Thermoplastic Surfaces Research Articles

Home Biofilm Management in Orthodontic Aligners: A Systematic Review.

Background. Transparent aligners are recently introduced orthodontic devices considered promising for the improvement of oral health conditions, in terms of faster treatment times and enhanced comfort, especially if compared with traditional fixed orthodontic therapy. This systematic review aimed to evaluate at-home protocols for proper oral hygiene and aligners cleaning during orthodontic treatment. Methods. A search was conducted using the following four databases: PubMed, Cochrane Library, Web of Science, and Scopus. The systematic review (registered as CRD 42024562215) followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines and included prospective studies, randomized controlled trials (RCTs), controlled clinical trials, and in vivo and ex vivo studies; they had to assess treatment with invisible orthodontics compared to treatment with fixed orthodontics, home oral hygiene, or aligner disinfection protocols. The evidence in the studies was evaluated for risk of bias using the RoB-2 (for RCTs and randomized crossover studies) and ROBINS-I tools (for observational studies). Results. Eleven studies were included in this systematic review: four RCTs, four crossover studies, and three cross-sectional observational studies. Seven studies considered patients undergoing orthodontic treatment, whereas four examined orthodontic aligners. The cleaning protocols of the aligners were evaluated based on the analysis of residual biofilm on the thermoplastic surfaces. Studies included were characterized by a low level of certainty, thus further evidence is needed. Conclusions. The most effective protocols entailed a combination of mechanical and chemical agents, suggesting that it is fundamental for patients undergoing aligner treatment to focus on individually tailored home oral hygiene protocols.

Microbiological Evaluation of Thermoplastic PETG Dental Appliances Related to Surface Characteristics.

(1) Background: The adhesion and microbiological behaviour of thermoplastic PETG dental appliance surfaces is governed by roughness parameters. The aim of this research was to evaluate the antibiofilm activity of alkaline peroxide-based disinfectant in Candida albicans biofilms on thermoplastic PETG, related to artificial ageing and surface characteristics, on multiscale levels. (2) Methods: In the present study, two PETG materials were investigated: Crystal® (Bio Art Dental Equipment, Sao Carlos, Brazil), noted as C, and Duran® (Scheu-Dental GmbH, Iserlohn, Germany)-noted as D. Half of the specimens were thermally cycled (TC), resulting in four sample groups, as follows: C, CTC, D, and DTC. Surface roughness was evaluated on different scale topographies. The biofilms were grown on the surfaces. An alkaline peroxide-based disinfectant was used. Statistical analyses were performed. (3) Results: Related to nanoroughness, there are insignificant differences among materials or related to thermocycling. More irregular surfaces are associated with larger grain sizes. After thermocycling, micro-roughness values increase. Disinfectant activity decreases the amount of biofilm developed on the surfaces, significantly in the two groups, but is not correlated to the material and artificial ageing. (4) Conclusion: The impact of surface roughness (Ra) on biofilm constitution is controlled by different scale topographies.

Characterization of atmospheric pressure plasma deposited (APPD) coatings to improve the friction behavior of thermoplastic surfaces

Achieving a significant friction reduction is crucial for using thermoplastic materials as substrates in tribological applications and presents an eligible alternative to the use of light metals. In this study, previously developed MoS2/graphite/zinc composite coatings, applied by an atmospheric pressure plasma deposition (APPD) process, were investigated to extend the understanding of their characteristics and the influence of the process and environmental parameters on friction behavior. Tribological tests were conducted in ambient conditions and at elevated temperatures (110 °C) to study the friction behavior under application-oriented conditions. The presence of atmospheric oxygen during the deposition process was shown to influence the durability of the coatings, which motivated the application of an inert gas atmosphere for the coating deposition. A novel shrouding plasma nozzle was introduced, which further lowered the friction coefficients. The oxidizing effect of the plasma spray deposition was studied with X-ray photoelectron spectroscopy to investigate the strong impact of the deposition current on the friction behavior and durability of the deposited coatings. Coating composition, morphology, and the effects of the tribological testing were evaluated using optical microscopy, 3D surface measurements, scanning electron microscopy, X-ray diffraction, and nanoindentation. The fabricated coatings with thicknesses in the 10 μm range and good adhesion on the polyamide substrate were stable under extended testing durations and at elevated temperatures and accomplished a significant friction reduction compared to the uncoated polyamide. Thus, APPD-fabricated MoS2/graphite/zinc coatings represent an excellent candidate for low-friction applications of thermoplastic substrates.

A flexible superhydrophobic thermoplastic polyurethane porous surface with good self-cleaning function prepared by supercritical CO2 foaming

Porous surfaces show great potential for superhydrophobic applications. Supercritical CO2 foaming is a green technology for preparing porous materials, but it is rarely used to prepare porous surfaces due to the non-porous skin caused by the escape of gas. In this study, a porous thermoplastic polyurethane (TPU) surface with dense cell and small cell spacing is prepared by employing bilayer TPU sheet to restrict the escape of gas from surfaces. The influence of the foaming pressure and temperature on the cells of the TPU surface is researched. Furthermore, bimodal cells are obtained by regulating the foaming process and the effect of cell structure on wettability is investigated. Subsequently, a flexible superhydrophobic material with low water-adhesion, mechanical stability, and self-cleaning properties is successfully prepared by modifying fluorinated silica particles on porous TPU surfaces.

Ultrasonic Plasticizing and Pressing of High-Aspect Ratio Micropillar Arrays with Superhydrophobic and Superoleophilic Properties

An ultrasonic plasticizing and pressing method (UPP) that fully utilizes ultrasonic vibration is proposed for fabricating thermoplastic polymer surface microstructures with high aspect ratios (ARs). The characteristics of UPP are elucidated based on the plasticization of the raw material, the melt flow, and the stress on the template microstructure during the forming process. Initially, the micronscale single-stage micropillar arrays (the highest AR of 4.1) were fabricated by using 304 stainless steel thin sheets with micronscale pore (through-hole) arrays as primary templates. Subsequently, anodic aluminum oxides (AAOs) with ordered nanoscale pore arrays were added as secondary templates, and the micro/nanoscale hierarchical micropillar arrays (the highest AR up to 24.1) were successfully fabricated, which verifies the feasibility and forming capability of UPP. The superiority and achievements of UPP are illustrated by comparing the prepared hierarchical micropillar arrays with those prepared in the previous work in four indexes: microstructure scale, aspect ratio, forming time, and preheating temperature of the raw material. Finally, the water contact angle (WCA) and oil droplet complete immersion time of the surface microstructures were measured by a droplet shape analyzer, and the results indicate that the prepared micropillar arrays are superhydrophobic and superoleophilic.

Hydroxyl silicone oil grafting onto a rough thermoplastic polyurethane surface created durable super-hydrophobicity

Indwelling medical catheters are frequently utilized in medical procedures, but they are highly susceptible to infection, posing a vital challenge for both health workers and patients. In this study, the superhydrophobic micro-nanostructure surface was constructed on the surface of thermoplastic polyurethane (TPU) membrane using heavy calcium carbonate (CaCO3) template. To decrease the surface free energy, hydroxyl silicone oil was grafted onto the surface, forming a super-hydrophobic surface. The water contact angle (WCA) increased from 91.1° to 143 ± 3° when the concentration of heavy calcium CaCO3 was 20% (weight-to-volume (w/v)). However, the increased WCA was unstable and tended to decrease over time. After grafting hydroxyl silicone oil, the WCA rose to 152.05 ± 1.62° and remained consistently high for a period of 30 min. Attenuated total reflection infrared spectroscopy (ATR-FTIR) analysis revealed a chemical crosslinking between silicone oil and the surface of TPU. Furthermore, Scanning electron microscope (SEM) image showed the presence of numerous nanoparticles on the micro surface. Atomic force microscope (AFM) testing indicated a significant improvement in surface roughness. This method of creating a hydrophobic surface demonstrated several advantages, including resistance to cell, bacterial, protein, and platelet adhesion and good biosecurity. Therefore, it holds promising potential for application in the development of TPU-based medical catheters with antibacterial properties.

Thermoplastic polyurethane surface coated with polymer brushes for reduced protein and cell attachment.

The objective of this study was to coat negatively charged polymer brushes covalently onto the surface of thermoplastic polyurethane (TPU) using a simple conventional surface free-radical polymerization technique. The coated surfaces were assessed with contact angle, protein adsorption, cell adhesion and bacterial adhesion. Bovine serum albumin (BSA) and bovine fibrinogen (BFG) were used for protein adsorption evaluation. Mouse fibroblasts (NIH-3T3) and Pseudomonas aeruginosa (P. aeruginosa) were used to assess surface adhesion. Results show that the TPU surface modified with the attached polymer brushes exhibited significantly reduced contact angle, protein adsorption, and cell as well as bacterial adhesion, among which the negatively charged polymers showed the extremely low values in all the tests. Its contact angle is 5°, as compared to 70° for original TPU. Its BSA, BFG, 3T3 adhesion and P. aeruginosa adhesion were 93%, 84%, 92%, and 93% lower than original TPU. Furthermore, the TPU surface coated with negatively charged polymer brushes exhibited a hydrogel-like property. The results indicate that placing acrylic acids using a simple surface-initiated free-radical polymerization onto a TPU surface and then converting those to negative charges can be an effective and efficient route for fouling resistant applications.

MC-Injection Molding with Liquid Silicone Rubber (LSR) and Acrylonitrile Butadiene Styrene (ABS) for Medical Technology.

The multicomponent injection molding of liquid silicone rubbers (LSR) with thermoplastics, such as polybutylene terephthalate (PBT) or polyamide (PA), is a state-of-the-art technique and is used in the manufacturing process for many components in the automotive industry and in the field of sanitary engineering. Standard thermoplastics, such as acrylonitrile butadiene styrene (ABS), cannot be bonded with silicone rubbers in injection molding because of their low heat deflection temperature. In this study, we investigated ABS grades approved for medical applications to show how dynamic mold heating and various pretreatment methods for thermoplastic surfaces can be used to produce ABS-LSR test specimens. In addition, such components' sterilization effect on the adhesive bond will be shown.

Microbial investigation of cleanability of different plastic and metal surfaces used by the food industry

Different conveyor belt materials used by the meat and other food industries were compared, regarding their cleanability as bacterial reduction rates in relation to their surface topography. Eleven thermoplastic polymers, four stainless steels, and five aluminized nanostructured surfaces were investigated under laboratory conditions. Cleanings were conducted with water only, and with an alkaline foam detergent. Overall, scanning electron microscopy revealed remarkable differences in the surface topography of the tested surfaces. Water cleaning results showed that nanostructured aluminized surfaces achieved significantly higher cleanability rates compared to the eight thermoplastic surfaces, as well as the glass-bead blasted rough stainless steel. Thermoplastic surfaces showed overall low cleanability rates when cleaned with alkaline detergent, while stainless steel and nanoporous aluminum showed high variations. Overall, nanoporous aluminum showed promising results as it can be used to coat conveyor belts. However, compatibility with cleaning detergent and sensitivity to scratches must be further investigated. Overall, it can be concluded that cleanability is not only influenced by surface roughness, but also by the overall surface finish, scratches, and defects.

Proposal and verification of a thermoplastic surface shear-strength evaluative method

A method for evaluating the surface shear strength of thermoplastics is proposed and validated. Thermoplastics are commonly used for their mass production and solid properties, but their surface properties, specifically friction and wear, are also required in some cases. The surface strength against shear loading, which has not been evaluated quantitatively as a material mechanical property, must be ascertained to elucidate these properties. We propose the overlapped short-beam shear tests to evaluate the surface shear strength of injection-molded thermoplastics. We also perform ball on disk testing to validate the results obtained from the overlapped short beam shear tests. Results show that the surface shear strength obtained from the proposed test is related to the frictional force obtained from the ball on disk tests, thereby validating the proposed method.

Optimization of interfacial bonding properties between thermoplastic liners and carbon fiber‐reinforced composites by atmospheric‐pressure plasma and failure mechanism study

AbstractWeak interfacial bonding properties between thermoplastic liners and carbon fiber‐reinforced composites (CFRP) can easily lead to debonding failure, which is a major challenge in development of type IV composite hydrogen storage vessels. We optimized Box–Behnken design atmospheric‐pressure plasma process parameters for maximizing interfacial bonding properties between thermoplastic liner (PA11 liner) and CFRP using Design‐Expert software. From various designs, plasma process parameters, including time (t), nozzle‐to‐specimen distance (d) and gas flow rate (r) of treatment were selected for optimization to assess the effects of their interactions on climbing drum peel (CDP), flatwise tensile (FWT) and asymmetric double cantilever beams (ADCB). The CDP strength, FWT strength and strain energy release rate (GADCB) of untreated samples were 4.2 N·mm/mm, 0.26 MPa and 87.2 J/m2, respectively. After the plasma treatment, optimum process parameters of t = 200 s, d = 12.5 mm, and r = 700 L/h were used to achieve 33.8 N·mm/mm, 2.97 MPa and 1008.4 J/m2, respectively, which were 8.0, 11.4 and 11.6 times that of untreated PA11 surface, respectively. This method has the potential for guiding thermoplastic liner surface treatment of type IV hydrogen storage vessels before winding.

THE EFFECT OF SPECIALIZED HYGIENE PRODUCTS ON THE MORPHOLOGY OF THE SURFACE OF THERMOPLASTIC POLYMERS USED AS THE BASES FOR REMOVABLE DENTURES

Despite the progress observed in implantology and the rapid evolution of preventive and treatment options employed to treat major dental issues, the number of patients who need prosthetics with removable dentures still remains high, with no decrease trend to be expected soon. Modern dentistry, when dealing with issues related to dentition restoration, makes full use of basic thermoplastic polymers incorporating injection molding technology, whereas the said polymers can boast of such properties as biological inertia, proper aesthetics, strength, flexibility, resistance to external effects, lightness and elasticity. The conventional techniques used for cleaning and disinfecting removable dentures made of thermoplastic polymers fail to be up to the respective advanced requirements – such dentures create environments that are favorable for adhesion and microbial colonization. Aiming to evaluate the effectiveness of the modern means used for cleaning and disinfecting removable denture structures based on thermoplastic polymers, there was a study carried out to investigate the surface of 60 experimental samples of Acry-free ® thermoplastic, including methods of scanning electron microscopy and atomic force microscopy. To analyze the effect that cleaning and disinfecting agents work on the hygienic status of partially removable dentures made of thermoplastics (manufactured for 74 patients suffering from partial adentia), the Ambjornsen E. questionnaire was employed. The developed original set of preventive measures involved thorough oral hygiene activities with a manual toothbrush and mouthwash balms, as well as a consistent use of a special toothbrush and gel paste to take care of the removable dentures, followed with ultrasonic treatment and cleansing with effervescent tablets. The data of scanning electron microscopy and atomic force microscopy showed that using the original set of preventive measures resulted in improved quality of the thermoplastic polymers surface – by 1.1 – 1.5 times, if compared with conventional hygiene and disinfection products. As the data of sociological monitoring reveal, 12 into using the developed preventive measures, over 69% of patients were satisfied with the aesthetic properties of their dentures based on thermoplastics; as for the patients sticking to the practice relying on traditional hygiene and disinfection products, the similar indicator would not exceed 25%. In order to prevent the occurrence of major dental issues, as well as to increase the useful life of dentures made of thermoplastics and used by patients with partial adentia, it is wise to employ an individual approach to the selection of preventive measures that involve specialized extra hygiene products.

Facile preparation of micropatterned thermoplastic surface for wearable capacitive sensor

Highly sensitive and flexible capacitive sensors are in great demand for wearable electronics, which can be achieved by preparing micropatterns on their dielectric layer surface. However, most micropatterns are often molded with the silicon template acquired by complex processes which are very time-consuming and costly. Here, a dielectric layer with micropatterned arrays was prepared on the thermal plastic polyurethane (TPU) film with the help of a hot-air-gun, then assembled with an ITO/PET electrode to develop a capacitive sensor with a sandwich structure. The capacitive sensor based on TPU/ITO/PET composites exhibits sensitivity of over 0.026 kPa−1, shorter response/recovery time of 99 ms, wide working range (0–13 kPa) and remarkable stability over 5000 cyclic pressing or bending. Interestingly, such sensor can monitor various physiological signals of people (e.g., voice signal, finger bending and breath). More importantly, it can distinguish different sign languages according to capacitive changes in the case of different finger gestures. The method proposed in this study will paves a new avenue for the facile preparation of micropatterned surface to improve the performance of flexible capacitive sensors.

Immobilization of Active Antibodies at Polymer Melt Surfaces during Injection Molding.

We demonstrate the transfer and immobilization of active antibodies from a low surface- energy mold surface to thermoplastic replica surfaces using injection molding, and we investigate the process at molecular scale. The transfer process is highly efficient, as verified by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) of the mold and replica surfaces. AFM analysis reveals partial nanometer-scale embedding of the protein into the polymer matrix as a possible mechanism of permanent immobilization. Replicas with rabbit anti-mouse IgG immobilized as capture antibody at the hot polymer melt surface during injection molding show similar affinity for their antigen (mouse IgG) in sandwich enzyme-linked immunosorbent assay (ELISA) as capture antibodies deposited by passive adsorption onto a bare thermoplastic replica. The transferred antibodies retain their functionality after incubation in serum-containing cell medium for >1 week. A mold coating time of 10 min prior to injection molding is sufficient for producing highly sensitive ELISA assays, thus enabling the short processing cycle times required for mass production of single-use biodevices relying on active immobilized antibodies.

Microwave-Assisted Solvent Bonding for Polymethyl Methacrylate Microfluidic Device.

This paper demonstrated a microwave-assisted solvent bonding method that uses organic solvent to seal the thermoplastic substrates with microwave assistance. This direct bonding is a simple and straightforward process that starts with solvent application followed by microwave irradiation without the need for expensive facilities or complex procedures. The organic solvent applied at the bonding interface is used in dissolving and dielectric heating of the thermoplastic surfaces to seal the thermoplastic substrates under microwave assistance. We evaluated acetone and ethanol to seal the polymethyl methacrylate (PMMA) microfluidic device. The bonding performance, such as bonding coverage, geometry stability, and bonding strength (tensile) were observed and compared with the oven-heating and non-heating control experiments under the same force applications. Results showed that the microwave-assisted solvent bonding method presents a high bonding yield (maximum > 99%) and bonding strength (maximum ~2.77 MPa) without microchannel distortion, which can be used for various microfluidic applications.

Epoxy mold adhesion on various plasma-treated thermoplastic polymer surfaces

Epoxy mold adhesion on various plasma-treated thermoplastic polymer surfaces

Effect of Thermocycling on Surface Roughness and Shear Bond Strength of Acrylic Soft Liner to the Surface of Thermoplastic Acrylic Treated with Ethyl Acetate

Objective: To enhance bonding strength between thermoplastic denture base and acrylic soft liner through ethyl acetate surface treatment.Materials and Methods: Modifications of thermoplastic acrylic denture base surface were investigated with SEM. FTIR was used to detect whether there was a chemical bond between thermoplastic acrylic and the organic solvent. A total of 80 samples were prepared and divided into 20 samples for the surface roughness test and 60 samples for the shear bond strength test. Failure type was assessed visually.Results: Shear bond strength and surface roughness values of un treated samples were lower in comparison to surface treated groups; the greatest post thermocycling bond strength value was recorded for the samples treated with ethyl acetate following 1500 cycles.Conclusions: Bonding strength was improved following ethyl acetate surface treatment.

In situ photografting during direct laser writing in thermoplastic microchannels

A method for in situ photografting during direct laser writing by two-photon polymerization is presented. The technique serves as a powerful approach to the formation of covalent bonds between 3D photoresist structures and thermoplastic surfaces. By leveraging the same laser for both pattern generation and localized surface reactions, crosslinking between the bulk photoresist and thermoplastic surface is achieved during polymerization. When applied to in-channel direct laser writing for microfluidic device fabrication, the process yields exceptionally strong adhesion and robust bond interfaces that can withstand pressure gradients as high as 7 MPa through proper channel design, photoinitiator selection, and processing conditions.

Effect of Sanding and Plasma Treatment of 3D-Printed Parts on Bonding to Wood with PVAc Adhesive.

Additive manufacturing is becoming increasingly important for manufacturing end products, not just prototyping. However, the size of 3D-printed products is limited due to available printer sizes and other technological limitations. For example, making furniture from 3D-printed parts and wooden elements requires adequate adhesive joints. Since materials for 3D printing usually do not bond very well with adhesives designed for woodworking, they require special surface preparation to improve adhesion. In this study, fused deposition modelling (FDM) 3D-printed parts made of polylactic acid (PLA), polylactic acid with wood flour additive (Wood-PLA), and acrylonitrile-butadiene-styrene (ABS) polymers were bonded to wood with polyvinyl acetate (PVAc) adhesive. The surfaces of the samples were bonded as either non-treated, sanded, plasma treated, or sanded and plasma treated to evaluate the effect of each surface preparation on the bondability of the 3D-printed surfaces. Different surface preparations affected the bond shear strength in different ways. The plasma treatment significantly reduced water contact angles on all tested printing materials and increased the bond tensile shear strength of the adhesive used. The increase in bond strength was highest for the surfaces that had been both sanded and plasma treated. The highest increase was found for the ABS material (untreated 0.05 MPa; sanded and plasma treated 4.83 MPa) followed by Wood-PLA (from 0.45 MPa to 3.96 MPa) and PLA (from 0.55 MPa to 3.72 MPa). Analysis with a scanning electron microscope showed the smooth surfaces of the 3D-printed parts, which became rougher with sanding with more protruded particles, but plasma treatment partially melted the surface structures on the thermoplastic polymer surfaces.

Manufacturing and metallization of hybrid thermoplastic-thermoset matrix composites

Metallization is a common strategy employed to enhance the electrical and thermal conductivity of polymer matrix composite materials. Nevertheless, metallic deposition on polymer-based materials is challenging due to the inherent limitations related to high temperature exposure of the substrate. In this article, a new technique for the manufacturing of composite laminates and the subsequent metallization by cold spraying of metallic powder is presented. The composite manufacturing route is based on the production of thermoplastic-thermoset hybrid substrates and consisted of two main stages: in the first stage the partial impregnation of a reinforcement textile by a thermoplastic film was promoted by hot pressing compaction. Afterwards, the prepared lamina was vacuum bagged with other reinforcing layers and impregnated by the thermoset catalyzed resin by a vacuum infusion process. Finally, the thermoset and thermoplastic layers were co-cured to increase the adhesion of the substrate with the thermoplastic film. The metallization of composite laminate was obtained through the cold spraying technique, depositing powders on the thermoplastic surface layer. The effect of processing parameters on the coating deposition, quality and microstructure was reported and discussed.