Core-shell structured nets for biofouling control in aquaculture

This study demonstrates a robust, flexible interpenetrated composite based on 3D spined fabrics as core material and polydimethylsiloxane (PDMS) as shell material. The penetration of the shell component into the core material enables the mechanical interlocking at the micro and macro scale, providing mechanical stability and at the same time, introducing hydrophobic surface properties. Pure PDMS is a well-known biofouling-release material, showing drawbacks with respect to mechanical strength and adhesion-to-substrate, which can be overcome by the presented approach. Nowadays, antifouling strategies for aquaculture nets are realized by using biocide-containing coatings to avoid the attachment of organisms or repel them. Up to now, there are no coatings available on the market that provide adequate biofouling protection for aquaculture nets during the whole production cycle of the cultured stock. Even biocidal coatings exhibit a limited efficiency and need to be regularly cleaned, causing a substantial loss of the coating and increased emissions of biocides into seawater. This proof-of-concept study covers the scope from the design and production of the composite up to the first field tests in the Baltic Sea. The presented approach enabled by material science facilitates a fundamentally different approach in biofouling management and contributes to sustainable aquaculture

Preventing algae adhesion using lubricant-modified polydimethylsiloxane/polythiourethane nanocomposite

To meet the need for an environmentally friendly fouling-release coating with high mechanical strength and good adhesion to substrates, a four-component nanocomposite was developed by a simple and industrially applicable blending approach. The nanocomposite consists of mechanically stable matrix polythiourethane (PTU), 1 wt% low surface free energy and rubber-like polydimethylsiloxane (PDMS), 1 wt% lubricant silicone oil, and 1 wt% tetrapodal shaped micro-nano ZnO (t-ZnO) filler particles, hereafter named PPZO. The rubber-like PDMS formed microdomains at the PTU/air interface, while silicone oil was distributed between the PDMS microdomains. The tensile strength of PPZO nanocomposite was approximately 63 MPa, two to four hundred times higher than the tensile strength of previously reported oil-modified coatings. The adhesion strength of PPZO to the substrate was 30 times higher than that of pure PDMS. After a five-month dynamic field test, the PPZO surface revealed much less biofouling than the references (AlMg3 and PTU), confirming its long-term biofouling control property. The attached algae on PPZO could easily and completely be removed by gentle brush cleaning. The good biofouling control property of PPZO can be attributed to the increased water repellency (signified by the increased water contact angle) and the surface slippage by silicone oil incorporation

Improved Long‐Term Stability and Reduced Humidity Effect in Gas Sensing: SiO 2 Ultra‐Thin Layered ZnO Columnar Films

The undoped and metal-doped zinc oxide columnar films (ZnO:Sn, ZnO:Fe, ZnO:Ag, and ZnO:Cu) are covered with an ultra-thin layer of SiO2 (10–20 nm). The electrical, UV, and volatile organic compounds (VOCs) sensing properties are evaluated under different ambient conditions for ≈7 months to investigate the impact of the top SiO2-layer on the long-term stability of samples. The obtained results show a high immunity of sensing properties of SiO2-coated samples to humidity. Furthermore, gas sensing measurements show that the loss in response after 203 days is significantly lower for coated samples indicating higher stability of sensing performance. For ZnO:Fe the gas response is reduced by about 90% after 203 days, but for SiO2-coated ZnO:Fe columnar films the gas response is slightly reduced by only 38%. The density functional theory (DFT) calculations show that water species bind strongly with the surface SiO2 layer atoms with a −0.129 e− charge transfer, which is, much higher compared to the interaction with ethanol and acetone. Calculations show strong binding of water species on the SiO2 layer indicating preferential absorption of water molecules on SiO2. The obtained results demonstrate an important role of the top SiO2 ultra-thin layer in order to produce humidity-tolerant sensitive devices

Zinc Oxide Tetrapods Modulate Wound Healing and Cytokine Release In Vitro -A New Antiproliferative Substance in Glaucoma Filtering Surgery

Glaucoma filtering surgery is applied to reduce intraocular pressure (IOP) in cases of uncontrolled glaucoma. However, postoperative fibrosis reduces the long-term success of both standard trabeculectomy and microstents. The aim of this study was to test the antiproliferative and anti-inflammatory potential of ZnO-tetrapods (ZnO-T) on human Tenon's fibroblasts (HTFs) for glaucoma surgery. The toxicity of ZnO-T on HTFs was determined using an MTT test. For analysis of fibroblast proliferation, migration, and transdifferentiation, cultures were stained for Ki67, alpha-smooth muscle actin (α-SMA), and p-SMAD. A fully quantitative multiplex ELISA was used to determine the concentrations of different cytokines, platelet-derived growth factor (PDGF), and hepatocyte growth factor (HGF) in culture supernatants with and without previous ZnO-T treatment. Treatment with higher concentrations (10 and 20 µg/mL) was associated with HTF toxicity, as shown in the wound healing assay. Furthermore, the number of Ki67, α-SMA-positive, and pSMAD-positive cells, as well as IL-6 and HGF in supernatants, were significantly reduced following incubation with ZnO-T. In conclusion, we were able to show the antiproliferative and anti-inflammatory potentials of ZnO-T. Therefore, the use of ZnO-T may provide a new approach to reducing postoperative fibrosis in glaucoma filtering surgery

Development of Polythiourethane/ZnO-Based Anti-Fouling Materials and Evaluation of the Adhesion of Staphylococcus aureus and Candida glabrata Using Single-Cell Force Spectroscopy

The attachment of bacteria and other microbes to natural and artificial surfaces leads to the development of biofilms, which can further cause nosocomial infections. Thus, an important field of research is the development of new materials capable of preventing the initial adhesion of pathogenic microorganisms. In this work, novel polymer/particle composite materials, based on a polythiourethane (PTU) matrix and either spherical (s-ZnO) or tetrapodal (t-ZnO) shaped ZnO fillers, were developed and characterized with respect to their mechanical, chemical and surface properties. To then evaluate their potential as anti-fouling surfaces, the adhesion of two different pathogenic microorganism species, Staphylococcus aureus and Candida glabrata, was studied using atomic force microscopy (AFM). Our results show that the adhesion of both S. aureus and C. glabrata to PTU and PTU/ZnO is decreased compared to a model surface polydimethylsiloxane (PDMS). It was furthermore found that the amount of both s-ZnO and t-ZnO filler had a direct influence on the adhesion of S. aureus, as increasing amounts of ZnO particles resulted in reduced adhesion of the cells. For both microorganisms, material composites with 5 wt.% of t-ZnO particles showed the greatest potential for anti-fouling with significantly decreased adhesion of cells. Altogether, both pathogens exhibit a reduced capacity to adhere to the newly developed nanomaterials used in this study, thus showing their potential for bio-medical applications

Development and Characterization of Mechanically Durable Silicone-Polythiourethane Composites Modified with Tetrapodal Shaped ZnO Particles for the Potential Application as Fouling-Release Coating in the Marine Sector

Ecological considerations strongly necessitate the development of environmentally friendly antifouling paints. A promising alternative to biocide containing antifouling paints are fouling-release coatings, which are non-toxic and designed to prevent permanent attachment of marine organisms to the surface, due to their low surface energy. However, these coatings suffer from insufficient mechanical properties, which make them unsuitable for mechanically stressed surfaces e.g., on ship hulls. To overcome those obstacles, polydimethylsiloxane (PDMS)-polythiourethane (PTU) composites modified with tetrapodal shaped micro-nano ZnO particles (t-ZnO) were produced and characterized by evaluating the surface energy, mechanical properties, and fouling-release performance. Among all variations, PTU/1 wt.% PDMS composites with 1 wt.% t-ZnO particles possess superior properties for applications as fouling-release coatings for maritime purposes

Electrochemical Surface Structuring for Strong SMA Wire–Polymer Interface Adhesion

Active hybrid composites represent a novel class of smart materials used to design morphing surfaces, opening up new applications in the aircraft and automotive industries. The bending of the active hybrid composite is induced by the contraction of electrically activated shape memory alloy (SMA) wires, which are placed with an offset to the neutral axis of the composite. Therefore, the adhesion strength between the SMA wire and the surrounding polymer matrix is crucial to the load transfer and the functionality of the composite. Thus, the interface adhesion strength is of great importance for the performance and the actuation potential of active hybrid composites. In this work, the surface of a commercially available one-way effect NiTi SMA wire with a diameter of 1 mm was structured by selective electrochemical etching that preferably starts at defect sites, leaving the most thermodynamically stable surfaces of the wire intact. The created etch pits lead to an increase in the surface area of the wire and a mechanical interlocking with the polymer, resulting in a combination of adhesive and cohesive failure modes after a pull-out test. Consequently, the force of the first failure determined by an optical stress measurement was increased by more than 3 times when compared to the as-delivered SMA wire. The actuation characterization test showed that approximately the same work capacity could be retrieved from structured SMA wires. Moreover, structured SMA wires exhibited the same shape of the stress–strain curve as the as-delivered SMA wire, and the mechanical performance was not influenced by the structuring process. The austenite start A$_s$ and austenite finish A$_f$ transformation temperatures were also not found to be affected by the structuring process. The formation of etching pits with different geometries and densities was discussed with regard to the kinetics of oxide formation and dissolution

In vivo evaluation of a nanotechnology-based microshunt for filtering glaucoma surgery

Abstract To carry out the preclinical and histological evaluation of a novel nanotechnology-based microshunt for drainage glaucoma surgery. Twelve New Zealand White rabbits were implanted with a novel microshunt and followed up for 6 weeks. The new material composite consists of the silicone polydimethylsiloxane (PDMS) and tetrapodal Zinc Oxide (ZnO-T) nano-/microparticles. The microshunts were inserted ab externo to connect the subconjunctival space with the anterior chamber. Animals were euthanized after 2 and 6 weeks for histological evaluation. Ocular health and implant position were assessed at postoperative days 1, 3, 7 and twice a week thereafter by slit lamp biomicroscopy. Intraocular pressure (IOP) was measured using rebound tonometry. A good tolerability was observed in both short- and medium-term follow-up. Intraocular pressure was reduced following surgery but increased to preoperative levels after 2 weeks. No clinical or histological signs of inflammatory or toxic reactions were seen; the fibrotic encapsulation was barely noticeable after two weeks and very mild after six weeks. The new material composite PDMS/ZnO-T is well tolerated and the associated foreign body fibrotic reaction quite mild. The new microshunt reduces the IOP for 2 weeks. Further research will elucidate a tube-like shape to improve and prolong outflow performance and longer follow-up to exclude medium-term adverse effects

In Vitro Evaluation of Zinc Oxide Tetrapods as a New Material Component for Glaucoma Implants

In our previous study we were able to show that zinc oxide (ZnO) tetrapods inhibit wound healing processes. Therefore, the aim of this study was to test the antiproliferative effect of two types of porous polydimethylsiloxane (PDMS)/ tetrapodal zinc oxide (ZnO-T) materials, as well as their usability for glaucoma implants. To find the best implant material, two different porous PDMS/ZnO-T materials were examined. One consisted of 3D interconnected PDMS coarse-pored foams with protruding ZnO-T particles; the other consisted of fine-pored 3D interconnected ZnO-T networks homogeneously coated by a thin PDMS film in the nanometer range. Fibroblast cell viability was investigated for both materials via MTT dye, and some implant material samples were further processed for electron microscopy. Both PDMS/ZnO-T materials showed reduced cell viability in the MTT staining. Furthermore, the electron microscopy revealed barely any fibroblasts growing on the implant materials. At the surface of the fine-pored implant material, however, fibroblasts could not be observed in the etched control samples without ZnO-T. It was found that post-processing of the material to the final stent diameter was highly challenging and that the fabrication method, therefore, had to be adapted. In conclusion, we were able to demonstrate the antiproliferative potential of the two different PDMS/ZnO-T materials. Furthermore, smaller pore size (in the range of tens of micrometers) in the implant material seems to be preferable