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In photopolymerization-based ceramic 3D printing, light cannot efficiently penetrate the opaque slurry, which is composed of particles and a photo-curable monomer. This can result in a difference of the crosslinking density within the layer, which can cause problems such as cracking and distortion. In this study, we used a photo cationic polymerizable cycloaliphatic epoxide as a photo-curable monomer to produce a green body with uniform crosslinking density by the living characteristics of photo cationic polymerized cycloaliphatic epoxide. The green body prepared with cycloaliphatic epoxide based ceramic slurry was subjected to an additional polymerization process, which involved heating at 150°C. Because of the living characteristics of the cycloaliphatic epoxide, a green body with a uniform crosslinking density was created and the fracture strength was improved. In addition, the green body exhibited good adhesion properties between layers. Finally, a sound fired body could be produced without any changes in shape after firing.

We herein report manufacturing of dental crowns made of 5-mol% yttria partially stabilized zirconia (5Y-PSZ) with desired mechanical properties, optical translucency and dimensional accuracy using digital light processing (DLP). To this end, all processing parameters were carefully controlled and optimized. First, 5Y-PSZ particles with a bimodal distribution were prepared via calcination of as-received granules and subsequent ball-milling and then used to formulate 5Y-PSZ suspensions with a high solid loading of 50 vol% required for high densification after sintering. Dispersant content was also optimized. To provide high dimensional accuracy, initial dimensions of dental crowns for 3D printing were precisely determined by considering increase and decrease in dimensions during photopolymerization and sintering, respectively. Photopolymerization time was also optimized for a given layer thickness of 50 μm to ensure good bonding between layers. A multi-step debinding schedule with a slow heating rate was employed to avoid formation of any defects. After sintering at 1500 °C for 2 h, 5Y-PSZ could be almost fully densified without noticeable defects within layers and at interfaces between layers. They had high relative densities (99.03 ± 0.39%) with a high cubic phase content (59.1%). These characteristics allowed for achievement of reasonably high mechanical properties (flexural strength = 625.4 ± 75.5 MPa and Weibull modulus = 7.9) and % transmittance (31.4 ± 0.7%). In addition, 5Y-PSZ dental crowns showed excellent dimensional accuracy (root mean square (RMS) for marginal discrepancy = 44.4 ± 10.8 μm and RMS for internal gap = 22.8 ± 1.6 μm) evaluated by the 3D scanning technique.

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).

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.

The purpose of this study is to develop mechanically robust soybean oil and polycaprolactone (PC)-based drug-eluting shape memory polymers (SMPs) containing polyrotaxane (PRX) cross-linkers. Essentially, the dynamic PRX cross-linker-containing methacrylate group is introduced to increase the cross-linking density and flexibility of the SMP to overcome its mechanical limitations. It was confirmed that the elongation and cross-linking density of the PRX-incorporated SMP were increased by 2-4 times compared to neat SMP. In addition, those high mechanical properties of the PRX-incorporated SMP could be maintained after the degradation of the PC by the drug-eluting process.

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%.

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.

This study demonstrates the utility of thermo-regulated phase separable alumina/camphene suspensions containing poly(methyl methacrylate) (PMMA) microspheres as porogens for the production of multi-scale porosity structures. The homogeneous suspension prepared at 60 °C could undergo phase separation during freezing at room temperature. This process resulted in the 3D networks of camphene crystals and alumina walls containing PMMA microspheres. As a consequence, relatively large dendritic pores with several tens of microns size could be created as the replica of frozen camphene crystals. In addition, after the removal of PMMA microspheres via heat-treatment, micron-sized small spherical pores could be generated in alumina walls. As the PMMA content with respect to the alumina content increased from 0 vol% to 40 vol%, while the camphene content in the suspensions was kept constant (70 vol%), the overall porosity increased from 45.7 ± 0.5 vol% to 71.4 ± 0.5 vol%. This increase in porosity is attributed to an increase in the fraction of spherical pores in the alumina walls. Thus, compressive strength decreased from 153 ± 18.3 MPa to 33 ± 7.2 MPa. In addition, multi-scale porosity alumina objects with a honeycomb structure comprising periodic hexagonal macrochannels surrounded by dual-scale porosity walls were constructed using a 3D plotting technique.

Herein, the cytocompatibility of selected MAX phases, Ti

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.

Herein, the cytocompatibility of selected MAX phases, Ti3AlC2, Ti3SiC2, and Ti2AlN, were systematically evaluated using in vitro tests for the first time. These phases were anoxic to preosteoblasts and fibroblasts. Compared with the strong viable fibroblasts, the different cellular responses of these materials were clearly distinguishable for the preosteoblasts. Under an osteoblastic environment, Ti2AlN exhibited better cell proliferation and differentiation performance than Ti3AlC2 and Ti3SiC2. Moreover, the performance was superior to that of a commercial Ti–6Al–4V alloy and comparable to that of pure Ti. A possible mechanism was suggested based on the different surface oxidation products, which were determined from the binding energy of adsorbed Ca2+ ions using first-principles calculations. Compared with the partially oxidized TiCxOy layer on Ti3AlC2 and Ti3SiC2, the partially oxidized TiNxOy layer on the Ti2AlN had a stronger affinity to the Ca2+ ions, which indicated the good cytocompatibility of Ti...

The objective of the present study is to demonstrate the versatility of the digital light processing (DLP) technique particularly when using a freeze-cast ceramic layer as the feedstock, which can manufacture porous calcium phosphate (CaP) scaffolds with arbitrarily designed macroporous structures with tailored microporous frameworks specially designed for bone scaffold applications. For this goal, we employed camphene-camphor as the freezing vehicle and porogen for the preparation of photocurable CaP suspensions containing diurethane dimethacrylate (UDMA) monomers. After freeze-casting, the CaP suspensions could be solidified at controlled temperatures (~33&ndash, 38 &deg, C) and then be photopolymerized by DLP. All produced CaP scaffolds fairly resembled the designed macroporous structures (the gyroid structure with two interpenetrating macropore networks). In addition, numerous micropores were created in the CaP filaments, while the microporosity increased with increasing the camphene-camphor amount from 40 vol % to 60 vol %. As a consequence, compressive strength and modulus of hierarchically porous CaP scaffolds decreased due to an increase in overall porosity. However, reasonable mechanical properties could be obtained at high porosities owing to the CaP frameworks constructed in a periodic manner. In addition, excellent water penetration capability, biocompatibility, and apatite-forming ability were obtained, which were attributed to the microporous CaP frameworks with good pore interconnectivity and large surface area.

This study demonstrates the utility of camphene as the pore-regulating agent for phase separation-based 3D plotting to produce hierarchical macro/micro-porous poly(&epsilon, caprolactone) (PCL)&ndash, calcium phosphate (CaP) composite scaffolds, specifically featuring highly microporous surfaces. Unlike conventional particulate porogens, camphene is highly soluble in acetone, the solvent for PCL polymer, but insoluble in coagulation medium (water). In this study, this unique characteristic supported the creation of numerous micropores both within and at the surfaces of PCL and PCL&ndash, CaP composite filaments when using high camphene contents (40 and 50 wt%). In addition, the incorporation of the CaP particles into PCL solutions did not deteriorate the formation of microporous structures, and thus hierarchical macro/micro-porous PCL&ndash, CaP composite scaffolds could be successfully produced. As the CaP content increased, the in vitro biocompatibility, apatite-forming ability, and mechanical properties (tensile strength, tensile modulus, and compressive modulus) of the PCL&ndash, CaP composite scaffolds were substantially improved.

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%.

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.

Hyaluronic acid (HAc) hydrogel exhibits excellent biocompatibility, but it has limited biomedical application due to its poor biomechanical properties as well as too-fast enzymatic degradation. In this study, we have developed an in situ precipitation process for the fabrication of a HAc-calcium phosphate nanocomposite hydrogel, after the formation of the glycidyl methacrylate-conjugated HAc (GMHA) hydrogels via photo-cross-linking, to improve the mechanical and biological properties under physiological conditions. In particular, our process facilitates the rapid incorporation of calcium phosphate (CaP) nanoparticles of uniform size and with minimal agglomeration into a polymer matrix, homogeneously. Compared with pure HAc, the nanocomposite hydrogels exhibit improved mechanical behavior. Specifically, the shear modulus is improved by a factor of 4. The biostability of the nanocomposite hydrogel was also significantly improved compared with that of pure HAc hydrogels under both in vitro and in vivo conditions.

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.

Target-ion induced plasma sputtering (TIPS) is a one-step self-organization nanofabrication method in which a conventional DC magnetron sputter with a negative substrate bias voltage is used. This process successfully leads to ion-induced sputtering on metal substrates, producing large-scale nanopatterns on various metal surfaces. We demonstrated that the obtained nanopatterns have size-tunability from nano- to micro-scales by modulating the negative substrate voltage. This large-scale, bottom-up nanofabrication technique will accelerate nanopattern applications in biomedical, chemical or magnetic devices through large surface-to-volume ratios and unique surface topography of induced ripple patterns on metals.

This study proposes an innovative way of creating porous ceramics with a unique gradient porous structure using three-dimensional extrusion of a multilayered ceramic/camphene feed rod, denoted as “3D-Exm”. This 3D-Exm technique utilizes the wall slip phenomenon during the extrusion process, which can create a gradient core/shell structure with a gradual change in the core/shell thickness ratio. In addition, the microstructure of ceramic filaments can be tuned through the use of the camphene as a pore-forming agent. Porous alumina ceramics produced using a bilayered feed rod comprised of the alumina/camphene mixtures with the relatively high (ϕH = 40 vol%) and low ceramic contents (ϕL = 10 vol%) showed a gradual change in porosity in the intermediate region between the relatively dense (porosity = ~3 vol%) and highly porous regions (porosity = ~85 vol%).

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 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.

Blends of ductile Ti metal with polyetheretherketone (PEEK) polymer were studied with regard to their mechanical properties and in vitro biocompatibility. PEEK/Ti composites with various Ti contents, ranging from 0 vol % to 60 vol %, were produced by compression molding at 370°C. In all composites produced, regardless of the initial Ti content, Ti particles were well distributed in the PEEK matrix. Addition of Ti led to a significant increase in mechanical properties of PEEK. Specifically, an increase in Ti content enhanced compressive strength and stiffness, while preserving ductile fracture behavior. In addition, the use of Ti for reinforcement of PEEK provided the composites with improved in vitro biocompatibility in terms of the attachment, proliferation, and differentiation of MC3T3-E1 cells.

We produced poro-us poly(ε-caprolactone) (PCL)/hydroxyapatite (HA) composite scaffolds for bone regeneration, which can have a tailored macro/micro-porous structure with high mechanical properties and excellent in vitro bioactivity using non-solvent-induced phase separation (NIPS)-based 3D plotting. This innovative 3D plotting technique can create highly microporous PCL/HA composite filaments by inducing unique phase separation in PCL/HA solutions through the non-solvent-solvent exchange phenomenon. The PCL/HA composite scaffolds produced with various HA contents (0 wt %, 10 wt %, 15 wt %, and 20 wt %) showed that PCL/HA composite struts with highly microporous structures were well constructed in a controlled periodic pattern. Similar levels of overall porosity (~78 vol %) and pore size (~248 µm) were observed for all the PCL/HA composite scaffolds, which would be highly beneficial to bone tissue regeneration. Mechanical properties, such as ultimate tensile strength and compressive yield strength, increased with an increase in HA content. In addition, incorporating bioactive HA particles into the PCL polymer led to remarkable enhancements in in vitro apatite-forming ability.

This study demonstrates the utility of the newly developed self-assembly-induced gelation technique for the synthesis of porous collagen/hydroxyapatite (HA) composite microspheres with a nanofibrous structure. This new approach can produce microspheres of a uniform size using the droplets that form at the nozzle tip before gelation. These microspheres can have a highly nanofibrous structure due to the immersion of the droplets in a coagulation bath (water/acetone), in which the collagen aggregates in the solution can self-assemble into fibrils due to pH-dependent precipitation. Bioactive HA particles were incorporated into the collagen solutions, in order to enhance the bioactivity of the composite microspheres. The composite microspheres exhibited a well-defined spherical morphology and a uniform size for all levels of HA content (0 wt %, 10 wt %, 15 wt %, and 20 wt %). Collagen nanofibers—several tens of nanometers in size—were uniformly present throughout the microspheres and the HA particles were also well dispersed. The in vitro apatite-forming ability, assessed using the simulated body fluid (SBF) solution, increased significantly with the incorporation of HA into the composite microspheres.

This study proposes a new type of calcium phosphate (CaP) scaffolds with a continuously gradient macro/microporous structure using the ceramic/camphene-based 3D extrusion process. Green filaments with a continuously gradient core/shell structure were successfully produced by extruding a bilayered feedrod comprised of a CaP/camphene mixture lower part and a pure camphene upper part. The extruded filaments were then deposited in a controlled manner to construct triangular prisms, followed by the assembly process for the production of CaP scaffolds with a gradient core/shell structure. In addition, a gradient microporous structure was created by heat-treating the green body at 43 °C to induce the overgrowth of camphene dendrites in the CaP/camphene walls. The produced CaP scaffold showed a highly macroporous structure within its inner core, where the size of macrochannels increased gradually with an increase in the distance from the outer shell, while relatively larger micropores were created in the outer shell.

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.

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.

Highly hierarchical pore structure (macro–micro–nano) for biomimetic nanofibrous scaffolds could efficiently enhance cell infiltration and tissue formation. However, it is difficult to prepare these structures by using traditional electrostatic spinning techniques. Here, we report a facile method to fabricate polycaprolactone (PCL) nanofibrous scaffolds with multi-scale pore structure by simple phase separation. By employing water–dioxane as solvents and tris spheres as macropore template, PCL nanofibrous scaffolds with pores 300–800 µm, 1–10 µm and 100–1000 nm in diameter can be facilely produced. All scaffolds possess controlled nanofibrous morphology and porosity (90–98%). This scaffold may provide promising applications in tissue engineering and drug delivery.

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).

We produced highly porous gelatin–siloxane (GLA-S) hybrid scaffolds with biomimetic anisotropic porous structure, physiochemical properties, mechanical behaviors and biological functions by treating gelatin–siloxane hybrid gels in an ammonium hydroxide solution. The siloxane used as an inorganic phase could effectively crosslink the gelatin polymer, which allowed for the unidirectional enlargement of ammonia vacuoles during ammonium hydroxide treatment. This created aligned pores in an axial direction when the siloxane contents (10 and 20 wt %) were high. In addition, the gelatin polymer could be uniformly hybridized with the siloxane phase at the molecular level, while intense interaction between these two phases could be achieved. This resulted in a significant increase in mechanical properties. The GLA-S hybrid scaffold with a siloxane content of 10 wt % showed reasonably high compressive yield strength of 4.2 ± 0.1 MPa and compressive modulus of 84 ± 5 MPa at a porosity of 86 vol %, which would be comparable to those of natural cancellous bone. In addition, the GLA-S hybrid scaffold had good biocompatibility assessed by in vitro cell tests using pre-osteoblast MC3T3-E1 cells. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 102B: 1528–1536, 2014.

Porous Ti has been widely investigated for orthopedic and dental applications on account of their ability to promote implant fixation via bone ingrowth into pores. In this study, highly aligned porous Ti scaffolds coated with a bone morphogenetic protein (BMP)-loaded silica/chitosan hybrid were produced, and their bone regeneration ability was evaluated by in vivo animal experiments. Reverse freeze casting allowed for the creation of highly aligned pores, resulting in a high compressive strength of 254 ± 21 MPa of the scaffolds at a porosity level of ∼51 vol %. In addition, a BMP-loaded silica/chitosan hybrid coating layer with a thickness of ∼1 μm was uniformly deposited on the porous Ti scaffold, which enabled the sustained release of the BMP over a prolonged period of time up to 26 days. The cumulative amount of the BMP released was ∼4 μg, which was much higher than that released from the specimen without a hybrid coating layer. In addition, the bone regeneration ability of the porous Ti scaffold with a BMP-loaded silica/chitosan coating layer was examined by in vivo animal testing using a rabbit calvarial defect model and compared with those of the as-produced porous Ti scaffold and porous Ti scaffold with a silica/chitosan coating layer. After 4 weeks of healing, the specimen coated with a BMP-loaded silica/chitosan hybrid showed a much higher bone regeneration volume (∼36%) than the as-produced specimen (∼15%) (p < 0.005) and even the specimen coated with a silica/chitosan hybrid (∼25%) (p < 0.05).

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 evaluated the utility of the creation of a nanoporous TiO2 surface to enhance the in vitro biocompatibility and in vivo osseoconductivity of polyetheretherketone (PEEK) implants by providing favorable sites for the effective immobilization of bone morphogenetic protein-2 (BMP-2). A uniform nanoporous TiO2 layer with a pore diameter of ∼70 nm was successfully created by anodizing a Ti film, which had been deposited onto a PEEK substrate via electron beam (e-beam) evaporation technique. This nanoporous, hydrophilic TiO2 surface enabled the efficient immobilization of BMP-2, resulting in a remarkable enhancement in in vitro biocompatibility that was assessed in terms of cell attachment, proliferation, and differentiation. The in vivo animal tests also confirmed that the nanoporous TiO2 surface immobilized with BMP-2 could significantly enhance the osseoconductivity of PEEK implants. The BMP-immobilized PEEK implant with the nanoporous TiO2 surface showed much higher bone-to-implant contact (BIC) ratio (60%) than the bare PEEK (30%), PEEK with the nanoporous TiO2 surface (50%) and even BMP-immobilized PEEK without the nanoporous TiO2 surface (32%).

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).

Magnesium and its alloys are candidate materials for biodegradable implants; however, excessively rapid corrosion behavior restricts their practical uses in biological systems. For such applications, surface modification is essential, and the use of anticorrosion coatings is considered as a promising avenue. In this study, we coated Mg with hydroxyapatite (HA) in an aqueous solution containing calcium and phosphate sources to improve its in vitro and in vivo biocorrosion resistance, biocompatibility and bone response. A layer of needle-shaped HA crystals was created uniformly on the Mg substrate even when the Mg sample had a complex shape of a screw. In addition, a dense HA-stratum between this layer and the Mg substrate was formed. This HA-coating layer remarkably reduced the corrosion rate of the Mg tested in a simulated body fluid. Moreover, the biological response, including cell attachment, proliferation and differentiation, of the HA-coated samples was enhanced considerably compared to samples without a coating layer. The preliminary in vivo experiments also showed that the biocorrosion of the Mg implant was significantly retarded by HA coating, which resulted in good mechanical stability. In addition, in the case of the HA-coated implants, biodegradation was mitigated, particularly over the first 6 weeks of implantation. This considerably promoted bone growth at the interface between the implant and bone. These results confirmed that HA-coated Mg is a promising material for biomedical implant applications.