It is of great interest to pattern biomaterials on the nanoscale and microscale to control diverse biomedical functions. We utilize soft lithographic technique to nanopattern poly (L-lactic acid) (PLLA) - a biodegradable and biocompatible polymer. We find that the PLLA surfaces nanopatterned with 750 nm pitch nanocup or nanocone arrays exhibit drug release rates 25-30% lower than that of the flat surface, which is counter-intuitive given the nanopattern-induced increase in their surface areas. Based on diffusion and microfluidic meniscus curvature minimization analyses, we attribute the decreased drug release rate to the incomplete wetting of the nanopatterned surface by the fluid.
Nanoscale patterned structures composed of biomaterials exhibit great potential for the fabrication of functional biostructures. In this paper, we report cost-effective, rapid, and highly reproducible soft lithographic transfer-molding techniques for creating periodic micro- and nano-scale textures on poly (L-lactic acid) (PLLA) surface. These artificial textures can increase the overall surface area and change the release dynamics of the therapeutic agents coated on it. Specifically, we use the double replication technique in which the master pattern is first transferred to the PDMS mold and the pattern on PDMS is then transferred to the PLLA films through drop-casting as well as nano-imprinting. The ensuing comparison studies reveal that the drop-cast PLLA allows pattern transfer at higher levels of fidelity, enabling the realization of nano-hole and nano-cone arrays with pitch down to ~700 nm. The nano-patterned PLLA film was then coated with rapamycin to make it drug-eluting.
Biological applications can benefit from nanoscale texturing of materials for biomedical functions. Texturing of
biomaterials can increase the available surface area so that they can be coated with larger doses of therapeutic agents.
We demonstrate nano-texturing of poly (L-lactic acid) (PLLA) – a prototypical material commonly used for drug-eluting
coronary stents and as a template for cell growth. A master pattern consisting of a periodic array was transferred to a
PDMS mold. Drop-casting PLLA achieves the best transfer of patterns, with nanoarrays of holes with pitch ~700 nm.
Nanoimprinting the PLLA films results in shallower and less resolved features.
Cu2ZnSnS4 (CZTS) was obtained from a sol-gel precursor which consists of copper chloride, zinc chloride, tin chloride, and thiourea. CZTS thin films were prepared by spin-coating the sol-gel precursor followed by annealing in a nitrogen atmosphere. The morphology, composition, and structure of the absorber layer were studied by scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction, and Raman scattering. The optical measurement shows the bandgap of these films is ∼1.51 eV, and the optical absorption coefficient is on the order of 104 cm−1. CZTS solar cells with a structure of low-alkali glass/Mo/CZTS/CdS/i-ZnO/ZnO:Al/Al grid were tentatively fabricated. The best solar cell showed a short-circuit current density of 5.06 mA/cm2, an open-circuit voltage of 358 mV, a fill factor of 34.66%, and an efficiency of 0.63% under AM1.5 (100 mW/cm2) illumination. These results demonstrate the CZTS thin films were successfully deposited by a cheap sol-gel technique.
Organic-inorganic hybrid solar cells with a cell structure of indium tin oxide/TiO2/TiOx:hyperbranched phthalocyanine/CuSCN/Au (or carbon) have been fabricated by solution based processing using three hyperbranched phthalocyanines (H2PPc, TiOPPc and CuPPc) as light-absorbing materials. These organic-inorganic hybrid solar cells are extremely thin absorber solar cells, which possess p-i-n heterojunctions ("i," an intrinsic absorber layer), as they were confirmed by scanning electron microscopy. With an illuminated area of 1 cm2, a solar cell made from H2PPc achieved conversion efficiency of 0.23% under 1-sun air mass 1.5 global illumination. The lower conversion efficiency for the cell made from CuPPc was likely due to the energy loss in the formation of triplet states with an intersystem crossing time of 0.76 ps.