Yumi Tanaka

Efficacy of polarized hydroxyapatite and silk fibroin composite dressing gel on epidermal recovery from full-thickness skin wounds.

Hydroxyapatite (HA) has been widely used to produce biomaterials. We reported that electrically polarized HA (pHA) induces cells as a scaffold. Recently, in the biomedical field, many studies are underway, seeking new applications of silk fibroin (SF), because SF can be gelatinized and still retain its biocompatibility and permeability. To develop an innovative composite material for effective wound dressings, we added pHA powder to SF and gelatinized the compound. We then applied the gel composite on full-thickness porcine skin wounds for investigation of its healing effect. The pHA transforms the SF structure into a porous three-dimensional scaffold. It was found that the SF gel containing pHA (pHA/SF) had higher promotive effects on wound healing, re-epithelization, and matrix formation than did the other prepared gel composites in the study. The pHA/SF effectively advanced the maturation of fibroblast cells benefiting from its structural advantages and stored charges. To our knowledge, this is the first report of the preparation of pHA/SF gel and identification of its wound-healing effects in vivo.

Polarized hydroxyapatite promotes spread and motility of osteoblastic cells

Osteoblast adhesion to surfaces of implant substrates is recognized as playing a fundamental role in the process of osteoconduction. The purpose of this study was to evaluate the in vitro adhesion of osteoblasts cultured on polarized hydroxyapatite (HA), which provides two kinds of surfaces; negatively charged HA (N-HA) and positively charged HA (P-HA). Those surfaces have been proved to enhance the osteobonding capabilities. Osteoblastic cells were seeded onto normal and polarized HA; adhesion and motility of each was observed. Polarization did not affect the percentage of the spread cells against all the adhered cells, but had a significant effect on the spreading of each cell as shown by the measured elongation of the adhered cells by fluorescence observation. The elongation of each cell was especially enhanced on the N-HA and P-HA, when compared with normal HA (O-HA). In addition, the polarization affected cell motility shown by wound healing. Motility analysis showed that the same number of cells started to migrate toward the wound areas on each type of surface. However, the migration of each cell type towards the wound area was accelerated on the N-HA and P-HA. The charges induced on the HA surface accelerated the cytoskeleton reorganization of the adhered cells. The acceleration was appeared as cell shape, actin filament pattern such as stress fiber formation, and prolongation of cell motility distance.

Comparison of enhancement of bone ingrowth into hydroxyapatite ceramics with highly and poorly interconnected pores by electrical polarization.

The effects of electrical polarization of porous hydroxyapatite ceramics with different structures on bone ingrowth were compared. Two types of cylindrical porous hydroxyapatite ceramics with high and low interpore connection (hydroxyapatite-H and hydroxyapatite-L, respectively) were utilized in this study. Hydroxyapatite-H or hydroxyapatite-L with and without electrical polarization was implanted into the right or left femoral condyle of rabbits (n=10 in each group) and histological examination was performed 3 and 6weeks after operation. Each cross-section was divided into three regions, outer, middle and inner region, and the percentage of total newly formed bone area/total area of each region (% bone area) was calculated. Bone ingrowth throughout the region of implant was significantly larger in the hydroxyapatite-H group than in the hydroxyapatite-L group. Electrical polarization was effective in enhancing bone ingrowth through all the pores of hydroxyapatite-H implant, however, this advantage was not apparent in the hydroxyapatite-L implant. It is suggested that enhanced bone ingrowth into hydroxyapatite porous bodies due to electrical polarization may be a cooperative interaction between the osteoconductivity of hydroxyapatite porous bodies and enhanced osteogenic cell activity induced by large charges stored on the pore surfaces.

Polarization and microstructural effects of ceramic hydroxyapatite electrets

To provide bioelectrets with controlled electrical energy, the polarization and relaxation characteristics of hydroxyapatite (HA) ceramic electrets were investigated in terms of poling conditions and microstructures. HA electrets were prepared between 250 and 500 °C for 5–120 min under a 5 kV cm−1 dc electrical field. Poling conditions and grain size of HA ceramics significantly influenced the thermally stimulated depolarization current (TSDC) spectra and charge storage (Q). Under a poling field of 5 kV cm−1, varying the poling temperature from 250 to 500 °C drastically shifted the TSDC peak temperature from 250 to 620 °C and increased Q from 0.5 to 45 μC cm−2. The change in the average grain size from 2 to 11 μm increased the Q value from 15 to 60 μC cm−2 with a negligible shift in the TSDC peak position. The measured difference of the TSDC peak shapes and positions, as well as the Q values, was theoretically due to the four polarization states with different activation energies (Edr) of dipole relaxatio...

Formation of calcite thin films by cooperation of polyacrylic acid and self-generating electric field due to aligned dipoles of polarized substrates

We demonstrated the formation of calcite thin films on positively and negatively charged surfaces of a hydroxyapatite (HAp) electret coexisting with polyacrylic acid (PAA) and self-generating surface electric fields due to HAp electrets with electrically aligned dipoles. The cooperation of PAA and the self-generating surface electric field due to the electrets favored the formation of calcite thin films and acted remarkably on the negatively charged surface. Calcite thin films, 4-10 microm thick, with a shell-like microstructure were produced on the negatively charged surfaces with a small amount of PAA. In contrast, under other reaction conditions, calcite thin films with a fan-like structure in the cross section formed on the polarized substrates, and their thickness ranged from 2 to 7 microm. The films were composed of hemispheric- or flat island-shaped aggregates that were made of the calcite crystals that elongated along the c-axis. The morphology of the PAA-Ca(2+) complex assembly, which adsorbed onto the polarized HAp substrates, was controlled by the balance of the spatial charge distribution in its structure and the properties of the self-generating surface electric field, which led to the different morphologies of the calcite thin films. We proposed that the formation mechanism of the films formed coexisting with PAA and the self-generating electric fields.

Polarization of hybridized calcium phosphoaluminosilicates with 45S5-type bioglasses

Hybridization of biocompatible glasses was examined in order to produce fibrous bioactive glass. This work employed two kinds of calcium phosphoaluminosilicates (CPSA) and the 45S5-type bioactive glass. The choice of these parent glasses was based on both electric conductivity and fiber-forming ability. Electrical conductivity was an important property in relation to polarization, which has recently been proved an effective method for bioactivation of calcium phosphate ceramics. CPSA was developed by one of the authors (MK) for biocompatible fibers several decades ago. CPSA exhibited poor conductivity, while 45S5-type glass was conductive due to the high content of Na(+), which can be the charge carriers for conduction according to our previous work. The electrical improvement of CPSA glass was carried out through hybridization with 45S5. The glasses with Na(+)-rich composition failed to be transformed into fibers, whereas the glasses with appropriate sodium content were successfully made into fibers. The appropriate compositions were in the range of 1/99 to 10/90 as 45S5/CPSA in mass ratio.

Fabrication processes for bioceramics

Publisher Summary The term “bioceramics” refers to biocompatible ceramic materials, applicable for biomedical or clinical uses. Clinical applications require various shapes of bioceramics from thin films and nano-sized powders to porous or dense bodies. Bone substitutes use massive porous Hydroxyapatite (HA) and β-Tricalcium Phosphate (β-TCP) and their mixture: defective bones that are not always exposed to high stress can be replaced by porous HA or β-TCP. Commercial porous products of HA with a porosity of 70–80% are already distributed to clinics and hospitals. Highly dense ceramics of Yttria-Stabilized Zirconia (Y-TZP) and alumina are applied to hip joint balls and cups, while thin films of HA are coated on hard metals for artificial teeth and hip joints. To satisfy these demands, an appropriate fabrication method and process must be chosen for each clinical device. For fine fabrication of tough Y-TZP cups and balls, fine-grained ceramics of Y-TZP must be sintered with pure and fine powders under a controlled sintering program. In general, tough and strong ceramics consist of fine-grained microstructure, whose average grain diameter is less than 1 μm. It is important to eliminate impurities from bioceramics; even minor impurities bring harm to a body or provoke critical defect in the mechanical properties of bioceramics during long implantation in vivo. To undertake advantageous sintering, it is essential to control chemical and ceramic powder processing. The preparation of pure, fine powders enables the microstructure of bioceramics to be controlled. This chapter presents an overview of the general principles and methods of conventional fabrications, introduces prevailing techniques with some examples from commercial products, and provides a summary of recent advances in potential methods.