Patterning hydroxyapatite biocoating by electrophoretic deposition

Regulation and Directing Stem Cell Fate by Tissue Engineering Functional Microenvironments: Scaffold Physical and Chemical Cues

It is well known that stem cells reside within tissue engineering functional microenvironments that physically localize them and direct their stem cell fate. Recent efforts in the development of more complex and engineered scaffold technologies, together with new understanding of stem cell behavior in vitro, have provided a new impetus to study regulation and directing stem cell fate. A variety of tissue engineering technologies have been developed to regulate the fate of stem cells. Traditional methods to change the fate of stem cells are adding growth factors or some signaling pathways. In recent years, many studies have revealed that the geometrical microenvironment played an essential role in regulating the fate of stem cells, and the physical factors of scaffolds including mechanical properties, pore sizes, porosity, surface stiffness, three-dimensional structures, and mechanical stimulation may affect the fate of stem cells. Chemical factors such as cell-adhesive ligands and exogenous growth factors would also regulate the fate of stem cells. Understanding how these physical and chemical cues affect the fate of stem cells is essential for building more complex and controlled scaffolds for directing stem cell fate.

Insights into the apatite mineralization potential of thermally processed nanocrystalline Ca10−xFex(PO4)6(OH)2

The thermal treatment of Ca_10−xFe_x(PO₄)₆(OH)₂ at different temperatures had an effect on the mineralization potential under non-cellular and cellular conditions by releasing its bioactive ions at optimal or excessive levels.

Scaffold Structural Microenvironmental Cues to Guide Tissue Regeneration in Bone Tissue Applications

In the process of bone regeneration, new bone formation is largely affected by physico-chemical cues in the surrounding microenvironment. Tissue cells reside in a complex scaffold physiological microenvironment. The scaffold should provide certain circumstance full of structural cues to enhance multipotent mesenchymal stem cell (MSC) differentiation, osteoblast growth, extracellular matrix (ECM) deposition, and subsequent new bone formation. This article reviewed advances in fabrication technology that enable the creation of biomaterials with well-defined pore structure and surface topography, which can be sensed by host tissue cells (esp., stem cells) and subsequently determine cell fates during differentiation. Three important cues, including scaffold pore structure (i.e., porosity and pore size), grain size, and surface topography were studied. These findings improve our understanding of how the mechanism scaffold microenvironmental cues guide bone tissue regeneration.

Advances in synthesis of calcium phosphate crystals with controlled size and shape

Calcium phosphate (CaP) materials have a wide range of applications, including biomaterials, adsorbents, chemical engineering materials, catalysts and catalyst supports and mechanical reinforcements. The size and shape of CaP crystals and aggregates play critical roles in their applications. The main inorganic building blocks of human bones and teeth are nanocrystalline CaPs; recently, much progress has been made in the application of CaP nanocrystals and their composites for clinical repair of damaged bone and tooth. For example, CaPs with special micro- and nanostructures can better imitate the biomimetic features of human bone and tooth, and this offers significantly enhanced biological performances. Therefore, the design of CaP nano-/microcrystals, and the shape and hierarchical structures of CaPs, have great potential to revolutionize the field of hard tissue engineering, starting from bone/tooth repair and augmentation to controlled drug delivery devices. Previously, a number of reviews have reported the synthesis and properties of CaP materials, especially for hydroxyapatite (HAp). However, most of them mainly focused on the characterizations and physicochemical and biological properties of HAp particles. There are few reviews about the control of particle size and size distribution of CaPs, and in particular the control of nano-/microstructures on bulk CaP ceramic surfaces, which is a big challenge technically and may have great potential in tissue engineering applications. This review summarizes the current state of the art for the synthesis of CaP crystals with controlled sizes from the nano- to the macroscale, and the diverse shapes including the zero-dimensional shapes of particles and spheres, the one-dimensional shapes of rods, fibers, wires and whiskers, the two-dimensional shapes of sheets, disks, plates, belts, ribbons and flakes and the three-dimensional (3-D) shapes of porous, hollow, and biomimetic structures similar to biological bone and tooth. In addition, this review will also summarize studies on the controlled formation of nano-/microstructures on the surface of bulk ceramics, and the preparation of macroscopical bone grafts with 3-D architecture nano-/microstructured surfaces. Moreover, the possible directions of future research and development in this field, such as the detailed mechanisms behind the size and shape control in various strategies, the importance of theoretical simulation, self-assembly, biomineralization and sacrificial precursor strategies in the fabrication of biomimetic bone-like and enamel-like CaP materials are proposed.

Electrodeposition of polymer nanodots with controlled density and their reversible functionalization by polyhistidine-tag proteins

We present a simple and rapid procedure for producing polymer-coated substrates that can be easily functionalized by ion-chelating proteins. The procedure consists of depositing 18 nm metal-chelating cyclam-modified polymer nanoparticles (cyclam-nps) onto a conductive substrate (an Indium Tin Oxide (ITO) electrode) from an aqueous dispersion of Cu(2+)-loaded cyclam-nps while being subjected to a direct current (DC) field. The density of deposited nps as measured by AFM is shown to be in direct correlation to the concentration of nps in the dispersion with deposition of the particles taking less than 5 s. Because of the functionalization of the nps with cyclam groups, they can be used as anchoring sites for 6-Histidine (6-His) tagged proteins through complexation with divalent metal ions. In this work 6-His Green Fluorescent Protein (6-His GFP) is used as a model protein. The characterization by fluorescence microscopy clearly shows that the protein affinity was ion dependent and that the 6-His GFP density can be controlled by np density, which is itself easily tunable. AFM observations confirmed the immobilization of 6-His GFP onto cyclam-nps and its subsequent removal by treatment with ethylenediaminetetraacetic acid (EDTA).

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.

Comparison of the osteoblast and myoblast behavior on hydroxyapatite microgrooves

Surface topography is one of the most important surface properties of biomaterials and microfabrication techniques provide new routes to produce precisely controlled surface topographies for investigating the topographic effects on cell behavior. In this study, hydroxyapatite (HA) microgrooved surfaces were used to study the osteoblast and myoblast response to the surface micro-features. The microgrooves were first produced on silicon wafers by photolithography, and then coated with HA using sputtering technique. Orientation angle (OA) was used to evaluate the contact guidance introduced by microgrooves and form index (FI) was introduced to describe the cell morphology change. The results show that the microgroove effects on myoblasts are more obvious than those on osteoblasts, and the two types of cells are sensitive to different sizes of microgrooves. The microgrooves with 8 microm width strongly affect both osteoblasts and myoblasts, while the microgrooves with 24 microm width strongly affect myoblasts only. These results confirm that the surface topographic effect is of cell specific, and therefore, design of surface topographic features must be different for myoblasts and osteoblasts.

Processing and Characterization of Biocompatible Titania Coatings by Electrophoretic Deposition

The electrophoretic deposition (EPD) technique was developed for depositing TiO2 films on stainless steel (SS) and titanium substrates. Titania coatings were obtained in conditions of optimal solution stability using acetylacetone suspensions of TiO2 nanoparticles and I2 at pH≈ 5. Deposition tests were carried out at 10V for varying times. The deposit thickness was seen to increase with EPD time, revealing that the deposits grew quickly for times <120 s, reaching a saturation value at longer times. The substrates were treated by physical and chemical methods before EPD in order to improve the adhesion of the films. The EPD coatings were sintered at 700, 800 and 900 °C under controlled argon atmosphere or in vacuum to study the influence of sintering atmosphere on crystalline phase transformation. The TiO2 coatings were characterized by XRD using Rietveld analysis. The results showed that TiO2 films on Ti substrates (chemically leached before deposition) had better adherence, homogeneity and density than those on SS. The coatings sintered al 700°C in vacuum resulted in a major proportion of anatasa phase. The porosity of the titania coatings sintered at 700°C (2 hr) in vacuum was calculated to be 19% .

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.