Ari Itälä

Effect of immersion in SBF on porous bioactive bodies made by sintering bioactive glass microspheres

Abstract Since the mid 90s it has been possible to draw fibers and manufacture microspheres of novel bioactive glasses. Thus, by sintering bioactive glass microspheres it is now possible to form porous textures, in which the bioactive surface area is increased manifold compared with non-porous bodies. Four different types of porous bodies were made by sintering glass microspheres of diameter 250–300 μm. Two of the body types contained only one kind of spheres; either highly bioactive glass spheres or spheres made of glass having a low bioactivity (biocompatible glass). Two additional types of test bodies were obtained by sintering mixtures of bioactive and biocompatible spheres (composites). The dissolution of silica and calcium into simulated body fluid (SBF) was determined at different time intervals using a direct current plasma atomic emission spectrometer (DCPAES). The influence of immersion on the mechanical strength of the porous structures was studied by means of a compression test. Further, the thickness of the silica-rich gel formation on the surface of bioactive glass spheres was measured at each time interval using back-scattered electron imaging of scanning electron microscopy (BEI-SEM). A non-porous glass rod made from the same bioactive glass was used as the control. The results showed that dissolution of silica and calcium into SBF from the porous glass texture was inversely related to the silica content of the glass. The rate of silica gel formation on the sintered bioactive microspheres was significantly higher than on a rod made from the same glass. The initial mechanical strength of porous bodies consisting of only one kind of glass was 17–20 MPa. However, these bodies lost their mechanical strength at an early stage of the immersion showing compression strength of only 7–8 MPa at 14 days of immersion. The initial strength of composite glass bodies (7–11 MPa) was lower compared with bodies containing only one kind of glass but the bodies showed no notable mechanical weakening during the test. Softening of the surface of smooth bioactive glass plates correlated well with the formation of the silica-rich layer on the plate. Interestingly, the study also showed that in porous glass structures containing both bioactive and biocompatible glass the biocompatible glass can act as a site for calcium phosphate precipitation.

Creation of microrough surface on sintered bioactive glass microspheres

Bioactive glasses are surface-active, generally silica-based, synthetic materials that form a firm chemical bond to bone. The aim of this study was to further enhance the bioactivity of glasses by creating a microroughness on their surface. Microroughness increases potential surface area for cell attachment and biomaterial-cell interactions. Three bioactive glasses of different composition were studied. Each material was flame-sprayed into microspheres, and a selected fraction of the spheres (250-300 microm) was sintered to form porous bioactive glass specimens. To create microrough surfaces, different acid etching techniques were tested. Atomic force microscopy (AFM) and back-scattered electron imaging of scanning electron microscopy (BEI-SEM) were used to characterize surface roughness. The degree of roughness was measured by AFM. A novel chemical-etching method, developed through intensive screening of different options, was found consistently to create the desired microroughness, with an average roughness value (R(a)) of 0.35-0.52 microm and a root mean-square roughness value (R(rms)) of 0.42-0.64 microm. Microroughening of the glass surface was obtained even in the internal parts of the porous glass matrices. Measured by BEI-SEM, the etching of a bioactive glass surface did not interfere with the formation of the characteristic surface reactions of bioactive glasses. This was confirmed by immersing the etched and control glass bodies in a simulated body fluid and tris(hydroxymethyl) aminomethane/HCl. The etching process did not significantly affect the mechanical strength of the sintered bioactive glass structures. Based on these experiments, it seems possible to create a reproducible microroughness of appropriate size on the surface of porous bioactive glass. The biologic benefits of such a surface treatment need to be validated with in vivo experiments.

An institutional review of clear cell chondrosarcoma.

Clear cell chondrosarcoma is a rare bone neoplasm with a slow progressive clinical course and infrequent metastasis, but with a high local recurrence rate. We sought to ascertain the long-term outcome of patients with this neoplasm and to identify possible factors predicting survival. Sixteen patients with clear cell chondrosarcomas treated at one institution and who had long-term clinical followup were identified. All patients were treated by surgical resection of the tumor, which was classified as clear (> 2 mm) in 10 patients and marginal or intralesional in six patients. Three patients had local recurrence after a median of 1.7 years. Metastatic disease developed in four patients with a median time to diagnosis of 8.1 years. Ten-year overall survival of patients with clear cell chondrosarcomas was 89%, and disease-free survival was 68%. Patients with surgical resections comprising clear margins had longer disease-free survival compared with patients with marginal and intralesional tumors. Inadequate surgical resection of clear cell chondrosarcoma leads to risk of local recurrence and metastatic disease. The malignancy has a tendency to metastasize relatively late, therefore, followup of patients is necessary after the generally accepted 5-year period. Level of Evidence: Prognostic study, Level III (case control study). See the Guidelines for Authors for a complete description of levels of evidence.

Bioactive Glass Granules as Extender of Autogenous Bone Grafting in Cementless Intercalary Implant of the Canine Femur

Background and Aims: Ceramic bone graft substitutes have a potential to be used as replacement of allogeneic bone grafting and, under optimal distribution of particle size, they may even provide mechanical support. The current study examined the efficacy of bioactive glass granules as an extender of autogenous bone grafting in a segmental bone replacement model of the canine femur. Material and Method: A 16 mm long segment of the femur shaft was bilaterally replaced with an intercalary titanium implant in eight animals. The implant had cementless grooved proximal and distal stems. In one leg, the peri-implant space was packed with composite graft consisting of a mixture of bioactive glass granules and autogenous bone graft in proportion of 50:50. In the opposite leg, the peri-implant space was treated with autogenous bone graft alone. After surgery, unlimited functional loading was allowed. The outcome was evaluated at three months. Results: Eight out of sixteen autografted implants and seven out of sixteen composite-grafted implants were radiographically incorporated and clinically stable at three months. In the paired comparison, the proximal components of composite-grafted implants showed lower maximum load under torsional testing (p=0.068), less new bone in the longitudinal grooves of the stems (p=0.036) and lower affinity of new bone to implant surface (p=0.046). The distal components of the two sides showed a similar trend for less new bone in the grooves and lower bone affinity of new bone in the distal composite-grafted components. Conclusions: The current study suggests that supplementation of periprosthetic bone graft with bioactive ceramic particles may not help to promote healing of cementless implants under high dynamic loading conditions.

Bioceramic inlays do not improve mechanical incorporation of grit-blasted titanium stems in the proximal sheep femur

The aim of the present study was to determine, if bioactive glass (BG) surface inlays improve osseointegration of titanium implants in the proximal femur of adult sheep. In simulation of uncemented primary stems (nine animals), only the proximal part of the implants was grit-blasted and three surface slots of the grit-blasted region were filled with sintered BG microspheres. Primary stems were implanted using press-fit technique. In revision stem simulation (eight animals), grit-blasting was extended over the whole implant and seven perforating holes of the stem were filled by sintered BG granules. Revision stems were implanted with a mixture of autogenous bone graft and BG granules. Comparison with solid partially or fully grit-blasted control stems implanted in the contralateral femurs was performed in the primary and revision stem experiments at 12 and 25 weeks, respectively. Implant incorporation was evaluated by torsional failure testing and histomorphometry. Only one-third of the primary stems anchored mechanically to bone. The revision stems incorporated better and the BG inlays of the revision stems showed ingrowth of new bone. However, there were no significant differences in the torsional failure loads between the stems with BG inlays and the control stems. In conclusion, surface BG inlays gave no measurable advantage in mechanical incorporation of grit-blasted titanium implants. Overall, the proximal sheep femur, characterized by minimal amount of cancellous bone and the presence of adipocytic bone marrow, seemed to present compromised bone healing conditions.