Vat Photopolymerization 3D Printing of Hydrogels Embedding Metal-Organic Frameworks for Photodynamic Antimicrobial Therapy.

Given the variability in wounds based on the underlying causes, personalized medicine and tailored care for patients with wounds are required to ensure optimal therapeutic outcomes. With the emergence of high-precision and high-efficiency photocuring 3D printing technology, there is the potential for its use in customizing precise shapes that can match complex wound sites, thereby providing better treatment for patients with wound infections. In this work, porphyrinic metal-organic framework (MOF) crystals, serving as the functional filler, were incorporated into gelatin methacrylate (GelMA) as a photocurable composite resin to investigate the capabilities of producing customizable wound dressings through vat photopolymerization 3D printing. The embedded MOF crystals allow for better control of the photopolymerization process due to photon competition with the photoinitiator, enabling the precise printing of complex structures. In addition, these crystals impart photothermal and photodynamic capabilities to the printed object. The antibacterial assay confirms the potent photothermal and photodynamic bactericidal properties of the printed GelMA/MOF hydrogels. The hydrogel with the highest MOF content exhibited over 99.99% antibacterial efficiency against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli after 30 min of light exposure (∼30 mW/cm2, λ ≥ 420 nm). Simultaneously, hemolysis and cytotoxicity evaluations validated their excellent biocompatibility. The findings presented here introduce a strategy for integrating photosensitive MOF and 3D printing to fabricate size-adjustable photothermal/photodynamic monoliths and patches, opening perspectives toward personalized treatment for wound management.

Influence of Spectral Bandwidth on the Working Curve in Vat Photopolymerization.

In vat photopolymerization, 3-dimensional parts are fabricated by using patterned light to spatially cure a liquid resin. One of the foundational measurements for vat photopolymerization is known as the working curve whereby the depth (i.e. thickness) of cured resin is measured as a function of radiant exposure. The commonly applied mathematical model for the working curve - known widely as the Jacobs model - assumes a monochromatic light source. The Jacobs model has been widely used, but in many cases significant deviations between the Jacobs model and the data have been observed. Herein, we extend the Jacobs model by deriving a polychromatic model that accounts for broadband light sources (e.g. light emitting diodes, LEDs). We demonstrate through experiment and theory that in certain cases the deviations from Jacobs' original model can be explained and understood as an optical 'inner filter' effect. The ability of the Jacobs model to capture the working curve behavior is shown to be dependent on the bandwidth of the light source in conjunction with the gradient in the absorption spectrum of the resin in the vicinity of the light source spectrum. Additionally, we offer an empirical model function that better fits experimental data and allows for an improved estimate of model parameters. Broadly, this work aims to strengthen the conceptual link between the working curve measurement and the photophysical parameters that are intrinsic to vat photopolymerization printing.

3D Printed Leaf-Vein-Like Al2O3/EP Biohybrid Structures with Enhanced Thermal Conductivity.

The high computility of electronic components put urgent requirements on the dissipation efficiency of a high thermal conductive substrate. Herein, inspired by the nature structure, leaf-vein-like Al2O3 skeleton was first designed though topology optimization algorithm and manufactured via vat photopolymerization (VPP) 3D printing, then compounded with epoxy (EP) to prepare leaf-vein-like biohybrid structures. The biohybrid structure had a high λ (14.65 Wm-1 K-1 with the solid fraction of 40 vol %), which was 5585% higher than neat EP and 269% higher than the random dispersed Al2O3/EP composite at the same solid amount. Moreover, it further showed a high enhancement in the cooling ecoefficiency of the lighting-emitting diode (LED) cooling system. Compared with 40 vol % random dispersed Al2O3/EP composite as a cooling substrate, the leaf-vein-like biohybrid structure with the same solid fraction reduced the working temperature of LED by 8.9 °C. Our strategy has a significant potential as a viable type and mass-producible bionic cooling substrate.

Fabrication of Zirconia Ceramic Dental Crowns by Digital Light Processing: Effects of the Process on Physical Properties and Microstructure.

Highly dense zirconia ceramic dental crowns were successfully fabricated by a digital light processing (DLP) additive manufacturing technique. The effects of slurry solid content and exposure density on printing accuracy, curing depth, shrinkage rate, and relative density were evaluated. For the slurry with a solid content of 80 wt%, the curing depth achieved 40 µm with minimal overgrowth under an exposure intensity of 16.5 mW/cm2. Solid content and sintering temperature had remarkable effects on physical properties and microstructure. Higher solid content resulted in better structural integrity, higher relative density, and denser microstructure. Compressive strength, Vickers hardness, fracture toughness, and wear resistance significantly increase with lifting solid content, reaching values of 677 MPa, 12.62 GPa, 6.3 MPa·m1/2, and 1.5 mg/min, respectively, for 1500°C sintered zirconia dental crowns printed from a slurry with 80 wt% solid content. DLP is deemed a promising technology for the fabrication of zirconia ceramic dental crowns for tooth repair.

Assessing the Dispersion Stability of Antimicrobial Fillers in Photosensitive Resin for Vat Polymerization 3D Printing.

Polymers are widely used in healthcare due to their biocompatibility and mechanical properties; however, the use of polymers in medical products can promote biofilm formation, which can be a source of hospital-acquired infections. Due to this, there is a rising demand for inherently antimicrobial polymers for devices in contact with patients. 3D printing as a manufacturing technology has increased exponentially in recent years. Surgical guides, orthotics, and prosthetics, among other medical devices, created by vat polymerization have been used in hospitals to treat patients. Biocompatible resins are available for these applications, but there is a lack of antimicrobial resins, which would further improve the technology for clinical use. The focus of this study was to assess settling of candidate antimicrobial metal and metal oxide fillers in vat polymerization resin to determine which fillers were compatible with the resin. Dispersion stability was assessed by measuring settling over the maximum print duration of the medium priced desktop 3D printers to evaluate printability of 17 potentially antimicrobial resins. Eight materials displayed settling behavior during the test period: molybdenum oxide, zirconium oxide nanopowder, scandium oxide, zirconium oxide, titanium oxide, tungsten oxide, lanthanum oxide, and magnesium oxide. No settling was observed for manganese oxide, magnesium oxide nanopowder, titanium oxide nanopowder, copper oxide, silver oxide, zinc oxide nanopowder, zinc oxide, silver nanopowder, and gold nanopowder during the test period. This method could be applied to assess settling of other fillers introduced into 3D printing resins before actual printing.

Vat photopolymerization of multifunctional fresnel lenses for ocular management.

In this study, multifunctional Fresnel lenses were explored as a potential solution for correcting vision in patients with color vision deficiency (CVD) and high myopia. Current studies have primarily focused on color vision correction through the 3D printing of glasses and contact lenses. However, the potential of 3D-printed multifunctional devices, such as Fresnel lenses, goes beyond addressing a single vision correction issue. For this study, computer-aided design (CAD) model of Fresnel lens with high diopter based on constant height configuration was developed. The CAD model was successfully fabricated using vat photopolymerization 3D printer, employing laboratory-prepared transparent HEMA resin. The resin was modified with two Atto dyes (565 nm and 488 nm), known for their ability to filter out problematic wavelengths (400-500 nm and 540-580 nm) to address color vision deficiency. The printed lenses were characterized by their chemical, physical, and optical properties using various characterization techniques. The focusing performance was evaluated using focal length measurements, and the results obtained were less than 2 mm deviation from the design value, having the potential to assist in higher myopic vision correction. The resulting optical spectra were compared with commercial glasses, revealing close agreement for CVD correction. These results expand the potential applications of multifunctional Fresnel lenses in ophthalmology, demonstrating their effectiveness as vision-correcting lenses and imaging systems.

Volumetric printing and non-destructive drug quantification of water-soluble supramolecular hydrogels.

Vat photopolymerisation 3D printing is being actively explored for manufacturing personalised medicines due to its high dimensional accuracy and lack of heat application. However, several challenges have hindered its clinical translation, including the inadequate printing speeds, the lack of resins that give soluble matrices, and the need for non-destructive quality control measures. In this study, for the first time, a rapid approach to producing water-soluble vat photopolymerised matrices and a means of non-destructively verifying their drug content were investigated. Volumetric printing, a novel form of vat photopolymerisation, was used to fabricate personalised warfarin-loaded 3D-printed tablets (printlets). Eight different formulations containing varying amounts of warfarin (0.5-6.0% w/w) were used to print two different sized torus-shaped printlets within 6.5 to 11.1 s. Nuclear magnetic resonance (NMR) spectroscopy revealed the presence of only trace amounts of unreacted acrylate monomers, suggesting that the photopolymerisation reaction had occurred to near completion. All printlets completely solubilised and released their entire drug load within 2.5 to 7 h. NIR spectroscopy (NIRS) was used to non-destructively verify the dose of warfarin loaded into the vat photopolymerised printlets. The partial least square regression model built showed strong linearity (R2 = 0.980), and high accuracy in predicting the drug loading of the test sample (RMSEP = 0.205%). Therefore, this study advances pharmaceutical vat photopolymerisation by demonstrating the feasibility of producing water-soluble printlets via volumetric printing and quantifying the drug load of vat photopolymerised printlets with NIRS.

Design Aspects in Vat Photopolymerization Additive Manufacturing of Hydrophobic Surfaces.

Hydrophobic surfaces require finely tuned process chains due to the scale, complexity, and patterning methods. For this purpose, vat photopolymerization (VPP) additive manufacturing is a promising method for surface generation; however, together with the fabrication process, the design phase needs to be optimized to achieve the desired surface property. This work presents the influence of the design features of hydrophobic surfaces through multiple studies on simple pillar structures, intrinsic single-unit geometries, and surface deposition on complex substrates. The results showed that depending on the dimensions of single pillar dimensions, wetting properties can extend between the contact angles (CA) of 83°-115.11°. The hydrophobicity was further increased by applying a re-entrant structure, reaching the CA of 115.24°. The surface deposition on the complex substrates significantly increased water droplet adhesion, preventing it from rolling off, which can be beneficial for manifold device protection from the hazardous influence of the environment. In addition, the influence of the surface on the acoustic properties was examined, which showed that the pattern application in the real-life device does not have a detrimental effect on the intrinsic functionality. This study showed that the design phase should be an essential part of the VPP process chain as it significantly influences the wetting properties of the surfaces.

The role of video-assisted thoracoscopy in chest trauma: a retrospective monocentric experience.

Video-assisted thoracoscopy (VAT) plays an essential role in the exploration of pleural cavity after thoracic trauma, although some doubts about the precise and specific indications persist. This study examines the eligibility criteria for videothoracoscopy and establishes the ideal timing for VAT. Between January 2011 and November 2022, we observed 923 polytraumatized patients. All patients underwent computed tomography (CT) scan total body with and without contrast enhancement. Two hundred and nine patients carried out VAT within 10 ± 2 h of injury while 8 patients after 20 ± 1 h. The Injury Severity Score (ISS) was 31 ± 1 and the Glasgow Coma Scale was 14.1 ± 0.3 upon arrival at the hospital. One hundred and nineteen patients displayed hemothorax (55%), 62 hemopneumothorax (28.5%), 21 penetrating wound (9.6%), 10 pneumothorax (4.6%) and 5 chylothorax (2.3%). In 18 patients (8.3%) without vascular, diaphragmatic, or parenchymal lesion the treatment consisted in chest tube placement. VAT was converted to video-assisted thoracoscopic surgery (VATS) in 190 patients (87.5%), to open surgery in 8 (3.7%) and to laparoscopy in 1 (0.5%). Twelve patients (5.5%) with diaphragm ruptures < 5 cm in diameter were treated by separate stitches suture in VATS. Only eight postoperative complications (4 pneumonia, three atelectasis and one pulmonary embolism) out of 217 VAT, positively resolved with medical treatment, were noted exclusively in patients undergoing minimally invasive approach 20 ± 1 h after trauma. Early VAT in selected patients is a safe and easy procedure that ensure a quick diagnosis of lesions and an accurate management of the most thoracic injuries among trauma patients. The prompt identification of injuries, to avoid life-threatening conditions requiring rapid intervention, responds to medico-legal needs to which VAT fulfills.

Polymer Matrix Nanocomposites Fabricated with Copper Nanoparticles and Photopolymer Resin via Vat Photopolymerization Additive Manufacturing.

This investigation explores the fabrication of polymer matrix nanocomposites via additive manufacturing (AM), using a UV photopolymerization resin and copper nanoparticles (Cu-NPs) with vat photopolymerization 3D printing technology. The aim in this study is to investigate the mentioned materials in different formulations in terms of inexpensive processing, the property related variability, and targeting multifunctional applications. After the AM process, samples were post-cured with UV light in order to obtain better mechanical properties. The particles and resin were mixed using an ultrasonicator, and the particle contents used were 0.0, 0.5, and 1.0 wt %. The process used in this investigation was simple and inexpensive, as the technologies used are quite accessible, from the 3D printer to the UV curing device. These formulations were characterized with scanning electron microscopy (SEM) to observe the materials' microstructure and tensile tests to quantify stress-strain derived properties. Results showed that, besides the simplicity of the process, the mixing was effective, which was observed in the scanning electron microscope. Additionally, the tensile strength was increased with the UV irradiation exposure, while the strain properties did not change significantly.

Vat-based photopolymerization 3D printing: From materials to topical and transdermal applications.

Three-dimensional (3D) printing is an innovative manufacturing method with the potential to revolutionize topical and transdermal dosage forms. Nowadays, it is established that Vat-based photopolymerization (VP) 3D printing technologies offer superior printing efficiency and versatility compared to other 3D printing technologies available on the market. However, there are some limitations that impair their full application in pharmaceutical contexts, such as the lack of a range of biocompatible materials for topical and transdermal applications. This review article explores all types of VP-based 3D printing and discusses the relevance of implementing this kind of technology. We start with a detailed description of the printing process, focusing on the commercial materials available and lab-made resins proposed by different authors. We also review recent studies in this field, which mainly focus on the fabrication of transdermal devices based on microneedle arrays. In the future, it is expected that the manufacturers of 3D printers invest in modifications to the printing apparatus to allow the simultaneous printing of different resins and/or compound types, which will open frontiers to the personalization of treatment approaches.

Spin-dyeing of cellulose fibres with vat dyes using the Ioncell process.

Estimated 20 % of global clean water pollution is attributed to textile production. Dyeing and finishing processes use an extensive amount of water and chemicals, and most of the effluents and wastewater is released into the environment. In this study, we explore spin-dyeing of man-made cellulosic fibres (MMCFs) with vat dyes using the Ioncell process, circumventing the ubiquitous use of fresh water and potentially reducing effluents streams to a great extent. Spin-dyeing is an established process for synthetic polymers but is not common for MMCFs. Regenerated cellulose fibres were produced through dissolution of dissolving pulp in the ionic liquid 1,5-diazabicyclo[4.3.0]non-5-ene acetate. The produced fibres were processed into yarn and a jersey fabric was knitted. Mechanical and colour fastness properties were tested. The fibres properties were also assessed through SEM, birefringence, and crystallinity measurements. Fibres with excellent mechanical properties (tenacity higher than 50 cN/tex) and colour fastness were produced, with most samples receiving the highest or next highest performance grade. The spun-dyed fibres also hold great potential to be recycled themselves without colour change or loss in colour intensity. Textiles with colours produced in large quantities such as black or navy blue could be the first market entry point.

A virtual visualization method for improving the manufacturing accuracy based VPP 3D printers.

Compared to traditional vat photopolymerization 3D printing methods, pixel blending technique provides greater freedom in terms of user-defined lighting sources. Based on this technology, scientists have conducted research on 3D printing manufacturing for elastic materials, biologically inert materials, and materials with high transparency, making significant contributions to the fields of portable healthcare and specialty material processing. However, there has been a lack of a universal and simple algorithm to facilitate low-cost printing experiments for researchers not in the 3D printing industry. Here, we propose a mathematical approach based on morphology to simulate the light dose distribution and virtual visualization of parts produced using grayscale mask vat photopolymerization 3D printing technology. Based on this simulation, we develop an auto-correction method inspired by circle packing to modify the grayscale values of projection images, thereby improving the dimensional accuracy of printed devices. This method can significantly improve printing accuracy with just a single parameter adjustment. We conducted experimental validation of this method on a vat photopolymerization printer using common commercial resins, demonstrating its feasibility for printing high precision structures. The parameters utilized in this method are comparatively simpler to acquire compared to conventional techniques for obtaining optical parameters. For researchers in non-vat photopolymerization 3D printing industry, it is relatively user-friendly.

Associations between visceral and liver fat and cardiac structure and function: a UK Biobank study.

CONTEXT: Different fat depots have connected to cardiovascular health. OBJECTIVE: We assessed the associations of abdominal magnetic resonance-quantified visceral adipose tissue (VAT) and liver fat (proton density fat fraction, PDFF) with cardiac magnetic resonance (CMR)-measured cardiac structure and function, and considered potential mechanism. METHODS: Our study encompassed 10,920 participants from the UK Biobank. We utilized multiple linear regression and multiple mediation analyses to estimate the connections between VAT or PDFF and CMR metrics. RESULTS: Elevated VAT or PDFF exhibited associations with adverse left ventricular (LV) structure (increased wall thickness, concentric LV remodeling), impaired LV function (lower LV global functional index, absolute value of LV global longitudinal strain), and diminished left atrial volumes and stroke volume (all p-values were significant）. Upon stratifying participants based on VAT and PDFF combinations, all groups, except the low VAT-low PDFF group, were linked to unfavorable cardiac remodeling metrics. The high VAT-high PDFF group displayed the most pronounced cardiac alterations. Multiple mediation analyses were employed to investigate potential mediating roles of systolic blood pressure (SBP), diabetes, dyslipidemia and blood biomarkers (lipidemia, transaminases) in the adipose-CMR relationship. The findings suggested that VAT or PDFF was related to SBP, diabetes, dyslipidemia, lipid profile, liver function, and glucose. Several potential mediating pathways were identified, primarily through SBP and triglyceride-glucose index, which only partially explained the adipose-CMR relationship. CONCLUSION: We established the independent associations of VAT and PDFF with unhealthy cardiac structure and function. Furthermore, it identifies SBP and insulin resistance as important mediating factors.

High-resolution stereolithography: Negative spaces enabled by control of fluid mechanics.

Stereolithography enables the fabrication of three-dimensional (3D) freeform structures via light-induced polymerization. However, the accumulation of ultraviolet dose within resin trapped in negative spaces, such as microfluidic channels or voids, can result in the unintended closing, referred to as overcuring, of these negative spaces. We report the use of injection continuous liquid interface production to continuously displace resin at risk of overcuring in negative spaces created in previous layers with fresh resin to mitigate the loss of Z-axis resolution. We demonstrate the ability to resolve 50-µm microchannels, breaking the historical relationship between resin properties and negative space resolution. With this approach, we fabricated proof-of-concept 3D free-form microfluidic devices with improved design freedom over device material selection and resulting properties.

VAT/GST harmonisation challenges for digital assets such as bitcoin and NFTs in the EU following Case C-264/14 (Skatteverket v David Hedqist).

The verdict in the case of Skatteverket v. David Hedqvist (Kokott, Advocate General (2015) Opinion delivered on 16 July 2015, Case C-264/14. ECLI:EU:C:2015:498. Available via TandF Online. 10.1080/20488432.2015.1096631.) is crucial for understanding how the EU treats virtual currencies, such as Bitcoin, in terms of Value-added Tax (VAT). This case involved the Swedish citizen David Hedqist who was seeking clarity from the Swedish Tax Authority Skatteverket on exchanging money for Bitcoins. The case set a precedent exempting such services from VAT under the EU's VAT Directive (Council Directive 2006/112/EC (2006) On the common system of value added tax. OJ L347. Available via EUR-Lex. https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32006L0112. Accessed 3 January 2024.). Specifically, Article 135(1)(e) of the EU's VAT Directive excludes those transactions from VAT that include money-related transactions, that include deals or negotiations about different kinds of money, including cash and coins that are officially legal tender, i.e., used for buying things, except for collectable items like special coins or notes that people collect but do not use as a means of payment. Skatteverket (Kokott, Advocate General (2015) Opinion delivered on 16 July 2015, Case C-264/14. ECLI:EU:C:2015:498. Available via TandF Online. 10.1080/20488432.2015.1096631.) clarified that cash transactions are not subject to VAT, even though they are considered services for VAT purposes. Despite this clarity, the evolving landscape of digital assets' uniqueness, including Non-Fungible Tokens (Alawadhi KM, Alshamali N (2022) NFTs Emergence in Financial Markets and their Correlation with DeFis and Cryptocurrencies. Applied Economics and Finance 9:108. 10.11114/aef.v9i1.5444. Available at CORE. https://core.ac.uk/download/pdf/524752899.pdf. Accessed 3 January 2024.), continues to challenge VAT frameworks across member states. Using insights from the European Commission's Working Paper 1060, this article advocates for a unified approach tailored to digital and crypto services, addressing complexities in NFT taxation to reduce uncertainty and foster market cohesion. The findings highlight the importance of legislative changes and increased cross-border collaboration, as well as provide recommendations for policymakers and stakeholders in the digital finance and platform sector (European Commission (2024) Working Paper 1060. Available at: https://ec.europa.eu/info/publications/working-paper-1060_en. Accessed 3 March 2024.). By proposing strategic harmonisation of VAT enforcement, the research helps to improve tax compliance and support long-term growth in the EU's digital market (Cappai M (2023) The role of private and public regulation in the case study of crypto-assets: The Italian move towards participatory regulation. Computer Law & Security Review 49:105831. Available at: https://www.sciencedirect.com/journal/computer-law-and-security-review/vol/49/suppl/C.; Hasa J (2021) Digitaalisten palvelujen rajat ylittävä kuluttajakauppa ja laajeneva arvonlisäveron erityisjärjestelmä. Licentiate thesis. University of Lapland, Faculty of Law. Available at: https://lauda.ulapland.fi/bitstream/handle/10024/64771/Hasa_Juho.pdf?sequence=1. Accessed 1 March 2024.).

Manufacture Dependent Differential Biodegradation of 3D Printed Shape Memory Polymers.

In the field of tissue engineering, 3D printed shape memory polymers (SMPs) are drawing increased interest. Understanding how these 3D printed SMPs degrade is critical for their use in the clinic, as small changes in material properties can significantly change how they behave after in vivo implantation. Degradation of 3D printed acrylated poly(glycerol-dodecanedioate) (APGD) was examined via in vitro hydrolytic, enzymatic, and in vivo subcutaneous implantation assays. Three APGD manufacturing modalities were assessed to determine differences in degradation. Material extrusion samples showed significantly larger mass and volume loss at 2 months, compared to lasercut and vat photopolymerization samples, under both enzymatic and in vivo degradation. Critically, melt transition temperatures of degraded PGD increased over time in vitro, but not in vivo. Histology of tissue surrounding APGD implants showed no significant signs of inflammation compared to controls, providing a promising outlook for use of 3D printed APGD devices in the clinic.

Can revenue collection for public funding in health care be progressive? An assessment of 29 Countries.

Most research on health care equity focuses on accessing services, with less attention given to how revenue is collected to pay for a country's health care bill. This article examines the progressivity of revenue collection among publicly funded sources: income taxes, social insurance (often in the form of payroll) taxes, and consumption taxes (e.g., value-added taxes). We develop methodology to derive a qualitative index that rates each of 29 high-income countries as to its progressivity or regressivity for each of the three sources of revenue. A variety of data sources are employed, some from secondary data sources and other from country representatives of the Health Systems and Policy Monitor of the European Observatory on Health Systems and Policies. We found that countries with more progressive income tax systems used more income-based tax brackets and had larger differences in marginal tax rates between the brackets. The more progressive social insurance revenue collection systems did not have an upper income cap and exempted poorer persons or reduced their contributions. The only pattern regarding consumption taxes was that countries that exhibited the fewest overall income inequalities tended to have least regressive consumption tax policies. The article also provides several examples from the sample of countries on ways to make public revenue financing of health care more progressive.

Fabrication of 3D printed mutable drug delivery devices: a comparative study of volumetric and digital light processing printing.

Mutable devices and dosage forms have the capacity to dynamically transform dimensionally, morphologically and mechanically upon exposure to non-mechanical external triggers. By leveraging these controllable transformations, these systems can be used as minimally invasive alternatives to implants and residence devices, foregoing the need for complex surgeries or endoscopies. 4D printing, the fabrication of 3D-printed structures that evolve their shape, properties, or functionality in response to stimuli over time, allows the production of such devices. This study explores the potential of volumetric printing, a novel vat photopolymerisation technology capable of ultra-rapid printing speeds, by comparing its performance against established digital light processing (DLP) printing in fabricating hydrogel-based drug-eluting devices. Six hydrogel formulations consisting of 2-(acryloyloxy)ethyl]trimethylammonium chloride solution, lithium phenyl-2,4,6-trimethylbenzoylphosphinate, varying molecular weights of the crosslinking monomer, poly(ethylene glycol) diacrylate, and paracetamol as a model drug were prepared for both vat photopolymerisation technologies. Comprehensive studies were conducted to investigate the swelling and water sorption profiles, drug release kinetics, and physicochemical properties of each formulation. Expandable drug-eluting 4D devices were successfully fabricated within 7.5 s using volumetric printing and were shown to display equivalent drug release kinetics to prints created using DLP printing, demonstrating drug release, swelling, and water sorption properties equivalent to or better than those of DLP-printed devices. The reported findings shed light on the advantages and limitations of each technology for creating these dynamic drug delivery systems and provides a direct comparison between the two technologies, while highlighting the promising potential of volumetric printing and further expanding the growing repertoire of pharmaceutical printing.

Zirconia specimens printed by vat photopolymerization: Mechanical properties, fatigue properties, and fractography analysis.

PURPOSE: The mechanical and fatigue properties of zirconia specimens printed by vat photopolymerization (VPP) were evaluated and compared with those of zirconia specimens milled by computer numerical control (CNC). MATERIALS AND METHODS: Bar-shaped specimens were printed by stereolithography (SL) and digital light processing (DLP). CNC-milled specimens were used as control samples. The fracture toughness, hardness, and flexural strength properties of the zirconia specimens were evaluated via single edge V-notch beam tests, Vickers hardness tests, and 3-point bending tests. Dynamic fatigue tests were carried out in distilled water using a step-stress test. After static bending and dynamic step-stress testing, fractography analysis was performed. Statistical analysis was carried out to compare the fracture toughness, hardness, flexural strength, and fatigue cycle results of each group (α = 0.05). RESULTS: The fracture toughness values did not significantly differ among the groups (p > 0.05). The flexural strength was 894.10 MPa for SL, 831.46 MPa for DLP, and 1140.39 MPa for CNC. The flexural strength of CNC was greater than that of SL and DLP (p < 0.01). The mean fatigue cycles were 23498.07 for SL, 19858.60 for DLP, and 31566.80 for CNC. The mean fatigue failure strength was 643.13 MPa for SL, 530.63 MPa for DLP, and 903.75 MPa for CNC. The fatigue failure strength of CNC was greater than that of SL and DLP (p < 0.05). Fractography analysis revealed material defects at the fracture origin for each group. A partially fused structure of the incompletely debonded resin could be observed in SL, and a porous region of incompletely sintered zirconia grains could be observed in CNC. CONCLUSIONS: The fracture toughness and hardness of zirconia printed by VPP are comparable to those of zirconia milled by CNC. However, zirconia milled by CNC has superior static flexural strength and dynamic fatigue resistance. Further studies are needed to explore the clinical applications of VPP-printed zirconia.