Apatite Biominerals

Calcium phosphate apatites offer outstanding biological adaptability that can be attributed to their specific physico-chemical and structural properties. The aim of this review is to summarize and discuss the specific characteristics of calcium phosphate apatite biominerals in vertebrate hard tissues (bone, dentine and enamel). Firstly, the structural, elemental and chemical compositions of apatite biominerals will be summarized, followed by the presentation of the actual conception of the fine structure of synthetic and biological apatites, which is essentially based on the existence of a hydrated layer at the surface of the nanocrystals. The conditions of the formation of these biominerals and the hypothesis of the existence of apatite precursors will be discussed. Then, we will examine the evolution of apatite biominerals, especially during bone and enamel aging and also focus on the adaptability of apatite biominerals to the biological function of their related hard tissues. Finally, the diagenetic evolution of apatite fossils will be analyzed

Tetracycline-Loaded Biomimetic Apatite: An Adsorption Study

Biomimetic apatites are appealing compounds for the elaboration of bioactive bone-repair scaffolds due to their intrinsic similarity to bone mineral. Bone surgeries are however often heavy procedures, and the infiltration of pathogens may not be totally avoided. To prevent their development, systemic antibiotic prophylaxis is widespread but does not specifically target surgical sites and involves doses not always optimized. A relevant alternative is a preliminary functionalization by an infection-fighting agent. In this work, we investigated from a physicochemical viewpoint the association of a wide-spectrum antibiotic, tetracycline (TC), and a biomimetic nanocrystalline apatite previously characterized. TC adsorption kinetics and isotherm were thoroughly explored. Kinetic data were fitted to various models(pseudo-first-order, pseudo-second-order, general kinetic model of order n, Elovich, double-exponential, and purely diffusive models). The best fit was found for a doubleexponential kinetic model or with a decimal reaction order of 1.4, highlighting a complex process with such TC molecules which do not expose high-affinity end groups for the surface of apatite. The adsorption isotherm was perfectly fitted to the Sips (Langmuir−Freundlich) model, while other models failed to describe it, and the Sips exponent greater than unity (1.08) suggested a joint impact of surface heterogeneity and positive cooperativity between adsorbed molecules. Finally, preliminary insights on TC release from pelletized nanocrystalline apatite, in aqueous medium and neutral pH, were obtained using a recirculation cell, indicating a release profile mainly following a Higuchi-like diffusion-limited rate. This work is intended to shed more light on the interaction between polar molecules not exhibiting high-affinity end groups and biomimetic apatites and is a starting point in view of the elaboration of biomimetic apatite-based bone scaffolds functionalized with polar organic drugs for a local delivery

From Coagulation to Oral Surgery Application: Platelets in Bone Regeneration

International audienceThe complexity of the treatment of tissue lesions, particularly bone lesions, in regenerative medicine depends on the origin of the substance loss (traumatic, tumoral, infectious, etc.), its size and mechanical requirements. In the field of dental surgery, the need to ensure rapid regeneration of injured bone tissue for periodontal, post-extractional or pre-implant corrective surgery leads dental surgeons to have a large number of biomaterials in their therapeutic arsenal. The mineral materials are most often used because of their chemical composition which is close to bone’s mineral phase. They also present a resorption time in agreement with the time of formation of new bone.However their benefits are inconstant and the need of new bioactive structures, well accepted by the host, and favoring tissue healing has grown. Here is the place for platelet concentrates such as Platelet Rich Plasma (PRP) and Platelet Rich Fibrin (PRF) which are rich in growth factors, cytokines and others proteins. PRF became the most commonly used in the last decade as it is easier to handle with its polymerized form which mimics an extracellular matrix favorable to cell proliferation and differentiation. A new option, called platelet lysate, has recently been highlighted in the general field of tissue regeneration and has the advantage of making platelet’s content directly available. Proteins concentrations are increased in these products even if their liquid form complicates their use in daily practice. This mini-review sums up the main clinical interests for the use of platelet concentrates and the new perspectives in the field of alveolar bone regeneration especially with platelet lysate

Biological mineralizations based on calcium phosphates

The mineral fractions of bones and teeth are non-stoichiometric apatite crystals. Their morphology, dimensions, composition and reactivity are adapted to their biological function. Bone apatites are made of very reactive nanocrystals possessing, on their surface, a structured hydrated layer responsible for their biological properties. This unstable layer becomes progressively and unavoidably transformed into a relatively inert apatite lattice. In spite of very different time periods, the laws that determine the biological and diagenetic evolution of bone mineral are the same, especially in processes involving dissolution-re-precipitation phenomena

Strontium-loaded mineral bone cements as sustained release systems : Compositions, release properties, and effects on human osteoprogenitor cells

This study aims to evaluate in vitro the release properties and biological behavior of original compositions of strontium (Sr)-loaded bone mineral cements. Strontium was introduced into vaterite CaCO3-dicalcium phosphate dihydrate cement via two routes: as SrCO3 in the solid phase (SrS cements), and as SrCl2 dissolved in the liquid phase (SrL cements), leading to different cement compositions after setting. Complementary analytical techniques implemented to thoroughly investigate the release/dissolution mechanism of Sr-loaded cements at pH 7.4 and 37°C during 3 weeks revealed a sustained release of Sr and a centripetal dissolution of the more soluble phase (vaterite) limited by a diffusion process. In all cases, the initial burst of the Ca and Sr release (highest for the SrL cements) that occurred over 48 h did not have a significant effect on the expression of bone markers (alkaline phosphatase, osteocalcin), the levels of which remained overexpressed after 15 days of culture with human osteoprogenitor (HOP) cells. At the same time, proliferation of HOP cells was significantly higher on SrS cements. Interestingly, this study shows that we can optimize the sustained release of Sr2þ, the cement biodegradation and biological activity by controlling the route of introduction of strontium in the cement paste

From compressibility to structural investigation of sodium dodecyl sulphate — Part 1: Powder and tablet physico-chemical characteristics

As a part of a study on detergent tablets, investigations were carried out to elucidate the compression behavior of a powdered surfactant, sodium dodecyl sulphate (SDS), based on a comparison with the main component of the formulation, i.e. the chorine provider (DCCNa). The compacted SDS exhibited poor cohesion as well as delayed dissolution whatever the compression pressure. The microscopic observations and the mercury porosimetry measurements both demonstrated that a residual porosity existed in the tablets but the dissolution times were always long. A modification of SDS in contact with water, forming a structure like a gel, probably occurred, inducing the closing of the pores and thereby limiting the water intrusion into the tablets

Mechanical properties of self-setting composites: influence of the carboxymethylcellulose content and hydration state

The impact of the carboxymethylcellulose (CMC) content on the mechanical properties of calcium phosphate–calcium carbonate–CMC composite cements for bone substitution was investigated. The relevance of the compressive test conditions (wet or dried composite cements) is discussed and models are proposed to better understand the mechanisms involved in the mechanical properties of the composite materials. Based on a modellisation using the Voigt model for dried composite cements, we show that a minimum of CMC content of around 10–20 % is needed to enhance the mechanical properties of the dried composite materials (up to 86 MPa for the composite including 50 wt% CMC) through the formation of a mineral–organic entangled network. The compressive strength of the wet samples is low (\3 MPa) but the gain observed in the dried composites is encouraging and might be extrapolated to wet conditions if we were to use a less hydrophilic polysaccharid

From Coagulation to Oral Surgery Application: Platelets in Bone Regeneration

The complexity of the treatment of tissue lesions, particularly bone lesions, in regenerative medicine depends on the origin of the substance loss (traumatic, tumoral, infectious, etc.), its size and mechanical requirements. In the field of dental surgery, the need to ensure rapid regeneration of injured bone tissue for periodontal, post-extractional or pre-implant corrective surgery leads dental surgeons to have a large number of biomaterials in their therapeutic arsenal. The mineral materials are most often used because of their chemical composition which is close to bone’s mineral phase. They also present a resorption time in agreement with the time of formation of new bone.However their benefits are inconstant and the need of new bioactive structures, well accepted by the host, and favoring tissue healing has grown. Here is the place for platelet concentrates such as Platelet Rich Plasma (PRP) and Platelet Rich Fibrin (PRF) which are rich in growth factors, cytokines and others proteins. PRF became the most commonly used in the last decade as it is easier to handle with its polymerized form which mimics an extracellular matrix favorable to cell proliferation and differentiation. A new option, called platelet lysate, has recently been highlighted in the general field of tissue regeneration and has the advantage of making platelet’s content directly available. Proteins concentrations are increased in these products even if their liquid form complicates their use in daily practice. This mini-review sums up the main clinical interests for the use of platelet concentrates and the new perspectives in the field of alveolar bone regeneration especially with platelet lysate

Injectability, microstructure and release properties of sodium fusidate-loaded apatitic cement as a local drug-delivery system

The introduction of an antibiotic, sodiumfusidate (SF), into the liquid phase of calcium carbonate–calcium phosphate(CaCO3–CaP) bone cement was evaluated, considering the effect of the liquid to powder ratio (L/P) on the composition and microstructure of the set cement and the injectability of the paste. In all cases, we obtained set cements composed mainly of biomimetic carbonated apatite analogous to bone mineral. With this study,we evidenced a synergistic effect of the L/P ratio and SF presence on the injectability (i.e., the filter-pressing phenomenon was suppressed) and the setting time of the SF-loaded cement paste compared to reference cement(without SF). In addition, the in vitro study of SF release, according to the European Pharmacopoeia recommendations, showed that, regardless of the L/P ratio, the cement allowed a sustained release of the antibiotic over 1 month in sodiumchloride isotonic solution at 37 °C and pH 7.4; this release is discussed considering the microstructure characteristics of SF-loaded cements (i.e., porosity, pore-size distribution) before and after the release test. Finally, modelling antibiotic release kinetics with severalmodels indicated that the SF releasewas controlled by a diffusion mechanism

Surface properties of biomimetic nanocrystalline apatites; applications in biomaterials

Several types of nanocrystalline apatites have been described, obtained in various ways. Among these, biomimetic nanocrystalline apatites (BNA), whose characteristics are close to those of biological apatites, have been shown to exhibit specific properties mainly related to their surface structure and composition. The aim of this paper is to review current knowledge of these compounds