Biological activity of lyophilized chitosan scaffolds with inclusion of chitosan and zinc oxide nanoparticles

The constant demand for biocompatible and non-invasive materials for regenerative medicine in accidents and various diseases has driven the development of innovative biomaterials that promote biomedical applications. In this context, using sol-gel and ionotropic gelation methods, zinc oxide nanoparticles (NPs-ZnO) and chitosan nanoparticles (NPs-CS) were synthesized with sizes of 20.0 nm and 11.98 nm, respectively. These nanoparticles were incorporated into chitosan scaffolds through the freeze-drying method, generating a porous morphology with small (<100 μm), medium (100-200 μm), and large (200-450 μm) pore sizes. Moreover, the four formulations showed preliminary bioactivity after hydrolytic degradation, facilitating the formation of a hydroxyapatite (HA) layer on the scaffold surface, as evidenced by the presence of Ca (4%) and P (5.1%) during hydrolytic degradation. The scaffolds exhibited average antibacterial activity of F1 = 92.93%, F2 = 99.90%, F3 = 74.10%, and F4 = 88.72% against four bacterial strains: K. pneumoniae, E. cloacae, S. enterica, and S. aureus. In vivo, evaluation confirmed the biocompatibility of the functionalized scaffolds, where F2 showed accelerated resorption attributed to the NPs-ZnO. At the same time, F3 exhibited controlled degradation with NPs-CS acting as initiation points for degradation. On the other hand, F4 combined NPs-CS and NPs-ZnO, resulting in progressive degradation, reduced inflammation, and an organized extracellular matrix. All the results presented expand the boundaries in tissue engineering and regenerative medicine by highlighting the crucial role of nanoparticles in optimizing scaffold properties.

Effect of Gelatin Coating and GO Incorporation on the Properties and Degradability of Electrospun PCL Scaffolds for Bone Tissue Regeneration

Polymer-based nanocomposites such as polycaprolactone/graphene oxide (PCL/GO) have emerged as alternatives for bone tissue engineering (BTE) applications. The objective of this research was to investigate the impact of a gelatin (Gt) coating on the degradability and different properties of PCL nanofibrous scaffolds fabricated by an electrospinning technique with 1 and 2 wt% GO. Uniform PCL/GO fibers were obtained with a beadless structure and rough surface. PCL/GO scaffolds exhibited an increase in their crystallization temperature (Tc), attributed to GO, which acted as a nucleation agent. Young's modulus increased by 32 and 63% for the incorporation of 1 and 2 wt% GO, respectively, in comparison with neat PCL. A homogeneous Gt coating was further applied to these fibers, with incorporations as high as 24.7 wt%. The introduction of the Gt coating improved the hydrophilicity and degradability of the scaffolds. Bioactivity analysis revealed that the hydroxyapatite crystals were deposited on the Gt-coated scaffolds, which made them different from their uncoated counterparts. Our results showed the synergic effect of Gt and GO in enhancing the multifunctionality of the PCL, in particular the degradability rate, bioactivity, and cell adhesion and proliferation of hGMSC cells, making it an interesting biomaterial for BTE.

Chitosan-Polyvinyl Alcohol Nanocomposites for Regenerative Therapy

Tissue accidents provide numerous pathways for pathogens to invade and flourish, causing additional harm to the host tissue while impeding its natural healing and regeneration. Essential oils (EOs) exhibit rapid and effective antimicrobial properties without promoting bacterial resistance. Clove oils (CEO) demonstrate robust antimicrobial activity against different pathogens. Chitosan (CS) is a natural, partially deacetylated polyamine widely recognized for its vast antimicrobial capacity. In this study, we present the synthesis of four membrane formulations utilizing CS, polyvinyl alcohol (PVA), and glycerol (Gly) incorporated with CEO and nanobioglass (n-BGs) for applications in subdermal tissue regeneration. Our analysis of the membranes' thermal stability and chemical composition provided strong evidence for successfully blending polymers with the entrapment of the essential oil. The incorporation of the CEO in the composite was evidenced by the increase in the intensity of the band of C-O-C in the FTIR; furthermore, the increase in diffraction peaks, as well as the broadening, provide evidence that the introduction of CEO perturbed the crystal structure. The morphological examination conducted using scanning electron microscopy (SEM) revealed that the incorporation of CEO resulted in smooth surfaces, in contrast to the porous morphologies observed with the n-BGs. A histological examination of the implanted membranes demonstrated their biocompatibility and biodegradability, particularly after a 60-day implantation period. The degradation process of more extensive membranes involved connective tissue composed of type III collagen fibers, blood vessels, and inflammatory cells, which supported the reabsorption of the composite membranes, evidencing the material's biocompatibility.

Preparation and characterization of novel poly (lactic acid)/calcium oxide nanocomposites by electrospinning as a potential bone tissue scaffold

Calcium oxide nanoparticles (n-CaO) ca. 22 nm were obtained from eggshell waste. The n-CaO was incorporated into the PLA matrix in 10 and 20 wt% of filler content by electrospinning process to get PLA/n-CaO fibers with homogenous morphology and diameter as a potential use in scaffold for bone tissue regeneration. The incorporation of n-CaO into PLA modifies the mechanical properties, having a reinforcement effect on the matrix. The Young modulus for PLA/n-CaO nanocomposites increased between 122 and 138 % concerning neat PLA fibers, showing a more rigid behavior. The PLA/n-CaO nanocomposite fibers showed in vitro bioactivity, capable of inducing the precipitation of hydroxyapatite (HA) layer in the fiber surface after seven days in SBF solution. The biocidal and biological properties of PLA/n-Cao with 20 wt% showed a 30 % reduction in bacterial viability against S. aureus and 11 % against E. coli after 6 h of bacterial exposure. Furthermore, the fibers did not show a cytotoxic effect on the bone marrow ST-2 cell line, allowing cell adhesion and proliferation in the RPMI medium. The PLA/n-CaO with 20 wt% of nanoparticles showed a higher capacity to promote osteogenic differentiation, significantly increasing the alkaline phosphatase (ALP) expression after seven days compared to PLA and cell control. The in vivo analysis corroborated the biocompatibility of the prepared scaffolds; the presence of n-CaO in PLA reduced the formation of fibrous encapsulation of the material, improving the healing process. These results validated using n-CaO to enhance the functionality of polymer matrices as a PLA, bringing bioactive, biocide, and biocompatible properties, opening a new and interesting route to develop new biomaterials as a scaffold for bone tissue engineering.

Green composites based on thermoplastic starch reinforced with micro- and nano-cellulose by melt blending - A review

Starch is a biodegradable biopolymer, a sustainable material that can replace conventional petrochemical-based plastics. However, starch has some limitations, as it must be processed by heating and treated mechanically with a plasticizer to become thermoplastic starch (TPS). Different variables such as mixing speeds, amount, and kind of plasticizers play a vital role in preparing TPS by melting. Despite this, the properties of the TPS are not comparable with those of traditional plastics. To overcome this limitation, microcellulose or nanocellulose is added to TPS by melt mixing, including the extrusion and internal mixing process, which enables large-scale production. This review aims to compile several studies that evaluate the effect of plasticizers, as well as the relevance of incorporating different cellulosic fillers of different dimensions on the properties of TPS obtained by melt mixing. Potential applications of these materials in food packaging, biomedical applications, and other opportunities are also described.

Biocompatibility Assessment of Polycaprolactone/Polylactic Acid/Zinc Oxide Nanoparticle Composites under In Vivo Conditions for Biomedical Applications

The increasing demand for non-invasive biocompatible materials in biomedical applications, driven by accidents and diseases like cancer, has led to the development of sustainable biomaterials. Here, we report the synthesis of four block formulations using polycaprolactone (PCL), polylactic acid (PLA), and zinc oxide nanoparticles (ZnO-NPs) for subdermal tissue regeneration. Characterization by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) confirmed the composition of the composites. Additionally, the interaction of ZnO-NPs mainly occurred with the C=O groups of PCL occurring at 1724 cm-1, which disappears for F4, as evidenced in the FT-IR analysis. Likewise, this interaction evidenced the decrease in the crystallinity of the composites as they act as crosslinking points between the polymer backbones, inducing gaps between them and weakening the strength of the intermolecular bonds. Thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyses confirmed that the ZnO-NPs bind to the carbonyl groups of the polymer, acting as weak points in the polymer backbone from where the different fragmentations occur. Scanning electron microscopy (SEM) showed that the increase in ZnO-NPs facilitated a more compact surface due to the excellent dispersion and homogeneous accumulation between the polymeric chains, facilitating this morphology. The in vivo studies using the nanocomposites demonstrated the degradation/resorption of the blocks in a ZnO-NP-dependant mode. After degradation, collagen fibers (Type I), blood vessels, and inflammatory cells continue the resorption of the implanted material. The results reported here demonstrate the relevance and potential impact of the ZnO-NP-based scaffolds in soft tissue regeneration.

Fabrication and assessment of bifunctional electrospun poly(l-lactic acid) scaffolds with bioglass and zinc oxide nanoparticles for bone tissue engineering

Electrospun scaffolds based on poly(l-lactic acid) (PLLA) with bioglass (n-BG) and zinc oxide (n-ZnO), and mixture of both, were developed to design bifunctional biomaterials with enhanced bioactive and biocidal properties. The presence of n-BG increased the fiber diameter of the pure PLA from 1.5 ± 0.3 μm to 3.0 ± 0.8 μm for 20 wt%. ZnO and the mixed nanoparticles did not significantly affect the morphology. The mechanical properties decreased with the presence of nanoparticles. Scaffolds based on PLA/n-BG promoted hydroxyapatite (HA) formation in simulated body fluid (SBF) that was inhibited with the presence of ZnO. Notably, mixed particles produced bioactivity although at longer times. The incorporation of n-ZnO produced a biocidal capacity against S. aureus in the polymeric scaffold, reaching a viability reduction of 60 % after 6 h of exposure. When both types of nanoparticles were combined, the bacterial viability reduction was 30 %. Pure PLA scaffolds and the composites with n-BG showed good ST-2 bone marrow-derived cell line viability, scaffolds with n-BG (pure or mixture) presented lower viability. Results validated the use of both n-BG and n-ZnO fillers for the development of novel bifunctional PLA-based scaffolds with both bioactive and biocidal properties for bone tissue engineering applications.

Numerical Study About Nanofluids of Spherical and Tube-Shaped TiO2 Nanomaterials on the Thermal Performance and Entropy Generation of Different Cross-Section Microchannel Heat Sinks

We numerically evaluated the thermal performance of microchannel heat sinks, considering rectangular, hexagonal, and circular cross-sections. Moreover, as a passive heat transfer augmentation technique, dimples were added to improve the rectangular microchannel heat sinks. These simulations use nanofluids based on TiO2 nanoparticles or nanotubes dispersed in bidistilled water as working fluids. The mathematical model considered variable thermophysical properties of the nanofluids; for this purpose, polynomial fittings correlate the dependence of the thermophysical properties on the temperature. We considered a heat flux of q″ = 50 W/cm2 at the microchannel’s lower surface as a boundary condition along with laminar flow conditions. The numerical simulations allowed the Nusselt numbers and entropy generation calculation, which were the basis for the thermal performance calculation. Regarding the effect of TiO2 nanoparticles shape, spherical TiO2 nanoparticles based nanofluids using rectangular microchannels improve the Nusselt number. Moreover, the frictional entropy decreases with nanofluids based on TiO2 nanotubes, but the thermal entropy decreases with nanofluids based on TiO2 nanotubes. Incorporating dimples in the rectangular microchannel enhances the Nusselt numbers and lowers the entropy generation. Considering the Reynolds number range and from the perspective of Nusselt number and entropy generation, we concluded that the microchannels must be operated at a high Reynolds number to improve the microchannel heat sinks thermal performance.

Synthesis, Characterization, and Optimization Studies of Polycaprolactone/Polylactic Acid/Titanium Dioxide Nanoparticle/Orange Essential Oil Membranes for Biomedical Applications

The development of scaffolds for cell regeneration has increased because they must have adequate biocompatibility and mechanical properties to be applied in tissue engineering. In this sense, incorporating nanofillers or essential oils has allowed new architectures to promote cell proliferation and regeneration of new tissue. With this goal, we prepared four membranes based on polylactic acid (PLA), polycaprolactone (PCL), titanium dioxide nanoparticles (TiO₂-NPs), and orange essential oil (OEO) by the drop-casting method. The preparation of TiO₂-NPs followed the sol-gel process with spherical morphology and an average size of 13.39 nm ± 2.28 nm. The results show how the TiO₂-NP properties predominate over the crystallization processes, reflected in the decreasing crystallinity percentage from 5.2% to 0.6% in the membranes. On the other hand, when OEO and TiO₂-NPs are introduced into a membrane, they act synergistically due to the inclusion of highly conjugated thermostable molecules and the thermal properties of TiO₂-NPs. Finally, incorporating OEO and TiO₂-NPs promotes tissue regeneration due to the decrease in inflammatory infiltrate and the appearance of connective tissue. These results demonstrate the great potential for biomedical applications of the membranes prepared.

Polycaprolactone (PCL)-Polylactic Acid (PLA)-Glycerol (Gly) Composites Incorporated with Zinc Oxide Nanoparticles (ZnO-NPs) and Tea Tree Essential Oil (TTEO) for Tissue Engineering Applications

The search for new biocompatible materials that can replace invasive materials in biomedical applications has increased due to the great demand derived from accidents and diseases such as cancer in various tissues. In this sense, four formulations based on polycaprolactone (PCL) and polylactic acid (PLA) incorporated with zinc oxide nanoparticles (ZnO-NPs) and tea tree essential oil (TTEO) were prepared. The sol-gel method was used for zinc oxide nanoparticle synthesis with an average size of 11 ± 2 nm and spherical morphology. On the other hand, Fourier Transformed infrared spectroscopy (FTIR) showed characteristic functional groups for each composite component. The TTEO incorporation in the formulations was related to the increased intensity of the C-O-C band. The thermal properties of the materials show that the degradative properties of the ZnO-NPs decrease the thermal stability. The morphological study by scanning electron microscopy (SEM) showed that the presence of TTEO and ZnO-NPs act synergistically, obtaining smooth surfaces, whereas membranes with the presence of ZnO-NPs or TTEO only show porous morphologies. Histological implantation of the membranes showed biocompatibility and biodegradability after 60 days of implantation. This degradation occurs through the fragmentation of the larger particles with the presence of connective tissue constituted by type III collagen fibers, blood vessels, and inflammatory cells, where the process of resorption of the implanted material continues.

Histological Evaluation of Cassava Starch/Chicken Gelatin Membranes

The use of biopolymers for tissue engineering has recently gained attention due to the need for safer and highly compatible materials. Starch is one of the most used biopolymers for membrane preparation. However, incorporating other polymers into starch membranes introduces improvements, such as better thermal and mechanical resistance and increased water affinity, as we reported in our previous work. There are few reports in the literature on the biocompatibility of starch/chicken gelatin composites. We assessed the in vivo biocompatibility of the five composites (T1–T5) cassava starch/gelatin membranes with subdermal implantations in biomodels at 30, 60, and 90 days. The FT-IR spectroscopy analysis demonstrated the main functional groups for starch and chicken gelatin. At the same time, the thermal study exhibited an increase in thermal resistance for T3 and T4, with a remaining mass (~15 wt.%) at 800 °C. The microstructure analysis for the T2–T4 demonstrated evident roughness changes with porosity presence due to starch and gelatin mixture. The decrease in the starch content in the composites also decreased the gelatinization heats for T3 and T4 (195.67, 196.40 J/g, respectively). Finally, the implantation results demonstrated that the formulations exhibited differences in the degradation and resorption capacities according to the starch content, which is easily degraded by amylases. However, the histological results showed that the samples demonstrated almost complete reabsorption without a severe immune response, indicating a high in vivo biocompatibility. These results show that the cassava starch/chicken gelatin composites are promising membrane materials for tissue engineering applications.

Comparison of Two Bovine Commercial Xenografts in the Regeneration of Critical Cranial Defects

Autologous bone is the gold standard in regeneration processes. However, there is an endless search for alternative materials in bone regeneration. Xenografts can act as bone substitutes given the difficulty of obtaining bone tissue from patients and before the limitations in the availability of homologous tissue donors. Bone neoformation was studied in critical-size defects created in the parietal bone of 40 adult male Wistar rats, implanted with xenografts composed of particulate bovine hydroxyapatite (HA) and with blocks of bovine hydroxyapatite (HA) and Collagen, which introduces crystallinity to the materials. The Fourier-transform infrared spectroscopy (FTIR) analysis demonstrated the carbonate and phosphate groups of the hydroxyapatite and the amide groups of the collagen structure, while the thermal transitions for HA and HA/collagen composites established mainly dehydration endothermal processes, which increased (from 79 °C to 83 °C) for F2 due to the collagen presence. The xenograft’s X-ray powder diffraction (XRD) analysis also revealed the bovine HA crystalline structure, with a prominent peak centered at 32°. We observed macroporosity and mesoporosity in the xenografts from the morphology studies with heterogeneous distribution. The two xenografts induced neoformation in defects of critical size. Histological, histochemical, and scanning electron microscopy (SEM) analyses were performed 30, 60, and 90 days after implantation. The empty defects showed signs of neoformation lower than 30% in the three periods, while the defects implanted with the material showed partial regeneration. InterOss Collagen material temporarily induced osteon formation during the healing process. The results presented here are promising for bone regeneration, demonstrating a beneficial impact in the biomedical field.

Electrospun fibers of poly (lactic acid) containing bioactive glass and magnesium oxide nanoparticles for bone tissue regeneration

Electrospun fibers of poly (lactic acid) (PLA) containing 10 and 20 wt% of bioactive glass (n-BG) and magnesium oxide (n-MgO) nanoparticles of ca. 27 and 23 nm respectively, were prepared toward to application in bone tissue engineering. The addition of both nanoparticles into the PLA will produce a synergic effect increasing its bioactivity and antimicrobial behavior. Neat PLA scaffold and the composites with MgO showed an average fiber diameter of 1.7 ± 0.6 μm, PLA/n-BG and PLA/n-BG/n-MgO fibers presented a significant diameter increase reaching values of ca. 3.1 ± 0.8 μm. Young's modulus of the electrospun scaffolds was affected by the direct presence of the particle and scaffold morphologies. All the composites having n-BG presented bioactivity through the precipitation of hydroxyapatite structures on the surface. Although n-MgO did not add bioactivity to the PLA fibers, they were able to render antimicrobial characteristics reducing the S. aureus viability around 30%, although an effect on E. coli strain was not observed. PLA/n-BG nanocomposites did not display any significant antimicrobial behavior. The different composites increased the alkaline phosphatase (ALP) expression as compared with pure PLA barely affecting the cell viability, meaning a good osteoblastic phenotype expression capacity, with PLA/n-BG presenting the highest osteoblastic expression.

Cytocompatible drug delivery hydrogels based on carboxymethylagarose/chitosan pH-responsive polyelectrolyte complexes

Several drugs are chemically unstable in the gastric environment and have low bioavailability restricted by intestinal absorption, which motivates the development of alternative routes for drug release, such as transdermal drug carriers for drug delivery to specific areas of the skin. Herein, novel polyelectrolyte complexes (PEC) consisting of carboxymethylagarose (CMA) and chitosan (CS) were prepared. pH-responsive CMA/CS hydrogels were obtained by mixing CMA and CS at various weight ratios. Swelling ratio was modulated by varying the CMA and CS weight ratio, and the highest swelling values were achieved for 2:1 wt% hydrogels at 25 °C and pH 6.0. PEC films were characterized by ATR-FTIR spectroscopy, TGA, DSC, and SEM. Results indicated that CMA and CS were successfully crosslinked by ionic complexation. As a model drug, diclofenac sodium (DS) was loaded in CMA/CS PECs. Association efficiency and loading capacity were ca. 69% and 79%, respectively, exhibiting 67% cumulative release after 72 h at 37 °C and pH 6.0 through Fickian diffusion mechanism. Viability assay of immortalized human keratinocyte (HaCat) cells showed ca. 100% survival in the presence of hydrogels and DS. Therefore, this work suggests that CMA/CS PECs can be applied as pH-responsive carriers for dermal drug delivery.

Study of the effect of the addition of plasticizers on the physical properties of biodegradable films based on kefiran for potential application as food packaging

Spectroscopies analysis indicated that kefiran contains branched hexasaccharide repeating units. Neat kefiran films, 2 and 5% w/w of glycerol, d-glucitol, d-galactitol, d-mannitol, and d-limonene were incorporated as plasticizers. Neat and plasticized kefiran films were characterized by physical, thermal, mechanical, optical, and water solubilization properties. Neat kefiran had a glass transition temperature (T_g) of -20 ± 2 °C and, with the addition of plasticizers between -15 to -17 ± 2 °C. The values were close to the neat kefiran, and the results could be attributed to a lower amount of plasticizer used. The solubility of the glycerol plasticized films increases by 33% and decreased with the concentration of other plasticizers in comparison with the neat kefiran. d-glucitol and d-galactitol decreased the microhardness and Young's Modulus of films around 30% and 74% respectively, obtaining more flexible kefiran films. Kefiran based films could find applications as potential materials in the food-packaging industry.

Optimization of Chitosan Glutaraldehyde-Crosslinked Beads for Reactive Blue 4 Anionic Dye Removal Using a Surface Response Methodology

The use of dyes at an industrial level has become problematic, since the discharge of dye effluents into water disturbs the photosynthetic activity of numerous aquatic organisms by reducing the penetration of light and oxygen, in addition to causing carcinogenic diseases and mutagenic effects in humans, as well as alterations in different ecosystems. Chitosan (CS) is suitable for removing anionic dyes since it has favorable properties, such as acquiring a positive charge and a typical macromolecular structure of polysaccharides. In this study, the optimization of CS beads crosslinked with glutaraldehyde (GA) for the adsorption of reactive blue dye 4 (RB4) in an aqueous solution was carried out. In this sense, the response surface methodology (RSM) was applied to evaluate the concentration of CS, GA, and sodium hydroxide on the swelling degree in the GA-crosslinked CS beads. In the same way, RSM was applied to optimize the adsorption process of the RB4 dye as a function of the initial pH of the solution, initial concentration of the dye, and adsorbent dose. The crosslinking reaction was investigated by scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR), and X-ray diffractometry (XRD). The design described for the swelling degree showed an R2 (coefficient of determination) adjusted of 0.8634 and optimized concentrations (CS 3.3% w/v, GA 1.7% v/v, and NaOH 1.3 M) that were conveniently applied with a concentration of CS at 3.0% w/v to decrease the viscosity and facilitate the formation of the beads. In the RB4 dye adsorption design, an adjusted R2 (0.8280) with good correlation was observed, where the optimized conditions were: pH = 2, adsorbent dose 0.6 g, and initial concentration of RB4 dye 5 mg/L. The kinetic behavior and the adsorption isotherm allowed us to conclude that the GA-crosslinked CS beads' adsorption mechanism was controlled mainly by chemisorption interactions, demonstrating its applicability in systems that require the removal of contaminants with similar structures to the model presented.

Mechanical and Antimicrobial Polyethylene Composites with CaO Nanoparticles

Low-density polyethylene composites containing different sizes of calcium oxide (CaO) nanoparticles were obtained by melt mixing. The CaO nanoparticles were synthesized by either the sol-gel or sonication methods, obtaining two different sizes: ca. 55 nm and 25 nm. These nanoparticles were used either as-synthesized or were modified organically on the surface with oleic acid (Mod-CaO), at concentrations of 3, 5, and 10 wt% in the polymer. The Mod-CaO nanoparticles of 25 nm can act as nucleating agents, increasing the polymer’s crystallinity. The Young’s Modulus increased with the Mod-CaO nanoparticles, rendering higher reinforcement effects with an increase as high as 36%. The reduction in Escherichia coli bacteria in the nanocomposites increased with the amount of CaO nanoparticles, the size reduction, and the surface modification. The highest antimicrobial behavior was found in the composites with a Mod-CaO of 25 nm, presenting a reduction of 99.99%. This strong antimicrobial effect can be associated with the release of the Ca²⁺ from the composites, as studied for the composite with 10 wt% nanoparticles. The ion release was dependent on the size of the nanoparticles and their surface modification. These findings show that CaO nanoparticles are an excellent alternative as an antimicrobial filler in polymer nanocomposites to be applied for food packaging or medical devices.

Effect of bioglass nanoparticles on the properties and bioactivity of poly(lactic acid) films

Bioglass nanoparticles (n-BGs, 54SiO₂ :40CaO:6P₂ O₅ mol %) with about 27 nm diameter were synthesized by the sol-gel method and incorporated into a poly(lactic acid) (PLA) matrix by the melting process in order to obtain nanocomposites with filler contents of 5, 10, and 25 wt %. Our results showed that during the cooling scan, the crystallization temperature (T_c ) of the PLA/n-BG nanocomposites decreased 13°C as compared to neat PLA. The presence of nanoparticles also decreased the thermal stability of the PLA matrix, as nanocomposites presented up to about 20°C lower degradation temperatures in a nitrogen atmosphere. The presence of n-BG increased the stiffness of the polymer matrix, and for instance the composite with 25 wt % of filler presented about 52.6% higher Young's modulus than neat PLA. n-BG incorporation into PLA increased also the hydrolytic degradation of the polymer over time. When the PLA composites were immersed in simulated body fluid, an apatite layer was formed on their surface, as verified by Fourier transform infrared, X-Ray Diffraction (XRD), and scanning electron microscopy-EDS, showing that the presence of n-BG induced bioactivity on the PLA matrix. Moreover, the viability of cervical uterine adenocarcinoma cells was higher on PLA/n-BG nanocomposite with 25 wt % of filler. The presence of n-BG barely gave an antibacterial effect on the polymer matrix, despite the well-known biocidal properties of these nanoparticles. Our results show that the presence of n-BGs is a proper route for improving the bioactivity of PLA with potential application in tissue engineering.

Polyethylene/silver-nanofiber composites: A material for antibacterial films

Silver nanofibers (Ag-Nfbs)~80nm in diameter were synthesized by hydrothermal treatment. The nanofibers (3 and 5wt%) were added in the initial feed together with the catalytic system. Polymerizations in an ethylene atmosphere were performed, yielding PE nanocomposites in situ with 3 and 5wt% content of Ag-Nfbs. The antibacterial effect of the silver-nanofiber composites was evaluated after incubation of Escherichia coli ATCC 25923 for 8h on their surface. Bacterial viability tests showed that the silver-nanofiber composites inhibited the growth of Escherichia coli ATCC 25923 by 88 and 56%. This behavior is attributed to increased silver ions release from the nanocomposite. TEM analysis showed that the antibacterial effect is associated with membrane disruption but not with changes in shape.

Antibacterial and non-cytotoxic effect of nanocomposites based in polyethylene and copper nanoparticles

In this study, an antibacterial, but not cytotoxic nanomaterial based on polyethylene and copper nanoparticles was prepared by in situ polymerization. PE-CuNps nanocomposites against Escherichia coli, completely suppressed the number of live bacteria after 12 h incubation compared to neat PE. TEM images showed that nanocomposites damage the plasma membrane of the bacteria, revealing a bacteriolytic effect. Toxic effects of copper nanoparticles on viability of neuroblastoma line cell also was evaluated, revealing a non cytotoxic effect for the doses used, showing that this nanocomposite is a ideal material for medical devices.

Release of silver and copper nanoparticles from polyethylene nanocomposites and their penetration into Listeria monocytogenes

Since infection is a major cause of death in a patient whose immune responses have been compromised (immunocompromised patient), considerable attention has been focused on developing materials for the prevention of infections. This has been directed primarily at suppressing or eliminating the host's endogenous microbial burden and decreasing the acquisition of new organisms. In this study, the antibacterial properties of two nanocomposites, polyethylene modified with silver nanoparticles (PE-AgNps) or copper nanoparticles (PE-CuNps), against Listeria monocytogenes have been investigated. In order to elucidate the antibacterial mechanism, specifically whether this mechanism corresponds to bactericidal or bacteriolytic activities, we have determined the extent of release of metal ions (Ag(+) and Cu(2+)) and, also, the morphology of the bacteria. The metal ion release from nanocomposites was followed by inductively coupled plasma spectrometry and the morphology of the bacteria was revealed through examination of ultramicrotomed sections of bacteria in a transmission electron microscope. The study of metal ion release from the nanocomposites shows that for both nanocomposites the amount of ions released varies with time, which initially displays a linear behavior until an asymptotic behavior is reached. Further, TEM images show that silver nanoparticles (AgNps) and copper nanoparticles (CuNps), which are released from the nanocomposites, can penetrate to the cell wall and the plasma membrane of bacteria. Resulting morphological changes involve separation of the cytoplasmic membrane from the cell wall, which is known to be an effect of plasmolysis. It was revealed that the antibacterial abilities of the two nanocomposites against L. monocytogenes are associated with both bactericidal and bacteriolytic effects.