Calcium Phosphate-based Biomaterials Research Articles

Calcium phosphate cement scaffolds with PLGA fibers

The use of calcium phosphate-based biomaterials has revolutionized current orthopedics and dentistry in repairing damaged parts of the skeletal system. Among those biomaterials, the cement made of hydraulic grip calcium phosphate has attracted great interest due to its biocompatibility and hardening “in situ”. However, these cements have low mechanical strength compared with the bones of the human body. In the present work, we have studied the attainment of calcium phosphate cement powders and their addition to poly (co-glycolide) (PLGA) fibers to increase mechanical properties of those cements. We have used a new method that obtains fibers by dripping different reagents. PLGA fibers were frozen after lyophilized. With this new method, which was patented, it was possible to obtain fibers and reinforcing matrix which furthered the increase of mechanical properties, thus allowing the attainment of more resistant materials. The obtained materials were used in the construction of composites and scaffolds for tissue growth, keeping a higher mechanical integrity.

Advanced Biomaterials and Technologies in Implantology

Advanced Biomaterials and Technologies in Implantology

The use of calcium phosphate-based biomaterials in implant dentistry

Since calcium phosphates (CaPs) were first proposed, a wide variety of formulations have been developed and continuously optimized, some of which (e.g. calcium phosphate cements, CPCs) have been successfully commercialized for clinical applications. These CaP-based biomaterials have been shown to be very attractive bone substitutes and efficient drug delivery vehicles across diverse biomedical applications. In this article, CaP biomaterials, principally CPCs, are addressed as alternatives/complements to autogenous bone for grafting in implant dentistry and as coating materials for enhancing the osteoinductivity of titanium implants, highlighting their performance benefits simultaneously as carriers for growth factors and as scaffolds for cell proliferation, differentiation and penetration. Different strategies for employing CaP biomaterials in dental implantology aim to ultimately reach the same goal, namely to enhance the osseointegration process for dental implants in the context of immediate loading and to augment the formation of surrounding bone to guarantee long-term success.

Electrochemical microelectrodes for improved spatial and temporal characterization of aqueous environments around calcium phosphate cements

Calcium phosphate compounds can potentially influence cellular fate through ionic substitutions. However, to be able to turn such solution-mediated processes into successful directors of cellular response, a perfect understanding of the material-induced chemical reactions in situ is required. We therefore report on the application of home-made electrochemical microelectrodes, tested as pH and chloride sensors, for precise spatial and temporal characterization of different aqueous environments around calcium phosphate-based biomaterials prepared from α-tricalcium phosphate using clinically relevant liquid to powder ratios. The small size of the electrodes allowed for online measurements in traditionally inaccessible in vitro environments, such as the immediate material–liquid interface and the interior of curing bone cement. The kinetic data obtained has been compared to theoretical sorption models, confirming that the proposed setup can provide key information for improved understanding of the biochemical environment imposed by chemically reactive biomaterials.

Bioactive Polymeric Composites for Tooth Mineral Regeneration: Physicochemical and Cellular Aspects

Our studies of amorphous calcium phosphate (ACP)-based dental materials are focused on the design of bioactive, non-degradable, biocompatible, polymeric composites derived from acrylic monomer systems and ACP by photochemical or chemically activated polymerization. Their intended uses include remineralizing bases/liners, orthodontic adhesives and/or endodontic sealers. The bioactivity of these materials originates from the propensity of ACP, once exposed to oral fluids, to release Ca and PO4 ions (building blocks of tooth and bone mineral) in a sustained manner while spontaneously converting to thermodynamically stable apatite. As a result of ACP's bioactivity, local Ca- and PO4-enriched environments are created with supersaturation conditions favorable for the regeneration of tooth mineral lost to decay or wear. Besides its applicative purpose, our research also seeks to expand the fundamental knowledge base of structure-composition-property relationships existing in these complex systems and identify the mechanisms that govern filler/polymer and composite/tooth interfacial phenomena. In addition to an extensive physicochemical evaluation, we also assess the leachability of the unreacted monomers and in vitro cellular responses to these types of dental materials. The systematic physicochemical and cellular assessments presented in this study typically provide model materials suitable for further animal and/or clinical testing. In addition to their potential dental clinical value, these studies suggest the future development of calcium phosphate-based biomaterials based on composite materials derived from biodegradable polymers and ACP, and designed primarily for general bone tissue regeneration.

Ion reactivity of calcium-deficient hydroxyapatite in standard cell culture media

Solution-mediated surface reactions occur for most calcium phosphate-based biomaterials and may influence cellular response. A reasonable extrapolation of such processes observed in vitro to in vivo performance requires a deep understanding of the underlying mechanisms. We therefore systematically investigated the nature of ion reactivity of calcium-deficient hydroxyapatite (CDHA) by exposing it for different periods of time to standard cell culture media of different chemical composition (DMEM and McCoy medium, with and without osteogenic supplements and serum proteins). Kinetic ion interaction studies of principal extracellular ions revealed non-linear sorption of Ca 2+ (∼50% sorption) and K + (∼8%) as well as acidification of all media during initial contact with CDHA (48 h). Interestingly, inorganic phosphorus (P i) was sorbed from McCoy medium (∼50%) or when using osteogenic media containing β-glycerophosphate, but not from DMEM medium. Non-linear sorption data could be perfectly described by pseudo-first-order and pseudo-second-order sorption models. At longer contact time (21 days), and with frequent renewal of culture medium, sorption of Ca 2+ remained constant throughout the experiment, while sorption of P i gradually decreased in McCoy medium. In great contrast, CDHA began to release P i slowly with time when using DMEM medium. Infrared spectra showed that CDHA exposed to culture media had a carbonated surface chemistry, suggesting that carbonate plays a key role in the ion reactivity of CDHA. Our data show that different compositions of the aqueous environment may provoke opposite ion reactivity of CDHA, and this must be carefully considered when evaluating the osteoinductive potential of the material.

The effect of loading icariin on biocompatibility and bioactivity of porous β-TCP ceramic

In order to enhance the ability of calcium phosphate-based biomaterials for bone defect repair, icariin (Ica), one natural product with ability of promoting osteoblasts differentiation in vitro and enhancing bone formation in vivo, was loaded into porous β-tricalcium phosphate ceramic (β-TCP) disks. The obtained Ica-loaded porous β-TCP ceramic (Ica/β-TCP) disks were characterized by SEM. The SEM photos indicated that the disks had porous structure and the surface morphology of the porous β-TCP ceramic (β-PTCP) disks had no obvious difference from the Ica/β-TCP disks. The Ica release curve of Ica/β-TCP disks showed a burst release during the first 1day and the concentration of released Ica during the first 3days had low cytotoxicity. The loading Ica in Ica/β-TCP disks hardly affected the attachment and morphology of Ros17/28 cells, however, the Ica/β-TCP disks were favorable to supporting the proliferation and differentiation of Ros17/28 cells better compared with the β-PTCP disks. There was plenty of bone-like apatite formed on the surface of Ica/β-TCP disks soaked in SBF solution for three days. After back intramuscular implantation of rats for three months, no obvious osteogenic evidence was detected in β-PTCP disks, but new bone formation was observed in Ica/β-TCP disks. Fibrous tissues and slight inflammatory reaction was also found in the Ica/β-TCP disks and β-TCP disks. Therefore, the loading Ica did not change the biocompatibility of β-TCP ceramic, but enhanced the bioactivity of β-TCP ceramic in vivo. The Ica/β-TCP ceramic had potential to be used for bone defect repair.

Next generation calcium phosphate-based biomaterials.

It has been close to a century since calcium phosphate materials were first used as bone graft substitutes. Numerous studies conducted in the last two decades have produced a wealth of information on the chemistry, in vitro properties, and biological characteristics of granular calcium phosphates and calcium phosphate cement biomaterials. An in depth analysis of several key areas of calcium phosphate cement properties is presented with the aim of developing strategies that could lead to break-through improvements in the functional efficacies of these materials.

Surface enrichment of biomimetic apatites with biologically-active ions Mg 2+ and Sr 2+: A preamble to the activation of bone repair materials

The surface activation of calcium phosphate-based biomaterials for bone repair is an emerging route for improving bone regeneration processes. One way for such activation is through the exchange of surface calcium ions with biologically-active cations such as Mg 2+ or Sr 2+. In this work, the interactions of non-carbonated and carbonated nanocrystalline apatites with Mg 2+ and Sr 2+ were investigated by means of ion exchange experiments in solution. Langmuir-type isotherms were determined. For both Sr and Mg, a greater uptake was observed on the carbonated sample, and on both types of apatites the maximum strontium uptake was greater than that of magnesium. Inverse exchanges showed that the proportion of reversibly fixed ions after surface exchange was close to 85% for Mg and 75–80% for Sr. The results are related to the presence of a surface hydrated layer on the nanocrystals and possible exchange mechanisms are discussed. Our results favor the hypothesis of hetero-ionic surface exchanges (Mg 2+↔Ca 2+, Sr 2+↔Ca 2+) within the hydrated layer, and some analogy with octacalcium phosphate (OCP) is considered. This work should prove helpful for the control and understanding of the activation of synthetic apatite-based powders or scaffolds with bioactive elements, as well as for the global understanding of biomineralization processes.

Reaction of Zoledronate with β-Tricalcium Phosphate for the Design of Potential Drug Device Combined Systems

The reaction of aqueous Zoledronate solutions with β-tricalcium phosphate resulted in the precipitation of a crystalline Zoledronate complex on the surface of the calcium phosphate. This complex (CaNa[(HO)(C4H5N2)C(PO3)(PO3H)]·xH2O) was found to be metastable, leading to a pure calcium complex [Ca3[(HO)(C4H5N2)C(PO3)(PO3H)]2·xH2O] upon washing with water. This latter compound was found to release the bisphosphonate in phosphate buffers, in direct proportion to the phosphate concentration, while using a specific in vitro bone resorption model, an inhibition of osteoclastic activity was observed with this material. This suggested that when this composite is implanted in bone tissues, the drug will be released in greater concentration the more the bone is being resorbed, resulting in a decrease of osteoclast activity and making this drug device combination suitable for practical application as a bisphosphonate local delivery system. In addition, the chemical environment of the bisphosphonate moiety in the two reported bisphosphonate/calcium phosphate composites was probed using 31P and 23Na magic-angle-spinning NMR and two-dimensional 31P homonuclear and 31P−1H heteronuclear correlation experiments, thus giving clear evidence that modern high-resolution solid-state NMR is a powerful tool for the characterization of calcium phosphate-based biomaterials.

Calcium Phosphate Phase Transformation Produced by the Interaction of the Portland Cement Component of White Mineral Trioxide Aggregate with a Phosphate-containing Fluid

The bioactivity of mineral trioxide aggregate (MTA) has been attributed to its ability to produce hydroxyapatite in the presence of phosphate-containing fluids. It is known that stoichiometric hydroxyapatites do not exist in biological systems and do not contribute to the osteogenic potential of calcium phosphate-based biomaterials. Because Portland cement is the active ingredient in white MTA, we have characterized the calcium phosphate phases produced when set white Portland cement was immersed in phosphate-buffered saline using pH and turbidity measurements, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, electron diffraction, x-ray diffraction, and Fourier transform-infrared spectroscopy. An amorphous calcium phosphate phase was initially formed that transformed to an apatite phase, with the latter consisting of calcium-deficient, poorly crystalline, B-type carbonated apatite crystallites. Amorphous calcium phosphate is a key intermediate that precedes biological apatite formation in skeletal calcification. Thus, the clinical manifestations of bioactivity with the use of MTA may at least be partially attributed to the mineralization induction capacity of its Portland cement component.

Next Generation Calcium Phosphate-based Biomaterials

It has been close to a century since calcium phosphate materials were first used as bone graft substitutes. Numerous studies conducted in the last two decades have produced a wealth of information on the chemistry, in vitro properties, and biological characteristics of granular calcium phosphates and calcium phosphate cement biomaterials. An in depth analysis of several key areas of calcium phosphate cement properties is presented with the aim of developing strategies that could lead to break-through improvements in the functional efficacies of these materials.

In vitro Cytotoxicity of Amorphous Calcium Phosphate Composites

Calcium phosphate-based biomaterials are being increasingly used as bone substitutes in dentistry and in reconstructive and orthopedic applications because of their good biocompatibility, osteoconductivity and/or bone-bonding properties. In this study, the in vitro cytotoxicity of the amorphous calcium phosphate (ACP) filler, the copolymer matrix derived from the polymerization of a resin system and the corresponding ACP composite was analyzed utilizing cell culture techniques. The photo cured polymer was derived from an activated resin comprised of an ethoxylated bisphenol A dimethacrylate, urethane dimethacrylate, triethylene glycol dimethacrylate, and 2-hydroxyethyl methacrylate. The resin was admixed with a zirconia-ACP filler to prepare the composite. Specimens were extracted in media overnight and then MC3T3-E1 osteoblast-like cells were cultured in the extracts for 3 days. Cytoxicity was evaluated by phase contrast microscopy and an enzymatic assay for mitochondrial dehydrogenase activity (Wst-1). Cellular response to the experimental ACP composite was compared to the cellular response of commercially available light-cure orthodontic adhesive. In addition to the cytotoxicity testing the ion release profiles of ACP composites was determined. Furthermore, a degree of vinyl conversion (DVC) attained in the experimental composite and in the commercial control was compared. No adverse response regarding cell morphology and/or viability was observed with ACP composites compared to the unfilled copolymers or to the commercial adhesives. Sustained release of potentially remineralizing calcium and phosphate ions and favorable DVC of these composites confirms their value in a variety of dental and possibly orthopedic applications where anti-demineralizing/remineralizing efficacy is the primary goal.

Bone induction by porous glass ceramic made from Bioglass� (45S5)

Porous glass ceramic, which was prepared from Bioglass powder (45S5, U.S. Biomaterials) by foaming with diluted H(2)O(2) solution and sintering at 1000 degrees C for 2 h, was implanted as cylinders (5 mm in diameter and 6 mm in length) in thigh muscles of dogs for 3 months. Histological observation was made on thin un-decalcified sections. Bone formation was histologically found in pores of all implants (X16) retrieved from 16 dogs. The bone tissue was also identified with backscattered scanning electron microscopy observation (BSE) and energy dispersive X-ray microanalysis (EDX). This is the first report of bone induction in soft tissues of animals by glass ceramic that has long been recognized as a bioactive (osteoconductive) biomaterial. The present results justify the impetus to investigate the osteoinductivity of calcium phosphate-based biomaterials, to study the mechanism of bone induction (osteoinduction) by calcium phosphate-based biomaterials, to develop osteoinductive calcium phosphate-based biomaterials, and to examine the relation between osteoinduction and osteoconduction.

The application of ion beam analysis to calcium phosphate-based biomaterials.

Ion beam technology may be applied in a straightforward fashion to the analysis and modification of biomaterials. For analytical purposes, characterization using megaelectron-volt He2+ ions provides a standardless, nondestructive means for accurately quantifying the composition of material surfaces and the thickness of thin films. In this study, three complementary ion backscattering techniques were utilized to characterize hydroxyapatite (HA) films: Rutherford backscattering spectrometry (RBS) can determine composition and amounts of elements heavier than He; forward recoil elastic spectrometry (FRES) can determine hydrogen content; resonance-enhanced RBS can quantify small amounts of light elements, e.g. carbon, by choosing a particular incident beam energy resulting in excitation of the light element nucleus. At this resonance energy, the scattering cross section greatly increases, improving elemental sensitivity. Sol-gel chemistry was used to synthesize HA films by spin coating and annealing in a rapid thermal processor. Using these techniques, the chemical composition of unfired films was Ca1.63O5.4H1.8C0.24P with a thickness of 3.01 x 10(18) atoms/cm2 and after firing at 800 degrees C as Ca1.66O4.0H0.26C0.09P with a thickness of 2.11 x 10(18) atoms/cm2. This compares favorably to stoichiometric HA, which has a composition of Ca1.67O4.33H0.33P.