Sintering of calcium phosphates with a femtosecond pulsed laser for hard tissue engineering

The authors acknowledge support from the sponsors of this work; the EPSRC LUMIN (EP/K020234/1) and EU-Marie-Curie-IAPP LUSTRE (324538) projects.Direct laser sintering on hard tissues is likely to open new pathways for personalised medicine. To minimise irradiation damage of the surrounding soft tissues, lasers operating at wavelengths that are ‘safe’ for the tissues and biomaterials with improved optical properties are required. In this work laser sintering is demonstrated with the use of an ultrafast, femtosecond (100 fs) pulsed laser operating at a wavelength of 1045 nm and two existing calcium phosphate minerals (brushite and hydroxyapatite) which have been improved after doping with iron (10 mol%). Femtosecond laser irradiation caused transformation of the Fe3+-doped brushite and Fe3+-doped HAp samples into β-calcium pyrophosphate and calcium-iron-phosphate, respectively, with simultaneous evidence for microstructural sintering and densification. After estimating the temperature profile at the surface of the samples we suggest that soft tissues over 500 μm from the irradiated zone would be safe from thermal damage. This novel laser processing provides a means to control the phase constitution and the morphology of the finished surfaces. The porous structure of β-pyrophosphate might be suitable for applications in bone regeneration by supporting osteogenic cell activity while, the densified Fe3+-rich calcium-iron-phosphate may be promising for applications like dental enamel restoration.PostprintPeer reviewe

β-pyrophosphate: A potential biomaterial for dental applications

Tooth hypersensitivity is a growing problem affecting both the young and ageing population worldwide. Since an effective and permanent solution is not yet available, we propose a new methodology for the restoration of dental enamel using femtosecond lasers and novel calcium phosphate biomaterials. During this procedure the irradiated mineral transforms into a densified layer of acid resistant iron doped β-pyrophosphate, bonded with the surface of eroded enamel. Our aim therefore is to evaluate this densified mineral as a potential replacement material for dental hard tissue. To this end, we have tested the hardness of β-pyrophosphate pellets (sintered at 1000 °C) and its mineral precursor (brushite), the wear rate during simulated tooth-brushing trials and the cytocompatibility of these minerals in powder form. It was found that the hardness of the β-pyrophosphate pellets is comparable with that of dental enamel and significantly higher than dentine while, the brushing trials prove that the wear rate of β-pyrophosphate is much slower than that of natural enamel. Finally, cytotoxicity and genotoxicity tests suggest that iron doped β-pyrophosphate is cytocompatible and therefore could be used in dental applications. Taken together and with the previously reported results on laser irradiation of these materials we conclude that iron doped β-pyrophosphate may be a promising material for restoring acid eroded and worn enamel

2-D Electronic Spectroscopy on the light-dependent enzyme protochlorophyllide oxidoreductase

In photosynthesis, quantum coherence in light harvesting complexes could form the basis for the highly efficient propagation of excited states within the photosynthetic membranes of bacteria and plants. Recent studies on Photosystem II reaction centres extends the possible relevance of electronic coherence to the photochemical steps of photosynthesis; it was shown that coherent states are sufficiently long-lived, at room temperature, to persist during the initial steps of electron transfer. This extension of quantum coherence, from the energy transfer to the energy trapping steps of photosynthesis, made it timely to investigate if quantum coherence also plays a role in the formation of product states in enzyme catalysis. Given the short timescales involved it was necessary to study an enzyme where the catalytic cycle can be triggered by femtosecond light pulses, so protochlorophyllide oxidoreductase (POR) was selected as an ideal model system. 2-dimensional electronic spectroscopy (2DES) was used to investigate the presence of quantum coherence in the intermediates of the light-dependent reduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide) catalysed by POR

Exogenous mineralization of hard tissues using photo-absorptive minerals and femto-second lasers; the case of dental enamel

A radical new methodology for the exogenous mineralization of hard tissues is demonstrated in the context of laser-biomaterials interaction. The proposed approach is based on the use of femtosecond pulsed lasers (fs) and Fe³⁺-doped calcium phosphate minerals (specifically in this work fluorapatite powder containing Fe₂O₃ nanoparticles (NP)). A layer of the synthetic powder is applied to the surface of eroded bovine enamel and is irradiated with a fs laser (1040 nm wavelength, 1 GHz repetition rate, 150 fs pulse duration and 0.4 W average power). The Fe₂O₃ NPs absorb the light and may act as thermal antennae, dissipating energy to the vicinal mineral phase. Such a photothermal process triggers the sintering and densification of the surrounding calcium phosphate crystals thereby forming a new, dense layer of typically 20 μm in thickness, which is bonded to the underlying surface of the natural enamel. The dispersed iron oxide NPs, ensure the localization of temperature excursion, minimizing collateral thermal damage to the surrounding natural tissue during laser irradiation. Simulated brushing trials (pH cycle and mechanical force) on the synthetic layer show that the sintered material is more acid resistant than the natural mineral of enamel. Furthermore, nano-indentation confirms that the hardness and Young’s modulus of the new layers are significantly more closely matched to enamel than current restorative materials used in clinical dentistry. Although the results presented herein are exemplified in the context of bovine enamel restoration, the methodology may be more widely applicable to human enamel and other hard-tissue regenerative engineering

What do antenatal care providers understand and do about oral health care during pregnancy: a cross-sectional survey in New South Wales, Australia

BACKGROUND: There is mounting evidence to support the lack of awareness among pregnant women about health consequences and long term risks associated with poor oral hygiene during pregnancy. A recognised and important point of influence is their interaction with health professionals, particularly when receiving Antenatal Care. However, there is limited evidence about the perceptions of ANC providers in Australia toward the provision of perinatal oral healthcare. This study was undertaken to explore the knowledge, attitudes and practices of Antenatal Care (ANC) providers in New South Wales (NSW), Australia providing perinatal oral healthcare and to identify barriers to and predictors of their practices in this area. METHODS: A cross sectional survey was undertaken of ANC providers (general practitioners, obstetricians/gynaecologists and midwives) practising in NSW, Australia. Participants were recruited through their professional organisations via email, postal mail, and networking at conferences. The survey addressed the domains of knowledge, attitude, barriers and practices towards oral healthcare, along with demographics. Data was entered into SPSS software and analysed using descriptive and inferential statistics. RESULTS: A total of 393 surveys (17.6% response rate) were completed comprising 124 general practitioners, 74 obstetricians/gynaecologists and 195 midwives. The results showed limited knowledge among ANC providers regarding the impact of poor maternal oral health on pregnancy/infant outcomes. Most (99%) participants agreed that maternal oral health was important yet few were discussing the importance of oral health or advising women to visit a dentist (16.4–21.5%). Further, less than a third felt they had the skills to provide oral health advice during pregnancy. ANC providers who were more knowledgeable about maternal oral health, had training and information in this area and greater experience, were more likely to engage in practices addressing the oral health of pregnant women. CONCLUSION: The findings suggest that ANC providers in NSW are not focussing on oral health with pregnant women. ANC providers seem willing to discuss oral health if they have appropriate education/training and information in this area. Further research at a national level is required to confirm whether these findings are similar in all Australian states

High temperature corrosion and protection

In this paper, different factors determining high temperature corrosion in simple and complex atmospheres are analysed. Various methods were investigated to obtain good corrosion protection by formation of barrier scales or by application of coatings.In the introductory section, the different diffusion transport mechanisms are reviewed. The influences of growth stresses are analysed and their evaluation techniques are examined; some examples of recent experimental methods are proposed. The effect of external applied stresses is also described.In the second section, various methods are proposed to increase the high temperature corrosion behaviour: design of new alloys, metallic or ceramic coatings formed by chemical reaction or deposition. Novel techniques like ion implantation or surface laser alloying are also examined. Technological applications are envisaged on the basis of our experimental results