Electrophoretic deposition of porous hydroxyapatite scaffold

Chitosan scaffolds: Expanding horizons in biomedical applications

Chitosan, a natural polysaccharide from chitin, shows promise as a biomaterial for various biomedical applications due to its biocompatibility, biodegradability, antibacterial activity, and ease of modification. This review overviews "chitosan scaffolds" use in diverse biomedical applications. It emphasizes chitosan's structural and biological properties and explores fabrication methods like gelation, electrospinning, and 3D printing, which influence scaffold architecture and mechanical properties. The review focuses on chitosan scaffolds in tissue engineering and regenerative medicine, highlighting their role in bone, cartilage, skin, nerve, and vascular tissue regeneration, supporting cell adhesion, proliferation, and differentiation. Investigations into incorporating bioactive compounds, growth factors, and nanoparticles for improved therapeutic effects are discussed. The review also examines chitosan scaffolds in drug delivery systems, leveraging their prolonged release capabilities and ability to encapsulate medicines for targeted and controlled drug delivery. Moreover, it explores chitosan's antibacterial activity and potential for wound healing and infection management in biomedical contexts. Lastly, the review discusses challenges and future objectives, emphasizing the need for improved scaffold design, mechanical qualities, and understanding of interactions with host tissues. In summary, chitosan scaffolds hold significant potential in various biological applications, and this review underscores their promising role in advancing biomedical science.

Bone biomaterials and interactions with stem cells

Bone biomaterials play a vital role in bone repair by providing the necessary substrate for cell adhesion, proliferation, and differentiation and by modulating cell activity and function. In past decades, extensive efforts have been devoted to developing bone biomaterials with a focus on the following issues: (1) developing ideal biomaterials with a combination of suitable biological and mechanical properties; (2) constructing a cell microenvironment with pores ranging in size from nanoscale to submicro- and microscale; and (3) inducing the oriented differentiation of stem cells for artificial-to-biological transformation. Here we present a comprehensive review of the state of the art of bone biomaterials and their interactions with stem cells. Typical bone biomaterials that have been developed, including bioactive ceramics, biodegradable polymers, and biodegradable metals, are reviewed, with an emphasis on their characteristics and applications. The necessary porous structure of bone biomaterials for the cell microenvironment is discussed, along with the corresponding fabrication methods. Additionally, the promising seed stem cells for bone repair are summarized, and their interaction mechanisms with bone biomaterials are discussed in detail. Special attention has been paid to the signaling pathways involved in the focal adhesion and osteogenic differentiation of stem cells on bone biomaterials. Finally, achievements regarding bone biomaterials are summarized, and future research directions are proposed.

Characterization of gelatin and chitosan scaffolds cross-linked by addition of dialdehyde starch

In this study the influence of the addition of dialdehyde starch on the properties of scaffolds based on gelatin and chitosan obtained by the freeze-drying method was investigated. In addition, the adhesion and proliferation of human osteosarcoma SaOS-2 cells on the obtained scaffolds was examined. Chitosan and gelatin were mixed in different weight ratios (75/25, 50/50, 25/75) with 1, 2 and 5 wt% addition of dialdehyde starch. The obtained scaffolds were subjected to mechanical testing, infrared spectroscopy, swelling measurements, low-pressure porosimetry and zeta potential measurement. Internal material structures were observed by scanning electron microscopy. The results showed that the cross-linking process occurred after the addition of dialdehyde starch and resulted in increased mechanical strength, swelling properties, zeta potential and porosity of studied materials. The attachment of SaOS-2 cells to all modified materials was better compared to an unmodified control and the proliferation of these cells was markedly increased on modified scaffolds.

Template-based syntheses for shape controlled nanostructures

A variety of nanostructured materials are produced through template-based synthesis methods, including zero-dimensional, one-dimensional, and two-dimensional structures. These span different forms such as nanoparticles, nanowires, nanotubes, nanoflakes, and nanosheets. Many physical characteristics of these materials such as the shape and size can be finely controlled through template selection and as a result, their properties as well. Reviewed here are several examples of these nanomaterials, with emphasis specifically on the templates and synthesis routes used to produce the final nanostructures. In the first section, the templates have been discussed while in the second section, their corresponding synthesis methods have been briefly reviewed, and lastly in the third section, applications of the materials themselves are highlighted. Some examples of the templates frequently encountered are organic structure directing agents, surfactants, polymers, carbon frameworks, colloidal sol-gels, inorganic frameworks, and nanoporous membranes. Synthesis methods that adopt these templates include emulsion-based routes and template-filling approaches, such as self-assembly, electrodeposition, electroless deposition, vapor deposition, and other methods including layer-by-layer and lithography. Template-based synthesized nanomaterials are frequently encountered in select fields such as solar energy, thermoelectric materials, catalysis, biomedical applications, and magnetowetting of surfaces.

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. Over 5000 publications on this topic were published since then. Therefore, a thorough analysis of the available literature has been performed and about 50 (this number is doubled, if all possible modifications are counted) deposition techniques of CaPO4 have been revealed, systematized and described. These CaPO4 deposits (coatings, films and layers) used to improve the surface properties of various types of artificial implants are the topic of this review.

Osteoconductivity and osteoinductivity of porous hydroxyapatite coatings deposited by liquid precursor plasma spraying: in vivo biological response study

The beneficial effect of a porous structure on the biological functions of calcium phosphate bulk ceramic or scaffold has been well documented. Nevertheless, the effect of a porous structure on the in vivo performance of hydroxyapatite (HA) coatings has been rarely reported, partly due to the difficulty in synthesizing porous HA coatings suitable for commercial applications. In this study, we have carried out a systematic in vivo study of porous HA-coated Ti implants (with and without surface modification) prepared by the liquid precursor plasma spraying process, in terms of its osteoconductivity and osteoinductivity. The results suggest the clear advantage of the porous structure over the dense structure, despite the pore structure (about 48% porosity and less than 100 μm average pore size) being far from the ideal pore structure reported for bulk ceramic. The porous HA-coated implant significantly promotes early bone ingrowth at the pre-generated defective region, and early fixation at the bone-implant interface, especially at early implantation time (one month), showing about 120% and 40% increases respectively over those of the dense HA-coated implants prepared by the conventional atmospheric plasma spraying process. Moreover, the porous structure can be readily used to incorporate collagen/rh-BMP2, which demonstrates clear ectopic bone formation. Overall, the results suggest the augmentation of bone ingrowth is significant for HA coatings with a porous structure, which is critical for the early fixation and long-term stability of medical implants.

Three-dimensional scaffolds for tissue engineering applications: role of porosity and pore size

Tissue engineering applications commonly encompass the use of three-dimensional (3D) scaffolds to provide a suitable microenvironment for the incorporation of cells or growth factors to regenerate damaged tissues or organs. These scaffolds serve to mimic the actual in vivo microenvironment where cells interact and behave according to the mechanical cues obtained from the surrounding 3D environment. Hence, the material properties of the scaffolds are vital in determining cellular response and fate. These 3D scaffolds are generally highly porous with interconnected pore networks to facilitate nutrient and oxygen diffusion and waste removal. This review focuses on the various fabrication techniques (e.g., conventional and rapid prototyping methods) that have been employed to fabricate 3D scaffolds of different pore sizes and porosity. The different pore size and porosity measurement methods will also be discussed. Scaffolds with graded porosity have also been studied for their ability to better represent the actual in vivo situation where cells are exposed to layers of different tissues with varying properties. In addition, the ability of pore size and porosity of scaffolds to direct cellular responses and alter the mechanical properties of scaffolds will be reviewed, followed by a look at nature's own scaffold, the extracellular matrix. Overall, the limitations of current scaffold fabrication approaches for tissue engineering applications and some novel and promising alternatives will be highlighted.

Synthesis of silver nanoparticles confined in hierarchically porous monolithic silica: a new function in aromatic hydrocarbon separations

Silver nanoparticles (Ag NPs) have been homogeneously introduced into hierarchically porous monolithic silica columns with well-defined macropores and SBA-15-type hexagonally ordered mesopores by using ethanol as the mild reductant. Within the cylindrical silica mesopores treated with aminopropyl groups as the host, monocrystalline Ag NPs and nanorods are obtained after being treated in silver nitrate/ethanol solution at room temperature for different durations of reducing time. The loading of Ag NPs in the monolith can be increased to 33 wt % by the repetitive treatment, which also led to the formation of polycrystalline Ag nanorods in the mesopores. Although the bare silica column cannot separate aromatic hydrocarbons, good separation of those molecules by noncharged Ag NPs confined in the porous structure of the monolith has been for the first time demonstrated with the Ag NP-embedded silica column. The NP-embedded monolithic silica would be a powerful separation tool for hydrocarbons with different number, position, and configuration of unsaturated bonds.

Evaluation of biological properties of electron beam melted Ti6Al4V implant with biomimetic coating in vitro and in vivo

Background

High strength porous titanium implants are widely used for the reconstruction of craniofacial defects because of their similar mechanical properties to those of bone. The recent introduction of electron beam melting (EBM) technique allows a direct digitally enabled fabrication of patient specific porous titanium implants, whereas both their in vitro and in vivo biological performance need further investigation.

Methods

In the present study, we fabricated porous Ti6Al4V implants with controlled porous structure by EBM process, analyzed their mechanical properties, and conducted the surface modification with biomimetic approach. The bioactivities of EBM porous titanium in vitro and in vivo were evaluated between implants with and without biomimetic apatite coating.

Results

The physical property of the porous implants, containing the compressive strength being 163 - 286 MPa and the Young’s modulus being 14.5–38.5 GPa, is similar to cortical bone. The in vitro culture of osteoblasts on the porous Ti6Al4V implants has shown a favorable circumstance for cell attachment and proliferation as well as cell morphology and spreading, which were comparable with the implants coating with bone-like apatite. In vivo, histological analysis has obtained a rapid ingrowth of bone tissue from calvarial margins toward the center of bone defect in 12 weeks. We observed similar increasing rate of bone ingrowth and percentage of bone formation within coated and uncoated implants, all of which achieved a successful bridging of the defect in 12 weeks after the implantation.

Conclusions

This study demonstrated that the EBM porous Ti6Al4V implant not only reduced the stress-shielding but also exerted appropriate osteoconductive properties, as well as the apatite coated group. The results opened up the possibility of using purely porous titanium alloy scaffolds to reconstruct specific bone defects in the maxillofacial and orthopedic fields.

Preparation and Characterization of Biphasic Calcium Phosphate Coatings on 316L Stainless Steel Fabricated by Electrophoretic Deposition

Biphasic calcium phosphate (BCP) ceramic is a synthetic biomaterial exhibiting a chemical composition similar to that of tooth mineral. Therefore, it is viably used in coating metallic implants manufactured from metals and alloys, such as titanium and stainless steel. In the present study, electrophoretic deposition (EPD) has been attempted for depositing BCP coatings on 316L Stainless Steel substrate followed by vacuum sintering at 800 °C for 1 h. The surface morphology, thickness, compositions and microstructure of the BCP coated 316L SS was investigated by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and the bond strength of the coating was measured.

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. Hence, a surface engineering is aimed to modify both the biomaterials, themselves, and biological responses through introducing desirable changes to the surface properties of the implants but still maintaining their bulk mechanical properties. To fulfill these requirements, a special class of artificial bone grafts has been introduced in 1976. It is composed of various mechanically stable (therefore, suitable for load bearing applications) biomaterials and/or bio-devices with calcium orthophosphate coatings, films and layers on their surfaces to both improve interactions with the surrounding tissues and provide an adequate bonding to bones. Many production techniques of calcium orthophosphate coatings, films and layers have been already invented and new promising techniques are continuously investigated. These specialized coatings, films and layers used to improve the surface properties of various types of artificial implants are the topic of this review.

Effect of Temperature on BCP Ceramics Coating on 316L Stainless Steel Using Electrophoretic Technique

Biphasic calcium phosphate (BCP) coatings on a medical grade 316L stainless steel substrate were prepared by electrophoretic deposition (EPD) using ethanol as a dispersive medium. The deposition voltage of 30V was applied for 1 min at 25, 40 and 60 °C, respectively. The coated substrates were sintered in a vacuum furnace at 800 °C for 1 h. The surface morphology, structure and phase composition of the coatings was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that by increasing deposition conditions of voltage and temperature, crack occurrence and morphological changes increased in the produced coatings. The optimum condition for crack-free surface was at 30 V at 25 °C.

Electrophoretic Deposition of Biphasic Calcium Phosphate (BCP) Coatings on 316L Stainless Steel at Room Temperature

Electrophoretically deposition of Biphasic calcium phosphate on 25 × 10 × 1.2 mm (length, width, and thickness) 316L stainless steel plates using ethanol as dispersing medium; It was achieved on the cathode with constant voltages 20, 30, 50, and 100 V during 20, 30, 60, 90 and 120 seconds, respectively. After deposition, the samples were dried at room temperature for 24 hours and deposition weight and thickness of the coatings were measured. The coated samples were sintered in a tube furnace at 800 °C for 1 h in an argon atmosphere. After the sintering, the surface morphology and structure and phase composition of the samples were studied by a scanning electron microscope (SEM), energy dispersive spectrometry (EDX) and phase purity of the coating material by X-ray diffraction.

Electrophoretic deposition of porous CaO-MgO-SiO2 glass-ceramic coatings with B2O3 as additive on Ti-6Al-4V alloy

The sub-micron glass-ceramic powders in CaO-MgO-SiO(2) system with 10 wt% B(2)O(3) additive were synthesized by sol-gel process. Then bioactive porous CaO-MgO-SiO(2) glass-ceramic coatings on Ti-6Al-4V alloy substrates were fabricated using electrophoretic deposition (EPD) technique. After being calcined at 850°C, the above coatings with thickness of 10-150 μm were uniform and crack-free, possessing porous structure with sub-micron and micron size connected pores. Ethanol was employed as the most suitable solvent to prepare the suspension for EPD. The coating porous appearance and porosity distribution could be controlled by adjusting the suspension concentration, applied voltage and deposition time. The heat-treated coatings possessed high crystalline and was mainly composed of diopside, akermanite, merwinite, calcium silicate and calcium borate silicate. Bonelike apatite was formed on the coatings after 7 days of soaking in simulated body fluid (SBF). The bonding strength of the coatings was needed to be further improved.

Electrophoretic deposition of biomaterials

Electrophoretic deposition (EPD) is attracting increasing attention as an effective technique for the processing of biomaterials, specifically bioactive coatings and biomedical nanostructures. The well-known advantages of EPD for the production of a wide range of microstructures and nanostructures as well as unique and complex material combinations are being exploited, starting from well-dispersed suspensions of biomaterials in particulate form (microsized and nanoscale particles, nanotubes, nanoplatelets). EPD of biological entities such as enzymes, bacteria and cells is also being investigated. The review presents a comprehensive summary and discussion of relevant recent work on EPD describing the specific application of the technique in the processing of several biomaterials, focusing on (i) conventional bioactive (inorganic) coatings, e.g. hydroxyapatite or bioactive glass coatings on orthopaedic implants, and (ii) biomedical nanostructures, including biopolymer-ceramic nanocomposites, carbon nanotube coatings, tissue engineering scaffolds, deposition of proteins and other biological entities for sensors and advanced functional coatings. It is the intention to inform the reader on how EPD has become an important tool in advanced biomaterials processing, as a convenient alternative to conventional methods, and to present the potential of the technique to manipulate and control the deposition of a range of nanomaterials of interest in the biomedical and biotechnology fields.

Electrophoretic deposition of nanobiocomposites for orthopedic applications: influence of current density and coating duration

Frequently metal implants undergo detachment from the host tissue due to inadequate biocompatibility and poor osteointegration. In view of this, bioactive porous apatite-wollastonite/chitosan nanocomposite coating was prepared using electrophoretic deposition (EPD) technique in the present work. The effect of coating duration and current density on surface characteristics of the nanocomposite coating was assessed using optical microscope and scanning electron microscope. EPD led to the formation of thick and homogeneous coating. Adhesion of the composite coating on titanium substrate was evaluated using tape test and bioactivity of the coatings was studied by immersing in simulated body fluid (SBF). The coating with higher current density and longer coating duration was found to be suitable with improved adhesion and bioactivity for intended metal implants.

Electrophoretic deposition of HA/MWNTs composite coating for biomaterial applications

A composite coating of hydroxyapatite (HA)/multi-walled carbon nanotubes (MWNTs) has been fabricated by electrophoretic deposition (EPD). The nano powders of HA and MWNTs were dispersed in ethanol with total concentration of 0.005 g/mL and MWNTs 20% and 30% contents (wt). And the pH value of suspension was adjusted in a range from 4 to 5. After stabilization the mixture was ultrasonically treated for 3 h to form a stable suspension. Prior to the electrophoretic deposition, the titanium substrate was hydrothermally treated at 140 in NaOH (10 mol/L) solution for 6 h. A titanium sheet and circinal net of stainless steel were used as a cathode and an anode respectively, and a constant deposition voltage of 30 V was applied for 50-60 s in the EPD process. The thickness of the coatings was controlled from 10 microm to 20 microm. The samples of composite coating were then sintered in a resistance tube furnace in flowing argon at 700 for 2 h. The structure of the as prepared coating was characterized by SEM and XRD, and the bonding force of the coating/substrate was measured by an interfacial shear strength test. It is shown that the bonding strengths between the coating and the titanium substrate is as high as 35 MPa. The cell culture experiments indicate that the prepared composite coating of HA/MWNTs possesses good biocompatibility.

Fabrication of porous substrates: a review of processes using pore forming agents in the biomaterial field

This paper is a review of solid and casting manufacturing processes able to create porous materials, mainly in the biomaterial field. The considered methods are based on pore forming agents that are removed either by heating or by dissolution. All techniques lead to products presenting pores with amount, size, and shape are close to those of the initial pore formers. Porosities up to 90% with pores ranging from 1 to 2000 microm are reported. Major differences concern macrointerconnections that are more frequently obtained using foams, or porogens which undergo a melting stage during firing. Casting methods combined with solid free form fabrication are promising for the design of porous network through the manufacturing of 3D scaffolds corresponding to the desired porosity.

Generation of hydroxyapatite patterns by electrophoretic deposition

Hydroxyapatite (HAp) patterns with distinct boundaries were generated by electrophoretic deposition (EPD) utilizing an insulating mask that partially blocks the electric field. For the EPD process, we selected two types of mask: a polytetrafluoroethylene (PTFE) board with holes and a resist pattern. A porous PTFE film, which differed from the mask PTFE, was employed as a substrate and attached to the mask. EPD was performed with a suspension of wollastonite particles in acetone, which were deposited on the substrate in the form of the patterned mask. The deposited wollastonite particles induced HAp patterns during a soak in simulated body fluid (SBF). As a result, minute HAp patterns, such as dots, lines, and corners were fabricated on the porous PTFE substrate with a minimum line width of about 100 microm.

Electrophoretic deposition of silicon substituted hydroxyapatite coatings from n-butanol-chloroform mixture

Silicon Substituted Hydroxyapatite (Si-HA) coatings were prepared on titanium substrates by electrophoretic deposition (EPD). The stability of Si-HA suspension in n-butanol and chloroform mixture has been studied by electricity conductivity and sedimentation test. The microstructure, shear strength and bioactivity in vitro has been tested. The stability of Si-HA suspension containing n-butanol and chloroform mixture as medium is better than that of pure n-butanol as medium. The good adhesion of the particles with the substrate and good cohesion between the particles were obtained in n-butanol and chloroform mixture. Adding triethanolamine (TEA) as additive into the suspension is in favor of the formation of uniform and compact Si-HA coatings on the titanium substrates by EPD. The shear strength of the coatings can reach 20.43 MPa after sintering at 700 degrees C for 2 h, when the volume ratio of n-butanol: chloroform is 2:1 and the concentration of TEA is 15 ml/L. Titanium substrates etched in H(2)O(2)/NH(3) solution help to improve the shear strength of the coatings. After immersion in simulated body fluid for 7 days, Si-HA coatings have the ability to induce the bone-like apatite formation.

Early weight bearing of porous HA/TCP (60/40) ceramics in vivo: a longitudinal study in a segmental bone defect model of rabbit

Porous interconnected hydroxyapatite (HA) and HA/tricalcium phosphate (TCP) (60/40) ceramics are promising materials for hard tissue repair. However, the mechanical properties of these materials have not been accurately determined under weight-bearing conditions. In this study, newly developed HA and HA/TCP (60/40) ceramics were used with intramedullary fixation in segmental bone defects of rabbits. Early radiological, histological, densitometric and biomechanical changes were evaluated. The mean radiological grade of healing and bonding to bone was higher in HA/TCP (60/40) ceramics than that of pure HA ceramics but the difference was not statistically significant. The densities of both implanted ceramics improved with time, supported by the histological evaluation of bone matrix ingrowth into ceramic pores, whereas the densities at the bone-ceramic interface decreased gradually. Flexural resonant frequencies and three-point bending strength increased, revealing an increase in mechanical stability during this early critical time interval where implant and/or bone-implant interface failures occur frequently. It can be concluded that both HA and HA/TCP (60/40) ceramics have a limited application in the treatment of load-bearing segmental bone defects but did not fail at the early stages of implantation.

Biocompatibility of electrophoretical deposition of nanostructured hydroxyapatite coating on roughen titanium surface:In vitroevaluation using mesenchymal stem cells

A nano hydroxyapatite (HAp) layer was coated on a roughen titanium surface by means of electrophoretic deposition with an acetic anhydride solvent system. The objectives of this current study are to investigate whether nano-HAp can improve mechanical strength at a lower sintering temperature and biocompatibility. Densification temperature was lowered from usual 1000 to 800 degrees C. The coating interfacial bonding strength, phase purity, microstructure, and biocompatibility were investigated. Degradation of HA phase was not detected in XRD. A porous TiO2 layer acts as a gradient coating layer with an intermediate thermal expansion coefficient between hydroxyapatite and titanium that reduces the thermal stress. From SEM image, the coating does not contain any crack. Mesenchymal stem cell (MSC) is the progenitor cell for various tissues in mature animals, which can improve integration of bone tissue into implant. In this in vitro study, rabbit MSCs culture indicated that the HAp/Ti nanocomposite biomaterial had good biocompatibility and bioactivity. Around materials and on its surface cell grew well with good morphology. Proliferation of the MSCs on the nano-HAp coating was higher than its micron counterpart in XTT assay. These properties show potential for the orthopaedic and dental applications.

Electrophoretic deposition of hydroxyapatite coating on Fecralloy and analysis of human osteoblastic cellular response

Hydroxyapatite has been successfully deposited onto Fecralloy substrate (a metal alloy with 22% Cr, 4.8% Al) by electrophoretic deposition in an attempt to promote the adhesion between coating and substrate, consequently to extend the lifetime of implants. Fecralloy has the ability to generate a dense and stable alpha-Al(2)O(3) layer "in situ" during thermal treatment, which will highly improve the adhesion and the corrosion resistance of the coating system. Phases and morphologies of HA coating were found to vary after sintering according to XRD and SEM analysis. Besides the physicochemical characterization, the effects of the Fecralloy, thermally generated oxide layer, and HA coating on the early and late responses of osteoblasts in vitro were determined. Cellular morphology and proliferation were studied up to 7 days. Quantitative assays of mineralization were conducted up to 14 days. Osteoblasts showed increased cell spreading and cell proliferation on metal substrates, with significantly higher mineralization on HA coating. The results in this study proved that Fecralloy is a biocompatible metal and the HA coating on Fecralloy provides a good candidate for orthopaedic and dental implants.

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.

Different Morphology of Hydroxyapatite Coatings on Titanium by Electrophoretic Deposition

Commercial hydroxyapatite powders were electrophoretically deposited on titanium substrates. In this study, the effect of deposition durations and applied voltages on deposition yield was investigated. Green and sintered coatings were studied by SEM and XRD. It was observed that by applying low voltages and presedimentation, uniform and smooth hydroxyapatite coating can be prepared. In order to obtain roughened hydroxyapatite coatings, high voltages have to be applied. It was concluded that experimental conditions of powder concentration, applied potential, and presedimentation have a significant effect on the deposited coating morphology.

Fabrication of hydroxyapatite sponges by dextran sulphate/amino acid templating

We report a new template-directed method for the fabrication of hydroxyapatite (HAp) sponges by using amino-acid-coated HAp nanoparticles dispersed within a viscous polysaccharide (dextran sulfate) matrix, and describe the use of these materials for the viability and proliferation of human bone marrow stromal cells. The nanoparticles were prepared in the presence of excess amounts of aspartic acid, alanine or arginine, and subsequently organised into macroporous frameworks with typical pore sizes of 100-200 microm during thermal degradation of the dextran matrix. The sponge macrostructure was influenced by changes in the heating rate and sintering time, as well as the use of different amino acids or variations in dextran functional groups. Biocompatibility testing showed retention of cell viability, production of extracellular matrix and alkaline phosphatase expression, suggesting that it should be possible to exploit this novel fabrication method for potential applications in cartilage or soft tissue engineering.

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.

Development of Hydroxyapatite Thin Film on Titanium Substrate by Electrophoretic Deposition

Electrophoretic deposition was used for HA coating on dental implants with different coating thickness. The HA coating thickness was examined in terms of applied voltage and time, and powder concentration in suspension. Nano-size HA and SiO2-CaO-P2O5-B2O3 bioglass powders were synthesized by sol-gel method. Polyvinyl alcohol (3 wt%) as a binder was resolved in ethyl alcohol, then, nano HA powder was dispersed ultrasonically in the mixture for 15 min and pH was adjusted with HNO3 for positive charging on particle. Titanium substrate was held on cathode and counter electrode was platinum. HA with 0.5 % and 0.03 % of powder concentration was deposited electrophoretically at 10~20 V for 1~20 minutes. The thickness of as-deposited HA layer decreased from nearly 80 µm (0.5 %, 20 V, 10 min) to 4~5 µm (0.03%, 10V, 1 min) as powder concentration, applied voltage and time decreased, respectively. The surface of HA coating layer deposited in lower powder concentration showed much more homogeneous and relatively dense morphology, in contrast, the surface in thick suspension became rough or porous and was easily spalled. In a co-deposition of HA and bioglass, co-deposited glass played an important role in increasing bonding strength between coating layer and substrate. It is believed that electrophoretic deposition method can be one of alternatives for relatively thin and easy HA coating.