Bee Yen Tay

Effect of silver content on the antibacterial and bioactive properties of silver-substituted hydroxyapatite.

The long-term success of a biomaterial used during surgery may be compromised by infection. A possible effective solution is to make the biomaterial osteoconductive and antibacterial. A range of silver-substituted hydroxyapatite (AgHA) of up to 1.1 wt. % of Ag was synthesized. AgHA displayed a rod-like morphology of dimensions ~50 nm in length and ~15 nm in width. Phase-pure AgHA was demonstrated in the X-ray diffraction patterns and Fourier transform infrared spectroscopy spectra. Comparing with hydroxyaptite (HA), 0.5AgHA exhibited a 3-log reduction in the number of bacteria. Diffusion of the entrapped Ag(+) ions towards the crystal structure surface was revealed by an increase of 6 at. % Ag in the X-ray photoelectron spectroscopy results. Furthermore, less than 0.5 ppm of Ag(+) ions being released from 0.5AgHA into the deionized water medium was evidenced from the inductively coupled plasma mass spectrometry results. AgHA produced by co-precipitation gave rise to minimal release of Ag(+) ions. It was hypothesized that the diffused surface Ag(+) ions damaged the bacteria cell membrane and impede its replication. With the culturing time, significant increase in the number of human mesenchymal stem cells (p < 0.05) was demonstrated on 0.5AgHA.

Fabrication of three‐dimensional porous scaffolds with controlled filament orientation and large pore size via an improved E‐jetting technique

Biodegradable polymeric scaffolds have been widely used in tissue engineering as a platform for cell proliferation and subsequent tissue regeneration. Conventional microextrusion methods for three-dimensional (3D) scaffold fabrication were limited by their low resolution. Electrospinning, a form of electrohydrodynamic (EHD) printing, is an attractive method due to its capability of fabricating high-resolution scaffolds at the nanometer/micrometer scale level. However, the scaffold was composed of randomly orientated filaments which could not guide the cells in a specific direction. Furthermore, the pores of the electrospun scaffold were small, thus preventing cell infiltration. In this study, an alternative EHD jet printing (E-jetting) technique has been developed and employed to fabricate 3D polycaprolactone (PCL) scaffolds with desired filament orientation and pore size. The effect of PCL solution concentration was evaluated. Results showed that solidified filaments were achieved at concentration >70% (w/v). Uniform filaments of diameter 20 μm were produced via the E-jetting technique, and X-ray diffraction and attenuated total reflectance Fourier transform infrared spectroscopic analyses revealed that there was no physicochemical changes toward PCL. Scaffold with a pore size of 450 μm and porosity level of 92%, was achieved. A preliminary in vitro study illustrated that live chondrocytes were attaching on the outer and inner surfaces of collagen-coated E-jetted PCL scaffolds. E-jetted scaffolds increased chondrocytes extracellular matrix secretion, and newly formed matrices from chondrocytes contributed significantly to the mechanical strength of the scaffolds. All these results suggested that E-jetting is an alternative scaffold fabrication technique, which has the capability to construct 3D scaffolds with aligned filaments and large pore sizes for tissue engineering applications.

Synthesis and characterization of silver/silicon‐cosubstituted nanohydroxyapatite

Favorable cell-material interaction and the absence of undesirable reaction from the host body defence system play a critical role in determining the success and long-term survival of the implants. Substitution of various elements into hydroxyapatite (HA) has been done to alter its chemical composition, thereby mimicking that of the bone mineral. In this study, a cosubstituted nanosized apatite (Ag/Si-HA) containing Ag (0.3 wt %) and Si (0.8 wt %) was synthesized by an aqueous precipitation technique. The synthesized Ag/Si-HA displayed a rod-like morphology of dimensions ~50 nm in length and ~15 nm in width, as observed from the transmission electron microscope image. With an increase in temperature, the aspect ratio of nanosized Ag/Si-HA decreased, whilst the size increased. Autoclaving was used to achieve sufficient crystallinity while maintaining the rod-like morphology and size that were comparable to that of the bone apatite. A pure Ag/Si-HA was produced without any undesirable secondary phases, as evidenced from the X-ray diffraction and thermal gravimetric results. The Ag/Si cosubstitution affected the lattice cell parameters, in particularly the a- and c- axes which further led to an expansion of the unit cell volume. In addition, the relative intensity of the hydroxyl vibrational bands was reduced. These results demonstrated that a stable phase-pure Ag/Si-HA was produced using an aqueous precipitation reaction.

Collagen grafted 3D polycaprolactone scaffolds for enhanced cartilage regeneration

Current surgical and repair treatments for articular cartilage defects still do not give satisfactory long-term results. Scaffold-based tissue engineering is the subject of much intensive interest. However, one major hurdle is that it is unable to accurately replicate the internal three dimensional (3D) microstructure of cartilage. In this work, a novel electrohydrodynamic printing (E-Jetting) technique was employed to fabricate 3D polycaprolactone (PCL) scaffolds, followed by collagen grafting mediated by polydopamine. Surface topography, chemical composition, and wettability of the scaffolds before and after surface functionalization were characterized. Porcine chondrocytes were seeded within the scaffolds for chondrogenesis evaluation. The results showed that a 3D PCL scaffold with controlled fibre diameter, orientation, and pore size was fabricated by the E-Jetting system. The surface functionalization made the PCL scaffold hydrophilic and favourable for cell attachment. The chondrocytes maintained their healthy phenotypes within the collagen grafted PCL scaffold. The increased production of sulfated glycosaminoglycan and highly expressed collagen type II demonstrated that collagen had a positive role in stimulating chondrogenesis and the collagen grafted PCL scaffold was effective in cartilage regeneration.

The effects of silver, silicon-containing apatite towards bacteria and cell responses

An integrated approach is proposed to incorporate silicon and silver into hydroxyapatite (HA) to enhance the biological response and reduce implant-related infection in bone substitutes. This study examined the responses of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria to silver, silicon-containing apatite (Ag,Si-HA). Scanning electron microscopy images revealed significant reduction in adherence of S. aureus and E. coli bacteria on Ag,Si-HA as compared to HA. The antibacterial property of Ag,Si-HA was shown from a 7-log reduction of S. aureus population in the test solution and on the samples surface as compared to HA at day 7. Rapid inhibition of the adherent bacteria suggested that the antibacterial action of Ag incorporated in Ag,Si-HA could be attributed to the Ag(+) ions on the crystal surface rather than the released Ag(+) ions. Presence of Ag may influence the biological response of HA and as such, the long-term interaction between human adipose-derived mesenchymal stem cells and Ag,Si-HA was evaluated in-vitro. An alamarBlue™ assay showed higher cell proliferation for Ag,Si-HA as compared to HA from day 3 onwards. Immunofluorescence staining revealed well-spread actin cytoskeletons on Ag,Si-HA. In addition, signs of extracellular matrix secretion and biomineralization were observed on Ag,Si-HA at day 14 onwards. Results demonstrated enhanced bone differentiation on Ag,Si-HA, as indicated by a higher level of protein expressions (type 1 collagen and osteocalcin) from day 14 to 21. Therefore, the incorporation of Ag and Si complement each other by endowing HA with antibacterial property, and concurrently promoting biological performance of the cells.

Silver-Doped Apatite as a Bioactive and an Antimicrobial Bone Material

Phase-pure nanostructured silver-doped hydroxyapatite (nAgHA) of various Ag contents was synthesised. These nAgHA were then evaluated in-vitro using human mesenchymal stem cells (hMSCs) and Escherichia coli (E. coli). Results revealed that hMSCs grew generally well on all nAgHA at all time points. In addition, fewer E. coli were seen attaching on the surface of all nAgHA. Hence, this work demonstrated that nAgHA offers considerable potential as a biomaterial.

Effect of Surface Silver Ions towards Inhibiting Bacterial Growth on Apatite

This work revealed the ability of silver,silicon co-substituted apatite (Ag,Si-HA) to inhibit the growth of Staphylococcus aureus (S. aureus), with a 7-log reduction of adherent bacteria on Ag,Si-HA as compared to HA. Furthermore, it demonstrated that surface-bound Ag+ ions was responsible for the antibacterial action since there was not much Ag+ ions being released.

Physiochemical stability of chemically-modified nanoapatites sintered at different temperatures

Nanostructured apatite has been widely used as a bone substitute material due to its biological similarity to the natural bone mineral. To enhance further the biomineralisation and introduce bactericidal property into HA, co-substitution of Ag and Si has been investigated. A co-substituted nanosized apatite (Ag/Si-HA) containing Ag (0.3 wt %) and Si (0.8 wt %) was synthesized by an aqueous precipitation technique. Bone-apatite mimicking morphology of dimensions ∼50 nm in length and ∼10 nm in width was observed for the Ag/Si-HA nano powder. XRF detected the presence of Ag and Si in phase-pure Ag/Si-HA. The Ag/Si-HA nano powders were then compacted and sintered at various temperatures (900–1300 °C) and found to achieve a maximum densification of 93 % at 1300 °C, with a grain size of approximately 1 µm. Phase-purity was maintained up to a temperature of 1300 ° C, as observed from the XRD pattern. This study thus demonstrated that a phase-pure Ag/Si-HA was synthesized via an aqueous precipitation technique.