Comparative Evaluation of Two Glass Polyalkenoate Cements: An In Vivo Pilot Study Using a Sheep Model.

Poly(methyl methacrylate) (PMMA) is used to manage bone loss in revision total knee arthroplasty (rTKA). However, the application of PMMA has been associated with complications such as volumetric shrinkage, necrosis, wear debris, and loosening. Glass polyalkenoate cements (GPCs) have potential bone cementation applications. Unlike PMMA, GPC does not undergo volumetric shrinkage, adheres chemically to bone, and does not undergo an exothermic setting reaction. In this study, two different compositions of GPCs (GPCA and GPCB), based on the patented glass system SiO2-CaO-SrO-P2O5-Ta2O5, were investigated. Working and setting times, pH, ion release, compressive strength, and cytotoxicity of each composition were assessed, and based on the results of these tests, three sets of samples from GPCA were implanted into the distal femur and proximal tibia of three sheep (alongside PMMA as control). Clinical CT scans and micro-CT images obtained at 0, 6, and 12 weeks revealed the varied radiological responses of sheep bone to GPCA. One GPCA sample (implanted in the sheep for 12 weeks) was characterized with no bone resorption. Furthermore, a continuous bone-cement interface was observed in the CT images of this sample. The other implanted GPCA showed a thin radiolucent border at six weeks, indicating some bone resorption occurred. The third sample showed extensive bone resorption at both six and 12 weeks. Possible speculative factors that might be involved in the varied response can be: excessive Zn2+ ion release, low pH, mixing variability, and difficulty in inserting the samples into different parts of the sheep bone.

In vivo analysis of a proprietary glass-based adhesive for sternal fixation and stabilization using rabbit and sheep models.

Wire cerclage remains the standard method of care for sternal fixation, following median sternotomy, despite being beset with complications. An emerging treatment option has been to augment the wires with an adhesive. A patented ionomeric glass (mole fraction: SiO2:0.48, ZnO:0.36, CaO:0.12, SrO:0.04) has been used to formulate GPC+, a glass polyalkenoate cement (GPC), by mixing it with poly(acrylic) acid (PAA) and de-ionized water. In a human cadaver study, this material, when applied with wire cerclage, was able to significantly reduce sternal instability. However, the material has yet to be tested in pertinent animal models. Here, after a series of physical and mechanical tests to confirm suitability of the experimental material for implantation, three samples of GPC+ were implanted in either the tibia or femur of three different rabbits, alongside sham defects, for two different time modalities. A further seven samples of GPC+ and one poly(methyl methacrylate) control (PMMA) were implanted in either the tibia or femur of two different sheep. The sheep containing the PMMA was sacrificed at 8 weeks and the other at 16 weeks, to evaluate time dependent biological response. Upon sacrifice, microCT images were acquired and histology slides prepared for analysis. All three GPC+ samples implanted in the rabbit model, for the two time modalities, were characterized by minimal bone resorption along with a mild inflammatory response. Five of the seven GPC+ materials implanted in the sheep model (all three implanted for 8 weeks and two of those implanted for 16 weeks) were associated with mild to moderate immune response, comparable to that observed with PMMA, as well as mild bone resorption. The remaining two GPC + materials (implanted in the sheep model for 16 weeks) exhibited no bone resorption or inflammatory response and appeared to stimulate increased bone density at the implant site. These results suggest that GPC + can be a viable bone adhesive for use in hard tissue applications such as sternal fixation and stabilization. Experiments performed to synthesize & test Sr-doped glass adhesive for sternal fixation. (1) Sr-doped ionomeric glass fired, ground down and mixed with aqueous polyacrylic acid to produce the adhesive. (2) Adhesive characterized and tested by a suite of laboratory-based tests to ensure suitability for implantation. (3) Adhesive implanted into a rabbit model (distal femur, 12 weeks post implantation) where micro-CT images confirmed an excellent bone/cement interface, no evidence of bone resorption and some bone remodelling. (4) Adhesive subsequently implanted into a sheep model; at 16-weeks, a continuous bone-adhesive interface is seen suggesting no bone resorption. There was an increase in the peri-implant radiodensity, suggesting enhanced mineral content of the bone surrounding the GPC+ implant.

Novel adhesives for sternal fixation and stabilization: A biomechanical analysis.

BACKGROUND: Cerclage wires remain the current standard of care following median sternotomy, despite significant complications including dehiscence and infection. This study uses a human cadaveric model to investigate the use of glass polyalkenoate cements formulated from two glasses, A (mole fraction: SiO2:0.48, ZnO:0.36, CaO:0.12, SrO:0.04) and B (mole fraction: SiO2:0.48, ZnO:0.355, CaO:0.06, SrO:0.08, P2O5:0.02, Ta2O5:0.005), to improve wired sternal fixation. METHODS: Median sternotomies were performed on fifteen cadaveric sterna. Fixation was performed with either traditional wire cerclage or adhesive-enhanced wire cerclage; the adhesive based on either Glass A or Glass B. Cyclic tensile loading of 10 N to 100 N was applied. Every 30 cycles, the maximum load was increased by 100 N up to a maximum of 500 N. Two adhered sterna were tested beyond 500 N. Mid-sternal displacement was measured to assess fixation stability. FINDINGS: Displacement for adhesive-enhanced sternal closures were significantly less (p < 0.05) than standard wire cerclage. There was no significant difference between adhesives. Up to 500 N, no adhesive-enhanced sternum experienced a pathological sternal displacement (>2 mm), while three out of five of traditional wire fixations did. Of the two adhered samples tested beyond 500 N, one showed pathological displacement at 800 N and the other at 1100 N. Failure of adhered sterna appeared to initiate within the trabecular bone rather than in the adhesive. INTERPRETATION: The adhesives were capable of providing immediate bone stability, significantly reducing sternal displacement. In vivo investigations are warranted to determine the effect the adhesives have on bone remodelling.

Novel adhesives for distal radius fixation: A biomechanical analysis.

Wrist fractures can be difficult to treat due to advanced age of the patient, medical co-morbidities, and comminution of the bone. This study examines the effectiveness of two injectable glass polyalkenoate cements (GPCs), derived from two different glasses (A and B), as minimally invasive treatments for distal radius fractures. Twenty-seven fresh cadaveric radial pairs were tested either in compressive fatigue or to quasi-static compressive failure. The radii tested to failure had one pair fixated with a GPC while the other was left intact. The radii tested under fatigue had one pair fixated with a GPC and the other with a volar locking plate. A wedge osteotomy was used to simulate a severely comminuted fracture. When loaded to failure, the radii fixated with a GPC made from glass A or B were found to be, respectively, at least 57% and 62% as strong as their intact biological pair (95% Confidence Interval, Lower). Using a paired t-test, the radii fixated with either adhesive were found to be significantly stiffer than their biological pairs fixated with a volar locking plate for all cycles of fatigue loading. The adhesives under investigation demonstrate promise as treatment for distal radius fractures. In vivo investigations are warranted to determine the effect that the adhesives have on the bone remodelling process.

A novel tantalum-containing bioglass. Part II. Development of a bioadhesive for sternal fixation and repair.

With over a million median sternotomy surgeries performed worldwide every year, sternal wound complications have posed a serious risk to the affected patients. A rigid therapeutic sternal fixation device has therefore become a necessity. In this work, the incorporation of up to 0.5mol% of tantalum pentoxide (Ta2O5), in exchange for zinc oxide (ZnO), into the SiO2-ZnO-CaO-SrO-P2O5 glass system is presented. The effect of Ta incorporation on the physical, chemical and biological properties of the glass polyalkenoate cements (GPCs) prepared from them have been presented in this manuscript. The data obtained have confirmed that Ta2O5 incorporation into the reference glass system results in increased working times, radiopacity, ion solubility, and long-term mechanical stability. The formulated glass systems have also shown clear antibacterial and antifungal activity against both Gram-negative (Escherichia coli) and Gram-positive prokaryotes (Staphylococcus aureus and Streptococcus epidermidis), as well as eukaryotes (Fusarium solani). Cytotoxicity testing showed that Ta incorporation results in no toxicity effect and may simulate osseo-integration when tested in animal models. These new metallic-containing biomaterial adhesives have been developed for sternal fixation and repair. As a permanent implant, the formulated adhesives can be used in conjunction with sternal cable ties to offer optimal fixation for patients and reduce post-operative complications such as bacterial infection and pain from micro-motion.

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.