Multiscale cohesive failure modeling of heterogeneous adhesives

A novel multiscale cohesive approach that enables prediction of the macroscopic properties of heterogeneous thin layers is presented. The proposed multiscale model relies on the Hill's energy equivalence lemma, implemented in the computational homogenization scheme, to couple the micro- and macro-scales and allows to relate the homogenized cohesive law used to model the failure of the adhesive layer at the macro-scale to the complex damage evolution taking place at the micro-scale. A simple isotropic damage model is used to describe the failure processes at the micro-scale. We establish the upper and lower bounds on the multiscale model and solve several examples to demonstrate the ability of the method to extract physically based macroscopic properties.     

Recent approaches in designing bioadhesive materials inspired by mussel adhesive protein

Marine mussels secret protein‐based adhesives, which enable them to anchor to various surfaces in a saline, intertidal zone. Mussel foot proteins (Mfps) contain a large abundance of a unique, catecholic amino acid, Dopa, in their protein sequences. Catechol offers robust and durable adhesion to various substrate surfaces and contributes to the curing of the adhesive plaques. In this article, we review the unique features and the key functionalities of Mfps, catechol chemistry, and strategies for preparing catechol‐functionalized polymers. Specifically, we reviewed recent findings on the contributions of various features of Mfps on interfacial binding, which include coacervate formation, surface drying properties, control of the oxidation state of catechol, among other features. We also summarized recent developments in designing advanced biomimetic materials including coacervate‐forming adhesives, mechanically improved nano‐ and micro‐composite adhesive hydrogels, as well as smart and self‐healing materials. Finally, we review the applications of catechol‐functionalized materials for the use as biomedical adhesives, therapeutic applications, and antifouling coatings. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 9–33     

High strength reversible adhesive closures

Closures such as buttons, clasps, zippers, and hook‐and‐loops find widespread use in daily life, and all work by mechanical interlocking. However, these traditional closures are often rigid, lose performance with age, and can produce a harsh sound during use. Here high strength (>50 N cm^?2), reusable, and nearly silent closure devices are fabricated based on recently developed fibril‐less gecko‐inspired adhesives. Guided by a reversible adhesion scaling law, the closure force capacity is tuned by modifying the closure materials and geometry. A simple analytical model is presented which accurately predicts system performance, based on the reversible adhesion scaling parameter. The force capacity of these adhesive closures is measured and compared to commercially‐available hook‐and‐loop closures, and it is found that the adhesive closures sustain forces that are 4.4 times greater for comparable geometry. The sound of release is also quantified and shown to be minimal for adhesive closures. This work provides motivation to develop new high strength, reusable closures for commercial and industrial applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1783–1790     

Diffusive Adhesives for Water-Rich Materials: Strong and Tunable Adhesion Beyond the Interface

It is notoriously difficult to adhere water-rich materials, such as hydrogels and biological tissues. Existing adhesives usually suffer from weak and nonadjustable adhesion strength, in part because the contact between the adhesive and substrate is largely restrained to the adhesive/substrate interface. In this study, we have attempted to overcome this shortcoming by developing a class of diffusive adhesives (DAs) that can extend adhesion deep into the substrate to maximize the adhesive/substrate contact. The DAs consist of hydrogel matrices and preloaded water-soluble monomers and crosslinkers that can diffuse extensively into the water-rich substrates after adhesive/substrate contact. Polymerization and crosslinking of the monomers are then triggered leading to a bridging network that interpenetrates the DA and substrate skeletons and topologically binds them together. This kind of adhesion, in the absence of adhesive/substrate covalent bonding, is of high strength and toughness, comparable to those of the best-performing natural and artificial adhesives. More importantly, we can precisely tune the adhesion strength on demand by manipulating the diffusion profile. It is envisioned that the DA family could be extended to include a large pool of hydrogel matrices and monomers, and that they could be particularly useful in biological and medical applications.     

Surface changes of yttria‐stabilized zirconia in water and Hanks solution characterized using XPS

Adhesion of soft and hard tissues to yttria‐stabilized zirconia (YSZ) has been reported, despite its chemical inertness. To investigate the underlying mechanism of adhesion of hard and soft tissues to YSZ in dental implants, YSZ disks with (100), (110), and (111) crystalline planes were immersed in water for 60 days and in Hanks solution for 7 days, and the changes in the surface chemical states were characterized using X‐ray photoelectron spectroscopy. After immersion in water for 60 days, the concentration of hydroxyl groups on the YSZ surface increased. Therefore, the surface of YSZ was hydrated during immersion in water. In addition, phosphate groups were formed on the surface of YSZ immersed in Hanks solution. We conclude that the formation of phosphate on the YSZ surface in physiological conditions can promote reaction with the surrounding tissues.     

Thermooxidative stability of hot melt adhesives based on metallocene polyolefins grafted with polar acrylic acid moieties

The present paper describes the thermal oxidation of a mixture applied as hot melt adhesive and particularly of its essential polymeric component ethylene-propylene copolymer Licocene 2602 either virgin or grafted by acrylic acid. Chemiluminescence in oxygen under both nonisothermal and isothermal conditions was used as the tool for evaluation of oxidation stability of samples. The effect of various concentrations of stabiliser Naugard XL1 acting as a metal deactivator and phenolic antioxidant was also determined and the antioxidant selected was found to be an efficient thermooxidative stabiliser. The results appear to be of importance for practical multiple application of hot melt adhesives to be used for binding books.     

Influence of gamma radiation and magnetic resonance imaging radiation on micro-structure,hardness and electrochemical corrosion behavior of Co‒Cr-based dental alloy

The effects of therapeutic gamma radiation at 10, 20 and 30 kGy and magnetic resonance imaging radiation from a 1.5 T MR scanner on the micro-structure, electrochemical corrosion behavior and micro-hardness of commercial dental Magnum H50 (Co=64%, Cr=29%, Mo=6.5%) alloy have been investigated. The corrosion rate, corrosion resistance, corrosion potential and corrosion current density values of the alloy treated with 0.5 M HCl vary due to gamma and magnetic resonance imaging radiation. At 30 kGy, the corrosion resistance of Magnum H50 reaches a minimum value and the corrosion rate obtains a maximum value. The Vickers hardness value of the Magnum H50 alloy decreases after both gamma and magnetic resonance imaging radiation.     

Recycling of polyurethane wastes using different carboxylic acids via acidolysis to produce wood adhesives

This study aims to provide further understanding on the depolymerization of polyurethanes (PU) via acidolysis. Therefore, polyurethane foams scraps are chemical recycled using different dicarboxylic acids, namely succinic and phthalic dicarboxylic acids, being the reaction products identified using Fourier-transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography. The results obtained show that succinic acid has higher efficiency as cleavage agent, as a result, the succinic acid ensuing recovered polyol (RP) presents higher hydroxyl value and lower viscosity. Additionally, from the oxidative-induction time measurements, it is observed that the RP is considerably more thermally stable, than the petroleum-based polyol, due to the higher content of aromatic moieties. Afterwards, the RP is used as substitute of petroleum-based polyol in the production of polyurethane adhesives (PUA) and compared with conventional polyol based PUA. Due to the higher content of aromatic moieties, higher bonding strength is achieved using the RP. Overall, further understanding on the acidolysis is obtained, proving the suitability of this method for the recycling of PU.     

Assessment of Binary Agarose–Carbopol Buccal Gels for Mucoadhesive Drug Delivery: Ex Vivo and In Vivo Characterization

Agarose (AG) is a naturally occurring biocompatible marine seaweed extract that is converted to hydrocolloid gel in hot water with notable gel strength. Currently, its mucoadhesion properties have not been fully explored. Therefore, the main aim of this study was to evaluate the mucoadhesive potential of AG binary dispersions in combination with Carbopol 934P (CP) as mucoadhesive gel preparations. The gels fabricated via homogenization were evaluated for ex vivo mucoadhesion, swelling index (SI), dissolution and stability studies. The mucoadhesive properties of AG were concentration dependent and it was improved by the addition of CP. Maximum mucoadhesive strength (MS) (27.03 g), mucoadhesive flow time (FT) (192.2 min), mucoadhesive time in volunteers (MT) (203.2 min) and SI (23.6% at 4 h) were observed with formulation F9. The mucoadhesive time investigated in volunteers (MT) was influenced by AG concentration and was greater than corresponding FT values. Formulations containing 0.3%, w/v AG (F3 and F9) were able to sustain the release (~99%) for both drugs till 3 h. The optimized formulation (F9) did not evoke any inflammation, irritation or pain in the buccal cavity of healthy volunteers and was also stable up to 6 months. Therefore, AG could be considered a natural and potential polymer with profound mucoadhesive properties to deliver drugs through the mucosal route.