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Chitosan nanoparticles are popular carriers for the delivery of macromolecular payloads, e.g. nucleic acids. In this study, nanoparticles were prepared via complexation with triphosphate (TPP) anions and were successively coated with hyaluronic acid (HA). Key variables of the preparative process (e.g. chitosan and HA molecular weight) were optimised in view of the maximisation of loading with DNA, of the Zeta potential and of the dimensional stability, and the resulting particles showed excellent storage stability. We have focused on the influence of chitosan molecular weight on nanoparticle properties. Larger molecular weight increased their porosity (=decreased cross-link density), and this caused also larger dimensional changes in response to variations in osmotic pressure or upon drying. The dependency of nanoparticle porosity on chitosan molecular weight had a profound effect on the adsorption of HA on the nanoparticles; HA was apparently able to penetrate deeply into the more porous high molecular weight (684 kDa) chitosan nanoparticles, while it formed a corona around those composed of more densely cross-linked low molecular weight (25 kDa) chitosan. Atomic Force Microscopy (AFM) allowed not only to highlight the presence of this corona, but also to estimate its apparent thickness to about 20-30 nm (in a dry state). The different morphology has a significant effect on the way HA is presented to biomolecules, and this has specific relevance in relation to interactions with HA receptors (e.g. CD44) that influence kinetics and mechanism of nanoparticle uptake. Finally, it is worth to mention that chitosan molecular weight did not appear to greatly affect the efficiency of nanoparticle loading with DNA, but significantly influenced its chitosanase-triggered release, with high molecular chitosan nanoparticles seemingly more prone to degradation by this enzyme.

Objectives To investigate the effect of UDMA %, of a range of filled UDMA:TEGDMA resins, on viscosity, degree of conversion and shear bond strength. Furthermore, to compare between model filled and unfilled UDMA adhesives, and clinically used orthodontic adhesives on these properties. Methods Four filled and four unfilled resins with a UDMA to TEGDMA weight ratio 50:50, 60:40, 70:30, 80:20 were formulated, tested and compared to the Bis-GMA control Transbond XT. The properties investigated were: viscosity (rotational viscometry), degree of conversion (DC) (FT-IR) and bond strength (shear bond strength test). One-way ANOVA and Tukey post hoc test was used to statistically analyze the data for viscosity and DC% while the non-parametric Kruskal–Wallis and Mann–Whitney U-test was used for the shear bond strength values. Results For SBS a comparable bond strength was obtained between the U80:T20(F) adhesive and the control Transbond XT (27.1 and 30.1 respectively). There was no significant difference between the U70:T30 adhesive and the control. Transbond XT (43.1%) had a significantly lower DC% than all the UDMA based adhesives. Furthermore, there was no significant difference between the DC% means of the various UDMA resins. There was a significant decrease in the viscosity for both filled and unfilled groups, as the TEGDMA concentration was increased. Significance The results indicate that adhesives formulated with UDMA and TEGDMA monomers, could produce resins with comparable viscosities to the Bis-GMA control, Transbond XT. Adhesives formulated with high UDMA %, can be used to produce resins with greater viscosity and increased bond strength, potentially without affecting their degree of conversion.

Titania (anatase) nanoparticles were successfully PEGylated through the use of catechol (dopamine)-terminated PEG derivatives. The resulting materials were characterized by excellent stability at neutral pH and extremely low toxicity (phagocytic and nonphagocytic cell lines). In particular, we focused on the comparison between mono- and bis-catechol PEGs. Due to the double terminal anchorage on the titania surface, bis-catechol ligands can produce chains differing from classical monoanchored PEG in conformation (horseshoe-shaped vs brush) and thus the possibility of interactions with biomolecules. At the same time, less than quantitative catechol binding may lead to the presence of dangling chains with unbound catechols which can polymerize and eventually produce PEG/titania nanocomposite colloids. Our results on double-functional PEG2000 show the latter to be the case. Pluronic F127 was also used as a bifunctional ligand, leading to nanocomposite aggregates with an even larger organic content.

In this study we report the preparation of a new family of core shell microgels that are water-swellable and have a morphology that is controllable by particle composition. Here, nearly monodisperse core shell PNVF-xGMA [poly(N-vinylformamide-co-glycidyl methacrylate)] particles (where x is the weight fraction of GMA used) were prepared via nonaqueous dispersion (NAD) polymerization in one step. The shells were PGMA-rich and were cross-linked by reaction of epoxide groups (from GMA) with amide groups (from NVF). The core of the particles was PNVF-rich. A bifunctional cross-linking monomer was not required to prepare these new microgels. The particles had a remarkable "cane-ball"-like morphology with interconnected ridges, and this could be controlled by the value for x. The particle size was tunable over the range 0.8-1.8 mu m Alkaline hydrolysis was used to hydrolyze the PNVF segments to poly(vinylamine), PVAM. The high swelling pressure of the cationic cores caused shell fragmentation and release of some of the core polymer when the hydrolyzed particles were dispersed in pure water. The extent to which this occurred was controllable by x. Remarkably, the PGMA-rich shells could be detached from the hydrolyzed particles by dispersion in water followed by drying. The hydrolyzed PNVF-0.4GMA particles contained both positively and negatively charged regions and the dispersions appeared to exhibit charge-patch aggregation at low ionic strengths. The new cross-linking strategy used here to prepare the PNVF-xGMA particles should be generally applicable for amide-containing monomers and may enable the preparation of a range of new water-swellable microgels.

Purpose Cell shape is a powerful indicator of cell activity. This study aimed to validate the use of numeric descriptors for the assessment of the effect of substrate mechanical properties on the morphology of 2d cultured fibroblasts. Methods Two fibroblast cell types, the 3t3 murine cell line and primary Human dermal Fibroblasts (HDF) were cultured on substrates (fibrin, silicone, tissue culture PolyStyrene (TCPS)) with modulus values spanning more than six orders of magnitude ( 1 GPa), using cell area, circularity, aspect ratio and solidity (ratio between actual and convex area) as morphologic descriptors of cell shape. In order to reduce differences in chemical composition, silicones and TCPS were pre-treated with fibrinogen. Results Cell area and solidity appeared to be the most sensitive indicators of the differential dependency of the cell morphology on the nature of the substrate. They highlighted complex behavior, where the increase in modulus did not correspond to clear trends in cell shape over the complete range of moduli investigated. Conclusions The analysis of cell shape descriptors appears to indicate that chemical differences may overwhelm mechanical effects in 2d culture. These indications are partial and purely phenomenologic, but suggest that specific care should be paid to also consider the role of substrate chemistry in the analysis of the dependency of cell behavior on substrate mechanical properties.

The study aimed to explore the influence of the network architecture on the mechanical properties and degradability of HA/PEG gels, and to highlight the relationship between Young's modulus and cell colonization with a selected architecture. Three different families of hyaluronic acid (HA)-based photopolymerized PEG diacrylate (PEGDA) hydrogels were compared, using different concentrations and molecular weights (64 and 234 kDa) of HA: semi-IPNs containing native HA in a PEG network (type I gels); co-networks obtained using thiolated HA as chain transfer agent during PEGDA polymerization (type II gels); co-networks obtained from the in situ preparation of a macromonomer derived from the Michael-type addition of thiolated HA on PEGDA (type III gels). From a comparative study of rheological properties and enzymatic degradability, type II gels were selected for a further study aiming to link their mechanical properties to cell spreading. Employing RGD-functionalized materials, Young's moduli were measured via AFM nanoindentation while the cell spreading behavior was quantitatively evaluated by monitoring morphology and metabolic activity (MTS assay) of L929 fibroblasts. By revealing a clear relation between increasing modulus and increasing cell spreading/proliferation, the study showed the possibility to fine tune the cell/material interactions with appropriate reactive processing techniques. © 2011 Elsevier Ltd.

The vast majority of matrices used in microencapsulation are spherical. This geometry has some drawbacks due to its low surface/volume ratio: for example the difficult diffusion of oxygen to the bulk of a cell-containing microbead may lead to hypoxia or necrosis of the encapsulated cells. Here we focused on toroidal microparticle (“doughnuts”); these structures have a higher surface area than spherical beads and dispersed objects will experience a lower average distance from the surface. The toroidal morphology is the result of the flattening of water drops impacting on a liquid surface, and is then “quenched” by the occurrence of a rapid gelation due to polyelectrolyte complexation. We have produced toroidal microparticles using chitosan with an appropriately low molecular weight in combination with triphosphate (TPP), optimizing the conditions of pH and concentration of the two components. We also present here an evaluation of the process used for chitosan depolymerisation and of the cytotoxicity of the resulting polymers, which marginally decreases with decreasing molecular weight. Under the conditions adopted, the “doughnuts” result more densely cross-linked than spherical microparticles and show a considerably improved physical stability.

In this work thermoassociative gel formation of a new family of aqueous temperature-responsive copolymer solutions has been investigated. This was achieved using a cationic poly( N -isopropyl acrylamide) (PNIPAm) graft copolymer recently prepared [Liu R, De Leonardis P, Cellesi F, Tirelli N, Saunders BR. Langmuir 2008;24:7099]. The PDMA + x - g -(PNIPAm n ) y copolymers have x and y values that originate from the macroinitiator; the value for n corresponds to the PNIPAm arm length. DMA + is quarternarized N , N -dimethylaminoethyl methacrylate. The copolymer solutions exhibited cloud point temperatures ( T clpt ) of about 33 °C, which were not significantly affected by x / y ratio or the value for n . Thermoassociative gel formation occurred above T clpt at copolymer concentrations ( C copol ) greater than or equal to 4 wt.%. This is a reasonably low C copol value and is a consequence of the graft copolymer architecture employed. We investigated the effect of temperature, C copol and copolymer structure on gelation and gel elasticity using variable – temperature dynamic rheology. For PDMA + 30 - g -(PNIPAm 210 ) 14 solutions at 39 °C it was found that G ′ (elastic modulus) scales with C copol according to G ′ ∼ C copol 3.85 . The data suggested that a significant proportion of PNIPAm units is not directly involved in network formation. Thermoassociative gel formation and the gel properties for these systems appear to be governed by a balance between electrostatic repulsion involving the DMA + units (favouring spatial extension of the copolymer backbones) and attractive hydrophobic interactions between PNIPAm side chains (favouring associative crosslink formation).

The very rapid gelation of a cell- or biomolecule-containing solution is at the basis of most processes employed in microencapsulation. Adequately quick ('instantaneous') gelation kinetics are provided by a number of phenomena based on physical association. On the other hand, physical gels are inherently reversible structures, which can be solubilized or disrupted in response to often poorly controllable phenomena in the environment of application, such as dilution, changes in temperature, ion strength and composition, pH, or other physical or chemical parameters. Chemically cross-linked hydrogels would have therefore significant advantages in terms of stability and end-properties; however, the time required for chemical reactions to produce a chemically cross-linked material is in a more general case hardly compatible with microencapsulation processes. In a recent study of our laboratory we have proposed a new approach for providing both quick gelation kinetics and good stability, by simply combining the rapid kinetics of a physical hardening phenomenon with a slower chemical curing; the former process is thus responsible of the morphogenesis of the material, while the latter develops its end-properties.

The contemporary occurrence of a thermal gelation (by the occurrence of a lower critical solubility temperature, LCST) and of a chemical curing has allowed to use biocompatible polyethers (PEG, Pluronic) for mimicking sodium alginate gelation and perspectively substituting it for encapsulation purposes. The final materials were easily formed in cell culture media and perfectly passed a preliminary biocompatibility assessment. Additionally, they showed a stimuli responsive behavior, e.g. in the modulation of their swelling degree with temperature (preserving the LCST character of the precursors) and solvent composition. Gel bead obtained via tandem gelation of Pluronic derivatives, for the perspective substitution of calcium alignate.

Fully synthetic polymers were used for the preparation of hydrogel beads and capsules, in a processing scheme that, originally designed for calcium alginate, was adapted to a "tandem" process, that is the combination a physical gelation with a chemical cross-linking. The polymers feature a Tetronic backbone (tetra armed Pluronics), which exhibits a reverse thermal gelation in water solutions within a physiological range of temperatures and pHs. The polymers bear terminal reactive groups that allow for a mild, but effective chemical cross-linking. Given an appropriate temperature jump, the thermal gelation provides a hardening kinetics similar to that of alginate. With slower kinetics, the chemical cross-linking then develops an irreversible and elastic gel structure, and determines its transport properties. In the present article this process has been optimized for the production of monodisperse, high elastic, hydrogel microbeads, and liquid-core microcapsules. We also show the feasibility of the use of liquid-core microcapsules in cell encapsulation. In preliminary experiments, CHO cells have been successfully encapsulated preserving their viability during the process and after incubation. The advantages of this process are mainly in the use of synthetic polymers, which provide great flexibility in the molecular design. This, in principle, allows for a precise tailoring of mechanical and transport properties and of bioactivity of the hydrogels, and also for a precise control in material purification.