PLLA Films Research Articles

Poly (L-lactic acid) coatings on 316 SS substrates for biomedical devices: The impact of surface silanization

Metals and their alloys make them critical materials in orthopaedic applications for bone support due to their biocompatibility and mechanical properties. Nevertheless, these materials do not stimulate bone regeneration. A way to overcome this problem, may involve the application of a coating over the alloys using biocompatible and biodegradable materials capable of stimulating bone regeneration. In this work, poly (L-lactic acid) (PLLA) films were used over 316 SS substrates and a silanization reaction was employed to improve the interfacial adhesion between polymer and metal, to achieve physicochemically stable PLLA coatings. PLLA was chosen as a coating due to its biocompatible, biodegradable and piezoelectric properties, stimulating the activity of the host bone tissue. Our results reveal that the functionalization of the metal substrate with silane reagents is effective and efficient in the adhesion of PLLA films to 316 SS. Differences in the degree of adhesion are demonstrated, as well as their dependence on film thickness, concentration of polymer solution, and crystallization degree of the polymeric film. These results have implications on the understanding of how to produce stable PLLA coatings on 316 SS substrates, with suitable adhesion to apply in medical devices, paving the way for the possibility of exploring other advantageous properties of PLLA for bone regeneration such as piezoelectricity.

Bottom-Up Development of Nanoimprinted PLLA Composite Films with Enhanced Antibacterial Properties for Smart Packaging Applications

In this work, polymer nanocomposite films based on poly(L-lactic acid) (PLLA) were reinforced with mesoporous silica nanoparticles, mesoporous cellular foam (MCF) and Santa Barbara amorphous-15 (SBA). PLLA is a biobased aliphatic polyester, that possesses excellent thermomechanical properties, and has already been commercialized for packaging applications. The aim was to utilize nanoparticles that have already been established as nanocarriers to enhance the mechanical and thermal properties of PLLA. Since the introduction of antibacterial properties has become an emerging trend in packaging applications, to achieve an effective antimicrobial activity, micro/nano 3D micropillars decorated with cone- and needle-shaped nanostructures were implemented on the surface of the films by means of thermal nanoimprint lithography (t-NIL), a novel and feasible fabrication technique with multiple industrial applications. The materials were characterized regarding their composition and crystallinity using Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD), respectively, and their thermal properties using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Their mechanical properties were examined by the nanoindentation technique, while the films’ antimicrobial activity against the bacteria Escherichia coli and Staphylococcus aureus strains was tested in vitro. The results demonstrated the successful production of nanocomposite PLLA films, which exhibited improved mechanical and thermal properties compared to the pristine material, as well as notable antibacterial activity, setting new groundwork for the potential development of biobased smart packaging materials.

Controllable surface morphology transition from inter-connected pores to flower-like structures for super-hydrophobic poly (L-lactic acid) films

Abstract The Poly(L-lactic acid) (PLLA) films with polytropic surface morphology were fabricated by a modified solvent evaporation-induced precipitation method. In this novel method, the diffusion rate between solvent and non-solvent is mainly driven by the volatilization of the solvent and can be effectively controlled by covering the solvent with a non-solvent layer. In addition, inspired by the general Breath-Figure self-assembly, the controllable humidity is introduced to the system to adjust the solubility parameters of non-solvents, which avoids the instantaneous phase separation induced by direct coagulation of water droplets. The surface morphology realizes the transformation from inter-connected pores to flower-like structures by controlling polymer solution concentration and humidity. The surface water contact angle can reach to 152.1° with the combination of micro-scale flowers and nano-scale lamellar structures. Furthermore, the porosity of the prepared PLLA films can increase up to 87.5%, which greatly exceeds the 60% porosity of PLLA foam prepared by the non-solvent induced phase separation. Thus, the resultant film exhibits an excellent oil-absorption capacity even up to 17.88 g/g, which makes it has great application potential in the field of oil-water separation.

Controllable Poly(L-lactic acid) Soft Film with Respirability and Its Effect on Strawberry Preservation

Gas permeability of films is essentially important for fresh products packaging. The flexible poly(e-caprolactone) (PCL) was incorporated into the backbone of poly(L-lactic acid) (PLLA) to improve the flexibility and gas permeability of PLLA. The effects of different PCL middle blocks on the mechanical properties, oxygen (O2), carbon dioxide (CO2) and water vapor permeative properties of PLLA-PCL-PLLA triblock copolymers were evaluated, as well as its preservation effect on strawberry. The results showed that both the PCL and PLLA blocks kept amorphous state, and phase separation occurred in this immiscible system. The PCL play a role of gas passage, the CO2 permeability and CO2/O2 perm-selective ratio of neat PLLA film improved 2–3 times with the incorporation of higher molecular weight PCL. In addition, the PLLA-PCL-PLLA films presented a better toughness after large insertion of flexible PCL. Storing experiments showed that the low O2 and high CO2 atmosphere was established inside the package due to the good gas exchange performance of films. Moreover, strawberries still maintained the good sensory quality and Vitamin C contents on 24th day. Such biodegradable PLLA soft films are of great potential in fresh product packaging.

Functionalization Strategies and Fabrication of Solvent-Cast PLLA for Bioresorbable Stents

Actual polymer bioresorbable stents (BRS) generate a risk of device thrombosis as a consequence of the incomplete endothelialization after stent implantation. The material-tissue interactions are not fully controlled and stent fabrication techniques do not allow personalized medical solutions. This work investigates the effect of different functionalization strategies onto solvent-cast poly(l-lactic acid) (PLLA) surfaces with the capacity to enhance surface endothelial adhesion and the fabrication of 3D printed BRS. PLLA films were obtained by solvent casting and treated thermally to increase mechanical properties. Surface functionalization was performed by oxygen plasma (OP), sodium hydroxide (SH) etching, or cutinase enzyme (ET) hydrolysis, generating hydroxyl and carboxyl groups. A higher amount of carboxyl and hydroxyl groups was determined on OP and ET compared to the SH surfaces, as determined by contact angle and X-ray photoelectron spectroscopy (XPS). Endothelial cells (ECs) adhesion and spreading was higher on OP and ET functionalized surfaces correlated with the increase of functional groups without affecting the degradation. To verify the feasibility of the approach proposed, 3D printed PLLA BRS stents were produced by the solvent-cast direct writing technique.

Tuning poly (L-lactic acid) scaffolds with poly(amidoamine) and poly(propylene imine) dendrimers: surface chemistry, biodegradation and biocompatibility

The aim of this comparative study was focused on the surface chemistry, in vitro biodegradation and biocompatibility of poly(L-lactic acid) (PLLA) scaffolds incorporated with poly(amidoamine) (PAMAM) and poly(propylene imine) (PPI) dendrimers. The functionality of these two types of dendrimers from second, third and fifth generations (G2, G3 and G5) onto the surface of PLLA film and electrospun scaffolds was investigated and characterized by a series of analyses including X-ray photoelectron spectroscopy, atomic force microscope, Fourier transform infrared spectroscopy, contact angle, scanning electron microscope, weight loss, water uptake and pH changes after degradation in different media. The successful incorporation of dendrimers into the surface of PLLA scaffolds was observed. PPI-G5 could further increase the hydrophilicity and surface roughness of PLLA scaffolds compared to PPI-G3 and PPI-G2. Further improvement on PLLA surface chemistry was observed when PAMAM-G5 was applied compared to PPI-G5. The pH value of Roswell Park Memorial Institute Medium (RPMI) media containing raw electrospun PLLA scaffold decreased to 5.2 from its original value of 7.2. However, the local acidity of RPMI medium caused by PLLA hydrolysis was greatly reduced on the surface of PLLA/PAMAM-G5 and PLLA/PPI-G5 with pH values of 7.8 and 7.5, respectively. Moreover, the viability of fibroblast cells on the surface of PLLA/dendrimer scaffolds was considerably increased compared to raw PLLA. Fibroblasts showed higher attachment and homogeneous spread morphology on the surface of PLLA/PAMAM-G5 and PLLA/PPI-G5. These observations underline the favorable surface properties of PLLA scaffolds incorporated with dendrimers, to be used as a biodegradable biocompatible scaffold tailored for biomedical applications.

Facile fabrication of soy protein isolate-functionalized nanofibers with enhanced biocompatibility and hemostatic effect on full-thickness skin injury.

Extensive full-thickness skin defect lacks self-healing ability. Tissue engineering wound dressing is considered as the most promising approach to promote wound healing. In this study, a series of biocompatible and hemostatic nanofiber dressings were fabricated. Soy protein isolate (SPI) and poly(L-lactic acid) (PLLA) solutions were mixed in certain proportions for high-voltage electrospinning. The obtained products were coded as SPNF-n (n = 100, 80, 60 and 40, corresponding to the weight percentage of PLLA solution). We found that SPNF-n (n = 100, 80, 60 and 40) could facilitate the adhesion and spread of L929 cells. In particular, SPNF-80 was capable of promoting fibroblast proliferation and diminishing inflammation. Compared with the neat PLLA film (SPNF-100), the biosafety and hemostatic effect of SPNF-80 got significantly improved. The hemostatic effect of SPNF-80 was comparable with that of a commercial gelatin sponge. In vivo wound healing assay demonstrated that SPNF-80 could accelerate the wound healing process by enhancing vascularization, re-epithelization and collagen formation. In conclusion, our results reveal that SPNF-n has good biocompatibility and hemostatic effect, and exhibits great application potential in wound healing.

Relationship between crystallization state and degradation behavior of poly(l‐lactide)/four‐armed poly(d,l‐lactide)‐block‐poly(d‐lactide) blends with different poly(d‐lactide) block lengths

AbstractA series of four‐armed poly(d,l‐lactide)‐block‐poly(d‐lactide) (4‐DL‐D) copolymers were synthesized by ring‐opening polymerization. By fixing the poly(d,l‐lactide) (PDLLA) block length (1 kg mol−1) and changing the poly(d‐lactide) (PDLA) block length (Mn,PDLA = 0, 0.5, 1.1, 1.3, 1.8 and 2.6 kg mol−1), the crystallization and alkaline degradation of the PLLA/4‐DL‐D blends were investigated. The four‐armed PDLLA core of the copolymer inhibited the crystallization of PLLA, while the outer PDLA block could affect the crystallization differently when its length changed. If Mn,PDLA was 0 or 0.5 kg mol−1, the crystallization of PLLA in the PLLA/4‐DL‐D blend was retarded markedly and the degradation rate of the blend films was much faster than that of neat PLLA film. Interestingly, when Mn,PDLA was 1.1 kg mol−1 or higher, stereocomplex (SC) crystallites with different morphologies were formed, and the degradation rate of the PLLA/4‐DL‐D blend decreased gradually with increasing Mn,PDLA. In the PLLA/4‐DL‐D1.1 blend, the SC crystallites acted as nucleators for PLLA homocrystallites, while in the PLLA/4‐DL‐D1.3 blend, small isolated SC crystallites were observed inside the PLLA homospherulites. When Mn,PDLA was 1.8 or 2.6 kg mol−1, a network structure of SC crystallites was formed and the degradation resistance of the films was markedly enhanced. A possible isothermal crystallization mechanism was proposed for the PLLA/4‐DL‐D blends, and the relationship between the crystallization state and degradation behavior was explored. This work revealed that the crystallization state, which was controlled by the PDLA block length, had a significant effect on the degradation behavior of PLLA/4‐DL‐D blend films. © 2020 Society of Chemical Industry

On the Optical Activity of Poly(l-lactic acid) (PLLA) Oligomers and Polymer: Detection of Multiple Cotton Effect on Thin PLLA Solid Film Loaded with Two Dyes

Optical rotatory dispersion (ORD) is a beautiful analytical technique for the study of chiral molecules and polymers. In this study, ORD was applied successfully to follow the degree of polycondensation of l-(+)-lactic acid toward the formation of poly(lactic acid) oligomers (PLAO) and high molecular weight poly(l-lactic acid) (PLLA) in a simple esterification reaction equipment. PLLA is a biodegradable polymer obtainable from renewable raw materials. The racemization of the intrinsically isotactic PLLA through thermal treatment can be easily followed through the use of ORD spectroscopy. Organic or molecular electronics is a hot topic dealing with the combination of π-conjugated organic compounds and polymers with specific properties (e.g., chirality) which can be exploited to construct optoelectronic devices, such as organic light-emitting diodes (OLEDs), organic photovoltaic (OPV) high efficiency cells, switchable chirality devices, organic field-effect transistors (OFETs), and so on. ORD spectroscopy was applied to study either the gigantic optical rotation of PLLA films, as well as to detect successfully the excitonic coupling, occurring in thin solid PLLA green film loaded with a combination of two dyes: SY96 (a pyrazolone dye) and PB16 (the metal-free phthalocyanine pigment). The latter compound PLLA loaded with SY96 and PB16 shows a really gigantic optical activity in addition to typical ORD signal due to exciton coupling and may be considered as a simple and easily accessible model composite of a chiral polymer matrix combined with π-conjugated dyes for molecular electronics studies.

Fabrication and characterization of ultrathin spin-coated poly(L-lactic acid) films suitable for cell attachment and curcumin loading

In the present study, ultrathin poly(L-lactic acid) (PLLA) films were fabricated using the spin-coating technique. Physicochemical properties of the formed materials, including their morphology, thickness, transparency, and contact angle, have been studied. We determined that the morphology of PLLA films could be regulated by changing the polymer concentration and humidity. By altering the humidity, microporous and flat PLLA films can be fabricated. The obtained samples were subsequently used for culturing mesenchymal stem cells and fibroblasts. It has been determined that cells effectively adhered to prepared films and formed on them a monolayer culture with high viability. It has been shown that PLLA films are suitable for the entrapment of curcumin (up to 12.1 μm cm−2) and provide its sustained release in solutions isotonic to blood plasma. The obtained PLLA films appear to be prospective materials for potential application in regenerative medicine as part of cell-containing tissue engineered dressings for chronic wound treatment.

Quantitative characterization of dielectric properties of polymer fibers and polymer composites using electrostatic force microscopy

We use a new method based on electrostatic force microscopy (EFM) to perform quantitative measurements of the dielectric constants of individual electrospun nanofibers of poly(L-lactic acid) (PLLA), as well as composite fibers of PLLA with embedded multiwall carbon nanotubes (MWCNT-PLLA). The EFM data record the oscillation phase of an atomic force microscope (AFM) cantilever as a function of the AFM tip position. In our experiments the relative dielectric constants ϵ of the sample are measured from the EFM phase shifts vs. the tip-surface separation, according to a simple analytical model describing the tip-surface interactions. We perform a comprehensive study of how the dielectric constant depends on the fiber diameter for both electrospun PLLA and MWCNT/PLLA fiber composites. Our measurements show that EFM can distinguish between dielectric properties of PLLA fibers and fiber composites with different diameters. Dielectric constants of both PLLA and MWCNT-PLLA composite fibers decrease with increasing fiber diameter. In the limit of large fiber diameters (D > 100 nm), we measure dielectric constants in the range: ϵ = 3.4–3.8, similar to the values obtained for unoriented PLLA films: ϵfilm = 2.4–3.8. Moreover, the dielectric constants of the small diameter MWCNT-PLLA composites are significantly larger than the corresponding values obtained for PLLA fibers. For MWCNT-PLLA nanofiber composites of small diameters (D < 50 nm), ϵ approaches the values measured for neat MWCNT: ϵCN = 12 ± 2. These results are consistent with a simple fiber structural model that shows higher polarizability of thinner fibers, and composites that contain MWCNTs. The experimental method has a high-resolution for measuring the dielectric constant of soft materials, and is simple to implement on standard atomic force microscopes. This non-invasive technique can be applied to measure the electrical properties of polymers, interphases, and polymer nanocomposites.

Texture Induced by Molecular Weight Dispersity: Polymorphism within Poly(L-lactic acid) Spherulites

Poly(L-lactic acid) (PLLA) has drawn much attention due to its excellent medical and pharmaceutical applications for decades. As a semi-crystalline polymer, morphology and crystal structure of PLLA greatly determine its properties. Here, we demonstrate, for PLLA films, a non-conventional texture featuring two types of spherulites emerging in pairs to form a distinct nested structure where a small spherulite (~10 µm) is embedded in a large one (100 µm to 300 µm). In addition to the size, the molecular weight and polymorph are different in the large and small spherulites. Crystallographic α-form and relatively low molecular weight are identified in the large spherulites, while meta-stable α′-form and relatively high molecular weight in the small ones. These differences suggest that the polydisperse PLLA polymers fractionate during film formation and the high-molecular-weight fraction crystallizes into the small spherulites with meta-stable structure because of its complicated polymer entanglement and high viscosity. In contrast, the rest of polymers crystallize into the large spherulites with the thermodynamically stable polymorph. Furthermore, this texture exhibits accelerated PLLA degradation initiated from the small spherulites, which is distinct from the typical PLLA spherulites. Insights provided by this work may lead to new texture-properties relationship associated with polydispersity of molecular weight.

High-resolution Imaging of Spherulitic Structures in PLLA and PDLA Solvent-cast Films

High-resolution Imaging of Spherulitic Structures in PLLA and PDLA Solvent-cast Films

Versatile Cell-Specific Ligand Arrangement System onto Desired Compartments of Biodegradable Matrices for Site-Selective Cell Adhesion Using DNA Tags.

A promising approach for the regeneration of tissues or organs with three-dimensional hierarchical structures is the preparation of scaffold-cell complexes that mimic these hierarchical structures. This requires an effective technique for immobilizing cell-specific ligands at arbitrarily chosen positions on matrices. Here, we report a versatile system for arranging cell-specific ligands onto desired compartments of biodegradable matrices for site-selective cell arrangement. We utilized the specific binding abilities of specific DNAs, immobilizing them as tags to arrange cell-recognition ligands at desired areas of the matrices by specific binding with cell-recognition ligand-DNA conjugates. We synthesized poly(l-lactide) (PLLA), a biodegradable polymer, with an oligo-DNA (trimer of deoxyguanosine: dG3) attached via a poly(ethylene glycol) (PEG) spacer to generate dG3-PEG-b-PLLA. The peptides Arg-Gly-Asp-Ser (RGDS) and Arg-Glu-Asp-Val (REDV) were chosen as cell-recognition ligands and were attached to an adapter DNA (aDNA), which can specifically bind to the dG3 moiety through G-quadruplex formation. The obtained dG3-PEG-b-PLLA was deposited on a small spot of the PLLA film, and the aDNA-RGDS or aDNA-REDV conjugate was added on the film to immobilize these ligands at the spot. We confirmed the specific adhesion of L929 cells (a mouse fibroblast cell line) and human umbilical vein endothelial cells (HUVECs) on the small areas coated with dG3-PEG-b-PLLA in the presence of aDNA-RGDS and aDNA-REDV, respectively, even after applying shear stress by flowing medium across the spot. Cell-specific attachment of the target cells was effectively achieved in a spatially controlled manner. This technique has the potential for the construction of cell-scaffold complexes that mimic the hierarchical structures of natural organs and may represent a breakthrough in realizing regenerative medicine and tissue engineering of complex organs.

Enzymatic Self-Biodegradation of Poly(l-lactic acid) Films by Embedded Heat-Treated and Immobilized Proteinase K.

Non-biodegradable microplastics have become a global problem. We propose a new enzyme-embedded biodegradable plastic that can be self-biodegraded anytime and anywhere. Proteinase K from Tritirachium album was embedded in poly(l-lactic acid) (PLLA). The PLLA solution-cast film with embedded proteinase K showed weight loss of 78% after 96 h incubation. In addition, PLLA extruded films embedding immobilized proteinase K encapsulated in polyacrylamide were produced at 200 °C and embedded-enzyme degradation was monitored. Immobilized proteinase K embedded in the extruded film maintained its degradation activity and degraded the PLLA film from inside to make small holes and cavities, suggesting that immobilization is a powerful technique to prepare thermoforms with embedded enzymes. The rate of embedded-enzyme degradation was accelerated by dividing the film into smaller pieces, which can be regarded as a model experiment for biodegradation of microplastics. Various biodegradable plastics with specific embedded enzymes will contribute to solve global environmental problems.

Synergic Effect of Nanolignin and Metal Oxide Nanoparticles into Poly(l-lactide) Bionanocomposites: Material Properties, Antioxidant Activity, and Antibacterial Performance.

Binary and ternary poly(l-lactide) (PLLA)-based nanocomposites, containing nanolignin (1 wt %) and different metal oxide nanoparticles (0.5 wt %, Ag2O, TiO2, WO3, Fe2O3, and ZnFe2O4), were realized by solvent casting, and their morphological, thermal, surface, optical, antioxidant, and antimicrobial characterizations were performed. The presence of metal oxide nanoparticles at the selected weight concentration affects the surface microstructure of the PLLA polymer, and this outcome is particle-type dependent, according to the shape, morphology, and chemical properties of the selected nanoparticles (NPs). Analogously, wettability of PLLA-based nanocomposites was slightly modified by the presence of hydrophobic lignin nanoparticles and different shaped metal oxides. Results of differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD) tests confirmed that nanoparticle addition confined the mobility of the amorphous phase, increasing at the same time the formation of more numerous but less perfect PLLA crystals. Interestingly, antioxidant activity was also obtained in ternary-based nanocomposites, where a synergic effect of lignin and metal oxide nanoparticles was obtained. Antibacterial tests showed manifest activity of TiO2 and Ag2O nanoparticles containing PLLA films, and the time dependence was more evident for Staphylococcus aureus than for Escherichia coli. Lignin nanoparticles are able to provide protection against UV light while still allowing visible light to pass and even surpass the UV-protection capacity provided by many inorganic nanoparticles. This makes them an attractive renewable additive for the realization of PLLA/metal oxide nanocomposites in the fields of food, drug packaging, and biomedical industry, where antibacterial and antioxidant properties are required.

Improvement of viscoelastic, elastic and plastic properties of Poly(L-lactide)/Graphene Oxide-Graft-Poly(L-lactide) nanocomposites by modulation of grafted chain length

The full potential of poly(L-lactide) (PLLA) reinforced with graphene oxide, GO, nanocomposites tends to be hindered by aggregation of the nanofillers. In order to promote a good dispersion of GO in the PLLA matrix, polymer grafting techniques have been explored to anchor PLLA onto functionalized GO surface to produce GO-PLLA hybrids. For this purpose, PLLA with a terminal triple bond was synthesized by ring-opening polymerization. By controlling the concentration of monomer to initiator, PLLA samples with three different chain lengths have been prepared and later coupled to azide-functionalized GO using click chemistry. These hybrids were then mixed with commercial PLLA and cast films have been prepared. The ensuing nanocomposite films were studied using Depth Sensing Indentation and the results have shown that PLLA matrix-filler interaction can be modulated by controlling the chain length of PLLA graft. This is a critical point because the enhancement of these interactions provides a stronger matrix-filler interphase which improves the stress transfer between both phases and increases the contribution of the interphase to the stiffening of the nanocomposites. Therefore, it has been proven that judicious functionalization of GO is an effective procedure for improving the strength, the stiffness and the creep resistance of the PLLA composites.

Preparation of multifunctional poly(l-lactic acid) film using heparin-mimetic polysaccharide multilayers: Hemocompatibility, cytotoxicity, antibacterial and drug loading/releasing properties

Poly(l-lactic acid) (PLLA) has been the most commonly used polymer for making bioresorbable vascular scaffolds (BVS). Despite owning remarkable properties, BVS made from PLLA are facing higher rates of early thrombosis compared with permanent metallic scaffolds. To solve this issue, we modified the PLLA film surface with heparin-mimetic polysaccharide multilayers consisting of sulfated Chinese yam polysaccharide (SCYP) and chitosan (CS) through layer-by-layer (LBL) assembly. The surface chemical compositions, morphologies and growth manner of SCYP/CS multilayers were investigated using X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and UV–vis spectroscopy. The relevant hemocompatibility results showed that multilayer-modified PLLA could effectively resist protein adsorption, suppress the platelet adhesion, prolong clotting time, prevent contact and complement activation as well as reduce hemolysis rate. Moreover, the multilayer-modified PLLA exhibited non-cytotoxicity, good antibacterial ability against E. coli and S. aureus, and drug loading/sustained releasing behavior. Overall, the multifunctional PLLA film with integrated properties of hemocompatibility, non-cytotoxicity, antibacterial and drug loading/releasing behavior could be successfully achieved by deposition of SCYP/CS multilayers, which will have potential application in blood-contacting biomedical materials.

Antibacterial chitosan electrostatic/covalent coating onto biodegradable poly (l-lactic acid)

Biodegradable, non-toxic and transparent poly (l-lactic acid) (PLLA) biopolymer is modified in order to obtain an improved material with antibacterial properties for its use as active packaging of food. For this, PLLA films were endowed with the bactericidal effect of ZnO nanoparticles by internal blending and the bacteria contact-killing properties of the biopolymer chitosan (CHI) by superficial modification. Surface functionalization with CHI was carried out by covalent or electrostatic functionalization which were comparatively analyzed in terms of yield and stability. Additionally, the effect of employed CHI concentration and molecular weight was also studied for both modification methods. Modified films were characterized by confocal fluorescence microscopy, contact angle measurements, UV–Vis spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and electrostatic force microscopy. The antibacterial properties of each modification on PLLA were studied against Escherichia coli, showing the greater microbial death after covalent functionalization with CHI. Moreover, stability of modified films was studied in enzymatic and non-enzymatic medium and it was improved by chemical crosslinking with the natural molecule genipin. The valuable properties of PLLA, as well as the derived antibacterial properties of the incorporation of ZnO nanoparticles and CHI, make prepared films highly attractive candidates for the innovative packaging industry.

Surface modification of poly (L-lactic acid) films to improve electrical conductivity by surface entrapment/in situ polymerization methods

Electrical properties play an important role in the interaction of cells and biomaterials. The aim of this study was to increase surface electrical conductivity of poly (L-lactic acid) (PLLA) films by polyaniline (PANI) using surface entrapment (SE) and surface entrapment in situ polymerization (SEIP) methods. The entrapment modification technique was performed by the reversible gelation of the PLLA surface region following exposure to a solvent and non-solvent mixture, while PANI chains were diffused into the swollen PLLA surface. In SEIP method, PANI was entrapped through in situ chemical oxidative polymerization of aniline on PLLA films. The effects of PANI concentration, the ratios of solvents and immersion time on the electrical conductivity were studied by SE method. The effects of aniline concentration, doping effect, temperature and time of polymerization were evaluated by SEIP method too. The results obtained by attenuated total reflection Fourier transformer infrared spectroscopy, scanning electron microscopy and energy dispersive x-ray mapping analysis confirmed the presence of PANI on the surface of PLLA films. UV-visible analysis was employed to investigate the doping effect on the reduction of energy and conductivity of the films. Experimental results also indicated that the electrical conductivity, uniformity and density of the SEIP modified films were significant in comparison to those of the modified films by SE method.