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.

Investigating the effect of SiO2-TiO 2-CaO-Na 2O-ZnO bioactive glass doped hydroxyapatite: characterisation and structural evaluation.

The effects of increasing bioactive glass additions, SiO2-TiO2-CaO-Na2O-ZnO up to 25 wt% in increments of 5 wt%, on the physical and mechanical properties of hydroxyapatite (HA) sintered at 900, 1000, 1100 and 1200 °C for 2 h was investigated. Increasing both the glass content and the temperature resulted in increased HA decomposition. This resulted in the formation of a number of bioactive phases. However the presence of the liquidus glass phase did not result in increased densification levels. At 1000 and 1100 °C the additions of 5 wt% glass resulted in a decrease in density which never recovered with increasing glass content. At 1200 °C a cyclic pattern resulted from increasing glass content. There was no direct relationship between strength and density with all samples experiencing no change or a decrease in strength with increasing glass content. Weibull statistics displayed no pattern with increasing glass content.

Mechanical properties of hydroxyapatite-zirconia compacts sintered by two different sintering methods.

Microwave sintering is traditionally employed to reduce the sintering temperature required to densify powder compacts. The effect of microwave heating on hydroxyapatite (HA)-zirconia (ZrO2) green bodies has been investigated in order to understand how microwave energy may affect the physical and mechanical properties of the resultant densified composites. Laboratory synthesised nano-sized HA and a commercial nano-sized ZrO2 powder have been ball milled to create mixtures containing 0-5 wt% ZrO2 loadings. Compacts were microwave sintered at either 700, 1000 or 1200 degrees C with a 1 h hold time. Comparative firings were also performed in a resistive element furnace using the same heating profile in order to assess the differences between conventional and microwave heating on the physical, mechanical and microstructural properties of the composites. Samples sintered at 700 degrees C show little sign of densification with open porosities of approximately 50%. Composites conventionally sintered at 1000 degrees C were between 65 and 75% dense, whereas the samples microwave sintered at this temperature were between 55 and 65% dense. Samples sintered at 1200 degreesbC showed the greatest degree of densification (>80%) with a corresponding reduction in open porosities. TCP generation occurred as a consequence of sintering at 1200 degrees C, even with 0 wt% ZrO2, and increased degradation of the HA phase to form significant amounts of TCP occurred with increasing additions of ZrO2, along with increasing open porosity. Nanosized ZrO2 prevents the densification of the HA matrix by effectively pinning grain boundaries and this effect is more pronounced in the MS materials. Similar strengths are achieved between the microwave and conventionally sintered samples. Greater amount of open porosity and pore interconnectivity are seen in the MS samples, which are considered to be useful for biomedical applications as they can promote osteo-integration.

Glass Polyalkenoate Cements Designed for Cranioplasty Applications: An Evaluation of Their Physical and Mechanical Properties.

Glass polyalkenoate cements (GPCs) have potential for skeletal cementation. Unfortunately, commercial GPCs all contain, and subsequently release, aluminum ions, which have been implicated in degenerative brain disease. The purpose of this research was to create a series of aluminum-free GPCs constructed from silicate (SiO2), calcium (CaO), zinc (ZnO) and sodium (Na2O)-containing glasses mixed with poly-acrylic acid (PAA) and to evaluate the potential of these cements for cranioplasty applications. Three glasses were formulated based on the SiO2-CaO-ZnO-Na2O parent glass (KBT01) with 0.03 mol % (KBT02) and 0.06 mol % (KBT03) germanium (GeO2) substituted for ZnO. Each glass was then mixed with 50 wt % of a patented SiO2-CaO-ZnO-strontium (SrO) glass composition and the resultant mixtures were subsequently reacted with aqueous PAA (50 wt % addition) to produce three GPCs. The incorporation of Ge in the glass phase was found to result in decreased working (142 s to 112 s) and setting (807 s to 448 s) times for the cements manufactured from them, likely due to the increase in crosslink formation between the Ge-containing glasses and the PAA. Compressive (σc) and biaxial flexural (σf) strengths of the cements were examined at 1, 7 and 30 days post mixing and were found to increase with both maturation and Ge content. The bonding strength of a titanium cylinder (Ti) attached to bone by the cements increased from 0.2 MPa, when placed, to 0.6 MPa, after 14 days maturation. The results of this research indicate that Germano-Silicate based GPCs have suitable handling and mechanical properties for cranioplasty fixation.

Raman Spectroscopy Applied to the Noninvasive Detection of Monosodium Urate Crystal Deposits.

An off-the-shelf Raman Spectrometer (RS) was used to noninvasively determine the presence of monosodium urate (MSU) crystals on the metatarsophalangeal joint (MTPJ) of a single gout sufferer. The spectrum sourced from the clinically diagnosed gout sufferer was compared to that sourced from an age-matched healthy subject scanned using the same protocol. Minimal signal processing was conducted on both spectra. Peaks characteristic of MSU crystals were evident on the spectrum sourced from the gout sufferer and not on the spectrum from the healthy control.

Comparative study of Weibull characteristic strength and mean strength of GPCs to confirm the minimum number of samples needed for confident strength reporting.

This short communication determines the strength of two glass polyalkenoate cements that differ from each other through the composition of their glass phase. Sample sets of n=5, 10, 20 and 30 were formulated and tested in biaxial flexure. The derived mean for each sample set was compared against the Weibull characteristic strength. The mean and corresponding characteristic strength show a maximum percentage difference 10.1%, and the 95% confidence intervals calculated from the mean data encompass the corresponding characteristic strength down to a sample set of n=5. This suggests that, for brittle materials such as glass polyalkenoate cements, it is acceptable to test only five samples of each material in biaxial flexure and the resultant 95% confidence intervals will encompass the corresponding Weibull characteristic strength of the material.

Investigating the addition of SiO2-CaO-ZnO-Na2O-TiO2 bioactive glass to hydroxyapatite: Characterization, mechanical properties and bioactivity.

Hydroxyapatite (Ca10(PO4)6(OH)2) is widely investigated as an implantable material for hard tissue restoration due to its osteoconductive properties. However, hydroxyapatite in bulk form is limited as its mechanical properties are insufficient for load-bearing orthopedic applications. Attempts have been made to improve the mechanical properties of hydroxyapatite, by incorporating ceramic fillers, but the resultant composite materials require high sintering temperatures to facilitate densification, leading to the decomposition of hydroxyapatite into tricalcium phosphate, tetra-calcium phosphate and CaO phases. One method of improving the properties of hydroxyapatite is to incorporate bioactive glass particles as a second phase. These typically have lower softening points which could possibly facilitate sintering at lower temperatures. In this work, a bioactive glass (SiO2-CaO-ZnO-Na2O-TiO2) is incorporated (10, 20 and 30 wt%) into hydroxyapatite as a reinforcing phase. X-ray diffraction confirmed that no additional phases (other than hydroxyapatite) were formed at a sintering temperature of 560 ℃ with up to 30 wt% glass addition. The addition of the glass phase increased the % crystallinity and the relative density of the composites. The biaxial flexural strength increased to 36 MPa with glass addition, and there was no significant change in hardness as a function of maturation. The pH of the incubation media increased to pH 10 or 11 through glass addition, and ion release profiles determined that Si, Na and P were released from the composites. Calcium phosphate precipitation was encouraged in simulated body fluid with the incorporation of the bioactive glass phase, and cell culture testing in MC-3T3 osteoblasts determined that the composite materials did not significantly reduce cell viability.

Comparison of the Weibull characteristics of hydroxyapatite and strontium doped hydroxyapatite.

The effects of two strontium (Sr) additions, 5% and 10% of the total calcium (Ca) content, on the phase assemblage and Weibull statistics of hydroxyapatite (HA) are investigated and compared to those of undoped HA. Sintering was carried out in the range of 900-1200 °C in steps of 1000 °C in a conventional furnace. Sr content had little effect on the mean particulate size. Decomposition of the HA phase occurred with Sr incorporation, while ß-TCP stabilization was shown to occur with 10% Sr additions. Porosity in both sets of doped samples was at a comparable level to porosity in the undoped HA samples, however the 5% Sr-HA samples displayed the greatest reduction in porosity with increasing temperature while the porosity of the 10% Sr-HA samples remain relatively constant over the full sintering temperature range. The undoped HA samples displayed the greatest Weibull strengths and the porosity was determined to be the major controlling factor. However, with the introduction of decompositional phases in the Sr-HA samples, the dependence of strength on porosity is reduced and the phase assemblage becomes the more dominant factor for Weibull strength. The Weibull modulus is relatively independent of the porosity in the undoped HA samples. The 5% Sr-HA samples experience a slight increase in Weibull modulus with porosity, indicating a possible relationship between the parameters. However the 10% Sr-HA samples show the highest Weibull modulus with a value of approximately 15 across all sintering temperatures. It is postulated that this is due to the increased amount of surface and lattice diffusion that these samples undergo, which effectively smooths out flaws in the microstructure, due to a saturation of Sr content occurring in grain boundary movement.

A Novel Glass Polyalkenoate Cement for Fixation and Stabilisation of the Ribcage, Post Sternotomy Surgery: An ex-Vivo Study.

This study investigates the use of gallium (Ga) based glass polyalkenoate cements (GPCs) as a possible alternative adhesive in sternal fixation, post sternotomy surgery. The glass series consists of a Control (CaO-ZnO-SiO2), and LGa-1 and LGa-2 which contain Ga at the expense of zinc (Zn) in 0.08 mol% increments. The additions of Ga resulted in increased working time (75 s to 137 s) and setting time (113 to 254 s). Fourier Transform Infrared (FTIR) analysis indicated that this was a direct result of increased unreacted poly(acrylic acid) (PAA) and the reduction of crosslink formation during cement maturation. LGa samples (0.16 wt % Ga) resulted in an altered ion release profile, particularly for 30 days analysis, with maximum Ca2+, Zn2+, Si4+ and Ga3+ ions released into the distilled water. The additions of Ga resulted in increased roughness and decreased contact angles during cement maturation. The presence of Ga has a positive effect on the compressive strength of the samples with strengths increasing over 10 MPa at 7 days analysis compared to the 1 day results. The additions of Ga had relatively no effect on the flexural strength. Tensile testing of bovine sterna proved that the LGa samples (0.16 wt % Ga) are comparable to the Control samples.

Mechanical parameters of strontium doped hydroxyapatite sintered using microwave and conventional methods.

The effects of ion substitution in hydroxyapatite (HA) on crystal structure and lattice stability is investigated in the green state and post sintering. The effects of ion incorporation on the biaxial flexural strength and hardness are also investigated. Sintering is carried out at 1200 °C using comparative conventional and microwave regimes. Post sintering, the effects of ion incorporation manifest as an increase in the lattice d-spacings and a reduction of the crystallite size. Some HA decomposition occurs with ß-TCP stabilisation in conventional sintering (CS), but this phase is destabilised during microwave sintering (MS), generating α-TCP. Conventional sintering (CS) allows higher densification in the undoped samples. Overall, for the Sr-doped compositions, the MS samples retain higher amounts of HA and experience higher density levels compared to the CS samples.