Investigating the structure, solubility, and antibacterial properties of silver- and copper-doped hydroxyapatite

Hydroxyapatite (HA) powders were synthesized by the wet precipitation method in which two experimental compositions were synthesized (10 mol% Ag-HA and Cu-HA) where the CaNO₃ content was partially substituted with AgNO₃ and Cu(NO₃ )₂ . X-ray diffraction (XRD) was employed to characterize changes to the HA structure as the dopants (Cu²⁺ , Ag⁺ ) were incorporated into the materials structure. Energy-dispersive X-ray spectroscopy (EDS) determined confirmed the compositions and found that the Ca/P ratio was 1.63 for the control (HA) while Ag-HA and Cu-HA exhibited (X + Ca)/P ratios of 1.79 and 1.65, respectively. Antibacterial efficacies were evaluated against E. coli and S. aureus, as a function of surface area and incubation time. The more prominent antibacterial effects were observed with both Ag-HA and Cu-HA and the materials antibacterial influence was maintained with respect to time. Ion release studies of each HA composition (15, 30, and 45 days) showed that Cu-HA released significantly more Cu²⁺ (36.1 ± 5.1 mg/L) than Ag⁺ (2.9 ± 1.2 mg/L) from Ag-HA. Analysis of each composition incubated in simulated body fluid (SBF) exhibited surface depositions that are likely calcium phosphate (CaP). Cytocompatibility testing in MC 3T3 Osteoblasts showed slight reductions in cell viability when tested using MTT assay, however cell adhesion studies were positive for each composition.

Synthesis, Processing and the Effect of Thermal Treatment on the Solubility, Antioxidant Potential and Cytocompatibility of Y2O3 and CeO2 doped SiO2-SrO-Na2O Glass-Ceramics

Thermal treatment of a 0.52SiO₂-0.24SrO-0.24-xNa₂O-xMO glass-ceramic series (where x = 0.08 and MO = Y₂O₃ or CeO₂) was conducted in order to synthesize yttrium (Y³⁺) and cerium (Ce³⁺) crystalline species that may act as radical oxygen specie (ROS) scavengers. The prominent phase for the Control is a sodium-strontium-silicate while the experimental glass-ceramics (HY, YCe, and HCe) present sodium-Y/Ce-silicate and oxide phases. Disk shrinkage during thermal processing ranges from 1-7% for Control, HY, YCe, and HCe in both diameter and thickness. Solubility studies determined that the release of Si⁴⁺ and Na⁺ are greatest from the Control disks which peaks at 1550 µg/mL. Release from the Y³⁺ and Ce³⁺ glass-ceramics reached 320 µg/mL for Si⁴⁺ and 630 µg/mL for Na⁺. The range of antioxidant capacity (ABTS assay) for all samples was 0.31-3.9 mMTE. No significant reduction in MC 3T3 Osteoblast cell viability was observed for any composition tested.

Antibacterial Efficacy of Silver or Arsenic Doped Polymer Composites Against Several Kinds of Bacteria

Structure and several properties of AgNO3 and As2O3 doped polymer composites have been investigated, including their antibacterial activity against E. coli, S. aureus, C. albicans and S. epidermidis. New silver or arsenic doped polymer composites have been characterized by an X-ray diffraction (XRD), a scanning electron microscopy combined with an energy dispersive X-ray spectroscopy (SEM/EDS) and ion release studies. The antibacterial evaluation of each of the composite samples was conducted using S. aureus in the liquid broth culture, with 10, 20 and 30 % of liquid extract added to the bacterial culture. Control S. aureus stocks were used for comparison at each time period and were recorded at 100 % at each time period. For samples with the PLA plasticizer the bacterial viability was significantly reduced for each composition containing Ag/As and was similar for each dosage concentration.

Bioactivity of Y2O3 and CeO2 doped SiO2-SrO-Na2O glass-ceramics

The bioactivity of yttrium and cerium are investigated when substituted for Sodium (Na) in a 0.52SiO2-0.24SrO-0.24 -xNa2O- xMO glass-ceramics (where x = 0.08 and MO = Y2O3 or CeO2). Bioactivity is monitored through pH and inductively coupled plasma-optical emission spectrometry where pH of simulated body fluid ranged from 7.5 to 7.6 and increased between 8.2 and 10.0 after 14-day incubation with the glass-ceramic disks. Calcium (Ca) and phosphorus (P) levels in simulated body fluid after incubation with yttrium and cerium containing disks show a continual decline over the 14-day period. In contrast, Con disks (not containing yttrium or cerium) caused the elimination of Ca in solution after 1 day and throughout the incubation period, and initially showed a decline in P levels followed by an increase at 14 days. Scanning electron microscopy and energy dispersive spectroscopy confirmed the presence of Ca and P on the surface of the simulated body fluid-incubated disks and showed precipitates on Con and HCe (8 mol% cerium) samples. Cell viability of MC3T3 osteoblasts was not significantly affected at a 9% extract concentration. Optical microscopy after 24 h cell incubation with disks showed that Con samples do not support osteoblast or Schwann cell growth, while all yttrium and cerium containing disks have direct contact with osteoblasts spread across the wells. Schwann cells attached in all wells, but only showed spreading with the HY-S (8 mol% yttrium, heated to sintering temperature) and YCe (4 mol% yttrium and cerium) disks. Scanning electron microscopy of the compatible disks shows osteoblast and sNF96.2 Schwann cells attachment and spreading directly on the disk surfaces.

Synthesis, characterization, and in vitro cytocompatibility of Ga-bioactive glass/polymer hydrogel composites

A bioactive glass series (0.42SiO₂-0.10Na₂O-0.08CaO-(0.40-x)ZnO-(x)Ga₂O₃) was incorporated in carboxymethyl cellulose-dextran hydrogels at three different loadings (0.05, 0.10, and 0.25 m²), and the resulting composites were characterized using scanning electron microscopy, physical swelling characteristics, and inductively coupled plasma optical emission spectroscopy. In vitro cytocompatibility was also evaluated for composite extracts in contact with L-929 mouse fibroblasts and MC3T3-E1 human osteoblasts. Scanning electron microscopy confirmed that glass particles were distributed throughout the hydrogels, and swelling studies showed that glass presence can increase the amount of fluid that can be absorbed by the hydrogels after seven days of immersion in phosphate-buffered saline by up to 180%. Several trends were observed in the inductively coupled plasma optical emission spectroscopy data, with the most important being the release of Ga³⁺ from both Ga-containing glasses at all three loadings, with a maximum of 4.7 mg/L released after 30 days of incubation in phosphate-buffered saline. Cell viability analysis suggested that most composite extracts did not decrease neither fibroblast nor osteoblast viability. These results indicate that it is possible to embed bioactive glass particles into carboxymethyl cellulose-dextran hydrogels, and upon submersion in aqueous media, release ions from the glass particles that may elicit therapeutic effects.

Antibacterial and antifungal potential of Ga-bioactive glass and Ga-bioactive glass/polymeric hydrogel composites

A bioactive glass series (0.42SiO₂ -0.10Na₂ O-0.08CaO-(0.40 - x)ZnO-(x)Ga₂ O₃ ) was synthesized, and it is efficacy against the Gram (-ve) bacteria Escherichia coli (E. coli), the Gram (+ve) bacteria Staphylococcus aureus (S. aureus), and the fungus Candida albicans (C. albicans), were characterized through liquid broth analysis. The glass series was also seeded in CMC-Dex hydrogels at three different loadings (0.05, 0.10, and 0.25 m² ), and the antibacterial and antifungal efficacies of the resulting composites were characterized using both liquid broth and agar diffusion analysis. Liquid broth analysis was conducted using liquid extracts, which for glass samples were obtained after incubation for up to 30 days in both ultrapure water and phosphate buffered saline (PBS), while glass-hydrogel extracts were obtained solely in PBS. Glass extracts (water) decreased C. albicans viability, while those obtained in PBS decreased the viability of both E. coli and C. albicans. Glass-hydrogel extracts exhibited slight inhibition of E. coli and C. albicans. However, none of the liquid extracts decreased S. aureus viability. Glass-hydrogel composites produced inhibition zones in all three microbial cultures, with the greatest efficacy against C. albicans. The results of this study suggest these materials have potential as bone void-filling materials which display antifungal, and possibly, antibacterial properties. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1102-1113, 2017.

A glass polyalkenoate cement carrier for bone morphogenetic proteins

This work considers a glass polyalkenoate cement (GPC)-based carrier for the effective delivery of bone morphogenetic proteins (BMPs) at an implantation site. A 0.12 CaO-0.04 SrO-0.36 ZnO-0.48 SiO2 based glass and poly(acrylic acid) (PAA, Mw 213,000) were employed for the fabrication of the GPC. The media used for the water source in the GPC reaction was altered to produce a series of GPCs. The GPC liquid media was either 100 % distilled water with additions of albumin at 0, 2, 5 and 8 wt% of the glass content, 100 % formulation buffer (IFB), and 100 % BMP (150 µg rhBMP-2/ml IFB). Rheological properties, compressive strength, ion release profiles and BMP release were evaluated. Working times (Tw) of the formulated GPCs significantly increased with the addition of 2 % albumin and remained constant with further increases in albumin content or IFB solutions. Setting time (Ts) experienced an increase with 2 and 5 % albumin content, but a decrease with 8 % albumin. Changing the liquid source to IFB containing 5 % albumin had no significant effect on Ts compared to the 8 % albumin-containing BT101. Replacing the albumin with IFB/BMP-2 did not significantly affect Tw. However, Ts increased for the BT101_BMP-2 containing GPCs, compared to all other samples. The compressive strength evaluated 1 day post cement mixing was not affected significantly by the incorporation of BMPs, but the ion release did increase from the cements, particularly for Zn and Sr. The GPCs released BMP after the first day, which decreased in content during the following 6 days. This study has proven that BMPs can be immobilized into GPCs and may result in novel materials for clinical applications.

Characterization of Y2O3 and CeO2 doped SiO2-SrO-Na2O glasses

The structural effects of yttrium (Y) and cerium (Ce) are investigated when substituted for sodium (Na) in a 0.52SiO2–0.24SrO–(0.24−x)Na2O–xMO (where x = 0.08; MO = Y2O3 and CeO2) glass series. Network connectivity (NC) was calculated assuming both Y and Ce can act as a network modifier (NC = 2.2) or as a network former (NC up to 2.9). Thermal analysis showed an increase in glass transition temperature (Tg) with increasing Y and Ce content, Y causing the greater increase from the control (Con) at 493∘C to 8 mol% Y (HY) at 660∘C. Vickers hardness (HV) was not significantly different between glasses. 29Si Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR) did not show peak shift with addition of Y, however Ce produced peak broadening and a negative shift in ppm. The addition of 4 mol% Ce in the YCe and LCe glasses shifted the peak from Con at −81.3 ppm to −82.8 ppm and −82.7 ppm respectively; while the HCe glass produced a much broader peak and a shift to −84.8 ppm. High resolution X-ray Photoelectron Spectroscopy for the O 1s spectral line showed the ratio of bridging (BO) to non-bridging oxygens (NBO), BO:NBO,was altered,where Con had a ratio of 0.7, HY decreased to 0.4 and HCe to 0.5.

Submaximal aerobic running economy and treadmill performance in prepubertal boys

Although the determinants of running economy and its relationship to endurance performance have been evaluated in adults, little data are available in pediatric subjects. Twenty-eight prepubertal boys with diverse athletic abilities underwent progressive maximal treadmill testing. Running economy was defined as (1) VO2 at 9.6 kph and (2) VO2 expenditure for increasing running speed 1.6 kph (delta VO2). Treadmill running times ranged from 12.6 to 23.0 min. Mean VO2 at 6 mph was 48.7 m.kg-1.min-1 (SD 4.3) and delta VO2 averaged 6.8 m.kg-1.min-1 (SD 1.7). VO2max correlated closely to treadmill time. Treadmill endurance times were significantly related to running economy by both definitions; submaximal VO2 levels did not, however, correlate with maximal aerobic power. Delta VO2 was associated with stride frequency, but no other relationships were observed between economy and height, age, respiratory exchange ratio, ventilatory equivalent for oxygen, stride length: leg length ratio, or body surface area: mass ratio. These findings suggest that among older prepubertal boys, greater running economy is associated with superior treadmill endurance performance and that stride frequency may influence submaximal VO2 expenditure in children.

Physiologic responses to treadmill running in adult and prepubertal males

Little data are available directly comparing physiologic responses to endurance exercise in children and adults. To evaluate age related differences during maximal and submaximal treadmill exercise, physiologic parameters recorded during testing of 20 active prepubertal boys (aged 9-13 years) were compared with values obtained in nonathletic adult males aged 23-33 years. Maximum oxygen consumption (VO2 max) was 57.9 ml.kg-1.min-1 (6.9 SD) in the boys and 48.3 ml.kg-1.min-1 (4.9 SD) in the adults. Running economy examined both as VO2 at a treadmill speed of 9.6 kph and as the slope of linear regression of VO2 at four submaximal speeds was less in boys compared to men when values were expressed per kg body mass. Differences in running economy between the two groups disappeared, however, when related to body surface area. As expected, children had a higher stride frequency at a given treadmill speed, but running stride frequency was unrelated to economy with the two groups. Lower respiratory exchange ratios were observed at maximal and submaximal exercise in the children, which may reflect diminished anaerobic capacity or differences in substrate utilization. These results substantiate the high aerobic capacity previously observed in children and suggest that lower running economy in younger subjects may largely relate to a greater body surface are/mass ratio.