Enhanced Energy Absorption of Additive-Manufactured Ti-6Al-4V Parts via Hybrid Lattice Structures.

In this study, we present the energy absorption capabilities achieved through the application of hybrid lattice structures, emphasizing their potential across various industrial sectors. Utilizing Ti-6Al-4V and powder bed fusion (PBF) techniques, we fabricated distinct octet truss, diamond, and diagonal lattice structures, tailoring each to specific densities such as 10, 30, and 50%. Furthermore, through the innovative layering of diverse lattice types, we introduced hybrid lattice structures that effectively overcome the inherent energy absorption limitations of single-lattice structures. As a result, we conducted a comprehensive comparison between single-lattice structures and hybrid lattice structures of equal density, unequivocally showcasing the latter's superior energy absorption performance in terms of compression. The single-lattice structure, OT, showed an energy absorption of 42.6 J/m3, while the reinforced hybrid lattice structure, OT-DM, represented an energy absorption of 77.8 J/m3. These findings demonstrate the significant potential of hybrid lattice structures, particularly in energy-intensive domains such as shock absorption structures. By adeptly integrating various lattice architectures and leveraging their collective energy dissipation properties, hybrid lattice structures offer a promising avenue for addressing energy absorption challenges across diverse industrial applications.

In-situ ionic crosslinking of 3D bioprinted cell-hydrogel constructs for mechanical reinforcement and improved cell growth.

Hydrogels are commonly used in 3D bioprinting technology owing to their ability to encapsulate living cells. However, their inherent delicate properties limit their applicability in the fabrication of mechanically reliable tissue engineering constructs. Herein, we propose a novel reinvented layering integration method for the functional enhancement of 3D cell-hydrogel bioprinting. This was implemented by inserting electrospun microfiber sheets with a crosslinker between the 3D bioprinted layers. When surface-modified microfiber sheets were combined with Ca2+ ionic crosslinkers, the as-printed cell-hydrogel strand was immediately crosslinked when it contacted the sheet surface. The in-situ crosslinking in the bioprinting process not only improved the overall structural stability, but also reinforced the compressive strength and elastic modulus. The enhanced structural stability guaranteed the shape fidelity of the 3D architecture, which included the internal channel network, resulting in improved perfusion conditions for cell growth. The growth of NIH3T3 fibroblasts in 3D bioconstructs with in-situ crosslinking increased by up to five times compared to that of normally bioprinted constructs. The strengthened structural integrity was distinctly sustainable during the cell culture period owing to the sustained release of Ca2+ ions from the embedded microfiber sheets. The synergistic effect of the reinforced mechanical properties with enhanced cell growth is expected to extend the applicability of the proposed hydrogel-based bioprinting technique for soft tissue engineering.

The effect of 3-D printed polylactic acid scaffold with and without hyaluronic acid on bone regeneration.

BACKGROUND: Three- dimensional (3D) technology has been suggested to overcome several limitations in guided bone regeneration (GBR) procedures because 3D-printed scaffolds can be easily molded to patient-specific bone defect site. This study aimed to investigate the effect of 3-D printed polylactic acid (PLA) scaffolds with or without hyaluronic acid (HA) in a rabbit calvaria model. METHODS: A calvaria defect with a diameter of 15 mm was created in 30 New Zealand white rabbits. The rabbits were randomly allocated into three groups including no graft group (control, n = 10), 3D printed PLA graft group (3D-PLA, n = 10), and 3D printed PLA with hyaluronic acid graft group (3D-PLA/HA, n = 10). Five animals in each group were sacrificed at 4 and 12 weeks after surgery. Microcomputed tomography and histologic and histomorphometric analyses were performed. RESULTS: Over the whole examination period, no significant adverse reactions were observed. There were no statistically significant differences in bone volume (BV) /tissue volume (TV) among the three groups at 4 weeks. However, the highest BV/TV was observed in the 3D-PLA/HA group at 12 weeks. The new bone area for control, 3D-PLA, and 3D-PLA/HA showed no statistical differences at 4 weeks. However, the value was significantly higher in the 3D-PLA and 3D-PLA/HA groups compared to the control group at 12 weeks. CONCLUSION: The 3D printed PLA scaffolds was biocompatible and integrated well with bone defect margin. They were also provided the proper space for new bone formation. Therefore, 3D printed PLA/HA might be a potential tool to enhance bone augmentation.

Optimized film processing of nanosilver colloids for photoluminescence enhancement.

Recently, various research strategies have been employed to improve light extraction efficiency in organic LEDs, including the recent development of localized surface plasmon resonance (LSPR), as well as the more widely-known application of a photonic crystal layer. Here, we report on the development of a process method for forming a two-dimensional nanosilver patterned array to achieve LSPR-coupled light-emission efficiency enhancement. The process scheme involves the spin-coating of nanosilver colloidal ink onto a glass substrate, followed by optimized thermal annealing to create an array of isolated nanosilver islands. The resulting Ag islands are in the size range 50 approximately 80 nm, which is larger than the diameter of the Ag nanoparticles in the colloidal suspension. Then, silicon oxide is thermally sputtered to provide a spacer layer to prevent luminescence quenching of the red-emitting nanocrystal quantum dot (NQD) layer, which is deposited in a subsequent spin-coating process. When the NQD layer is excited, the energy of the photoelectron is confined to the surfaces of the nanosilver islands in the near-field. In this study, the localized surface plasmon resonance peaks were at a wavelength of 625 nm, and out-coupling efficiency was enhanced more than sixfold.

Additive manufacturing of the core template for the fabrication of an artificial blood vessel: the relationship between the extruded deposition diameter and the filament/nozzle transition ratio.

An artificial blood vessel with a tubular structure was additively manufactured via fused deposition modeling (FDM) starting from a single strand of polyvinyl alcohol (PVA) filament coated with a specific thickness of biocompatible polydimethylsiloxane (PDMS), followed by removal of the inner core via hydrogen peroxide leaching under sonication. In particular, we examined the relationship between the extruded deposition diameter and the filament migration speed/nozzle control speed (referred to as the filament/nozzle transition ratio), which is almost independent of the extruded deposition flow rate due to the weak die-swelling and memory effects of the extruded PVA arising from its intrinsically low viscoelasticity. The chemical stability of the PDMS during sonication in the hydrogen peroxide solution was then determined by spectroscopic techniques. The PDMS displayed no mechanical degradation in the hydrogen peroxide solution, resulting in similar fracture elongation and yield strength to those of the pristine specimen without the leaching treatment. As a further advantage, the inside surface of the PDMS was smooth regardless of the hydrogen peroxide leaching under sonication. The potential application of the as-developed scaffold in soft tissue engineering (particularly that involving vascular tissue regeneration) was demonstrated by the successful transplantation of the artificial blood vessel in a right-hand surgical replica used in a clinical simulation.

Fabrication of 3D freeform porous tubular constructs with mechanical flexibility mimicking that of soft vascular tissue.

Three-dimensional (3D) printing, with its capability for producing arbitrary shapes, has been extensively studied for tissue engineering applications. However, clinical applications, especially for soft tissues, have been limited due to mechanical mismatch between the 3D-printed artificial tissues and the native tissues. Here, we suggest an integrative method of 3D printing, dip coating, and salt leaching for the fabrication of soft 3D freeform porous tubes, which are expected to be applied to the engineering of vascular tissues. Owing to their porous morphology and controlled wall thickness, the processed tubular constructs had flexible properties comparable to those of native soft tissues with a modulus range of several MPa. When thermoplastic polyurethane (TPU) was used as the dip-coating material, the porous tube exhibited a low tensile modulus from 1.47 to 2.47 MPa and a high elongation limit of over 400%. These flexible properties, which were clearly differentiated from the stiffness of 3D-printed samples with moduli of tens or hundreds of MPa, were confirmed to mimic the mechanical properties of native tissues. Furthermore, by varying the material composition in the dip-coating process, the flexibility of the tube could be modulated when stiffer polycaprolactone (PCL) layers were combined. In addition, such a combination using biocompatible materials could be expected to provide safer interaction at surgical interfaces. Synergistically with the mechanical flexibility, since the proposed method was based on a 3D-printed template, the resulting construct would have extensive applicability in patient-specific tissue engineering.

Enhanced bioactivity of titanium-coated polyetheretherketone implants created by a high-temperature 3D printing process.

Polyetheretherketone (PEEK), one of the potential alternatives to metallic materials for implants, necessarily involves high temperature process conditions to be three-dimensionally (3D) printed. We developed a 3D printing setup equipped with thermally stabilized modules of the printing nozzle and building chamber, by which the PEEK implants could be successfully manufactured. Under optimized printing conditions, the maximal mechanical strength of the 3D printed sample attained over 80% of the original bulk property of PEEK. To enhance the interfacial biocompatibility, the as-printed implants were postprocessed with titanium (Ti) sputtering. The Ti-coated surfaces were evaluated through characterization studies of x-ray diffraction spectra, microscopic topographies, and wetting properties. For the in vitro tests, preosteoblasts were cultured on the developed PEEK-Ti structures and evaluated in terms of cell adhesion, proliferation, and osteogenic differentiation. In addition, the bone regeneration capability of the PEEK-Ti implants was confirmed by animal experiments using a rabbit tibia defect model for a period of 12 weeks. In the overall in vitro and in vivo tests, we confirmed the superior bioactivities of the Ti-modified and 3D printed interface by comparisons between the samples of machined and printed samples with or without Ti coating. Taken together, the comprehensive manufacturing approaches that involve 3D printing and biocompatible postprocessing are expected to have universal applicability in a wide range of bone tissue engineering.

Fine Microstructured In-Sn-Bi Solder for Adhesion on a Flexible PET Substrate: Its Effect on Superplasticity and Toughness.

A novel In-Sn-Bi solder with a low electrical resistivity of 14.3 × 10-6 Ω cm and a melting temperature of 99.3 °C was produced for use in adhesive joining on a flexible poly(ethylene terephthalate) substrate. We determined that the fine microstructure of the In-based solder (which had an average phase size of 62.2 nm) strongly influenced its superplasticity and toughness at diffusive temperatures of 55-85 °C because the late-forming BiIn intermetallic compound (IMC) suppressed the growth of two other IMCs, In3Sn and In0.2Sn0.8, which formed earlier in the soldering process. Thus, an elongation of 858.3% and toughness of 36.0 MPa were obtained at a temperature of 85 °C and a strain rate of 0.0020 s-1. However, due to phase boundary fracturing, the phase-refined solder exhibited a slightly more brittle nature (with an elongation of 74.3%) at room temperature compared with a standard In-Sn solder consisting only of the In3Sn and In0.2Sn0.8 IMCs, which had a slightly larger phase size of 84.9 nm and higher ductility (with an elongation of 80.7%). In terms of superplastic deformation, the conventional fracture system based on the Hall-Petch effect transformed into phase boundary sliding at the solder operating temperature, significantly enhancing ductility.

Characteristics of Carrier Collection of Nanopillar-Patterned Silicon Solar Cells.

Nanopillar-patterned Si solar cells were investigated. Ag nanoparticles were coated on a polished Si substrate as an etching mask. Reactive ion etching caused Si nanopillars to replicate in a reverse fashion on the Ag nanoparticles over a large area. The nanopillar structures efficiently reduced the light reflection on the surface and effectively drove the incident light into a Si absorber. This induced a significant enhancement of the photogenerated-current with an improved solar cell efficiency of 16.07%. The Si nanopillar-patterned solar cells showed improved carrier collection for long wavelengths; however, the surface-defect induced recombination degraded the quantum efficiency at short wavelengths. We suggest that the reduction of recombination loss should be considered for efficient nanostructure solar cells.

An Antireflective Nanostructure Array Fabricated by Nanosilver Colloidal Lithography on a Silicon Substrate.

An alternative method is presented for fabricating an antireflective nanostructure array using nanosilver colloidal lithography. Spin coating was used to produce the multilayered silver nanoparticles, which grew by self-assembly and were transformed into randomly distributed nanosilver islands through the thermodynamic action of dewetting and Oswald ripening. The average size and coverage rate of the islands increased with concentration in the range of 50-90 nm and 40-65%, respectively. The nanosilver islands were critically affected by concentration and spin speed. The effects of these two parameters were investigated, after etching and wet removal of nanosilver residues. The reflection nearly disappeared in the ultraviolet wavelength range and was 17% of the reflection of a bare silicon wafer in the visible range.

Nanosilver Colloids-Filled Photonic Crystal Arrays for Photoluminescence Enhancement.

For the improved surface plasmon-coupled photoluminescence emission, a more accessible fabrication method of a controlled nanosilver pattern array was developed by effectively filling the predefined hole array with nanosilver colloid in a UV-curable resin via direct nanoimprinting. When applied to a glass substrate for light emittance with an oxide spacer layer on top of the nanosilver pattern, hybrid emission enhancements were produced from both the localized surface plasmon resonance-coupled emission enhancement and the guided light extraction from the photonic crystal array. When CdSe/ZnS nanocrystal quantum dots were deposited as an active emitter, a total photoluminescence intensity improvement of 84% was observed. This was attributed to contributions from both the silver nanoparticle filling and the nanoimprinted photonic crystal array.