Preparation and Characterization of PHBV/PCL-Diol Blend Films.

Biodegradable thin films based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(caprolactone diol) (PCL-diol) blend were developed using the solution casting method. PHBV is biodegradable, biocompatible, and produced naturally by bacterial activity, but its use is restricted by high crystallinity and low resistance to thermal degradation with melting temperatures close to degradation thus narrowing the processing window. Solution casting was chosen as a cost-effective method reducing energy consumption and avoiding thermal degradation during processing. The increase in PCL-diol in blend composition (40-60 wt%) enhances the film-forming ability of PHBV and the wettability along with the decrease in the roughness of the resulting materials as revealed by contact angle measurements, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Optimal composition in terms of filmogenity and surface structure has been achieved by the addition of PCL-diol in the amount of 60 wt%. FTIR confirmed the expected chemical structures with no evidence of chemical interactions between the two polymers.

The Influence of Soft Segment Structure on the Properties of Polyurethanes.

A series of polyurethanes (PU) were synthesised via one-step polymerisation without a chain extender, using toluene diisocyanate as well as a variety of soft segments composed of different macrodiols. Poly(D,L-lactide) (PDLLA) and polycaprolactone diol (PCL) were synthesised as a polyester type polyols to obtain soft segments. The process of varying the molar ratio of newly synthesised PDLLA in soft segments has been confirmed as a powerful tool for fine-tuning the final properties of PU. Fourier-transformed infrared spectroscopy was used for evaluation of molecular structures of synthesised PDLLA polyol and final PU. Nuclear magnetic resonance spectrometry was used to confirm the presumed structure of PU. The influence of soft segment composition on polyurethane thermal characteristics was examined using thermogravimetric analysis and differential scanning calorimetry. The composition of soft segments had little impact on the thermal stability of PU materials, which is explained by the comparable structures of both polyester polyols. Wide-angle X-ray scattering was utilised to evaluate the effect of amorphous PDLLA on the degree of crystallinity of PCL in soft PU segments. It was discovered that not only did the PDLLA ratio in the soft segment have a substantial influence on the degree of microphase separation in the soft and hard segments, but it also influenced the crystallisation behaviour of the materials. Furthermore, the restriction of crystallisation of the PCL soft segment has been verified to be dependent on the hard segment concentration and the ratio of PDLLA/PCL polyols. The sample with pure PCL as the polyol component achieved the highest degree of crystallinity (34.8%). The results demonstrated that the composition of soft segments directly affected the properties of obtained polyurethane films. These results can be utilised to easily achieve a desirable set of properties required for application in biomaterials.

Development of Light-Polymerized Dental Composite Resin Reinforced with Electrospun Polyamide Layers.

As the mechanical properties of resin-based dental composite materials are highly relevant in clinical practice, diverse strategies for their potential enhancement have been proposed in the extant literature, aiming to facilitate their reliable use in dental medicine. In this context, the focus is primarily given to the mechanical properties with the greatest influence on clinical success, i.e., the longevity of the filling in the patient's mouth and its ability to withstand very strong masticatory forces. Guided by these objectives, the goal of the present study was to ascertain whether the reinforcement of dental composite resins with electrospun polyamide (PA) nanofibers would improve the mechanical strength of dental restoration materials. For this purpose, light-cure dental composite resins were interspersed with one and two layers comprising PA nanofibers in order to investigate the influence of such reinforcement on the mechanical properties of the resulting hybrid resins. One set of the obtained samples was investigated as prepared, while another set was immersed in artificial saliva for 14 days and was subsequently subjected to the same set of analyses, namely Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Findings yielded by the FTIR analysis confirmed the structure of the produced dental composite resin material. They also provided evidence that, while the presence of PA nanofibers did not influence the curing process, it strengthened the dental composite resin. Moreover, flexural strength measurements revealed that the inclusion of a 16 µm-thick PA nanolayer enabled the dental composite resin to withstand a load of 3.2 MPa. These findings were supported by the SEM results, which further indicated that immersing the resin in saline solution resulted in a more compact composite material structure. Finally, DSC results indicated that as-prepared as well as saline-treated reinforced samples had a lower glass transition temperature (Tg) compared to pure resin. Specifically, while pure resin had a Tg of 61.6 °C, each additional PA nanolayer decreased the Tg by about 2 °C, while the further reduction was obtained when samples were immersed in saline for 14 days. These results show that electrospinning is a facile method for producing different nanofibers that can be incorporated into resin-based dental composite materials to modify their mechanical properties. Moreover, while their inclusion strengthens the resin-based dental composite materials, it does not affect the course and outcome of the polymerization reaction, which is an important factor for their use in clinical practice.

Electrospun Poly(lactide) Fibers as Carriers for Controlled Release of Biochanin A.

The aim of this study is to investigate the possibility of using electrospun polylactide (PLA) fibers as a carrier of the phytoestrogen biochanin A. Polylactide fibers were prepared with different contents of biochanin A by using an electrospinning method at specific process parameters. The obtained electrospun polylactide fibers, as carriers of biochanin A, were characterized by means of different methods. The presented results showed that the mechanical properties of PLA have not changed significantly in the presence of biochanin A. Scanning electron microscopy showed that the fine fiber structure is retained without visible deformations and biochanin A crystals on the surface of the fibres. The analysis by infrared spectroscopy showed that there are no strong interactions between polylactide and biochanin A molecules, which is a good prerequisite for the diffusion release of biochanin A from PLA fibers.The release of biochanin A from PLA fibers in buffer solution pH 7.4 at 37 °C was monitored by applying the HPLC method. The rate and time of the release of biochanin A from PLA fibers is in correlation with the amount of the active ingredient in the matrix of the carrier and follows zero-order kinetics. PLA fibers with biochanin A exhibit concentration-dependent activity on proliferation and migration of L929 fibroblasts in direct culture system in vitro, and proved to be suitable for a potential formulation for use in wound healing.

Influence of Metallic Oxide Nanoparticles on the Mechanical Properties of an A-TIG Welded 304L Austenitic Stainless Steel.

Austenitic stainless steels represent a significant aerospace material, being used for various castings, structural components, landing gear components, afterburners, exhaust components, engine parts, and fuel tanks. The most common joining process is tungsten inert gas (TIG) welding, which possesses many advantages such as suitability to weld a wide range of ferrous and non-ferrous metals and alloys, providing high quality welds with good mechanical properties. Its major disadvantage is low productivity due to low penetration and welding speed. This can be overcome by introducing an activating flux before welding. The activating flux reverses the material flow of the weld pool, significantly increasing penetration. Therefore, shielding gas consumption is reduced and welding without a consumable is enabled. However, the consumable in conventional TIG also enables the conditioning of the mechanical properties of welds. In this study, Si and Ti metallic oxide nanoparticles were used to increase the weld penetration depth, while bend testing, tensile, and impact toughness were determined to evaluate the mechanical properties of welds. Furthermore, optical emission spectroscopy, light, and scanning electron microscope were used to determine the chemical compositions and microstructures of the welds. Chemical compositions and weld mechanical properties were similar in all specimens. The highest tensile and impact properties were obtained with the specimen welded with the flux containing 20% TiO2 and 80% SiO2 nanoparticles. Although lower than those of the base metal, they were well within the nominal base metal mechanical properties.

Modification of PLA-Based Films by Grafting or Coating.

Recently, the demand for the use of natural polymers in the cosmetic, biomedical, and sanitary sectors has been increasing. In order to meet specific functional properties of the products, usually, the incorporation of the active component is required. One of the main problems is enabling compatibility between hydrophobic and hydrophilic surfaces. Therefore, surface modification is necessary. Poly(lactide) (PLA) is a natural polymer that has attracted a lot ofattention in recent years. It is bio-based, can be produced from carbohydrate sources like corn, and it is biodegradable. The main goal of this work was the functionalization of PLA, inserting antiseptic and anti-inflammatory nanostructured systems based on chitin nanofibrils-nanolignin complexes ready to be used in the biomedical, cosmetics, and sanitary sectors. The specific challenge of this investigation was to increase the interaction between the hydrophobic PLA matrix with hydrophilic chitin-lignin nanoparticle complexes. First, chemical modification via the "grafting from" method using lactide oligomers was performed. Then, active coatings with modified and unmodified chitin-lignin nanoparticle complexes were prepared and applied on extruded PLA-based sheets. The chemical, thermal, and mechanical characterization of prepared samples was carried out and the obtained results were discussed.

Bioactive Properties of Nanofibres Based on Concentrated Collagen Hydrolysate Loaded with Thyme and Oregano Essential Oils.

This research aimed to obtain biocompatible and antimicrobial nanofibres based on concentrated collagen hydrolysate loaded with thyme or oregano essential oils as a natural alternative to synthesis products. The essential oils were successfully incorporated using electrospinning process into collagen resulting nanofibres with diameter from 471 nm to 580 nm and porous structure. The presence of essential oils in collagen nanofibre mats was confirmed by Attenuated Total Reflectance -Fourier Transform Infrared Spectroscopy (ATR-FTIR), Ultraviolet-visible spectroscopy (UV-VIS) and antimicrobial activity. Scanning Electron Microscopy with Energy Dispersive Spectroscopy analyses allowed evaluating the morphology and constituent elements of the nanofibre networks. Microbiological tests performed against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans showed that the presence of essential oils supplemented the new collagen nanofibres with antimicrobial properties. The biocompatibility of collagen and collagen with essential oils was assessed by in vitro cultivation with NCTC clone 929 of fibroblastic cells and cell viability measurement. The results showed that the collagen and thyme or oregano oil composites have no cytotoxicity up to concentrations of 1000 µg·mL-1 and 500 µg mL-1, respectively. Optimization of electrospinning parameters has led to the obtaining of new collagen electrospun nanofibre mats loaded with essential oils with potential use for wound dressings, tissue engineering or protective clothing.

Poly(methyl-methacrylate) nanocomposites with low silica addition.

STATEMENT OF PROBLEM: Poly(methyl-methacrylate) (PMMA) represents the most popular current denture material. However, its major drawbacks are insufficient ductility and strength. PURPOSE: The purpose of this study was to improve the mechanical properties of PMMA in denture base application by adding small quantities of nanosilica. MATERIAL AND METHOD: Silica nanoparticles were added to the liquid component of the tested materials. The standard heat polymerizing procedure was followed to obtain 6 PMMA--silicon dioxide (/SiO2) concentrations (0.023%, 0.046%, 0.091%, 0.23%, 0.46%, and 0.91% by volume). Microhardness and fracture toughness of each set of specimens was compared with the unmodified specimens. Furthermore, differential scanning calorimetry and scanning electron microscopy analyses were conducted, and the results obtained were correlated with the results of mechanical properties. RESULTS: It was found that the maximum microhardness and fracture toughness values of the materials tested were obtained for the lowest nanosilica content. A nanosilica content of 0.023% resulted in an almost unchanged glass transition temperature (Tg), whereas the maximum amount of nanosilica induced a considerable increase in Tg. A higher Tg indicated the possible existence of a thicker interfacial layer caused by the chain immobility due to the presence of the particles. However, scanning electron microscopy results demonstrated extensive agglomeration at 0.91% nanosilica, which may have prevented the formation of a homogenous reinforced field. At a nanosilica content of 0.023%, no agglomeration was observed, which probably influenced a more homogenous distribution of nanoparticles as well as uniform reinforcing fields. CONCLUSIONS: Low nanoparticle content yields superior mechanical properties along with the lower cost of nanocomposite synthesis.

Improving mechanical properties of flowable dental composite resin by adding silica nanoparticles.

BACKGROUND/AIM: The main drawback of flowable dental composite resin is low strength compared to conventional composite resin, due to a low amount of filler, neccessary for achieving low viscosity and ease of handling. The aim of this study was to improve mechanical properties of flowable dental composite resin by adding small amount of nanoparticles, which would not compromise handling properties. METHODS: A commercially available flowable dental composite resin material was mixed with 7 nm aftertreated hydrophobic fumed silica and cured by an UV lamp. Four sets of samples were made: control sample (unmodified), the sample containing 0.05%, 0.2% and 1% nanosilica. Flexural modulus, flexural strength and microhardness were tested. One-way ANOVA followed by Tukey's test with the significance value of p < 0.05 was performed to statistically analyze the obtained results. Furthermore, differential scanning calorimetry (DSC) and SEM analysis were performed. To asses handling properties, slumping resistance was determined. RESULTS: It was found that 0.05% is the most effective nanosilica content. All the tested mechanical properties were improved by a significant margin. On the other hand, when 0.2% and 1% nanosilica content was tested, different results were obtained, some of the mechanical properties even dropped, while some were insignificantly improved. The difference between slumping resistance of unmodified and modified samples was found to be statistically insignificant. CONCLUSIONS: Low nanosilica addition proved more effective in improving mechanical properties compared to higher additions. Furthermore, handling properties are unaffected by nanosilica addition.