Ceramics used for the repair and reconstruction of diseased or damaged parts of the musculo-skeletal system, termed bioceramics, may be bioinert (alumina, zirconia), resorbable (tricalcium phosphate), bioactive (hydroxyapatite, bioactive glasses, and glass-ceramics), or porous for tissue ingrowth (hydroxyapatite-coated metals, alumina). Applications include replacements for hips, knees, teeth, tendons, and ligaments and repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jaw bone, spinal fusion, and bone fillers after tumor surgery. Carbon coatings are thromboresistant and are used for prosthetic heart valves. The mechanisms of tissue bonding to bioactive ceramics are beginning to be understood, which can result in the molecular design of bioceramics for interfacial bonding with hard and soft tissues. Composites are being developed with high toughness and elastic modulus match with bone. Therapeutic treatment of cancer has been achieved by localized delivery of radioactive isotopes via glass beads. Development of standard test methods for prediction of long-term (20-year) mechanical reliability under load is still needed.

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Bioceramics: From Concept to Clinic

Bioceramics : from concept to clinic

Biodegradable and bioactive porous polymer/inorganic composite scaffolds for bone tissue engineering

Historically the function of biomaterials has been to replace diseased or damaged tissues. First generation biomaterials were selected to be as bio-inert as possible and thereby minimize formation of scar tissue at the interface with host tissues. Bioactive glasses were discovered in 1969 and provided for the first time an alternative; second generation, interfacial bonding of an implant with host tissues. Tissue regeneration and repair using the gene activation properties of Bioglass® provide a third generation of biomaterials. This article reviews the 40 year history of the development of bioactive glasses, with emphasis on the first composition, 45S5 Bioglass®, that has been in clinical use since 1985. The steps of discovery, characterization, in vivo and in vitro evaluation, clinical studies and product development are summarized along with the technology transfer processes.

The story of Bioglass

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.

Summary

Calcium-phosphate ceramic particulates are often used as filler material for enhanced repair of dental bone defects. Although evidence of bone ingrowth in the scaffold of these particles has been described, it is not observed consistently. Fibrous tissue often encapsulates these particles, which can subsequently become dispersed into the surrounding tissues or even exfoliated. The aim of the present study was to evaluate bioactive glass granules (Biogran ™)* as a filler for osseous lesions, and to compare them with two commercially available Hydroxylapatite (HA) granules. The particulates were implanted in the jaws of five beagle dogs, resected and evaluated after 1, 2, 3, 6 and 12 months of implantation. Histological analysis revealed an improvement in repair of all the lesions. A massive osteoconductive bone growth was seen near the walls of the bony cavities, but in greater amounts around the bioactive glass granules than around the HA materials. On top of this massive growth a trabecular bone growth was observed in the centre of the bony cavities. These trabeculae were associated with the glass particles, which exhibited osteophilic properties, while fibrous tissue separated the bone tissue from the HA particles. The centres of many of the particles are excavated, and are subsequently filled by newly formed bone tissue. This internally formed bone tissue is not necessarily connected to the surrounding bone tissue, and functions as a nucleation site for further bone repair. For the mesenchymal cells within the eroded glass particles this inner environment acts as a stimulus to differentiate into osteoblasts and to start their osteogenetic potential. This phenomenon was not observed around the HA materials. If the latter were surrounded by fibrous tissue, disintegration of the surface by giant cells was observed.

Bioactive glass particulate material as a filler for bone lesions

Bioactive glass can form an effective bond with bone. Essential for this connection are the interfacial reactions which lead to the development of a Si-rich film covered by a CaP-rich film. The presence of these layers can be demonstrated clearly by EDX analysis of fiber-reinforced bioactive glass and bulk bioactive glass implants installed for 4 and 16 months in the partial edentulous jaws of beagle dogs. EDX analysis reveals three types of microchemical interface. The first type develops when the implant is bonded to bone. Here, a smooth transition of the CaP profile can be observed between bioactive glass and the bone, thus providing for a compositional gradient between the implant and the surrounding tissues. The second type is seen when the implant surface is surrounded by fibrous tissue. This causes a discontinuity in the CaP profile. The third type is characterized by a gradual decrease in the Ca and P concentrations across the interface, caused by the presence of Ca and P in the fibrous tissue near the implant surface. This suggests that the interface is dynamic in time and transforms to a functionally better optimized interface. EDX analysis does not reveal any metal fiber ion contamination of the outer glass rim of the implant. When stainless-steel or wrought Co-Cr alloy is exposed to the surrounding fluids, the interfacial osteogenesis is disturbed, possibly by a synergistic effect of glass ions and metal ions. Exposure of titanium does not interfere with this osteogenesis. The bone bonding can also be influenced by surgical trauma. However, with precise implantation techniques, an enhancement of bone growth by osteoconductivity can be measured.

Interfacial analysis of fiber-reinforced bioactive glass dental root implants.

Summary

Bioactive glass has the ability to bond with bone, but it cannot be used as a load bearing device due to its limited mechanical properties. By reinforcing bioactive glass with a ductile second phase, a structurally reliable material is obtained.



The aim of the present study was to evaluate histologically and morphometrically the interfacial behaviour of submerged composite dental root implants. Therefore, bulk and composite implants were subgingivally installed in the partially edentulous jaws of Beagle dogs and harvested after 4 and 16 months.



Histologically, the connection between the implants and bone tissue could be clearly demonstrated. This bone connection is mainly located at the cortical bone level. In the vicinity of the infraalveolar nerve a fibrous tissue contact was found.



It is shown that surgical trauma, motion at the glass to tissue interface, and gross ion dissolution from the material adversely affect the interfacial osteogenesis. If these factors are controlled, bone bonding is found over a larger area than the initial area of contact between the implant and bone tissue. This means that bone grows out along the implant surface, starting from the initial contact area.



No difference was observed between the interfacial behaviour of bulk bioactive glass and intact fibre reinforced bioactive glass implants.

Histological and histomorphometrical analysis of bioactive glass and fibre reinforced bioactive glass dental root implants.

Finishing procedures for the preparation of crown margins

Bone bonding of surface active glasses paralleled compositional changes of the reacting glass surface. These reaction layers, however, were susceptible to mechanical failure upon loading. The objective of the current work was to study the relationship between the kinetics of the thickness of the interracial layers and the glass composition. Specifically the composition was changed by adding CaF2 and by increasing the Si02 concentration. Three samples of each of five glass compositions were implanted in the partial edentulous jaws of beagle dogs. After 3 months, they were resected and prepared for histological analysis with the implants in situ. Bone bonding was observed at the surface of all five glass compositions. The glasses with low CaF2 content showed large areas of bone bonding and the bone growth along the implant surface was enhanced by osteoconductivity. The bone bonding around glasses with high CaF 2 content was rather patchy. Small areas of bone bonding alternated with small islands of fibrous tissue contact. 0steoconductivity was observed also around these glass compositions. Scanning electron microscopy analysis revealed that the thickness of the reacted glass decreased with an increase of the CaF 2 concentration. The glasses with high CaF 2 concentrations showed spots of excessive ion dissolution which could delay the bone bonding in this area. This was due probably to local variations of the microstructure of the glass. CaF2 addition increased the risk for crystallization of the glass. It was suggested that the interface boundaries between the crystalline and amorphous phases were more susceptible for ion dissolution.

M De Clercq

Papers

Bioactive glass particulate material as a filler for bone lesions

Interfacial analysis of fiber-reinforced bioactive glass dental root implants.

Histological and histomorphometrical analysis of bioactive glass and fibre reinforced bioactive glass dental root implants.

Finishing procedures for the preparation of crown margins

Interfacial tissue response to bioactive glasses with reduced surface reactivity