Sergey V. Dorozhkin

Bio: Sergey V. Dorozhkin is an academic researcher from Ruhr University Bochum. The author has contributed to research in topics: Calcium & Simulated body fluid. The author has an hindex of 45, co-authored 168 publications receiving 10117 citations. Previous affiliations of Sergey V. Dorozhkin include Yandex & Queen's University.

Biological and medical significance of calcium phosphates.

Abstract: The inorganic part of hard tissues (bones and teeth) of mammals consists of calcium phosphate, mainly of apatitic structure. Similarly, most undesired calcifications (i.e. those appearing as a result of various diseases) of mammals also contain calcium phosphate. For example, atherosclerosis results in blood-vessel blockage caused by a solid composite of cholesterol with calcium phosphate. Dental caries result in a replacement of less soluble and hard apatite by more soluble and softer calcium hydrogenphosphates. Osteoporosis is a demineralization of bone. Therefore, from a chemical point of view, processes of normal (bone and teeth formation and growth) and pathological (atherosclerosis and dental calculus) calcifications are just an in vivo crystallization of calcium phosphate. Similarly, dental caries and osteoporosis can be considered to be in vivo dissolution of calcium phosphates. On the other hand, because of the chemical similarity with biological calcified tissues, all calcium phosphates are remarkably biocompatible. This property is widely used in medicine for biomaterials that are either entirely made of or coated with calcium phosphate. For example, self-setting bone cements made of calcium phosphates are helpful in bone repair and titanium substitutes covered with a surface layer of calcium phosphates are used for hip-joint endoprostheses and tooth substitutes, to facilitate the growth of bone and thereby raise the mechanical stability. Calcium phosphates have a great biological and medical significance and in this review we give an overview of the current knowledge in this subject.

Calcium Orthophosphates in Nature, Biology and Medicine

Abstract: The present overview is intended to point the readers’ attention to the important subject of calcium orthophosphates. These materials are of the special significance because they represent the inorganic part of major normal (bones, teeth and dear antlers) and pathological ( i.e. those appearing due to various diseases) calcified tissues of mammals. Due to a great chemical similarity with the biological calcified tissues, many calcium orthophosphates possess remarkable biocompatibility and bioactivity. Materials scientists use this property extensively to construct artificial bone grafts that are either entirely made of or only surface-coated with the biologically relevant calcium ortho-phosphates. For example, self-setting hydraulic cements made of calcium orthophosphates are helpful in bone repair, while titanium substitutes covered by a surface layer of calcium orthophosphates are used for hip joint endoprostheses and as tooth substitutes. Porous scaffolds made of calcium orthophosphates are very promising tools for tissue engineering applications. In addition, technical grade calcium orthophosphates are very popular mineral fertilizers. Thus ere calcium orthophosphates are of great significance for humankind and, in this paper, an overview on the current knowledge on this subject is provided.

American Society for Testing and Materials

Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

Bone structure and formation: A new perspective

Abstract: Bone is a hierarchically structured composite material which, in addition to its obvious biological value, has been well studied by the materials engineering community because of its unique structure and mechanical properties. This article will review the existing bone literature, with emphasis on the prevailing theories regarding bone formation and structure, which lay the groundwork for proposing a new model to explain how intrafibrillar mineralization of collagen can be achieved during bone formation. Intrafibrillar refers to the fact that growth of the mineral phase is somehow directed by the collagen matrix, which leads to a nanostructured architecture consisting of uniaxially oriented nanocrystals of hydroxyapatite embedded within and roughly [0 0 1] aligned parallel to the long collagen fibril axes. Secondary (osteonal) bone, the focus of this review, is a laminated organic–inorganic composite composed primarily of collagen, hydroxyapatite, and water; but minor constituents, such as non-collagenous proteins (NCPs), are also present and are thought to play an important role in bone formation. To date, there has been no clear understanding of the role of these NCPs, although it has been generally assumed that the NCPs regulate solution crystal growth via some type of ‘epitaxial’ relationship between specific crystallographic faces and specific protein conformers. Indeed, ‘epitaxial’ relationships have been calculated; but in practice, it has not been demonstrated that intrafibrillar mineralization can be accomplished via this route. Because of the difficulty in examining biomineralization processes in vivo , the authors of this article have turned to using in vitro model systems to investigate the possible physicochemical mechanisms that may be involved in biomineralization. In the case of bone biomineral, we have now been able to duplicate the most fundamental level of bone structure, the interpenetrating nanostructured architecture, using relatively simple anionic polypeptides that mimic the polyanionic character of the NCPs. We propose that the charged polymer acts as a process-directing agent, by which the conventional solution crystallization is converted into a precursor process. This polymer-induced liquid-precursor (PILP) process generates an amorphous liquid-phase mineral precursor to hydroxyapatite which facilitates intrafibrillar mineralization of type-I collagen because the fluidic character of the amorphous precursor phase enables it to be drawn into the nanoscopic gaps and grooves of collagen fibrils by capillary action. The precursor then solidifies and crystallizes upon loss of hydration waters into the more thermodynamically stable phase, leaving the collagen fibrils embedded with nanoscopic hydroxyapatite (HA) crystals. Electron diffraction patterns of the highly mineralized collagen fibrils are nearly identical to those of natural bone, indicating that the HA crystallites are preferentially aligned with [0 0 1] orientation along the collagen fibril axes. In addition, studies of etched samples of natural bone and our mineralized collagen suggest that the long accepted “deck of cards” model of bone's nanostructured architecture is not entirely accurate. Most importantly, this in vitro model demonstrates that a highly specific, epitaxial-type interaction with NCPs is not needed to stimulate crystal nucleation and regulate crystal orientation, as has long been assumed. Instead, we propose that collagen is the primary template for crystal organization, but with the important caveat that this templating occurs only for crystals formed from an infiltrated amorphous precursor. These results suggest that the 25-year-old debate regarding bone formation via an amorphous precursor phase needs to be revisited. From a biomedical perspective, in addition to providing possible insight into the role of NCPs in bone formation, this in vitro system may pave the way toward the ultimate goal of fabricating a synthetic bone substitute that not only has a composition similar to bone, but has comparable mechanical properties and bioresorptive potential as natural bone. From a materials chemistry perspective, the non-specificity of the PILP process and capillary infiltration mechanism suggests that non-biological materials could also be fabricated into nanostructured composites using this “biomimetic” strategy.