Sung-Mi Lee

Effect of lead zinc niobate addition on sintering behavior and piezoelectric properties of lead zirconate titanate ceramic

We investigated the effect of lead zinc niobate (PZN) on the sintering behavior and piezoelectric properties of lead zirconate titanate (PZT) ceramics. The addition of PZN improved the sinterability of PZT ceramic so remarkably, that at additions of more than 10%, the specimens were fully dense at a temperature as low as 900 °C. The phase of the PZT-PZN ceramics was affected by PZN content and the Zr/Ti ratio in the PZT. With increasing PZN content, a lower Zr/Ti ratio was required for the morphotropic phase boundary (MPB). Specimens with the MPB composition showed the highest piezoelectric properties; d 33 = 500 pC/N, k p = 0.68, and S 33 = 0.38% at 2 kV/mm.

Biocompatibility and Biocorrosion of Hydroxyapatite-Coated Magnesium Plate: Animal Experiment

Magnesium (Mg) has the advantage of being resorbed in vivo, but its resorption rate is difficult to control. With uncontrolled resorption, Magnesium as a bone fixation material has minimal clinical value. During resorption not only is the strength rapidly weakened, but rapid formation of metabolite also occurs. In order to overcome these disadvantages, hydroxyapatite (HA) surface coating of pure magnesium plate was attempted in this study. Magnesium plates were inserted above the frontal bone of Sprague-Dawley rats in both the control group (Bare-Mg group) and the experimental group (HA-Mg group). The presence of inflammation, infection, hydrogen gas formation, wound dehiscence, and/or plate exposure was observed, blood tests were performed, and the resorption rate and tensile strength of the retrieved metal plates were measured. The HA-Mg group showed no gas formation or plate exposure until week 12. However, the Bare-Mg group showed consistent gas formation and plate exposure beginning in week 2. WBC (White Blood Cell), BUN (Blood Urea Nitrogen), Creatinine, and serum magnesium concentration levels were within normal range in both groups. AST (Aspartate Aminotransferase) and ALT (Alanine Aminotransferase) values, however, were above normal range in some animals of both groups. The HA-Mg group showed statistically significant advantage in resistance to degradation compared to the Bare-Mg group in weeks 2, 4, 6, 8, and 12. Degradation of HA-Mg plates proceeded after week 12. Coating magnesium plates with hydroxyapatite may be a viable method to maintain their strength long enough to allow bony healing and to control the resorption rate during the initial period.

The Bioresorption and Guided Bone Regeneration of Absorbable Hydroxyapatite-coated Magnesium Mesh

Introduction: Nonabsorbable metallic membrane for guided bone regeneration is remained permanently even though after complete healing. There would be metallic exposure followed by the risk of infection; the membrane should be removed for the additional procedure such as implant installation. Since absorbable nonmetallic mesh is absorbed within 3 to 6 months, it is unnecessary to be removed. However, the absorbable membrane shows lower retention, lower mechanical strength, and difficulty of manipulation than the nonabsorbable ones. The purpose of this study is to evaluate the ability of absorbable metallic mesh (hydroxyapatite-coated magnesium mesh) with acceptable mechanical properties and satisfying biocompatibility. Methods: The bioresorption and fate of magnesium were evaluated in Sprague Dawley rat (SD rat) with critical defect of calvarium. The critical defect with a diameter of 8 mm was made on calvarium using trephine bur in 18 SD rats. The defected models were divided into 2 groups: the control group (9 SD rat) without mesh and the experimental group (9 SD rat) with the insertion of prototype HA-coated magnesium mesh. The 3 SD rats were sacrificed at 6, 12, and 18 weeks. The histopathological and radiographic examinations were performed afterward. Results: In the control group, there was no specific symptom. The experimental group also showed no specific symptom including swelling and dehiscence related to hydrogen gas formation. From 6 to 18 weeks, the experimental group showed the progressive absorption and fracture of magnesium mesh. However, there was no specific effectiveness of guided bone regeneration in both groups. There was no significant difference in bone volume, bone surface, and bone volume fraction between the negative control group and the group with magnesium mesh (P >0.05). Conclusion: Hydroxyapatite-coated magnesium mesh showed reasonable process of bioresorption and bony reaction; however, the effectiveness of guided bone regeneration and management of the bioresorption rate should be reconsidered.

Innovative micro-textured hydroxyapatite and poly(l-lactic)-acid polymer composite film as a flexible, corrosion resistant, biocompatible, and bioactive coating for Mg implants

The utility of a novel ceramic/polymer-composite coating with a micro-textured microstructure that would significantly enhance the functions of biodegradable Mg implants is demonstrated here. To accomplish this, bioactive hydroxyapatite (HA) micro-dots can be created by immersing a Mg implant with a micro-patterned photoresist surface in an aqueous solution containing calcium and phosphate ions. The HA micro-dots can then be surrounded by a flexible poly(l-lactic)-acid (PLLA) polymer using spin coating to form a HA/PLLA micro-textured coating layer. The HA/PLLA micro-textured coating layer showed an excellent corrosion resistance when it was immersed in a simulated body fluid (SBF) solution and good biocompatibility, which was assessed by in vitro cell tests. In addition, the HA/PLLA micro-textured coating layer had high deformation ability, where no apparent changes in the coating layer were observed even after a 5% elongation, which would be unobtainable using HA and PLLA coating layers; furthermore, this allowed the mechanically-strained Mg implant with the HA/PLLA micro-textured coating layer to preserve its excellent corrosion resistance and biocompatibility in vitro.

Radiological, histological, and hematological evaluation of hydroxyapatite-coated resorbable magnesium alloy screws placed in rabbit tibia

Titanium (Ti) screw has excellent mechanical property, and osseointegration capacity. However, they require surgery for removal. In contrast, polymer screws are resorbable, but they have poor mechanical properties. In this research, magnesium alloy screws (WE43: Mg-Y-Nd-Zr) that have advantages of titanium and polymer were manufactured. In addition, to increase biocompatibility and control degradation rate, the Mg alloy was coated with hydroxyapatite (HA). Torsion test and corrosion test were performed in vitro. For clinical, radiological and histological evaluation, on the eight rabbits, two HA-coated screws were installed in left tibia, and two noncoated screws were installed in right tibia. Each four rabbits were sacrificed 6 and 12 weeks postoperatively. For hematological evaluation, the same type of screws were installed on both legs. Complete blood count (CBC), Mg2+ concentrate were sampled from the ear central artery on the operation day for a control point, and at 1, 2, 4, 6, 8, and 12 weeks. Mg alloy screws have no differences of biocompatibility according to the HA coating. However, resorption of screw was slower in case of the HA coating. The hematological problem related releasing of Mg was not found. The results suggest that Mg alloy screws have feasibility for clinical application.

Piezoelectric properties of lead-free (Na0.5Bi0.5)TiO3–(Na0.5K0.5)NbO3–BaTiO3 ceramics

The microstructural evolution and piezoelectric properties of lead-free ceramics (0.98-x)(Na0.5Bi0.5)TiO3–x(Na0.5K0.5)NbO3–0.02BaTiO3 (0 x 0.98, abbreviated as (0.98-x)NBT–xNKN–0.02BT) were investigated. The effects of the amount of NKN on the crystal structure, microstructural evolution, and piezoelectric properties were examined. The 0.93NBT–0.05NKN–0.02BT ceramics having a lower NKN content gave good performances with piezoelectric properties of d33 140 pC/N and kp 21%, because of the soft additive Nb 5+ ions at the B sites. However, a paraelectric cubic phase was observed in the wide range of compositions between x 0.1 and x 0.9. At a higher NKN content of x > 0.9, a morphotropic phase boundary (MPB) between the tetragonal and orthorhombic phases was found in the 0.015NBT–0.965NKN–0.02BT ceramics, and the piezoelectric properties were enhanced (d33 135 pC/N, kp 29%). The piezoelectric properties of this system were closely related to its crystal structure.

Hydroxyapatite Microspheres as an Additive to Enhance Radiopacity, Biocompatibility, and Osteoconductivity of Poly(methyl methacrylate) Bone Cement

This study demonstrates the utility of hydroxyapatite (HA) microspheres as an additive to enhance the radiopaque properties, biocompatibility, and osteoconductivity of poly(methyl methacrylate) (PMMA)-based bone cements. HA microspheres were synthesized using spray drying. They had well-defined spherical shapes, thus allowing for the production of PMMA/HA composites with a very high HA content (20 vol % and 40 vol %). The uniform distribution of these HA microspheres in the PMMA matrix resulted in a remarkable increase in compressive modulus (p < 0.05), while preserving a reasonably high compressive strength. The PMMA/HA bone cements showed much higher radiopacity than PMMA containing BaSO4 as the additive. This was attributed to the high HA content up to 40 vol %. In addition, the biocompatibility and osteoconductivity of PMMA/HA bone cements were significantly enhanced compared to those of PMMA bone cements containing BaSO4, which were assessed using in vitro tests and in vivo animal experiments.