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The present study demonstrates the manufacturing of macroporous hydroxyapatite (HA) scaffolds, comprised of microporous hollow filaments with high shape retention, by UV curing-assisted 3D plotting using a feedrod comprised of a photocurable HA shell and a carbon black (CB) core. Two types of scaffolds with different filament interspaces (0.5 mm and 1 mm) were produced by depositing core-shelled filaments extruded through a 1.07-mm-diameter nozzle with in situ polymerization process. Both scaffolds exhibited that the hollow HA filaments were produced after the removal of CB core by heat-treatment, while micropores in the HA walls were created as the replica of camphene-camphor crystals. Overall porosity and macroporosity obtained using a camphene-camphor content of 60 vol% increased from 74.3 vol% to 79.3 vol% and from 50.7 vol% and 64.6 vol%, respectively, with an increase in filament interspace sizes from 0.5 mm to 1 mm. Both scaffolds exhibited reasonably high compressive strengths (2.36 ― 3.58 MPa) and modulus (68–86 MPa).

Poly(ether imide) (PEI) has shown satisfactory corrosion protection capability with good adhesion strength as a coating for magnesium (Mg), a potential candidate of biodegradable orthopedic implant material. However, its innate hydrophobic property causes insufficient osteoblast affinity and a lack of osseointegration. Herein, we modify the physical and chemical properties of a PEI-coated Mg implant. A plasma immersion ion implantation technique is combined with direct current (DC) magnetron sputtering to introduce biologically compatible tantalum (Ta) onto the surface of the PEI coating. The PEI-coating layer is not damaged during this process owing to the extremely short processing time (30 s), retaining its high corrosion protection property and adhesion stability. The Ta-implanted layer (roughly 10-nm-thick) on the topmost PEI surface generates long-term surface hydrophilicity and favorable surface conditions for pre-osteoblasts to adhere, proliferate, and differentiate. Furthermore, in a rabbit femur study, the Ta/PEI-coated Mg implant demonstrates significantly enhanced bone tissue affinity and osseointegration capability. These results indicate that Ta/PEI-coated Mg is promising for achieving early mechanical fixation and long-term success in biodegradable orthopedic implant applications., Graphical abstract Image 1, Highlights • PEI coating with subsequent Ta ion implantation was prepared on WE43 Mg alloy implant. • The corrosion resistance of Mg alloy implant was improved by Ta embedded PEI coating. • The wettability of PEI coating layer was enhanced by embedded Ta on its top-surface. • Ta embedded PEI coating significantly improved in vitro and in vivo responses. • Ta embedded PEI-coated Mg is highly suitable as a biodegradable orthopedic implant material.

This study demonstrates a novel type of biphasic calcium phosphate (BCP) gyroid scaffolds featuring of gyroid macroporous structure and micropous BCP walls using poly(methyl methacrylate) (PMMA) microspheres as the porogen for ceramic digital light processing (DLP) technique. To tailor the microporosity of the BCP walls and the overall porosity of the dual-scale porous BCP scaffolds, the PMMA content with regard to the BCP powder was controlled in the range of 40 vol% to 70 vol%. After debinding at 600 °C and sintering at 1200 °C for 3 h, micropores were uniformly created throughout each BCP framework, while preserving 3−dimensional gyroid macroporous structures. As the PMMA content increased from 40 vol% to 70 vol%, the microporosity remarkably increased from 31.9 (±2.5) vol% to 55.2 (±1.4) vol%. This approach allowed the achievement of very high overall porosities (82.2–89.7 vol%) for the dual-scale porous scaffolds. However, all the scaffolds showed reasonable compressive strengths (0.8 MPa −2.1 MPa), which are comparable to those of cancellous bones.

The present study reports the manufacturing of a novel type of porous calcium phosphate scaffolds with elongated gyroid structures using digital light processing (DLP), in order to offer significantly enhanced mechanical properties. In particular, solid camphor was employed as the diluent, in order to offer sufficiently low viscosity at high solid loading for conventional layer-by-layer DLP process. Four types of porous CaP scaffolds with different percent elongation (%EL = 0, 20, 40, and 60) were manufactured, and their porous structures and mechanical properties were characterized. All porous CaP scaffolds showed that CaP walls were elongated along the z-direction, while the degree of pore elongation increased with an increase in the designed %EL. Owing to the use of controlled processing parameters, such as layer thickness and exposure time for layer-by-layer photocuring process, and carefully designed debinding process, the photocured layers could be completely bonded together with high densification after sintering at 1,200 °C for 3 h. Such elongation of a gyroid structure offered significantly enhanced mechanical properties − compressive strengths of 4.33 ± 0.26 MPa and 11.51 ± 1.75 MPa were obtained for the porous CaP scaffold with the %EL of 0 and 60, respectively.

This study proposes camphene/photopolymer solutions as a novel pore-forming agent for the photocuring-assisted additive manufacturing of porous ceramics. Unlike conventional techniques using molten camphene, solid camphene can be directly dissolved in the photocurable monomer hexanediol diacrylate (HDDA) at room temperature, which can then crystallize with a dendrite-like morphology based on phase separation at lower temperatures. This unique approach allows alumina suspensions to solidify at ―2 °C and then effectively be photopolymerized using a digital light processing engine, resulting in camphene-rich crystals surrounded by photopolymerized alumina/HDDA walls. Sintered samples exhibited a highly porous structure, with the pores created after the removal of the camphene-rich crystals. Two different pore sizes were obtained in the lower and upper regions of a single layer, due to a decrease in the solidification rate along the building direction, although their porosities were similar (∼ 52 vol%). The porous samples exhibited a compressive strength of ∼ 265 MPa.

The present study describes the manufacturing of 4 mol% yttria partially stabilized zirconia (4Y-PSZ) prostheses with high mechanical properties and translucency using digital light processing (DLP). To formulate 4Y-PSZ suspensions with high solid loading and appropriate viscosity, as-received granules were calcined at 900 °C for 3 h and then crushed into fine particles. In addition, a mixture of low-viscosity hexanediol diacrylate (HDDA) monomer and decalin as the diluent was employed as the photopolymerizable medium. To achieve strong bonding between layers and high accuracy, the photocuring time during DLP process was optimized. 4Y-PSZ prostheses were almost fully densified after sintering at 1,500 °C for 2 h, which had a relative density of 99.4%. Also, no visible interfaces between the layers were noticed. The sintered 4Y-PSZ samples showed high flexural strength of 831 (±74) MPa and high optical transmittance of 30 (±1.2) %.

This study presents a novel strategy to construct ceramic structures comprised of microporous filaments using photocurable ceramic/monomer feedstocks containing terpene crystals as sublimable porogens for UV curing-assisted 3D plotting technique. The biphasic calcium phosphate (BCP) feedstock, composed of frozen terpene crystals surrounded by BCP/UDMA walls, could be favorably extruded through a fine nozzle and then effectively photopolymerized by UV light. Thus, green filaments with high shape retention could be obtained. In addition, a number of pores could be created in BCP filaments after removing terpene crystals via freeze-drying and the porosity could be tailored by adjusting terpene content in BCP feedstocks. This approach allowed for the construction of dual-scale porous structures comprising microporous filaments in a periodic pattern, with tailored overall porosities and compressive strengths. Several types of self-supporting structures were also successfully constructed using our approach.

This paper proposes a photocurable ceramic slurry containing a freezing vehicle as a novel feedstock for digital light processing (DLP) technique, which can produce hierarchical porous ceramic structures. A thin layer, comprised of a 3-dimensionally interconnected ceramic/monomer network surrounded by a frozen camphene-camphor alloy network, can be effectively photopolymerized by the DLP process, and thus micropores can be created after the removal of the camphene-camphor network via freeze-drying. Several processing parameters for the DLP process, including the temperature of the building vat, layer thickness, and UV exposure time, were optimized to produce hierarchical porous ceramic structures. The effect of freezing vehicle content on the microporous structures (e.g., porosity and pore size) and mechanical properties of ceramic frameworks was examined. In addition, hierarchical macro/micro-porous ceramic scaffolds comprised of microporous ceramic frameworks separated by microporous CaP frameworks were produced, and their porous structures and mechanical properties were characterized.

This study presents the utility of solid camphor as a novel type of diluent for the preparation of photocurable ceramic slurries with sufficiently low viscosity at high solid loading (48 vol%), which can be applicable for the conventional digital light processing (DLP) process. The camphor addition remarkably decreased the viscosity of calcium phosphate (CaP) ceramic slurries without affecting their photopolymerization behavior. This approach could effectively mitigate the clogging of pores with residual slurries, and thus the porous structure of porous CaP scaffolds with 3D channels could be tightly controlled. Furthermore, the high densification of CaP frameworks after sintering at 1250 °C for 3 h could be achieved owing to the use of the high solid loading in the CaP slurry. The porous CaP scaffolds produced displayed high compressive strength (˜ 23.8 MPa) and modulus (˜ 276 MPa) at a high porosity of ˜ 50.6 vol%.

The surface characteristics of coronary stents play a pivotal role in inhibiting in-stent restenosis and late-stent thrombosis. In this study, a sol-gel-derived silica xerogel-chitosan hybrid coating was applied to Co-Cr stent and was reported, for the first time, as a biocompatible drug delivery tool in vascular stent application. A dense and uniform chitosan-silica xerogel hybrid coating (1-μm thick) was applied on bare Co-Cr material. Sirolimus was well incorporated into the hybrid coatings without re-crystallization. The chitosan-silica hybrid coating with 30 wt% silica xerogel showed better mechanical stability and good adhesive strength without any cracking or delamination. The chitosan-silica hybrid coated Co-Cr surface exhibited significantly improved wettability and corrosion resistance compared to the chitosan coated Co-Cr surface. In addition, the hybrid coating layer enabled efficient loading of sirolimus, owing to the unique mesoporous structure of silica xerogel, which further allowed the sustained release of sirolimus over 3 weeks. In-vitro tests with human umbilical cord vein endothelial cells and blood platelets confirmed that the chitosan-silica hybrid coating had excellent cytocompatibility and hemocompatibilty. Thus, this study demonstrated that the chitosan-silica hybrid material is a promising material for coating coronary stents, with minimal risk of in-stent restenosis and thrombogenicity.

We herein propose a novel type of additive manufacturing (AM) technique, denoted as “in situ photocuring-assisted 3D plotting”, which can rapidly solidify extruded green filaments comprised of ceramic powders and photocurable monomers using UV light during 3D plotting. To accomplish this, the rheological properties and photocuring behavior of the ceramic slurry were carefully tailored, particularly by using a mixture of diruethane dimethacrylate (UDMA) and triethylene glycol dimethacrylate (TEGDMA) monomers as the photocurable vehicle. This innovative approach enabled the favorable extrusion of the ceramic slurry through a fine nozzle with high green strength after photocuring, and thus complex-shaped ceramic architectures with high shape retention could be constructed. As an example, a free-standing helical structure with a circular cross-section was successfully produced even without the use of any supporting materials. In addition, a porous ceramic scaffold with a tightly controlled porous structure could be produced.

A silane-modified hyaluronic acid (HA) hydrogel was prepared using a facile one-pot method with 3-glycidyloxypropyl-trimethoxysilane (GPTMS). The sol-gel route, specifically the self-condensation of the silane, was combined with the HA hydrogel system to modify its network structure. Nuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the chemical functionalization of GPTMS. The morphological, rheological properties, and enzymatic degradation of the hydrogels were also evaluated. The sol-gel-stabilized HA hydrogel exhibited superior mechanical properties and biochemical stability as well as excellent biocompatibility without triggering any negative biological effects. Furthermore, an efficient drug-loading strategy is suggested that uses sol-gel encapsulation without the need for any chemical reagents, resulting in sustained release characteristics. Vancomycin was used as a model drug, and enhanced efficacy was demonstrated in antibacterial tests. The proposed approach is expected to have great potential for biomedical applications, and our findings will provide insight into the structure-property relationship of hydrogels.

The creation of a moist environment and promotion of cell proliferation and migration together with antibacterial property are critical to the wound-healing process. Alginate (Alg) is an excellent candidate for injectable wound dressing materials because it can form a gel in a mild environment. Taking advantage of its gelation property, an injectable nano composite hydrogel containing nano-sized (about 90 nm) calcium fluoride (CaF2) particles was developed using in-situ precipitation process. The amount of released fluorine (F−) ion from the nanocomposite hydrogel increased with increasing CaF2 content inside the composite hydrogel and the ions stimulated both the proliferation and migration of fibroblast cells in vitro. The antibacterial property of the composite hydrogel against E. coli and S. aureus was confirmed through colony formation test where the number of bacterial colonies significantly decreased compared to Alg hydrogel. The in vivo results based on a full-thickness wound model showed that the nanocomposite hydrogel effectively enhanced the deposition of the extracellular matrix compared to that of the Alg hydrogel. This study demonstrates the potential of this nanocomposite hydrogel as a bioactive injectable wound-dressing material with the ability to inhibit bacterial growth and stimulate cell proliferation and migration for accelerated wound healing.

The medical applications of porous Mg scaffolds are limited owing to its rapid corrosion, which dramatically decreases the mechanical strength of the scaffold. Mimicking the bone structure and composition can improve the mechanical and biological properties of porous Mg scaffolds. The Mg structure can also be coated with HA by an aqueous precipitation coating method to enhance both the corrosion resistance and the biocompatibility. However, due to the brittleness of HA coating layer, cracks tend to form in the HA coating layer, which may influence the corrosion and biological functionality of the scaffold. Consequently, in this study, hybrid poly(ether imide) (PEI)-SiO2 layers were applied to the HA-coated biomimetic porous Mg to impart the structure with the high corrosion resistance associated with PEI and excellent bioactivity with SiO2. The porosity of the Mg was controlled by adjusting the concentration of the sodium chloride (NaCl) particles used in the fabrication via the space-holder method. The mechanical measurements showed that the compressive strength and stiffness of the biomimetic porous Mg increased as the portion of the dense region increased. In addition, following results show that HA/(PEI-SiO2) hybrid-coated biomimetic Mg is a promising biodegradable scaffold for orthopedic applications. In-vitro testing revealed that the proposed hybrid coating reduced the degradation rate and facilitated osteoblast spreading compared to HA- and HA/PEI-coating scaffolds. Moreover, in-vivo testing with a rabbit femoropatellar groove model showed improved tissue formation, reduced corrosion and degradation, and improved bone formation on the scaffold. STATEMENT OF SIGNIFICANCE: Porous Mg is a promising biodegradable scaffold for orthopedic applications. However, there are limitations in applying porous Mg for an orthopedic biomaterial due to its poor mechanical properties and susceptibility to rapid corrosion. Here, we strategically designed the structure and coating layer of porous Mg to overcome these limitations. First, porous Mg was fabricated by mimicking the bone structure which has a combined structure of dense and porous regions, thus resulting in an enhancement of mechanical properties. Furthermore, the biomimetic porous Mg was coated with HA/(PEI-SiO2) hybrid layer to improve both corrosion resistance and biocompatibility. As the final outcome, with tunable mechanical and biodegradable properties, HA/(PEI-SiO2)-coated biomimetic porous Mg could be a promising candidate material for load-bearing orthopedic applications.

Here, we present a novel strategy to fabricate hyaluronic acid (HA) hydrogels with excellent physical and biological properties. The cross-linking of HA hydrogel by butanediol diglycidyle ether (BDDE) was characterized under different reaction temperatures, and the resulting physical properties (i.e., the storage modulus and swelling ratio) were measured. The ratio between the cross-linking rate (a strengthening effect) and the hydrolysis rate (a weakening effect) was much greater with lower cross-linking temperatures after sufficient cross-linking time, resulting in a noticeably higher storage modulus. As the cross-linking temperature decreased, the formed HA hydrogel structure became denser with smaller pores. Moreover, the introduction of low-temperature HA cross-linking strategy also resulted in an enhanced several important characteristics of HA hydrogels including its enzymatic resistivity and its ability to elicit a cellular response. These results indicate the performance of HA hydrogels can be markedly enhanced without further additives or modifications, which is expected to contribute to the advancement of applications of HA hydrogels in all industrial fields.

Herein, strong and biocompatible Ti3C2Tz-enhanced poly(lactic acid) (PLA) nanocomposite membranes were prepared. The interface of the Ti3C2Tz nanosheets with the hydrophobic PLA matrix was mediated using n-octyltriethoxysilane (OTES). The optimized ultimate tensile strength of the OTES-Ti3C2Tz/PLA nanocomposite membrane was 72 MPa (33% higher than that of a pure PLA membrane). The addition of Ti3C2Tz enhanced the biological properties of the membrane, including the in vitro adhesion, proliferation, and osteogenic differentiation of MC3T3-E1 mouse preosteoblasts.

Titanium (Ti) is used in dental applications owing to their excellent mechanical properties, corrosion resistance, and biocompatibility. However, postoperative bacterial infection may cause serious complications and remains one of the most difficult challenges hindering the development of long term Ti dental implants. Therefore, the desire for high quality dental care has led to significant interest in designing implant surfaces that offer stable antibacterial activity with excellent cellular response. In this study, we propose a simple and efficient approach for fabricating an antibacterial stabilized Ag nanostructure on a Ti surface, which is based on a two-step process involving target-ion induced plasma sputtering (TIPS) and Ag sputtering. The TIPS process generates a nanostructured Ti surface that provides a nanotemplate on which the Ag nanostructure may be deposited through Ag sputtering. The Ag nanoclusters adhere tightly to the TIPS-treated Ti (TIPS-Ti) nanostructured surface with no noticeable defects, and the amount of stabilized Ag deposited may be controlled by simply adjusting the Ag-sputtering time. The silver ion is released continuously from the Ag-TIPS-Ti surface for 7 d. The Ag nanostructured TIPS-Ti (Ag-TIPS-Ti) surface not only offers outstanding antibacterial activity toward Escherichia coli and Staphylococcus aureus over 12 h of culturing but also exhibits no severe cytotoxicity for fibroblast cells for up to 10 days. In particular, Ag stabilization by 10 s Ag-sputtering on TIPS-Ti provides the best balance between antibacterial activity and cellular performances, and the resulting fibroblast cell-attachment morphology and proliferation level are similar to those for a polished Ti surface. Therefore, the controllable antibacterial activity and fibroblast tissue affinity of the Ag-TIPS-Ti present a promising avenue for producing reliable, long term dental implants.

Objective Susceptibility artifacts from metal clips in magnetic resonance (MR) imaging present an obstacle to evaluating the status of clipped aneurysms, parent arteries, and adjacent brain parenchyma. We aimed to develop MR-compatible aneurysm clips. Methods Considering the mechanical and biologic properties, as well as MR compatibility of candidate materials, a prototype clip with a zirconia body and a polyurethane head spring (zirconia clip [ZC], straight, 9-mm long) was developed. The closing forces, opening width of blades, and in vitro and in vivo artifact volumes in 3 tesla MR imaging were compared among the prototype and commercial metal clips such as a Yasargil clip (YC, curved type, 8.3-mm long) and a Sugita clip (SC, straight type, 10-mm long). An in vivo animal study was performed with a canine venous pouch aneurysm model. Results The closing forces (N) at 1 mm and 8 mm from the blade tip were 2.09 and 3.77 in YC, 1.85 and 3.04 in SC, and 2.05 and 4.60 in ZC. The maximum opening widths (mm) was 6.8, 9.0, and 3.0 in YC, SC, and ZC, respectively. The in vitro artifact volumes of YC, SC, and ZC in time-of-flight MR imaging were 26.9, 29.7, and 1.9 times larger than the respective real volumes. The in vivo artifact volumes of YC, SC, and ZC were respectively 21.4, 29.4, and 2.6 times larger than real ones. Conclusions ZC showed the smallest susceptibility artifacts and satisfactory closing forces. However, the narrow opening width of the blades was a weak point.

Polytetrafluoroethylene (PTFE) inherently exhibits deficient bonding to other materials because of its low surface energy. In this study, large-scale nanopatterns were introduced to nickel–titanium (NiTi) to achieve strongly tightened PTFE coating layers on the metal substrate. The nano-roughened NiTi surface was produced using target-ion induced plasma sputtering. Typical porous PTFE coating layers were observed, and PTFE was partially infiltrated into nanoscale pores. The mechanical stability of the PTFE coating was consequently enhanced, indicating the great potential of this coating for medical devices including catheters, stents, and guide wires.

Surface patterns can be used as a selective coating platform on metal surfaces, in particular, under various deformation conditions because they induce local strain gradients along with pattern geometry. In this study, hard and flexible coating materials were introduced to regions with small and large deformations, respectively, on patterned magnesium (Mg) surfaces. Despite significant deformation, a polymer-ceramic coating on patterned Mg maintained its protection, as opposed to a ceramic coating on a flat Mg surface. Our proposed approach can be implemented in various Mg-based medical-device platforms by optimizing surface patterns on Mg depending on their loading conditions for clinical use. MOE (Min. of Education, S’pore)

For hard tissue engineering applications, biodegradable composite scaffolds have been extensively investigated because of their satisfactory mechanical properties and biocompatibility. Recently, 3D printing processes have received substantial attention in the tissue engineering field because of their ability to be customized for tissues that have suffered different types of loss or damage for each patient. However, previous studies on material extrusion-based techniques lack flexibility in the filler loading amount and cannot fulfill requirements that aim to enhance mechanical properties and biocompatibility. Herein, we propose a biodegradable polymer-based composite scaffolds with high ceramic loadings fabricated using the binder jetting (BJ) technique conjugated with capillary rise infiltration. A calcium sulfate hemihydrate (CSH) scaffold was fabricated using BJ-based 3D printing. Thereafter, CSH was transformed into biphasic calcium phosphate (BCP) using hydrothermal treatment, followed by heat treatment. Melted polycaprolactone (PCL) was infiltrated in the resulting BCP scaffold. BCP was then completely dispersed in the PCL matrix, and the calculated PCL loading in the BCP matrix exceeded 40 vol%. The PCL/BCP composite scaffold demonstrated the highest compressive strength, moduli, and toughness with the fracture mode shifted from brittle to less brittle. Moreover, a stable PCL/BCP surface promotes initial cell responses and shows sufficient proliferation and differentiation of pre-osteoblast cells.

Titanium implants with sufficient mechanical properties and biocompatibility have been in demand for rapid healing and successful surgery. Herein, porous Ti6Al4V scaffolds with multi-scale porosity were obtained by coupling dynamic freeze-casting with micro-arc oxidation (MAO). The fabricated scaffolds exhibited tailored pore sizes and interconnected pores. Compressive strength and elastic modulus were controlled by adjusting the porosity of the scaffolds. MAO was successfully conducted on the porous Ti6Al4V scaffolds by inhibiting gaseous emission from the electrolysis of water with the addition of ethanol to the MAO solution. Moreover, the biological response of preosteoblasts on the multi-scale porous Ti6Al4V scaffolds was enhanced owing to their porous topography and modified chemical composition.

We herein demonstrate a novel, versatile approach to produce calcium phosphate (CaP) ceramics with continuously gradient macrochannels using three-dimensional extrusion of a bilayered ceramic-camphene mixture/pure camphene feedrod. In this technique, the pure camphene used as the upper part could be preferentially extruded because of the wall slip phenomenon. This enabled the formation of green filaments comprised of a camphene core surrounded by a ceramic/camphene shell, where the core/shell thickness ratio increased gradually as extrusion proceeded. CaP ceramics with continuously gradient macrochannels could be successfully produced by three-dimensionally depositing the extruded filaments layer-by-layer. With increasing the distance from the dense bottom layer, macrochannels created after the removal of the camphene cores via freeze-drying became larger, while the CaP walls became thinner. The local porosity could increase gradually and continuously from the dense bottom and reach up to ~72 vol%.

Mechanically stable tantalum (Ta) coatings were deposited onto nano-roughened and Ta-incorporated nickel-titanium (NiTi) alloy substrates to enhance their radiopacity and biocompatibility. A target-ion induced plasma sputtering process was used to induce highly uniform nanoscale roughness on the NiTi alloys, with Ta implantation. Characterization by field-emission scanning electron microscopy, X-ray diffraction, and transmission electron microscopy revealed that a dense alpha-phase Ta coating layer was tightly anchored to the NiTi substrate via the nano-roughened interface structures. The mechanical stability and stretchability of the Ta coating was examined using scratch and tensile tests, respectively. The adhesion strength and mechanical stability of the Ta coating on the nano-roughened NiTi surface showed remarkable improvement compared with the Ta coating on a flat NiTi surface. X-ray microscopic images showed that the radiopacity of a NiTi stent was enhanced by the Ta coating layer because of its high X-ray absorption coefficient and large thickness. In vitro cell adhesion and MTS assay revealed that the Ta coating was beneficial for endothelial cell attachment and proliferation. These results demonstrate that the Ta coating deposited onto nano-roughened NiTi substantially improved the mechanical stability, radiopacity, and biocompatibility of the NiTi stent.

Magnesium (Mg) and its alloys are promising materials for biodegradable drug-eluting stent applications, but their rapid corrosion remains a major challenge for clinical practice. Considerable efforts have been made to develop an efficient surface coating that can provide higher Mg stent corrosion resistance, sustained drug-delivery capability, and vascular compatibility. Herein, we introduce poly(ether imide) (PEI) and poly(lactic-co-glycolic acid) (PLGA) as surface coating polymers for WE43 Mg-alloy stent. Using a sequential spray-coating method, we developed a novel asymmetric stent coating comprising an inner surface coated with a PEI single layer and outer/side surfaces coated with sirolimus-loaded PLGA/PEI double layers. PEI coating layer has excellent adhesiveness to WE43 surface and considerably improves WE43 corrosion resistance and in vitro endothelial cell compatibility. PLGA/PEI double coating layer ensures a low release rate of sirolimus and stable surface morphology during drug-release process. Only vascular smooth muscle cells are directly affected by sirolimus owing to the asymmetric geometry of PLGA/PEI double coating, which has a satisfactory anti-proliferation effect. These results indicate that the developed asymmetrically PEI- and PLGA/PEI-coated WE43 stents have significant potential for achieving enhanced re-endothelialization and suppressed in-stent restenosis in vascular stent applications.

The composite material Li x Ni 0.25 Co 0.10 Mn 0.65 O (3.4 + x) / 2 (x = 1.6, 1.4, 1.2, 1.0, 0.8) were synthesized and characterized for their structural, morphological, and performance as cathode materials in Li-ion batteries. The Rietveld refinement results indicate the presence of two phases at high lithium levels (x = 1.6 and 1.4): Li 2 MnO 3 ( C 2/ m ) and Li M O 2 ( M Ni, Co, Mn) ( R 3¯ m ); the latter contains Ni 2 + and Ni 3 + . At low lithium levels (x = 1.2, 1.0, and 0.8) an additional spinel phase Li M 2 O 4 ( Fd 3¯ m ) emerges, which is known to affect the electrochemical performance of the oxide. Structural analysis reveals that the spinel phase contains mixed transition metals Ni, Co, and Mn as [Li + ,Co 2 + ][Ni 2 + ,Co 3 + ,Mn 4 + ] 2 O 4 . A low lithium level is found to induce primary particle growth, as well as Co and Ni segregation within the secondary particles. These results are expected to contribute to material optimization and commercialization of lithium-rich oxide cathodes.

This study proposes a simple, useful approach to produce three-dimensionally macrochanneled titanium (Ti) scaffolds with tailored porosities and mechanical properties using porous polylactic acid (PLA) templates that can be prepared by conventional solid freeform fabrication (SFF) technique. Specifically, methylcellulose (MC) polymer was used as a binder since it could effectively bind coarse Ti particles and remain chemically stable inert in organic solvents used to dissolve PLA polymer. A Ti slurry-filled PLA was immersed in chloroform to remove the PLA template, followed by sintering at 1300 °C for 3 h in a vacuum. The use of a relatively small amount of a MC binder and removal of the PLA template in solvent enabled the construction of straight Ti frameworks and macrochannels in a 3-D periodic pattern without severe impurity contamination. This tightly controlled porous structure enabled the achievement of high compressive strengths without a catastrophic failure, while the compressive strength increased from ~ 72 MPa to 121 MPa with a decrease in overall porosity from ~ 75 vol% to ~ 67 vol%. In addition, the porous Ti scaffolds showed good biocompatibility, which was assessed by in vitro cell tests in terms of attachment, proliferation, and differentiation of MC3T3-E1 cells.

We herein demonstrate the utility of the rapid direct deposition of a titanium hydride (TiH2) paste for the production of porous titanium (Ti) scaffolds with tailored porous structures and mechanical properties. In particular, methylcellulous (MC) polymer was used as the binder, since it can rapidly solidify in acetone through solvent extraction, thus enabling deposited green filaments to have high structural integrity. In addition, TiH2 powder was used as the Ti source because of its smaller particle size than commercial Ti powder and conversion to Ti metal through a two-step dehydrogenation process. The uses of fine TiH2 powder and MC binder allowed for the creation of three−dimensionally interconnected periodic macrochannels with sizes of ∼165 ± 14 × 167 ± 25 μm. The produced Ti scaffold had a porosity of ∼42 ± 7 vol % and a reasonably high compressive strength of 48 ± 15 MPa. In addition, the porosity and mechanical properties of porous Ti scaffolds could be tailored simply by adjusting the initial distances between deposited green TiH2/MC filaments. All of the porous Ti scaffolds produced with various porosities showed good in vitro biocompatibility.

This study demonstrates a novel, simple way of synthesizing bone morphogenetic protein (BMP)-loaded hydroxyapatite (HA) microspheres for enhanced bone regeneration. To accomplish this, calcium phosphate cement (CPC) microspheres, consisting of α-TCP and TTCP powders, were prepared using water-in-oil (W/O) emulsion, followed by treatment at 37 °C for 3 days to convert the CPC to HA. The BMP-loaded HA microspheres with a well-defined spherical shape had a highly porous structure, which was created by the entanglement of precipitated HA crystals with a needle-like morphology. The unique porous structure with the bone mineral-like HA phase resulted in a considerable improvement in in vitro biocompatibility. In addition, the bone regeneration ability of the HA microspheres was significantly enhanced by BMP loading, which was examined by in vivo animal testing using a rabbit vertical guided bone regeneration model.

This study proposes a novel type of macroporous ceramic scaffolds, which are comprised of hollow tubular filaments with a highly microporous structure, using 3-dimensional ceramic/camphene-based co-extrusion (3D-CoEx). The use of an initial feedrod, comprised of a camphene core and an alumina/camphene shell, enabled the construction of hollow tubular frameworks and micropores through the removal of the camphene phase. The produced scaffolds showed 3-dimensionally interconnected macropores with dimensions of ∼250–300 μm × 400–550 μm, which were surrounded by hollow alumina filaments (∼500 μm in diameter) featuring a number of micropores (several tens of microns in size). This unique macro/micro-porous structure could achieve a combination of both the reasonably high compressive strength of ∼5.4 MPa and very high porosity of 86 vol%. In addition, the final mechanical properties and overall porosity of the porous alumina scaffolds could be fine-tuned by adjusting initial alumina content in the alumina/camphene.

This study demonstrates the versatility of 3-dimensional ceramic/camphene-based extrusion (3D-Ex) using a frozen alumina/camphene body as a feedstock for the production of porous alumina scaffolds with a biomimetic macro/micro-porous structure. Three-dimensionally interconnected macropores were constructed through the deposition of frozen alumina/camphene filaments at a stacking sequence of 0°/90°, while aligned micropores were created in alumina frameworks as the replica of camphene dendrites that had been extensively elongated by the extrusion of a frozen alumina/camphene body. The macro/micro-porous structure and compressive strength of porous alumina scaffolds could be tailored by adjusting initial alumina content in alumina/camphene slurries.

This study presents a novel type of poly(e-caprolactone) (PCL) scaffold comprised of tailored core/shell-structured filaments. The scaffold can be produced using a nonsolvent-induced phase separation phenomenon during the 3D plotting of PCL solutions in a coagulation bath. Specifically, a mixture of water and ethanol was employed as the nonsolvent, in order to tailor the phase separation behavior of a PCL/acetone solution. The addition of water to ethanol allowed for the creation of dense shells due to the fast exchange between acetone and water during the early stage of the 3D plotting process, while in the cores a number of micropores were formed. In addition, the thickness of the dense shell increased with an increase in water content in the water/ethanol mixture, increasing the mechanical properties (i.e., tensile strength, modulus, and strain at failure) of the porous PCL scaffolds with tailored core/shell-structured filaments remarkably.

Microspheres are beneficial for filling defects of various shapes and provide a large surface area for cell attachment. Porous microspheres have attracted particular attention because they can deliver cells and bioactive molecules such as growth factors. In this study, BCP–collagen composite microspheres were developed for growth factor delivery in bone regeneration. Firstly, porous biphasic calcium phosphate (BCP) microspheres were fabricated by applying a water-in-oil emulsion technique using camphene as a pore generator. Then, porous BCP–collagen composite microspheres were fabricated by repetitively dip coating the microspheres in a collagen solution to effectively deliver growth factor to bone defects. Characterization of the microspheres and in vitro studies were conducted to investigate the effect of collagen infiltration on bone regeneration. In addition, in vitro evaluation demonstrated the sustained bone morphogenetic protein-2 (BMP-2) delivery of the microspheres and the effect of cell differentiation, and in vivo assessment with rabbits revealed that the microspheres filled the defect well and that bone could be regenerated through the microspheres. Moreover, the composite system was more effective for bone regeneration than the bare BCP microspheres because of the drug retention of collagen. These findings indicate that the porous microspheres are effective for tissue regeneration by continuous growth factor delivery.

Ideal bone substitutes should ensure good integration with bone tissue and are therefore required to exhibit good mechanical stability and biocompatibility. Consequently, the high elastic modulus (similar to that of bone), thermoplasticity, and biocompatibility of poly(lactic acid) (PLA) make it well suited for the fabrication of such substitutes by fused filament fabrication (FFF)-based 3D printing. However, the demands of present-day applications require the mechanical and biological properties of PLA to be further improved. Herein, we fabricated PLA/Ti composite scaffolds by FFF-based 3D printing and used thermogravimetric analysis to confirm the homogenous dispersion of Ti particles in the PLA matrix at loadings of 5–20 vol%. Notably, the thermal stability of these composites and the crystallization temperature/crystallinity degree of PLA therein decreased with increasing Ti content, while the corresponding glass transition temperature and melting temperature concomitantly increased. The compressive and tensile strengths of PLA/Ti composites increased with Ti increasing loading until it reached 10 vol% and were within the range of real bone values, while the impact strengths of the above composites significantly exceeded that of pure PLA. The incorporation of Ti resulted in enhanced in vitro biocompatibility, promoting the initial attachment, proliferation, and differentiation of pre-osteoblast cells, which allowed us to conclude that the prepared PLA/Ti composite scaffolds with enhanced mechanical and biological properties are promising candidates for bone tissue engineering applications.

In vascular surgical applications, small-diameter vascular grafts made from synthetic polymers are rarely commercialized, owing to delayed reendothelialization and subsequent thrombus formation and occlusion. Here, we describe a novel design for a small-diameter poly-ε-caprolactone (PCL) vascular graft with a functional, bilayered nanofibrous structure and a composition that enables a suitable healing process and gradual degradation/replacement by natural blood vessels. To improve vascular cell responses to the PCL, a natural bioactive polymer (collagen) and a sol–gel-derived bioceramic (silica) were incorporated into the inner and outer layer of the PCL vascular graft, respectively. An electrospinning technique enabled the development of uniform electrospun PCL/collagen and PCL/silica nanofibers. In particular, the orientations of PCL/collagen nanofibers prepared with a high-speed rotating collector were highly aligned, and no breaks or irregular shapes were observed. The thin inner layer, composed of PCL/collagen with longitudinally aligned nanofibers, was favorable for the adhesion, elongation, and migration of endothelial cells, thus eliciting rapid reendothelialization of luminal surfaces of a vascular graft. The relatively thick outer layer, composed of PCL/silica with randomly distributed nanofibers, provided a superior mechanical strength and showed satisfactory biocompatibility. The findings of this study demonstrate a strong potential of PCL-based bilayer vascular grafts for vascular tissue applications. Keywords: Vascular graft, Poly-ε-caprolactone, Collagen, Silica, Electrospinning

In this study a gradient grain structure was produced by processing rod billets through three roll planetary milling (also known as PSW process). This kind of gradient structure is reported to provide an excellent combination of strength and ductility owing to an ultrafine-grained surface layer and a coarse-grained interior of the billet. Specifically, copper rod samples were subjected to up to six passes of PSW at room temperature. To study the evolution of the microstructure during the deformation, microhardness measurements and Electron Backscatter Diffraction (EBSD) analysis were performed after one, three and six passes. Additionally, the distributions of the equivalent stress during PSW and the equivalent strain after processing were studied by finite element analysis using the commercial software QFORM. The results showed the efficacy of PSW as a means of imparting a gradient ultrafine-grained structure to copper rods. A good correlation between the simulated equivalent strain distribution and the measured microhardness distribution was demonstrated.

This study proposes self-assembly-induced 3D plotting as an innovative solid freeform fabrication (SFF) technique for the production of macro/nano-porous collagen scaffolds, particularly comprised of nanofibrous collagen filaments. In this technique, collagen filaments deposited in a coagulation bath could be effectively gelled through the self-assembly of collagen molecules into fibrils, accordingly, enabling the 3-dimensional deposition of collagen filaments with a collagen nanofiber network. The unique macro/nano-structure could be structurally stabilized by dehydration process coupled with chemical cross-linking. The porous collagen scaffolds produced had 3-dimensionally interconnected macropores (~ 451×305 μm in pore width) separated by nanoprous collagen filaments. In addition, the macro/nano-porous collagen scaffolds showed the tensile strength of~353 kPa and compressive strength of~31 kPa at a porosity of~95 vol% and excellent in vitro biocompatibility, assessed using pre-osteoblast MC3T3-E1 cells.

We herein propose a novel way of creating porous biphasic calcium phosphate (BCP) scaffolds with tightly controlled 3-D macrochannels using rapid direct deposition of ceramic paste (RDD-C). This newly developed RDD-C technique can rapidly solidify deposited green BCP filaments through the precipitation of a methylcellulose (MC) polymer used as the binder in aqueous BCP paste via solvent extraction mechanism. This allowed porous scaffolds produced with various initial distances between green filaments (0.5 mm, 1 mm, and 1.5 mm) to have tightly controlled 3-D macrochannels with good shape tolerance. As the initial distance between green filaments increased from 0.5 mm to 1.5 mm, overall porosity increased from 44.3±4.9 vol% to 63.5±2.5 vol%, while compressive strength decreased from 30.1±7.6 MPa to 11.6±3.8 MPa. The porous scaffold showed good biocompatibility assessed by in vitro cell tests.

Changes in the internal structure of nonwoven mats during tensile testing were investigated in situ with micro X-ray computer tomography (CT). Fiber orientation and volume fraction, as well as fiber–fiber contact, were quantitatively characterized at several strain levels. These parameters are apt to change under tensile loading and are important in determining the mechanical properties of nonwoven mats. The reorientation of fibers along the tensile direction was restricted at large deformations due to interlocked structures, which formed as a result of inherent entanglements in the nonwoven mats. In addition, contact efficiency, which describes the relative degree of fiber–fiber contact and was shown to be a suitable geometrical parameter for characterizing the microstructure of nonwoven mats, decreased at low strain and then increased with increasing strain until failure.

In this study three-roll planetary milling was used to trial its potential for enhancing the mechanical properties of pure magnesium. The material was subjected to several passes of planetary milling at progressively decreased temperatures, down to room temperature for the last pass. It was shown that with increased number of passes the grain size was reduced, eventually to the micron range. Concurrently, the microstructure became increasingly more uniform across the billet. After six passes pure magnesium showed an excellent combination of tensile properties at room temperature, with a yield stress of 116 MPa and a strain to failure of 13%.

We created a hierarchical micro/nano-porous TiO 2 surface layer onto a Ti substrate to enhance its biocompatibility by mimicking the hierarchical architecture of the native extracellular matrix. To accomplish this, a rough, micro-porous TiO 2 layer with pore sizes in the range of 0.5–2 μm was first formed on the surfaces of a Ti substrate using micro-arc oxidation (MAO) and then coated with a thin layer of pure Ti, ~ 0.5 μm in thickness, using electron beam (e-beam) evaporation. Subsequently, anodic oxidation was conducted to create a uniform nano-porous TiO 2 surface layer with a pore size of ~ 70 nm on the micro-porous layer. This hierarchical micro/nano-porous surface showed considerably enhanced hydrophilicity and in vitro biocompatibility compared to the dense surface and even the micro-porous and nano-porous surfaces. These improvements were attributed to the synergistic effect of micropores and nanopores created by a combination of MAO and anodic oxidation. In addition, protein adsorption capacity was remarkably improved due to the high affinity of the nano-porous TiO 2 surface for proteins.

Highly porous gelatin–silica hybrid scaffolds with high porosity, large pores and large interconnections, as well as tailored surface textures were produced using a newly developed direct foaming/freezing. Two different types of precursors as the silica source, 3-glycidoxyproyltrimethoxysilane (denoted as “GS”) and sol–gel derived silica (denoted as “SS”), were used for producing the porous GLA–GS and GLA–GS–SS hybrid scaffolds. In this method, air bubbles could be vigorously incorporated into the GLA–GS and GLA–GS–SS mixtures and then stabilized by rapid freezing of the foamed mixtures at −70 °C. Both the porous GLA–GS and GLA–GS–SS hybrid scaffolds produced herein had a highly porous structure (porosity > 90 vol%, pore size = 200–500 μm, interconnection size = 100–200 μm) with a uniform distribution of the silica phase in the gelatin matrix. In addition, surface textures with a rugged morphology could be created after immersion of the porous GLA–GS and GLA–GS–SS hybrid scaffolds in ethanol at −20 °C for 24 h. The porous GLA–GS and GLA–GS–SS hybrid scaffolds showed much higher mechanical properties than the porous GLA scaffold, while preserving excellent in vitro biocompatibility, demonstrating potential application as the bone scaffold.

This study demonstrates the utility of nonsolvent induced phase separation (NIPS)-based 3D plotting as a novel SFF technique for the production of 3-dimensionally macrochanneled poly( e -caprolactone) (PCL) scaffolds with highly porous PCL frameworks. In particular, a PCL/tetrahydrofuran (THF) solution was deposited in an EtOH bath to rapidly solidify PCL filaments with a highly porous structure through exchange of THF solvent and EtOH nonsolvent. All the scaffolds produced with various PCL concentrations (14 wt%, 18 wt%, and 22 wt%) showed well-constructed 3-D macrochannels with highly porous PCL frameworks. However, the mechanical properties of the scaffolds, measured by compressive and tensile strength tests, increased with an increase in PCL concentration owing to a decrease in the overall porosity.

We produced highly porous titanium (Ti) scaffolds with large interconnected pores using vacuum-assisted foaming. To achieve this, a titanium hydride (TiH2) suspension was vigorously foamed under reduced pressure, then rapidly frozen at −70 °C, and finally freeze dried to remove frozen ice. The resulting green samples were heat-treated in a vacuum at 400 °C for 2 h to remove the organic phases and then at 1300 °C for 2 h to densify the Ti walls. Samples produced both with and without vacuum-assisted foaming showed good shape tolerance with a uniform porous structure. The samples produced using vacuum-assisted foaming had higher porosity (82±1.3 vol%) and larger pore size (150±65 μm), but lower compressive strength (8.9±1.6 MPa).

Commercial purity titanium (Grade 4) was processed by encapsulation-aided equal-channel angular pressing. Encapsulation in a copper cartridge made it possible to carry out the process repeatedly, up to 8 passes, at a relatively low temperature of 300 °C. Extremely high values of yield strength and tensile strength close to record literature values for this titanium grade and matching, or even surpassing, the levels for conventional Ti–6Al–4V alloy were obtained. A bi-modal grain structure observed may be responsible for a favorable combination of strength and ductility the processed material exhibits.

Polyetheretherketone (PEEK) has attracted much interest as biomaterial for interbody fusion cages due to its similar stiffness to bone and good radio-transparency for post-op visualization. Hydroxyapatite (HA) coating stimulates bone growth to the medical implant. The objective of this work is to make an implant consisting of biocompatible PEEK with an osteoconductive HA surface for spinal or orthopedic applications. Highly dense and well-adhered HA coating was developed on medical-grade PEEK using aerosol deposition (AD) without thermal degradation of the PEEK. The HA coating had a dense microstructure with no cracks or pores, and showed good adhesion to PEEK at adhesion strengths above 14.3 MPa. The crystallinity of the HA coating was remarkably enhanced by hydrothermal annealing as post-deposition heat-treatment. In addition, in vitro and in vivo biocompatibility of PEEK, in terms of cell adhesion morphology, cell proliferation, differentiation, and bone-to-implant contact ratio, were remarkably enhanced by the HA coating through AD.

This paper reports a new approach to fabricating biocompatible porous titanium with controlled pore structure and net-shape. The method is based on using sacrificial Mg particles as space holders to produce compacts that are mechanically stable and machinable. Using magnesium granules and Ti powder, Ti/Mg compacts with transverse rupture strength (~ 85 MPa) sufficient for machining were fabricated by warm compaction, and a complex-shape Ti scaffold was eventually produced by removal of Mg granules from the net-shape compact. The pores with the average size of 132–262 μm were well distributed and interconnected. Due to anisotropy and alignment of the pores the compressive strength varied with the direction of compression. In the case of pores aligned with the direction of compression, the compressive strength values (59–280 MPa) high enough for applications in load bearing implants were achieved. To verify the possibility of controlled net-shape, conventional machining process was performed on Ti/Mg compact. Compact with screw shape and porous Ti scaffold with hemispherical cup shape were fabricated by the results. Finally, it was demonstrated by cell tests using MC3T3-E1 cell line that the porous Ti scaffolds fabricated by this technique are biocompatible.

We produced highly porous triphasic calcium phosphate (CaP) scaffolds, comprising of hydroxyapatite (HA), β-tricalcium phosphate (β-TCP), and α-TCP phases, using vacuum-assisted foaming of a ceramic suspension (VFC) technique. In particular, vigorously foamed CaP green bodies with a composition of ∼60 wt% HA and 40 wt% β-TCP were sintered at relatively high temperatures (1200, 1250, 1300, and 1350 °C) to control the amount of three constituent phases. All the produced samples showed a highly porous structure (porosity ∼ 83.5–84.5 vol%, pore size ∼ 312–338 μm, and interconnection size ∼ 61–74 μm) with a number of microchannels in the CaP walls. However, sintering at relatively high temperatures≥1250 °C induced considerable phase transformation of the β-TCP to α-TCP phases. The presence of the more soluble α-TCP phase in the triphasic CaP scaffolds significantly enhanced the in vitro bioactivity of the porous CaP scaffolds, which was assessed in terms of their apatite-forming ability in simulated body fluid (SBF).

This study reports the utility of tantalum (Ta) coating for improving the surface hardness, in vitro bioactivity and biocompatibility of Co–Cr implants. The use of direct current sputtering allowed for the deposition of a dense and uniform Ta film onto a Co–Cr substrate, which was composed of β-phase Ta grains. This hard Ta coating significantly improved the surface hardness of the Co–Cr by a factor of > 2.3. In addition, the Ta-deposited Co–Cr substrate showed a vigorous precipitation of apatite crystals on its surface after 4 weeks of immersion in simulated body fluid, suggesting its excellent in vitro bioactivity. This bioactive Ta coating led to a considerable improvement in the in vitro biocompatibility of the Co–Cr, which was assessed in terms of the attachment, proliferation and differentiation of pre-osteoblasts (MC3T3-E1).