Histomorphometric and Microchemical Characterization of Bone Around Strontium-containing Silica-based Bioactive Glass Particles Implanted in Rat Tibia Bone Marrow

A.A. GORUSTOVICH; T.STEIMETZ; M.B. GUGLIELMOTTI; R.L. CABRINI; J.M.PORTO LÓPEZ

Brighton, UK

Conferencia; 21th European Conference on Biomaterials; 2007

European Society of Biomaterials

Histomorphometric and Microchemical Characterization of Bone Around Strontium-containing Silica-based Bioactive Glass Particles Implanted in Rat Tibia Bone Marrow   A.A. Gorustovich,1,2 T. Steimetz,3 M.B. Guglielmotti2,3, R.L. Cabrini3, J.M. Porto López2,4 1 Research Laboratory, National Atomic Energy Commission (CNEA-Regional Noroeste), Salta, A4408FTV, Argentina 2 National Research Council (CONICET), Argentina 3 Department of Oral Pathology, School of Dentistry, University of Buenos Aires, Buenos Aires, C1122AAH, Argentina 4 Ceramics Division, Research Institute for Materials Science and Technology (INTEMA-CONICET), Mar del Plata, B7608FDQ, ArgentinaE-mail: agorustovich@gmail.com   Introduction There is accumulating evidence that strontium (Sr) has positive effects on bone formation both in vitro and in vivo.  Thus, it is reasonable to expect that its presence in biomaterials can enhance the bone healing leading to osseointegration. The aim of the present study was to characterize the neoformed bone tissue around Sr-containing silica-based bioactive glass particles implanted in rat tibia bone marrow by histologic, histomorphometric and microchemical evaluation.     Materials and Methods Bioactive glasses Melt-derived bioactive glasses (BGs)(45S5 and 45S5.6Sr) were prepared from a base 45S5 BG of nominal composition (45% SiO2, 24.5% CaO, 24.5% Na2O and 6% P2O5 in wt%). Sr-containing glass was prepared by the substitution of CaO in 45S5 BG with 6 wt% SrO (45S5.6Sr). In vivo bioassay Thirty Wistar rats were used throughout. The guidelines of  the National Institutes of Health for the care ad use of laboratory animals (NIH Pub. N°85-23, Rev. 1985) were observed. Under anesthesia, 45S5 BG particles (300-350 µm) were placed inside the medullary compartment of the tibia (control), while in the contralateral tibia (experimental) 45S5.6Sr BG particles (300-350 µm) were implanted. The animals were sacrificed, in groups of ten, at 15, 30, and 60 days post-implantation. The tibiae were resected, fixed in formalin solution and radiographed. Histologic processing The tibiae were processed for embedding in methyl-methacrylate resin. Undecalcified ground sections were stained with 1% toluidine blue and analyzed by light microscopy. Histomorphometry The percentage of bone-implant contact (affinity index) of the BGs were evaluated quantitatively. The affinity index, which equaled the length of bone in direct contact with the BG particles surface expressed as a percentage of the total length of the BG particles surface, was calculated for each bioactive glass at 30 days post-implantation. Microchemical analysis The sections were coated with a thin, 20 nm layer of silver in a vacuum evaporator for energy-dispersive X-ray analysis (EDX). The presence of strontium (Sr), calcium (Ca), and phosphorus (P) was evaluated in the peri-implant bone tissue for each of the experimental times. The Ca:P ratio was determined. Results Histologically, new lamellar bone had formed along the surface of both 45S5 and 45S5.6Sr BG particles within 4 weeks. At 30 days post-implantation, 45S5 and 45S5.6Sr BGs had almost identical affinity indices (%) (88±7 and 87±9; p>0.05). X-ray microanalysis allowed the focal measurement of bone Sr content as well as other elements constituting bone mineral as Ca and P. There was no bone Sr uptake by the neoformed bone tissue around 45S5.6Sr BG particles. No statistically significant differences were observed in  Ca:P ratio of bone tissue between both groups at any of the time points studied (Table 1).     15d 30d 60d 45S5 1.44±0.08 1.51±0.06 1.53±0.04 45S5.6Sr 1.44±0.09 1.51±0.04 1.53±0.03   Table 1: Microchemical characterization of bone, Ca:P Mean ± SD   Discussion For the first time, this study describes the in vivo behavior of Sr-containing bioactive glass particles in the SiO2-CaO-Na2O-P2O5 system. The results of the present study provide evidence that there were no significant differences among the osteoconductive potentials of 45S5 and 45S5.6Sr BG particles. A preservation of the normal bone mineralization was observed in the neoformed bone tissue around 45S5.6Sr BG particles. It has been shown that Sr-containing calcium phosphate ceramics promoted better osteoprecursor cell attachment and proliferation and showed no deleterious effects on osteoblast cell adhesion, extracellular matrix formation and mineralization in vitro. Several studies show that the Sr-containing hydroxyapatite (Sr-HA) bioactive bone cement promotes osteoblast attachment and mineralization in vitro and bone growth and osseointegration in vivo. The affinity of bone on Sr-HA cement injected into the iliac crest of rabbits was increased from 73.55±3.50% after 3 months up to 85.15 ±2.74% after 6 months. In our work, the overall affinity index of bone on both BGSs was ~88% at 30 days post-implantation.   Conclusion Results suggested good bone-bonding ability of the 45S5.6Sr BG particles when implanted into the intramedullary canal of rat tibiae, making the use of the Sr-containing silica-based BGs a potential alternative in bone tissue engineering and regenerative medicine procedures.