Xiangqiong Zeng

A new water absorbable mechanical Epidermal skin equivalent: The combination of hydrophobic PDMS and hydrophilic PVA hydrogel

Research on human skin interactions with healthcare and lifestyle products is a topic continuously attracting scientific studies over the past years. It is possible to evaluate skin mechanical properties based on human or animal experimentation, yet in addition to possible ethical issues, these samples are hard to obtain, expensive and give rise to highly variable results. Therefore, the design of a skin equivalent is essential. This paper describes the design and characterization of a new Epidermal Skin Equivalent (ESE). The material resembles the properties of epidermis and is a first approach to mimic the mechanical properties of the human skin structure, variable with the length scale. The ESE is based on a mixture of Polydimethyl Siloxane (PDMS) and Polyvinyl Alcohol (PVA) hydrogel cross-linked with Glutaraldehyde (GA). It was chemically characterized by XPS and FTIR measurements and its cross section was observed by macroscopy and cryoSEM. Confocal Microscope analysis on the surface of the ESE showed an arithmetic roughness (Ra) between 14-16 μm and contact angle (CA) values between 50-60°, both of which are close to the values of in vivo human skins reported in the literature. The Equilibrium Water Content (ECW) was around 33.8% and Thermo Gravimetric Analysis (TGA) confirmed the composition of the ESE samples. Moreover, the mechanical performance was determined by indentation tests and Dynamo Thermo Mechanical Analysis (DTMA) shear measurements. The indentation results were in good agreement with that of the target epidermis reported in the literature with an elastic modulus between 0.1-1.5 MPa and it showed dependency on the water content. According to the DTMA measurements, the ESE exhibits a viscoelastic behavior, with a shear modulus between 1-2.5MPa variable with temperature, frequency and the hydration of the samples.

The Tribological Chemistry of a Novel Borate Ester Additive and Its Interaction with ZDDP Using XANES and XPS

A novel borate ester containing heterocyclic group, 2,5-bis((2-((6-octadecyl-1,3,6,-dioxazaborocan-2-yl)oxy)propyl)thio)-1,3,4-thiadiazole (BDOT), was prepared and characterized. Its tribological properties and synergistic effect with zinc dialkyl dithiophosphate were evaluated using a four-ball tribometer. The results show that the novel borate additive possesses excellent anti-wear and friction-reducing properties compared with the performance of ZDDP. BDOT combined with ZDDP has a synergistic effect on the tribological properties, especially for the friction-reducing performance. The chemical state of nitrogen, boron and sulfur in thermal films and tribofilms was analyzed by XPS and XANES. XPS analysis suggests that the additive forms a protective film on the rubbing surfaces which is composed of B2O3, BN, FeSO4, FeS2 and Fe2O3. However, the B K-edge XANES shows that no BN was detected in the film. The synergistic effect between BDOT and ZDDP may be due to the formation of right concentration of FeS and FeSO4 in the tribofilm.

The tribological behaviour and tribochemical study of B–N type borate esters in rapeseed oil—compound versus salt

Two novel borate ester additives, (2-(2-(bis(2-hydroxyethyl)amino)ethoxy)-1,3,2-dioxaborolan-4-yl)methyl oleate and a tris(2-hydroxyethyl)amine salt of (2-hydroxy-1,3,2-dioxaborolan-4-yl)methyl oleate were prepared and used as anti-wear and extreme pressure agents in rapeseed oil. The tribological performance was evaluated using a four-ball machine. The results show that the additives possess high anti-wear and extreme pressure properties. XANES, XPS and AFM were used to analyse the composition and structure of boundary films at the worn surfaces. The results for the compound and salt of borate esters are compared, and it is shown that the boundary films formed by compound or salt are similar and mainly composed of B2O3.

An ultrasensitive fluorescent probe for rapid determination of thiophenols

An ultrasensitive fluorescent probe TPP was developed for the highly selective detection of thiophenols based on excited-state intramolecular proton transfer (ESIPT) mechanism, its synthesis through a simple straightforward combination of HBT fluorophore with 2,4-dinitrobenzene functional group. A kinetic study of TPP towards thiophenol displayed a fast response time (~150s) and significant turn-on fluorescence enhancement (~60 fold). Selective and competitive experiments exhibited an excellent selectivity of TPP toward thiophenols over biothiols (Cys, GSH) and other aliphatic thiols or nucleophiles. Using this ultrasensitive probe (LOD, 1.05×10-8M), we have successfully monitored and quantified highly toxic thiophenols in aqueous media and real-water samples.

Tribological studies of S‐N type triazinyl‐containing polysulfides as additives in biodegradable grease

Purpose – This paper sets out to study tribological properties, anticorrosive performances and thermal stabilities of two novel S‐N type triazinyl‐containing polysulfides {Bis[2,4‐bis(diethylamino)‐s‐triazin‐6‐yl] polysulfide (BBET‐PS) and Bis[2,4‐bis(di‐n‐butylamino)‐s‐triazin‐6‐yl] polysulfide (BBBT‐PS)} as additives in biodegradable grease, and to estimate the tribochemical mechanism.Design/methodology/approach – Extreme pressure (EP) and anti‐wear (AW) properties of two compounds at different addition concentration were evaluated using a four‐ball machine. Their wear scar was analyzed with X‐ray photoelectron spectroscopy (XPS) and a scanning electron microscope.Findings – Two novel S‐N type triazinyl‐containing polysulfides possess excellent load‐carrying capacity, good AW and show good corrosion‐inhibiting performance. The thermal stability of BBB‐PS is better than that of BBE‐PS. According to the XPS results, the triazinyl‐containing polysulfides react with the metal to generate a surface protectiv...

Texture Design for Reducing Tactile Friction Independent of Sliding Orientation on Stainless Steel Sheet

Surface texture is important for contact mechanical and tribological phenomena such as the contact area and friction. In this research, three different types of geometrical microstructures were designed and fabricated by pulsed laser surface texturing as semi-symmetric (grooved channel), asymmetric fractal (Hilbert curve), and symmetric patterns (grid). A conventionally finished surface as a reference sample from the same stainless steel sheet material was compared. From the experimental approach, a multiaxis force/torque transducer was used to investigate the functionality of surface texture based on measuring the tactile friction in three different sliding directions: perpendicular, parallel, and 45° to the textures. According to the dynamic friction measurements, the grid texture was indeed orientation independent. The other samples showed orientation-dependent frictional behavior, especially the grooved channel texture and reference sample. Furthermore, an analytical approach was applied to estimate the values of the friction coefficient by the pressure distribution method. From both the experimental and analytical approaches, the grid pattern was validated to be the optimal texture design in the concern of friction reduction and orientation-independent behavior.

Study on phosphorous‐free triazinyl disulfides as additives in combustion engine base oil

Purpose – This paper seeks to study the tribological properties, corrosion inhibition properties and action mechanism of two triazine‐containing disulfides, TOSS and TOMA, as additives in combustion engine base oil (5CST); those properties of an alkyl disulfide dodecyl disulfide and zinc dialkyldithiophosphate (ZDDP) were also evaluated for comparison to discover whether these additives could be used as potential substitute candidates for ZDDP.Design/methodology/approach – Their tribological performances were evaluated using a four‐ball machine. The worn surfaces were investigated by scanning electron microscopy and X‐ray photoelectron spectroscopy (XPS)Findings – The three additives have good load‐carrying capacity and corrosion inhibition properties comparable with those of ZDDP. The anti‐wear properties of the triazine‐containing disulfides TOSS and TOMA are good but a little inferior to those of ZDDP. The friction‐reducing performances of the additives are better than those of ZDDP. The XPS results sh...

Development of a penetration friction apparatus (PFA) to measure the frictional performance of surgical suture

Nowadays there is a wide variety of surgical sutures available in the market. Surgical sutures have different sizes, structures, materials and coatings, whereas they are being used for various surgeries. The frictional performances of surgical sutures have been found to play a vital role in their functionality. The high friction force of surgical sutures in the suturing process may cause inflammation and pain to the person, leading to a longer recovery time, and the second trauma of soft or fragile tissue. Thus, the investigation into the frictional performance of surgical suture is essential. Despite the unquestionable fact, little is actually known on the friction performances of surgical suture-tissue due to the lack of appropriate test equipment. This study presents a new penetration friction apparatus (PFA) that allowed for the evaluation of the friction performances of various surgical needles and sutures during the suturing process, under different contact conditions. It considered the deformation of tissue and can realize the puncture force measurements of surgical needles as well as the friction force of surgical sutures. The developed PFA could accurately evaluate and understand the frictional behaviour of surgical suture-tissue in the simulating clinical conditions. The forces measured by the PFA showed the same trend as that reported in literatures.

Biological and Tribological Assessment of Poly(Ethylene Oxide Terephthalate)/Poly(Butylene Terephthalate), Polycaprolactone, and Poly (L\DL) Lactic Acid Plotted Scaffolds for Skeletal Tissue Regeneration

Additive manufactured scaffolds are fabricated from three commonly used biomaterials, polycaprolactone (PCL), poly (L\DL) lactic acid (P(L\DL)LA), and poly(ethylene oxide terephthalate)/poly(butylene terephthalate) (PEOT/PBT). Scaffolds are compared biologically and tribologically. Cell-seeded PEOT/PBT scaffolds cultured in osteogenic and chondrogenic differentiation media show statistical significantly higher alkaline phosphatase (ALP) activity/DNA and glycosaminoglycans (GAG)/DNA ratios, followed by PCL and P(L\DL)LA scaffolds, respectively. The tribological performance is assessed by determining the friction coefficients of the scaffolds at different loads and sliding velocities. With increasing load or decreasing sliding velocity, the friction coefficient value decreases. PEOT/PBT show to have the lowest friction coefficient value, followed by PCL and P(L\DL)LA. The influence of the scaffold architecture is further determined with PEOT/PBT. Reducing of the fiber spacing results in a lower friction coefficient value. The best and the worst performing scaffold architecture are chosen to investigate the effect of cell culture on the friction coefficient. Matrix deposition is low in the cell-seeded scaffolds and the effect is, therefore, undetermined. Taken together, our studies show that PEOT/PBT scaffolds support better skeletal differentiation of seeded stromal cells and lower friction coefficient compared to PCL and P(L/DL)A scaffolds.

The tribological performance of a long chain alkyl phenylboric ammonium derivative and its interaction with ZDDP

A long chain alkyl phenylboric ammonium derivative (DBBM) was synthesized as a lubricating additive. The tribological performances of DBBM and combinations of DBBM and ZDDP as additives were evaluated, which suggests that DBBM has better tribological properties than ZDDP. X-ray absorption near edge structure spectroscopy was used for the analysis of thermal films and tribofilms. The results indicate that the boron in additive mainly forms trigonal and tetrahedral coordination boron both in thermal films and tribofilms, while sulfur mainly generates iron sulfate in thermal films and iron sulfide, iron disulfide, and iron sulfate in tribofilms. It also can be found that it is more likely to form low valence sulfur when the concentration of ZDDP increases in the combinations.