Optimisation of a novel glass-alginate hydrogel for the treatment of intracranial aneurysms.

The current gold standard for aneurysm treatment is endovascular coiling. However, recurrence is observed in over 20% of cases. A novel hydrogel has been developed to treat aneurysms. This hydrogel is composed of a polymeric alginate, a novel ion releasing glass and glucono-delta-lactone. This is an internally setting alginate hydrogel, wherein the setting rate can be controlled by both the glass and the alginate chemistry. The aim of this work is to examine the effect of each component of the hydrogel and optimise the composition of the hydrogel, specifically the alginate molecular weight, M/G ratio and concentration. The effects of gamma sterilisation will also be examined. The results show that alginate concentration, chemical composition and molecular weight affect the compressive strength, working time, hardening time and deliverability of the hydrogel. Gamma irradiation of the alginate reduces the molecular weight, which has a negative effect on the usability of this hydrogel.

A bioactive metallurgical grade porous silicon-polytetrafluoroethylene sheet for guided bone regeneration applications.

The properties of porous silicon make it a promising material for a host of applications including drug delivery, molecular and cell-based biosensing, and tissue engineering. Porous silicon has previously shown its potential for the controlled release of pharmacological agents and in assisting bone healing. Hydroxyapatite, the principle constituent of bone, allows osteointegration in vivo, due to its chemical and physical similarities to bone. Synthetic hydroxyapatite is currently applied as a surface coating to medical devices and prosthetics, encouraging bone in-growth at their surface and improving osseointegration. This paper examines the potential for the use of an economically produced porous silicon particulate-polytetrafluoroethylene sheet for use as a guided bone regeneration device in periodontal and orthopaedic applications. The particulate sheet is comprised of a series of microparticles in a polytetrafluoroethylene matrix and is shown to produce a stable hydroxyapatite on its surface under simulated physiological conditions. The microstructure of the material is examined both before and after simulated body fluid experiments for a period of 1, 7, 14 and 30 days using Scanning Electron Microscopy. The composition is examined using a combination of Energy Dispersive X-ray Spectroscopy, Thin film X-ray diffraction, Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy and the uptake/release of constituents at the fluid-solid interface is explored using Inductively Coupled Plasma-Optical Emission Spectroscopy. Microstructural and compositional analysis reveals progressive growth of crystalline, 'bone-like' apatite on the surface of the material, indicating the likelihood of close bony apposition in vivo.

Fabrication of CaO-NaO-SiO(2)/TiO (2) scaffolds for surgical applications.

A series of titanium (Ti) based glasses were formulated (0.62 SiO(2)-0.14 Na(2)O-0.24 CaO, with 0.05 mol% TiO(2) substitutions for SiO(2)) to develop glass/ceramic scaffolds for bone augmentation. Glasses were initially characterised using X-ray diffraction (XRD) and particle size analysis, where the starting materials were amorphous with 4.5 µm particles. Hot stage microscopy and high temperature XRD were used to determine the sintering temperature (~700 °C) and any crystalline phases present in this region (Na(2)Ca(3)Si(6)O(16), combeite and quartz). Hardness testing revealed that the Ti-free control (ScC-2.4 GPa) had a significantly lower hardness than the Ti-containing materials (Sc1 and Sc2 ~6.6 GPa). Optical microscopy determined pore sizes ranging from 544 to 955 µm. X-ray microtomography calculated porosity from 87 to 93 % and surface area measurements ranging from 2.5 to 3.3 SA/mm(3). Cytotoxicity testing (using mesenchymal stem cells) revealed that all materials encouraged cell proliferation, particularly the higher Ti-containing scaffolds over 24-72 h.

The effect of glass synthesis route on mechanical and physical properties of resultant glass ionomer cements.

Glass ionomer cements (GICs) have potential orthopaedic applications. Solgel processing is reported as having advantages over the traditional melt-quench route for synthesizing the glass phase of GICs, including far lower processing temperatures and higher levels of glass purity and homogeneity. This work investigates a novel glass formulation, BT 101 (0.48 SiO(2)-0.36 ZnO-0.12 CaO-0.04 SrO) produced by both the melt-quench and the solgel route. The glass phase was characterised by X-ray diffraction (XRD) to determine whether the material was amorphous and differential thermal analysis (DTA) to measure the glass transition temperature (T (g)). Particle size analysis (PSA) was used to determine the mean particle size and X-ray photoelectron spectroscopy (XPS) was used to investigate the structure and composition of the glass. Both glasses, the melt-quench BT 101 and the solgel BT 101, were mixed with 50 wt% polyacrylic acid (M (w), 80,800) and water to form a GIC and the working time (T (w)) and the setting time (T (s)) of the resultant cements were then determined. The cement based on the solgel glass had a longer T (w) (78 s) as compared to the cement based on the melt derived glass (19 s). T (s) was also much longer for the cement based on the solgel (1,644 s) glass than for the cement based on the melt-derived glass (25 s). The cements based on the melt derived glass produced higher strengths in both compression (sigma(c)) and biaxial flexure (sigma(f)), where the highest strength was found to be 63 MPa in compression, at both 1 and 7 days. The differences in setting and mechanical properties can be associated to structural differences within the glass as determined by XPS which revealed the absence of Ca in the solgel system and a much greater concentration of bridging oxygens (BO) as compared to the melt-derived system.

Comparison of an experimental bone cement with a commercial control, Hydroset.

Glass polyalkenoate cements based on strontium calcium zinc silicate glasses (Zn-GPCs) and high molecular weight polyacrylic acids (PAA) (MW; 52,000-210,000) have been shown to exhibit mechanical properties and in vitro bioactivity suitable for arthroplasty applications. Unfortunately, these formulations exhibit working times and setting times which are too short for invasive surgical applications such as bone void filling and fracture fixation. In this study, Zn-GPCs were formulated using a low molecular weight PAA (MW; 12,700) and a modifying agent, trisodium citrate dihydrate (TSC), with the aim of improving the rheological properties of Zn-GPCs. These novel formulations were then compared with commercial self-setting calcium phosphate cement, Hydroset, in terms of compressive strength, biaxial flexural strength and Young's modulus, as well as working time, setting time and injectability. The novel Zn-GPC formulations performed well, with prolonged mechanical strength (39 MPa, compression) greater than both vertebral bone (18.4 MPa) and the commercial control (14 MPa). However, working times (2 min) and rheological properties of Zn-GPCs, though improved, require further modifications prior to their use in minimally invasive surgical techniques.

Comparison of an experimental bone cement with surgical Simplex P, Spineplex and Cortoss.

Conventional polymethylmethacrylate (PMMA) cements and more recently Bisphenol-a-glycidyl dimethacrylate (BIS-GMA) composite cements are employed in procedures such as vertebroplasty. Unfortunately, such materials have inherent drawbacks including, a high curing exotherm, the incorporation of toxic components in their formulations, and critically, exhibit a modulus mismatch between cement and bone. The literature suggests that aluminium free, zinc based glass polyalkenoate cements (Zn-GPC) may be suitable alternative materials for consideration in such applications as vertebroplasty. This paper, examines one formulation of Zn-GPC and compares its strengths, modulus, and biocompatibility with three commercially available bone cements, Spineplex, Simplex P and Cortoss. The setting times indicate that the current formulation of Zn-GPC sets in a time unsuitable for clinical deployment. However during setting, the peak exotherm was recorded to be 33 degrees C, the lowest of all cements examined, and well below the threshold level for tissue necrosis to occur. The data obtained from mechanical testing shows the Zn-GPC has strengths of 63 MPa in compression and 30 MPa in biaxial flexure. Importantly these strengths remain stable with maturation; similar long term stability was exhibited by both Spineplex and Simplex P. Conversely, the strengths of Cortoss were observed to rapidly diminish with time, a cause for clinical concern. In addition to strengths, the modulus of each material was determined. Only the Zn-GPC exhibited a modulus similar to vertebral trabecular bone, with all commercial materials exhibiting excessively high moduli. Such data indicates that the use of Zn-GPC may reduce adjacent fractures. The final investigation used the well established simulated body fluid (SBF) method to examine the ability of each material to bond with bone. The results indicate that the Zn-GPC is capable of producing a bone like apatite layer at its surface within 24 h which increased in coverage and density up to 7 days. Conversely, Spineplex, and Simplex P exhibit no apatite layer formation, while Cortoss exhibits only minimal formation of an apatite layer after 7 days incubation in SBF. This paper shows that Zn-GPC, with optimised setting times, are suitable candidate materials for further development as bone cements.

Zinc-based glass polyalkenoate cements with improved setting times and mechanical properties.

The suitability of glass polyalkenoate cements (GPCs) for skeletal applications is limited by the presence, in the glass phase, of the aluminium ion (Al3+), a neurotoxin. The zinc ion (Zn2+), a bacteriocide, has been incorporated into aluminium-free GPCs based on zinc silicate glasses. However, these GPCs have considerably shorter working times and poorer mechanical properties than their Al3+-containing counterparts. Based on results for calcium phosphate cements, there is an indication that mixing a GPC with an organic compound, tricalcium citrate (TSC), may lead to cements with improved rheological and mechanical properties. We developed a range of Zn-based GPCs and determined their working times (Tw), setting times (Ts), compressive strength (CS) and biaxial flexural strengths (BFS). A GPC composed of 1g of a calcium-zinc silicate glass (BT100) mixed with a 50wt.% aqueous solution on polyacrylic acid (coded E9, Mw 80,800) at a powder liquid ratio of 2:1.5 exhibited the best combination of Tw, Ts, CS and BFS. We also found that the addition of TSC (over the range 5-15wt.%) to a GPC led to significant increases in both Tw (from 40+/-3 to 100+/-4s) and Ts (from 70+/-2 to 3000+/-4s) accompanied by changes in both CS and BFS that were affected by the duration of the aging time of the specimens in distilled water (for example, after aging for 7 days CS dropped from 62+/-2 to 17+/-1MPa, while after aging for 30 days, BFS increased 27+/-6 to 31+/-7MPa and then dropped to 17+/-1MPa). Future modification and characterization of the examined GPCs are needed before they may be considered as candidates for orthopaedic applications.