Surface functionalization superparamagnetic nanoparticles conjugated with thermoresponsive poly(epsilon-lysine) dendrons tethered with carboxybetaine for the mild hyperthermia-controlled delivery of VEGF.

UNLABELLED: Vascular endothelial growth factor (VEGF) is the growth factor responsible for the triggering of angiogenesis, the process of blood vessel formation supporting the long-term viability of any repaired or regenerated tissue. As the growth factor is effective only when concentration gradients are generated, new shuttles need to be developed that ensure both the control of gradients at the site of tissue repair and the release of VEGF at physiological levels. Magnetic hyperthermia is the production of heat induced by magnetic materials through their exposure to an external oscillating magnetic field. In this paper, magnetic nanoparticles capable of generating controllable hyperthermia were functionalised with hyperbranched poly(epsilon-lysine) peptides integrating in their core parallel thermoresponsive elastin-like peptide sequences and presenting an uppermost branching generation tethered by the zwitterionic amino acid carboxybetaine. The results show that these functionalised magnetic nanoparticles avidly bind VEGF and release it only upon generation of mild-hyperthermic pulses generated by oscillating magnetic filed. The VEGF release occurred in a temperature range at which the elastin-like peptides collapse. It is proposed that, through the application of an external magnetic field, these magnetic carriers could generated gradients of VEGF in vivo and allow its tuned delivery in a number of clinical applications. STATEMENT OF SIGNIFICANCE: The present paper for the first time reveals the possibility to control the delivery of VEGF through mild hyperthermia stimuli generated by a oscillating magnetic field. To this purpose, magnetic nanoparticles of high size homogeneity and coated with a thin coating of poly(acrylic acid) were functionalised with a novel class of poly(epsilon lysine) dendrimers integrating in their structure a thermoresponsive amino acid sequence mimicking elastin and exposing at high density a zwitterionic modified amino acid, the carboxybetaine, known to be able to bind macromolecules. Physicochemical and biochemical characterisation elegantly show the link between the thermal properties of the nanoparticles and of the dendrimer change of conformation and how this enable the release of VEGF at temperature values compatible with the growth factor stability.

Silver-doped self-assembling di-phenylalanine hydrogels as wound dressing biomaterials.

Chronic and acute wounds can be quickly contaminated and infected by microorganisms such as bacteria, multi-resistant organisms or fungi. The introduction of silver as anti-microbial agent into wound management has widely been demonstrated to be effective and contribute to wound healing. As a consequence, many approaches and different materials have been employed to synthesize antibacterial silver-hydrogels. In this work the introduction of silver particles into the fibrillar structure of self-assembling aromatic di-phenylalanine derivatives modified with aromatic groups such as 9-fluorenylmethoxycarbonyl is proposed to produce antibacterial wound dressings. Hydrogels doped with increasing amounts of silver were tested and adopted to modify flax textiles. The influence of silver on the structure of hydrogels was studied using light and confocal microscopy, while SEM-EDX allowed the characterization of the hydrogel coating on the surface of the textile substrates as well as the identification and distribution of silver nanoparticles. The antibacterial potential of the treated flax was demonstrated through microbiological tests on Staphylococcus aureus. The combination of the physico-chemical and anti-bacterial properties, together with the ease of preparation of these biomaterials, fulfils the requirement of clinically-effective wound dressings.

Osteoconductive phosphoserine-modified poly({varepsilon}-lysine) dendrons: synthesis, titanium oxide surface functionalization and response of osteoblast-like cell lines.

The lack of direct bonding between the surface of an implant and the mineralized bony tissue is among the main causes of aseptic loosening in titanium-based implants. Surface etching and ceramic coatings have led to improved osteointegration, but their clinical performance is still limited either by partial bonding or by coating delamination. In this work, a solid-phase synthesis method has been optimized to produce poly(ε-lysine) dendrons, the outermost branching generation of which is functionalized by phosphoserine (PS), a known catalyst of the biomineralization process. The dendrons were deposited onto etched titanium oxide surfaces as a near-to-monolayer film able to induce the formation of a homogeneous calcium phosphate phase in a simulated body fluid over 3 days. The dendron films also stimulated MG63 and SAOS-2 osteoblast-like cells to proliferate at a rate significantly higher than etched titanium, with SAOS-2 also showing a higher degree of differentiation over 14 days. PS-tethered dendron films were not affected by various sterilization methods and UV treatment appeared to improve the cell substrate potential of these films, thus suggesting their potential as a surface functionalization method for bone implants.

The rapid and specific real-time detection of Legionella pneumophila in water samples using Optical Waveguide Lightmode Spectroscopy.

The detection of Legionella pneumophila in water samples using standard microbiological culture techniques is both prolonged and problematic. The bacterium is slow-growing and nutritionally fastidious, such that other indigenous species can out-compete the Legionella even when using antibiotic supplemented media. Optical Waveguide Lightmode Spectroscopy (OWLS) is a real-time analytical system whereby a change to a higher coupling angle where the refractive index of a bacterial cell is higher than that of the covering medium. In this study an aqueous suspension of L. pneumophila was passed across the surface of waveguides functionalised with a specific anti-Legionella antibody. The binding between the bacterial cells and the antibody specific for that cell resulted in an increase in the refraction indices of the transverse electric and transverse magnetic photoelectric currents. We report the optimisation of a rapid and sensitive (1.3 x 10(4) CFU mL-1) detection method for L. pneumophila contamination in a water sample in less than 25 min. This is a significant reduction in the time taken to determine the presence of the bacterium which with conventional techniques normally takes up to fourteen days. In addition, the specificity of the technique to L. pneumophila was demonstrated. The OWLS results were validated by conventional microbiology screening and atomic force microscopy of the surface of the waveguide, showing its species specificity and potential applications in environmental and clinical analysis.

Bacterial adhesion to bisphosphonate coated hydroxyapatite.

Staphylococcus aureus (S. aureus) is commonly associated with microbial infection of orthopaedic implants. Such infections often lead to osteomyelitis, which may result in failure of the implant due to localised bone destruction. Bacterial adhesion and subsequent colonisation of the device may occur as a consequence of contamination during surgery, or by seeding from a distant site through the blood circulation. Coating of the hydroxyapatite (HA) ceramic component of artificial hip joints with the bisphosphonates clodronate (C) and pamidronate (P) has been proposed as a means to minimise osteolysis and thereby prevent loosening of the implant. However, the effect of the bisphosphonate coating on bacterial adhesion to the HA materials must be determined before this approach can be implemented. In this study coated HA materials were incubated with the S. aureus and the number of adherent bacteria determined using the Modified Vortex Device (MVD) method. The number of bacteria adherent to the P coated HA material was significantly greater than that adherent to uncoated HA (60-fold increase) or to the C coated HA (90-fold increase). Therefore, even though earlier studies suggested that P bound to HA may improve osseointegration, the results presented would suggest that the use of this coating may be limited by the potential increased susceptibility of the coated device to infection.

The interactions of bisphosphonates in solution and as coatings on hydroxyapatite with osteoblasts.

Aseptic loosening is one of the major causes of failure of artificial hip joints, and it can occur for several reasons, including osteolysis of the bone tissue in response to stress shielding or cellular reactions to wear debris. Any treatment of the prosthesis which could minimize the osteolytic response of bone tissue may be able to extend the life-time of the implant. Bisphosphonates are potent inhibitors of osteoclastic bone resorption, and they bind avidly to hydroxyapatite (HA). Coating the prostheses with bisphosphonates may therefore inhibit osteolysis. We have investigated the potential for this approach by determining whether bisphosphonates interact with osteoblasts in vitro. The effects of pamidronate (P), clodronate (C), and etidronate (E) in solution and when coated onto HA were investigated. P inhibited protein and collagen syntheses potently when in solution, but not after being bound to HA. When bound to HA, both P and C increased DNA, protein and collagen syntheses of osteoblasts and may encourage the osseointegration of implants. The pharmacological effects of the bisphosphonates studied altered dramatically after binding to HA. This must be fully investigated before this approach to prolonging prostheses stability can be evaluated.