Akiko Nagai

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.

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 500u2009°C for 5–120 min under a 5u2002kVu2009cm−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 5u2002kVu2009cm−1, varying the poling temperature from 250 to 500u2009°C drastically shifted the TSDC peak temperature from 250 to 620u2009°C and increased Q from 0.5 to 45u2002μCu2009cm−2. The change in the average grain size from 2 to 11u2002μm increased the Q value from 15 to 60u2002μCu2009cm−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...

Hydroxyapatite electret accelerates reendothelialization and attenuates intimal hyperplasia occurring after endothelial removal of the rabbit carotid artery.

The present experiments were designed to investigate whether electrically polarized hydroxyapatite (HA electret) modifies reendothelialization and intimal hyperplasia occurring after endothelial removal of the rabbit carotid artery. Both HA electret and non-polarized HA, which served as a control, had been powdered and mixed with agarose gel. One of the two was applied around the external surface of the carotid artery. Histological analyses revealed that HA electret but not control HA significantly inhibited intimal hyperplasia. The number of Ki67-positive cells detectable in the intimal layer was significantly fewer in the HA electret group. In the HA electret group, abundant TUNEL-positive cells were detected in the media. The number of CD31-positive cells detected on the luminal surface was significantly higher in the HA electret group. Endothelium- and nitric oxide (NO)-dependent relaxation in response to carbachol was significantly improved only in the HA electret group. In conclusion, this is the first report demonstrating that HA electret significantly improved intimal hyperplasia by accelerating the regeneration of functioning endothelial cells and enhancing the apoptosis of medial smooth muscle cells.

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.

Regulation of Osteoblast-Like Cell Behaviors on Hydroxyapatite by Electrical Polarization

The osteoblast adhesion to the substrates are recognized to play a fundamental role in osteoconduction process. The purpose of this study was to evaluate the in vitro behavior of osteoblasts cultured on polarized hydroxyapatite (HA), having the enhanced osteobonding abilities. Osteoblast-like cells were seeded onto the polarized HA and investigated the adhesion and motility. The polarization had no effects on the percentage of the number of the spreaded cells against all the adhered cells, but had significant effects on the elongation of adhered cells from fluorescent observation and on the cell motility showed by the wound healing assay. The charges induced on the HA surface accelerated the cytoskeleton reorganization of the adhered cells cultured on HA specimens. The acceleration was emerged as the cells shape, actin filament pattern such as stress fiber formation, and the prolongation of the cell movement distances.

Regulation of myometrial contractivity during pregnancy in the rat: potential role for DDAH

There has been little information demonstrating the roles of dimethylarginine dimethylaminohydrolase (DDAH), which is the hydrolyzing enzyme of endogenous nitric oxide synthase (NOS) inhibitors and, in turn, modulates the intracellular concentrations of NOS inhibitors, in the myometrium during the course of pregnancy. Therefore, the present experiments were designed to investigate whether or not DDAH activity, protein and mRNA expression levels are altered during gestation of the rat and, if altered, those changes reflect on the levels of endogenous inhibitors and endothelin-1 (ET-1), and NO-dependent cyclic GMP generation in the myometrium. The up-regulated changes in DDAH activity, DDAH-2 protein and DDAH-2 mRNA expression at mid-gestation were accompanied by the reduced monomethylarginine and asymmetric dimethylarginine as NOS inhibitors, and ET-1 levels, and by the enhanced NO-dependent cyclic GMP production. At term gestation, on the other hand, down-regulated changes in DDAH activity, DDAH-2 protein and DDAH-2 mRNA expression were accompanied by the increased NOS inhibitors and ET-1 levels, and decreased NO-dependent cyclic GMP generation. These results suggest that alterations in DDAH/NOS inhibitors/NO-dependent cyclic GMP/ET-1 pathway are possibly involved in maintaining myometrial quiescence during gestation and controlling delivery at term.

Involvement of altered arginase activity, arginase I expression and NO production in accelerated intimal hyperplasia following cigarette smoke extract

In the present experiments, we tried to elucidate whether changes in arginase activity, protein expression of arginase-I and -II, and NO production are involved in accelerating the intimal hyperplasia following administration of cigarette smoke extract (CSE). The intimal hyperplasia was caused by removing endothelial cells with the aid of balloon embolectomy catheter in the right carotid artery of the male rabbit. The left carotid artery underwent sham operation and served as control. CSE was prepared by bubbling a stream of cigarette smoke into phosphate buffered saline. Rabbits were given subcutaneously with CSE once a day for 5 weeks from 1 week before to 4 weeks after the surgery. The specimens were assessed histologically and the intima/media ratio (%) was evaluated as an index of the intimal hyperplasia. The accelerated intimal hyperplasia with CSE was accompanied by the augmentation of the impaired cyclic GMP production, enhanced overall arginase activity and up-regulation of arginase-I. Pearsons correlation coefficient analyses revealed the close relationships among the arginase activities in endothelial cells and smooth muscle layer, the intimal/media ratio and cyclic GMP production. These results suggest that the enhanced arginase activity together with facilitated up-regulation of arginase-I with CSE, which was associated with the augmented impairment of NO production, shed a new light on the processes associated with accelerating the intimal hyperplasia in rabbit carotid arteries following CSE.

Electrical and biological properties of polarized hydroxyapatite electrets

Electrically polarized ceramics are classified as electrets, when ions are displaced or dipole moments are aligned in a direction for a considerable period due to an external electric force. An electret can independent irradiate an electrostatic force to the surrounding constituents. As briefly mentioned above, polarization takes place due to the off-centered displacement of cations and anions in the structure of a solid. The centers of these ions are generally difficult to be moved even in a strong dc field because of rigid chemical bonding. Actually, it is true that most ceramics are unsuitable for polarization. The ionic center of a very few materials, however, is liable to off-centered by a dc field and we have experimentally proved that the biocompatible hydroxyapatite (Ca5(P04)3OH; HA) is polarizable material. The polarized HA is an excellent electret which has desirable biological effects upon surrounding alive and non-alive components in vivo as well as in vitro: Using HA electrets, we have observed that crystal growth from a simulated body fluid can be accelerated or decelerated, and microorganism can be manipulated on the surfaces of HA, depending upon the electric signs. Hence we consider that one of the most promising approaches to the innovation in medical technology is use of biomedical electrets. This paper introduces the important electrical properties of HA ceramics.