Poly L-lactic Acid Substrates Research Articles

Nanoimprint assisted free standing porous vanadium oxide nanosheet based ammonia sensor

Artificial intelligence in healthcare sector endures a largest share in non-invasive and point-of-care disease diagnosis by interfacing human behaviour through wearable pathway. In a view to develop sensing element for wearables, the concept of free standing poly-l-lactic acid (PLLA)/V2O5 nanosheets using sacrificial layer - (poly vinyl alcohol- PVA)method has been proposed in this work and the studies on ammonia (NH3) sensing has been briefly discussed. In a view to enhance the sensing performance of vanadium pentoxide (V2O5) film, surface modified PLLA substrates using nanoimprint lithography (NIL) have been implemented. The V+5 stoichiometry of the free standing PLLA/V2O5 films were confirmed using x-ray photoelectron spectroscopy (XPS). From field emission scanning electron microscopy (FE-SEM), it was observed that the patterned structure of about ~250 nm diameter was uniformly distributed on the surface of PLLA/V2O5 film. The chemiresistive sensing studies proved that the sensor response of V2O5 films on patterned PLLA substrate exhibited enhanced response about ~17 towards 75 ppm than the V2O5 film on unpatterned PLLA substrate. We believe that this strategy of patterned free standing PLLA/V2O5 nanosheets will help in fabricating the wearable sensors with better sensing performance.

Tailored functionalization of poly(L-lactic acid) substrates at the nanoscale to enhance cell response

Poly(L-lactic) acid (PLLA) has been widely employed in tissue engineering due to its mechanical properties, biodegradability and biocompatibility. The layer-by-layer (LbL) technique was here proposed as a simple method to impart bioactivity to the surface of PLLA substrates. Aminolysis treatment was applied to introduce amino groups on the surface of PLLA solvent cast films. Then, PLLA films were coated with heparin (HE)/chitosan (CH) multilayer by the LbL technique. Each functionalization step was characterized through physico-chemical and morphological analyses. Aminolysis treatment increased film surface wettability (64.8° ± 2.4° against 74.6° ± 1.3° for untreated PLLA) due to the formation of surface amino groups, which were quantified by acid orange colorimetric assay (0.05 nmol/mm2). After the deposition of 9 layers, the static contact angle varied between values close to 40° C (HE-based layer) and 60 °C (CH-based layer), showing the typical alternate trend of LbL coating. The successful HE/CH deposition was confirmed by ATR-FTIR and X-ray photoelectron spectroscopy (XPS) analyses. Particularly, XPS spectra of coated samples showed the presence of nitrogen (indicative of HE and CH deposition), and sulfur (indicative of HE deposition). The amount of deposited HE was quantified by Taylor’s Blue colorimetric method: after the deposition of 19 and 20 layers the HE concentration was around 33 µg/cm2. Finally, in vitro studies performed using HaCaT immortalized human skin keratinocytes, C2C12 immortalized mouse myoblasts and human fibroblasts demonstrated that HE/CH multilayer-coated PLLA is a promising substrate for soft tissue engineering, as cell response may be modulated by changing the surface chemical properties.

PLLA scaffolds surface-engineered via poly (propylene imine) dendrimers for improvement on its biocompatibility/controlled pH biodegradability

Novel aminolyzed Poly (L) Lactic Acid (PLLA) films and electrospun nanofibrous scaffolds were fabricated and characterized as potential substrates for tissue engineering. The second generation polypropylene imine dendrimer (PPI-G2) was used as the aminolysis agent to functionalize the inert surface of PLLA substrates directly without any pre-modification process. The effect of the solvent type, G2 concentration, reaction temperature and time were studied by following weight reduction percentage, FTIR and contact angle measurements due to determined optimum conditions. In addition, the modified scaffolds abbreviated by PLLA/G2 were analyzed using mechanical properties, SEM images and dye assays as host-guest modeling. The results indicate that under the 0.5 (wt.%) G2 concentration, ethanol as the solvent, room temperature and 4h of treatment, the optimum conditions were obtained. It was shown that the hydrophilic properties of PLLA/G2 were greatly enhanced. Also, pH value analysis revealed that after 4 weeks, the biodegradation of PLLA caused massive immune cells infusion and inflammation in the medium through increasing the acidic rate by secretion the lactic acid, whereas the PLLA/G2 scaffolds greatly reduced and stabilize the acidic rate through aminolysis reaction. Finally, promoted cell adhesion and viability underlined the favorable properties of PLLA/G2 scaffolds as a biodegradable biomaterial for biomedical implants.

Electrospinning 3D Scaffolds for use in Neural Tissue Engineering

ABSTRACTPolymer nanofiber scaffolds for use in neural tissue engineering have been fabricated via electrospinning of poly-L-lactic acid (PLLA) directly onto a 3D printed support. Previously, the investigators have shown success in promoting the directed growth of neural axons on highly aligned PLLA substrates both in vitro and in vivo. However, one criticism of the earlier in vitro studies is that by spinning fibers on a flat, two-dimensional surface, the growth of the axons is restricted to one plane. Thus the axon-to-fiber attachment may not be the sole mechanism for aligning the growth of the axons along the fibers, and the channels between the fibers and the substrate could contribute to the results. Using 3D-printing, elevated or “bridge” spinning stages were made with supports at varying heights, allowing the fibers to be suspended 2 to 5 mm above the substrate surface in different configurations. This 3D structure promotes better access of in vitro cell cultures on the fibers to the growth media during incubation, reduces substrate effects, allows more degrees of freedom for axonal growth, and more closely simulates the growth environment found in vivo. Using these 3D stages, we have electrospun free-standing, highly-aligned pure PLLA fiber scaffolds. We are exploring spinning coaxial fibers with a PLLA sheath and a second core polymer. These coaxial fiber scaffold structures offer additional opportunities for in situ delivery of growth agents and/or electrical stimulation for improved axonal growth results.

Construction and Biofunction of 3‐Dimensional Self‐assembly Collagen Nanostructure on PLLA Substrate

AbstractA 3‐dimensional and multi‐layered network nanostructure of collagen assembled on the poly(L‐lactic) acid (PLLA) substrate was reported. Collagen adsorption layers were prepared by dipping PLLA substrates into collagen solutions with various pH. The influences of adsorption interval, pH of collagen solutions and properties of PLLA substrate on the adsorption behavior of collagen were investigated by using atomic force microscopy and ellipsometry measurements. It was found that the multiple association degrees of collagen molecules in solution at a certain pH value seemed to play an important role in the adsorption process. The distinct adsorption behavior determined a specific 3‐dimensional structure formed at the interface. Furthermore, calcium carbonate (CaCO3) can be biomimetically crystallized by the inducement of biomineralization on these collagen layers.

Hydroxyapatite film coated on poly-L-lactic acid by Aerosol Deposition Method

The new apatite coating method, aerosol deposition method (ADM), was carried out on poly-L-lactic acid (PLLA) substrates by a following process. Hydroxyapatite (HAp) particles formed on aerosol flow by mixing with a helium carrier gas with the velocity of about 300 m/s were accumulated on PLLA substrates via impact adhesion at room temperature. Subsequently the thus prepared HAp coating film on PLLA by ADM was treated by heating. Then it was assessed by in vitro simulated body fluid (SBF) test. As a result, it was proved that the HAp film coated on PLLA by ADM with the heat treatment has bioactivity and that bonelike apatite was formed on the substrate. It is expected that the HAp film fabricated by ADM on PLLA with the heat treatment can be used in clinical orthopedics.

Biodegradable polymer solar cells

Polymer photovoltaic devices were prepared using a biodegradable poly- l-lactic acid (PLLA) substrate loaded with nanoclay in an attempt to improve the thermal properties and possibly reduce permeation of water and oxygen. The nanoclay-loaded PLLA substrates were prepared by compounding and extrusion. The substrate thickness was 200 μm and the substrates had good transparency in the range 300–800 nm of, respectively, >80% for PLA and >60% for PLLA loaded with nanoclay. Devices were realized by application of a conducting transparent anode comprising an aluminium grid with a thin overlayer of silver and spin-coated PEDOT:PSS. The active layer consisted of microfibrillar P3HT and PCBM to encompass the low processing temperatures for PLLA and finally an evaporated aluminium cathode. It was found that PLLA as a substrate holds potential, but there are several challenges beyond the photovoltaic itself which must be met before general application within this field can be envisaged. The most important aspects are the planarity of the PLLA surface, the mechanical stresses induced by the extrusion process, the limitation in processing temperature, and the limitation in the available range of solvents for solution processing.

Soft tissue reaction to microgrooved poly-L-lactic acid implants loaded with transforming growth factor beta(3).

In both normal and disturbed wound healing, the generation of large, contracting scars can raise serious functional and cosmetic problems. A possible strategy to minimize or avoid the generation of scar tissue surrounding an implant is to apply transforming growth factor-beta(3) (TGF-beta(3)) to the implant. TGF-beta(3) (0, 1, or 2.5 microg) was freeze-dried onto poly-L-lactic acid (PLA) microgrooved substrates (width, 10 microm; depth, 1 microm) and implanted subcutaneously on the backs of rats for 2 and 8 weeks. After sacrifice, implants and surrounding tissue were histologically processed. Light microscopic and histomorphometric evaluation of capsule thickness, capsule quality, and implant-tissue interface was performed. In addition, we stained for alpha-smooth muscle actin (SMA), collagen, and ED-1 (a monocyte-macrophage marker). All implants were surrounded by a fibrous capsule. Capsules of the implants loaded with 1 or 2.5 microg of TGF-beta(3) showed significantly higher capsule quality. This meant that capsules were more mature compared with implants without TGF-beta(3). However, no significant differences were found in terms of thickness of the capsules or quality of the interface. Finally, apparently significant differences were also found in the expression of alpha-SMA, when comparing the various growth factor concentrations at both implantation points. In conclusion, the use of microgrooved PLA substrates with TGF-beta(3) did not lead to an overall improvement of periimplant tissue healing.