Novel bioactive materials with different mechanical properties

Effects of intraosseous implantation of silica-based bioactive glass particles on rat kidney under experimental renal failure

The aim of the present study is to evaluate the effects of intraosseous implantation of silica-based bioactive glass (BG) particles on rat kidney under experimental renal failure. The animals are assigned to one of the two groups: renal failure (RF) and renal failure + bioactive glass (RF + BG). Particles of melt-derived 45S5 BG are implanted in the marrow of one tibia of each animal in the RF + BG group. The animals are killed 24 h and 14 days postimplantation. The RF + BG group exhibits a statistically significant increase in serum urea 24 h postimplantation. The tibiae of the RF + BG group are resected and embedded in methyl-methacrylate resin. Ground sections are analyzed by light microscopy and energy-dispersive X-ray (EDX) analysis. The presence of silicon, calcium, and phosphorus is evaluated in the BG particles. A 55% reduction in silicon content is observed at 14 days postimplantation as compared with that at 24 h.Light microscopy analysis reveals lesions in kidney parenchyma. Hyperplasia associated with nuclear vacuolization in the tubules and a marked thickening of the basal membrane are observed in the renal cortex of the RF + BG animals killed at 24 h postimplantation, but not in those at 14 days. The present results demonstrate reversible renal cell injury in rats exposed to intraosseous implantation of silica-based BG particles under experimental RF.

The mechanism of biomineralization of bone-like apatite on synthetic hydroxyapatite: an in vitro assessment

The mechanism of biomineralization of bone-like apatite on synthetic hydroxyapatite (HA) has been investigated in vitro, in which the HA surface was surveyed as a function of soaking time in simulated body fluid (SBF). In terms of surface structure by transmission electron microscopy with energy-dispersive X-ray spectrometry, the HA whose Ca/P atomic ratio was 1.67 revealed three different characteristic soaking periods in SBF, i.e. the first soaking period, in which the HA surface increased the Ca/P ratio up to 1.83 to form an amorphous phase of Ca-rich calcium phosphate; the second soaking period, in which the HA surface decreased the Ca/P ratio up to 1.47 to form an amorphous phase of Ca-poor calcium phosphate; and the third soaking period, in which the HA surface gradually increased the Ca/P ratio up to 1.65 to eventually produce the bone-like nano-cerystallites of apatite, which grew forming complex crystal assemblies with a further increase in immersion time. Analysis using electrophoresis spectroscopy indicated that, immediately after immersion in SBF, the HA revealed a highly negative surface potential, which increased to reach a maximum positive value in the first soaking period. The surface potential then decreased to again reach a negative value in the second soaking period and thereafter converge to a constant negative value in the third soaking period. This implies that the HA induces biomineralization of apatite by smartly varying its surface potential to trigger an electrostatic interaction, first with positive calcium ions and second with negative phosphate ions in the SBF.

Bioglass® Coatings on Superelastic NiTi Wires by Electrophoretic Deposition (EPD)

45S5 Bioglass® coatings have been produced on superelastic nickel-titanium wires using electrophoretic deposition (EPD). Aqueous suspensions of Bioglass® particles (< 5 &m mean particle size) were used. EPD led to the formation of thick and uniform coatings covering the wires very homogeneously, without the development of any microcracks during the drying stage. Best results were achieved with suspensions containing 20 wt% Bioglass®, an applied voltage of 5 V, and a deposition time of 5 min. Samples sintered for 1 hour at temperatures > 800 °C exhibited diffusion of nickel and titanium into the Bioglass® coating. Scanning electron microscopy (SEM) was used to analyse the microstructure of the Bioglass® coatings in terms of level of uniformity, densification, and to discover the possible presence of microcracks, as well as to gain information about the thickness of the coating produced on the different substrates. The results demonstrate that the EPD technique is a very convenient method to produce uniform Bioglass® coatings on wires for biomedical applications.

Experimental and clinical performance of porous tantalum in orthopedic surgery

Porous tantalum, a new low modulus metal with a characteristic appearance similar to cancellous bone, is currently available for use in several orthopedic applications (hip and knee arthroplasty, spine surgery, and bone graft substitute). The open-cell structure of repeating dodecahedrons is produced via carbon vapor deposition/infiltration of commercially pure tantalum onto a vitreous carbon scaffolding. This transition metal maintains several interesting biomaterial properties, including: a high volumetric porosity (70-80%), low modulus of elasticity (3MPa), and high frictional characteristics. Tantalum has excellent biocompatibility and is safe to use in vivo as evidenced by its historical and current use in pacemaker electrodes, cranioplasty plates and as radiopaque markers. The bioactivity and biocompatibility of porous tantalum stems from its ability to form a self-passivating surface oxide layer. This surface layer leads to the formation of a bone-like apatite coating in vivo and affords excellent bone and fibrous in-growth properties allowing for rapid and substantial bone and soft tissue attachment. Tantalum-chondrocyte composites have yielded successful early results in vitro and may afford an option for joint resurfacing in the future. The development of porous tantalum is in its early stages of evolution and the following represents a review of its biomaterial properties and applications in orthopedic surgery.

Calcium phosphate cements as bone drug delivery systems: A review

Since calcium phosphate cements were proposed, several formulations have been developed, some of them commercialised, and they have proven to be very efficient bone substitutes in different applications. Some of their properties, such as the injectability, or the low-temperature setting, which allows the incorporation of different drugs, make them very attractive candidates as drug carriers. In this article, the performance of calcium phosphate cements as carriers of different types of drugs, such as antibiotics, analgesics, anticancer, anti-inflammatory, as well as growth factors is reviewed.

Behaviour of MG-63 osteoblast-like cells on wood-based biomorphic SiC ceramics coated with bioactive glass

The aim of this study was to test the in vitro cytotoxicity of wood-based biomorphic Silicon Carbide (SiC) ceramics coated with bioactive glass, using MG-63 human osteoblast-like cells, with a view to their application in bone implantology. To better understand the scope of this study, it should be taken into account that biomorphic SiC ceramics have only recently been developed and this innovative product has important properties such as interconnected porosity, high strength and toughness, and easy shaping. In the solvent extraction test, all the extracts had almost no effect on cellular activity even at 100% concentration, and cells incubated in the bioactive glass-coated SiC ceramics extracts showed a proliferation rate similar to that of the Thermanox control. There were no significant differences when the cellular attachment response of the cells on the wood-based biomorphic SiC ceramics, uncoated or coated with bioactive glass, was compared to the one exhibited by reference materials like Ti6Al4V and bulk bioactive glass. This fact looks very promising for biomedical applications.

Bioactive ceramic composites sintered from hydroxyapatite and silica at 1,200 degrees C: preparation, microstructures and in vitro bone-like layer growth

Bioceramic composites were synthesized by sintering the powders of hydroxyapatite (HAp) mixed directly with additive of 0.5, 1.0, 2.0, 5.0 and 10 wt.%SiO(2), respectively, at 1,200( composite function)C. X-ray diffraction (XRD) analysis indicated that the phase transformation from HAp to tricalcium phosphate (TCP) comprising alpha-TCP and Si-TCP occurred and became more prominent with the addition of SiO(2) and the increase in SiO(2) content. The observations of their surface microstructures showed that the addition of SiO(2) suppressed the grain growth and promoted the formation of crystalline-glassy composites denoted HAp + TCP/Bioglass. As the SiO(2) content is as high as 5 wt.%, the composite made a feature of crystalline clusters with different sizes consisting of HAp and TCP grains surrounded by the matrix of glassy phase. Furthermore, the dependence of in vitro bioactivity of these composites on the SiO(2) content was biomimetically assessed by determining the changes in surface morphology, i.e., bone-like apatite layer growth, after soaking in an acellular stimulated body fluid (SBF) for 3 days at 36.5( composite function)C. It was found that the HAp-SiO(2) composites showed a much faster bone-like layer growth than pure HAp, and the propensity of composites to exhibit a better bioactivity was getting more notable with increasing SiO(2) content, except for the case of the highest content of 10 wt.%. It was believed that the formation of the bone-like layer on the surfaces of these bio-composites is closely related to the increasingly provided silanol groups and transformed TCP phase in materials associated with the content of SiO(2) added.

Bioceramics as nanomaterials

Nanostructured materials possess unique capabilities for specific interactions with biological entities. This article reviews several types of nanostructured ceramics, cements and coatings that are being considered for use in medical applications. The processing methods for obtaining ceramics are presented and related to the properties (such as wettability, topography and charge) that directly affect interactions with biological entities (ions, biomacromolecules and cells). The literature reviewed demonstrates that these interactions are directly affected by the nanostructure of the ceramic surfaces. Thus, the understanding and control of the interactions between nanoceramics and biological entities may play one of the leading roles in the development of nanomedicine.

Craniofacial bone tissue engineering

Repair and reconstruction of the craniofacial skeleton represents a significant biomedical burden, with thousands of procedures per-formed annually secondary to injuries and congenital malformations. Given the multitude of current approaches, the need for more effective strategies to repair these bone deficits is apparent. This article explores two major modalities for craniofacial bone tissue engineering: distraction osteogenesis and cellular based therapies. Current understanding of the guiding principles for each of these modalities is elaborated on along with the knowledge gained from clinical and investigative studies. By laying this foundation, future directions for craniofacial distraction and cell-based bone engineering have emerged with great promise for the advancement of clinical practice.

Molecular Dynamics Modelling of the Structure of Bioactive (CaO)0.3 (SiO2)0.7 Sol-Gel

Enhanced bioactivity has been observed for amorphous CaO-SiO2 sol-gels with 30mol% CaO, and several structural techniques have recently been used to investigate the structural basis for this bioactivity. The current work presents the first detailed atomic model of (CaO)0.3(SiO2)0.7 solgel after heat treatment at 600°C, produced using molecular dynamics. The model contains 1056 atoms in cubic box with length 24.1Å, and specifically incorporates hydroxyl groups which are characteristic of the sol-gel. The model is in good agreement with experimental X-ray and neutron diffraction results. Inspection of the model shows a network of SiO4 tetrahedra with an average connectivity of approximately 3. Ca have coordination of NCaO=5.3, in agreement with experimental results. On average, each Ca is surrounded by 4 other Ca, and visual inspection shows several large clusters of Ca. These clusters should influence the dissolution of Ca, and hence the bioactivity of (CaO)0.3(SiO2)0.7 sol-gel.

Influence of Sintering Temperature on Mechanical Properties of Biologically Derived Hydroxyapatite Bodies

The properties of sintered hydroxyapatite (HA), obtained from bovine femoral shafts via calcination method, were investigated utilizing scanning electron microscopy (SEM) and X-ray diffraction analysis together with measurements of microhardness, density, and compression strength. The production of HA from natural sources is preferred due to money and time saving reasons. The results indicate the new HA materials as promissing in biomedicine, since similar mechanical behaviour was obtained with previous studies.

Formation of Bone-Like Apatite on Polymeric Surfaces Modified with -SO3H Groups

Sulfonic groups (-SO3H) were covalently attached on different polymeric surfaces enabling them to induce apatite nucleation, for developing bioactive apatite-polymer composites with a bonelike 3-dimensional structure. High molecular weight polyethylene (HMWPE) and ethylene-co-vinyl alcohol co-polymer (EVOH) were used. The polymers were soaked in two types of sulphate-containing solutions with different concentrations, sulphuric acid (H2SO4) and chlorosulfonic acid (ClSO3H). To incorporate calcium ions into to the sulfonated polymers, the samples were soaked in a saturated Ca(OH)2 solution for 24 hours. After soaking of the samples in a simulated body fluid (SBF), formation of an apatite layer on both surfaces was observed. The results obtained prove the validity of the proposed concept and show that the -SO3H groups are effective on inducing apatite nucleation on the surface of these polymers.

The engineering of craniofacial tissues in the laboratory: a review of biomaterials for scaffolds and implant coatings

Tissue engineering is a rapidly growing interdisciplinary field that focuses on the interactions between cells, growth factors, and scaffolds to produce replacement tissue and organs. Recent developments in tissue engineering technology include refinements in isolation and differentiation of progenitor cells, 3-D printing technology to produce scaffolds, new biomaterials for scaffolds, and growth factor delivery systems. The purpose of this article is to review advances in biomaterials, scaffolds, and implant coatings for craniomaxillofacial (bone) tissue engineering.

Multifunctional Ti-(Ca,Zr)-(C,N,O,P) films for load-bearing implants

Films of Ti-Ca-P-C-O-(N), Ti-Ca-C-O-(N) and Ti-Zr-C-O-(N) were deposited by DC magnetron sputtering or ion implantation-assisted magnetron sputtering of composite targets TiC0.5 + 10%Ca10(PO4)6(OH)2, TiC0.5 + 20%(CaO + TiO2) and TiC0.5 + 10%ZrO2 in an Ar atmosphere or reactively in a gaseous mixture of Ar + 14%N2. The microstructure, elemental and phase composition of films were studied by means of X-ray diffraction, transmission electron microscopy, scanning force microscopy, X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy. The films were characterized in terms of their hardness, Young's modulus, elastic recovery, adhesion strength, and friction and wear both in air and under physiological solution. Particular attention was paid to the analysis of deformation and fracture for various film/substrate systems during scratch testing. The biocompatibility of the films was evaluated by both in vitro and in vivo experiments. In vitro studies involved the investigation of adhesion, spreading, and proliferation of MC3T3-E1 osteoblasts and IAR-2 epithelial cells, morphometric analysis, actin cytoskeleton, focal contacts staining, alkaline phosphatase activity and von Kossa staining of osteoblastic culture. Cell culture experiments demonstrated an increase of osteoblastic proliferation on Ca- and P-incorporated films. In vivo studies were fulfilled by subcutaneous implantation of Teflon plates coated with the tested films in mice and analysis of the population of adherent cells on their surfaces. The results obtained show that multicomponent nanostructured Ti-(Ca, Zr)-(C, N, O, P) films possess a combination of high hardness, wear resistance and adhesion strength, reduced Young's modulus, low friction coefficient and high biocompatibility.

Nucleation and growth of apatite by a self-assembled polycrystalline bioceramic

The formation aspects of a polycrystalline self-assembled bioceramic leading to the nucleation of hard-tissue mineral from a supersaturated solution are discussed. Scanning electron imaging and surface-sensitive interrogations of the nucleated mineral indicated the presence of an intermediate amorphous layer encompassing a rather crystalline phase that formed on niobium oxide (Nb(2)O(5)) microstructures. The crystalline phase was identified from Raman spectroscopy as hydroxyapatite (HAP), while the phosphorous-rich amorphous layer is suggested to have the chemical form CaO-P(2)O(5). In addition, the mechanism favoring HAP nucleation is discussed in terms of the (0 0 2) and (0 0 1) diffraction planes of HAP and Nb(2)O(5), respectively. The small mismatch along several lattice dimensions strongly suggests epitaxy as a dominant mode in the heterogeneous nucleation of HAP. Furthermore, the effectiveness of this mode was shown to critically depend on the self-organization of the Nb(2)O(5) microstructures. Because nucleation does not appear to depend solely on the integrity of Nb(2)O(5) crystals, the self-organization of Nb(2)O(5) crystals also contributes significantly to HAP nucleation. Based on our results, we propose the organized arrangement of bioceramic crystals as a new mode for the bioinspiration of hydroxyapatite and other hard-tissue mineral.

Formation of bone-like apatite on organic polymers treated with a silane-coupling agent and a titania solution

Polyethylene terephthalate (PET), ethylene-vinyl alcohol copolymer (EVOH) and Nylon 6 in plate form were treated with silane-coupling agents, a titanium alkoxide-alcohol solution and a hot HCl solution to form a thin crystalline titanium oxide layer. When placed in a simulated body fluid with ion concentrations nearly equal to those of the human blood plasma, nanosized bone-like apatite formed uniformly on the surfaces of these treated polymers: within 2 days for PET and Nylon 6, and 7 days for EVOH. This indicates that such titania-modified polymers might form bone-like apatite in the living body, and bond to living bone through this apatite layer. Three-dimensional fabrics of these polymer fibers, with open spaces in various sizes, are expected to be useful as bone substitutes, as they will be integrated with the natural bone.

Biodegradable and bioactive porous polymer/inorganic composite scaffolds for bone tissue engineering

Biodegradable polymers and bioactive ceramics are being combined in a variety of composite materials for tissue engineering scaffolds. Materials and fabrication routes for three-dimensional (3D) scaffolds with interconnected high porosities suitable for bone tissue engineering are reviewed. Different polymer and ceramic compositions applied and their impact on biodegradability and bioactivity of the scaffolds are discussed, including in vitro and in vivo assessments. The mechanical properties of today's available porous scaffolds are analyzed in detail, revealing insufficient elastic stiffness and compressive strength compared to human bone. Further challenges in scaffold fabrication for tissue engineering such as biomolecules incorporation, surface functionalization and 3D scaffold characterization are discussed, giving possible solution strategies. Stem cell incorporation into scaffolds as a future trend is addressed shortly, highlighting the immense potential for creating next-generation synthetic/living composite biomaterials that feature high adaptiveness to the biological environment.

The optimal SAM surface functional group for producing a biomimetic HA coating on Ti

Commercial interest is growing in biomimetic methods that employ self assembled mono-layers (SAMs) to produce biocompatible HA coatings on Ti-based orthopedic implants. Recently, separate studies have considered HA formation for various SAM surface functional groups. However, these have often neglected to verify crystallinity of the HA coating, which is essential for optimal bioactivity. Furthermore, differing experimental and analytical methods make performance comparisons difficult. This article investigates and evaluates HA formation for four of the most promising surface functional groups: --OH, --SO(3)H, --PO(4)H(2) and --COOH. All of them successfully formed a HA coating at Ca/P ratios between 1.49 and 1.62. However, only the --SO(3)H and --COOH end groups produced a predominantly crystalline HA. Furthermore, the --COOH end group yielded the thickest layer and possessed crystalline characteristics very similar to that of the human bone. The --COOH end group appears to provide the optimal SAM surface interface for nucleation and growth of biomimetic crystalline HA. Intriguingly, this finding may lend support to explanations elsewhere of why human bone sialoprotein is such a potent nucleator of HA and is attributed to the protein's glutamic acid-rich sequences.

Hydroxyapatite growth on anodic TiO2 nanotubes

In the present work, we study the growth of hydroxyapatite formation on different TiO(2) nanotube layers. The nanotube layers were fabricated by electrochemical anodization of titanium in fluoride-containing electrolytes. To study various nanotube lengths, layers with an individual tube diameter of 100 nm were grown to a thickness of approximately 2 mum or 500 nm. The ability to form apatite on the nanotube layers was examined by immersion tests combined with SEM, XRD and FT-IR investigations. For reference, experiments were also carried out on compact anodic TiO(2) layers. The results clearly show that the presence of the nanotubes on a titanium surface enhances the apatite formation and that the 2-mum thick nanotube layer triggers deposition faster than the thinner layers. Tubes annealed to anatase, or a mixture of anatase and rutile are clearly more efficient in promoting apatite formation than the tubes in their "as-formed" amorphous state.

A new in vivo screening model for posterior spinal bone formation: Comparison of ten calcium phosphate ceramic material treatments

This study presents a new screening model for evaluating the influence of multiple conditions on the initial process of bone formation in the posterior lumbar spine of a large animal. This model uses cages designed for placement on the decorticated transverse process of the goat lumbar spine. Five conduction channels per cage, each be defined by a different material treatment, are open to both the underlying bone and overlying soft tissue. The model was validated in ten adult Dutch milk goats, with each animal implanted with two cages containing a total of ten calcium phosphate material treatments according to a randomized complete block design. The ten calcium phosphate ceramic materials were created through a combination of material chemistry (BCP, TCP, HA), sintering temperature (low, medium, high), calcination and surface roughness treatments. To monitor the bone formation over time, fluorochrome markers were administered at 3, 5 and 7 weeks and the animals were sacrificed at 9 weeks after implantation. Bone formation in the conduction channels was investigated by histology and histomorphometry of non-decalcified sections using traditional light and epifluorescent microscopy. According to both observed and measured bone formation parameters, materials were ranked in order of increasing magnitude as follows: low sintering temperature BCP (rough and smooth) approximately medium sintering temperature BCP approximately = TCP > calcined low sintering temperature HA > non-calcined low sintering temperature HA > high sintering temperature BCP (rough and smooth) > high sintering temperature HA (calcined and non-calcined). These results agree closely with those obtained in previous studies of osteoconduction and bioactivity of ceramics thereby validating the screening model presented in this study.

An in vitro evaluation of PCL-TCP composites as delivery systems for platelet-rich plasma

In this study, we first investigated the in vitro degradation properties of biodegradable, bioresorbable polycaprolactone-20% tricalcium phosphate (PCL-TCP) composites immersed in simulated body fluid (SBF) and phosphate buffered saline (PBS). Then, the release profiles of the growth factors present in platelet-rich plasma (PRP) loaded onto the composites incubated in SBF and PBS were compared. Composites immersed in both buffers showed water uptake of 13.7%+/-0.75 at day 1, followed by a constant uptake of 12.1%+/-0.3 until day 12. Henceforth the water uptake declined for SBF- and increased for PBS-soaked composites. The weight loss data did not reveal any trend. SBF- and PBS-soaked samples displayed 1-2% weight loss for 2 and 5 of the ten time points measured respectively. The original protein retention (PR) of the composites was 49.1%+/-1.50. After immersion in SBF and PBS for 4 weeks, the PR was augmented to 88.5%+/-1.40 and 69.1%+/-1.40 correspondingly. PRP after activation contained 164.7+/-24.8, 194+/-43 and 18.3+/-4.75 ng/ml of TGF-beta1, PDGF-BB and IGF-1. Microscopic analysis verified the attachment of PRP to the rods and pores of the composites. Interestingly, the buffers played an important role in determining the release profiles of TGF and PDGF. Firstly, PBS-soaked composites manifested a tri-phasic burst-like profile that was absent in SBF. Secondly, SBF-soaked composites experienced delayed release of the growth factors and total release was not achieved (64.4% for TGF and 60.5% for PDGF), whereas total release was realized for PBS-soaked composites. Lastly, release profiles from SBF-soaked composites were growth factor mediated in terms of their amounts and sizes. This was not observed for PBS-soaked composites. IGF-1, on the other hand, exhibited a progressive reduction in levels over the entire experimental period for both buffers. The mechanisms of release were theorized to be a combination of diffusion, degradation and bioactivity. Since SBF is analogous to our body fluids in terms of its ionic constituents, we expect the elution profiles derived from SBF-soaked samples to more accurately emulate the in vivo situation. In conclusion, this study has deemed PCL-TCP composites as suitable delivery systems for platelet-rich plasma.

Sol–gel synthesis of a multifunctional, hierarchically porous silica/apatite composite

In this study, a degradable, hierarchically porous silica/apatite composite material is developed from a simple low-temperature synthesis. Mesoporosity is induced in the silica portion by the use of supramolecular templating. The template is further removed by calcination. Firstly, hydroxyapatite is synthesized through a sol-gel method at near room temperature conditions. After the mineralization process, the crystal surface is coated with a mesoporous silica matrix using the templates already present in the bulk solution. The material is characterized by XRD, N(2)-sorption, FT-IR, SEM/EDS, and TEM. The coating layer is distributed fairly homogeneously over the apatite surface and the coating thickness is easily adjustable and dependent on the amount of added silica precursor. The hybrid material is shown to efficiently induce calcium phosphate formation under in vitro conditions and simultaneously work as a carrier system for drugs.

Biomimetic deposition of apatite coating on surface-modified NiTi alloy

TiO(2) coatings were prepared on NiTi alloy by heat treatment in air at 300, 400, 600 and 800 degrees C. The heat-treated NiTi alloy was subsequently immersed in a simulated body fluid for the biomimetic deposition of the apatite layer onto the surface of TiO(2) coating. The apatite coatings as well as the surface oxide layer on NiTi alloy were characterized using scanning electron microscopy equipped with energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. Results showed the samples heat-treated at 600 degrees C produced a layer of anatase and rutile TiO(2) on the surface of NiTi. No TiO(2) was detected on the surface of NiTi after heat treatment at 300 and 400 degrees C by X-ray diffraction, while rutile was formed on the surface of the 800 degrees C heat-treated sample. It was found that the 600 degrees C heat-treated NiTi induced a layer consisted of microcrystalline carbonate containing hydroxyapatite on its surface most effectively, while 300 and 400 degrees C heat-treated NiTi did not form apatite. This was due to the presence of anatase and/or rutile in the 600 and 800 degrees C heat-treated NiTi which could provide atomic arrangements in their crystal structures suitable for the epitaxy of apatite crystals, and anatase had better apatite-forming ability than rutile. XPS and Raman results revealed that this apatite layer was a carbonated and non-stoichiometric apatite with Ca/P ratio of 1.53, which was similar to the human bone. The formation of apatite on 600 degrees C heat-treated NiTi following immersion in SBF for 3 days indicated that the surface modified NiTi possessed excellent bioactivity.

Characterization and bond strength of electrolytic HA/TiO2 double layers for orthopaedic applications

Insufficient bonding of juxtaposed bone to an orthopaedic/dental implant could be caused by material surface properties that do not support new bone growth. For this reason, fabrication of biomaterials surface properties, which support osteointegration, should be one of the key objectives in the design of the next generation of orthopaedic/dental implants. Titanium and titanium alloy have been widely used in several bioimplant applications, but when implanted into the human body, these still contain some disadvantages, such as poor osteointegration (forming a fibrous capsule), wear debris and metal ion release, which often lead to clinical failure. Electrolytic hydroxyapatite/titanium dioxide (HA/TiO2) double layers were successfully deposited on titanium substrates in TiCl4 solution and subsequently in the mixed solution of Ca(NO3)2 and NH4H2PO4, respectively. After annealing at 300 degrees C for 1 h in the air, the coated specimens were evaluated by dynamic cyclic polarization tests, immersion tests, tensile tests, surface morphology observations, XRD analyses and cells culture. The adhesion strength of the HA coating were improved by the intermediate coating of TiO2 from 11.3 to 46.7 MPa. From cell culture and immersion test results, the HA/TiO2 coated specimens promoted not only cells differentiation, but also appeared more bioactive while maintaining non-toxicity.

Microstructural and in vitro characterization of SiO2-Na2O-CaO-MgO glass-ceramic bioactive scaffolds for bone substitutes

In the present research work, the preparation and characterization of bioactive glass-ceramic scaffolds for bone substitutes are described. The scaffolds were prepared by starch consolidation of bioactive glass powders belonging to the SiO2-Na2O-CaO-MgO system using three different organic starches (corn, potatoes and rice) as reported in a previous screening process. The scaffolds, characterized by scanning electron microscopy, showed a porous structure with highly interconnected pores. The pores sizes assessed by mercury intrusion porosimetry put in evidence the presence of pores of 50-100 microm. The structure of the scaffolds was investigated by X-ray diffraction and revealed the glass-ceramic nature of the obtained material. The mechanical properties of the scaffolds were evaluated by means of compressive tests on cubic samples and the obtained results demonstrated their good mechanical strength. The in vitro bioactivity of the scaffolds was tested by soaking them in a simulated body fluid (SBF) and by subsequently characterizing the soaked surfaces by SEM, EDS and X-ray diffraction. Good in vitro bioactivity was found for the starting glass and for the obtained scaffolds. Moreover, the scaffold bioresorption, tested by measuring the samples weight loss in SBF at different periods of time, showed a partial resorption of the scaffolds. Cell culture testing of the three different scaffolds indicated no differences in cell number and in alkaline phosphatase activity; the morphology of the osteoblasts showed good spreading, comparable to bulk material which was used as the control.

SiO2-CaO-K2O coatings on alumina and Ti6Al4V substrates for biomedical applications

Alumina and Ti6Al4V alloys are widely used for orthopedics and dental applications due to their good mechanical properties and biocompatibility. Unfortunately they can not provide a satisfactory osteointegration when implanted. In fact, both alumina and Ti6Al4V are not bioactive and thus they can only guarantee a morphological fixation with the surrounding tissues without a suitable chemical anchorage. Aiming to impart bioactive properties to these materials a coating can be proposed. At this purpose, a bioactive glass belonging to the SiO2-CaO-K2O system was selected and prepared. This glass, named SCK, possess a thermal expansion coefficient matching with the alumina (8.5x 10(- 6)/ degrees C) and Ti6Al4V (9 x 10(- 6)/ degrees C) ones and thus is a good candidate to produce coatings on both of them. Simple and low-cost enameling and glazing techniques were used to realize the coatings. Structural, morphological and compositional characterizations of the coatings were carried out by means of X-ray diffraction, optical and scanning microscopy and compositional analyses. The in vitro properties of the coatings were investigated by soaking them in a simulated body fluid (SBF) in order to study the precipitation, on their surfaces, of a biologically active layer of hydroxylapatite (HAp).

Process and kinetics of bonelike apatite formation on sintered hydroxyapatite in a simulated body fluid

The surfaces of two hydroxyapatites (HA), which have been sintered at different temperatures of 800 and 1200 degrees C, was investigated as a function of soaking time in simulated body fluid (SBF) using transmission electron microscopy (TEM) attached with energy-dispersive spectrometry (EDX) and laser electrophoresis spectroscopy. The TEM-EDX indicated that after soaking in SBF, both the HAs form bonelike apatite by undergoing the same surface structural change, i.e., formations of a Ca-rich amorphous or nano-crystalline calcium phosphate (ACP) and a Ca-poor ACP, which eventually crystallized into bonelike apatite. Zeta potential characterized by the electrophoresis indicated that during exposure to SBF, the HA surfaces reveal negative surface charge, thereby interacting with the positive calcium ions in the fluid to form the Ca-rich ACP, which gains positive surface charge. The Ca-rich ACP on the HAs then interacts with the negative phosphate ions in the fluid to form the Ca-poor ACP, which stabilizes by being crystallized into bonelike apatite with a low solubility in the SBF. The exposure times for formations of these phases of the Ca-rich ACP, the Ca-poor ACP as well as the apatite were, however, all late on HA sintered at 1200 degrees C, compared with the HA sintered at 800 degrees C. This phenomenon was attributed to a lower initial negative surface charge of the HA sintered at 800 degrees C than of that one sintered at 1200 degrees C, owing to poverty in surface hydroxyl and phosphate groups which are responsible for the surface negativity of the HA. These indicate that sintered temperature of HA might influence not in terms of the process but in terms of the rate of formation of biologically active bonelike apatite on its surface, through which the HA integrates with living bone.

A composite of hydroxyapatite with electrospun biodegradable nanofibers as a tissue engineering material

Biodegradable and biocompatible poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a copolymer of microbial polyester, was fabricated as a nanofibrous film by electrospinning and composited with hydroxyapatite (HAp) by soaking in simulated body fluid. Compared with a PHBV cast (flat) film, the electrospun PHBV nanofibrous film was hydrophobic. However, after HAp deposition, both of the surfaces were extremely hydrophilic. The degradation rate of HAp/PHBV nanofibrous films in the presence of polyhydroxybutyrate depolymerase was very fast. Nanofiber formation increased the specific surface area and HAp enhanced the invasion of enzyme into the film by increasing surface hydrophilicity. The surface of the nanofibrous film showed enhanced cell adhesion over that of the flat film, although cell adhesion was not significantly affected by the combination with HAp.

In vivo evaluation of plasma-sprayed titanium coating after alkali modification

In this paper, plasma-sprayed titanium coatings were modified by alkali treatment. The changes in chemical composition and structure of coatings were examined by SEM and AES. The results obtained indicated that a net-like microscopic texture feature, which was full of the interconnected fine porosity, appeared on the surface of alkali-modified titanium coatings. The surface chemical composition was also altered by alkali modification. A sodium titanate compound was formed on the surface of the titanium coating and replaced the native passivating oxide layer. Its thickness was measured as about 150 nm which was about 10 times of that of the as-sprayed coating. The bone bonding ability of titanium coatings were investigated using a canine model. The histological examination and SEM observation demonstrated that more new bone was formed on the surface of alkali-modified implants and grew more rapidly into the porosity. The alkali-modified implants were found to appose directly to the surrounding bone. In contrast, a gap was observed at the interface between the as-sprayed implants and bone. The push-out test showed that alkali-modified implants had a higher shear strength than as-sprayed implants after 1 month of implantation. An interfacial layer, containing Ti, Ca and P, was found to form at the interface between bone and the alkali-modified implant by EDS analysis.

In vivo evaluation of plasma-sprayed wollastonite coating

Wollastonite coatings were prepared by plasma spraying. The bioactivity of wollastonite coatings was investigated in vivo by implanting in dog's muscle, cortical bone and marrow, respectively. The behaviour of bone tissue around wollastonite coatings were examined by histological and SEM observation. After 1 month in the muscle, a bone-like apatite layer was found to form on the surface of the wollastonite coating. When implanted in cortical bone, histological observation demonstrated that bone tissue could extend and grow along the surface of the wollastonite coating. The coating bonded directly to the bone without any fibrous tissue, indicating good biocompatibility and bone conductivity. SEM and EDS analysis revealed that bone did not bond to wollastonite coating directly, but through a Ca/P layer. This suggested that the formation of bone-like apatite layer was very important for bonding to the bone tissue. The amount of bone-implant contact was also measured. Wollastonite coating was shown to stimulate more bone formation on its surface than titanium coating after implantation for 1 month, enhancing the short-term osseointegration properties of implant. The test in marrow indicated that wollastonite coatings could induce new bone formation on their surface showing good bone inductivity property.

Design, characterization and testing of Ti-based multicomponent coatings for load-bearing medical applications

A comparative investigation of multicomponent thin films based on the systems Ti-Ca-C-O-(N), Ti-Zr-C-O-(N), Ti-Si-Zr-O-(N) and Ti-Nb-C-(N) is presented. TiC(0.5) + 10%CaO, TiC0.5 + 20%CaO, TiC0.5 + 10%ZrO2, TiC0.5 + 20%ZrO2, Ti5Si3 + 10%ZrO2, TiC0.5 + 10%Nb2C and TiC0.5 + 30%Nb2C composite targets were manufactured by means of self-propagating high-temperature synthesis, followed by DC magnetron sputtering in an atmosphere of argon or in a gaseous mixture of argon and nitrogen. The films were characterized in terms of their structure, chemical composition, surface topography, hardness, elastic modulus, elastic recovery, surface charge, friction coefficient, and wear rate. The biocompatibility of the films was evaluated by both in vitro and in vivo experiments. In vitro studies involved the investigation of the proliferation of Rat-1 fibroblasts and IAR-2 epithelial cells on the tested films, morphometric analysis and actin cytoskeleton staining of the cells cultivated on the films. In vivo studies were fulfilled by subcutaneous implantation of Teflon plates coated with the tested films in mice and analysis of the population of cells on the surfaces. The films deposited under optimal conditions showed high hardness in the range of 30-37 GPa, significant reduced Young's modulus, low friction coefficient down to 0.1-0.2 and low wear rate in comparison with conventional magnetron-sputtered TiC and TiN films. The surface of all films was negatively charged with an outstanding shift between the Ar and Ar + N2 Zeta potential curves that reaches 5 mV at the highest pH values. We did not detect statistically significant differences in the attachment, spreading and cell shape of cultured IAR-2 and Rat-1 cells on the Ti-Ca-C-O-(N), Ti-Zr-C-O-(N) (TiC0.5 + 10%ZrO2 target), Ti-Si-Zr-O-(N) films and the uncoated substrata. The adhesion and proliferation of cultured cells in vitro was perfect at all investigated films. Assessment of the population of cells covering on the Teflon plates coated with the Ti-Ca-C-O-(N) and Ti-Zr-C-O-(N) films after 16 weeks of subcutaneous implantation revealed the high biocompatibility level of tested films and absence of inflammatory reactions in mice. Contrary, the epitheliocytes and fibroblasts cultivated on the Ti-Zr-C-O-(N) (TiC0.5 + 20%ZrO2 target) and Ti-Nb-C-(N) films had disturbing actin cytoskeleton.

Surface properties and cell response of low metal ion release Ti-6Al-7Nb alloy after multi-step chemical and thermal treatments

Ti-6Al-7Nb samples treated by innovative multi-step chemical and thermal processes were characterized in order to evaluate their surface properties and cell interaction. The main object was to asses if the treatments were effective in order to obtain a surface presenting at the same time bone-like apatite induction ability, low metal ion release, good cell response and high protein binding. The morphology, crystallographic structure, porosity and wettability of the treated materials were investigated, as well as their interaction with simulated body fluid during soaking for different times. Cytotoxicity, protein adsorption tests and in vitro fibroblast and osteoblast-like cell cultures were also performed.

In Vivo Biocompatibility of a Novel Ceramic-Metal Biocomposite

An in vivo biocompatibility test of a novel biocomposite, with major phases of CaTiO3 and Ti2O, and minor phases of AlTi3, TiO, CaO and Al2O3, was conducted on rats using subcutaneous implantation. The biocomposite and titanium alloy control specimens were removed at 6 and 14 weeks post-implantation. Histological examination revealed no significant adverse reaction of the surrounding tissue to the either the biocomposite or the control material. We conclude that the composite is well tolerated in a physiological environment.

Apatite Formation on Organic-Inorganic Hybrid Containing Sulfonic Group

Apatite formation in living body is essential condition for artificial materials to exhibit bone-bonding ability, i.e. bioactivity. It has been recently revealed that sulfonic group triggers apatite nucleation in body environment. Organic-inorganic hybrids consisting of organic polymer and the sulfonic group are therefore expected to be useful for novel bone-repairing materials exhibiting flexibility as well as bioactivity. In the present study, organic-inorganic hybrids were prepared from vinylsulfonic acid sodium salt and hydroxyethylmethacrylate (HEMA), a kind of acrylic polymer. Bioactivity of the hybrids was assessed in vitro by examining their acceptance of apatite formation in simulated body fluid (SBF, Kokubo solution). The obtained hybrids showed the apatite deposition after soaking in SBF within 7 d.

Effects of silica on the bioactivity of calcium phosphate composites in vitro

In the present study, silica-calcium phosphate composites (SiO(2)-CaP composites) were developed by mixing the starting materials (SiO(2) and CaHPO(4)) in different ratios with the addition of 0.1% w/v NaOH solution. The phase composition of the SiO(2)-CaP composites was determined by XRD and FTIR. After thermal treatment at 350 degrees C/1 h and at 1000 degrees C/3.5 h; all SiO(2)-CaP composites composed of beta-quartz, alpha-cristobalite and beta-Ca2P2O7. The presence of calcium phosphate enhanced the transformation of beta-quartz into alpha-cristobalite at 1000 degrees C. SEM observation indicated favorable attachment and spreading of neonatal rat calvaria osteoblasts onto the surface of silica-rich SiO(2)-CaP composites. After attachment, these cells produced significantly higher amount of protein and expressed higher AP activity than cells attached to silica-poor samples. Results of the study suggested that the silica-based composites are more bioactive than calcium phosphate-based composites. Silica promoted the expression of osteoblast phenotype by both solution-mediated effect and direct interaction with the surface of the substrate.

Characterization of surface modified Ti-6Al-7Nb alloy

In the last years different types of surface modifications were developed with the aim of improving the osteointegration ability of titanium alloys. The chemical composition, crystallographic structure and morphology of a surface layer can be modified in order to obtain a better interaction between the implant, the cells and the organic fluids. The final goal is to obtain a more efficient bone growth also in critical clinical cases. In the present paper were reported several data about the characterization of the Ti-6Al-7Nb alloy treated by two innovative surface treatments. They consist of blasting, followed by a two step chemical etching and heat treatment performed in air or in vacuum. TEM, XRD and SEM investigations were performed in order to assess the structure and morphology of the modified surfaces. The surface chemical composition was investigated by XPS ad AES analyses. The ability to interact with physiological fluids was tested by immersion of the treated materials in an acellular simulated body fluid (SBF). Metal ion concentration analyses of the fluid and SEM observations of the samples were performed after different times of soaking. The mechanical characterization involved scratch and fatigue tests. The surface of treated samples shows chemical, structural and morphological modifications. The passivation pre-treatment has influence on the surface modification. The treated samples evidenced a quite low metal ion release and interact with SBF solution, showing a moderate bioactivity. A relevant decrease in fatigue strength was observed on modified samples.

Effect of particulate bioactive glasses on human macrophages and monocytesin vitro

Bioactive glasses, originally developed to promote tissue adhesion, are finding an increasing array of biomedical applications. The aim of the current study was to assess the ability of silicate- and zinc phosphate-based bioactive glasses to modulate the secretion of cytokines from activated human macrophages and monocytes. Human macrophages and monocytes were isolated and cultured on surfaces coated with a range of quantities of the bioactive glasses. Nontoxic concentrations of the glasses were selected and assessed further for their ability to modulate the secretion of tumor necrosis factor (TNF)-alpha, interleukin (IL)-10 and -6, in the presence or absence of the stimulant lipopolysaccharide. 45S5 glass produced a significant reduction to the amount of TNF-alpha (p<0.05) and IL-6 (p<0.01) secreted by stimulated cells compared with cells stimulated in the absence of bioactive glass. A significant reduction in IL-6 secretion was also observed with the other silicate- and zinc phosphate-based glasses tested. IL-10 secretion was increased (but not significantly) in presence of all glasses tested. TNF-alpha and IL-6 secretion from stimulated cells was lower in presence of the silicate glasses compared with the zinc phosphate glasses, indicating that this system of bioactive glass might be of clinical use in conditions associated with inflammation.

Surface Charge of Bioactive Polyethylene Modified with –SO3H Groups and Its Apatite Inducing Capability in Simulated Body Fluid

A bioactive polyethylene polymer substrate can be produced by incorporation of sulfonic functional groups (-SO3H ) on its surface. Variation of the surface potential of the polyethylene modified with -SO3H groups with soaking in SBF were investigated using a laser electrophoresis zeta-potential analyzer. To complement the study using the laser electrophoresis, the surface was examined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with an attached energy dispersive electron probe X-ray analyser (FE-SEM/EDS). It was found that the surface potential of the polyethylene was highly negative charged after soaking in SBF for 0.5 h, increased for higher soaking times (up to 48 h), and then decreased. The negative charge of the polymer at soaking time of 0.5 h is attributed to the presence of –SO3H groups on the surface. The initial increase in the surface potential was attributed to the incorporation of positively charged calcium ions to form a calcium sulphate, and then the subsequent decrease was assigned to the incorporation of negatively charged phosphate ions to form an amorphous calcium phosphate, which eventually transformed into apatite.

Increased Osteogenesis Elicited by Boron-Modified Bioactive Glass Particles in the SiO2-CaO-P2O5-Na2O System: A Histomorphometric Study in Rats

The effect of boron-containing bioactive glass (BG) particles in the SiO2-CaO-P2O5-Na2O system on the bone formation was studied by histologic, histomorphometric and microchemical evaluation. Wistar rats were used throughout. Under anesthesia, 45S5 BG particles were placed inside the medullary compartment of the tibia (Control), while in the contralateral tibia (Experimental) 45S5.2B BG particles were implanted. The animals were sacrificed 15 days postimplantation. The tibiae were resected, radiographed, and embedded in methyl methacrylate resin. Sections were stained with toluidine blue and analyzed by light microscopy, backscattered scaning electron microscopy and energy-dispersive X-ray analysis (EDX). Histomorphometric determinations were performed. Light microscopy of the histologic sections showed lamellar bone formation surrounding both biomaterials. The histomorphometric study revealed a statistically significant increase in bone tissue around 45S5.2B BG particles. EDX of newly formed bone tissue showed a rise in the Ca:P ratio when 45S5.2B BG particles were employed. The results described in the present study reveal that this boron-containing bioactive glass may be used as scaffold for bone tissue regeneration.

Theoretical analysis of calcium phosphate precipitation in simulated body fluid

The driving force and nucleation rate of calcium phosphate (Ca-P) precipitation in simulated body fluid (SBF) were analyzed based on the classical crystallization theory. SBF supersaturation with respect to hydroxyapatite (HA), octacalcium phosphate (OCP) and dicalcium phosphate (DCPD) was carefully calculated, considering all the association/dissociation reactions of related ion groups in SBF. The nucleation rates of Ca-P were calculated based on a kinetics model of heterogeneous nucleation. The analysis indicates that the nucleation rate of OCP is substantially higher than that of HA, while HA is most thermodynamically stable in SBF. The difference in nucleation rates between HA and OCP reduces with increasing pH in SBF. The HA nucleation rate is comparable with that of OCP when the pH value approaches 10. DCPD precipitation is thermodynamically impossible in normal SBF, unless calcium and phosphate ion concentrations of SBF increase. In such case, DCPD precipitation is the most likely because of its highest nucleation rates among Ca-P phases. We examined the influences of different SBF recipes, interfacial energies, contact angle and molecular volumes, and found that the parameter variations do not have significant impacts on analysis results. The effects of carbonate incorporation and calcium deficiency in HA were also estimated with available data. Generally, such apatite precipitations are more kinetically favorable than HA.

In Vitro Apatite Formation on Surface-Modified Titanium Coatings Prepared by Reactive Plasma Spraying

In vitro nucleation of apatite was studied over surface-modified Ti coatings prepared by reactive plasma spraying (RPS). An in-situ surface-modification of Ti particles is conducted by making use of plasma-enhanced reactions between the Ti particles and the reactive gaseous species in the plasma flame during plasma spraying. Surface-modified Ti coatings were deposited on Ti substrates by radio-frequency (rf)-RPS using a thermal plasma of Ar gas containing 1-6% N2 and/or 1-6% O2 at an input power of 16 kW. As a means of surface modification, Ti powders impregnated with 0.05-0.2 mol% Ca were also sprayed. Compositional changes in the coatings' surface after soaking in simulated body fluid (SBF) were examined by Fourier transform infrared spectroscopy (FT-IR) and thin film X-ray diffraction (TF-XRD). The Ti coatings prepared with Ar-O2 and Ar-N2-O2 plasma formed apatite after 3 days of soaking in SBF. On the other hand, no compositional change was observed in the surface of the Ti coatings sprayed with Ar-N2 plasma, even after 7 days of soaking in SBF. In SBF tests, we observed a retardation of apatite deposition for the Ca-added Ti coatings prepared with Ar-O2 and Ar-N2-O2 plasmas. Analyses by X-ray photoelectron spectroscopy indicated that the Ca impregnated in the RPS-Ti coatings formed a Ca-O compound.