E.S. Thian

Collagen-hyaluronic acid scaffolds for adipose tissue engineering.

Three-dimensional (3-D) in vitro models of the mammary gland require a scaffold matrix that supports the development of adipose stroma within a robust freely permeable matrix. 3-D porous collagen-hyaluronic acid (HA: 7.5% and 15%) scaffolds were produced by controlled freeze-drying technique and crosslinking with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride. All scaffolds displayed uniform, interconnected pore structure (total porosity approximately 85%). Physical and chemical analysis showed no signs of collagen denaturation during the formation process. The values of thermal characteristics indicated that crosslinking occurred and that its efficiency was enhanced by the presence of HA. Although the crosslinking reduced the swelling of the strut material in water, the collagen-HA matrix as a whole tended to swell more and show higher dissolution resistance than pure collagen samples. The compressive modulus and elastic collapse stress were higher for collagen-HA composites. All the scaffolds were shown to support the proliferation and differentiation 3T3-L1 preadipocytes while collagen-HA samples maintained a significantly increased proportion of cycling cells (Ki-67+). Furthermore, collagen-HA composites displayed significantly raised Adipsin gene expression with adipogenic culture supplementation for 8 days vs. control conditions. These results indicate that collagen-HA scaffolds may offer robust, freely permeable 3-D matrices that enhance mammary stromal tissue development in vitro.

The role of surface wettability and surface charge of electrosprayed nanoapatites on the behaviour of osteoblasts

A new deposition method is presented, based on electrospraying, that can build bioceramic structures with desirable surface properties. This technology allows nanoapatite crystals, including hydroxyapatite (nHA), carbonate-substituted HA (nCHA) and silicon-substituted HA (nSiHA), to be electrosprayed on glass substrates. Human osteoblast cells cultured on nSiHA showed enhanced cell attachment, proliferation and protein expression, namely alkaline phosphatase, type 1 collagen and osteocalcin, as compared to nHA and nCHA. The modification of nanoapatite by the addition of silicon into the HA lattice structure renders the electrosprayed surface more hydrophilic and electronegatively charged.

The role of electrosprayed apatite nanocrystals in guiding osteoblast behaviour.

Apatite nanocrystals, which mimic the dimensions of natural bone mineral, were electrosprayed on glass substrates, as a suitable synthetic biomedical material for osteoblast outgrowth was explored. A variety of topographic patterns were deposited and the influence of these designs on osteoblast alignment and cell differentiation was investigated. Patterned cell growth and enhanced cell differentiation were seen. Osteoblasts were also cultured on apatite nanocrystals chemically modified with either carbonate or silicon ions. Enhanced cell proliferation and early formation of mineral nodules were observed on apatite nanocrystals with silicon addition. This work highlights the importance of the combined effects of surface topography and surface chemistry in the guidance of cell behaviour.

A Novel Way of Dispersing Fine Ceramic Particles in PLGA Matrix

α-tricalcium phosphate (α-TCP) was prepared by a wet precipitation reaction between calcium hydroxide and orthophosphoric acid solutions. The as-synthesised powder was then characterised using a Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscope (EDS), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscope (FTIR). Analyses revealed that a phase-pure powder with a Ca/P ratio of 1.5 was produced. In addition, nanosized α-TCP particles of diameter ~ 70 nm were agglomerated to form larger particles of 10μm in diameter. It was found that by the combination of attritor milling and solution evaporation, the agglomerates of α-TCP nanoparticles could be broken down, and distributed evenly within the poly(D,L-lactic-co-glycolic acid) (PLGA) matrix. Thus, a α-TCP/PLGA nanocomposite was successfully produced by a modified solution evaporation method at room temperature followed by hot pressing at 150 °C. The achievable ceramic loading was approximately 38 wt.%, which was confirmed by thermal gravimetric analysis (TGA).

Surface Wettability Enhances Osteoblast Adhesion on Silicon-Substituted Hydroxyapatite Thin Films

Crystalline hydroxyapatite (HA) and 0.8 wt.% silicon-substituted HA (SiHA) thin films were produced using magnetron co-sputtering. These films were subjected to contact angle measurements and in vitro cell culture study using human osteoblast-like (HOB) cells. A wettability study showed that SiHA has a lower contact angle, and thus is more hydrophilic in nature, as compared to HA. Consequently, enhanced cell growth was observed on SiHA at all time-points. Furthermore, distinct and well-developed actin filaments could be seen within HOB cells on SiHA. Thus, this work demonstrated that the surface properties of the coating may be modified by the substitution of Si into the HA structure.

Apatite Formation on α-Tricalcium Phosphate/Poly(D,L-Lactide-Co-Glycolide) Nanocomposite

In this study, a biocomposite comprising nanostructured α-tricalcium phosphate (α-TCP) in a poly(D,L-lactic-co-glycolic acid) (PLGA) matrix was fabricated by a modified solution evaporation method. As a potential temporary bone fixation and substitution material, its bioactivity was evaluated by its ability to form bone-like apatite layer in simulated body fluid (SBF). Owing to the increased surface area covered by the osteoconductive bioceramic of α-TCP, rapid apatite formation was observed. After 7 days of immersion, enhanced nucleation of apatite was observed on the nanocomposite. At day 14, dense lamellar-like apatite was formed on the nanocomposite whilst apatite nucleation had only just started to develop on the surface of pure PLGA. At the same time, a preliminary in-vitro cell culture study was conducted using human osteoblast-like (HOB) cells. A significant increase in cell number with culturing time was observed for the nanocomposite. After 9 days incubation, a confluent lamellar-like apatite layer was formed on the composite surface. This apatite layer was also shown beneath the proliferating HOB cells at Day 16.

Nanostructured Apatite Coatings for Rapid Bone Repair

Nanostructured hydroxyapatite (nHA) thin coatings of thickness 0.5 µm have been successfully produced using a radio-frequency magnetron sputtering technique, through careful selection and control of the processing conditions. nHA coatings were immersed in simulated body fluid (SBF) to determine the rate of nucleation and growth of an apatite layer on their surface. A dense, newlyformed apatite layer with similar characteristics to that of the biological bone apatite, was observed after 7 days of immersion in SBF. X-ray diffraction and infrared analyses confirmed this layer to be calcium-deficient nanocrystalline carbonate HA. All these results demonstrated that the novel nHA coatings were highly bioactive, and the time-frame required to form a dense apatite layer was reduced significantly as compared to the micrometer-sized, sintered HA pellets (from 28 days to 7 days).

Silicon-Substituted Hydroxyapatite Thin Films

There have been numerous interests in the development of hydroxyapatite (HA) coatings on metallic orthopedic implants to maintain mechanical strength while exploiting the excellent biological properties of HA. The addition of silicon (Si) to HA has been demonstrated to enhance the rate of bone repair processing. Magnetron sputtering is a physical vapor deposition technique with the ability to achieve dense, well adhered thin coatings. This chapter describes the synthesis and characterization of Si-substituted HA thin coatings on a titanium substrate, giving good physical, chemical, and biological characteristics for bone ingrowth.

Si-substituted hydroxyapatite

Publisher Summary The idea of developing Silicon-Substituted Hydroxyapatite (SiHA) is largely based on the role of silicon (Si) ions in bone and the excellent bioactivity of silica-based glasses and glass ceramics. Studies suggested that Si incorporation into the HA structure would certainly lead to an enhancement of bioactive performance of HA. This chapter discusses the production and processing of SiHA and presents a review of the physical, mechanical, and biological properties of SiHA, together with its clinical applications. It provides a general overview of the scientific research conducted so far concerning the fabrication, physical, chemical, mechanical, and biological properties of SiHA. More in-depth studies are necessary to understand the mechanism that makes SiHA a better choice of biomaterial, especially at the genomic and proteomic levels. SiHA is usually synthesized via an aqueous precipitation reaction. However, due to its thermal instability and consequently, decomposition at high temperatures, reproducible production of phase-pure SiHA requires careful process control. The incorporation of Si into the HA lattice affects the crystallinity, microstructure, solubility, mechanical, and biological properties of HA. In vitro and in vivo studies have indicated that Si substitution significantly enhanced the bioactivity of HA.

Three-Dimensional Characterization of the Microstructure of Bioglass/Polyethylene Composite by X-Ray Microtomography

A Bioglass® reinforced polyethylene (Bioglass®/polyethylene) composite has been prepared, which combines the high bioactivity of Bioglass® and the toughness of polyethylene. The spatial distribution of Bioglass® particles within the composite is important for the performance of composites in-vivo. Recent developments in X-ray microtomography (XμT) have made it possible to visualize internal and microstructural details with different X-ray absorbencies, nondestructively, and to acquire 3D information at high spatial resolution. In this study, the volume fraction and 3D spatial distribution of Bioglass® particles has been acquired quantitatively by XμT. The information obtained provides a foundation for understanding the mechanical and bioactive properties of the Bioglass®/polyethylene composites.