Erik Vedel

Subchondral bone and cartilage repair with bioactive glasses, hydroxyapatite, and hydroxyapatite-glass composite.

The repair of an osteochondral defect in rabbit femur was studied with three kinds of bioactive glasses (BG), hydroxyapatite (HA), and hydroxyapatite-glass (HAG) composite. Seventy-two osteochondral defects were created in 18 rabbits. Sixty-four cylinders were implanted and eight defects were left empty as controls. Histomorphometry, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA) were used for evaluation. Small osteochondral defects in rabbit femur found to heal themselves by regeneration. The three BGs, HA, and HAG led to direct lamellar bone repair of subchondral bone and restoration of articular surfaces mostly with hyalinelike cartilage in 12 weeks. However, the composition of the materials affects their behavior. Chondrogenesis took place earlier with the BGs than with HA. HAG degraded too much, glass 14 was too reactive and brittle, and the high alumina content in glass 11 disturbed its bone-bonding ability. Glass 7 and HA were the most balanced in the repair process. A special preparation method was used to retain soft tissues fairly unchanged and enable them to the observed together with hard tissues in SEM analysis.

Mechanical verification of soft-tissue attachment on bioactive glasses and titanium implants

Soft-tissue attachment is a desired feature of many clinical biomaterials. The aim of the current study was to design a suitable experimental method for tensile testing of implant incorporation with soft-tissues. Conical implants were made of three compositions of bioactive glass (SiO(2)-P(2)O(5)-B(2)O(3)-Na(2)O-K(2)O-CaO-MgO) or titanium fiber mesh (porosity 84.7%). The implants were surgically inserted into the dorsal subcutaneous soft-tissue or back muscles in the rat. Soft-tissue attachment was evaluated by pull-out testing using a custom-made jig 8 weeks after implantation. Titanium fiber mesh implants had developed a relatively high pull-out force in subcutaneous tissue (12.33+/-5.29 N, mean+/-SD) and also measurable attachment with muscle tissue (2.46+/-1.33 N). The bioactive glass implants failed to show mechanically relevant soft-tissue bonding. The experimental set-up of mechanical testing seems to be feasible for verification studies of soft-tissue attachment. The inexpensive small animal model is beneficial for large-scale in vivo screening of new biomaterials.

Radio-opaque bioactive glass markers for radiostereometric analysis

The objective of the study was to test the hypothesis that resorbable radio-opaque bioactive glass markers can be used in radiostereometric analysis (RSA). Cones made from (1) bioactive glass 1-06 with 2.5 wt.% BaSO(4), (2) glass 1-06 with 10 wt.% BaSO(4), (3) glass 1-06 without any additives and (4) nearly inert glass were created. The in vitro surface reactivity, as a surrogate of bioactivity, was analyzed using a simulated body fluid (SBF) immersion test. The in vivo performance was evaluated in the rat femur using biomechanical testing as well as histological and microcomputed tomography analysis of marker incorporation into bone. A phantom model RSA study using a porcine radius with a soft tissue envelope was carried out to determine the accuracy and precision of spherical markers for the measurement of fracture micromotion. SBF immersion studies and bone implantation studies showed that the addition of BaSO(4) slightly reduced surface reactivity in vitro and the bone-bonding properties of the bioactive glass in vivo. In the simulated RSA study with the selected resorbable marker composition (bioactive glass with 10 wt.% BaSO(4)), the accuracy of translation and rotation measurements in the longitudinal axis was +/-51 microm and +/-0.87 degrees , respectively. The precision of translation and rotation measurements in the longitudinal axis were 9 microm and 0.18 degrees , respectively. Bioactive glass markers with BaSO(4) additive appear to have adequate bone-bonding properties for marker stability and sufficient radio-opacity for RSA, but further preclinical comparison studies with tantalum markers are necessary.

In Vitro Characterization of Bioactive Glasses

In vitro behavior of 30 new glasses in the system Na2O-K2O-MgO-CaO-B2O3 -P2O5-SiO2 was investigated by immersing them into a simulated body fluid for 4 to168 hours. This study involved the observation of both the changes in the properties of the immersion solution and on the glasses surface after immersion. In vitro reactivity was different for each experimental glass depending on its chemical composition. By comparing these glasses to four established bioactive glasses showing different in vivo bioactivity, a fast estimation of the bioactivity of glasses can be done; thereby the optimization of bioactive glasses for various clinical applications can be developed.

Measuring the Devitrification of Bioactive Glasses

The devitrification tendency during heat-treatment was measure d for four bioactive glasses in the system Na 2O-K2O-MgO-CaO-B2O3-P2O5-SiO2. The measurements where performed by high-temperature optical microscopy, X-ray diffraction, sca nning electron microscopy and differential thermal analysis. The combination of these methods proved t be a reliable way to define the devitrification temperatures and the composition of crysta l ph ses formed. This information is vital in choosing glasses for implant production, especi ally in cases where thermal treatment is required.

Creation of Bioactive Glass Coating on Titanium by Local Laser Irradiation; Part 2: Effect of the Irradiation on the Bioactivity of the Glass

Bioactive glass coatings were created by scanning bioactive gl ass powder with a focused CO2 laser beam. SEM/EDX analysis performed on the coating revealed no significant changes in the chemical composition of the glass after laser treatment. T he ability of the coatings to precipitate CaP in SBF was studied in comparison with bioactive glass plates, granules (fraction 315-500 μm) and powder (< 45 μm) made of the same glass. A coating made of an i nert glass (flat glass), was used as a control. Introduction Bioactive glasses are materials that develop reactive layer s at their surface when in contact with tissues and body fluids. The layers attract calcium and phosphate from the body fluid and the glass and a bonelike hydroxyapatite forms on their surface. In vivo the later becomes integrated into the bone [1]. The formation of a calcium phosphate layer can be simulated in vitro by immersing the samples in a simulated body fluid (SBF) introduced by Kokubo et al., [2]. The concentration of inorganic ions in SBF solution is similar to that of human blood plasma. The first generation bioactive glasses were not possible to repeatedl y heat-treat due to crystallization of the glass and changes in their bioactive properties [3]. However, s ome of the new bioactive glasses developed at Åbo Akademi University are well suited for r epeated heat treatments [4]. Thus, a focused CO2-laser beam can be applied for the melting of a bioactive glass powder on grit blasted titanium substrate. A momentary heat exposure hits one area of the surface at a time and affects primarily the uppermost glass [5]. As a result, a glass coating is obtained consisting of repeated rows of melted glass micro spheres attached to the titanium subst rate. The risk of the diffusion of ions during the momentary heat exposure, and detachment of the coating due to the different thermal expansion of the coating and the substrate, is clearly lowe r compared to that after a conventional heat treatment of the whole device during the coating procedure [6,7]. The goal of the first part of the study (Creation of Bioactive Gl ass Coating on Titanium by Local Laser Irradiation. Part I: Optimization of the Processing Para meters. [8]) was to find the optimal processing parameters for the creation of bioactive glass coating s using a CO2-laser. That included characterization of the coatings with SEM-EDXA and i vitro bioactivity tests. The goal of this second part was to study the in vitro bioactivity of bioactive glass coatings created with the use of a CO2-laser. The properties were compared with those of an intact bioact ive glass with the same composition. Also an inert glass (flat glass) coating produced by CO 2-laser irradiation was used as the control. Methods The bioactive glass (1-98) [9] was manufactured at Åbo Akademi Univer sity, Turku, Finland. After the normal melting procedure, the glass was cut into plates (10 x 10 x 0.5 mm), crushed into Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 225-228 doi:10.4028/www.scientific.net/KEM.240-242.225

Bioactive Glass Compositions Suitable for Repeated Heat-Treatments

The crystallization tendency for 30 experimental glasses in the system Na2O-K2O-MgOCaO-B2O3-P2O5-SiO2 was studied with thermal methods, DTA, HSM and XRD. The glasses were also immersed into simulated body fluid for 8 and 72 hours. The formation of the silica-rich gel and calcium phosphate layer on the glasses were analyzed with SEM. The in vitro behavior and crystallization tendency for heat-treated glasses were then related. This information is essential for choosing glass compositions that can be manufactured to desired products with controlled bioactivity for different applications. In general, glasses with low alkali content can tolerate heattreatment without crystallization but have less initial Si-gel formation ability and show less in vitro bioactivity than glasses with high alkali content.

Creation of Bioactive Glass Coating on Titanium by Local Laser Irradiation; Part 1: Optimization of the Processing Parameters

A focused CO2 laser beam was used to create coatings of bioactive glass on t itanium substrates. Beam position remained fixed, while a computer-controlled motor stage was utilized to scan the specimens through the beam. Processing was performed in an a tmosphere of air or N 2. Processing parameters, such as number of coating layers and laser power, were optimized to produce optimal results in terms of in vitro bioactivity of the coating.

In vitro Behavior of Fiber Bundles and Particles of Bioactive Glasses

In vitro reactions of bundles of fibers with diameters 20-500 μm and crushed glasses of fractions 500-800 μm were compared with the reactions of plates of the same bioactive glasses. The samples were immersed in simulated body fluid (SBF) for 2-7 days. After immersion the changes on the surfaces of the samples were observed by SEM/EDXA. Layer formation on the glass surface was found to vary with glass composition, sample shape and local condition of single particle/fiber. However, only some fibers or particles formed similar in vitro reaction layers as the plates. The product form did not change the in vitro bioactivity of particles or fibers exposed to the bulk immersion solution. When the glasses were used as fiber bundles or particle beds, the packing degree and the flow of body fluids within the system interfered with the reactivity. Also a clear correlation between in vivo layer formation in bone and in vitro of the glass plates could be found.

Bioactive Glass And Sol-gel-derived TiO2 Coatings

peratures of about 180°C is also present. 2) Low temperature pho phate crystalline phases, in principle capable of being used as bone implant material are produced. EDS and X-ray diffraction demonstrate that HAP is the prin· cipal phase obtained and that it has a high degree ofcrystallin. ity. 3) Transmission and polarization of light demonstrate the wide range ofapplication and innovations po iblewith the method of trapping organic molecules within the gel. Particularly, the design of devices capable of differential transmittivity is suggested to be worth pursu ing.