3D printing of highly conductive and strongly adhesive PEDOT:PSS hydrogel-based bioelectronic interface for accurate electromyography monitoring.

PEDOT: PSS hydrogel-based bioelectronic interfaces have gained significant attention in various fields including biomedical devices, wearable devices, and epidermal electronics. However, the development of high-performance bioelectronic interfaces that integrate excellent conductivity, strong adhesion, and advanced processing compatibility remains a challenge. Herein, we develop a high-performance bioelectronic interface by 3D printing of a novel poly(vinyl alcohol-formaldehyde) (PVAF)-PEDOT:PSS composite ink. Such a PEDOT:PSS-PVAF ink exhibits favorable rheological properties for direct-ink-writing 3D printing, enabling the fabrication of high-resolution patterns and three-dimensional structures with high aspect ratios. Hydrogel bioelectronic interface printed by such PEDOT:PSS-PVAF ink simultaneously achieves high conductivity (over 100 S m-1), strong adhesion (31.44 ± 7.07 kPa), as well as stable electrochemical performance (charge injection capacity of 13.72 mC cm-2 and charge storage capacity of 18.80 mC cm-2). We further integrate PEDOT:PSS-PVAF hydrogel bioelectronic interface to fabricate adhesive skin electrodes for electromyography (EMG) signal recording. The resultant EMG skin electrodes demonstrate superior performance and stability compared to commercial products, maintaining high signal-to-noise ratio of > 10 dB under varying weights and repetitive motions. These advantageous performance of PEDOT:PSS-PVAF based hydrogel bioelectronic interfaces may be helpful for diverse bioelectronic applications like healthcare monitoring and epidermal bioelectronics.

Architectural design and optimization of internal structures in 3D printed electrodes for superior supercapacitor performance.

The architecture of electrodes plays a pivotal role in the transfer and transportation of charges during electrochemical reactions. Selecting optimal electrode materials and devising well-conceived electrode structures can substantially enhance the electrochemical performance of devices. This manuscript leverages 3D printing technology to fabricate asymmetric supercapacitor devices featuring regular layered configurations. By investigating the impact of various materials on the internal architecture of printed electrodes, we establish a stratified electrode structure with an orderly arrangement, thereby significantly improving asymmetric charge transfer between electrodes. The application of 3D printing technology to construct electrode structures effectively mitigates the agglomeration of electrode materials. The 3D-printed VCG//MXene devices demonstrate exceptional areal capacitance (205.57 mF cm-2) and energy density (60.03 µWh cm-2), with a power density of 0.174 W cm-2. Consequently, selecting appropriate materials for fabricating printable electrode structures and achieving efficient 3D printing is anticipated to offer novel insights into the construction and enhancement of miniature asymmetric micro-supercapacitor (MSCs) devices.

Wetting of soap bubbles on topographic surfaces.

HYPOTHESIS: There is a relationship between the static contact angle of droplets and soap bubbles on flat homogeneous surfaces, therefore, it should be possible to derive a relationship between the static contact angle of a soap bubble on a periodic topographic surface and a droplet on a flat homogeneous surface. EXPERIMENTS: A free energy model of the static contact angle of soap bubbles on a topographic surface in the Cassie-Baxter state was derived. Polydimethylsiloxane surfaces of varying area fraction (0.125, 0.250, 0.500, 0.750, and 1.00) and periodic topographies (lined and pillared) were fabricated using 3D printed moulds for pattern transfer. A bubble goniometer was developed to accommodate bubbles of 40,000 ± 5,000 mm3 and 50,000 ± 5,000 mm3 volumes. Then, the static contact angle of bubbles of both volumes were measured on the varying topographic surfaces. FINDINGS: The derived predictions imply that the relationship between the static contact angle for bubbles on a flat homogeneous surface and on a composite surface, has the same form as the Cassie-Baxter equation for a droplet. The experimental results for the measured static contact angle for both bubble volumes on the varying surfaces had good agreement with the predicted trends.

Three-dimensional printing in orthopaedic surgery: A review of current and future applications.

Three-dimensional (3D) printing is a form of technology in which 3D physical models are created. It has been used in a variety of surgical specialities ranging from cranio-maxillo-facial to orthopaedic surgery and is currently an area of much interest within the medical profession. Within the field of orthopaedic surgery, 3D printing has several clinical applications including surgical education, surgical planning, manufacture of patient-specific prostheses/patient specific instruments and bone tissue engineering. This article reviews the current practices of 3D printing in orthopaedic surgery in both clinical and pre-clinical settings along with discussing its potential future applications.

Influence of silver coated zeolite fillers on the chemical and mechanical properties of 3D-printed polyphenylene sulfone restorations.

OBJECTIVES: To investigate the chemical and mechanical properties of polyphenylene sulfone (PPSU) depending on its composition and manufacturing. METHODS: Unfilled-PPSU1 and with antimicrobial silver coated zeolites filled-PPSU2 specimens were made of granulate-GR, filament-FI, or printed-3D. Scanning microscopy and X-ray spectroscopy were performed. Martens hardness-HM, elastic indentation modulus-EIT and flexural strength-FS were determined initially and after aging. Shear bond strength-SBS to veneering and luting composite after conditioning with 7 adhesive systems were examined after aging. Silver leaching was tested after 1-, 3-, 7-, 14-, 21-, 28- and 42 days. Analyses of variance, Kolmogorov-Smirnov, Kruskal-Wallis, Mann-Whitney U, unpaired t-tests and Weibull modulus were computed (p < 0.05). RESULTS: Zeolites were homogeneously distributed. PPSU1-GR and PPSU1-FI showed the highest HM/EIT, followed by PPSU2-GR, PPSU1-3D and PPSU2-3D. PPSU2-FI presented the lowest HM/EIT, displaying micro pits. Aging showed reduced HM/EIT in PPSU1 and no impact on PPSU2, while FS increased (PPSU1) or decreased (PPSU2). PPSU2-3D presented lower FS than PPSU1-3D. High SBS to the luting (7.0-16.2 MPa) and veneering composite (11.8-22.2 MPa), except for adhesive system PR, were observed. PPSU2-3D showed the highest silver release (9.6%), with all compositions dispensing silver over 42 days. CONCLUSIONS: For the examined period of 6 weeks, antimicrobial silver ions were released from filled PPSU. The high SBS between PPSU and veneering/luting composite confirmed the feasibility of esthetically veneering and luting filled PPSU. To achieve mechanical properties like unfilled PPSU, the processing parameters of filled PPSU require refinement. CLINICAL SIGNIFICANCE: This investigation provides proof of principle that PPSU can be successfully doped with silver-coated zeolites. The combination of 3D-printing with an antimicrobial thermoplastic constitutes a great opportunity in the field of prosthetic dentistry. Potential applications include clasps for removable dental prostheses, provisional or permanent fixed dental prostheses and implant abutments.

3D-Printed-Cryogel-Impregnated Functionalized Scaffold Augments Bone Regeneration in Critical Tibia Fracture in Goat.

Critical-size bone trauma injuries present a significant clinical challenge because of the limited availability of autografts. In this study, a photocurable composite comprising of polycaprolactone, polypropylene fumarate, and nano-hydroxyapatite (nHAP) (P─P─H) is printed, which shows good osteoconduction in a rat model. A cryogel composed of gelatin-nHAP (GH) is developed to incorporate osteogenic components, specifically bone morphogenetic protein-2 (BMP-2) and zoledronic acid (ZA), termed as GH+B+Z, which is investigated for osteoinductive property in a rat model. Further, a 3D-printed P─P─H scaffold impregnated with GH+B+Z is designed and implanted in a critical-size defect (25 × 10 × 5 mm) in goat tibia. After 4 months, the scaffold is well-integrated with adjacent native bone, with osteoinduction observed in the cryogel-filled region and osteoconduction over the printed scaffold. X-ray radiography and micro-CT analysis showed bone in-growth in the treatment group with 45 ± 1.4% bone volume/tissue volume (BV/TV), while the defect remained unhealed in the control group with BV/TV of 10.5 ± 0.5%. Histology showed significant cell infiltration and matrix deposition over the printed P─P─H scaffold and within the GH cryogel site in the treatment group. Immunohistochemical staining depicted significantly higher normalized collagen I intensity in the treatment group (34.45 ± 2.61%) compared to the control group (4.22 ± 0.78).

An alternative filament fabrication method as the basis for 3D-printing personalized implants from elastic ethylene vinyl acetate copolymer.

In this work, a novel tool for small-scale filament production is presented. Unlike traditional methods such as hot melt extrusion (HME), the device (i) allows filament manufacturing from small material amounts as low as three grams, (ii) ensures high diameter stability almost independent of the viscoelastic behavior of the polymer melt, and (iii) enables processing of materials with rheological profiles specifically tailored toward fused filament fabrication (FFF). Hence, novel materials, previously difficult to process due to HME limitations, become easily accessible for FFF for the first time. Here, we showcase the production of highly flexible drug-free, and drug-loaded filaments based on ethylene-vinyl acetate polymers with a vinyl acetate content of 28 w% (EVA28) and unprecedented high melt flow rates of up to 400 g/10 min. Owing to their low viscosity, FFF with low print nozzle sizes of 250 µm was achieved for the first time for EVA28. These small nozzle diameters facilitate 3D-printing of high-resolution structures in small-dimensional dosage forms such as subcutaneous implantable drug delivery systems, which can later be used for personalization. Consequently, the material portfolio for FFF is tremendously broadened, allowing material and formulation optimization toward FFF, independent of a preliminary extrusion process.

Three-dimensional printed titanium chest wall reconstruction for tumor removal in the sternal region.

Resection of thoracic wall tumors results in significant defects in the chest wall, leading to various complications. In recent years, the use of three-dimensional (3D) printed titanium alloy prostheses in clinical practice has demonstrated enhanced outcomes in chest wall reconstruction surgery. A cohort of seven patients with sternal tumors was identified for this study. Following a helical CT scan, a digital model was generated for the design of the prosthesis. Subsequently, the tumors were then removed together with the affected sternum and ribs. The chest wall was then reconstructed using 3D-printed titanium alloy prosthesis for bone reconstruction, mesh for pleural reconstruction, and flap for soft tissue reconstruction. Patients were monitored for a period of one year post-surgery. In the seven cases examined, the tumors were found in various locations with varying degrees of invasion. Based on the scope of surgical resection and the size of the defect, 3D-printed titanium alloy prosthesis was custom-designed for chest wall reconstruction. Prior to bone reconstruction, pleural reconstruction was achieved with Bard Composix E/X Mesh, while soft tissue repair involved muscle flap and musculocutaneous flap procedures. A one-year follow-up assessment revealed that the utilization of the 3D-printed titanium alloy prosthesis led to secure fixation, favorable histocompatibility, and enhanced lung function. The findings demonstrate that the utilization of 3D printed titanium alloy prostheses represents a significant advancement in the field of chest wall reconstruction and thoracic surgical procedures.

Thiol-Acrylate polyHIPEs via Facile Layer-by-Layer Photopolymerization.

A highly reactive thiol-ene high internal phase emulsion based on the monomers 1,6-hexanediol diacrylate and tris 2-(3-mercaptopropionyloxy)ethyl isocyanurate was developed for the purpose of light-driven additive manufacturing, resulting in highly porous customizable poly(high internal phase emulsion) materials. The formulation was specifically designed to facilitate short irradiation times and low amounts of photoinitiator. Furthermore, the developed emulsion does not rely on employing harmful solvents to make scale-up and industrial applications feasible. The selected thiol was added to the printing formulation as a chain-transfer agent, decreasing the brittleness of the acrylate-based system and potential of oxygen inhibition. The thickness of the printed layers lay <50 µm, and the average pore size of all samples was <5 µm.

Cork Powder Residues Processing by Binder Jetting.

Cork-based formulations adapted to binder jetting processes were herein developed and investigated. Two cork powder sets with different particle size distributions were studied to evaluate cork particles' ability to pack. Cork powders exhibiting a coarse distribution revealed a higher packing ability. In addition, owing to cork's lower affinity to water-based binders, the addition of two hydrophilic additives was explored. 3D-printed (3DP) cork parts with a simple geometry were first printed. An innovative technique was evaluated as a postprocessing phase to improve cork particle adhesion after printing. Inspired by the production of expanded cork agglomerates, use of autoclave technique as a postprocessing phase for cork parts was proposed. After the autoclave, 3DP parts exhibited an improved adhesion of cork particles, demonstrated by morphological and mechanical analyses. Fourier transform infra-red analyses demonstrated that the polysaccharide and suberinic fractions were also affected by the autoclave. 3DP cork parts with a complex design solution were successfully printed. This study contributes to new and complex design solutions for cork-based products maintaining cork's natural lightness, warmness, and softness to the touch.

Recycling of Acrylonitrile Butadiene Styrene from Electronic Waste for the Production of Eco-Friendly Filaments for 3D Printing.

In this work, acrylonitrile butadiene styrene (ABS) copolymer from electronic waste (e-waste) was used to produce filaments for application in 3D printing. Recycled ABS (rABS) from e-waste was blended with virgin ABS (vABS) in different concentrations. By differential scanning calorimetry, it was observed that the values of the glass transition temperatures for vABS/rABS blends ranged between the values of vABS and rABS. Torque rheometry analysis showed that the processability of vABS was not compromised with the addition of rABS. Rheological measurements showed that the viscosity of vABS was higher than that of rABS at low frequencies and indicated that vABS and rABS are immiscible. Impact strength (IS) tests of the 3D printed samples showed an increase in the IS with an increase in the rABS content up to 50 wt%. Blending vABS with rABS from e-waste is promising and proved to be feasible, making it possible to recycle a considerable amount of plastics from e-waste and, thus, contributing to the preservation of the environment.

3D Printing Process Research and Performance Tests on Sodium Alginate-Xanthan Gum-Hydroxyapatite Hybridcartilage Regenerative Scaffolds.

Cartilage injury is a common occurrence in the modern world. Compared with traditional treatment methods, bio-3D printing technology features better utility in the field of cartilage repair and regeneration, but still faces great challenges. For example, there is currently no means to generate blood vessels inside the scaffolds, and there remains the question of how to improve the biocompatibility of the generated scaffolds, all of which limit the application of bio-3D printing technology in this area. The main objective of this article was to prepare sodium alginate-xanthan gum-hydroxyapatite (SA-XG-HA) porous cartilage scaffolds that can naturally degrade in the human body and be used to promote cartilage damage repair by 3D printing technology. First, the viscosities of SA and XG were analyzed, and their optimal ratio was determined. Second, a mathematical model of the hybrid slurry was established based on the power-law fluid model, in which the printing pressure, needle movement speed, and fiber spacing were established as important parameters affecting the printing performance of the composite. Third, by performing a finite element simulation of the printing process and combining it with the actual printing process, suitable printing parameters were determined (air pressure of 1 bar, moving speed of 9 mm/s, line spacing of 1.6 mm, and adjacent layers of 0-90°). Fourth, composite scaffolds were prepared and tested for their compressive properties, degradation properties, cytotoxicity, and biocompatibility. The results showed that the novel composite scaffolds prepared in this study possessed good mechanical and biological properties. Young's modulus of the composite scaffolds reached 130 KPa and was able to maintain a low degradation rate in simulated body fluid solution for >1 month. The activity of the C5.18 chondrocytes in the scaffold leach solution exceeded 120%. The cells were also able to proliferate densely on the scaffold surface.

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.

Optimization of 3D Printing Parameters of Polylactic-Co-Glycolic Acid-Based Biodegradable Antibacterial Materials Using Fused Deposition Modeling.

A high incidence of ureteral diseases was needed to find better treatments such as implanting ureteral stents. The existing ureteral stents produced a series of complications such as bacterial infection and biofilm after implantation. The fused deposition modeling (FDM) of 3D printing biodegradable antibacterial ureteral stents had gradually become the trend of clinical treatment. But it was necessary to optimize the FDM 3D printing parameters of biodegradable bacteriostatic materials to improve the precision and performance of manufacturing. In this study, polylactic-co-glycolic acid (PLGA), polycaprolactone (PCL), and nanosilver (AgNP) were mixed by the physical blending method, and the 3D printing parameters and properties were studied. The relationship between printing parameters and printing errors was obtained by single-factor variable method and linear fitting. The performance of 3D printing samples was obtained through infrared spectrum detection, molecular weight detection, and mechanical testing. The printing temperature and the printing pressure were proportional to the printing error, and the printing speed was inversely proportional to the printing error. The 3D printing has little effect on the functional groups and molecular weights of biodegradable antibacterial materials. The addition of AgNP increases the compressive strength and breaking strength by 8.332% and 37.726%, which provided ideas for regulating the mechanical properties. The parameter range of biodegradable bacteriostatic materials for thermal melting 3D printing was precisely established by optimizing the parameters of printing temperature, printing pressure, and printing speed, which would be further applied to the advanced manufacturing of biodegradable implant interventional medical devices.

Magnetic Stimulation for Programmed Shape Morphing: Review of Four-Dimensional Printing, Challenges and Opportunities.

In the field of Additive Manufacturing, four-dimensional (4D) printing has emerged as a promising technique to fabricate smart structures capable of undergoing shape morphing in response to specific stimuli. Magnetic stimulation offers a safe, remote, and rapid actuation mechanism for magnetically responsive structures. This review provides a comprehensive overview of the various strategies and manufacturing approaches employed in the development of magnetically stimulated shape morphing 4D-printed structures, based on an extensive literature search. The review explores the use of magnetic stimulation either individually or in combination with other stimuli. While most of the literature focuses on single-stimulus responsive structures, a few examples of multi-stimuli responsive structures are also presented. We investigate the influence of the orientation of magnetic particles in smart material composites, which can be either random or programmed during or after printing. Finally, the similarities and differences among the different strategies and their impact on the resulting shape-morphing behavior are analyzed. This systematic overview functions as a guide for readers in selecting a manufacturing approach to achieve a specific magnetically actuated shape-morphing effect.

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.

Mechanical Characterization and Constitutive Modeling of 3D Printable Soft Materials.

Numerical modeling of soft matter has the potential to enable exploration of the soft robotic field's next frontier: human/machine cooperative design. However, access to material models suitable for predicting the behavior of soft matter is limited, and analysts typically conduct their own mechanical characterization on every new material they work with. In this work we present detailed mechanical characterization of 14 3D-printable soft materials suitable for fabricating soft robots. To allow the extension of this work by other researchers, our test procedures, raw data, constitutive model coefficients, and code used for curve fitting is freely available at www.SoRoForge.com.

4D Printing Technology Based on Magnetic Intelligent Materials: Materials, Processing Processes, and Application.

4D printing technology refers to the manufacturing of products using 3D printing techniques that are capable of changing shape or structure in response to external stimuli. Compared with traditional 3D printing, the additional dimension is manifested in the time dimension. Facilitated by the advancement of magnetic smart materials and 3D printing technology, magnetically controlled 4D printing technology has a wide range of application prospects in many fields such as medical treatment, electronic flexible devices, and industrial manufacturing. Magnetically controlled 4D printing technology is a new scientific research field in the 21st century, which includes but is not limited to the following disciplines: mechanics, materials, dynamics, physics, thermodynamics, and electromagnetism. It involves many fields and needs to be summarized systematically. First, this article introduces various magnetic intelligent materials, which are suitable for magnetically controlled 4D printing, and discusses their programmability. Second, regarding the printing process, the article introduces how to preset the material distribution as well as the research progress about the optimization of magnetically controlled 4D printing platforms and the distribution of magnetic field profiles. Third, the article also makes a brief introduction to the applications of magnetically controlled 4D printing technology in medical, electronic flexible devices, and industrial manufacturing fields.

Large-Scale Hollow-Core 3D Printing: Variable Cross-Section and Printing Features for Lightweight Plastic Elements.

Hollow-core 3D printing (HC3DP) proposes a new method for the production of lightweight, material-efficient thermoplastic 3D printed elements. This new fabrication approach promises material savings of 50-80%, while increasing the extrusion rate significantly (factor 10). This development pushes HC3DP to a similar fabrication speed as high-resolution concrete 3D printing. However, fundamental research on printing features enabled by this novel 3D printing approach is missing. Therefore, this article investigates printing with user-controlled bead dimensions (same nozzle, different size). It is showcased that the size of the extruded cross-section is determined by the positive air pressure used to inflate the beads. Multiple samples are printed, changing the layer height and width significantly without making changes to the hardware setup. Sections of 3DP samples are analyzed and the parameters of 3DP beads are determined. Furthermore, a set of bespoke 3D printed nozzles is introduced to subdivide the HC3DP beads into distinct areas. So far only regular beads, such as hollow tubes, have been used for 3D printing. Samples of those bespoke sections are analyzed to investigate their behavior when used for 3D printing. Finally, large-scale 3D printing experiments are conducted to investigate how printing features like bridging, cantilevering, or nonplanar 3D printing can be manufactured with hollow extrusion beads. In summary, this article provides insights into the fundamental 3D printing behaviors of HC3DP, showcases new design possibilities with bespoke and variable cross-sections, and finally proposes new research trajectories based on the findings presented.

Development of 3D-Printable Albumin-Alginate Foam for Wound Dressing Applications.

In this article, a method to develop 3D printable hybrid sodium alginate and albumin foam, crosslinked with calcium chloride mist is introduced. Using this method, highly porous structures are produced without the need of further postprocessing (such as freeze drying). The proposed method is particularly beneficial in the development of wound dressing as the printed foams show excellent lift-off and water absorption properties. Compared with methods that use liquid crosslinker, the use of mist prevents the leaching of biocompounds into the liquid crosslinker. 3D printing technique was chosen to provide more versatility over the wound dressing geometry. Calcium chloride and rhodamine B were used as the crosslinking material and the model drug, respectively. Various biomaterial inks were prepared by different concentrations of sodium alginate and albumin, and the fabricated scaffolds were crosslinked in mist, liquid, or kept without crosslinking. The effects of biomaterial composition and the crosslinking density on the wound dressing properties were assessed through printability studies. The mist-crosslinked biomaterial ink composed of 1% (w/v) sodium alginate and 12% (w/v) albumin showed the superior printability. The fabricated scaffolds were also characterized through porosity, mechanical, degradation, and drug release tests. The mist-crosslinked scaffolds showed superior mechanical properties and provided relatively prolonged drug release.