrate through controlling the crosslinking degree of the gelatin. After degrading for 14 days, the composite scaffolds at 1.0 % genipin concentration exhibited the highest compressive strength of 8.6 ± 0.8 MPa, much higher than that of the pure ceramic scaffold (1.5 ± 0.3 MPa). It can be found that the toughness of the composite scaffolds were almost over 13.2 times higher than that of the pure ceramic scaffold during degradation, despite the higher toughness loss for the former. Furthermore, the composite scaffolds showed enhanced cell biocompatibility and viability. These results demonstrate that the calcium silicate/gelatin composite scaffolds can be a promising candidate in bone tissue regeneration.

Digital light 4D printing of bioresorbable shape memory elastomers for personalized biomedical implantation

Four-dimensional (4D) printing unlocks new potentials for personalized biomedical implantation, but still with hurdles of lacking suitable materials. Herein, we demonstrate a bioresorbable shape memory elastomer (SME) with high elasticity at both below and above its phase transition temperature (Ttrans). This SME can be digital light 3D printed by co-polymerizing glycerol dodecanoate acrylate prepolymer (pre-PGDA) with acrylic acid monomer to form crosslinked Poly(glycerol dodecanoate acrylate) (PGDA)-Polyacrylic acid (PAA), or PGDA-PAA network. The printed complex, free-standing 3D structures with high-resolution features exhibit shape programming properties at a physiological temperature. By tuning the pre-PGDA weight ratios between 55 wt% and 70 wt%, Ttrans varies between 39.2 and 47.2 ℃ while Young's moduli (E) range 40-170 MPa below Ttrans with fractural strain (εf) of 170 %-200 %. Above Ttrans, E drops to 1-1.82 MPa which is close to those of soft tissue. Strikingly, εf of 130-180 % is still maintained. In vitro biocompatibility test on the material shows > 90 % cell proliferation and great cell attachment. In vivo vascular grafting trials underline the geometrical and mechanical adaptability of these 4D printed constructs in regenerating the aorta tissue. Biodegradation of the implants shows the possibility of their full replacement by natural tissue over time. To highlight its potential for personalized medicine, a patient-specific left atrial appendage (LAA) occluder was printed and implanted endovascularly into an in vitro heart model. STATEMENT OF SIGNIFICANCE: 4D printed shape-memory elastomer (SME) implants particularly designed and manufactured for a patient are greatly sought-after in minimally invasive surgery (MIS). Traditional shape-memory polymers used in these implants often suffer from issues like unsuitable transition temperatures, poor biocompatibility, limited 3D design complexity, and low toughness, making them unsuitable for MIS. Our new SME, with an adjustable transition temperature and enhanced toughness, is both biocompatible and naturally degradable, particularly in cardiovascular contexts. This allows implants, like biomedical scaffolds, to be programmed at room temperature and then adapt to the body's physiological conditions post-implantation. Our studies, including in vivo vascular grafts and in vitro device implantation, highlight the SME's effectiveness in aortic tissue regeneration and its promising applications in MIS.

Effect of post-curing conditions on surface characteristics, physico-mechanical properties, and cytotoxicity of a 3D-printed denture base polymer

OBJECTIVE

This study aims to investigate the influence of post-polymerization (post-curing) conditions on surface characteristics, flexural properties, water sorption and solubility, and cytotoxicity of additively manufactured denture base materials.

METHODS

The tested specimens were additively manufactured using digital light processing and classified into different post-curing condition groups: submerged in water (WAT), submerged in glycerin (GLY), and air exposure (AIR). An uncured specimen (UNC) was used as a control. The surface topography and roughness were observed. The flexural strength and modulus were determined via a three-point bending test. The water sorption and solubility were subsequently tested. Finally, an extract test was performed to assess cytotoxicity.

RESULTS

Different post-curing conditions had no significant effects on the surface topography and roughness (Sa value). Various post-curing conditions also had no significant effects on the flexural strength. Notably, the flexural modulus of the WAT group (2671.80 ± 139.42 MPa) was significantly higher than the AIR group (2197.47 ± 197.93 MPa, p = 0.0103). After different post-curing conditions, the water sorption and solubility of the specimens met the ISO standards. Finally, all post-curing conditions effectively reduced cytotoxic effects.

SIGNIFICANCES

Post-curing with different oxygen levels improved flexural properties, and flexural modulus significantly increased after the specimens were submerged in water. In addition, water sorption and solubility, and cytocompatibility were optimized by post-curing, irrespective of the post-curing conditions. Therefore, the water-submerged conditions optimized the flexural modulus of the 3D-printed denture base materials.

Results of an interlaboratory study on the working curve in vat photopolymerization

The working curve informs resin properties and print parameters for stereolithography, digital light processing, and other photopolymer additive manufacturing (PAM) technologies. First demonstrated in 1992, the working curve measurement of cure depth vs radiant exposure of light is now a foundational measurement in the field of PAM. Despite its widespread use in industry and academia, there is no formal method or procedure for performing the working curve measurement, raising questions about the utility of reported working curve parameters. Here, an interlaboratory study (ILS) is described in which 24 individual laboratories performed a working curve measurement on an aliquot from a single batch of PAM resin. The ILS reveals that there is enormous scatter in the working curve data and the key fit parameters derived from it. The measured depth of light penetration Dp varied by as much as 7x between participants, while the critical radiant exposure for gelation Ec varied by as much as 70x. This significant scatter is attributed to a lack of common procedure, variation in light engines, epistemic uncertainties from the Jacobs equation, and the use of measurement tools with insufficient precision. The ILS findings highlight an urgent need for procedural standardization and better hardware characterization in this rapidly growing field.

4D-printed microneedles from dual-sensitive chitosan for non-transdermal drug delivery

Microneedles are a promising micro-scale drug delivery platform that has been under development for over two decades. While 3D printing technology has been applied to fabricate these systems, the challenge of achieving needle sharpness remains. In this study, we present an innovative approach for microneedle fabrication using digital light processing (DLP) 3D printing and smart chitosan biomaterial. For the first time, we used hydroxybutyl methacrylated chitosan (HBCMA), which possesses dual temperature- and photo-sensitive properties, to create microneedles. The DLP approach enabled a quick generation of HBCMA-based microneedles with a high resolution. The microneedles exhibited 4D properties with a change in needle dimensions upon exposure to temperature, which enhances resolution, sharpens needles, and improves mechanical strength. We demonstrated the ability of these microneedles to load, deliver, sustained release small molecular drugs and penetrate soft tissue. Overall, the HBCMA-based microneedles show promising potential in non-dermal drug delivery applications.

3D-printed and conventional provisional single crown fabrication on anterior implants: A randomized clinical trial

OBJECTIVES

The present study aims to compare provisional single crowns on anterior implants made using conventional PMMA and 3D-printed workflows. The study assessed the occurrence of failures, color variation, signs of early deterioration, operating time, and patients' satisfaction with the treatment through a randomized controlled trial.

METHODS

This study was conducted as a randomized controlled trial, following the SPIRIT and CONSORT guidelines. Patients were included in the study after meeting the eligibility criteria and were randomly assigned to one of two groups (conventional and 3D-printed). FDI criteria, visible plaque index (VPI), bleeding on probing (BOP), and color variation were considered as the primary outcomes. Operating time and patient satisfaction were also assessed as secondary outcomes. Fisher's exact test was performed to analyze the association between the primary and secondary outcomes and the study groups. Mann-Whitney test was used to compare the mean VAS satisfaction scores between the conventional PMMA and 3D-printed groups (STATA 14™, with an α = 0.05).

RESULTS

A total of 42 provisional single crowns (n = 21) were made for 33 patients. Only the fracture parameter (FDI) showed a statistically significant difference, with 3D-printed provisionals exhibiting higher rates of catastrophic failures compared to conventional ones (p = 0.05). Although the operating time for the 3D-printed group was shorter (p < 0.001), no statistical difference observed in patients' satisfaction regarding esthetics, phonetics, chewing, or comfort.

SIGNIFICANCE

3D-printed and conventional PMMA provisional single crowns showed comparable clinical performance, except for the observed fracture types. Although 3D-printed provisional restorations showed a shorter operating time, overall patients' satisfaction was not affected.

Accuracy of zirconia crown manufactured using stereolithography and digital light processing

OBJECTIVES

The aim of this study is to evaluate the accuracy of zirconia crowns fabricated using stereolithography (SLA) and digital light processing (DLP) and to compare their accuracy with those fabricated using the subtractive manufacturing (SM) method.

METHODS

A typodont model with a prepared maxillary first molar was scanned, and the anatomical contour crown was designed using dental computer-aided-design (CAD) software. The designed file in standard tessellation language (STL) format was used to fabricate 10 crowns per group. The crowns were manufactured using a dental milling machine (Datron D5; MLC group), SLA (CERAMAKER 900; SLAC group), and DLP (ZIPRO; DLPC group) printers. The fabricated crowns were scanned using a dental laboratory scanner and saved in three parts: the external, intaglio, and marginal surfaces. For accuracy assessment, these parts were superimposed to the reference file. Root mean square (RMS) values were evaluated using three-dimensional analysis software (Geomagic Control X). Statistical significance was evaluated using a nonparametric Kruskal-Wallis test (α = 0.05) and a post-hoc Mann-Whitney U test with Bonferroni correction (α = 0.016).

RESULTS

Trueness evaluation revealed the lowest RMS value in all areas in the MLC group, followed by that in the DLPC group. The precision evaluation revealed the lowest RMS value in all areas in the MLC group. Statistically significant differences were observed among the groups in the external, intaglio, and marginal surface (P < 0.05).

CONCLUSIONS

Although the restorations fabricated using SM revealed higher accuracy, the crowns manufactured using SLA and DLP methods were considered clinically acceptable.

CLINICAL SIGNIFICANCE

In the production of zirconia crowns, subtractive manufacturing continues to demonstrate significantly higher accuracy compared to additive manufacturing. However, crowns fabricated using the additive manufacturing method also demonstrated high accuracy.

Bilayer osteochondral graft in rabbit xenogeneic transplantation model comprising sintered 3D-printed bioceramic and human adipose-derived stem cells laden biohydrogel

Reconstruction of severe osteochondral defects in articular cartilage and subchondral trabecular bone remains a challenging problem. The well-integrated bilayer osteochondral graft design expects to be guided the chondrogenic and osteogenic differentiation for stem cells and provides a promising solution for osteochondral tissue repair in this study. The subchondral bone scaffold approach is based on the developed finer and denser 3D β-tricalcium phosphate (β-TCP) bioceramic scaffold process, which is made using a digital light processing (DLP) technology and the novel photocurable negative thermo-responsive (NTR) bioceramic slurry. Then, the concave-top disc sintered 3D-printed bioceramic incorporates the human adipose-derived stem cells (hADSCs) laden photo-cured hybrid biohydrogel (HG + 0.5AFnSi) comprised of hyaluronic acid methacryloyl (HAMA), gelatin methacryloyl (GelMA), and 0.5% (w/v) acrylate-functionalized nano-silica (AFnSi) crosslinker. The 3D β-TCP bioceramic compartment is used to provide essential mechanical support for cartilage regeneration in the long term and slow biodegradation. However, the apparent density and compressive strength of the 3D β-TCP bioceramics can be obtained for ~ 94.8% theoretical density and 11.38 ± 1.72 MPa, respectively. In addition, the in vivo results demonstrated that the hADSC + HG + 0.5AFnSi/3D β-TCP of the bilayer osteochondral graft showed a much better osteochondral defect repair outcome in a rabbit model. The other word, the subchondral bone scaffold of 3D β-TCP bioceramic could accelerate the bone formation and integration with the adjacent host cancellous tissue at 12 weeks after surgery. And then, a thicker cartilage layer with a smooth surface and uniformly aligned chondrocytes were observed by providing enough steady mechanical support of the 3D β-TCP bioceramic scaffold.

Effect of exposure energy dose on lateral resolution and flexural strength of three-dimensionally printed dental zirconia

PURPOSE

This study aims to evaluate the effects of exposure energy on the lateral resolution and mechanical strength of dental zirconia manufactured using digital light processing (DLP).

MATERIALS AND METHODS

A zirconia suspension and a custom top-down DLP printer were used for in-office manufacturing. The viscosity of the suspension and uniformity of the exposed light intensity were controlled. Based on the exposure energy dose delivered to each layer, the specimens were classified into three groups: low-energy (LE), medium-energy (ME), and high-energy (HE). For each energy group, a simplified molar cube was used to measure the widths of the outline (Xo and Yo) and isthmus (Xi and Yi), and a bar-shaped specimen of the sintered body was tested. A Kruskal-Wallis test for the lateral resolution and one-way analysis of variance for the mechanical strength were performed (α = .05).

RESULTS

The zirconia green bodies of the ME group showed better lateral resolution than those of the LE and HE groups (both P < .001). Regarding the flexural strength of the sintered bodies, the ME group had the highest mean value, whereas the LE group had the lowest mean value (both P < .05). The ME group exhibited fewer agglomerates than the LE group, with no distinctive interlayer pores or surface defects.

CONCLUSION

Based on these findings, the lateral resolution of the green body and flexural strength of the sintered body of dental zirconia could be affected by the exposure energy dose during DLP. The exposure energy should be optimized when fabricating DLP-based dental zirconia.

Effect of build angle, resin layer thickness and viscosity on the surface properties and microbial adhesion of denture bases manufactured using digital light processing

OBJECTIVES

To investigate differences in the surface properties and microbial adhesion of denture base resins for digital light processing (DLP) with varying resin layer thicknesses (LT), build angles (BA), and resin viscosities.

METHODS

Two denture base resins for DLP with different viscosities (high and low) were used to prepare disk specimens applying two manufacturing parameters: 1) LT (50 or 100 μm) and 2) BA (0-, 45-, and 90-degree). Surface roughness and contact angle values were measured on the test surfaces (n=10 per group). Streptococcus oralis and Candida albicans absorbance was measured to assess microorganism attachment (n=6 per group). A three-way analysis of variance (ANOVA) was conducted, considering the main effects and their interactions (viscosity, LT, and BA). Post-hoc multiple pairwise comparisons were performed. All data were analyzed at a level of significance (P) of 0.05.

RESULTS

LT and BA significantly affected the surface roughness and contact angle of the specimens, depending on resin viscosity (P<.001). Absorbance measurement showed no significant interaction between the three factors (P>.05). However, significant interactions were observed between viscosity and BA (P<.05) and between LT and BA (P<.05).

CONCLUSIONS

Regardless of the viscosity and LT, discs with a 0-degree BA showed the least roughness. High-viscosity specimens fabricated with a 0-degree BA had the lowest contact angle. Regardless of the LT and viscosity, discs with a 0-degree BA showed the lowest S. oralis attachment. Attachment of C. albicans was the least on the disk with 50 μm LT, irrespective of the viscosity.

CLINICAL SIGNIFICANCE

Clinicians should consider the effects of LT and BA on surface roughness, contact angle, and microbial adhesion of DLP-generated dentures, which can differ depending on resin viscosity. A 50 μm LT and 0-degree BA can be used with a high-viscosity resin to fabricate denture bases with less microbial adhesion.

Effect of layer thickness, build angle, and viscosity on the mechanical properties and manufacturing trueness of denture base resin for digital light processing

OBJECTIVES

To investigate effects of layer thickness, build angle, and viscosity on the mechanical properties and trueness of denture base resins used for digital light processing (DLP).

METHODS

Two denture base resins for DLP in different viscosity (high and low) were tested by using two manufacturing parameters:1) layer thickness (LT) (50- or 100-μm) and 2) build angle (BA) (0-, 45-, and 90-degree). disk- and bar-shaped specimens were used to evaluate hardness and flexural strength, respectively. Denture base specimens were used to examine trueness, and the deviation was calculated as the root mean square. Three-way analysis of variance (ANOVA) was conducted to determine the interaction among the three factors (viscosity, LT, and BA). Statistical significance was set at P < .05.

RESULTS

Effects of LT and BA on hardness differed according to viscosity, with significant interactions among three factors (P=.027). Regardless of LT or BA, the low-viscosity group had higher hardness than the high-viscosity group (P<.001). In terms of flexural strength, no significant interaction was detected between the factors (P=.212), however, the effects of LT and BA were significant (P=.003 and P<.001, respectively). Regarding trueness, a significant interaction was observed between viscosity and BA (P=.001). Low-viscosity group had higher trueness than high-viscosity group when the 45- and 90-degree BA were applied (P<.001).

CONCLUSIONS

LT and BA significantly affected the mechanical properties and trueness of the 3DP denture base, depending on the viscosity. For hardness and trueness, using low-viscosity resin and manufacturing with 50-μm LT and 45-degree BA are recommended.

CLINICAL SIGNIFICANCE

Resin viscosity affects the influence of LT and BA on the hardness, flexural strength, and trueness of DLP-generated denture bases. A 50-μm LT and 45-degree BA can be used with a low-viscosity resin to fabricate denture bases with higher hardness and trueness.

DLP printed hDPSC-loaded GelMA microsphere regenerates dental pulp and repairs spinal cord

Dental pulp regeneration is ideal for irreversible pulp or periapical lesions, and in situ stem cell therapy is one of the most effective therapies for pulp regeneration. In this study, we provided an atlas of the non-cultured and monolayer cultured dental pulp cells with single-cell RNA sequencing and analysis. Monolayer cultured dental pulp cells cluster more closely together than non-cultured dental pulp cells, suggesting a lower heterogeneous population with relatively consistent clusters and similar cellular composition. We successfully fabricated hDPSC-loaded microspheres by layer-by-layer photocuring with a digital light processing (DLP) printer. These hDPSC-loaded microspheres have improved stemness and higher multi-directional differentiation potential, including angiogenic, neurogenic, and odontogenic differentiation. The hDPSC-loaded microspheres could promote spinal cord regeneration in rat spinal cord injury models. Moreover, in heterotopic implantation tests on nude mice, CD31, MAP2, and DSPP immunofluorescence signals were observed, implying the formation of vascular, neural, and odontogenetic tissues. In situ experiments in minipigs demonstrated highly vascularized dental pulp and uniformly arranged odontoblast-like cells in root canals of incisors. In short, hDPSC-loaded microspheres can promote full-length dental pulp regeneration at the root canals' coronal, middle, and apical sections, particularly for blood vessels and nerve formation, which is a promising therapeutic strategy for necrotic pulp.

Tuning the fabrication of knotted reactors via 3D printing techniques and materials

Although three-dimensional (3D) printing technologies can customize a diverse range of devices, cross-3D printing technique/material comparisons aimed at optimizing the fabrication of analytical devices have been rare. In this study, we evaluated the surface features of the channels in knotted reactors (KRs) fabricated using fused deposition modeling (FDM) 3D printing [with poly(lactic acid) (PLA), polyamide, and acrylonitrile butadiene styrene filaments], and digital light processing and stereolithography 3D printing with photocurable resins. Also, their ability to retain Mn, Co, Ni, Cu, Zn, Cd, and Pb ions was evaluated to achieve the maximal sensitivities of these metal ions. After optimizing the techniques and materials for 3D printing of the KRs, the retention conditions, and the automatic analytical system, we observed good correlations (R > 0.9793) for the three 3D printing techniques in terms of the surface roughnesses of their channel sidewalls with respect to the signal intensities of their retained metal ions. The FDM 3D-printed PLA KR provided the best analytical performance, with the retention efficiencies of the tested metal ions all being greater than 73.9% and with the detection limits of the method ranging from 0.1 to 5.6 ng L^-1. We used this analytical method to perform analyses of the tested metal ions in several reference materials (CASS-4, SLEW-3, 1643f, and 2670a). Spike analyses of complicated real samples verified the reliability and applicability of this analytical method, highlighting the possibility of tuning 3D printing techniques and materials to optimize the fabrication of mission-oriented analytical devices.

Influence of fluorescent dopants on the vat photopolymerization of acrylate-based plastic scintillators for application in neutron/gamma pulse shape discrimination

Plastic scintillators, a class of solid-state materials used for radiation detection, were additively manufactured with vat photopolymerization. The photopolymer resins consisted of a primary dopant and a secondary dopant dissolved in a bisphenol A ethoxylate diacrylate-based matrix. The absorptive dopants significantly influence important print parameters, for example, secondary dopants decrease the light penetration depth by a factor > 12 ×. The primary dopant 2,5-diphenyloxazole had minimal impact on the printing process even when loaded at 25 % by mass of the resin. Working curve measurements, which relate energy dose to cure depth, were performed as a function of feature size to further assess the influence of dopants. Photopatterns smaller than 150 μm width had apparent increases in critical energy dose compared to larger photopatterns, while all resins maintained printed features in line gratings with 50 μm of separation. Printed scintillator monoliths were compared to scintillators cast by traditional molding, demonstrating that the layer-by-layer printing process does not decrease scintillation response. A maximum light output of 31 % of a benchmark plastic scintillator (EJ-200) and successful pulse shape discrimination were achieved with 20 % by mass 2,5-diphenyloxazole as the primary dopant and 0.1 % by mass 9,9-dimethyl-2,7-distyrylfluorene as the secondary dopant in printed scintillator samples.

3D bioprinting of corneal decellularized extracellular matrix: GelMA composite hydrogel for corneal stroma engineering

Millions of individuals across the world suffer from corneal stromal diseases that impair vision. Fortunately, three-dimensional (3D) bioprinting technology which has revolutionized the field of regenerative tissue engineering makes it feasible to create personalized corneas. In this study, an artificial cornea with a high degree of precision, smoothness, and programmable curvature was prepared by using digital light processing (DLP) 3D bioprinting in one piece with no support structure, and the construct was then confirmed by optical coherence tomography (OCT). On the basis of this approach, we developed a novel corneal decellularized extracellular matrix/gelatin methacryloyl (CECM-GelMA) bioink that can produce complex microenvironments with highly tunable mechanical properties while retaining high optical transmittance. Furthermore, the composite hydrogel was loaded with human corneal fibroblasts (hCFs), and in vitro experiments showed that the hydrogel maintained high cell viability and expressed core proteins. In vivo tests revealed that the hydrogel might promote epithelial regeneration, keep the matrix aligned, and restore clarity. This demonstrates how crucial a role CECM plays in establishing a favorable environment that encourages the transformation of cell function. Therefore, artificial corneas that can be rapidly customized have a huge potential in the development of in vitro corneal matrix analogs.

Matching mechanical heterogeneity of the native spinal cord augments axon infiltration in 3D-printed scaffolds

Scaffolds delivered to injured spinal cords to stimulate axon connectivity often match the anisotropy of native tissue using guidance cues along the rostral-caudal axis, but current approaches do not mimic the heterogeneity of host tissue mechanics. Although white and gray matter have different mechanical properties, it remains unclear whether tissue mechanics also vary along the length of the cord. Mechanical testing performed in this study indicates that bulk spinal cord mechanics do differ along anatomical level and that these differences are caused by variations in the ratio of white and gray matter. These results suggest that scaffolds recreating the heterogeneity of spinal cord tissue mechanics must account for the disparity between gray and white matter. Digital light processing (DLP) provides a means to mimic spinal cord topology, but has previously been limited to printing homogeneous mechanical properties. We describe a means to modify DLP to print scaffolds that mimic spinal cord mechanical heterogeneity caused by variation in the ratio of white and gray matter, which improves axon infiltration compared to controls exhibiting homogeneous mechanical properties. These results demonstrate that scaffolds matching the mechanical heterogeneity of white and gray matter improve the effectiveness of biomaterials transplanted within the injured spinal cord.

The comparison of the accuracy of temporary crowns fabricated with several 3D printers and a milling machine

PURPOSE

The purpose of this in vitro study was to compare the accuracy of various 3D printers and a milling machine.

MATERIALS AND METHODS

The die model was designed using CAD (Autodesk Inventor 2018 sp3). The 30 µm cement space was given to the die and the ideal crown of the mandibular left first molar was designed using CAD (ExoCAD). The crowns were produced using the milling machine (Imes-icore 250i) and the 3D printers (Zenith U, Zenith D, W11) and they were divided into four groups. In all groups, the interior of each crown was scanned (Identica blue) and superimposed (Geomagic Control X) with the previously designed die. The difference between the die and the actual crown was measured at specific points. The Kruskal-Wallis test, the Mann-Whitney test, and Bonferroni's method were performed with a statistical analysis software (P < .008 in inter-group comparison P < .001 in intra-group comparison).

RESULTS

In all groups, the center of the occlusal area and the anti-rotational dimple area showed significantly greater difference and the marginal area showed the smallest difference comparatively. The mean value of the difference in each area and the sum of the differences were higher in order of W11, Imes-icore 250i, Zenith D, and Zenith U.

CONCLUSION

The digital light processing (DLP) method shows higher accuracy compared to the sereolithography (SLA) method using the same resin material.

DLP-printed GelMA-PMAA scaffold for bone regeneration through endochondral ossification

Intramembranous ossification (IMO) and endochondral ossification (ECO) are two pathways of bone regeneration. The regeneration of most bone, such as limb bone, trunk bone, and skull base bone, mainly occurs in the form of endochondral ossification, which has also become one of the effective ways for bone tissue engineering. In this work, we prepared a well-structured and biocompatible methacrylated gelatin/polymethacrylic acid (GelMA/PMAA) hydrogel by digital light processing (DLP) printing technology, which could effectively chelate iron ions and continuously activate the hypoxia-inducible factor-1 alpha (HIF-1α) signaling pathway to promote the process of endochondral ossification and angiogenesis. The incorporation of PMAA endowed the hydrogel with remarkable viscoelasticity and high efficacy in chelation of iron ions, giving rise to the activation of HIF-1α signaling pathway, improving chondrogenic differentiation in the early stage, and facilitating vascularization in the later stage and bone remodeling. Therefore, the findings have significant implications on DLP printing technology of endochondral osteogenesis induced by the iron-chelating property of biological scaffold, which will provide an effective way in the development of novel bone regeneration.

Effect of build orientation and layer thickness on manufacturing accuracy, printing time, and material consumption of 3D printed complete denture bases

OBJECTIVES

To evaluate the influence of build orientation and layer thickness on manufacturing accuracy, material consumption, and printing time of complete denture (CD) bases fabricated using digital light processing (DLP).

METHODS

The CD base was designed on the basis of a standard maxillary edentulous model. Seventy CD bases were fabricated using a DLP 3D printer (Pro95, SprintRay, USA) and printable CD base material (DENTCA Denture Base II, Dentca, USA) at seven build orientations (0°, labial 45°, labial 90°, posterior 45°, posterior 90°, buccal 45°, and buccal 90°) and two types of layer thicknesses (50- and 100 μm) (n = 5). All test CD bases were digitalized and superimposed on the reference cast by section-based best-fit alignment. For evaluating manufacturing accuracy, deviation analysis was performed to compare the test data with the reference cast using the "3D Compare" in the 3D metrology software. The printing time and material consumption were calculated using slicing software and recorded, respectively. The two-way ANOVA test was used for accuracy evaluation, and the non-parametric test was used to evaluate printing time and material consumption (α = 0.05).

RESULTS

Statistically significant differences were found in the manufacturing accuracy (p < 0.001), printing time (p < 0.001), and material consumption (p < 0.001) among the build orientation groups. The labial 45° and labial 90° groups showed the best accuracy. The 90° build orientations required the least material consumption and longest printing time; the labial 45° group consumed the most printing materials; the 0° group required the shortest printing time to fabricate a CD base. Moreover, the layer thickness influenced the printing time (p < 0.001) rather than the accuracy (p = 0.560) and material consumption (p = 1.000).

CONCLUSIONS

When DLP was used to fabricate the CD bases, the build orientation influenced the manufacturing accuracy, material consumption, and printing time. However, the layer thickness only affected the printing time.

CLINICAL SIGNIFICANCE

This study suggests that optimizing the build orientation can improve the manufacturing accuracy and reduce the material consumption and printing time of a DLP-printed CD base. The fast-printing setting (100 μm layer thickness) can reduce the printing time without compromising the manufacturing accuracy of the CD base.

Ink Material Selection and Optical Design Considerations in DLP 3D Printing

Digital light processing (DLP) 3D printing has become a powerful manufacturing tool for the fast fabrication of complex functional structures. The rapid progress in DLP printing has been linked to research on optical design factors and ink selection. This critical review highlights the main challenges in the DLP printing of photopolymerizable inks. The kinetics equations of photopolymerization reaction in a DLP printer are solved, and the dependence of curing depth on the process optical parameters and ink chemical properties are explained. Developments in DLP platform design and ink selection are summarized, and the roles of monomer structure and molecular weight on DLP printing resolution are shown by experimental data. A detailed guideline is presented to help engineers and scientists to select inks and optical parameters for fabricating functional structures for multi-material and 4D printing applications.

An In Vitro Evaluation of the Effect of 3D Printing Orientation on the Accuracy of Implant Surgical Templates Fabricated By Desktop Printer

PURPOSE

To evaluate the effect of different 3D printing orientations on internal and seating accuracy of implant surgical templates fabricated by a digital light processing (DLP) printer.

MATERIALS AND METHODS

A single maxillary model with a missing central incisor was used to design a surgical template for single implant placement. According to the printing orientation, three surgical template groups were included in the study: horizontal (H), angled (A) and vertical (V) (n = 10). For the H group, the templates were produced parallel to the printing platform, while for the V group, the templates were perpendicular to the platform. The A group templates had a 45° angle orientation to the platform. Each template was scanned at the fitting surface and after seating on the master model. The internal accuracy involved measuring the trueness and precision of the internal surface, while for the seating accuracy, the vertical discrepancy after seating the template was measured. To determine the difference among the groups, ANOVA test was applied followed by Tukey post hoc tests (α = 0.05).

RESULTS

The H group had the lowest internal surface inaccuracy (trueness = 100.7 μm; precision = 69.1 μm) followed by A (trueness = 114.0 μm; precision = 77.3 μm) and V (trueness = 120.3 μm; precision = 82.4 μm) groups, respectively (p < 0.001). Similarly, the H group had the most superior seating accuracy (543.8 μm) followed by A group (1006.0 μm) and V group (1278.0 μm), respectively (p < 0.001).

CONCLUSIONS

The orientation of 3D printing of implant surgical templates fabricated by the DLP desktop printer influenced the accuracy of the templates. The horizontally printed templates consistently exhibited superior accuracy. To reduce deviation of implant placement, it is recommended to print the surgical templates with their largest dimension parallel to the printing platform.

Physical and biological implications of accelerated aging on stereolithographic additive-manufactured zirconia for dental implant abutment

PURPOSE

This study aimed to comparatively investigate the effects of accelerated aging on the physical and biological features of zirconia manufactured by digital light processing (DLP) and conventional subtractive manufacturing (SM) with similar composition.

METHODS

Both the DLP- and SM-fabricated zirconia samples (7 mm × 7.5 mm × 1.5 mm) were grouped according to aging (134 °C, 0.2 MPa, 100% humidity) times, including 0 h, 5 h, and 10 h. Phase assemblage and surface topography of zirconia manufactured by different technologies were evaluated before and after aging. The biological effects of zirconia on human gingival fibroblast (HGF) cell events, including cell viability, proliferation, morphology and adhesion, were also evaluated by live/dead viability assay, cck-8 assay, scanning electron microscopy and confocal laser scanning microscopy respectively.

RESULTS

The DLP-fabricated zirconia showed a higher initial cubic phase content and rate of phase transformation than the SM-fabricated zirconia. Among the different aging time-based groups, the 5 h-aged group exhibited significantly lower sub-micron scale surface roughness compared with the other groups. Aging did not significantly alter cellular behavior in any zirconia type, except for minor changes in adhesive cell numbers recorded in an aging time/culturing time-dependent manner. In addition to small differences in cell alignment patterns and overall cell morphology, the two zirconia types presented comparable biological performance before and after aging.

CONCLUSION

Although the microstructure and surface characteristics of DLP-fabricated zirconia can be affected by autoclave aging, this newly manufactured zirconia is likely to maintain desirable long-term biocompatibility as an implant abutment material.

Effect of phytochemical-filled microcapsules with antifungal activity on material properties and dimensional accuracy of denture base resin for three-dimensional printing

BACKGROUND

Studies on the material properties and dimensional accuracy of three-dimensionally (3D) printed denture base containing microcapsules with antifungal phytochemicals are lacking.

METHODS

Two types of phytochemicals (phytoncide A and B) with antifungal activity were microencapsulated. The 3D-printed denture base specimens with minimum and maximum effective concentrations of microcapsules (6 and 8 wt% for phytoncide A; 15 and 25 wt% for phytoncide B) were prepared. The morphological changes of C. albicans on 3D-printed denture base with microcapsules was microscopically observed. The degree of conversion of 3D-printed denture base with microcapsules investigated. The microhardness and flexural strength values were also measured to evaluate the mechanical properties of 3D-printed denture bases. The dimensional accuracy (trueness) of the specimens with microcapsules was measured as root-mean-square values (RMS) for the whole, upper, and side surfaces of the specimens as well as their total height. For the degree of conversion, microhardness, and flexural strength values, the Kruskal-Wallis analysis and a post-hoc comparison using Mann-Whitney U test was performed. For the analysis of trueness (RMS), the one-way analysis of variance and a post-hoc comparison using Tukey's method was conducted (α = 0.05).

RESULTS

At both maximum and minimum effective concentrations of microcapsules, cell surface disruption or membrane breakdown of fungal cells were observed in the specimens. The groups with microcapsules (both phytoncide A- and B-filled) showed significantly lower microhardness and elastic modulus values than the control group (all, P = 0.001). For the trueness, all the RMS values of the whole, upper, and side surfaces of the specimens with microcapsules were less than 100 µm, although significantly higher than those without (all, P = 0.001). The mean flexural strength values of the groups with phytoncide A-filled microcapsule were higher than 65 MPa, not statistically different from that of the control group (all, P > 0.05). However, the groups with phytoncide B-filled microcapsules showed significantly lower values than the control (all, P = 0.001).

CONCLUSIONS

Within the limitations of this in-vitro study, the 3D-printed denture base containing 6 wt% of phytoncide A-filled microcapsules was clinically acceptable in terms of antifungal activity, dimensional accuracy, and flexural strength.

Light-based 3D bioprinting of bone tissue scaffolds with tunable mechanical properties and architecture from photocurable silk fibroin

Three-dimensional (3D) bioprinting based on digital light processing (DLP) offers unique opportunities to prepare scaffolds that mimic the architecture and biomechanical properties of human tissues. Limited availability of biocompatible and biodegradable bioinks amenable for DLP-bioprinting is an impediment in this field. This study presents a bioink prepared from silk fibroin (SF) tailored for DLP bioprinting. Photocurable methacrylated-SF (SF-MA) was synthesized with 67.3% of methacrylation. Physical characterization of rheological and mechanical properties revealed that the 3D printed hydrogels of SF-MA (spanning from 10 to 25 wt%) exhibit bone tissue-like viscoelastic behavior and compressive modulus ranging from ≈12 kPa to ≈96 kPa. The gels exhibited favorable degradation (≈48 to 91% in 21 days). This SF-MA bioink afforded the printing of complex structures, with high precision. Pre-osteoblasts were successfully encapsulated in 3D bioprinted SF-MA hydrogels with high viability. 15% SF-MA DLP bioprinted hydrogels efficiently supported cell proliferation with favorable cell morphology and cytoskeletal organization. A progressive increase in cell-mediated calcium deposition up to 14 days confirmed the ability of the gels to drive osteogenesis, which was further augmented by soluble induction factors. This work demonstrates the potential of silk fibroin-derived bioinks for DLP-based 3D bioprinting of scaffolds for tissue engineering.

Nano-Hydroxyapatite Bone Scaffolds with Different Porous Structures Processed by Digital Light Processing 3D Printing

The morphologies and structures of the scaffold have a significant influence on their mechanical and biological properties. In this work, different types of porous structures: Triply periodic minimal surface-Schwarz primitive (P), body-centered cubic, and cubic pore-shaped (CPS) hydroxyapatite scaffolds with ~70% porosity were fabricated through digital light processing (DLP) 3D printing technology. The compressive properties and in vitro cell evaluations such as cell proliferation and attachment morphology of these scaffolds were systematically compared. The results showed that the CPS scaffolds exhibited the highest compressive strength (~22.5 MPa) and modulus (~400 MPa). In addition, the CPS scaffolds also performed the most active cell metabolisms as compared to other two structures, which may account for the larger pore size and smaller curvature of the substrate. This study provides a general guidance for the fabrication and selection of porous bone scaffolds processed by DLP 3D printing.

Three-dimensional printing of gyroid-structured composite bioceramic scaffolds with tuneable degradability

Customisation of bioactivity and degradability of porous bioceramic scaffolds is a formidable challenge in the field of regenerative medicine. In this study, we developed gyroid-structured ternary composite scaffolds (biphasic calcium phosphate (BCP) and 45S5 bioglass® (BG)) using digital light processing 3D printing technology based on material and structural design. Additionally, the mechanical strength, bioactivity, degradability, and biocompatibility of the composite ceramic scaffolds were evaluated. The results revealed that BG reacted with BCP to generate major active crystalline phases of CaSiO₃ and Na₃Ca₆(PO₄)₅. These active crystalline phases accelerated the exchange rate of Si⁴⁺, Ca²⁺, and PO₄^3- with HCO^3- in simulated body fluids and resulted in the rapid formation of carbonated hydroxyapatite (CHA), analogous to the formation of natural bone tissue. Interestingly, the precipitated CHA showed petal- and needle-like morphologies, which provided a large surface area to promote cell adhesion and proliferation. Furthermore, an increase in the BG content improved the degradability of ternary composite scaffolds after soaking in Tris-HCl solution. The tuneable degradability increased by three times at 30 wt% BG and sharply increased by 6.8 times at 40 wt% BG. This study provides a promising strategy to design scaffolds with improved bioactivity and tuneable degradability to assist a diverse population suffering from orthopedic conditions.

Adjusting the accuracy of PEGDA-GelMA vascular network by dark pigments via digital light processing printing

Vascularization is one of the most important factors greatly influencing scaffold regeneration. In this study, a precise network of hollow vessels was printed by digital light processing (DLP) with poly(ethylene glycol) diacrylate (PEGDA)/gelatin-methacryloyl (GelMA), and dark pigmentation absorbers were added to ensure printing accuracy. First, the compound bio-inks of the PEGDA-GelMA hydrogel were prepared for direct vascular printing, and a high-precision DLP system was established. Second, the printing effects of three dark absorbers, namely, nigrosin, brilliant black, and brilliant blue, on the x-, y-, and z-axes were studied. By printing models with different densities, it was determined that 0.2% nigrosin, 0.1% brilliant black, and 0.3% brilliant blue had better effects on the x- and y-axes accuracy, and the absorbance of the absorbers played a decisive role in adjusting the accuracy. Additionally, to solve the problem of uneven curing on the upper and lower surfaces caused by the addition of an absorber with high absorbance, a model of the difference in curing width between the upper and lower surfaces of a unit-layer slice based on high-absorbance absorbers was established, and the reference value for the slice thickness was calculated. Third, the biological and mechanical properties of the bio-inks were verified with scanning electron microscopy and Fourier transform infrared, and by tensile, swelling, degradation, and cytotoxicity tests on different concentrations of PEGDA-GelMA hydrogel and absorbers. The results showed that 30% PEGDA-7% GelMA/0.1% brilliant black was the optimal preparation to print a hollow vascular network. The error of the printing tube wall and cavity was between 1% and 3%, which demonstrates the high precision of the method. Human umbilical vein endothelial cells were planted in the lumen, and the survival rate achieved 107% on the seventh day, demonstrating the good biocompatibility of the composite hydrogel.

Development of hierarchical porous bioceramic scaffolds with controlled micro/nano surface topography for accelerating bone regeneration

Mimicking hierarchical porous architecture of bone has been considered as a valid approach to promote bone regeneration. In this study, hierarchical porous β-tricalcium phosphate (β-TCP) scaffolds were constructed by combining digital light processing (DLP) printing technique and in situ growth crystal process. Macro/micro hierarchical scaffolds with designed macro pores for facilitating the ingrowth of bone tissue were fabricated by DLP printing. Three types of micro/nano surface topography were obtained by in situ growth crystal process to regulate stem cells behavior. The attachment and proliferation of rat bone marrow mesenchymal stem cells (rBMSCs) were strongly dependent on the surface roughness and the specific surface area. The micro/nano surface topography distinctly facilitated the differentiation of rBMSCs by targeting MAPK, STAT and AKT signaling pathways, in which the sodium hydroxide treatment group showed the highest promoting effect. Furthermore, in vivo results of skull defect repair model of rats indicated that hierarchical scaffolds with micro/nano topographies exhibited appealing bone regeneration capacity. The hierarchical porous bioceramic scaffolds constructed by integrating structural design and physical stimulation of the external surface topography have great potential for rapid bone repair via modulation of microenvironmental regulatory pathways at the bone defect site.

Fabrication and biological evaluation of porous β-TCP bioceramics produced using digital light processing

Beta-tricalcium phosphate (β-TCP) refers to one ideal bone repair substance with good biocompatibility and osteogenicity. A digital light processing (DLP)-system used in this study creates bioceramic green part by stacking up layers of photocurable tricalcium phosphate-filled slurry with various β-TCP weight fractions. Results show that the sintering shrinkage is anisotropic and the shrinkage vertically reaches over that horizontally. The obtained porous β-TCP parts have both macroporous outer structure and microporous inner structure, the macropore size is 400-600 μm and the micropore size is 500-1500 nm. The mechanical tests show that the porous β-TCP bioceramic's compressive strength reaches 16.53 MPa. The cell culture confirmed that the porous β-TCP bioceramic is capable of achieving the effective attaching, growing, and proliferating pertained to mouse osteoblast cells. This study identified considerable blood vessels and significant ectopic bone forming obviously based on the histologically-related assessment when implanting to rabbit femoral condyle deficiency for 3 months. Thus, under high bioactive property and osteoinductivity, and large precision and mechanical strength that can be adjusted, the DLP printed porous β-TCP ceramics is capable of being promising for special uses of bones repairing.

High-resolution lithographic biofabrication of hydrogels with complex microchannels from low-temperature-soluble gelatin bioresins

Biofabrication via light-based 3D printing offers superior resolution and ability to generate free-form architectures, compared to conventional extrusion technologies. While extensive efforts in the design of new hydrogel bioinks lead to major advances in extrusion methods, the accessibility of lithographic bioprinting is still hampered by a limited choice of cell-friendly resins. Herein, we report the development of a novel set of photoresponsive bioresins derived from ichthyic-origin gelatin, designed to print high-resolution hydrogel constructs with embedded convoluted networks of vessel-mimetic channels. Unlike mammalian gelatins, these materials display thermal stability as pre-hydrogel solutions at room temperature, ideal for bioprinting on any easily-accessible lithographic printer. Norbornene- and methacryloyl-modification of the gelatin backbone, combined with a ruthenium-based visible light photoinitiator and new coccine as a cytocompatible photoabsorber, allowed to print structures resolving single-pixel features (∼50 ​μm) with high shape fidelity, even when using low stiffness gels, ideal for cell encapsulation (1-2 ​kPa). Moreover, aqueous two-phase emulsion bioresins allowed to modulate the permeability of the printed hydrogel bulk. Bioprinted mesenchymal stromal cells displayed high functionality over a month of culture, and underwent multi-lineage differentiation while colonizing the bioresin bulk with tissue-specific neo-deposited extracellular matrix. Importantly, printed hydrogels embedding complex channels with perfusable lumen (diameter <200 ​μm) were obtained, replicating anatomical 3D networks with out-of-plane branches (i.e. brain vessels) that cannot otherwise be reproduced by extrusion bioprinting. This versatile bioresin platform opens new avenues for the widespread adoption of lithographic biofabrication, and for bioprinting complex channel-laden constructs with envisioned applications in regenerative medicine and hydrogel-based organ-on-a-chip devices.

Evaluating the accuracy (trueness and precision) of interim crowns manufactured using digital light processing according to post-curing time: An in vitro study

PURPOSE

This study aimed to compare the accuracy (trueness and precision) of interim crowns fabricated using DLP (digital light processing) according to post-curing time.

MATERIALS AND METHODS

A virtual stone study die of the upper right first molar was created using a dental laboratory scanner. After designing interim crowns on the virtual study die and saving them as Standard Triangulated Language files, 30 interim crowns were fabricated using a DLP-type 3D printer. Additively manufactured interim crowns were post-cured using three different time conditions-10-minute post-curing interim crown (10-MPCI), 20-minute post-curing interim crown (20-MPCI), and 30-minute post-curing interim crown (30-MPCI) (n = 10 per group). The scan data of the external and intaglio surfaces were overlapped with reference crown data, and trueness was measured using the best-fit alignment method. In the external and intaglio surface groups (n = 45 per group), precision was measured using a combination formula exclusive to scan data (₁₀C₂). Significant differences in accuracy (trueness and precision) data were analyzed using the Kruskal-Wallis H test, and post hoc analysis was performed using the Mann-Whitney U test with Bonferroni correction (α=.05).

RESULTS

In the 10-MPCI, 20-MPCI, and 30-MPCI groups, there was a statistically significant difference in the accuracy of the external and intaglio surfaces (P <.05). On the external and intaglio surfaces, the root mean square (RMS) values of trueness and precision were the lowest in the 10-MPCI group.

CONCLUSION

Interim crowns with 10-minute post-curing showed high accuracy.

Effect of rinsing time on the accuracy of interim crowns fabricated by digital light processing: An in vitro study

PURPOSE

This study was to evaluate the effect of rinsing time on the accuracy of interim crowns fabricated by digital light processing.

MATERIALS AND METHODS

The maxillary right first molar master die was duplicated using a silicone material, while a study die was produced using epoxy resin. Scans of the epoxy resin die were used in combination with CAD software to design a maxillary right first molar interim crown. Based on this design, 24 interim crowns were fabricated with digital light processing. This study examined the trueness and precision of products that were processed with one of the three different postprocessing rinsing times (1 min, 5 min, and 10 min). Trueness was measured by superimposing reference data with scanned data from external, intaglio, and marginal surfaces. Precision was measured by superimposing the scan data within the group. The trueness and precision data were analyzed using Kruskal-Wallis, nonparametric, and post-hoc tests, and were compared using a Mann-Whitney U test with Bonferroni correction (α=.05).

RESULTS

The trueness of the external and intaglio surfaces of crowns varied significantly among the different rinsing times (P =.004, P =.003), but there was no statistically significant difference in terms of trueness measurements of the marginal surfaces (P =.605). In terms of precision, statistically significant differences were found among the external, intaglio, and marginal surfaces (P =.001).

CONCLUSION

Interim crowns rinsed for 10 minutes showed high accuracy.

Elution behavior of a 3D-printed, milled and conventional resin-based occlusal splint material

OBJECTIVE

The elution of unpolymerized (co-)monomers and additives from methacrylic resin-based materials like polymethyl methacrylate (PMMA) can cause adverse side effects, such as mutagenicity, teratogenicity, genotoxicity, cytotoxicity and estrogenic activity. The aim of this study was to quantify the release and the cytotoxicity of residual (co-)monomers and additives from PMMA-based splint materials under consideration of real splint sizes. Three different materials used for additive (3D printing), subtractive (milling) and conventional (powder and liquid) manufacturing were examined.

METHODS

The splint materials SHERAprint-ortho plus (additive), SHERAeco-disc PM20 (subtractive) and SHERAORTHOMER (conventional) were analysed. 16 (n = 4) sample discs of each material (6 mm diameter and 2 mm height) were polished on the circular and one cross-section area and then eluted in both distilled water and methanol. The discs were incubated at 37 °C for 24 h or 72 h and subsequently analysed by gas chromatography/mass spectrometry (GC/MS) for specifying and quantifying released compounds. XTT-based cell viability assays with human gingival fibroblasts (HGFs) were performed for Tetrahydrofurfuryl methacrylate (THFMA), 1,4-Butylene glycol dimethacrylate (BDDMA) and Tripropylenglycol diacrylate (TPGDA). In order to project the disc size to actual splint sizes in a worst-case scenario, lower and upper jaw occlusal splints were designed and volumes and surfaces were measured.

RESULTS

For SHERAeco-disc PM20 and for SHERAORTHOMER no elution was determined in water. SHERAprint-ortho plus eluted the highest THFMA concentration of 7.47 μmol/l ±2,77 μmol/l after 72 h in water. Six (co-)monomers and five additives were detected in the methanol eluates of all three materials tested. The XTT-based cell viability assays resulted in a EC₅₀ of 3006 ± 408 μmol/l for THFMA, 2569.5 ± 308 μmol/l for BDDMA and 596.7 ± 88 μmol/l for TPGDA.

SIGNIFICANCE

With the solvent methanol, released components from the investigated splint materials exceeded cytotoxic concentrations in HGFs calculated for a worst-case scenario in splint size. In the water eluates only the methacrylate THFMA could be determined from SHERAprint-ortho plus in concentrations below cytotoxic levels in HGFs.

Digital light processing in a hybrid atomic force microscope: In Situ, nanoscale characterization of the printing process

Stereolithography (SLA) and digital light processing (DLP) are powerful additive manufacturing techniques that address a wide range of applications including regenerative medicine, prototyping, and manufacturing. Unfortunately, these printing processes introduce micrometer-scale anisotropic inhomogeneities due to the resin absorptivity, diffusivity, reaction kinetics, and swelling during the requisite photoexposure. Previously, it has not been possible to characterize high-resolution mechanical heterogeneity as it develops during the printing process. By combining DLP 3D printing with atomic force microscopy in a hybrid instrument, heterogeneity of a single, in situ printed voxel is characterized. Here, we describe the instrument and demonstrate three modalities for characterizing voxels during and after printing. Sensing Modality I maps the mechanical properties of just-printed, resin-immersed voxels, providing the framework to study the relationships between voxel sizes, print exposure parameters, and voxel-voxel interactions. Modality II captures the nanometric, in situ working curve and is the first demonstration of in situ cure depth measurement. Modality III dynamically senses local rheological changes in the resin by monitoring the viscoelastic damping coefficient of the resin during patterning. Overall, this instrument equips researchers with a tool to develop rich insight into resin development, process optimization, and fundamental printing limits.

Folding photopolymerized origami sheets by post-curing

The paper presents a novel manufacturing approach to fabricate origami based on 3D printing utilizing digital light processing. Specifically, we propose to leave part of the model uncured during the printing step, and then cure it in the post-processing step to set the shape in a folded configuration. While the cured regions in the first step try to regain their unfolded shape, the regions cured in the second step attempt to keep their folded shape. As a result, the final shape is obtained when both regions’ stresses reach equilibrium. Finite element analysis is performed in ANSYS to obtain the stress distribution on common hinge designs, demonstrating that the square-hinge has a lower maximum principal stress than elliptical and triangle hinges. Based on the square-hinge and rectangular cavity, two variables—the hinge width and the cavity height—are selected as principal variables to construct an empirical model with the final folding angle. In the end, experimental verification shows that the developed method is valid and reliable to realize the proposed deformation and 3D development of 2D hinges.

In-hospital professional production of patient-specific 3D-printed devices for hand and wrist rehabilitation

The reported use of 3D printing in hand and wrist rehabilitation has been mostly limited to feasibility studies and case series so far. Some of the reasons are the lack of purpose-built scanning applications, complicated digital design software, and lengthy and error-prone printing processes. We propose a multidisciplinary workflow for in-hospital mass production of patient-specific 3D-printed devices for hand and wrist rehabilitation.

Accuracy of 3D printed polymers intended for models and surgical guides printed with two different 3D printers

The purpose of the study was to evaluate the accuracy: trueness and precision of photopolymers used for dental models and surgical guides printed with two different digital light processing (DLP) printers. Forty specimens of four materials; E-dentstone^®, E-shell^®, NextDent™ Model, NextDent™ SG, and two designs; models A and B (n=5), were manufactured (DDDP, EvoDent). Trueness was evaluated by comparing values for 26 parameters with the CAD models' reference values and precision through standard deviation. The trueness and precision were higher for linear than for angle parameters. X- and Y-axes showed higher trueness than Z-axis and model B higher trueness than model A. The conclusions are; the accuracy is dependent on the design of the object. The linear precision appears to be high. The highest trueness was observed for a surgical guide polymer (NextDent™ SG). The definition of clinically relevant accuracy and acceptable production tolerance should be evaluated in future studies.

Anti-biofilm multi drug-loaded 3D printed hearing aids

Over 5% of the world's population has disabling hearing loss, which affects approximately one third of individuals over 65 years. Hearing aids are commonly used in this population group, but prolonged use of these devices may cause ear infections. We describe for the first time, the use of 3D printing to fabricate hearing aids loaded with two antibiotics, ciprofloxacin and fluocinolone acetonide. Digital light processing 3D printing was employed to manufacture hearing aids from two polymer resins, ENG hard and Flexible. The inclusion of the antibiotics did not affect the mechanical properties of the hearing aids. All multi-drug-loaded devices exhibited a hydrophilic surface, excellent blood compatibility and anti-biofilm activity against P. aeruginosa and S. aureus. Hearing aids loaded with ciprofloxacin (6% w/w) and fluocinolone acetonide (0.5% w/w) sustained drug release for more than two weeks and inhibited biofilm formation on the surface of the devices and bacteria growth in the surrounding medium. In summary, this work highlights the potential of vat photopolymerization 3D printing as a versatile manufacturing approach to fabricate high-fidelity patient-specific medical devices with anti-bacterial properties.

Digital Light Processing Based Three-dimensional Printing for Medical Applications

An additive manufacturing technology based on projection light, digital light processing (DLP), three-dimensional (3D) printing, has been widely applied in the field of medical products production and development. The precision projection light, reflected by a digital micromirror device of million pixels instead of one focused point, provides this technology both printing accuracy and printing speed. In particular, this printing technology provides a relatively mild condition to cells due to its non-direct contact. This review introduces the DLP-based 3D printing technology and its applications in medicine, including precise medical devices, functionalized artificial tissues, and specific drug delivery systems. The products are particularly discussed for their significance in medicine. This review indicates that the DLP-based 3D printing technology provides a potential tool for biological research and clinical medicine. While, it is faced to the challenges of scale-up of its usage and waiting period of regulatory approval.

Zirconia toughened hydroxyapatite biocomposite formed by a DLP 3D printing process for potential bone tissue engineering

The construction of ceramic components with UV curing is a developing trend by an additive manufacturing (AM) technology, due to the excellent advantages of high precision selective fixation and rapid prototyping, the application of this technology to bone defect repair had become one of the hotspots of research. Hydroxyapatite (HAP) is one of the most popular calcium phosphate biomaterials, which is very close to the main ingredient of human bones. Thus, hydroxyapatite biomaterials are popular as bone graft materials. In summary, the preparation of HAP bioceramics by a 3D printing of digital light processing (DLP) is a promising work. However, the preparation of HAP hybrid suspensions with high solid loading and good fluidity that can be printed by DLP encountered some challenges. Therefore, the purpose of this work is to improve and develop a novel UV-curing suspension with a high solids loading, which the suspension with the hydrodynamic properties and stability are suitable for DLP printer, in order to compensate for the brittleness of HAP ceramics itself to a certain extent, a low amount of zirconia was added in the suspension as an additive to fabricate a zirconia toughened HAP bioceramic composite by a DLP of 3D printing. In this work, the HAP powder was pre-modified by two organic modifiers to improve the compatibility in the acrylic resin system, and the addition of the castor oil phosphate further reduced the shear stress of the suspension to ensure strong liquidity. The UV suspension with 60 wt% powder particle loading had a minimum viscosity of 7495 mPa·s at 30 rpm, which was vacuum sintered at 1100 °C, 1200 °C, and 1250 °C, respectively. The composite ceramics (with 6 wt% ZrO₂) at 1200 °C had a relative density of 90.7%, while the sintered samples at 1250 °C had stronger tensile strength and bending strength. The toughening effect of zirconia incorporation on HAP ceramics was also confirmed by the change of tensile modulus and bending modulus, whereas the corresponding mechanical properties were also significantly enhanced.

Influence of the three-dimensional printing technique and printing layer thickness on model accuracy

OBJECTIVE

The accuracies of three-dimensional (3D) printed dental models using various digital light processing (DLP) and stereolithography (SLA) printers at different thicknesses were compared.

MATERIALS AND METHODS

Based on digital dental models (originally digitized using R700; 3Shape, Copenhagen, Denmark), physical dental models were printed using three types of DLP printers: (1) EvoDent (UnionTec, Shanghai, China) with layer thicknesses of 50 μm and 100 μm; (2) EncaDent (Encashape, WuXi, China) with layer thicknesses of 20, 30, 50 and 100 μm; (3) Vida HD (Envisioned, Dearborn, MI, USA) with layer thicknesses of 50 and 100 μm. Models with the SLA printer Form 2 (Formlabs, Somerville, MA, USA) were printed with layer thicknesses of 25, 50 and 100 μm. All 22 printed models were converted to digital dental models using a D2000 model scanner (3 Shape, Copenhagen, Denmark) and compared three-dimensionally to the source files using Geomagic Qualify 12.0 (3D Systems, Rock Hill, SC, USA).

RESULTS

The printing accuracy of all printers was higher at 50 μm. When the layer thickness was set at 100 μm, the printing speed and printing accuracy of DLP printer were both superior to those of the SLA printer. In all groups, the EvoDent 50 μm group had the highest consistency with the source files (mean absolute deviation of 0.0233 mm in the maxilla and 0.0301 mm in the mandible). While the accuracy of Form 2 100 μm group was the lowest (mean absolute deviation of 0.0511 mm in the maxilla and 0.0570 mm in the mandible).

CONCLUSION

For the 3D printers studied, 50 μm was the optimum layer thickness for DLP technology, and the printing accuracy using SLA technology increased with decreasing layer thickness. The DLP technology also had higher printing accuracy at a layer thickness of 100 μm. EvoDent 50 μm had the highest and Form 2 100 μm the lowest printing accuracy.

Comparing accuracy of denture bases fabricated by injection molding, CAD/CAM milling, and rapid prototyping method

PURPOSE

The accuracy of denture bases was compared among injection molding, milling, and rapid prototyping (RP) fabricating method.

MATERIALS AND METHODS

The maxillary edentulous master cast was fabricated and round shaped four notches were formed. The cast was duplicated to ten casts and scanned. In the injection molding method, designed denture bases were milled from a wax block and fabricated using SR Ivocap injection system. Denture bases were milled from a pre-polymerized block in the milling method. In the RP method, denture bases were printed and post-cured. The intaglio surface of the base was scanned and surface matching software was used to measure inaccuracy. Measurements were performed between four notches and two points in the mid-palatal suture to evaluate inaccuracy. The palatine rugae resolution was evaluated. One-way analysis of variance was used for statistical analysis at α=.05.

RESULTS

No statistically significant differences in distances among four notches (P>.05). The accuracy of the injection molding method was lower than those of the other methods in two points of the mid-palatal suture significantly (P<.05). The degree of palatine rugae resolution was significantly higher in the injection molding method than that in other methods (P<.05).

CONCLUSION

The overall accuracy of the denture base is higher in milling and RP method than the injection molding method. The degree of fine reproducibility is higher in the injection molding method than the milling or RP method.

Direct 3D printing of monolithic ion exchange adsorbers

Monolithic adsorbers with anion exchange (AEX) properties have been 3D printed in an easy one-step process, i.e. not requiring post-functionalization to introduce the AEX ligands. The adsorber, 3D printed using a commercial digital light processing (DLP) printer, was obtained by copolymerisation of a bifunctional monomer bearing a positively charged quaternary amine as well as an acrylate group, with the biocompatible crosslinker polyethylene glycol diacrylate (PEGDA). To increase the surface area, polyethylene glycol was introduced into the material formulation as pore forming agent. The influence of photoinitiator (Omnirad 819) and photoabsorber (Reactive Orange 16, RO16) concentration was investigated in order to optimize printing resolution, allowing to reliably 3D print features as small as 200 μm and of highly complex Schoen Gyroids. Protein binding was measured on AEX adsorbers with a range of ligand densities (0.00, 2.03, 2.60 and 3.18 mmol/mL) using bovine serum albumin (BSA) and c-phycocyanin (CPC) as model proteins. The highest equilibrium binding capacity was found for the material presenting the lowest ligand density analysed (2.03 mmol/mL), adsorbing 73.7 ± 5.9 mg/mL and 38.0 ± 2.2 mg/mL of BSA and CPC, respectively. This novel 3D printed material displayed binding capacities in par or even higher than commercially available chromatographic resins. We expect that the herein presented approach of using bifunctional monomers, bearing commonly used chromatography ligands, will help overcome the material limitations currently refraining 3D printing applications in separation sciences.

Evaluation of the marginal and internal fit of a single crown fabricated based on a three-dimensional printed model

PURPOSE

To evaluate the fit of a crown produced based on a 3D printed model and to investigate its clinical applicability.

MATERIALS AND METHODS

A master die was fabricated with epoxy. Stone dies were fabricated from conventional impressions (Conventional stone die group: CS, n=10). Digital virtual dies were fabricated by making digital impressions (Digital Virtual die group: VD, n=10). 3D data obtained from the digital impression was used to fabricate 3D printed models (DLP die group: DD, n=10, PolyJet die group: PD, n=10). A total of 40 crowns were fabricated with a milling machine, based on CS, VD, DD and PD. The inner surface of all crowns was superimposed with the master die files by the “Best-fit alignment” method using the analysis software. One-way and 2-way ANOVA were performed to identify significant differences among the groups and areas and their interactive effects (α=.05). Tukey's HSD was used for post-hoc analysis.

RESULTS

One-way ANOVA results revealed a significantly higher RMS value in the 3D printed models (DD and PD) than in the CS and DV. The RMS values of PD were the largest among the four groups. Statistically significant differences among groups (P<.001) and between areas (P<.001) were further revealed by 2-way ANOVA.

CONCLUSION

Although the fit of crowns fabricated based on the 3D printed models (DD and PD) was inferior to that of crowns prepared with CS and DV, the values of all four groups were within the clinically acceptable range (<120 µm).