Calcium level-responsive in-vitro zinc release from zinc containing tricalcium phosphate (ZnTCP)

Analytical Evaluation of Wet and Dry Mechanochemical Syntheses of Calcium-Deficient Hydroxyapatite Containing Zinc Using X-ray Diffractometry and Near-Infrared Spectroscopy

Calcium-deficient zinc-containing calcium phosphate (ZnAP), which has sustained zinc release properties that are effective for treating osteoporosis, can be efficiently synthesized as a biomaterial through wet grinding. To elucidate the physicochemical mechanism of these mechanochemical syntheses, ground products were obtained from the starting material powder (S-CP), consisting of calcium hydrogen phosphate dihydrate (CHPD), calcium oxide (CaO), and zinc oxide (ZnO), by wet and dry grinding for 0–3 h in a centrifugal ball mill. The ground S-CP products were analyzed using powder X-ray diffraction (XRD) and near-infrared spectroscopy (NIRS); the crystal transformations and molecular interactions of the ground products were kinetically analyzed. The XRD and second-derivative NIRS results indicate that the S-CP is primarily transformed into ZnAP via amorphous solid formation in wet grinding, and the reaction follows a consecutive reaction model. In contrast, in dry grinding, the ground product of CHPD and CaO is transformed into an amorphous solid following an equilibrium reaction model; however, ZnO is predominantly not transformed and remains crystalline.

Mechanical, Biological, and Antibacterial Characteristics of Plasma-Sprayed (Sr,Zn) Substituted Hydroxyapatite Coating

Implant-related infections are a major concern in total joint prostheses, occurring up to 3% in operations. In this work, 5% Zn²⁺ was added in HA to offset bacterial activity and 5% Sr²⁺ was also incorporated as a binary dopant to reduce the cytotoxic effect of Zn²⁺. The nanosized HA powder was synthesized by the hydrothermal method and then heat-treated at 600 °C for 4 h. The heat-treated powder was plasma-sprayed on a titanium alloy Ti-6Al-4V substrate. The addition of the dopant did not significantly influence the physical and mechanical properties of the coating. However, the cytocompatibility, antimicrobial, and contact-angle properties statistically enhanced. Moreover, the (Sr,Zn)-HA coating was post-heat treated at 500 and 600 °C for 3 h. X-ray diffraction confirmed that after heat treatment phase purity and crystallinity increased and residual stress decreased. Mechanical stability was evaluated by adhesive bond strength, and the results showed that after heat-treatment bonding strength increased from 26.81 ± 2.93 to 29.84 ± 3.62 and 34.66 ± 2.57 MPa, at 500 and 600 °C, respectively. Similar to the mechanical property, antibacterial activities and biological functions are also significantly improved. More interestingly, it was also observed that the Zn²⁺ ions released from the coating depend on Ca²⁺, P, and Sr²⁺ ions while Ca²⁺, P, and Sr²⁺ ions relied on heat treatment temperatures. However, (Sr,Zn)-HA coating at 600 °C demonstrates cytotoxic effects on MC3T3-E1 cells, characterized by poor cellular morphology on the coating surface and ultimately, cell death. The doping of Sr²⁺ with Zn²⁺, therefore, can offset the cytotoxic effects and enhanced biological performance. All of the outcomes of this study signify that (Sr,Zn)-HA coating heat-treated at 500 °C showed not only excellent mechanical and biological performance but also enhanced the antibacterial properties.

Bio-sourced phosphoprotein-based synthesis of silver-doped macroporous zinc phosphates and their antibacterial properties

The usual sources of phosphorus for metal phosphates are obtained from phosphate rocks, of which resources are depleted. As a substitute for these mineral sources, an original method of synthesis has been developed to prepare macroporous zinc phosphates using casein phosphoprotein. This bio-sourced reactant plays during the synthesis the roles of both a phosphorus source and a reducing agent for silver nanoparticles. Thus, zinc phosphates loaded with different Ag contents (up to 6.4 wt%) are prepared via hydrothermal treatment at 100 °C. Silver nanoparticles co-crystallized with hopeite, Zn₃(PO₄)₂ and/or Zn₂P₂O₇. In addition, casein induces porosity within the zinc phosphate framework and provides macropores (diameter of >50 nm) during calcination. The antibacterial properties against Escherichia coli K12 bacteria of Ag-containing and Ag-free porous zinc phosphates (calcined at 750 °C) were also tested for the first time.

Phosphoproteins as key reactants in an original method of synthesis of silver-doped macroporous zinc phosphates with antibacterial properties.

IGF-loaded silicon and zinc doped brushite cement: physico-mechanical characterization and in vivo osteogenesis evaluation

Dopants play critical roles in controlling the physical, mechanical, degradation kinetics, and in vivo properties of calcium phosphates. The aim of the present study was to evaluate the effects of silicon (Si) and zinc (Zn) dopants on the physico-mechanical and in vivo osteogenesis properties of brushite cements (BrCs) alone and in combination with insulin like growth factor 1 (IGF-1). Addition of 0.5 wt% Si did not alter the setting time, β-TCP content, and compressive strength of BrCs significantly; however, 0.25 wt% Zn incorporation was accompanied by a significant decrease in mechanical strength from 4.78 ± 0.21 MPa for pure BrC to 3.78 ± 0.59 MPa and 3.28 ± 0.22 MPa for Zn-BrC and Si/Zn-BrC, respectively. The in vivo bone regeneration properties of doped BrCs alone and in combination with IGF-1 were assessed and compared using chronological radiography, histology, scanning electron microscopy and fluorochrome labeling at 2 and 4 months post implantation in a rabbit femoral defect model. Based on in vivo characterization focusing on osteogenesis and vasculogenesis, Si-BrC and Si/Zn-BrC showed the best performance followed by Zn-BrC and pure BrCs. Addition of IGF-1 further improved bone regeneration. Our findings confirm that addition of Si and/or Zn alters the physico-mechanical properties of BrCs and promotes the early stage in vivo osseointegration and bone remodeling properties.

Mechanochemical synthesis of zinc-apatitic calcium phosphate and the controlled zinc release for bone tissue engineering

In this study, in order to control zinc (Zn)-release from calcium phosphate (CaP), the crystalline forms of CaP-containing Zn were modified by wet ball milling and/or heat treatment. The CaP (CaO:CaHPO4:ZnO = 7:20:3, molar ratio) was ground in a ball mill with the addition of purified water, and the ground products were heated to 400 °C and 800 °C. The physicochemical properties of these ground products were measured by powder X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy and energy-dispersive X-ray spectroscopy. Zn release characteristics from the samples were evaluated using a dissolution tester. The results of XRD and IR suggested that the structures of the starting materials were destroyed after 2.5 h of grinding, and new apatite-like amorphous solid containing Zn was generated. The Zn-release from the ground products was markedly suppressed after 2.5 h of grinding.

Bone regeneration of rat tibial defect by zinc-tricalcium phosphate (Zn-TCP) synthesized from porous Foraminifera carbonate macrospheres

Foraminifera carbonate exoskeleton was hydrothermally converted to biocompatible and biodegradable zinc-tricalcium phosphate (Zn-TCP) as an alternative biomimetic material for bone fracture repair. Zn-TCP samples implanted in a rat tibial defect model for eight weeks were compared with unfilled defect and beta-tricalcium phosphate showing accelerated bone regeneration compared with the control groups, with statistically significant bone mineral density and bone mineral content growth. CT images of the defect showed restoration of cancellous bone in Zn-TCP and only minimal growth in control group. Histological slices reveal bone in-growth within the pores and porous chamber of the material detailing good bone-material integration with the presence of blood vessels. These results exhibit the future potential of biomimetic Zn-TCP as bone grafts for bone fracture repair.

The therapeutic effect on bone mineral formation from biomimetic zinc containing tricalcium phosphate (ZnTCP) in zinc-deficient osteoporotic mice

The aim of this study was to evaluate the therapeutic efficacy of biomimetic zinc-containing tricalcium phosphate (ZnTCP) produced by hydrothermally converting calcium carbonate exoskeletons from foraminifera, in the treatment of osteoporotic mice. X-Ray powder diffraction showed crystallographic structures matching JCPDS profile for tricalcium phosphate. Mass spectroscopy used to calculate total composition amount showed similar amount of calcium (5×10⁴ µg/g) and phosphate (4×10⁴ ppm) after conversion and the presence of zinc (5.18×10³ µg/g). In vitro zinc release showed no release in PBS buffer and <1% zinc release in 7 days. In vivo evaluation was done in ovariectomized mice by implanting the ZnTCP samples in the soft tissues near the right femur bone for four weeks. Thirty ddY mice (5 weeks old, average weight of 21 g) were divided into six experimental groups (normal, sham, OVX, β-TCP, ZnTCP and direct injection of zinc). CT images were taken every two weeks where the bone mineral density (BMD) and bone mineral content (BMC) were calculated by software based on CT images. The ZnTCP group exhibits cortical and cancellous bone growth of 45% and 20% respectively. While sham, OVX and β-TCP suffered from bone loss. A correlation was made between the significant body weight increase in ZnTCP with the significant increase in plasma zinc level compared with OVX. The presented results indicate that biomimetic ZnTCP were effective in preventing and treating bone loss in osteoporotic mice model.

Zinc-containing apatite layers on external fixation rods promoting cell activity

Zinc-containing apatite layers were successfully formed on commercially available anodically oxidized Ti external fixation rods using ZnCl(2)-containing supersaturated calcium phosphate solutions. With an increase in concentration of ZnCl(2) in the supersaturated calcium phosphate solutions, the amounts of zinc that precipitated on the Ti external fixation rods increased (from 0 to 0.195 + or - 0.020 microg cm(-2)); meanwhile, the amounts of calcium and phosphorus that precipitated on the Ti external fixation rods decreased (from 11.2 + or - 1.5 and 4.8 + or - 0.5 microg cm(-2) to 2.9 + or - 1.6 and 1.3 + or - 0.9 microg cm(-2), respectively). The zinc-containing apatite layers precipitated on the Ti external fixation rods caused a significant increase in fibroblastic proliferation, osteoblastic proliferation and differentiation in vitro. The Ti external fixation rods coated with zinc-containing apatite layers are expected to be more effective in accelerating the tissue regeneration around the surgical site than those coated with an apatite layer.

Brushite-Forming Mg-, Zn- and Sr-Substituted Bone Cements for Clinical Applications

Calcium phosphate cements have been in clinical use for the last 10 years. Their most salient features include good biocompatibility, excellent bioactivity, self-setting characteristics, low setting temperature, adequate stiffness, and easy shaping to accomodate any complicated geometry. They are commonly used in filling bone defects and trauma surgeries as mouldable paste-like bone substitute materials. Substitution of trace elements, such as Mg, Sr and Zn ions, into the structure of calcium phosphates is the subject of widespread investigation nowadays, because of their impending role in the biological process. Subtle differences in composition and structure of these materials may have a profound effect on their in vivo behaviour. Therefore, the main goal of this paper is to provide a simple, but comprehensive overview of the present achievements relating to brushite-forming cements doped with Mg, Zn and Sr, and to identify new developments and trends. In particular, the influence of ionic substitution on the chemical, physical and biological properties of these materials is discussed.

Efficacy of the injectable calcium phosphate ceramics suspensions containing magnesium, zinc and fluoride on the bone mineral deficiency in ovariectomized rats

The purpose of this study was to evaluate the therapeutic efficacy of a new calcium phosphate (CaP)-based formulation in improving the bone mineral deficiency in ovariectomized (OVX) rats. The ions release experiments for CaP preparations (G2: 0.46% Mg, 5.78% Zn, and 2.5% F; G3:3.1% Mg, 0.03% Zn, and 3.01% F; G4: 1.25% Mg, 1.77% Zn, 1.35% F) and of a Zn-TCP (G1: 6.17% Zn) powders, the initial Mg and Zn ion release rates of MZF-CaPs were performed in acetate buffer at pH 4.5 (37 degrees C). Wistar rats were divided into six groups including a normal (not OVX) group (GN) and a control, OVX group (GC). Rats in groups GC, G1, G2, G3, G4 were OVX. Suspensions consisting of CaP preparations (G2, G3, G4) and of a Zn-TCP (G1) powders were injected in the right thighs of OVX rats in all groups except for GN and GC, once a week for 4 weeks. GN and GC rats were injected with saline solutions. Plasma was analyzed for Zn land alkaline phosphatase levels. The bone mineral density (BMD) was measured using DEXA and the bone (femur) strength determined using three-point-bending analysis. G1 and G2 groups showed high plasma Zn levels. The area under the curve of plasma Zn was significantly greater in the G1, G2, and GN groups than in the G3, G4, and GC groups (p < 0.05). The BMD and bone mechanical strength of the right femur were significantly higher in the G1, G2, G3, and G4 groups than GC group on day 28. The right femur had significantly greater BMD and bone mechanical strength than the left femur in G1, G2, G3, and G4 groups. However, there was no significant difference in the BMD of the right femur between the G1, G2, G3, and G4 groups. Results indicate that the new injectable CaP formulations are effective in improving bone properties of OVX rats and may be useful in osteoporosis therapy.

Characterization and in vitro bioactivity of zinc-containing bioactive glass and glass-ceramics

Zinc-containing glass is prepared by the substitution of CaO in 58S bioactive glass with 0.5 and 4 wt% ZnO, and glass-ceramics are obtained by heat-treating the glass at 1,200 C. The bending strength and in vitro bioactivity of the glass and glass-ceramics are evaluated. The results indicate that Zn promotes the crystallization of SiO(2) and wollastonite in glass-ceramics, and proper crystallization can enhance the bending strength of the glass-ceramic. The in vitro results show that ZnO in glass retards the hydroxyapatite (HA) nucleation at the initial stage of simulated body fluid (SBF) soaking, but does not affect the growth of HA after long periods of soaking, and the ionic products of 58S4Z glass can stimulate the proliferation of osteoblast at certain concentrations. Osteoblasts attach well on both glass samples and glass-ceramic samples, but the high Si ion concentration released from glass samples restrains the proliferation of osteoblasts after 3 days of culture. In contrast, osteoblasts show good proliferation on glass-ceramic samples, and ZnO in glass-ceramics promotes the proliferation rate. The results in this study suggest that the glass and glass-ceramics with different ZnO content might be used as bioactive bone implant materials in different applications.

Zinc phosphate as versatile material for potential biomedical applications Part II

Surface chemical reactivity of two modifications of synthetic zinc phosphate tetrahydrate (alpha - and beta -form of Hopeite, alpha -,beta -ZPT) has been studied by selective chemical and e-beam etching in presence of diluted phosphoric acid and ammonia by Scanning Electron Microscopy (SEM) and microelectrophoresis (zeta potential measurements) in correlation with the corresponding bulk properties and crystal size distributions. The subtitle crystallographic differences between alpha -and beta -ZPT originating from a unique hydrogen bonding pattern, induce drastic variations of both surface potential and surface charge. Biogenic Hydroxyapatite (HAP) and one of its metastable precursors, a calcium dihydrogen phosphate dihydrate (DCPD) or Brushite were used to underline this resulting variation of chemical reactivity in zinc phosphates. In-situ monitoring of the transformation of Brushite in Hydroxyapatite is also reported.

Selective protein adsorption property and characterization of nano-crystalline zinc-containing hydroxyapatite

Nano-crystalline Zn-containing hydroxyapatite (ZnHAp) was prepared by the wet-chemical method and the selective adsorption of essential proteins was examined, taking bovine serum albumin (BSA) and pathogenic protein such as beta(2)-microglobulin (beta(2)-MG) as model proteins. Transmission electron microscopy observation and X-ray diffraction analysis indicated that the increase of Zn content led to smaller crystallites and their specific surface area of ZnHAps increased with increasing Zn content, accordingly. Furthermore, the amounts of BSA adsorption on ZnHAp particles decreased with increasing Zn content in spite of the increase in the specific surface area. It is thus concluded that nano-crystalline ZnHAps had a highly selective adsorption property with regard to beta(2)-MG.

Effect of controlled zinc release on bone mineral density from injectable Zn-containing ?-tricalcium phosphate suspension in zinc-deficient diseased rats

The purpose of this study was to evaluate the efficacy of zinc (Zn)-containing beta-tricalcium phosphate (Zn-TCP) in correcting the bone mineral deficiency noted in osteoporosis using ovariectomized rat model. Four rats were used for each of the four experimental groups: D0, D10, D20, and N10. The rats in D0, D10, and D20 groups were ovariectomized, and fed a vitamin D-, Ca-, and Zn-deficient diet, and induced Zn-deficient osteoporoses for 9 weeks. In contrast, the N10 group was the normal rats fed normal healthy diet for 9 weeks. D0 group was injected with pure beta-TCP suspension, D10 and D20 groups were injected with suspensions containing 10 mg of 10 mol % (6.17 wt % Zn) and 20 mol % (12.05 wt % Zn) Zn-TCP, respectively, and the healthy group, N10 were injected with 10 mol %. Zn-TCP suspensions. Injections were administered intramuscularly in the left thigh once a week in all rats, and fed a vitamin D- and Zn-deficient diet for 9 weeks. The plasma calcium (Ca) and Zn levels, plasma alkaline phosphatase activity (ALP) and bone mineral density (BMD) of the lumbar vertebra and femora were measured. The plasma Zn levels in all the rats were between 1.1 and 2.8 microg/mL. The areas under the curves for the Ca, Zn, and ALP (Ca-AUC, Zn-AUC, and ALP-AUC) levels between 0 and 63 days were calculated. Results for the AUCs were as follows: (1) the Zn-AUCs were in the order of N10 = D20 > D10 > D0; (2) the Ca-AUCs for D0, D10 groups were significantly lower than that for the N10 group; (3) the ALP-AUCs for the D10 and D20 groups were significantly higher than that for the N10 group, and that of the D0 group was in between those. The body weight of D10 and D20 groups significantly increased with time, that of the D0 group increased slightly, and that of the N10 group remained unchanged for the entire experimental period. The BMD of the lumbar vertebrae of the D10 and D20 groups (about 100 mg/cm(2)) was significantly higher than that of the D0 group but lower than that of the N10 group. The BMD of the left femur increased more than that of the right femur with the increase in the amount of Zn in the suspension. The results of this study suggest that the local effect on BMD was more pronounced than the effect on the whole body.