Manufacturing mechanical characterization and In vitro Performance of bioactive glass 13-93 Fibers E Pirhonen, H. Niranen, T. Niemela, 1 M. Brink, 2 P. Tormala' Tampere University of Technology, Institute of Biomaterials, Tampere, Finland 2 Sydvast Polytechnic, Malmgatan 5, Abo, Finland Received 11 March 2005: revised 21 June 2005: accepted 22 June 2005 shedonline28October2005inWileyInterscience(www.interscience.wileycom).Dol:10.1002/jbn.b Abstract: Fibers were manufactured from the bioactive glass 13-93 by melt spinning. The fibers were further characterized by measuring their tensile and flexural strength, and their in vitro performance was characterized by immersing them in simulated body fluid, which analyzed changes in their mass, their flexural strength, and surface reactions. The strength of glass fibers is highly dependent on fiber diameter, test method, and possible surface flaws, for example, cracks due to abrasion. In this study, the thinnest fibers(diameter between 24 and 33 um) possessed the highest average tensile strength of 861 MPa. The flexural strength nitially 1353.5 MPa and it remained at that level for 2 weeks. The Weibull modulus for both ensile and flexural strength values was initially about 2. 1. The flexural strength started to decrease and was only 20%o of the initial strength after 5 weeks. During the weeks 5-40, only a slight decrease was detected. The fiexural modulus decreased steadily from 68 to 40 GPa during this period. The weight of the samples initially decreased due to leaching of ions and further started to increase due to precipitation of calcium phosphate on the fiber surfaces. The mass change of the bioactive glass fibers was dependent on the surface area rather than initial weight of the sample The compositional analysis of the fiber surface after 24 h and 5 weeks immersion did confirm the initial leaching of ions and later the precipitation of a calcium phosphate layer on the bioactive glass 13-93 fiber surface in vitro. 2005 Wiley Periodicals, Inc J Biomed Mater Res Part B: Appl Biomater 77B: 227-233, 2006 Keywords bioactive glass; mechanica al properties; degradation; fiber NTRODUCTION phosphorus oxides, and silica. Brink et al. studied different glasses in a system containing boron, sodium, potassium, Tissue engineering has brought new challenges to the area of magnesium, calcium and phosphorus oxides, and silica. They biomaterials research. Especially in bone and cartilage tissue found that some of the glasses had a wide working range, engineering applications, there is a need for even more suit- which enables the production of fibers. One of the most able scaffold materials to be developed. Bioactive glasses promising glasses was the glass coded 13-93. Histological have been clinically used over three decades and have been studies by Brink et al. on glass 13-93 rods have shown that this found to possess an osteoconductive nature. Also an osteo- glass is bioactive in bone tissue and slowly resorbable in soft promotive performance of bioactive glass, namely Bio- tissue . In the early tests on bioactive glass 13-93, thin fibers glass@, has been reported. Therefore, bioactive glasses are were also produced by drawing from the melt. The in vivo considered advantageous compared with many other materi- performance of these fibers was tested by implanting fit als used as bone fillers today. For clinical purpose, the use of subcutaneously in rats. The resorbtion of fibers was initiated almost immediately, but no inflammation reaction was detect the use of bioactive glass as fibers has provoked lots of ed. 0 The use of bioactive glass as fibers does extend the variety interest amongst a number of research groups. Vita Finzi of possible implants. For example, there is Zalman et al. developed bioactive glass fibers with glass bioactive glass fibers as a reinforcing phase in biopolymers and system containing sodium, potassium, calcium, aluminum, in the manufacturing of porous scaffolds. 1.12 The aim of this study was to manufacture bioactive glass 13-93 fibers and study the mechanical properties of these orrespondence to: E Pirhonen, Inion Oy, Laakirinkatu 2, F1-33520 Tampere. fibers when immersed in simulated body fluid(SBF). The Contract grant sponsor: Academy of Finland mass loss and surface reactions of in vitro conditions were o 2005 Wiley Periodicals, Inc also studiedManufacturing, Mechanical Characterization, and In Vitro Performance of Bioactive Glass 13–93 Fibers E. Pirhonen,1 H. Niiranen,1 T. Niemela¨ ,1 M. Brink,2 P. To¨ rma¨ la¨ 1 1 Tampere University of Technology, Institute of Biomaterials, Tampere, Finland 2 Sydva¨ st Polytechnic, Malmgatan 5, Åbo, Finland Received 11 March 2005; revised 21 June 2005; accepted 22 June 2005 Published online 28 October 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.b.30429 Abstract: Fibers were manufactured from the bioactive glass 13–93 by melt spinning. The fibers were further characterized by measuring their tensile and flexural strength, and their in vitro performance was characterized by immersing them in simulated body fluid, which analyzed changes in their mass, their flexural strength, and surface reactions. The strength of glass fibers is highly dependent on fiber diameter, test method, and possible surface flaws, for example, cracks due to abrasion. In this study, the thinnest fibers (diameter between 24 and 33
m) possessed the highest average tensile strength of 861 MPa. The flexural strength was initially 1353.5 MPa and it remained at that level for 2 weeks. The Weibull modulus for both tensile and flexural strength values was initially about 2.1. The flexural strength started to decrease and was only
20% of the initial strength after 5 weeks. During the weeks 5– 40, only a slight decrease was detected. The flexural modulus decreased steadily from 68 to 40 GPa during this period. The weight of the samples initially decreased due to leaching of ions and further started to increase due to precipitation of calcium phosphate on the fiber surfaces. The mass change of the bioactive glass fibers was dependent on the surface area rather than initial weight of the sample. The compositional analysis of the fiber surface after 24 h and 5 weeks immersion did confirm the initial leaching of ions and later the precipitation of a calcium phosphate layer on the bioactive glass 13–93 fiber surface in vitro. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 77B: 227–233, 2006 Keywords: bioactive glass; mechanical properties; degradation; fiber INTRODUCTION Tissue engineering has brought new challenges to the area of biomaterials research. Especially in bone and cartilage tissue engineering applications, there is a need for even more suit￾able scaffold materials to be developed.1,2 Bioactive glasses have been clinically used over three decades and have been found to possess an osteoconductive nature. Also an osteo￾promotive performance of bioactive glass, namely Bio￾glass®, has been reported.3–5 Therefore, bioactive glasses are considered advantageous compared with many other materi￾als used as bone fillers today. For clinical purpose, the use of bioactive glasses has mainly been limited to particulates, but the use of bioactive glass as fibers has provoked lots of interest amongst a number of research groups. Vita Finzi Zalman et al. developed bioactive glass fibers with glass system containing sodium, potassium, calcium, aluminum, phosphorus oxides, and silica.6 Brink et al. studied different glasses in a system containing boron, sodium, potassium, magnesium, calcium and phosphorus oxides, and silica. They found that some of the glasses had a wide working range, which enables the production of fibers.7 One of the most promising glasses was the glass coded 13–93. Histological studies by Brink et al. on glass 13–93 rods have shown that this glass is bioactive in bone tissue and slowly resorbable in soft tissue.8,9 In the early tests on bioactive glass 13–93, thin fibers were also produced by drawing from the melt. The in vivo performance of these fibers was tested by implanting fibers subcutaneously in rats. The resorbtion of fibers was initiated almost immediately, but no inflammation reaction was detect￾ed.10 The use of bioactive glass as fibers does extend the variety of possible implants. For example, there is an interest to use bioactive glass fibers as a reinforcing phase in biopolymers and in the manufacturing of porous scaffolds.11,12 The aim of this study was to manufacture bioactive glass 13–93 fibers and study the mechanical properties of these fibers when immersed in simulated body fluid (SBF). The mass loss and surface reactions of in vitro conditions were also studied. Correspondence to: E. Pirhonen, Inion Oy, La¨a¨ka¨rinkatu 2, FI-33520 Tampere, Finland (e-mail: eija.pirhonen@inion.fi) Contract grant sponsor: Academy of Finland © 2005 Wiley Periodicals, Inc. 227