A comprehensive review on the preparation and application of calcium hydroxyapatite: A special focus on atomic doping methods for bone tissue engineering

Hydroxyapatite (HAP) has been considered to be one of the most preferred scaffold materials among many in the last decade for the bone tissue engineering. Be it prosthetic implants, scaffolds or artificial bone cement, hydroxyapatite has received highest attraction among all due to its chemical and physical properties similar to that of human bone. Although it can be used in the bone tissue engineering as the original composition; for enhancing its different properties relevant to in vivo applications, the calcium in HAP may also be replaced by other atomic dopants depending on usage. Here, we review various HAP coating agents and methods, their merits and demerits. We also review various HAP doping materials, including both cationic as well as anionic materials. We discuss the effects and usage of substitution of hydroxyapatite and their subsequent usage in both bone tissue engineering and maxillofacial surgeries. We consider various research articles published in recent times to accomplish detailed discussion on the subject.     

Effects of sandblasting distance and angles on resin cement bonding to zirconia and titanium

ObjectivesThe aim of this study was to evaluate effects of sandblasting distance and angles resin to zirconia and titanium bonding.MethodsDensely sintered zirconia and cp2 titanium specimens were prepared and randomly divided into groups, and then sandblasted with various distance (5 mm, 10 mm and 15 mm) and angles (45°, 60°, 75° and 90°). After surface treatment, each specimen surface underwent a silane primer application (RelyX, 3M ESPE), followed by bonding of a resin cement (RelyX Unicem Aplicap, 3M ESPE). Then, each cylindrical resin stub (diameter 3.6 mm×2 mm) underwent a shear adhesive (bond) strength test and surface roughness evaluation. SEM evaluation and EDX analysis were used to observe surface properties of both zirconia and titanium samples. Results were statistically analyzed using analysis of variance (ANOVA) and Turkey test (α=0.05).ResultsSurface roughness showed a significant difference amongst the different distances and angles for both the zirconia and titanium materials and these changes in surface roughness were evident in the SEM imaging photos. As for the adhesive strength, there was a significant difference in the adhesive strength for the titanium and zirconia with different angles. In general, 75° gives the best results although this is not significantly different from 90°. However, no significant difference was observed in changes of sandblasting distance for both materials. EDX analysis at the surface revealed elements carbon, oxygen, silicon, aluminum, and zirconia on the surface.ConclusionsSandblasting at various distance and angles contributes differences in surface roughness when it comes to both zirconia and titanium materials. Despite both 75° or 90° sandblasting angle could yield a sufficiently high adhesive strength for resin to titanium or zirconia bonding, sandblasting at 75° seems to be optimal to increase the adhesive strength.     

Particle-induced Phagocytic Cell Responses are Material Dependent: Foreign Body Giant Cells Vs. Osteoclasts from a Chick Chorioallantoic Membrane Particle-implantation Model

There is increasing concern about particles generated from wear-prone implants that are placed in body tissues, including artificial hip, knee, and jaw joints. Although phagocytes and foreign body giant cells are associated with inhaled or embedded particulate debris, some particles also induce bone digestion by eliciting the differentiation and proliferation of highly specialized osteoclastic cells. This report describes the differential phagocytic cellular responses to four implant-related types of ground, model wear particles in a live-egg cell-response model, as implants to the chick chorioallantoic membrane (CAM): polymethylmethacrylate (PMMA), a main constituent of some temporomandibular joint (TMJ) implants and orthopedic cements used to retain artificial hips and knees; Proplast-HA, an implantable composite of polytetrafluoroethylene (PTFE) and degradable mineral (hydroxyapatite) that has been associated with bone erosion around failed TMJ implants; talc, a nondegradable mineral sometimes found in tissues as a contaminant from talc-coated surgical gloves; and authentic bone, known to induce the formation of osteoclastic cells. Light and electron microscopy of CAM tissues harvested, sectioned and stained with special reagents for the enzymes tartrate-resistant acid phosphatase (TRAP) and tartrate-resistant adenosine triphosphatase (TrATPase), and for the osteoclast-specific antigen 121F, showed that only authentic bone and the degradable HA-rich particles induced osteoclast formation. From these results, and supporting data with polypropylene particles, it is concluded that nonbiodegradable polymer particles, alone, do not induce bone dissolution. Inert polymers do induce foreign body giant cells without the external mineral digestion qualities unique to osteoclasts, however. The chick embryo model system allows quick and affordable examination of material-dependent differences in phagocytic cellular responses to implant wear debris and particles from various occupational environments.     

Reprint of: Improved cytotoxicity testing of magnesium materials

Metallic magnesium (Mg) and its alloys are highly suitable for medical applications as biocompatible and biodegradable implant materials. Magnesium has mechanical properties similar to bone, stimulates bone regeneration, is an essential non-toxic element for the human body and degrades completely within the body environment. In consequence, magnesium is a promising candidate as implant material for orthopaedic applications. Protocols using the guideline of current ISO standards should be carefully evaluated when applying them for the characterization of the cytotoxic potential of degradable magnesium materials. For as-cast material we recommend using 10 times more extraction medium than recommended by the ISO standards to obtain reasonable results for reliable cytotoxicity rankings of degradable materials in vitro. In addition primary isolated human osteoblasts or mesenchymal stem cells should be used to test magnesium materials.     

Improved cytotoxicity testing of magnesium materials

Metallic magnesium (Mg) and its alloys are highly suitable for medical applications as biocompatible and biodegradable implant materials. Magnesium has mechanical properties similar to bone, stimulates bone regeneration, is an essential non-toxic element for the human body and degrades completely within the body environment. In consequence, magnesium is a promising candidate as implant material for orthopaedic applications. Protocols using the guideline of current ISO standards should be carefully evaluated when applying them for the characterization of the cytotoxic potential of degradable magnesium materials. For as-cast material we recommend using 10 times more extraction medium than recommended by the ISO standards to obtain reasonable results for reliable cytotoxicity rankings of degradable materials in vitro. In addition primary isolated human osteoblasts or mesenchymal stem cells should be used to test magnesium materials.     

Power Trench MOSFETs with very low specific on-resistance for 25V applications

In this paper, an investigation of the benefits of deep ultra violet lithography for the manufacturing of Trench MOSFETs and its impact on device performance is presented. We discuss experimental results for devices with a pitch size down to 0.6 μm fabricated with an unconventional implant topology and a simplified manufacturing scheme. The fabricated Trench MOSFETs are benchmarked against previously published TrenchMOS technologies by de-embedding the parasitic substrate resistance, revealing a record-low specific on-resistance of 5.3 mΩ mm² at a breakdown voltage of 30 V (V_gs = 10 V).     

CerAMfacturing of silicon nitride by using lithography-based ceramic vat photopolymerization (CerAM VPP)

Hardness, high mechanical strength, wear and corrosion resistance, for instance, are the most important properties of silicon nitride. Next to technical application, the material becomes more and more important for medical applications, especially for implants and the focus in research for this increase steadily. Up to now, the demands on the geometry of silicon nitride-based components could largely be met by using conventional shaping methods such as pressing and green machining or injection moulding. However, requirements in terms of complexity and function are constantly increasing. By using additive manufacturing (AM) technologies, the complexity of components can be significantly increased and additional functions such as transport channels or features like triple periodic minimal surfaces (TPMS), which seem to be advantageous for osseointegration can be integrated, for instances. High-resolution AM processes such as stereolithography enable the production of very accurate and complex ceramic components. In this work a silicon nitride suspension suitable for biomedical applications was developed and the influence of the formulation on the properties (especially flow and curing behavior) were analyzed. Afterwards, various test samples were generated by ceramic additive manufacturing via vat photopolymerization (CerAM VPP), thermally processed and the sintered parts were characterized with common ceramic methods, like mechanical tests and microstructure analyses, showing satisfying results for the described development state.     

Effects of build orientation induced surface modifications on the in vitro biocompatibility of electron beam melted Ti6Al4V

Titanium and its alloys may be processed via additive manufacturing techniques such as electron beam melting (EBM).This field is receiving increased attention from various manufacturing sectors including the medical devices sector. While the economic and engineering potential of EBM for the manufacture of musculo-skeletal implants is clear, the impact on the biocompatibility of the materials has been less investigated. In this study, the effects of part orientation-induced surface modifications on the in vitro biocompatibility of the EBM Ti6Al4V alloy were investigated. The study assessed the suitability of three different Ti6Al4V surfaces produced via the EBM process as variables for proliferation and attachment of mouse fibroblast L929 cells. The three different surface topographies were obtained by orienting the parts in vertical, horizontal and inclined (55°) orientation in the EBM build chamber. The mouse fibroblasts were cultured in vitro on the Ti6Al4V alloy discs with three different surface finishes. Cell viability studies, fluorescent microscopy as well as scanning electron micrographs were used to assess the L929 cell attachment and proliferation. After 2 and 8 days of incubation, there was a higher vitality and proliferation of L929 cells on the vertical and inclined surfaces (R_a?=?38 and 46?µm, respectively) than on the horizontal surfaces (R_a?=?18?µm). On the vertical and inclined samples, the cells spread over a wider area, whereas on the horizontal samples cell spread was affected by the topographical features. The results showed that the implants produced by EBM meet basic biocompatibility requirements and also showed that part orientation of titanium during EBM can produce surfaces with different characteristics and these can affect cell growth.     

3D打印医用钛合金研究进展

钛合金拥有较高的比强度、较好的耐蚀性能与生物相容性,其在医用植入物的应用市场前景十分引人关注。但传统医用钛合金植入物常采取铸造的生产方式,产品种类单一,无法满足"精准医疗"的诊疗目标。3D打印技术以其丰富的加工方式在医用钛合金方面应用优势逐渐凸显。本文介绍多孔医用钛合金的发展历史及3D打印钛合金的制造现状,分析现有3D打印医用钛合金的技术壁垒,并为未来3D打印医用钛合金的发展方向提供建议。     

Relationship between processing and mechanical properties of injection molded high molecular mass polyethylene + hydroxyapatite composites

We apply a macromolecular-orientation approach to produce high molecular weight polyethylene (HMWPE) + hydroxyapatite (HA) ductile composites with the stiffness and strength within the range of human cortical bone. Our composites are produced with different amounts (10 to 50% by weight) of the reinforcement by two procedures: bi-axial rotating drum and twin screw extrusion (TSE). The processing is by conventional injection molding and by Scorim (shear controlled orientation in injection molding) under a wide range of processing windows. Tensile testing is performed and the corresponding performance related to the morphology evaluated by polarized light microscopy and scanning electron microscopy. The control of the processing parameters led to significant improvements of the tensile properties. Compounding by TSE and then processing by Scorim produces the maximum modulus of 7.4 GPa and the ductility as high as 19%, for the HA weight fraction of 30%. These mechanical properties match those of bone, and were obtained with much smaller amounts of HA reinforcement then has been previously reported in literature. Our PE + HA composites present the additional benefit of being ductile even for 50% HA amounts. The use Scorim is a unique way of inducing anisotropy to thick sections and to produce very stiff composites that may be used in biomedical applications with important mechanical loads. This fact, combined with the bioactive behavior of the HA phase, makes our composite usable for orthopedic load-bearing implants. Received: 9 October 2000 / Reviewed and accepted: 10 October 2000