Search

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.

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.

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 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.

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.

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.

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.

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.

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 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.

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 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).

In this study, a silica xerogel-chitosan hybrid is utilized as a coating material to incorporate bone morphogenic protein-2 (BMP-2) on a porous hydroxyapatite (HA) scaffold for bone tissue engineering. BMP-2 is known as a therapeutic agent for improving bone regeneration and repair. Silica xerogel-chitosan hybrids have been used for the delivery of a growth factor as well as osteoconductive coatings. The biological properties of the hybrid coating incorporated with BMP-2 were evaluated in terms of the BMP-2 release behavior, osteoblastic cellular responses and in vivo performance. BMP-2 was continuously released from the hybrid coating layer on the porous HA scaffold for up to 6 weeks. The hybrid coating containing BMP-2 showed significantly enhanced osteoblastic cell responses in comparison with the hybrid coating and HA substrate. Consequently, new bone formation was significantly increased within the hybrid coating containing BMP-2. These results reveal that the hybrid coating containing BMP-2 has the potential to be used as a bone implant, whose osteogenic properties are promoted by the release of BMP-2 in a controlled manner for a prolonged period of time.

We produced highly aligned porous poly(e-caprolactone) (PCL)/hydroxyapatite (HA) scaffolds by unidirectionally freezing PCL/HA solutions with various HA contents (0, 5, 10 and 20 wt% in relation to the PCL polymer) and evaluated their mechanical properties and in vitro biocompatibility to examine their potential applications in bone tissue engineering. All the prepared scaffolds had a highly aligned porous structure, in which the HA particles were uniformly dispersed in the PCL walls. The elastic modulus of the PCL/HA scaffolds significantly increased from 0.12 ± 0.02 to 2.65 ± 0.05 MPa with increasing initial HA content from 0 to 20 wt%, whereas the pore size decreased from 9.2 ± 0.7 to 4.2 ± 0.8 μm. In addition, the PCL/HA scaffolds showed considerably enhanced in vitro cellular responses that were assessed in terms of cell attachment, proliferation and osteoblastic differentiation.

This paper reports a novel way of enhancing the hardness of a zirconia-toughened alumina (ZTA) composite with a zirconia content of 20 vol% by surface treatments with a boehmite sol. More specifically, a ZTA composite was first prepared by heat-treating a mixture of alumina and zirconia powders containing Cr 2 O 3 and SrAl 11 CrO 19 , as a reinforcement at 1400 °C for 1 h, and then infiltrating them with the boehmite sol, followed by heat-treatment at 1650 °C for 1 h to densify them. This treatment led to a significant increase in the surface hardness of the ZTA composite, which was attributed mainly to an increase in the volume fraction of an alumina phase with greater hardness, whereas the flexural strength and fracture toughness decreased slightly. The Vickers hardness, flexural strength and fracture toughness were 17.1 ± 2.5 GPa, 738 ± 88 MPa and 4.2 ± 0.11 MPa m 1/2 , respectively.

We herein propose a novel way of producing highly aligned porous alumina tubes by co-extruding an initial feed rod, which comprised of a pure camphene core and a frozen alumina/camphene shell. This new and simple technique produced alumina tubes (~4.4 ± 0.1 mm in outer diameter) having uniform alumina walls (~1.1 ± 0.12 mm in thickness) with highly aligned pores, which were created by removing the extensively elongated camphene dendrites in the extruded alumina/camphene shell. Furthermore, the heat treatment of the extruded bodies at 33°C, which is close to the freezing point of the alumina/camphene slurry, led to a considerable increase in the size of the aligned pores formed in the alumina walls, from ~

This study reports a new way of enhancing the compressive strength of porous calcium phosphate (CaP) ceramics by creating highly elongated pores. These elongated pores were produced by casting a CaP/camphene slurry into stretched polymeric sponges with a thick carbon coating layer used as a template. The sample produced after sintering at 1250 °C for 3 h showed a highly elongated porous structure with a porosity of 38 ± 1.2 vol%, where elongated pores with a size of 512 ± 96 μm were formed as a replica of the template. In addition, CaP walls with a thickness of 841 ± 239 μm were fully densified without any noticeable defects due to the high CaP content of 40 vol% in the CaP/camphene slurry. The compressive strength of the sample was as high as 21 ± 4.9 MPa when tested parallel to the direction of pore elongation, which is much higher than that (12 ± 2.4 MPa) of the sample tested normal to the direction of pore elongation. The sample also showed good biocompatibility, as assessed by the in vitro cell test using a pre-osteoblast cell line.

This article reports a novel, simple route for synthesis of sol–gel derived porous, bioactive glass (BG) microspheres using chitosan (CTS) as a biomolecular template in the acid-catalyzed sol–gel process. The use of CTS, which is a natural biocompatible polymer with a unique molecular structure, allowed the synthesis of BG microparticles with a spherical shape, 5–10 μm in size. Furthermore, pores with a size of 5–40 nm were created entirely throughout BG microspheres, which were formed by removing the network of CTS present initially in the CTS-BG composite microparticles via heat-treatment at 600°C for 2 h. These porous BG microspheres induced the vigorous precipitation of apatite crystals on their surface when immersed in simulated body fluid for 24 h, thus suggesting their excellent bioactivity .

Hydroxyapatite (HA) was coated onto pure magnesium (Mg) with an MgF(2) interlayer in order to reduce the surface corrosion rate and enhance the biocompatibility. Both MgF(2) and HA were successfully coated in sequence with good adhesion properties using the fluoride conversion coating and aerosol deposition techniques, respectively. In a simulated body fluid (SBF), the double layer coating remarkably enhanced the corrosion resistance of the coated Mg specimen. The in vitro cellular responses of the MC3T3-E1 pre-osteoblasts were examined using a cell proliferation assay and an alkaline phosphatase (ALP) assay, and these results demonstrated that the double coating layer also enhanced cell proliferation and differentiation levels. In the in vivo study, the HA/MgF(2) coated Mg corroded less than the bare Mg and had a higher bone-to-implant contact (BIC) ratio in the cortical bone area of the rabbit femora 4 weeks after implantation. These in vitro and in vivo results suggested that the HA coated Mg with the MgF(2) interlayer could be used as a potential candidate for biodegradable implant materials.

This paper proposes a novel, simple way to improve the compressive strength of reticulated porous hydroxyapatite (HA) ceramics using carbon-coated polymeric sponges with elongated pores as a novel template. This template allowed samples to have two interconnected pore networks with a preferential orientation, in which an addition pore network was newly formed by removing the carbon-coated polymeric struts, while preserving the pre-existing pore network. The compressive strength of the sample was as high as 2.9 ± 0.3 MPa with a porosity of 76% when tested parallel to the direction of pore elongation. In addition, the in vitro cell test using a pre-osteoblast cell line revealed the samples to have good biocompatibility.

This study reports the deposition of TiN films on Co-Cr substrates to improve the substrates' mechanical properties and biological properties. In particular, the argon to nitrogen (Ar:N(2)) gas flow ratio was adjusted to control the microstructure of the TiN films. A Ti interlayer was also used to enhance the adhesion strength between the Co-Cr substrate and TiN films. A series of TiN films, which are denoted as TiN-(Ar/N(2))1:1, Ti/TiN-(Ar/N(2))1:1, and Ti/TiN-(Ar:N(2))1:3, were deposited by reactive DC sputtering. All the deposited TiN films showed a dense, columnar structure with a preferential orientation of the (200) plane. These TiN films increased the mechanical properties of Co-Cr, such as the critical load during scratch testing, hardness, elastic modulus and plastic resistance. In addition, the biological properties of the Co-Cr substrates, i.e. initial attachment, proliferation, and cellular differentiation of the MC3T3-E1 cells, were improved considerably by deposition of the TiN films. These results suggest that TiN films would effectively enhance both the mechanical properties and biocompatibility of biomedical Co-Cr alloys.

Sol–gel bioactive glasses have been developed for bone tissue regeneration and drug delivery systems as they have the unique mesoporous structure and high bioactivity in vitro. To develop more reliable drug delivery and bone tissue repair systems, it is necessary to control the morphology and microstructure of bioactive glasses. For this purpose, bioactive glass microspheres (BGMs) were prepared by a sol–gel co-template technology using acids as catalysts. We studied the effects of different acids (citric acid, lactic acid and acetic acid) on the microstructure and apatite-forming bioactivity of BGM. The apatite-forming bioactivity was carried out in simulated body fluid (SBF). The microstructure and apatite-forming bioactivity of BGMs were characterized by various methods. Results showed that acetic acid had little effect on the structure and bioactivity of BGMs. Differently, the morphology and microstructure of BGMs could be controlled by changing citric acid and lactic acid concentrations. In vitro bioactivity test indicated that citric acid and lactic acid derived BGMs possessed the better apatite-forming capacity than that derived by acetic acid.

Highly porous calcium phosphate (CaP) ceramics were fabricated by freezing foamed aqueous CaP suspensions with various CaP contents (15, 20, and 25 vol %) containing polyvinyl alcohol (PVA) as the binder and emulsifying agent. All the samples fabricated showed uniformly dispersed macropores, which were created by air bubbles introduced in the suspensions. In addition, aligned micropores were formed in the sintered CaP walls as a replica of the preferentially grown ice dendrites during freezing when CaP contents of 15 and 20 vol % were used. The overall porosity decreased from 83 to 73 vol % with increasing initial CaP content from 15 to 25 vol %, whereas the compressive strength and elastic modulus increased significantly from 1.2 ± 0.2 to 4.7 ± 0.9 MPa and from 20 ± 11 to 163 ± 42 MPa, respectively. The samples showed good biocompatibility, as assessed by the in vitro cell test using a pre-osteoblast cell line.

This study demonstrates the usefulness of the lithography-based ceramic 3-dimensional printing technique with a specifically designed top-down process for the production of porous calcium phosphate (CaP) ceramic scaffolds with tailored pore orientations and mechanical properties. The processing parameters including the preparation of a photocurable CaP slurry with a high solid loading (&phi, = 45 vol%), the exposure time for photocuring process, and the initial designs of the porous scaffolds were carefully controlled. Three types of porous CaP scaffolds with different pore orientations (i.e., 0&deg, /90&deg, 0&deg, /45&deg, /135&deg, and 0&deg, /30&deg, /60&deg, /120&deg, /150&deg, ) were produced. All the scaffolds exhibited a tightly controlled porous structure with straight CaP frameworks arranged in a periodic pattern while the porosity was kept constant. The porous CaP scaffold with a pore orientation of 0&deg, demonstrated the highest compressive strength and modulus due to a number of CaP frameworks parallel to the loading direction. On the other hand, scaffolds with multiple pore orientations may exhibit more isotropic mechanical properties regardless of the loading directions. The porous CaP scaffolds exhibited an excellent in vitro apatite-forming ability in a stimulated body fluid (SBF) solution. These findings suggest that porous CaP scaffolds with tailored pore orientations may provide tunable mechanical properties with good bone regeneration ability.

A novel fibrous membrane was developed for guided bone regeneration (GBR) through electrospinning a uniform poly(e-caprolactone) (PCL)–silica hybrid sol. The membrane was composed of fibers with a mean diameter of approximately 400 nm. The hybrid fibers were nano-sized with uniform patterns throughout the fibers, in contrast to the homogeneous structure of pure PCL fibers. The tensile strengths and elastic moduli of the membranes were significantly enhanced with increasing silica content up to 40%. The surfaces of the hybrid membranes were highly hydrophilic with a water contact angle of almost zero. The hybrid membranes possessed excellent in vitro cellular responses in terms of proliferation and differentiation of pre-osteoblast cells. The in vivo animal tests not only confirmed excellent biocompatibility but also revealed bioresorbability of the membranes. These mechanical and biomedical properties make the hybrid membranes very attractive as GBR applications.

In this study, a poly(e-caprolactone) (PCL)/bioactive glass (BG) nanocomposite was fabricated using BG nanofibers (BGNFs) and compared with an established composite fabricated using microscale BG particles. The BGNFs were generated using sol–gel precursors via the electrospinning process, chopped into short fibers and then incorporated into the PCL organic matrix by dissolving them in a tetrahydrofuran solvent. The biological and mechanical properties of the PCL/BGNF composites were evaluated and compared with those of PCL/BG powder (BGP). Because the PCL/BG composite containing 20 wt % BG showed the highest level of alkaline phosphatase (ALP) activity, all evaluations were performed at this concentration except for that of the ALP activity itself. In vitro cell tests using the MC3T3 cell line demonstrated the enhanced biocompatibility of the PCL/BGNF composite compared with the PCL/BGP composite. Furthermore, the PCL/BGNF composite showed a significantly higher level of bioactivity compared with the PCL/BGP composite. In addition, the results of the in vivo animal experiments using Sprague–Dawley albino rats revealed the good bone regeneration capability of the PCL/BGNF composite when implanted in a calvarial bone defect. In the result of the tensile test, the stiffness of the PCL/BG composite was further increased when the BGNFs were incorporated. These results indicate that the PCL/BGNF composite has greater bioactivity and mechanical stability when compared with the PCL/BG composite and great potential as a bone regenerative material. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009

Calcium sulfate hemihydrate (CSH) powders were synthesized for use as bone cement by heat treating calcium sulfate dihydrate (CSD) powders in boiling CaCl2 solutions with various CaCl2 concentrations, ranging from 23.5 to 35.5 wt%, in order to control their morphology. All of the prepared CSH powders showed X-ray diffraction peaks corresponding to the CSH structure without any secondary phases, implying complete conversion from the CSD phase to the CSH phase. It was also observed that the concentration of CaCl2 significantly affected the morphology of the CSH powder that was synthesized. In other words, as the CaCl2 concentration was decreased from 35.5 to 23.5 wt%, the morphology notably changed from long-and-slim hexagonal rods with an aspect ratio of 5.5 to fat-and-short hexagonal columns with an aspect ratio of 1.4. This reduction in the aspect ratio led to a significant improvement in the compressive strength of the CSD cement prepared by mixing the CSH powders with water.

Porous lead zirconate titanate–lead zinc niobate (PZT–PZN) piezoelectric ceramics with a high degree of pore alignment were fabricated using directional freeze casting of a ceramic/camphene slurry. Well-aligned pores were formed as the replica of the camphene dendrites that grew in a preferential orientation, while a high porosity of 90% was achieved by employing a low initial solid loading of 5 vol%. As the orientation angle of the pores to the poling direction was decreased, the hydrostatic piezoelectric properties, such as hydrostatic piezoelectric strain coefficient (dh), the hydrostatic piezoelectric voltage coefficient (gh), and the hydrostatic figure of merit, increased significantly. The sample containing pores aligned parallel to the poling direction showed an extremely high HFOM of 161019 × 10−15 Pa−1, which was ∼1300 times higher than that (124 × 10−15 Pa−1) of the dense sample, owing to the presence of aligned pores.

The objective of this study was to fabricate porous hydroxyapatite (HA) scaffolds coated with bioactive A/W glass–ceramics and to examine their mechanical and biological properties. Firstly, the HA scaffolds were prepared by the polymeric sponge replication method, and then A/W glasses were coated on the surface of the struts. All of the scaffolds had a highly porous structure with well-interconnected pores. It was observed that the bioactive glass coating markedly increased the strength of the HA scaffolds. This enhancement was attributed to the formation of a dense and strong coating layer on the weak HA struts. The in vitro bioactivities of the scaffolds were markedly improved by the coatings. When the coated scaffolds were soaked in a simulated body fluid (SBF), the bone-like apatite crystals were well mineralized on their surfaces. Osteoblast-like cells (MC3T3) adhered, spread, and grew well on the porous scaffolds. The cells placed on the glass-coated HA scaffold showed a higher proliferation rate and alkaline phosphatase (ALP) activity than those on the pure HA scaffold. These results demonstrate that the bioactive glass coating is effective in improving the strength and bioactivity of the porous HA scaffolds.

Porous lead zirconate titanate–lead zinc niobate (PZT–PZN) piezoelectric ceramics with interconnected pore channels were fabricated using the camphene-based freeze-casting method. In this method, warm PZT–PZN/camphene slurries with various solid loadings (10, 15, 20, and 25 vol%) were prepared by ball milling at 60°C and then cast into molds at 20°C, resulting in the formation of solidified green bodies comprised of three-dimensionally interconnected camphene dendrite networks and concentrated ceramic particle walls. After the removal of the frozen camphene via sublimation, the samples were sintered at 1200°C for 2 h. All of the fabricated samples showed highly porous structures, consisting of fully dense PZT–PZN walls without defects, such as cracks or pores. As the initial solid loading was decreased from 25 to 10 vol%, the porosity was linearly increased from 50% to 82%. This increase in the porosity led to a reduction in the permittivity, a moderate decline in the d33 value, and a rapid decline in the d31 value, which endowed the porous samples with a high hydrostatic figure of merit (HFOM). The highest HFOM value of 35650 × 10−15 Pa−1 was achieved for the sample with a porosity of 82%, as well as ɛ33=284, dh=298 pC/N, and gh=118 × 10−3 V·(m·Pa)−1.

The present study reports an innovative way to produce large pore channels with a size >100 μm for applications in bone tissue engineering using the camphene-based freeze casting method, and using an unusually high freezing temperature, which is close to the solidification temperature of the slurry, in order to allow the formation of excessively overgrown camphene dendrites due to the extremely low solidification velocity. To accomplish this, hydroxyapatite (HA)/slurries with various solid loadings (10, 15, and 20 vol%) were frozen at 35°C for 20 h. The frozen samples were freeze dried and sintered at 1250°C for 3 h. All of the fabricated samples showed highly porous structures with large pore channels >100 μm in size and dense HA walls without any noticeable defects, such as cracks or pores. As the initial solid loading was increased from 10 to 20 vol%, the porosity of the sample decreased linearly from 76% to 55%, while the pore channels became narrower. However, the compressive strength was remarkably improved from 2.5 to 16.7 MPa.

We fabricated highly aligned porous silicon carbide (SiC) ceramics with well-defined pore structures by freezing a polycarbosilane (PCS)/camphene solution. In this method, the solution prepared at 60°C was cast into a mold at temperatures ranging from 20° to -196°C, which resulted in a bicontinuous structure, in which each phase (camphene or PCS) was interconnected in a regular pattern. After the removal of the frozen camphene network, the samples showed highly porous structures, in which long straight and short elongated pore channels were formed parallel and normal to the direction of freezing, respectively. Thereafter, porous SiC ceramics were produced by the pyrolysis of the porous PCS objects at 1400°C for 1 h in a flowing Ar atmosphere, while preserving their mother pore structures having aligned pore channels.

Biometal systems have been widely used for biomedical applications, in particular, as load-bearing materials. However, major challenges are high stiffness and low bioactivity of metals. In this study, we have developed a new method towards fabricating a new type of bioactive and mechanically reliable porous metal scaffolds-densified porous Ti scaffolds. The method consists of two fabrication processes, 1) the fabrication of porous Ti scaffolds by dynamic freeze casting, and 2) coating and densification of the porous scaffolds. The dynamic freeze casting method to fabricate porous Ti scaffolds allowed the densification of porous scaffolds by minimizing the chemical contamination and structural defects. The densification process is distinctive for three reasons. First, the densification process is simple, because it requires a control of only one parameter (degree of densification). Second, it is effective, as it achieves mechanical enhancement and sustainable release of biomolecules from porous scaffolds. Third, it has broad applications, as it is also applicable to the fabrication of functionally graded porous scaffolds by spatially varied strain during densification.

Background Calcium phosphate (CaP) ceramics are one of the most valuable biomaterials for uses as the bone scaffold owing to their outstanding biocompatability, bioactivity, and biodegradation nature. In particular, these materials with an open porous structure can stimulate bone ingrowth into their 3-dimensionally interconnected pores. However, the creation of pores in bulk materials would inevitably cause a severe reduction in mechanical properties. Thus, it is a challenge to explore new ways of improving the mechanical properties of porous CaP scaffolds without scarifying their high porosity. Results Porous CaP ceramic scaffolds with aligned pores were successfully produced using ceramic/camphene-based co-extrusion. This aligned porous structure allowed for the achievement of high compressive strength when tested parallel to the direction of aligned pores. In addition, the overall porosity and mechanical properties of the aligned porous CaP ceramic scaffolds could be tailored simply by adjusting the initial CaP content in the CaP/camphene slurry. The porous CaP scaffolds showed excellent in vitro biocompatibility, suggesting their potential as the bone scaffold. Conclusions Aligned porous CaP ceramic scaffolds with considerably enhanced mechanical properties and tailorable porosity would find very useful applications as the bone scaffold.

We investigated the effect of polystyrene (PS) addition on the freezing behavior of a very dilute alumina/camphene slurry with an initial solid loading of 5 vol% for the fabrication of ultra-high porosity ceramics with aligned pore channels. To accomplish this, slurries with various PS contents (10, 20, and 30 vol% in relation to the alumina powders) were prepared by ball milling at 60°C and then cast into molds at a constant temperature of 20°C. After removing the frozen camphene, the samples were heat treated to burn out the organic phases and sinter the alumina walls. The addition of the PS binder remarkably enhanced the green strength of the sample, making it possible to handle it without difficulty. All of the sintered samples showed ultra-high porosities of >88% without the collapse of the porous structure, wherein the pore channels were completely interconnected. Three distinctive zones having different pore structures were observed, viz. the outer shell with elongated pores, the inner zone with long aligned pore channels, and the center with equiaxed pores. The content of the PS polymer significantly affected the pore morphologies in the three distinctive zones. In addition, it was found that the addition of the PS polymer was highly beneficial to the alignment of the pore channels.

Highly porous alumina ceramics with completely interconnected pore channels were fabricated by freezing dilute alumina/camphene slurries with solid loadings ranging from 5 to 20 vol%. This method fundamentally made full use of the three-dimensional camphene dendritic network for producing interconnected pore channels and the concentrated alumina powder network for achieving dense alumina walls. Firstly, alumina/camphene slurries were prepared at 60°C using ball milling and then cast into molds at 20°C. After subliming the frozen camphene, the samples were sintered at 1400°C for 5 h. This method enabled us to freeze very dilute ceramic slurries with a low solid loading of ≤20 vol% without the collapse of the sample after sintering. As the initial solid loading decreased from 20 to 5 vol%, the porosity linearly increased from 66% to 90% with an increase in the pore size, while completely interconnected pore networks were obtained in all cases. In addition, the free surfaces of the alumina walls showed full densification after sintering even at a low temperature of 1400°C, while some pores were present in the inner regions of the alumina walls.

A novel design for a three-dimensional (3-D) solid oxide fuel cell (SOFC) along with its method of fabrication is reported. This structure utilizes two 3-D channels that are separated by unique anode/electrolyte/cathode walls that thereby increases the active volumetric surface areas of the electrodes used for the chemical reactions. To implement this structure, a graphite template having one 3-D interconnected channel is successively coated with anode (NiO–YSZ), electrolyte (YSZ), and cathode (LSM–YSZ) slurries, followed by heat-treatment at elevated temperatures. This produces an additional 3-D channel that has the NiO–YSZ layer as a replica of the graphite template, while preserving the pre-existing channel that has the LSM–YSZ layer. The thickness of the NiO–YSZ layer, which provides mechanical stability, is controlled by adjusting the number of dip-coating cycles. Using this approach, it is possible to fabricate a ∼10 mm cubic SOFC without any notable defects, as well as to control the microstructures of the NiO–YSZ/YSZ/LSM–YSZ walls.

A combination of bi-axial machining and lamination was used to fabricate macrochanneled poly (epsilon-caprolactone) (PCL)/hydroxyapatite (HA) scaffolds. Thermoplastic PCL/HA sheets with a thickness of 1 mm, consisting of a 40 wt% PCL polymer and 60 wt% HA particles, were bi-axially machined. The thermoplastic PCL/HA exhibited an excellent surface finish with negligible tearing of the PCL polymer and pull-out of the HA particles. The bi-axially machined sheets were laminated with a solvent to give permanent bonding between the lamina. This novel process produced three-directionally connected macrochannels in the dense PCL/HA body. The macrochanneled PCL/HA scaffold exhibited excellent ductility and reasonably high strength. In addition, good cellular responses were observed due to the osteoconductive HA particles.

The room-temperature freeze-casting method was used to fabricate porous bioactive glass-ceramics. In this method, a glass/ camphene slurry prepared at 60°C was cast into a mold at 20°C, resulting in the production of a rigid green body that was comprised of three-dimensional dendritic camphene networks surrounded by highly concentrated glass powder walls. After the sublimation of camphene, the samples were sintered for 3 h at elevated temperatures ranging from 700° to 1100°C. As the sintering temperature was increased to 1000°C, the densification of the glass-ceramic wall was remarkably enhanced, while its highly porous structure was preserved. The sample sintered at 1000°C showed a high porosity of 53% and pore channels with a size of several tens of micrometers, as well as dense glass-ceramic walls. In addition, the fabricated samples effectively induced the deposition of apatite on their surfaces when immersed in simulated body fluid, implying that they are very bioactive.