Geraldine Merle

In vitro degradation and in vivo resorption of dicalcium phosphate cement based grafts

There are two types of DCP: dihydrated (brushite) and anhydrous (monetite). After implantation, brushite converts to hydroxyapatite (HA) which resorbs very slowly. This conversion is not observed after implantation of monetite cements and result in a greater of resorption. The precise mechanisms of resorption and degradation however of these ceramics remain uncertain. This study was designed to investigate the effect of: porosity, surface area and hydration on in vitro degradation and in vivo resorption of DCP. Brushite and two types of monetite cement based grafts (produced by wet and dry thermal conversion) were aged in phosphate buffered saline (PBS) and bovine serum solutions in vitro and were implanted subcutaneously in rats. Here we show that for high relative porosity grafts (50-65%), solubility and surface area does not play a significant role towards in vitro mass loss with disintegration and fragmentation being the main factors dictating mass loss. For grafts having lower relative porosity (35-45%), solubility plays a more crucial role in mass loss during in vitro ageing and in vivo resorption. Also, serum inhibited dissolution and the formation of HA in brushite cements. However, when aged in PBS, brushite undergoes phase conversion to a mixture of octacalcium phosphate (OCP) and HA. This phase conversion was not observed for monetite upon ageing (in both serum and PBS) or in subcutaneous implantation. This study provides greater understanding of the degradation and resorption process of DCP based grafts, allowing us to prepare bone replacement materials with more predictable resorption profiles.

Hydrocaffeic acid–chitosan nanoparticles with enhanced stability, mucoadhesion and permeation properties

Catechol-containing molecules, such as hydrocaffeic acid (HCA) have been shown to increase the mucoadhesion of several polymers. We report here a simple and bioinspired approach to enhance chitosan (CS) mucoadhesion and stabilize it in nanoparticulate form by preparing HCA-CS conjugates. HCA-CS conjugates containing 6 and 15mol% HCA were synthesized and characterized by FT-IR, (1)H NMR and UV-vis spectrophotometry. HCA-CS nanoparticles prepared by ionic gelation with sodium tripolyphosphate (TPP) ranged in size between 100 and 250nm depending on the polymer and TPP/CS weight ratio. In contrast to CS nanoparticles, which aggregate at pH>6.5, HCA-CS nanoparticles did not show any sign of aggregation or precipitation over the 4-10 pH range and maintain their size. Unexpectedly, HCA-CS nanoparticles also maintained their size and polydispersity index at pH 7.4 and NaCl concentrations of up to 500mM. Partial oxidation of HCA resulted in nanoparticle cross-linking and improved stability at pH<4. HCA-CS mucoadhesion to rabbit small intestine was 6 times higher than unmodified CS. CS and HCA-CS nanoparticles were able to induce reversible tight junction opening in Caco-2 cell monolayers. Tight junction opening facilitated the permeability of a model hydrophilic molecule, fluorescein isothiocyanate-labeled dextran (FD4) and was 3 times higher in the cells treated with HCA-CS 15% nanoparticles compared to control groups. HCA-CS conjugates were found to be excellent candidates for stable nanodelivery systems with enhanced oral absorption of hydrophilic molecules.

Electrocatalytic Oxygen Reduction Performance of Silver Nanoparticle Decorated Electrochemically Exfoliated Graphene

We have developed a potentiostatic double-pulse technique for silver nanoparticle (Ag NP) deposition on graphene (GRn) with superior electronic and ionic conductivity. This approach yielded a two-dimensional electrocatalyst with a homogeneous Ag NP spatial distribution having remarkable performance in the oxygen reduction reaction (ORR). GRn sheets were reproducibly prepared by the electrochemical exfoliation of graphite (GRp) at high yield and purity with a low degree of oxidation. Polystyrenesulfonate added during exfoliation enhanced the stability of the GRn solution by preventing the restacking of the graphene sheets and increased its ionic conductivity. The potentiostatic double-pulse technique is generally used to electrodeposit Pt nanoparticles and remains challenging for silver metal that exhibits nucleation and growth potentials relatively close to each other. We judiciously exploited this narrow margin of potential, and for the first time we report Ag NP electrodeposited onto graphene with the subsequent ability to control both the density and the size of metallic nanoparticles. Considering the high activity along with the lower cost of Ag compared to Pt, these findings are highly relevant to the successful commercialization of fuel cells and other electrochemical energy devices.

Electropolymerized carbonic anhydrase immobilization for carbon dioxide capture.

Biomimetic carbonation carried out with carbonic anhydrase (CA) in CO2-absorbing solutions, such as methyldiethanolamine (MDEA), is one approach that has been developed to accelerate the capture of CO2. However, there are several practical issues, such as high cost and limited enzyme stability, that need to be overcome. In this study, the capacity of CA immobilization on a porous solid support was studied to improve the instability in the tertiary amine solvent. We have shown that a 63% porosity macroporous carbon foam support makes separation and reuse facile and allows for an efficient supply and presentation of CO2 to an aqueous solvent and the enzyme catalytic center. These enzymatic supports conserved 40% of their initial activity after 42 days at 70 °C in an amine solvent, whereas the free enzyme shows no activity after 1 h in the same conditions. In this work, we have overcome the technical barrier associated with the recovery of the biocatalyst after operation, and most of all, these electropolymerized enzymatic supports have shown a remarkable increase of thermal stability in an amine-based CO2 sequestration solvent.

Ultrasonic Phosphate Bonding of Nanoparticles

Low intensity ultrasound-induced radicals interact with surface adsorbed orthophosphate to bond nanoparticles with high mechanical strength and surface area. Dissimilar materials could be bonded to form robust metallic, ceramic, and organic composite microparticles. 3D nanostructures of a hydrated and amorphous electrocatalyst with carbon nanotubes were also constructed which exceeded the resistance-limited efficiency of 2D electrodes.

Silk fibroin hydroxyapatite composite thermal stabilisation of carbonic anhydrase

Carbonic anhydrase was entrapped in a matrix of ultrasonically bonded hydroxyapatite microparticles coated with β-sheet structured silk fibroin. Transfer of the reactant and product between the enzyme and the assembly surface was evident and the system showed a remarkable operational, storage and thermal stability, with enzymatic activity almost unchanged after a one hours treatment at 110 °C and the assembly retained 45% of its initial activity after 3 weeks of continuous heating at 80 °C in an amine solution. This thermal stability was excellent compared with described CA immobilization systems and indicates that silk fibroin may limit thermally induced enzyme conformation changes and prevent desorption.

Electrically wired enzyme/TiO2 composite for glucose detection

TiO2, glucose oxidase and carbon nanotube microparticles were ultrasonically formed to provide a large surface area for enzyme immobilisation and a favorable microenvironment for direct electron transfer. This simple architecture nanostructure was used to construct a glucose oxidase biosensor, which demonstrated good analytical performance with high reproducibility, and good detection for pathological glucose level.

Self-assembled photoactive heterojunction phase gradient

The high photocatalytic activity of anatase is markedly enhanced by the presence of a rutile interface. Such phase heterojunctions have previously been formed by sintering admixtures, which results in biphasic particles or agglomerated powders. Current efforts to orientate these heterojunctions relative to the incident light and electrodes to optimize and further improve photoactivity have focussed on sputter coating, dip coating and doctor blading. These techniques offer two ways by which photoactivity may be increased; firstly by maximizing the area of the heterojunction relative to the volume of the two phases and secondly by optimizing spatial ordering of the phases, charge carrier flow direction and path length. Here we report a one step room temperature self-assembly technique which reproducibly creates microstructurally phase graduated photoanodes consisting of a base layer of rutile nanorods and increasing concentrations of anatase in subsequent layers. A large increase in current density and OCP was observed (0.4 to 0.75 mA cm−2) that coincided with the appearance of anatase in the coating i.e. the initial formation of a heterojunction, and longer deposition times were concomitant with increasing current density to a maximum of 1.1 mA cm−2 The resulting nanostructured electrodes were evaluated in non-optimised N3-dye-sensitized solar cells (DSSCs) where they demonstrated 188% higher short current density than P25 controls.

Non-invasive localized cold therapy: a mode of bone repair enhancement

IMPACT STATEMENT A variety of biological, mechanical, and physical therapeutic modalities of varying complexity, efficacy, cost, and safety profile have been developed to enhance bone healing. There have been sporadic reports of spontaneous bone formation after repeated cold exposure. In this study we report for the first time, the anabolic effect of cold exposure on bone healing in vivo resulting in a doubling of bone volume. Although the precise mechanism is not fully understood, cold is well known to stimulate osteoclastogenesis and modulate inflammation. The impact of this finding is considerable for tissue regeneration because cold application is noninvasive, safe, and easily implemented.