Synthetic amorphous calcium phosphates (ACPs): preparation, structure, properties, and biomedical applications.

Amorphous calcium phosphates (ACPs) represent a metastable amorphous state of other calcium orthophosphates (abbreviated as CaPO) possessing variable compositional but rather identical glass-like physical properties, in which there are neither translational nor orientational long-range orders of the atomic positions. In nature, ACPs of a biological origin are found in the calcified tissues of mammals, some parts of primitive organisms, as well as in the mammalian milk. Manmade ACPs can be synthesized in a laboratory by various methods including wet-chemical precipitation, in which they are the first solid phases, precipitated after a rapid mixing of aqueous solutions containing dissolved ions of Ca and PO in sufficient amounts.

Functionalized calcium orthophosphates (CaPO) and their biomedical applications.

Due to the chemical similarity to natural calcified tissues (bones and teeth) of mammals, calcium orthophosphates (abbreviated as CaPO) appear to be good biomaterials for creation of artificial bone grafts. However, CaPO alone have some restrictions, which limit their biomedical applications. Various ways have been developed to improve the properties of CaPO and their functionalization is one of them.

The effect of simulating body fluid on the structural properties of hydroxyapatite synthesized in the presence of citric acid.

In present work, the effect of citric acid (CA) addition in different amounts (0, 1, 5 and 10 ml) on the structure of hydroxyapatite (HAp) was investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy techniques. The crystallite dimensions, lattice parameters, unit cell volume, crystallinity percentage and Ca/P molar ratio were found to be affected by the CA content. To investigate the influence of CA on the bioactive properties of the HAp samples and to determine the optimum amount of CA, in vitro soaking tests in simulated body fluid (SBF) were performed.

Biphasic calcium phosphates bioceramics (HA/TCP): Concept, physicochemical properties and the impact of standardization of study protocols in biomaterials research.

Biphasic calcium phosphates (BCP) bioceramics have become the materials of choice in various orthopedic and maxillofacial bone repair procedures. One of their main advantages is their biodegradation rate that can be modified by changing the proportional ratio of the composition phases. For enhanced bone tissue regeneration, the bioactivity of BCP should be increased by optimizing their physicochemical properties.

Calcium orthophosphates (CaPO): occurrence and properties.

The present overview is intended to point the readers' attention to the important subject of calcium orthophosphates (CaPO). This type of materials is of the special significance for the human beings because they represent the inorganic part of major normal (bones, teeth and antlers) and pathological (i.e.

Calcium Orthophosphate-Containing Biocomposites and Hybrid Biomaterials for Biomedical Applications.

The state-of-the-art on calcium orthophosphate (CaPO4)-containing biocomposites and hybrid biomaterials suitable for biomedical applications is presented. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through the successful combinations of the desired properties of matrix materials with those of fillers (in such systems, CaPO4 might play either role), innovative bone graft biomaterials can be designed.

Strontium substituted hydroxyapatites: Synthesis and determination of their structural properties, in vitro and in vivo performance.

The objective of this study is to present a detailed report related to the synthesis and characterization of strontium substituted hydroxyapatites. Based on this purpose, hydroxyapatite (HAp) bioceramics with different amounts of strontium (e.g.

Calcium orthophosphate deposits: Preparation, properties and biomedical applications.

Since various interactions among cells, surrounding tissues and implanted biomaterials always occur at their interfaces, the surface properties of potential implants appear to be of paramount importance for the clinical success. In view of the fact that a limited amount of materials appear to be tolerated by living organisms, a special discipline called surface engineering was developed to initiate the desirable changes to the exterior properties of various materials but still maintaining their useful bulk performances. In 1975, this approach resulted in the introduction of a special class of artificial bone grafts, composed of various mechanically stable (consequently, suitable for load bearing applications) implantable biomaterials and/or bio-devices covered by calcium orthophosphates (CaPO4) to both improve biocompatibility and provide an adequate bonding to the adjacent bones.

Structural and dielectric properties of yttrium-substituted hydroxyapatites.

Hydroxyapatite (HAp) samples doped with 0, 2 and 4 at.% of yttrium (Y) were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy attached with energy dispersive X-ray (EDX) spectroscopy, antimicrobial activity tests and dielectric studies. The hydroxyl groups observed in FTIR spectra confirmed the formation of HAp phase in the studied samples.

Synthesis and characterization of Ce-substituted hydroxyapatite by sol-gel method.

Both undoped hydroxyapatite (HAp) and three Ce-substituted HAp samples with variable amounts (from 0.5 to 2 at.%) of Ce were synthesized by sol-gel method.

Calcium orthophosphate coatings on magnesium and its biodegradable alloys.

Biodegradable metals have been suggested as revolutionary biomaterials for bone-grafting therapies. Of these metals, magnesium (Mg) and its biodegradable alloys appear to be particularly attractive candidates due to their non-toxicity and as their mechanical properties match those of bones better than other metals do. Being light, biocompatible and biodegradable, Mg-based metallic implants have several advantages over other implantable metals currently in use, such as eliminating both the effects of stress shielding and the requirement of a second surgery for implant removal.

Calcium Orthophosphate-Based Bioceramics.

Various types of grafts have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A bit later, such synthetic biomaterials were called bioceramics.

A detailed history of calcium orthophosphates from 1770s till 1950.

Due to the chemical similarity with human bones and teeth, calcium orthophosphates are the inorganic substances of a special importance for the human being: they appear to be the excellent compounds to construct artificial bone grafts. In addition, calcium orthophosphates are necessary for both animals and plants as the source of important chemical elements. Obviously, these facts have not become apparent immediately; thus, providing the detailed annals of the knowledge development on the subject is the purpose of this review.

Calcium orthophosphates and human beings: a historical perspective from the 1770s until 1940.

The historical development of a scientific knowledge on calcium orthophosphates from the 1770s until 1940 is described. Many forgotten and poorly known historical facts and approaches have been extracted from old publications and then they have been analyzed, systematized and reconsidered from the modern point of view. The chosen time scale starts with the earliest available studies of 1770s (to the best of my findings, calcium orthophosphates had been unknown before), passes through the entire 19th century and finishes in 1940, because since then the amount of publications on calcium orthophosphates rapidly increases and the subject becomes too broad.

Calcium orthophosphates in dentistry.

Dental caries, also known as tooth decay or a cavity, remains a major public health problem in the most communities even though the prevalence of disease has decreased since the introduction of fluorides for dental care. Therefore, biomaterials to fill dental defects appear to be necessary to fulfill customers' needs regarding the properties and the processing of the products. Bioceramics and glass-ceramics are widely used for these purposes, as dental inlays, onlays, veneers, crowns or bridges.

Self-setting calcium orthophosphate formulations.

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are bioactive and biodegradable grafting bioceramics in the form of a powder and a liquid. After mixing, both phases form pastes, which set and harden forming either a non-stoichiometric calcium deficient hydroxyapatite or brushite. Since both of them are remarkably biocompartible, bioresorbable and osteoconductive, self-setting calcium orthophosphate formulations appear to be promising bioceramics for bone grafting.

Calcium orthophosphate coatings, films and layers.

In surgical disciplines, where bones have to be repaired, augmented or improved, bone substitutes are essential. Therefore, an interest has dramatically increased in application of synthetic bone grafts. As various interactions among cells, surrounding tissues and implanted biomaterials always occur at the interfaces, the surface properties of the implants are of the paramount importance in determining both the biological response to implants and the material response to the physiological conditions.

Dissolution mechanism of calcium apatites in acids: A review of literature.

Eight dissolution models of calcium apatites (both fluorapatite and hydroxyapatite) in acids were drawn from the published literature, analyzed and discussed. Major limitations and drawbacks of the models were conversed in details. The models were shown to deal with different aspects of apatite dissolution phenomenon and none of them was able to describe the dissolution process in general.

Calcium orthophosphates: occurrence, properties, biomineralization, pathological calcification and biomimetic applications.

The present overview is intended to point the readers' attention to the important subject of calcium orthophosphates. This type of materials is of special significance for human beings, because they represent the inorganic part of major normal (bones, teeth and antlers) and pathological (i.e.

Biphasic, triphasic and multiphasic calcium orthophosphates.

Biphasic, triphasic and multiphasic (polyphasic) calcium orthophosphates have been sought as biomaterials for reconstruction of bone defects in maxillofacial, dental and orthopedic applications. In general, this concept is determined by advantageous balances of more stable (frequently hydroxyapatite) and more resorbable (typically tricalcium orthophosphates) phases of calcium orthophosphates, while the optimum ratios depend on the particular applications. Therefore, all currently known biphasic, triphasic and multiphasic formulations of calcium orthophosphate bioceramics are sparingly soluble in water and, thus, after being implanted they are gradually resorbed inside the body, releasing calcium and orthophosphate ions into the biological medium and, hence, seeding new bone formation.

Biocomposites and hybrid biomaterials based on calcium orthophosphates.

The state-of-the-art of biocomposites and hybrid biomaterials based on calcium orthophosphates that are suitable for biomedical applications is presented in this review. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through successful combinations of the desired properties of matrix materials with those of fillers (in such systems, calcium orthophosphates might play either role), innovative bone graft biomaterials can be designed.

Amorphous calcium (ortho)phosphates.

Amorphous calcium phosphates (ACPs) represent a unique class of biomedically relevant calcium orthophosphate salts, having variable chemical but essentially identical glass-like physical properties, in which there is neither translational nor orientational long-range ordering of the atomic positions. Normally, ACPs are the first solid phases, precipitated after a rapid mixing of aqueous solutions containing ions of Ca(2+) and PO₄³⁻; however, other production techniques are known. Interestingly, ACPs prepared by wet-chemical techniques were found to have a relatively constant chemical composition over a relatively wide range of preparation conditions, which suggests the presence of a well-defined local structural unit, presumably with the structure of Ca₉(PO₄)₆ - so-called Posner cluster.

Calcium orthophosphates as bioceramics: state of the art.

In the late 1960s, much interest was raised in regard to biomedical applications of various ceramic materials. A little bit later, such materials were named bioceramics. This review is limited to bioceramics prepared from calcium orthophosphates only, which belong to the categories of bioactive and bioresorbable compounds.

Bioceramics of calcium orthophosphates.

A strong interest in use of ceramics for biomedical applications appeared in the late 1960's. Used initially as alternatives to metals in order to increase a biocompatibility of implants, bioceramics have become a diverse class of biomaterials, presently including three basic types: relatively bioinert ceramics, bioactive (or surface reactive) and bioresorbable ones. Furthermore, any type of bioceramics could be porous to provide tissue ingrowth.

Nanosized and nanocrystalline calcium orthophosphates.

Recent developments in biomineralization have already demonstrated that nanosized crystals and particles play an important role in the formation of hard tissues of animals. Namely, it is well established that the basic inorganic building blocks of bones and teeth of mammals are nanosized and nanocrystalline calcium orthophosphates in the form of apatites. In mammals, tens to hundreds nanocrystals of a biological apatite have been found to be combined into self-assembled structures under the control of bioorganic matrixes.