1,720,983 research outputs found
Strategies for Drug Encapsulation and Controlled Delivery Based on Vapor-Phase Deposited Thin Films
No full textVapor-phase deposition methods allow the synthesis and engineering of organic and inorganic thin films, with high control on the chemical composition, physical properties, and conformality. In this review, the recent applications of vapor-phase deposition methods such as initiated chemical vapor deposition (iCVD), plasma enhanced chemical vapor deposition (PE-CVD), and atomic layer deposition (ALD), for the encapsulation of active pharmaceutical drugs are reported. The strategies and emergent routes for the application of vapor-deposited thin films on the drug controlled release and for the engineering of advanced release nanostructured devices are presented
Wrinkling of an Enteric Coating Induced by Vapor-Deposited Stimuli-Responsive Hydrogel Thin Films
No full textIn this contribution, we report on the thin-film synthesis of a thermoresponsive polymer onto another polymer used as an enteric coating in drug applications. In particular, we deposit cross-linked poly(N-vinylcaprolactam) (pNVCL) thin films by initiated chemical vapor deposition (iCVD) onto spin-coated Eudragit (EUD) layers. Already upon iCVD synthesis, the layered structure starts to form wrinkles at a minimum iCVD thickness of 30 nm. By changing the EUD layer thickness and the amount of cross-linking used during iCVD, the morphology of the wrinkles is demonstrated to be readily tunable. Laterally, the double-layer structures vary in morphology from being ultrasmooth to exhibiting up to a 3.5 μm wrinkle wavelength. The surface roughness and, thus, the wrinkles' height can be tailored from below 1 nm up to 100 nm. From the resulting wavelength of wrinkles, an estimation of the elastic modulus of pNVCL proves its tunability over a wide range of values thanks to the iCVD process. This study elucidates an uncomplicated way to tune the wrinkles' morphology and, thus, the surface area of a system that can be employed in drug delivery applications. Hence, an enteric coating of EUD together with an iCVD-synthesized thermoresponsive thin film is proposed as a promising composite encapsulation layer to outperform established systems in terms of tunability of the response to multiple external stimuli
Interlink between Tunable Material Properties and Thermoresponsiveness of Cross-Linked Poly(N-vinylcaprolactam) Thin Films Deposited by Initiated Chemical Vapor Deposition
No full textIn this contribution, we report on the thin-film synthesis of a novel thermoresponsive polymer, namely, poly(N-vinylcaprolactam) cross-linked by di(ethylene glycol)divinyl ether [p(NVCL-co-DEGDVE)] by initiated chemical vapor deposition (iCVD). Its transition between swollen and shrunken states in film thickness and the corresponding lower critical solution temperature (LCST) was investigated by spectroscopic ellipsometry in water. Water contact angle measurements and nano-indentation experiments reveal that the transition is accompanied by a change in wettability and elastic modulus. The amount of cross-linking was used to tune the thermoresponsive behavior of the thin films, resulting in higher swelling and LCST, increased surface rearrangement, and lower stiffness for less cross-linked polymers. For the first time, the filament temperature during iCVD synthesis was used to vary the chain length of the resulting polymeric systems and, thus, the position of their thermoresponsive transition. With that, swelling of up to 250% compared to the dry thickness and transition temperatures ranging from 16 to 40 °C could be achieved
Epitaxial relation of carbamazepine and its precursor template extracted from rotating grazing incidence X-ray diffraction
No full textDirected crystal growth often requires considerable experimental effort to achieve epitaxial control. In this work a simple solution step is shown to yield crystals of two different molecules simultaneously within a thin film and with defined epitaxial relations to each other. This was achieved by dissolving simultaneously carbamazepine (CBZ), a drug molecule, and iminostilbene (ISB), its precursor, in a single solution. When the sample is prepared using slow solvent evaporation rates, both molecules grow into needle-shaped crystals. The ISB crystals contact the substrate surface and extend for hundreds of μm. CBZ tends to minimize the contact with the substrate and assembles on top or is ledge-directed. In both cases a defined inclination of CBZ to the underlying ISB crystals is seen with optical microscopy showing a 36° inclination of the elongated crystals. In a similar way to pole figure measurements, rotating grazing incidence X-ray diffraction allows the determination of crystallographic properties and epitaxial relation, i.e. how the unit cells of both molecules align with respect to each other in terms of contact plane and azimuthal orientation. A point-on-line coincidence was identified, which can be related to the herringbone packing in the ISB crystals. Furthermore, changing the solute content as well as the processing times/kinetics, the appearance and the quality of crystal growth changes, but with the epitaxial relations remaining unaffected; crystals grow more frequent on top when processed slowly and when processed fast, growth takes place more often at facet inclined 90° from the top one
Initial growth and crystallization onset of plasma enhanced-atomic layer deposited ZnO
Full text linkDirect plasma enhanced-atomic layer deposition (PE-ALD) is adopted for the growth of ZnO on c-Si with native oxide at room temperature. The initial stages of growth both in terms of thickness evolution and crystallization onset are followed ex-situ by a combination of spectroscopic ellipsometry and X-ray based techniques (diffraction, reflectivity, and fluorescence). Differently from the growth mode usually reported for thermal ALD ZnO (i.e., substrate-inhibited island growth), the effect of plasma surface activation resulted in a substrate-enhanced island growth. A transient region of accelerated island formation was found within the first 2 nm of deposition, resulting in the growth of amorphous ZnO as witnessed with grazing incidence X-ray diffraction. After the islands coalesced and a continuous layer formed, the first crystallites were found to grow, starting the layer-by-layer growth mode. High-temperature ALD ZnO layers were also investigated in terms of crystallization onset, showing that layers are amorphous up to a thickness of 3 nm, irrespective of the deposition temperature and growth orientation
Manipulating drug release from tridimensional porous substrates coated by initiated chemical vapor deposition
No full textIn the recent years, modern wound dressings have attracted much interest to accelerate wound healing processes with the topical delivery of drugs directly on wounds having a significant effect on wound rehabilitation. The objective of this study was to develop a model dressing that would not only provide wound protection from the environment but might also provide the possibility to keep it moist and deliver a drug for potential speeding the healing process. Poly(ethylene terephthalate), cotton fabrics, and polycaprolactone (PCL) nanofibers were used as different tridimensional porous substrates, loaded with a model drug, clotrimazole. The results show that the chemical structure and surface area to volume ratio of the pristine substrates affect the drug release profile. Coating of such substrates by hydrogels poly(2-hydroxyethyl methacrylate) (p-HEMA) and poly(methacrylic acid) (p-MAA) was successfully achieved by initiated chemical vapor deposition. This method was chosen because it is gentle and solventless and most important it can coat free areas within the three-dimensional structures. Scanning electron microscopy results revealed that p-HEMA and p-MAA conformally coated the fibers of the substrates. Moreover, drug release experiments showed that p-HEMA and p-MAA coatings provide barriers preventing sudden drug release. In conclusion, our results indicated the possibility of fabricating dressings containing a drug with tunable drug release profile depending on several parameters even though a strong porous structure exists. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47858
Drug release from thin films encapsulated by a temperature-responsive hydrogel
No full textControl over drug delivery may be interestingly achieved by using temperature responsive encapsulants, which change their thickness and mesh size with temperature. The prototype N-isopropylacrylamide hydrogel cross-linked with di(ethylene glycol) divinyl ether p(NIPAAm-co-DEGDVE) swells at low temperature and collapses above the lower critical solution temperature (LCST), ∼29 °C in a buffer. It might be expected that drug release from such encapsulation is always favored below the LCST, due to the larger free volume present in the swollen polymer film. Recent results show contradicting behavior where some cases behave as expected and others release much less when the polymer layer is swollen. In this study, layers of the drugs phenytoin, clotrimazole and indomethacin were drop cast on glass and p(NIPAAM-co-DEGDVE) layers were then synthesized directly on top of these drug layers via initiated chemical vapor deposition (iCVD), a solvent-free and gentle polymerization technique. Dissolution experiments were then performed, in which the drug release through the hindrance of the hydrogel was measured at different pH values. The results show that not only the swelling but also the permeate (drug in this case)-polymer interaction plays an important role in the release
Biaxial growth of pentacene on rippled silica surfaces studied by rotating grazing incidence X-ray diffraction
No full textPentacene is known to grow on isotropic silicon oxide surfaces in a substrate-induced phase with fiber textured crystallites. This growth study reports on the growth of pentacene crystallites on uniaxially oriented surfaces. Silica substrates have been treated by ion beam sputtering so that ripples with a lateral corrugation length of 38 nm and a surface roughness of 1.3 nm are formed. Pentacene thin films with a nominal thickness in the range from 20 nm up to 300 nm are deposited on top of the rippled surfaces. The films are characterized by atomic force microscopy and grazing incidence X-ray diffraction. Bi-axially oriented crystals are formed due to the grooves of the substrate surface opening up the possibility of a defined in-plane alignment of the crystals. In a first stage of thin film growth, the thin film phase (TFP)of pentacene is formed, while in the later stage the bulk crystal structure (C, Campbell phase)also appears. Due to the bi-axial alignment of the crystallites the transition from the thin film phase to the bulk crystal structure can be directly investigated. An epitaxial relationship with (1 2 0)TFP || (2 1 0)C and [−2 1 0]TFP ||[1 −2 0]C is observed which can be explained by an adaption of the herringbone layers of both crystal structures. This work reveals one possible microscopic mechanism for the transition from the metastable substrate-induced phase of pentacene to its equilibrium bulk structure
Wrinkle formation in a polymeric drug coating deposited via initiated chemical vapor deposition
No full textPolymer encapsulation of drugs is conventionally used as a strategy for controlled delivery and enhanced stability. In this work, a novel encapsulation approach is demonstrated, in which the organic molecule clotrimazole is enclosed into wrinkles of defined sizes. Having defined wrinkles at the drug/encapsulant interface, the contact between the encapsulating polymer and the drug can be improved. In addition, this can also allow for some control on the drug delivery as the available surface area changes with the wrinkle size. For this purpose, thin films of clotrimazole were deposited onto silica substrates and were then encapsulated by crosslinked poly(2-hydroxyethyl methacrylate) (pHEMA) via initiated chemical vapor deposition (iCVD). The thickness and the solid state (crystalline or amorphous) of the clotrimazole layer were varied so that the conditions under which surface wrinkles emerge can be determined. A (critical) clotrimazole thickness of 76.6 nm was found necessary to induce wrinkles, whereby the wrinkle size is directly proportional to the thickness of the amorphous clotrimazole. When the pHEMA was deposited on top of crystalline clotrimazole instead, wrinkling was absent. The wrinkling effect can be understood in terms of elastic mismatch between the relatively rigid pHEMA film and the drug layer. In the case of amorphous clotrimazole, the relatively soft drug layer causes a large mismatch resulting in a sufficient driving force for wrinkle formation. Instead, the increased elastic modulus of crystalline clotrimazole reduces the elastic mismatch between drug and polymer, so that wrinkles do not form
Polymer Encapsulation of an Amorphous Pharmaceutical by initiated Chemical Vapor Deposition for Enhanced Stability
No full textThe usage of amorphous solids in practical applications, such as in medication, is commonly limited by the poor long-term stability of this state, because unwanted crystalline transitions occur. In this study, three different polymeric coatings are investigated for their ability to stabilize amorphous films of the model drug clotrimazole and to protect against thermally induced transitions. For this, drop cast films of clotrimazole are encapsulated by initiated chemical vapor deposition (iCVD), using perfluorodecyl acrylate (PFDA), hydroxyethyl methacrylate (HEMA), and methacrylic acid (MAA). The iCVD technique operates under solvent-free conditions at low temperatures, thus leaving the solid state of the encapsulated layer unaffected. Optical microscopy and X-ray diffraction data reveal that at ambient conditions of about 22 °C, any of these iCVD layers extends the lifetime of the amorphous state significantly. At higher temperatures (50 or 70 °C), the p-PFDA coating is unable to provide protection, while the p-HEMA and p-MAA strongly reduce the crystallization rate. Furthermore, p-HEMA and p-MAA selectively facilitate a preferential alignment of clotrimazole and, interestingly, even suppress crystallization upon a temporary, rapid temperature increase (3 °C/min, up to 150 °C). The results of this study demonstrate how a polymeric coating, synthesized directly on top of an amorphous phase, can act as a stabilizing agent against crystalline transitions, which makes this approach interesting for a variety of applications
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