Transparency Change Mechanochromism Based on a Robust PDMS-Hydrogel Bilayer Structure.

Hydrogels and polydimethylsiloxane (PDMS) are complementary to each other, since the hydrophobic PDMS provides a more stable and rigid substrate, while the water-rich hydrogel possesses remarkable hydrophilicity, biocompatibility, and similarity to biological tissues. Herein a transparent and stretchable covalently bonded PDMS-hydrogel bilayer (PHB) structure is prepared via in situ free radical copolymerization of acrylamide and allylamine-exfoliated-ZrP (AA-e-ZrP) on a functionalized PDMS surface. The AA-e-ZrP serves as cross-linking nano-patches in the polymer gel network. The covalently bonded structure is constructed through the addition reaction of vinyl groups of PDMS surface and monomers, obtaining a strong interfacial adhesion between the PDMS and the hydrogel. A mechanical-responsive wrinkle surface, which exhibs transparency change mechanochromism, is created via introducing a cross-linked polyvinyl alcohol film atop the PHB structure. A finite element model is implemented to simulate the wrinkle formation process. The implication of the present finding for the interfacial design of the PHB and PDMS-hydrogel-PVA trilayer (PHPT) structures is discussed.

Protection of Nanostructures-Integrated Microneedle Biosensor Using Dissolvable Polymer Coating.

Real-time transdermal biosensing provides a direct route to quantify biomarkers or physiological signals of local tissues. Although microneedles (MNs) present a mini-invasive transdermal technique, integration of MNs with advanced nanostructures to enhance sensing functionalities has rarely been achieved. This is largely due to the fact that nanostructures present on MNs surface could be easily destructed due to friction during skin insertion. In this work, we reported a dissolvable polymer-coating technique to protect nanostructures-integrated MNs from mechanical destruction during MNs insertion. After penetration into the skin, the polymer could readily dissolve by interstitial fluids so that the superficial nanostructures on MNs could be re-exposed for sensing purpose. To demonstrate this technique, metallic and resin MNs decorated with vertical ZnO nanowires (vNWs) were employed as an example. Dissolvable poly(vinyl pyrrolidone) was spray-coated on the vNW-MNs surface as a protective layer, which effectively protected the superficial ZnO NWs when MNs penetrated the skin. Transdermal biosensing of H2O2 biomarker in skin tissue using the polymer-protecting MNs sensor was demonstrated both ex vivo and in vivo. The results indicated that polymer coating successfully preserved the sensing functionalities of the MNs sensor after inserting into the skin, whereas the sensitivity of the MN sensor without a coating protection was significantly compromised by 3-folds. This work provided unique opportunities of protecting functional nanomodulus on MNs surface for minimally invasive transdermal biosensing.

Assessment of heavy metal pollution in surficial sediments from a tropical river-estuary-shelf system: A case study of Kelantan River, Malaysia.

To understand the source-to-sink of pollutants in the Kelantan River estuary and the adjacent shelf area in Malaysia, a total of 42 surface sediment samples were collected in the Kelantan River-estuary-shelf system to analyze for grain size, total organic carbon (TOC) content, Al and heavy metals (Cr, Ni, Cu, Zn, Cd and Pb). The surficial sediments were mainly composed of clayey silt and the TOC content in sediments decreased from the river to the shelf. The surficial sediments experienced Pb pollution; Cr only showed a certain level of pollution in the coastal area of the estuary but not in other areas, and Ni, Cu, Zn, and Cd showed no pollution. The heavy metals mainly originated from natural weathering and erosion of rocks and soils in the catchment and enriched near the river mouth. Total organic carbon can promote the enrichment of heavy metals in sediments.