Selective area growth of a-plane GaN nanocolumns by molecular beam epitaxy was performed for the first time on a-plane GaN templates. Ti masks with 150 nm diameter nanoholes were fabricated by colloidal lithography, an easy, fast and cheap process capable to handle large areas. Even though colloidal lithography does not provide a perfect geometrical arrangement like e-beam lithography, it produces a very homogeneous mask in terms of nanohole diameter and density, and is used here for the first time for the selective area growth of GaN. Selective area growth of a-plane GaN nanocolumns is compared, in terms of anisotropic lateral and vertical growth rates, with GaN nanocolumns grown selectively on the c-plane.The main advantages of one-dimensional structures such as nanocolumns, compared to thin films, is the dislocation-and strain-free growth on different substrates. This higher crystal quality yields a better efficiency in devices such as light emitting diodes (LEDs) based on InGaN/GaN quantum disks (QDisks) [1][2][3][4].Much effort has been dedicated to the growth of self-assembled nanocolumns (NCs) by Plasma-Assisted Molecular Beam Epitaxy (PAMBE), allowing a better knowledge of the material physical properties and growth mechanisms [5][6][7][8]. However, the strong morphology dispersion, typical of a self-assembled process, hinders both the processing of nanodevices arrays and their electrical behavior (NCs merging, defect generation, current injection inhomogeneities). Indeed, arrays of self-assembled nanoLEDs show in general much lower electroluminescence efficiency than the corresponding one measured by photoluminescence (PL). In addition to that InGaN active regions embedded in self-assembled NCs of different diameters and lengths always show fluctuations in the composition, leading to multicolor emission. Arrays of nanostructures grown by selective area growth (SAG) provide a much better homogeneity in terms of morphology, electrical and optical characteristics. SAG of Ill-nitride NCs [9][10][11][12] and other nanostructures [13,14], is generally performed on very thin metal (Ti, Mo) or dielectric (Si0 2 , SiN) masks with an array of nanoholes.A relevant issue concerning optoelectronic devices based on Ill-nitrides is the presence of strong polarization fields that may reduce efficiency. This is the case in layers grown along the c-axis and, a huge effort is nowadays dedicated to the growth of high quality non-polar and semi-polar material [15], with a particular emphasis on non-polar LEDs [16].In the case of SAG of GaN NCs on c-plane GaN templates, the growth front is generally formed by semi-polar (r-planes) that yield a "pencil-like" profile [12]. This profile is then transferred to InGaN QDisks embedded within the GaN NC. Though in this structure the effects of internal fields in the active region of the device (i.e. nanoLED) may be reduced compared with polar planes, the most effective solution is to grow along non-polar directions, either by growing core-shell heterostructures on the latera...

Flexible and biodegradable film substrates prepared by solvent casting from poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) solutions in chloroform were microperforated by ultraviolet laser ablation and subsequently characterized using infrared (IR) microspectroscopy and imaging techniques and scanning electron microscopy (SEM). Both transmission synchrotron IR microspectroscopy and attenuated total reflectance microspectroscopy measurements demonstrate variations in the polymer at the ablated pore rims, including evidence for changes in chemical structure and crystallinity. SEM results on microperforated PHBHV substrates after cell culture demonstrated that the physical and chemical changes observed in the biomaterial did not hinder cell migration through the pores.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) films prepared by solvent casting were treated with oxygen, argon, and nitrogen radiofrequencygenerated plasmas. The analysis by attenuated total reflectance infrared spectroscopy and X-ray absorption near edge spectroscopy of modified surfaces showed an increase of hydroxyl and unsaturated groups, compared with unmodified surfaces. Water contact angles decreased after a short time of exposure (<30 s) for all types of plasma. At long exposure times (>30 s), the water contact angles appeared to be independent of treatment time for nitrogen and argon plasmas, whereas they continuously decreased for films treated with oxygen. HaCaT cultures on nontreated and treated PHBHV films showed that short plasma exposures of 10-20 s improve cell attachment to a greater extent than long exposure times habitually used in polymer surface plasma treatment. The film surface topology did not influence cell attachment. These results illustrate the importance of a detailed characterization of the surface physicochemistry in plasma-modified substrates designed as part of a strategy to optimize specific cell-biomaterial interactions.

Often bladder dysfunction and diseases lead to therapeutic interventions that require partial or complete replacement of damaged tissue. For this reason, the development of biomaterials to repair the bladder by promoting the adhesion and growth of urothelial cells is of interest. With this aim, a modified copolyester of biocompatible and biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB-co-HV)] was used as scaffold for porcine urothelial cell culture. In addition to good biocompatibility, the surface of P(HB-co-HV) substrates was modified to provide both, higher hydrophilicity and a better interaction with urothelial cells. Chemical treatments with ethylenediamine (ED) and sodium hydroxide (NaOH) led to substrate surfaces with decreasing hydrophobicity and provided functional groups that enable the grafting of bioactive molecules, such as a laminin derived YIGSR sequence. Physico-chemical properties of modified substrates were studied and compared with those of the pristine P(HB-co-HV). Urothelial cell morphology on treated substrates was studied. The results showed that focal attachment and cell-related properties were improved for peptide grafted polymer compared with both, the unmodified and functionalized copolyester.

No abstract