Key Engineering Materials Vol. 904

Abstract: In order to explore influence on tribological behavior of PEEK composite film layer in PEEK-PTFE composite radial alumina ball bearings, rolling contact fatigue tests were performed by using the PEEK bearing’s inner rings with the artificial defects in dry condition. When rotation speed and applied load were 600 rpm and 98 N, the number of cycles of the PEEK-PTFE bearings reached 1.0×10⁷ fatigue cycles. The artificial defects with 0.02 mm depth on the raceway surface of the PEEK inner ring was covered with PEEK composite film accumulation.

Abstract: In this study, PVA/CS composite hydrogels were prepared by means of freezing and thawing cycles of agricultural wastes, corn straw (CS) and polyvinyl alcohol (PVA). The mechanical properties of the composite hydrogels were analyzed by universal tensile device. The effects of CS on tensile strength and elongation at break of PVA/CS composite hydrogels were analyzed. On the other hand, PVA and PVA/CS composite hydrogels were also freeze-dried to investigate the mechanical properties of all hydrogels after drying.

Abstract: This paper intended to measure the material's rigidity according to the orientation of the PLA specimen produced by the FDM method. To measure the change of strength and stiffness according to the direction of stacking of FDM PLA, the specimen was manufactured and tested not only in the direction of stacking but also infill using line pattern and concentric pattern. The intensity of each direction was 38.11MPa with a 0 degree tensile in the line pattern, 3.45 times higher than 11.9MPa with a 90 degree tensile, and 2.15 times higher shear strength with 28.05MPa and 13.88MPa. In concentric pattern, 0 degree tensile was 50.62MPa, 6.25 times higher than 8.46MPa, and 2.23 times higher in shear strength at 13.52MPa compared to 29.56MPa. The biggest difference in zero-degree concentric pattern tensile was the 37% difference in the 0 degree concentric pattern factor. This shows that the difference in intensity according to direction is more pronounced in concentric patterns than line patterns, and the behavior under load will be similar until the breaking point regardless of the direction.

Abstract: The paper presents a study on the performance of cutter tip for wood milling process. The tests were performed with the tropical wood samples which were milled in the double sided wood planer, the measured micro-geometrical parameters encompassing the linear wear and tooltip radius. The study primarily contributes to developing a far better understanding of the physical nature of cutting tool wear in response with the growing concern of many researchers. Given this basis, it does not only assist the selection of reasonable cutting tool but also enable the detection of the patterns in the cutting tool wear process. In terms of tool wear and bluntness, there has been a number of researches taking account into the physical nature of cutting tools, - providing basis for selection of cutting tools apart from clarification of the current pattern of tool wear and bluntness. The load applied to the cutter during wood milling is the load that changes marks periodically. When starting to work after tool sharpening and finishing, the first stage changes the microscopic geometry - tool run-in process (rapid initial wear), followed by constant conditions of wear before a rapid wear which leads to failure at last. The objective of this study is to determine the influence of the cutting path to the tooltip radius and linear wear of the cutting edge. The paper employs method of least squares and variance analysis in application of the Minitab software to determine regression equations for relation of the tooltip radius and linear wear to the relative cutting length. The ultimate goal is to predict the life of cutting tool when milling tropical wood.

Abstract: The normal stress of each layer of the laminate composite material will undergo complex changes after normal compression, and shear stress will also appear between the layers. In order to explore the distribution laws of normal stress and shear stress, this paper uses Hooke's law and the equilibrium condition of force to carry out mathematical derivation, the analytical formulas for normal stress and shear stress are obtained, and their respective maximum values ​​are given. Studies have shown that the maximum normal stress occurs at the center of the laminate, and its value is proportional to the external load, and is also closely related to the length, width, thickness, elastic modulus of the cementing agent, elastic modulus and Poisson’s ratio of the laminate; The maximum shear stress occurs at the four corners of the laminate, and its value is proportional to the external load and the shear modulus of the cementing agent, inversely proportional to the thickness of the cementing agent layer, and its value is also closely related to the length, width, elastic modulus and Poisson's ratio of the laminate. The analytical formulas for normal stress and interlayer shear stress is helpful to deepen the understanding of the internal force distribution law of laminated plates, and the maximum value calculation formula can greatly facilitate the calculation of strength.

Abstract: Early childhood caries (ECC), or baby bottle tooth decay is one of the most common chronic diseases that affect young children at 6 years of age or younger. The disease is resulted from complex interactions between tooth structures and cariogenic microorganisms in dental biofilm after exposure to fermentable carbohydrates through improper feeding practices. This leads to a rapid development of demineralization of teeth shortly after they erupt in the oral cavity. Candida albicans have been reported recently to be associated with the pathogenesis of ECC. One of the general approaches currently used for the prevention of ECC is the application of dental sealant to occlusal (chewing surface) pits and fissures of caries-susceptible teeth. Many types of dental sealants have been extensively used and various antimicrobial agents were introduced to dental sealants to increase their caries preventive effect. The aim of the present study was to evaluate the antimicrobial effect of vanillin incorporated resin-based dental sealant on C. albicans biofilm. Resin-based dental sealants (Clinpro; 3M ESPE, USA) containing different concentrations of vanillin (0%, 0.5%, 1% and 5% w/v) were prepared in 96-well plate. The suspension (10⁷ colony forming unit/mL) of each strain of Candida albicans (ATCC 10231, ATCC 18804 and 2 clinical isolates) was added to saliva-coated sealant resin samples and incubated at 37°C in 5% CO₂ atmosphere for 24 h to allow the Candida biofilm formation. The quantity of vital biofilm was determined by WST Microbial Cell Counting Kit (Dojindo Molecular Technologies, USA) at 460 nm. All tests were done in triplicate and repeated three times. Kruskal-Wallis test followed by Dunn’s method were used to account for multiple comparisons. Statistical significance was set at p-value less than 0.05. The results showed that 0.5-5% vanillin-incorporated dental sealant resins showed a significant suppressive effect against all strains of Candida. No significant differences of anti-biofilm effects were found among Candida strains. Approximately 30-50% Candida biofilm reduction was noticed in sealant resins containing vanillin compared with controls without vanillin. In conclusion, the adding of vanillin (0.5-5% w/v) to dental sealant resins is effective in inhibiting biofilm formation of fungus related to early childhood caries, C. albicans. Therefore, the use of dental sealants containing vanillin has the potential to prevent this type of dental caries in young children and biofilm formation by oral Candida. Further clinical studies are required to investigate physical properties of this sealant and clinical evaluation in the patients.

Abstract: The proportion of older people within the general population is expanding due to the decline of birth rate and the increase of life expectancy. Increasing elderly populations, which is retaining its teeth longer, leads to oral health problems, for example, root caries. The main etiological factor for the initiation and development of root caries is the appearance of cariogenic biofilm. The acid-producing and acid-tolerant bacteria and oral yeast, such as Candida albicans are the major contributors in root caries formation. A new generation of adhesives is developed with several modifications for the prevention of dental caries by incorporating antimicrobial components. The aim of this study was to investigate the antimicrobial effect of adhesive containing calcium salt of acidic monomers on the biofilm formation of oral Candida related to root caries. In the experiments, the flat-bottom surfaces of 96-well plate were painted with an adhesive containing calcium salts of 4-methacryloxyethyl trimellitic acid (CMET) and 10-methacryloyloxydecyl dihydrogen calcium phosphate (MDCP) (Bio-Coat, CA, Sun Medical, Japan). Then they were LED light-cured and coated with sterile saliva at 37 °C for 60 min. The biofilm formation was made by adding of Candida albicans (ATCC 10238 and two clinical strains) suspensions (10⁷ colony forming unit/mL) and incubated at 37°C for 24 h. The amount of vital biofilm was determined by WST-8 Microbial Cell Counting Kit (Dojindo Molecular Technologies, USA). All experiments were done in triplicate and repeated three times. Statistical analysis was performed using Student’s t-test. The results clearly showed that adhesive could significantly inhibit biofilm formation of all tested Candida compared with a control. This suppressive effect was not different among the strains of Candida. The percentages of vital biofilm reduction were 25% to 40%. The ability of this adhesive to suppress biofilm of oral yeast may be its antimicrobial property of acidic monomer or the effect of calcium ion within the adhesive, which can alter Candida cell morphology, and influence their structures or process of biofilm formation. In conclusion, an adhesive containing calcium salts of acidic monomers could significantly inhibit biofilm formation of C. albicans. This adhesive could be effectively applied to exposed root surfaces to prevent or inhibit the progression of root caries. Further studies are necessary to clarify the effect on multispecies biofilm, on long-term activity, and in vivo conditions.

Abstract: Endothelial cells (EC), which line the internal surface of blood vessels, play various essential roles in controlling vascular function. The mouse is an important animal model for the study of vascular biology and cardiovascular diseases. However, the isolation of primary EC from the murine aorta is challenging because they are readily contaminated by smooth muscle cells (SMC). A previous study developed a simple method to isolate murine EC from SMC. By taking advantage of the differential sedimentation rate between the two cells, the EC was selectively enriched with collagen-coated polystyrene surfaces. Our study further improved this method by introducing a biomimetic peptide REDV (Arg-Glu-Asp-Val), which may bind specifically to EC but not to SMC or fibroblasts. Firstly, REDV-gelatin conjugate was synthesized by using the amine-to-sulfhydryl crosslinker SMCC. REDV-gelatin coating was then prepared on polystyrene surfaces, and their affinities to EC and SMC were subsequently investigated. Fluorescence microscopy and flow cytometric analysis showed that EC adhesion to the gelatin coating was significantly promoted by REDV peptide conjugation. Moreover, cell migration assay and cell viability assay also showed that the conjugation of REDV does not affect EC migration, and this coating did not show cytotoxicity against EC. This gelatin-REDV coating provides a cost-effective and straightforward tool for isolating EC from SMC, which may facilitate in vitro investigations of EC from mice.

Abstract: Background: Carious lesions can occur on the proximal surfaces of the posterior teeth. Streptococcus mutans and Streptococcus sobrinus, are the main acidogenic bacteria that are commonly associated to dental caries. Interproximal cleaning is an important form of oral self-care habits, considering such areas of the dentition are easily affected by caries. Accordingly, dental floss has been used as an additional tool to enhance the quality of the cleaning process. It is reasonable that dental flossing should reduce interproximal caries risk because it is capable of removing parts of the interproximal plaque. The aim of this study was to evaluate the antibacterial activity of gold nanoparticle (AuNPs), when coated on unwaxed dental floss.Methods: Streptococcus mutans and Streptococcus sobrinus were cultured in Brain Heart Infusion (BHI) agar. Broth microdilution method was used to determine the minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs) of the AuNPs with subcultures so obtained. Then, the bacteria were grown and spread on blood agar on which identical lengths (20mm) of unwaxed dental floss coated with gold nanoparticles (AuNPs) at concentration of 0.05, 0.1, and 0.5 mg/mL were placed. Control included untreated unwaxed dental floss and unwaxed dental floss with 0.2% Chlorhexidine (CHX). Five randomized sites of the inhibition zones were measured in millimeters in each concentration per floss. Means ± S.D. of the inhibition zones were calculated.Results: The MIC and MBC of AuNPs against S. sobrinus and S. mutans were 0.5 μg/mL and 1.0 μg/mL, respectively. The results indicated that gold nanoparticles (AuNPs) coated unwaxed dental floss, placed on blood agar with S. mutans and S. sobrinus demonstrated significant inhibition of bacterial growth. Gold nanoparticles (AuNPs) coated unwaxed dental floss at 0.05, 0.1, 0.5 mg/mL resulted in zones of inhibition ranging from 2.93 ± 0.30 mm to 4.71 ± 0.32 mm for S. sobrinus and 2.95 ± 1.73 mm to 5.18 ± 0.61 mm for S. mutans, respectively.Conclusion: In vitro study demonstrated that the AuNPs-coated unwaxed dental floss had antibacterial activities against cariogenic bacteria.

Abstract: Enamel decalcification usually can be found around orthodontic bracket after debonding. Orthodontic adhesives resistant to bacterial colonization were used to prevent white spot lesion and dental caries in orthodontic treatment with fixed appliance. The objectives of this study were to evaluate the antibacterial properties of expeimental orthodontic adhesive containing gold nanoparticles (AuNPs). 108 orthodontic adhesive discs containing 1.0 wt%, 0.5 wt%, 0.25 wt% AuNPs and without AuNPs were prepared from in-house orthodontic adhesive (27 discs per group). The antibcterial properties of adhesive discs were evaluated by direct contact test. Streptococcus mutans and Streptococcus sobrinus suspensions were placed on the discs and incubated at 37 °C for 1 hour. The adhesive discs were transferred to BHI broth and were incubated at 37°C for 16, 20 and 24 h. Bacterial growth was evaluated by optical density (OD) measurement at 590nm. The results showed that experimental orthodontic adhesives with 1.0 wt% and 0.5 wt% AuNPs exhibited higher antibacterial activity compared to the control group (p < 0.05). At 24 h of incubation, the median OD of 1.0 wt%, 0.5 wt%, 0.25 wt% and control in S. mutans were 0.109, 0.006, 0.007 and 0.372, rescpectively. In S. sobrinus, the median OD were 0.173, 0.012 , 0.007 and 0.328. The incorporation of gold nanoparticles into orthodontic adhesives exhibited antibacterial activity against cariogenic microorganism. At a concentration of 0.5 wt% and 1.0 wt% AuNPs, experimental orthodontic adhesive could reduce bacterial growth of both S. mutans and S. sobrinus.