Biocompatible polymeric microparticles produced by a simple biomimetic approach

The use of superhydrophobic surfaces to produce polymeric particles proves to be biologically friendly since it entails the pipetting and subsequent cross-linking of polymeric solutions under mild experimental conditions. Moreover, it renders encapsulation efficiencies of ∼100%. However, the obtained particles are 1 to 2 mm in size, hindering to a large extent their application in clinical trials. Improving on this technique, we propose the fabrication of polymeric microparticles by spraying a hydrogel precursor over superhydrophobic surfaces followed by photo-cross-linking. The particles were produced from methacrylamide chitosan (MA-CH) and characterized in terms of their size and morphology. As demonstrated by optical and fluorescence microscopy, spraying followed by photo-cross-linking led, for the first time, to the production of spherical particles with diameters on the order of micrometers, nominal sizes not attainable by pipetting. Particles such as these are suitable for medical applications such as drug delivery and tissue engineering.We thank Ivo Aroso and Ana Isabel Neto for their valuable support with FTIR and compression experiments, respectively. A.M.S.C. thanks FCT for financial support through grant BIM/PTDC/CTM-BPC/112774/2009_02. M.A.-M. thanks CONACyT (Mexico) for financial support through post-doc grant no. 203732. N.M.O. thanks FCT for financial support through Ph.D. scholarship no. SFRH/BD/73172/2010. This work was funded by the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. REGPOT-CT2012-316331-POLARIS, by FEDER through the Competitive Factors Operation Program-COMPETE, and by national funds through FCT - Fundacao para a Ciencia e a Tecnologia in the scope of project PTDC/CTM-BIO/1814/2012

Wetting laws for polymer solutions

We measure the contact angle $\theta(\phi)$ of polymer solutions (polymer volume fraction ϕ) on a solid surface. The polymer is repelled at both solid and air interfaces. The pure solvent wets the solid, but the polymer does not. Thus the spreading coefficient $S(\phi)$ is positive for $\phi=0$ and negative for $\phi=1$. Naively we could expect a wetting transition at the concentration $\phi_{\rm w}$ such that $S(\phi_{\rm w})$ vanishes. We show here that $\theta(\phi)$ has a plateau $(\theta=\theta_{\rm L})$ for ϕ below a critical value $\phi_{\rm L}$ larger than $\phi_{\rm w}$. For $\phi > \phi_{\rm L}$, $\theta(\phi)$ increases monotonously. In the plateau regime, the solution droplet is in equilibrium with a precursor film of pure solvent. At $\phi_{\rm L}$, we have a “leak-out transition”, and the value of $\phi_{\rm L}$ results from a balance between the osmotic pressure of the polymer solution and the disjoining pressure of the solvent film. These ideas can be extended to other liquid mixtures, again assuming that the solute does not adsorb at the interfaces and, more precisely, that the thickness of the depletion layers is larger than the natural thickness of the solvent film

Dewetting of Supported Viscoelastic Polymer Films: Birth of Rims

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