An investigation into the structure and reactivity of calcium-zinc-silicate ionomer glasses using MAS-NMR spectroscopy.
ABSTRACT The suitability of Glass Polyalkenoate Cements (GPCs) for orthopaedic applications is retarded by the presence in the glass phase of aluminium, a neurotoxin. Unfortunately, the aluminium ion plays an integral role in the setting process of GPCs and its absence is likely to hinder cement formation. However, the authors have previously shown that aluminium-free GPCs may be formulated based on calcium zinc silicate glasses and these novel materials exhibit significant potential as hard tissue biomaterials. However there is no data available on the structure of these glasses. (29)Si MAS-NMR, differential thermal analysis (DTA), X-ray diffraction (XRD), and network crosslink density (CLD) calculations were used to characterize the structure of five calcium zinc silicate glasses and relate glass structure to reactivity. The results indicate that glasses capable of forming Zn-GPCs are predominantly Q(2)/Q(3) in structure with corresponding network crosslink densities greater than 2. The correlation of CLD and MAS-NMR results indicate the primary role of zinc in these simple glass networks is as a network modifier and not an intermediate oxide; this fact will allow for more refined glass compositions, with less reactive structures, to be formulated in the future.
- SourceAvailable from: Marianne Toft Vestermark[Show abstract] [Hide abstract]
ABSTRACT: Total hip replacement surgery is being performed on an increasingly large part of the population and at increasingly younger age. Because we live and stay physically active longer, and since hip replacement surgery has become quite successful, the treatment is being offered to progressively more patients. Unfortunately, about 17% of hip replacement surgeries currently involve revisions. Consequently, the longevity of both the primary and revision implant is an issue and warrants further investigation. Implants undergoing early instability or even subsidence correlate with an increased risk of aseptic loosening, subsequently requiring revision. Thus, the goal is early fixation by osseointegration of the implant. For revision implants, this is an even greater challenge since an allograft is often needed during surgery to obtain immediate stability of the implant. Bone grafts are rapidly resorbed. Thus, instability of the prosthesis may develop before new bone formation is well established and can mechanically secure the prosthesis. Strontium is a dual action drug; being both bone anabolic and anti-catabolic. In the form of strontiumranelate, it is used in the treatment of osteoporosis. Strontium may potentially improve the early osseointegration and fixation of implants. This dissertation consists of three studies investigating the effect of strontium at the bone-implant interface. The questions were firstly, what is the optimal delivery method for strontium to the interface, and secondly, can strontium exercise its dual action at the interface? The studies were performed in a cementless, experimental gap model in canine. The effects of strontium were evaluated by histomorphometrical analysis of the osseointegration and mechanical push-out test of implant fixation. Different stereological methods were used for the histomorphometrical analysis of each study. The methods used were reviewed critically and found valid. Study I compared a 5% strontium-substituted hydroxyapatite (HA) coating with an HA coating after 4 weeks and 12 weeks observation time. We examined whether fixation of the implant was improved by the strontium substitution. It was found that fixation of the implant was not improved by the strontium substituted HA coating at any of the two time points. Study II compared a 5% strontium-doped HA bone graft extender with an HA bone graft extender. The bone graft extender was mixed with allograft and impacted around a titanium implant. The objective of this study was to determine whether strontium doping of the bone graft extender could protect the allograft from fast resorption and increase gap healing, leading to the improved fixation of the implant. We found that the strontium doping increased gap healing and protected the allograft, however, results of the mechanical test were inconclusive. The reason might have been that the increased gap healing had not yet reached the implant during the 4 weeks observation time, so ongrowth onto the implant was not improved. Study III investigated the effects of bioactive glass coating with a 0%, 10% or 50% strontium-substitution versus HA coating of grit-blasted titanium alloy implants. The goal was to determine whether fixation of the implant would be improved by the bioactive glass coating, and then further improved by the strontium-substitution of the coating in a dose-dependent manner. Unfortunately, the bioactive glass coating failed, presumably due to aluminum contamination originating from the grit-blasting powder. The HA coated implants were superior in all parameters of osseointegration and the mechanical fixation of the implants. These studies show the importance of performing further experimental investigation. Even when investigating a known agent for use in a new application. Strontium delivered as doping of an HA bone graft extender showed potential as a dual acting agent in the interface. However, delivery methods of strontium to the bone-implant interface clearly need further investigation.Danish medical bulletin 05/2011; 58(5):B4286. · 1.01 Impact Factor
- Advanced Biomaterials: Fundamentals, Processing, and Applications, 07/2010: pages 411 - 433; , ISBN: 9780470891315
- [Show abstract] [Hide abstract]
ABSTRACT: One of the desired properties for any new biomaterial composition is its long-term stability in a suitable animal model and such property cannot be appropriately assessed by performing short-term implantation studies. While hydroxyapatite (HA) or bioglass coated metallic biomaterials are being investigated for in vivo biocompatibility properties, such study is not extensively being pursued for bulk glass ceramics. In view of their inherent brittle nature, the implant stability as well as impact of long-term release of metallic ions on bone regeneration have been a major concern. In this perspective, the present article reports the results of the in vivo implantation experiments carried out using 100% strontium (Sr)-substituted glass ceramics with the nominal composition of 4.5 SiO2–3Al2O3–1.5P2O5–3SrO–2SrF2 for 26 weeks in cylindrical bone defects in rabbit model. The combination of histological and micro-computed tomography analysis provided a qualitative and quantitative understanding of the bone regeneration around the glass ceramic implants in comparison to the highly bioactive HA bioglass implants (control). The sequential polychrome labeling of bone during in vivo osseointegration using three fluorochromes followed by fluorescence microscopy observation confirmed homogeneous bone formation around the test implants. The results of the present study unequivocally confirm the long-term implant stability as well as osteoconductive property of 100% Sr-substituted glass ceramics, which is comparable to that of a known bioactive implant, that is, HA-based bioglass. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2014.Journal of Biomedical Materials Research Part B Applied Biomaterials 10/2014; DOI:10.1002/jbm.b.33270 · 2.33 Impact Factor