Nano-hydroxyapatite formation via co-precipitation with chitosan-g-poly(N-isopropylacrylamide) in coil and globule states for tissue engineering application

Fish Bone Derived Bi-Phasic Calcium Phosphate Coatings Fabricated by Pulsed Laser Deposition for Biomedical Applications

We report on new biomaterials with promising bone and cartilage regeneration potential, from sustainable, cheap resources of fish origin. Thin films were fabricated from fish bone-derived bi-phasic calcium phosphate targets via pulsed laser deposition with a KrF * excimer laser source (λ = 248 nm, τ_FWHM ≤ 25 ns). Targets and deposited nanostructures were characterized by SEM and XRD, as well as by Energy Dispersive X-ray (EDX) and FTIR spectroscopy. Films were next assessed in vitro by dedicated cytocompatibility and antimicrobial assays. Films were Ca-deficient and contained a significant fraction of β-tricalcium phosphate apart from hydroxyapatite, which could contribute to an increased solubility and an improved biocompatibility for bone regeneration applications. The deposited structures were biocompatible as confirmed by the lack of cytotoxicity on human gingival fibroblast cells, making them promising for fast osseointegration implants. Pulsed laser deposition (PLD) coatings inhibited the microbial adhesion and/or the subsequent biofilm development. A persistent protection against bacterial colonization (Escherichia coli) was demonstrated for at least 72 h, probably due to the release of the native trace elements (i.e., Na, Mg, Si, and/or S) from fish bones. Progress is therefore expected in the realm of multifunctional thin film biomaterials, combining antimicrobial, anti-inflammatory, and regenerative properties for advanced implant coatings and nosocomial infections prevention applications.

Mannan-based conjugates as a multimodal imaging platform for lymph nodes

We show that mannan-based conjugates possess exceptional features for multimodal imaging because of their biocompatibility, biodegradability and self-targeting properties. Two new mannan conjugates, containing a gadolinium complex and a fluorescent probe, one based only on polysaccharide and the other one comprising polysaccharide with poly(2-methyl-2-oxazoline) grafts, were prepared and simultaneously visualized in vitro and in vivo by magnetic resonance and fluorescence imaging. The synthesis of these mannan-based complexes was based on alkylation with allyl bromide or grafting with poly(2-methyl-2-oxazoline) chains, followed by a thiol-ene click reaction with cysteamine to introduce primary amino groups into their structure. Finally, the obtained conjugates were functionalized with contrast labels using the corresponding N-hydroxysuccinimide esters. When used to detect lymph nodes, the polymers showed better imaging properties than a commercially available contrast agent.

Poly(N-isopropylacrylamide) and Copolymers: A Review on Recent Progresses in Biomedical Applications

The innate ability of poly(N-isopropylacrylamide) (PNIPAAm) thermo-responsive hydrogel to copolymerize and to graft synthetic polymers and biomolecules, in conjunction with the highly controlled methods of radical polymerization which are now available, have expedited the widespread number of papers published in the last decade-especially in the biomedical field. Therefore, PNIPAAm-based hydrogels are extensively investigated for applications on the controlled delivery of active molecules, in self-healing materials, tissue engineering, regenerative medicine, or in the smart encapsulation of cells. The most promising polymers for biodegradability enhancement of PNIPAAm hydrogels are probably poly(ethylene glycol) (PEG) and/or poly(ε-caprolactone) (PCL), whereas the biocompatibility is mostly achieved with biopolymers. Ultimately, advances in three-dimensional bioprinting technology would contribute to the design of new devices and medical tools with thermal stimuli response needs, fabricated with PNIPAAm hydrogels.

Poly(N-isopropylacrylamide)-hydroxyapatite nanocomposites as thermoresponsive filling materials on dentinal surface and tubules

HYPOTHESIS

Dental decay, asa consequence of exposure to acidic foods and drinks, represents one of the most important tooth pathologies. Recently, enamel and dentinal surface remineralization using hydroxyapatite nano- and microparticles has been proposed; however, commercial remineralizing toothpastes are quite expensive, mostly due to the high costs of hydroxyapatite. Hence, we propose a thermoresponsive hybrid nanocomposite material as filler for tooth defects. The use of thermoresponsive composite particles aims at filling exposed dentinal tubules in response to a change of temperature in the oral cavity. In addition, the presence of the organic matrix contributes to the occlusion of the dentinal tubules, therefore reducing the needed amount of hydroxyapatite.

EXPERIMENTS

Poly-N-isopropylacrylamide microgels containing different amounts of hydroxyapatite nanoparticles were prepared via radical polymerization in the presence of N-N'-methylenebisacrylamide as cross-linker followed by mechanical grinding. The nano- and microstructure of the hydrogels and their thermal behavior were studied via small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Defected teeth were treated with a dispersion of nanocomposite microparticles to simulate toothpaste action.

FINDINGS

The hydrogels maintain their structure and thermal responsiveness when loaded with an amount of hydroxyapatite nanoparticles up to 2.3%w/w. In addition, the lower critical solution temperature is not affected by the presence of the mineral particles. Exposed dentinal tubules on the surface of test tooth samples were successfully occluded after 15 cycles of treatment with a dispersion of nanocomposite microparticles alternated with washing steps.