Search

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).

This study reports a novel way of increasing the pore size of highly aligned porous alumina ceramics by heat-treating an extruded alumina/camphene body at a temperature near its solidification point. The pore size obtained increased remarkably from 51 ± 8 to 125 ± 27 μm with increasing heat-treatment time from 1 to 24 h, due to the continuative overgrowth of the camphene dendrites during heat-treatment, while a highly aligned porous structure was preserved. In addition, interestingly, this heat-treatment enabled alumina walls to be densified quite well, whereas porous walls were observed in the sample produced without heat-treatment, which led to a considerable increase in compressive strength. The sample produced with a heat-treatment time of 12 h showed a high compressive strength of 11.6 ± 1.2 MPa at a porosity of approximately 84 vol%, which was much higher than that (0.28 ± 0.1 MPa) of the sample produced without heat-treatment.

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 .

We herein propose a new technique for producing highly aligned porous ceramics by extruding a frozen ceramic/camphene body. To accomplish this, an alumina/camphene slurry with an initial alumina content of 10 vol% was first frozen unidirectionally in a 20 mm × 20 mm mold and extruded through a reduction die with a cross-section of 5 mm × 5 mm at room-temperature. This simple process enabled the formation of porous alumina ceramics with highly aligned pores as a replica of the camphene dendrites with a preferential orientation parallel to the extrusion direction. The sample showed much higher compressive strength of 280 ± 80 kPa with a porosity of 83 vol% when tested parallel to the direction of pore alignment. In addition, these materials could be used as a valuable framework for the production of ceramic/epoxy composites, particularly with a lamellar structure, which would result in a remarkable increase in mechanical properties.

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 paper proposes a novel way of producing aligned porous alumina ceramics with larger dimensions by assembling unidirectionally frozen alumina/camphene bodies, particularly those containing polystyrene (PS) polymer as the binder. The compressive strength of the samples sintered at 1450 °C for 3 h increased remarkably from 2 ± 0.1 to 16 ± 2 MPa with increasing PS content from 5 to 20 vol.% due to the prevention of cracks generally caused by drying shrinkage. In addition, frozen samples with a PS content of 20 vol.% could be assembled into larger dimensions without difficulty. The height of the assembled sample produced with a lamination number of 5 could be increased to ∼24 mm without a severe decrease in compressive strength (16 ± 3 MPa at a porosity of ∼79 vol.%) due to the maintenance of an aligned porous structure with good interfacial bonding between the laminations.

A novel type of porous hydroxyapatite (HA) scaffolds with a functionally graded core/shell structure was fabricated by freeze casting HA/camphene slurries with various HA contents into fugitive molds containing a graphite template with three-dimensionally interconnected pores for the creation of a highly porous core. All the fabricated samples had functionally graded core/shell structures with 3-D periodic pore networks in a core surrounded by a relatively dense shell. The overall porosity of the sample decreased from 60 to 38 vol% with increasing HA content in the HA/camphene slurry from 20 to 36 vol% due to a decrease in porosity in both the core and shell regions. In addition, the compressive strength was improved remarkably from 12 ± 1.1 to 32 ± 3.0 MPa. The in vitro cell test using a pre-osteoblast cell line showed that the samples had good biocompatibility.

We report the utility of three-dimensional ceramic/camphene-based coextrusion, newly developed in this study, for the production of unidirectionally macrochanneled alumina ceramics with three-dimensionally interconnected porous alumina walls. In this technique, a continuous ceramic/camphene filament with a diameter of 1 mm, comprised of a pure camphene core and a frozen alumina/camphene shell, was produced by the coextrusion process and then deposited in a layer-by-layer sequence using a computer-controlled 3-axis moving table. Unidirectionally aligned macrochannels (~400 μm in diameter) and three-dimensionally interconnected pores (several tens of micrometers in size) in the alumina walls were created by removing the camphene core and the camphene dendrites formed in the alumina/camphene region, respectively. The sample showed much higher compressive strength in the macrochannel direction than in the perpendicular direction. In addition, the compressive strength of the sample could increase with an increase in initial alumina content owing to a decrease in the total porosity.

This article proposes a new way of producing highly porous biphasic calcium phosphate (BCP) ceramics with large interconnected pores by freezing a vigorously foamed BCP suspension under reduced pressure, which allows the air bubbles incorporated into the BCP suspension to expand extensively. All the fabricated samples produced with various degrees of expansion of the BCP suspension (0, 150, 200, and 250 vol%) showed a highly uniform porous structure with their unique microporous BCP walls. The sizes of the pores and interconnections between the pores increased remarkably from 74 ± 21 μm to 295 ± 93 μm and 22 ± 8 μm to 123 ± 60 μm, respectively, with increasing degree of expansion from 0 to 250 vol%. However, the compressive strength decreased from 1.2 ± 0.29 MPa to 0.4 ± 0.07 MPa with increasing degree of expansion from 150 to 250 vol%.

We herein propose a novel way of producing nanofibrous gelatin–silica hybrid scaffolds through thermally induced phase-separation (TIPS) particularly using mixtures of gelatin solution and silica sol, which can mimic the physical structure, chemical composition, and eventually functions of the native bone extracellular matrix (ECM). The gelatin solutions were homogeneously hybridized with various contents of a silica sol using simple magnetic stirring, which enabled the construction of a nanofibrous structure with a uniform distribution of the silica in the gelatin nanofibers. The nanofibrous gelatin–silica hybrid scaffolds showed much better mechanical properties and in vitro biodegradation stability and apatite-forming ability than the nanofibrous pure gelatin scaffold, which were achieved by the presence of a stiff, bioactive silica phase in the nanofibers and the interaction between the silica hydroxyls and the amino group in the gelatin polymer. In addition, the nanofibrous gelatin–silica hybrid scaffold with a silica content of 30 wt% showed reasonably high in vitro biocompatibility. These findings suggest that the highly porous, nanofibrous hybrid structure mimicking the bone ECM can provide an excellent matrix for bone tissue regeneration.