The processing, mechanical properties and bioactivity of zinc based glass ionomer cements

Efficacy and bone-contact biocompatibility of glass ionomer cement as a biomaterial for bone regeneration: A systematic review

Bone regeneration is a rapidly growing field that seeks to develop new biomaterials to regenerate bone defects. Conventional bone graft materials have limitations, such as limited availability, complication, and rejection. Glass ionomer cement (GIC) is a biomaterial with the potential for bone regeneration due to its bone-contact biocompatibility, ease of use, and cost-effectiveness. GIC is a two-component material that adheres to the bone and releases ions that promote bone growth and mineralization. A systematic literature search was conducted using PubMed-MEDLINE, Scopus, and Web of Science databases and registered in the PROSPERO database to determine the evidence regarding the efficacy and bone-contact biocompatibility of GIC as bone cement. Out of 3715 initial results, thirteen studies were included in the qualitative synthesis. Two tools were employed in evaluating the Risk of Bias (RoB): the QUIN tool for assessing in vitro studies and SYRCLE for in vivo. The results indicate that GIC has demonstrated the ability to adhere to bone and promote bone growth. Establishing a chemical bond occurs at the interface between the GIC and the mineral phase of bone. This interaction allows the GIC to exhibit osteoconductive properties and promote the growth of bone tissue. GIC's bone-contact biocompatibility, ease of preparation, and cost-effectiveness make it a promising alternative to conventional bone grafts. However, further research is required to fully evaluate the potential application of GIC in bone regeneration. The findings hold implications for advancing material development in identifying the optimal composition and fabrication of GIC as a bone repair material.

Effect of germanium oxide on the structural aspects and bioactivity of bioactive silicate glass

Ternary silicate glass (69SiO₂-27CaO-4P₂O₅) was synthesized with the sol-gel route, and different percentages of germanium oxide GeO₂ (6.25, 12.5, and 25%) and polyacrylic acid (PAA) were added. DFT calculations were performed at the B3LYP/LanL2DZ level of theory for molecular modelling. X-ray powder diffraction (XRPD) was used to study the effect of GeO₂/PAA on the structural properties. The samples were further characterized using DSC, ART-FTIR, and mechanical tests. Bioactivity and antibacterial tests were assessed to trace the influence of GeO₂ on biocompatibility with biological systems. Modelling results demonstrate that molecular electrostatic potential (MESP) indicated an enhancement of the electronegativity of the studied models. While both the total dipole moment and HOMO/LUMO energy reflect the increased reactivity of the P₄O₁₀ molecule. XRPD results confirmed the samples formation and revealed the correlation between the crystallinity and the properties, showing that crystalline hydroxyapatite (HA) is clearly formed in the highest percentages of GeO₂, proposing 25% as a strong candidate for medical applications, consistent with the results of mechanical properties and the rest of the characterization results. Simulated body fluid (SBF) in vitro experiments showed promising biocompatibility. The samples showed remarkable antimicrobial and bioactivity, with the strongest effect at 25%. The experimental findings of this study revealed that the incorporation of GeO2 into the glass in terms of structural characteristics, bioactivity, antimicrobial properties, and mechanical properties is advantageous for biomedical fields and especially for dental applications.

Nano-cellulose Reinforced Glass Ionomer Restorations: An In Vitro study

OBJECTIVE

Various modifications in formulation of glass ionomer cements (GICs) have been made in order to improve the clinical performance of these restorations. The aim of this work was to evaluate the microleakage and microshear bond strength (μSBS) of bacterial cellulose nanocrystal (BCNC)-modified glass ionomer cement (GIC) restorations in primary dentition.

METHODS

A total number of 60 freshly extracted primary molar teeth were selected. Half of the samples were used for μSBS testing (in 2 groups, n = 15). In group 1, conventional GIC (CGIC) of Fuji IX (GC) was placed in cylindrical molds on dentinal surfaces. In group 2, CGIC of Fuji IX containing 1% wt of BCNCs was used. μSBS was evaluated using a universal testing machine. In another part of the study, microleakage of class V restorations was assessed according to the mentioned groups (n = 15). The sectioned samples were observed under stereomicroscope, and microleakage scores were recorded. SPSS version 16.0 (SPSS), independent samples t test, and Mann-Whitney U test were used for statistical analysis at a significance level of P < .05.

RESULTS

Results showed statistically significant differences between the μSBS of CGIC and modified GIC groups (P < .0001). The BCNC-modified GIC group recorded significantly higher bond strength values (3.51 ± 0.033 vs 1.38 ± 0.034 MPa). Also, microleakage scores of CGIC and BCNC-modified GIC restorations were not significantly different (P = .57).

CONCLUSIONS

Based on our findings, it was concluded that incorporating BCNCs (1% wt) into the CGIC of Fuji IX significantly increased the μSBS to the dentin structure of the primary teeth.

Effect of zinc oxide nanoparticles on physical and antimicrobial properties of resin-modified glass ionomer cement

Background:

To improve the limitations, many modifications in the resin-modified glass ionomer (RMGI) composition have been proposed. In this study, we evaluated the effect of different concentrations of zinc oxide (ZnO) nanoparticles incorporated into RMGI cement on its physical and antimicrobial properties.

Materials and Methods:

In this in vitro study, ZnO nanoparticles with 0–4 wt.% concentrations were incorporated into RMGI. The following tests were carried out: (a) Antibacterial activity against Streptococcus mutans tested by disc diffusion method, (b) mechanical behavior assessment by measuring flexural strength (FS) and flexural modulus (FM), (c) micro-shear bond strength (μ-SBS), and (d) fluoride and zinc release. Data were analyzed using the statistical tests of ANOVA, t-test, and Tukey's HSD post hoc in SPSS V22. The level of significancy was 0.05.

Results:

In the disc diffusion method, specimens with 2 wt.% ZnO nanoparticles showed the highest antimicrobial efficacy (P < 0.05). After 1 month of water storage, no significant difference was observed in FS and FM of the samples (P > 0.05). In 2 wt.% ZnO nanoparticles group, μSBS increased in the first 7 days but decreased by 17% after one month, which showed a significant difference with that of the control group. The fluoride release did no change in the ZnO nanoparticle-containing group compared with the control group at all time intervals.

Conclusion:

Incorporation of 2 wt.% ZnO nanoparticles into the RMGI cement adds antimicrobial activity to the cement without sacrificing FS and fluoride release properties, while decreased μSBS.

Evaluation of bioactive glass scaffolds incorporating SrO or ZnO for bone repair: In vitro bioactivity and antibacterial activity

A series of bioactive glass scaffolds doped with SrO or ZnO (0, 5, and 10 mol%) were synthesized by the foam replica and melting method. The thermodynamic evolution, phase composition, microstructure, ion release, in vitro bioactivity, and oxygen density of the scaffolds were characterized. The proliferation of murine long bone osteocyte Y4 cells was studied by cell culture. The survival rate of the BGs evaluated the antibacterial activity and Escherichia coli strains in co-culture. The results indicated that the process window decreases with the increase of dopants. All the samples have a pore structure size of 200-400 μm. When the scaffolds were immersed in simulated body fluid for 28 days, hydroxyapatite formation was not affected, but the degradation process was retarded. The glass network packing and ionic radii variations of the substitution ions control surface degradation, glass dissolution, and ion release. MTT results revealed that 5Sr-BG had a significant effect on promoting cell proliferation and none of the BGs were cytotoxicity. Sr-BGs and Zn-BGs exhibited significantly inhibited growth against E. coli bacterial strains. Generally, these results showed the 5Sr-BG scaffold with high vitro bioactivity, cell proliferation, and antibacterial property is an important candidate material for bone tissue regeneration and repair.

Mechanical Properties of Glass Ionomer Cements after Incorporation of Marine Derived Porous Cuttlefish Bone Hydroxyapatite

The purpose of this study was to evaluate the effects of the incorporation of hydroxyapatite (HA) derived from cuttlefish bone on the mechanical properties of glass ionomer cements (GIC). Fuji II LC and Fuji IX GP Extra (GC Corporation, Tokyo, Japan) were used in the study. There were four groups (n = 11–18) for each material: a group without the addition of HA particles and three groups modified by incorporation of 2, 5, and 10 wt% HA. The tests were performed on a universal testing machine (Shimadzu, Duisburg, Germany) and descriptive statistics, two-way analysis of variance (ANOVA) for the comparison of three mechanical properties, and one-way ANOVA for the comparison of different concentrations for each material were performed. Regarding the Fuji IX groups, compressive strength (CS) and flexural strength (FS) were highest in the group without HA particles added. The differences in CS between the Fuji IX group without HA particles and the Fuji IX groups with 2 wt% HA and 10 wt% HA were significant. The Fuji II 5 wt% HA group exhibited higher diametral tensile strength (DTS) and CS than other Fuji II groups, but not significantly. The Fuji II group, modified with 10 wt% HA, exhibited significantly higher FS than the Fuji II group without HA particles (p < 0.05). Porous HA incorporated into the Fuji IX groups had a significant impact on mechanical properties only in the Fuji IX 5 wt% HA group. Fuji II groups modified with 10 wt% HA showed the most favorable results with respect to FS.

Modifications of Glass Ionomer Cement Powder by Addition of Recently Fabricated Nano-Fillers and Their Effect on the Properties: A Review

The aim of this article is to provide a brief insight regarding the recent studies and their recommendations related to the modifications to glass ionomer cement (GIC) powder in order to improve their properties. An electronic search of publications was made from the year 2000 to 2018. The databases included in the current study were EBSCOhost, PubMed, and ScienceDirect. The inclusion criteria for the current study include publication with abstract or full-text articles, original research, reviews or systematic reviews, in vitro, and in vivo studies that were written in English language. Among these only articles published in peer-reviewed journals were included. Articles published in other languages, with no available abstract and related to other nondentistry fields, were excluded. A detailed review of the recent materials used as a filler phase in GIC powder has revealed that not all modifications produce beneficial results. Recent work has demonstrated that modification of GIC powder with nano-particles has many beneficial effects on the properties of the material. This is due to the increase in surface area and surface energy, along with better particle distribution of the nano-particle. Therefore, more focus should be given on nano-particle having greater chemical affinity for GIC matrix as well as the tooth structure that will enhance the physicochemical properties of GIC.

Mechanical and optical properties of conventional restorative glass-ionomer cements - a systematic review

Objectives

To perform a systematic review of test methodologies on conventional restorative glass-ionomer cement (GIC) materials for mechanical and optical properties to compare the results between different GICs.

Material and Methods

Screening of titles and abstracts, data extraction, and quality assessments of full-texts were conducted in search for in vitro studies on conventional GICs that follow the relevant specifications of ISO standards regarding the following mechanical and optical properties: compressive strength, flexural strength, color, opacity and radiopacity.

Sources

The Latin American and Caribbean Health Sciences (LILACS), Brazilian Bibliography of Dentistry (BBO) databases from Latin-American and Caribbean System on Health Sciences Information (BIREME) and PubMed/Medline (US National Library of Medicine - National Institutes of Health) databases were searched regardless of language. Altogether, 1146 in vitro studies were selected. Two reviewers independently selected and assessed the articles according to pre-established inclusion/exclusion criteria. Among all the properties investigated, only one study was classified as being of fair quality that tested compressive strength and was included. It was observed that many authors had not strictly followed ISO recommendations and that, for some properties (diametral tensile strength and microhardness), there are no guidelines provided.

Conclusions

It was not possible to compare the results for the mechanical and optical properties of conventional restorative GICs due to the lack of standardization of studies.

Investigating the effect of Copper Addition on SiO2-ZnO-CaO-SrO-P2O5 Glass Polyalkenoate Cements: Physical, Mechanical and Biological Behavior

The physical, mechanical, and biological behaviour of copper containing glass polyalkenotare cements were investigated, where copper (Cu2+) was incorporated into a SiO2-ZnO-CaO-SrO-P2O5 based glass system. Three GPCs were formulated for this study, a Control and two Cu-GPCs with 6 (Cu-1) and 12 (Cu-2) Mol.% of CuO substituted for the SiO2 in the glass. Rheological evaluation of GPCs determined that the addition of the Cu decreases the working and setting times in the cements. The mechanical properties of the cements were evaluated after 1 - 21 days incubation in DI water. The compressive strength of the cements were found to range between 21-36 MPa, with Cu-1 having the highest compressive strength. Biaxial flexural strength and Shear Bond Strength of the GPCs were found to increase with respect to time and were higher for the Cu-GPCs at 14 MPa and 2.1 MPa respectively. Bioactivity testing was conducted using Simulated Body Fluid (SBF) which revealed CaP precipitants on each of the GPCs surfaces. The effect o f Cu addition to the GPCs greatly enhanced the antibacterial inhibition zone (IZ) when tested in E.coli (3mm), S.aureus (24mm) and S.epidermidis (22mm). Cytocompatibility testing revealed more favorable MC3T3 osteoblast cell viability when compared to the Control GPC.

Effects of the reinforced cellulose nanocrystals on glass-ionomer cements

OBJECTIVE

Glass-ionomer cements (GICs) modified with cellulose nanocrystals (CNs) were characterized and evaluated for compressive strength (CS), diametral tensile strength (DTS) and fluoride release (F^-).

METHODS

Commercially available GICs (Maxxion, Vidrion R, Vitro Molar, Ketac Molar Easy Mix and Fuji Gold Label 9) were reinforced with CNs (0.2% by weight). The microstructure of CNs and of CN-modified GICs were evaluated by transmission electron microscopy (TEM) and by scanning electron microscopy (SEM) while chemical characterization was by Fourier transform infrared spectroscopy (FTIR). Ten specimens each of the unmodified (control) and CN-modified materials (test materials) were prepared for CS and DTS testing. For the fluoride release evaluation, separate specimens (n=10) of each test and control material were made. The results obtained were submitted to the t-test (p<0.05).

RESULTS

The CN reinforcement significantly improved the mechanical properties and significantly increased the F^- release of all GICs (p<0.05). The GICs with CNs showed a fibrillar aggregate of nanoparticles interspersed in the matrix. The compounds with CNs showed a higher amount of C compared to the controls due to the organic nature of the CNs. It was not possible to identify by FTIR any chemical bond difference in the compounds formed when nanofibers were inserted in the GICs.

SIGNIFICANCE

Modification of GICs with CNs appears to produce promising restorative materials.

Modification of glass ionomer cements on their physical-mechanical and antimicrobial properties

OBJECTIVE

The aim of this review was to provide an insight about the factors affecting the properties of glass ionomer cements and provides a review regarding studies that are related to modification of glass ionomer cements to improve their properties, particularly on physical-mechanical and antimicrobial activity.

METHODS

PubMed and Science Direct were searched for papers published between the years 1974 and 2018. The search was restricted to articles written in English related to modification of glass ionomer cements. Only articles published in peer-reviewed journals were included. The search included literature reviews, in vitro, and in vivo studies. Articles written in other languages, without available abstracts and those related to other field were excluded. About 198 peer-review articles in the English language were reviewed.

CONCLUSION

Based on the finding, most of the modification has improved physical-mechanical properties of glass ionomer cements. Recently, researchers have attempted to improve their antimicrobial properties. However, the attempts were reported to compromise the physical-mechanical properties of modified glass ionomer cements.

CLINICAL SIGNIFICANCE

As the modification of glass ionomer cement with different material improved the physical-mechanical and antimicrobial properties, it could be used as restorative material for wider application in dentistry.

Incorporating Germanium Oxide into the Glass Phase of Novel Zinc/Magnesium-Based GPCs Designed for Bone Void Filling: Evaluating Their Physical and Mechanical Properties

The structural role of Germanium (Ge), when substituting for Zinc (Zn) up to 8 mol % in the 0.48SiO₂⁻0.12CaO⁻0.36ZnO⁻0.04MgO glass series, was investigated with respect to both the glass chemistry and also the properties of glass polyalkenoate cements (GPCs) manufactured from them. The Network connectivity (NC) of the glass was calculated to increase from 1.83 to 2.42 with the addition of GeO₂ (0⁻8 mol %). Differential thermal analysis (DTA) results confirmed an increase in the glass transition temperature (T_g) of the glass series with GeO₂ content. X-ray photoelectron spectroscopy (XPS) showed an increase in the ratio of bridging oxygens (BO) to non-bridging oxygens (NBO) with the addition of GeO₂, supporting the NC and DTA results. ²⁹Si magic angle spinning nuclear magnetic resonance spectroscopy (²⁹Si MAS-NMR) determined a chemical shift from -80.3 to -83.7 ppm as the GeO₂ concentration increased. These ionomeric glasses were subsequently used as the basic components in a series of GPCs by mixing them with aqueous polyacrylic acid (PAA). The handling properties of the GPCs resulting were evaluated with respect to the increasing concentration of GeO₂ in the glass phase. It was found that the working times of these GPCs increased from 3 to 15 min, while their setting times increased from 4 to 18 min, facilitating the injectability of the Zn/Mg-GPCs through a 16-gauge needle. These Ge-Zn/Mg-GPCs were found to be injectable up to 96% within 12 min. Zn/Mg-GPCs containing GeO₂ show promise as injectable cements for use in bone void filling.

An Injectable Glass Polyalkenoate Cement Engineered for Fracture Fixation and Stabilization

Glass polyalkenoate cements (GPCs) have potential as bio-adhesives due to their ease of application, appropriate mechanical properties, radiopacity and chemical adhesion to bone. Aluminium (Al)-free GPCs have been discussed in the literature, but have proven difficult to balance injectability with mechanical integrity. For example, zinc-based, Al-free GPCs reported compressive strengths of 63 MPa, but set in under 2 min. Here, the authors design injectable GPCs (IGPCs) based on zinc-containing, Al-free silicate compositions containing GeO₂, substituted for ZnO at 3% increments through the series. The setting reactions, injectability and mechanical properties of these GPCs were evaluated using both a hand-mix (h) technique, using a spatula for sample preparation and application and an injection (i) technique, using a 16-gauge needle, post mixing, for application. GPCs ability to act as a carrier for bovine serum albumin (BSA) was also evaluated. Germanium (Ge) and BSA containing IGPCs were produced and reported to have working times between 26 and 44 min and setting times between 37 and 55 min; the extended handling properties being as a result of less Ge. The incorporation of BSA into the cement had no effect on the handling and mechanical properties, but the latter were found to have increased compression strength with the addition of Ge from between 27 and 37 MPa after 30 days maturation.

Exploring the unexpected influence of the Si:Ge ratio on the molecular architecture and mechanical properties of Al-free GICs

Germanium (Ge)-based glass ionomer cements have demonstrated the ability to balance strength with extended setting times, a unique set of characteristics for aluminum-free glass ionomer cements. However, the mechanical properties of current Ge-based glass ionomer cements significantly deteriorate over time, which jeopardizes their clinical potential. This work explores the effect of incrementally decreasing the Si:Ge ratio in the glass phase of zinc-silicate glass ionomer cements to identify potential mechanisms responsible for the time-induced mechanical instability of Ge-based glass ionomer cements. The influence of Ge was evaluated on the basis of changes in mechanical properties and molecular architecture of the cements over a 180-day period. It was observed that the compressive strength and modulus of the cements were sustained when Si:Ge ratios were ≥1:1, but when Si:Ge ratios are <1:1 these properties decreased significantly over time. These mechanical changes were independent of structural changes in the glass ionomer cement matrices, as the level of metal–carboxylate crosslinks remained constant over time across the various Si:Ge ratios explored. However, it was noted the temporal decline of mechanical properties was proportional to the increased release of degradation byproducts, in particular Ge that was released from the cements in substantially greater quantities than other glass constituents. Unexpectedly, the slowest setting cement (Si:Ge 1:1) was also the strongest; behavior that is uncommon in Si-based glass ionomer cements, supports the potential of Ge-containing glass ionomer cements as injectable bone cements in applications such as percutaneous vertebroplasty.

Influence of niobium pentoxide addition on the properties of glass ionomer cements

Objective: To determine the influence of niobium pentoxide (Nb₂O₅) addition on the physical and chemical properties of glass ionomer cements (GICs).

Materials and methods: Five, 10 or 20 wt.% of Nb₂O₅ were incorporated into commercial GICs (Maxxion R, Vitro Molar, Vitro Fil R) and one group of each GIC remained without Nb₂O₅ (control groups). The GICs were evaluated by Knoop hardness, compressive strength, acid erosion, particle size and radiopacity. Data were analyzed by two-way ANOVA followed by Tukey's test.

Results: The addition of 10% and 20% reduced the microhardness of two GICs (p < .05). Compressive strength showed no difference among groups (p > .05). Nb₂O₅ did not influence Maxxion R and Vitro Fil R regarding the acid erosion test (p > .05). Vitro Molar increased its acid erosion with 10% of Nb₂O₅ (p < .05). Maxxion R presented 15.78 μm, while Vitro Molar and Vitro Fil R showed 5.14 μm and 6.18 μm, respectively. As the Nb₂O₅ concentration increased, the radiopacity increased for all groups. Vitro Molar and Vitro Fil R did not present significant difference to at least 1 mm aluminum (p > .05).

Conclusion: The addition of 5 wt.% Nb₂O₅ did not affect the tested physical and chemical properties of the GICs and improved the radiopacity of one of the cements. These materials are therefore suitable for further testing of biomimetic remineralization properties.

Modifications in Glass Ionomer Cements: Nano-Sized Fillers and Bioactive Nanoceramics

Glass ionomer cements (GICs) are being used for a wide range of applications in dentistry. In order to overcome the poor mechanical properties of glass ionomers, several modifications have been introduced to the conventional GICs. Nanotechnology involves the use of systems, modifications or materials the size of which is in the range of 1–100 nm. Nano-modification of conventional GICs and resin modified GICs (RMGICs) can be achieved by incorporation of nano-sized fillers to RMGICs, reducing the size of the glass particles, and introducing nano-sized bioceramics to the glass powder. Studies suggest that the commercially available nano-filled RMGIC does not hold any significant advantage over conventional RMGICs as far as the mechanical and bonding properties are concerned. Conversely, incorporation of nano-sized apatite crystals not only increases the mechanical properties of conventional GICs, but also can enhance fluoride release and bioactivity. By increasing the crystallinity of the set matrix, apatites can make the set cement chemically more stable, insoluble, and improve the bond strength with tooth structure. Increased fluoride release can also reduce and arrest secondary caries. However, due to a lack of long-term clinical studies, the use of nano-modified glass ionomers is still limited in daily clinical dentistry. In addition to the in vitro and in vivo studies, more randomized clinical trials are required to justify the use of these promising materials. The aim of this paper is to review the modification performed in GIC-based materials to improve their physicochemical properties.

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.

The role of poly(acrylic acid) in conventional glass polyalkenoate cements

Glass polyalkenoate cements (GPCs) have been used in dentistry for over 40 years. These novel bioactive materials are the result of a reaction between a finely ground glass (base) and a polymer (acid), usually poly(acrylic acid) (PAA), in the presence of water. This article reviews the types of PAA used as reagents (including how they vary by molar mass, molecular weight, concentration, polydispersity and content) and the way that they control the properties of the conventional GPCs (CGPCs) formulated from them. The article also considers the effect of PAA on the clinical performance of CGPCs, including biocompatibility, rheological and mechanical properties, adhesion, ion release, acid erosion and clinical durability. The review has critically evaluated the literature and clarified the role that the polyacid component of CGPCs plays in setting and maturation. This review will lead to an improved understanding of the chemistry and properties of the PAA phase which will lead to further innovation in the glass-based cements field.

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.

Biological and mechanical properties of an experimental glass-ionomer cement modified by partial replacement of CaO with MgO or ZnO

Some weaknesses of conventional glass ionomer cement (GIC) as dental materials, for instance the lack of bioactive potential and poor mechanical properties, remain unsolved.

Evidence of a complex species controlling the setting reaction of glass ionomer cements

OBJECTIVE

To elucidate the mechanism(s) responsible for the profound impact germanium has on the setting reaction of zinc silicate glass ionomer cements (GICs).

METHODS

Five <45μm glass powder compositions (0.48-xSiO2, xGeO2, 0.36 ZnO, 0.16 CaO; where x=0.12, 0.24, 0.36, 0.48mol. fraction) were synthesized. Glass degradation was assessed under simulated setting conditions using acetic acid from 0.5 to 60min, monitoring the concentrations of ions released using ICP-OES. Subsequently, GICs were prepared by mixing fresh glass powders with polyacrylic acid (PAA, Mw=12,500g/mol, 50wt% aq. solution) at a 1:0.75 ratio. Cement structure and properties were evaluated using ATR-FTIR and rheology (for 60min), as well as 24h biaxial flexural strength.

RESULTS

Reduced Si:Ge ratios yielded faster degrading glasses, yet contrary to expectation, the corresponding ATR-FTIR spectra indicated slower crosslinking within the GIC matrix. Rheology testing found the initial viscosity cement pastes reduced with decreased Si:Ge, and Ge containing cements all set significantly slower than the Si based GIC. Interestingly, biaxial flexural strength remained consistent regardless of setting behavior.

SIGNIFICANCE

This counter-intuitive combination of behaviors is attributed to the presence of a chemical complex species specific to Ge-containing glasses that delays, but does not hinder, the formation of the GIC matrix. These findings embody chemical complex species as a mechanism to decouple glass reactivity from cement setting rate, a mechanism with the potential to enhance the utility of GICs in both dental and orthopaedic applications.

Bioactive glass for long bone infection: a systematic review

BACKGROUND

Long bone infection remains a challenging situation for the orthopaedic surgeon. For most, treatment comprises a thorough debridement of all the infected bone, the filling of the resultant cavity with a bone substitute, and general antibiotics for a certain time. However, the type of bone substitute to insert in the cavity is still debated.

PURPOSE

In this study, we aimed to systematically review the results of studies using bioactive glass for long bone infection in the clinical setting.

MATERIAL AND METHOD

We searched systematically Medline via Pubmed for studies published until August 2015 that report the results of bioactive glass for long bone infection in humans.

RESULTS

Three studies, including a total of 41 patients, met the inclusion criteria. Mean age was 46.5 (16-84). Twenty-nine were male and twelve were female. Period of inclusion went from 2007 to 2013. All the patients had a clinically and radiologically diagnosed osteomyelitis. They all underwent a state of the art surgical procedure to address osteomyelitis. All the patients were implanted with BAG-S53P4 granules (BonAlive Biomaterials Ltd, Turku, Finland) to fill in the resultant cavity. Mean volume inserted was 16.8 milliliters (2-60). After a mean follow-up of 21 months (10-38), three cases of osteomyelitis recurred. In two cases, a new procedure was performed. No complication directly related to the bioactive glass was reported.

DISCUSSION

Despite a limited use for long bone infection in humans, bioactive glass seems to be an interesting option as bone substitute after thorough bone debridement and skin coverage. It associates antibacterial activities, osteoconductive properties and vascular stimulation.

CONCLUSION

From this review, bioactive glass seems to be a useful bone substitute for long bone infection in humans. Few recurrences occurred after its use. In these cases, the volume of bone glass to insert was frequently underestimated and/or the skin coverage not adequate.

Review and the state of the art: Sol-gel and melt quenched bioactive glasses for tissue engineering

Biomaterial development is currently the most active research area in the field of biomedical engineering. The bioglasses possess immense potential for being the ideal biomaterials due to their high adaptiveness to the biological environment as well as tunable properties. Bioglasses like 45S5 has shown great clinical success over the past 10 years. The bioglasses like 45S5 were prepared using melt-quenching techniques but recently porous bioactive glasses have been derived through sol-gel process. The synthesis route exhibits marked effect on the specific surface area, as well as degradability of the material. This article is an attempt to provide state of the art of the sol-gel and melt quenched bioactive bioglasses for tissue regeneration. Fabrication routes for bioglasses suitable for bone tissue engineering are highlighted and the effect of these fabrication techniques on the porosity, pore-volume, mechanical properties, cytocompatibilty and especially apatite layer formation on the surface of bioglasses is analyzed in detail. Drug delivery capability of bioglasses is addressed shortly along with the bioactivity of mesoporous glasses. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1248-1275, 2016.

Methotrexate-loaded glass ionomer cements for drug release in the skeleton: An examination of composition-property relationships

Chemotherapeutic-loaded bone cement may be an effective method of drug delivery for the management of cancer-related vertebral fractures that require cement injection for pain relief. Recent advancements in the development of aluminum-free glass ionomer cements (GICs) have rendered this class of biomaterials clinically viable for such applications. To expand the therapeutic benefits of these materials, this study examined, for the first time, their drug delivery potential. Through incrementally loading the GIC with methotrexate (MTX) by up to 10-wt%, composition-property relationships were established, correlating MTX loading with working time and setting time, as well as compressive strength, drug release, and cytotoxic effect over 31 days. The most significant finding of this study was that MTX was readily released from the GIC, while maintaining cytotoxic activity. Release correlated linearly with initial loading and appeared to be diffusion mediated, delivering a total of 1-2% of the incorporated drug. MTX loading in this range exerted minimal effects to handling and strength, indicating the clinical utility of the material was not compromised by MTX loading. The MTX-GIC systems examined herein are promising materials for combined structural delivery applications.

Predicting composition-property relationships for glass ionomer cements: a multifactor central composite approach to material optimization

Adjusting powder-liquid ratio (P/L) and polyacrylic acid concentration (AC) has been documented as a means of tailoring the handling and mechanical properties of glass ionomer cements (GICs). This work implemented a novel approach in which the interactive effects of these two factors on three key GIC properties (working time, setting time, and compressive strength) were investigated using a central composite design of experiments. Using nonlinear regression analysis, formulation-property relationships were derived for each property, which enabled prediction of an optimal formulation (P/L and AC) through application of the desirability approach. A novel aluminum free GIC was investigated, as this material may present the first clinically viable GIC for use in injectable spinal applications, such as vertebroplasty. Ultimately, this study presents the first series of predictive regression models that explain the formulation-dependence of a GIC, and the first statistical method for optimizing both P/L and AC depending on user-defined inputs.

Calcium polyphosphate as an additive to zinc-silicate glass ionomer cements

Aluminum-free glass ionomer cements (GICs) are under development for orthopedic applications, but are limited by their insufficient handling properties. Here, the addition of calcium polyphosphate (CPP) was investigated as an additive to an experimental zinc-silicate glass ionomer cement. A 50% maximum increase in working time was observed with CPP addition, though this was not clinically significant due to the short working times of the starting zinc-silicate GIC. Surprisingly, CPP also improved the mechanical properties, especially the tensile strength which increased by ∼33% after 30 days in TRIS buffer solution upon CPP addition up to 37.5 wt%. This strengthening may have been due to the formation of ionic crosslinks between the polyphosphate chains and polyacrylic acid. Thus, CPP is a potential additive to future GIC compositions as it has been shown to improve handling and mechanical properties. In addition, CPP may stimulate new bone growth and provide the ability for drug delivery, which are desirable modifications for an orthopedic cement.

Composition-structure-property relationships for non-classical ionomer cements formulated with zinc-boron germanium-based glasses

Non-classical ionomer glasses like those based on zinc-boron-germanium glasses are of special interest in a variety of medical applications owning to their unique combination of properties and potential therapeutic efficacy. These features may be of particular benefit with respect to the utilization of glass ionomer cements for minimally invasive dental applications such as the atruamatic restorative treatment, but also for expanded clinical applications in orthopedics and oral-maxillofacial surgery. A unique system of zinc-boron-germanium-based glasses (10 compositions in total) has been designed using a Design of Mixtures methodology. In the first instance, ionomer glasses were examined via differential thermal analysis, X-ray diffraction, and 11B MAS NMR spectroscopy to establish fundamental composition – structure-property relationships for the unique system. Secondly, cements were synthesized based on each glass and handling characteristics (working time, Wt, and setting time, St) and compression strength were quantified to facilitate the development of both experimental and mathematical composition-structure-property relationships for the new ionomer cements. The novel glass ionomer cements were found to provide Wt, St, and compression strength in the range of 48–132 s, 206–602 s, and 16–36 MPa, respectively, depending on the ZnO/GeO2 mol fraction of the glass phase. A lower ZnO mol fraction in the glass phase provides higher glass transition temperature, higher N4 rate, and in combination with careful modulation of GeO2 mol fraction in the glass phase provides a unique approach to extending the Wt and St of glass ionomer cement without compromising (in fact enhancing) compression strength. The data presented in this work provide valuable information for the formulation of alternative glass ionomer cements for applications within and beyond the dental clinic, especially where conventional approaches to modulating working time and strength exhibit co-dependencies (i.e. the enhancement of one property comes at the expense of the other) and therefore limit development strategies.

Development of a novel aluminum-free glass ionomer cement based on magnesium/strontium-silicate glasses

The effects of strontium substitution for magnesium in a novel aluminum-free multicomponent glass composition for glass ionomer cements (GICs) were investigated. A series of glass compositions were prepared based on SiO2-P2O5-CaO-ZnO-MgO(1-X)-SrOX-CaF2 (X=0, 0.25, 0.5 and 0.75). The mechanical properties of GICs prepared were characterized by compressive strength, flexural strength, flexural modules, and microhardness. Cell proliferation was evaluated indirectly by CCK-8 assay using various dilutions of the cement and rat mesenchyme stem cells. Incorporation of strontium instead of magnesium in the glasses has a significant influence on setting time of the cements and the properties. All mechanical properties of the GICs with SrO substitution at X=0.25 were significantly increased, then gradually decreased with further increase of the amount of strontium substitution in the glass. The GIC at X=0.25, also, showed an improved cell viability at low doses of the cement extracts in comparison with other groups or control without extracts. The results of this study demonstrate that the glass compositions with strontium substitution at low levels can be successfully used to prepare aluminum-free glass ionomer cements for repair and regeneration of hard tissues.

An in vitro study on the maturation of conventional glass ionomer cements and their interface to dentin

The objective of the study was to investigate the influence of long-term storage (up to 1 year) and coating on the variation of micro-mechanical properties of four conventional restorative glass ionomer cements (GICs) within 3.5 mm deep class I cavities. Four commercially available GICs (Riva Self Cure (SDI), ChemFil Rock (Dentsply), Fuji IX Fast and Fuji IX GP Extra/Equia (GC)) were applied to 100 teeth. In each tooth, two similar 3.5 mm deep class I cavities were prepared and filled with the GICs, with and without resin coating. The samples were stored in artificial saliva at 37 °C for 1 week, 1 month, 3 months, 6 months and 1 year. The variation in mechanical properties (indentation modulus (E) and Vickers hardness (HV)) were determined in 100 μm steps starting from the filling surface, through the intermediate layer in between dentine and GIC, and ending 100 μm in dentin. HV and E were strongly influenced by the material (P<0.05, partial eta-squared ηP(2) = 0.31 and 0.23) but less by aging duration (P<0.05, ηP(2) = 0.02 and 0.12) and resin coating (P<0.05, ηP(2) = 0.02 and 0.03). The depth of measurement (0-2 mm) has no influence on HV (P = 0.789). HV shows a gentle increase over the 1 year storage period (P = 0.002). A ∼300 μm GIC zone at the areas close to dentin with weaker properties as those measured in dentin or GIC was identified in all fillings, irrespective of the presence of coating, and at all storage periods. The thickness of this zone is more strongly influenced by storage (P<0.05, ηP(2) = 0.081) than by material type (P<0.05, ηP(2) = 0.056), while coating showed no influence (P = 0.869). Filler morphology and dimension were similar to upper parts of the GIC filling; however, the amount of low cations was higher. We concluded that the development of an intermediate layer in between dentine and GIC with lower mechanical properties might be responsible for the bond quality of GIC to dentine. Moreover, class I GIC restorations are unlikely to feature constant mechanical properties throughout the cavity, regardless of conditions such as aging and coating.

Novel adaptations to zinc-silicate glass polyalkenoate cements: the unexpected influences of germanium based glasses on handling characteristics and mechanical properties

Aluminum-free glass polyalkenoate cements (GPC) have been hindered for use as injectable bone cements by their inability to balance handling characteristics with mechanical integrity. Currently, zinc-based, aluminum-free GPCs demonstrate compression strengths in excess of 60MPa, but set in c. 1-2 min. Previous efforts to extend the setting reaction have remained clinically insufficient and are typically accompanied by a significant drop in strength. This work synthesized novel glasses based on a zinc silicate composition with the inclusion of GeO2, ZrO2, and Na2O, and evaluated the setting reaction and mechanical properties of the resultant GPCs. Germanium based GPCs were found to have working times between 5 and 10 min, setting times between 14 and 36 min, and compression strengths in excess of 30 MPa for the first 30 days. The results of this investigation have shown that the inclusion of GeO2, ZrO2, and Na2O into the glass network have produced, for the first time, an aluminum-free GPC that is clinically viable as injectable bone cements with regards to handling characteristics and mechanical properties.

Microstructure and chemistry affects apatite nucleation on calcium phosphate bone graft substitutes

The bioactivity of calcium phosphate bone grafts of varying chemistry and strut-porosity was compared by determining the rate of formation of hydroxycarbonate apatite crystals on the material surface after being soaked in simulated body fluid for up to 30 days. Three groups of silicate-substituted hydroxyapatite material were tested, with each group comprising a different quantity of strut-porosity (23, 32, and 46 % volume). A commercially available porous β-tricalcium phosphate bone graft substitute was tested for comparison. Results indicate that strut-porosity of a material affects the potential for formation of a precursor to bone-like apatite and further confirms previous findings that β-tricalcium phosphate is less bioactive than hydroxyapatite.

Mixture designs to assess composition–structure–property relationships in SiO2–CaO–ZnO–La2O3–TiO2–MgO–SrO–Na2O glasses: Potential materials for embolization

Embolization with micron-sized particulates is widely applied to treat uterine fibroids. The objective of this work was to develop mixture designs to predict materials composition–structure–property relationships for the SiO2–CaO–ZnO–La2O3–TiO2–MgO–SrO–Na2O glass system and compare its fundamental materials properties (density and cytocompatibility), against a state-of-the-art embolic agent (contour polyvinyl alcohol) to assess the potential of these materials for embolization therapies. The glass structures were evaluated using 29Si MAS NMR to identify chemical shift and line width; the particulate densities were determined using helium pycnometry and the cell viabilities were assessed via MTT assay. 29Si MAS NMR results indicated peak maxima for each glass in the range of −82.3 ppm to −89.9 ppm; associated with Q2 to Q3 units in silicate glasses. All experimental embolic compositions showed enhanced in vitro compatibility in comparison to Contour PVA with the exceptions of ORP9 and ORP11 (containing no TiO2). In this study, optimal compositions for cell viability were obtained for the following compositional ranges: 0.095–0.188 mole fraction ZnO; 0.068–0.159 mole fraction La2O3; 0.545–0.562 mole fraction SiO2 and 0.042–0.050 mole fraction TiO2. To ensure ease of producibility in obtaining good melts, a maximum loading of 0.068 mole fraction La2O3 is required. This is confirmed by the desirability approach, for which the only experimental composition (ORP5) of the materials evaluated was presented as an optimum composition; combining high cell viability with ease of production (0.188 mole fraction ZnO; 0.068 mole fraction La2O3; 0.562 mole fraction SiO2 and 0.042 mole fraction TiO2).

Gallium containing glass polyalkenoate anti-cancerous bone cements: glass characterization and physical properties

A gallium (Ga) glass series (0.48SiO(2)-0.40ZnO-0.12CaO, with 0.08 mol% substitution for ZnO) was developed to formulate a Ga-containing Glass Polyalkenoate Cement (GPC) series. Network connectivity (NC) and X-ray Photoelectron Spectroscopy (XPS) was employed to investigate the role of Ga(3+) in the glass, where it is assumed to act as a network modifier. Ga-GPC series was formulated with E9 and E11 polyacrylic acid (PAA) at 50, 55 and 60 wt% additions. E11 working times (T(w)) ranged from 68 to 96 s (Lcon.) and 106 s for the Ga-GPCs (LGa-1 and LGa-2). Setting times (T(s)) ranged from 104 to 226 s (Lcon.) and 211 s for LGa-1 and LGa-2. Compression (σc) and biaxial flexural (σf) testing were conducted where Lcon. increased from 62 to 68 MPa, LGa-1 from 14 to 42 MPa and LGa-2 from 20 to 47 MPa in σc over 1-30 days. σf testing revealed that Lcon. increased from 29 to 42 MPa, LGa-1 from 7 to 32 MPa and LGa-2 from 12 to 36 MPa over 1-30 days.

Evaluation of a conventional glass ionomer cement with new zinc formulation: effect of coating, aging and storage agents

OBJECTIVE

The study focused on a recently launched conventional glass ionomer cement (GIC) with a particular chemical formulation of both, filler and acrylic liquid, by analysing its mechanical behaviour in comparison to three conventional GICs. Furthermore, the effect of resin coating and storage conditions was evaluated.

MATERIALS AND METHODS

Three commercially available GICs were chosen: Riva Self Cure (SDI), Fuji IX Fast (GC) and Fuji IX GP Extra/Equia (GC). Additionally a newly developed zinc-containing GIC--ChemFil Rock (Dentsply)--was tested. Mechanical properties were determined at macro- [flexural strength (FS) and modulus of elasticity (E (flexural))] and micro-scale [Vickers hardness (VH) and indentation modulus (E)] after storing coated and uncoated specimens in artificial saliva and distilled water for 7 and 30 days.

RESULTS

ChemFil Rock revealed the highest FS, but the lowest VH and E. The micro-mechanical properties of the analysed GICs did neither benefit from the new zinc formulation nor from resin coating. A resin coating is nevertheless a valuable support for GIC fillings, since it offers the absence of visible surface defects like crazing and voids, and thus, it led to significant improvements in flexural strength. This statement is also valid for ChemFil Rock, contrary to manufacture recommendation. The impact of storage agent and storage duration on the measured properties was low.

CONCLUSIONS

The new development (ChemFil Rock) might represent a promising approach regarding longevity of GIC fillings in molar regions, due to the high flexural strength and the absence of visible surface defects like crazing and voids.

CLINICAL RELEVANCE

All GICs should receive surface protection in order to perform their maximum in stability.

Does elevating silver content in zinc-based glass polyalkenoate cements increase their antibacterial efficacy against two common bacteria using the agar gel diffusion method?

The authors have previously shown that it is possible to incorporate silver into a soda-zinc-silicate glass and subsequently form a glass polyalkenoate cement from it. The objective of the research described herein is to determine if incremental increases in the silver content of these glass polyalkenoate cements will increase their antibacterial efficacy against gram-positive and gram-negative bacteria using the accepted spread plate method. Four glass polyalkenoate cements were formulated; three contained increasing amounts of silver incorporated into them (cements A, B, and C, containing 0.33 mol%, 0.66 mol%, and 0.99 mol% silver, respectively) and a fourth contained no silver, which acted as a control (control cement). The handling properties of the glass polyalkenoate cements were evaluated, where working times were around 2 min and setting times ranged from 1 h 17 min to 2 h 41 min. Inductively coupled plasma atomic emission spectroscopy was employed to determine silver ion release with cement maturation for up to 14 days. The majority of silver ions were released within the first 24 h, with up to 2 mg/L cumulative ion release recorded up to 14 days. The antibacterial properties of the coatings were evaluated against Staphylococcus aureus and Pseudomonas aeruginosa bacteria. The silver-glass polyalkenoate cements exhibited antibacterial effect against both bacterial strains. The maximum inhibition zones recorded against S. aureus was 14.8 mm (SD ± 1.11) and against P. aeruginosa was 20.6 mm (SD ± 0.81). Cement B had a greater antibacterial effect compared to cement A, however, cements B and C had comparable antibacterial effects after 14 days even though cement C contained 0.33 mol% more silver than B. This indicates that by increasing the silver content in these cements, the antibacterial efficacy increases to a point, but there is a threshold where further silver ion release does not increase the antibacterial effect.

Bioactive glass S53P4 as bone graft substitute in treatment of osteomyelitis

Bioactive glass (BAG)-S53P4 is an osteoconductive bone substitute with proven antibacterial and bone bonding properties. In a multicentre study 11 patients with verified chronic osteomyelitis in the lower extremity and the spine were treated with BAG-S53P4 as a bone substitute. The cavitary bone defect and the surrounding of a spinal implant were filled with BAG-S53P4. The most common pathogen causing the infection was Staphylococcus aureus. The mean follow-up was 24 months (range 10-38). BAG-S53P4 was well tolerated. Nine patients healed without complications. One patient who achieved good bone formation sustained a superficial wound infection due to vascular problems in the muscle flap, and one patient had an infection due to a deep haematoma. This study shows that BAG-S53P4 is a good and well-tolerated bone substitute, and can be used in treatment of osteomyelitis with good primary results.

Release of sodium fusidate from glass-ionomer dental cement

Restorative grade glass-ionomer cement has been studied for its potential as a controlled release material for the antimicrobial compound sodium fusidate. Sodium fusidate powder was incorporated into the cement at the mixing stage at levels of 1% and 5% by mass, and disc shaped specimens (6 mm diameter x 2 mm depth) prepared. After curing for 1 hour at 37 degrees C, specimens were placed in water and release of sodium fusidate at set time intervals determined using reverse-phase HPLC. Sets of five specimens were used in all experiments. Early release of sodium fusidate was shown to occur by diffusion for each level of addition, as shown by M(t)/M(infinity) being linear with respect to [square root]time in both cases. Diffusion coefficients were calculated as 4.4 x 10(-8) cm(2) s(-1) and 3.0 x 10(-8) cm(2) s(-1) for 1 and 5% respectively. These were an order of magnitude lower than had been found previously for water transport in glass-ionomer cements, a result that is attributed to the greater size of the sodium fusidate molecule compared with that of water. Cements released 20.4 and 22.8% respectively of the total sodium fusidate added after 2 weeks, values which were not significantly different from each other, and which exceeded total release previously reported for benzalkonium chloride and chlorhexidine.

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 failure mechanisms for cements used in skeletal luting applications

Glass Polyalkenoate Cements (GPCs) based on strontium calcium zinc silicate (Sr-Ca-Zn-SiO(2)) glasses and low molecular weight poly(acrylic acid) (PAA) have been shown to exhibit suitable compressive strength (65 MPa) and flexural strength (14 MPa) for orthopaedic luting applications. In this study, two such GPC formulations, alongside two commercial cements (Simplex P and Hydroset) were examined. Fracture toughness and tensile bond strength to sintered hydroxyapatite and a biomedical titanium alloy were examined. Fracture toughness of the commercial Poly(methyl methacrylate) cement, Simplex P, (3.02 MPa m(1/2)) was superior to that of the novel GPC (0.36 MPa m(1/2)) and the commercial calcium phosphate cement, Hydroset, for which no significant fracture toughness was obtained. However, tensile bond strengths of the novel GPCs (0.38 MPa), after a prolonged period (30 days), were observed to be superior to commercial controls (Simplex P: 0.07 MPa, Hydroset: 0.16 MPa).

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.

Strontium-based Glass Polyalkenoate Cements for Luting Applications in the Skeleton

Glass Polyalkenoate Cements (GPCs) based on strontium calcium zinc silicate (Sr-Ca-Zn-SiO2) glasses and high molecular weight poly(acrylic acid) (PAA) have been shown to exhibit suitable mechanical properties for orthopaedic arthroplasty applications, however for vertebroplasty and other medical luting applications these cements have working and setting times which are unsuitable for such applications. In this study GPCs based on Sr-Ca-Zn-SiO 2 glasses and low molecular weight PAA were evaluated for orthopaedic luting applications. GPCs based on four different glasses; BT100 (0.16CaO, 0.36ZnO, 0.48SiO2), BT101 (0.04SrO, 0.12CaO, 0.36ZnO, 0.48SiO 2), BT102 (0.08SrO 0.08CaO, 0.36ZnO, 0.48SiO2) and BT103 (0.12SrO 0.04CaO, 0.36ZnO, 0.48SiO2) and two PAAs (MW; 12,700 and 25,700) were examined. These cement formulations exhibited handling properties potentially suitable for luting applications as well as mechanical strengths which were similar to those of trabecular bone. Upon immersion in simulated body fluid, the GPCs showed sustained growth of a calcium phosphate layer on the surface of the cement indicating that these cements were bioactive in nature.

Antibacterial coatings for medical devices based on glass polyalkenoate cement chemistry

A biofilm is an accumulation of micro-organisms and their extracellular products forming a structured community on a surface. Biofilm formation on medical devices has severe health consequences as bacteria growing in this lifestyle are tolerant to both host defense mechanisms and antibiotic therapies. However, silver and zinc ions inhibit the attachment and proliferation of immature biofilms. The objective of this study is to evaluate whether it is possible to produce silver and zinc-containing glass polyalkenoate cement (GPC) coatings for medical devices that have antibacterial activity and which may therefore inhibit biofilm formation on a material surface. Two silver and zinc-containing GPC coatings (A and B) were synthesised and coated onto Ti6Al4V discs. Their handling properties were characterised and atomic absorption spectrometery was employed to determine zinc and silver ion release with coating maturation up to 30 days. The antibacterial properties of the coatings were also evaluated against Staphylococcus aureus and a clinical isolate of Pseudomonas aeruginosa using an agar diffusion assay method. The majority of the zinc and silver ions were released within the first 24 h; both coatings exhibited antibacterial effect against the two bacterial strains, but the effect was more intense for B which contained more silver and less zinc than A. Both coatings produced clear zones of inhibition with each of the two organisms tested. In this assay, Ps. aeruginosa was more sensitive than S. aureus. The diameters of these zones were reduced after the coating had been immersed in water for varying periods due to the resultant effect on ion release.

Comparison of in vitro and in vivo Bioactivity of SrO—CaO—ZnO—SiO2 Glass Grafts

A range of calcium—strontium—zinc—silicate glass grafts are developed. Following characterization, their ability to form an apatite layer in simulated body fluid (SBF) is evaluated. Concurrently, their in vivo biocompatibility is determined. These glasses are incapable of forming an apatite layer in SBF. However, in vivo, each glass is well tolerated with new bone formation apparent in close apposition to implanted particles and no evidence of an inflammatory response. Such results are contrary to much of the literature and indicate that forecasting a materials ability to bond to bone based on SBF experiments may provide a false negative result.