At present, strong requirements in orthopaedics are still to be met, both in bone and joint substitution and in the repair and regeneration of bone defects. In this framework, tremendous advances in the biomaterials field have been made in the last 50 years where materials intended for biomedical purposes have evolved through three different generations, namely first generation (bioinert materials), second generation (bioactive and biodegradable materials) and third generation (materials designed to stimulate specific responses at the molecular level). In this review, the evolution of different metals, ceramics and polymers most commonly used in orthopaedic applications is discussed, as well as the different approaches used to fulfil the challenges faced by this medical field.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2008.0151

Biomaterials in orthopaedics.

Bioactive glasses react chemically with the body fluids. The reaction product is an apatite, which, with the intervention of biological drivers, assists the generation of bone matrix and bone growth. The main application of these bioactive glasses in the clinical field is the filling of osseous cavities, manufacture of small parts for middle ear bone replacement and maxilofacial reconstruction and dental applications. Thanks to advances in related medical technologies, bioactive glasses are now undergoing a new stage of development, resulting in different mechanical properties, drug de

Glasses with Medical Applications

Over the past 30 years, an enormous array of biomaterials proposed as ideal scaffolds for cell growth have emerged, yet few have demonstrated clinical efficacy. Biomaterials, regardless of whether they are permanent or biodegradable, naturally occurring or synthetic, need to be biocompatible, ideally osteoinductive, osteoconductive, integrative, porous and mechanically compatible with native bone to fulfill their desired role in bone tissue engineering. These materials provide cell anchorage sites, mechanical stability and structural guidance and in vivo, provide the interface to respond to physiologic and biologic changes as well as to remodel the extracellular matrix in order to integrate with the surrounding native tissue. Calcium phosphate ceramics and bioactive glasses were introduced more than 30 years ago as bone substitutes. These materials are considered bioactive as they bond to bone and enhance bone tissue formation. The bioactivity property has been attributed to the similarity between the surface composition and structure of bioactive materials, and the mineral phase of bone. The drawback in using bioactive glasses and calcium phosphate ceramics is that close proximity to the host bone is necessary to achieve osteoconduction. Even when this is achieved, new bone growth is often strictly limited because these materials are not osteoinductive in nature. Bone has a vast capacity for regeneration from cells with stem cell characteristics. Moreover, a number of different growth factors including bone morphogenetic proteins, have been demonstrated to stimulate bone growth, collagen synthesis and fracture repair both in vitro and in vivo. Attempts to develop a tissue-engineering scaffold with both osteoconductivity and osteoinductivity have included loading osteoinductive proteins and/or osteogenic cells on the traditional bioactive materials. Yet issues that must be considered for the effective application of bioceramics in the field of tissue engineering are the degree of bioresorption and the poor mechanical strength. The synthesis of a new generation of biomaterials that can specifically serve as tissue engineering scaffolds for drug and cell delivery is needed. Nanotechnology can provide an alternative way of processing porous bioceramics with high mechanical strength and enhanced bioactivity and resorbability.

Bone reconstruction: from bioceramics to tissue engineering.

Bioactive glasses contain oxides of calcium, sodium, phosphorus, and silicon in a proportion that provides the material with surface activity and concomitantly with the property of forming a strong bond with bone. Bioactive glasses have been tested as bone substitutes in different clinical situations. In an aqueous environment, Ca2+, Na+, PO43-, and Si4+ are released from the glass, resulting in a rise in pH and in osmotic pressure in its vicinity. Since these are factors that potentially influence the viability of oral microorganisms at the dentogingival margin, we studied the effects of bioactive glass S53P4 on the oral microorganisms Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Actinomyces naeslundii, Streptococcus mutans, and Streptococcus sanguis. This was done by incubating each microbe in a suspension, in the presence of bioactive glass S53P4 in powder form. A. naeslundii was found to lose its viability within 10 min under the experimental conditions. A. actinomycetemcomitans, P....

Antibacterial effects of a bioactive glass paste on oral microorganisms

Effect of pH and ionic strength on the reactivity of Bioglass 45S5.

The calcium phosphate formation at the surface of bioactive glass was studied in vitro. Glass rods and grains were immersed in different aqueous solutions and studied by means of scanning electron microscopy and energy dispersive x-ray analysis. Surface morphological changes and weight loss of corroded grains were monitored. In-depth compositional profiles were determined for rods immersed in the different solutions. The solutions used were tris-buffer (tris-hydroxymethylaminomethane + HCl), tris-buffer prepared using citric acid (tris-hydroxymethylaminomethane + C6H8O7.H2O), and a simulated body fluid, SBF, containing inorganic ions close in concentration to those in human blood plasma. It was found that the calcium phosphate formation at the surface of bioactive glass in vitro proceeds in two stages. When immersing the glass in tris or in SBF a Ca,P-rich surface layer forms. This accumulation takes place within the silica structure. Later, apatite crystals forming spherulites appear on the surface. The Ca/P-ratio of initially formed calcium phosphate was found to be about unity. It is proposed that this is due to bonding of phosphate to a silica gel. The surface is stabilized, i.e., leaching is retarded, by the rapid Ca,P-accumulation within the silica structure before apatite crystals are observed on the surface. It is proposed that the initially formed calcium phosphate is initiated within the silica gel. The crystallizing surface provides nucleation sites for extensive apatite formation on the glass surface. In the presence of citrate no Ca,P-accumulation occur at the glass surface, but soluble Ca-citrate complexes form. By comparing the weight loss during corrosion in tris with that in the calcium and phosphate containing SBF, it is possible to establish whether the glass can induce apatite formation at its surface or not.

Calcium phosphate formation at the surface of bioactive glass in vitro

Five glass compositions in or near the bioactive region in the system SiO2Na2OCaOP2O5Al2O3 were studied in vitro by immersion in Tris buffer. The Si concentration can be taken as a measure of the amount of dissolved glass, whereas the Na concentration can be used to estimate the thickness of the Si-rich (Si gel) layer. Upon immersing a bioactive glass into Tris buffer, a surface layer of a few micrometer thickness is dissolved during the first 8 h. During the first few hours of immersion, the rate of dissolution of the glass network is equal to or exceeds that of the growth of the Si-rich layer. If the glass contains Al2O3, most of the aluminum that would be released due to dissolution of the silica network is enriched in the Si-rich surface layer that forms due to leaching. Al2O3 is not only bonded by the Si gel but also interferes with formation of culcium phosphate. © 1993 John Wiley & Sons, Inc.

Ö. H. Andersson

Papers

Calcium phosphate formation at the surface of bioactive glass in vitro

Dissolution, leaching, and Al2O3 enrichment at the surface of bioactive glasses studied by solution analysis.