Micromechanical measurement of adhesion of dehydrating silicone hydrogel contact lenses to corneal tissue

Stiffer Is Stickier: Adhesion in Elastic Nanofilms

When two objects are brought into contact, separating them typically requires overcoming a detachment force. While this adhesion-induced force is vital for thin film materials in a range of nature and engineering systems, its quantitative understanding remains elusive due to the complex interplay between nonlinear deformation and adhesion. Here we perform controlled experiments and develop formal theories for the detachment force in a canonical configuration: separation of a sphere from an elastic graphene film. We observe that applying tension to the film can increase both its apparent out-of-plane stiffness and its detachment force, a behavior that cannot be explained by macroscopic adhesion theories. We attribute this unusual "stiffer-stickier" behavior to long-range intermolecular forces and demonstrate that it is a general phenomenon for elastic nanofilms, explainable through a multiscale theory that we develop. The ideas introduced here offer a generic strategy to understand the adhesion of slender structures across various length scales.

Hybrid three-dimensional printing and encapsulation process for cellulose hydrogel sensors

The advancement of three-dimensional (3D) printing technology has further promoted the scientific progression of hydrogels within the realm of wearable devices. However, when the viscosity of the hydrogel precursor is large but does not meet the self-supporting requirements, or lacks the participation of monomer with gel phase change characteristics, the 3D printing preparation of hydrogels often becomes difficult. This study delves into a novel 3D printing method aimed at combining direct ink writing (DIW) with vat photopolymerization (VPP) to achieve a broad spectrum of adjustable mechanical properties by introducing cellulose as a medium to modulate both the mechanical and rheological properties of hydrogels. This hybrid method facilitates the efficacious printing preparation of low-viscosity hydrogels, thereby mitigating the stringent viscosity prerequisites inherent in printable hydrogels. Furthermore, the employment of a dual-core coaxial printing technique for the hybrid printing of hydrogel and elastomer serves to ameliorate hydrogel water loss predicaments. As a result, this new 3D printing method broadens the mechanical properties of printable hydrogels and the adjustable range of system viscosity. At the same time, it realizes the integrated printing of encapsulation layer, and improves the service life of hydrogels, and can be applied to the hydrogel-based sensors.

Interaction between eye movements and adhesion of extraocular muscles

The contact and pull-off tests and finite element simulations were used to study the extraocular muscle-sclera adhesion and its variation with eye movement in this research. The effect of the adhesion on the eye movements was also determined using equilibrium equations of eye motion. The contact and pull-off tests were performed using quasi-static and non-quasi-static unloading velocities. Finite element models were developed to simulate these tests in cases with high unloading velocity which could not be achieved experimentally. These velocities range from the eye's fixation to saccade movement. The tests confirmed that the pull-off force is related to the unloading velocity. As the unloading velocity increases, the pull-off force increases, with an insignificant increase at the high ocular saccade velocities. The adhesion moment between the extraocular muscles and the sclera exhibited the same trend, increasing with higher eye movement velocities and higher separation angles between the two interfaces. The adhesion moment ratio to the total moment was calculated by the traditional model and the active pulley model of eye movements to assess the effect of adhesion behavior on eye movements. At the high ocular saccade velocities (about 461 deg/s), the adhesion moment was found to be 0.53% and 0.50% of the total moment based on the traditional and active pulley models, respectively. The results suggest that the adhesion behavior between the extraocular muscles and the sclera has a negligible effect on eye movements. At the same time, this adhesion behavior can be ignored in eye modeling, which simplifies the model reasonably well. STATEMENT OF SIGNIFICANCE: 1. Adhesion behavior between the extraocular muscles and the sclera at different indenter unloading velocities determined by contact and pull-off tests. 2. A finite element model was developed to simulate the adhesive contact between the extraocular muscles and the sclera at different indenter unloading velocities. The bilinear cohesive zone model was used for adhesive interactions. 3. The elastic modulus and viscoelastic parameters of the extraocular muscle along the thickness direction were obtained by using compressive stress-relaxation tests. 4. The influence of the adhesion moment between the extraocular muscles and the sclera on eye movement was obtained according to the equation of oculomotor balance. The adhesion moment between the extraocular muscles and the sclera was found to increase with increased eye movement velocity and increased separation angle between the two interfaces.

Roadmap for phase change materials in photonics and beyond

Phase Change Materials (PCMs) have demonstrated tremendous potential as a platform for achieving diverse functionalities in active and reconfigurable micro-nanophotonic devices across the electromagnetic spectrum, ranging from terahertz to visible frequencies. This comprehensive roadmap reviews the material and device aspects of PCMs, and their diverse applications in active and reconfigurable micro-nanophotonic devices across the electromagnetic spectrum. It discusses various device configurations and optimization techniques, including deep learning-based metasurface design. The integration of PCMs with Photonic Integrated Circuits and advanced electric-driven PCMs are explored. PCMs hold great promise for multifunctional device development, including applications in non-volatile memory, optical data storage, photonics, energy harvesting, biomedical technology, neuromorphic computing, thermal management, and flexible electronics.

The adhesion behavior of the retina

Ocular diseases and treatment related to rhegmatogenous retinal detachment (RRD) are highly correlated with retinal adhesion behavior. Therefore, this paper proposes to study the adhesion behavior of the intact retina. This can provide theoretical guidance for the treatment and research of retinal detachment (RD) related diseases. To systematically analyze this aspect, two experiments were performed on the porcine retina. The pull-off test combined with the modified JKR theory was used to study the adhesion behavior of the vitreoretinal interface, while the peeling test was used to study the adhesion behavior of the chorioretinal interface. In addition, the adhesion phase involved in the pull-off test was simulated and analyzed by building the corresponding finite element method (FEM). The experimental results of adhesion force on the vitreoretinal interface were obtained by pull-off test with five sizes of rigid punch. The experimental value of the pull-off force F_PO tends to increase gradually with increasing punch radius in the range of 0.5-4 mm. A comparison of the experimental results with the simulation results shows that they are in a well agreement. And there is no statistical difference between the experimental and theoretical values of the pull-off force F_PO. In addition, the values of retinal adhesion work were also obtained by pull-off test. Interestingly, there is a significant scale effect of the retinal work of adhesion. Finally, the peeling test gave a maximum peeling strength T_Max of about 13 mN/mm and a stable peeling strength T_D of about 11 mN/mm between the retina and the choroid. The pull-off test well shows the process of retinal traction by the diseased vitreous at the beginning of RRD. A comparison of the experimental results with the finite element results verifies the accuracy of the simulation. The peeling test well investigated the adhesion behavior between the retina and the choroid and obtained key biomechanical data (peeling strength, etc.). The combination of the two experiments allows a more systematic study of the whole retina. This research can provide more complete material parameters for finite element modeling of retina-related diseases, and it also can provide the theoretical guidance for individualized design of retinal repair surgery.

Nonfouling and Antibacterial Zwitterionic Contact Lenses Loaded with Heme-Mimetic Gallium Porphyrin for Treating Keratitis

Antifouling and antibacterial are two critical challenges in the development of contact lenses (CLs). Herein, we presented nonfouling and antibacterial bifunctionalized CLs by encapsulating cationic heme-mimetic gallium porphyrin (Ga-CHP) into zwitterionic-elastomeric-networked (ZEN) hydrogel. Results proved that the ZEN hydrogel showed excellent abilities to resist non-specific protein adsorption, bacterial adhesion, and biofilm formation. Moreover, Ga-CHP could be sustainably released and kill >99.9% planktonic bacteria and >99.9% mature biofilms. In vivo, the symptoms of bacterial keratitis in mice were significantly alleviated after wearing the CLs for 7 days via iron-blocking and photodynamic synergistic antibacterial therapy with the help of natural sunlight. This study highlights the nonfouling and antibacterial superiority of the Ga-CHP-functional zwitterionic CLs and proposes a portable yet efficient non-antibiotic keratitis treatment strategy.

Corneal Adhesion Possesses the Characteristics of Solid and Membrane

Adhesion behavior usually occurs in corneas associated with clinical treatments. Physiologically, an intact natural cornea is inflated by intraocular pressure. Due to the inflation, the physiological cornea has a mechanical property likeness to membrane. This characteristic is ignored by the classical theory used to analyze the adhesion behavior of soft solids, such as the Johnson–Kendall–Roberts (JKR) model. Performing the pull-off test, this work evidenced that the classical JKR solution was suitable for computing the corneal adhesion force corresponding to the submillimeter scale of contact. However, when the cornea was contacted at a millimeter scale, the JKR solutions were clearly smaller than the related experimental data. The reason was correlated with the membranous characteristic of the natural cornea was not considered in the JKR solid model. In this work, the modified JKR model was superimposed by the contribution from the surface tension related to the corneal inflation due to the intraocular pressure. It should be treated as a solid when the cornea is contacted at a submillimeter scale, whereas for the contact at a larger size, the characteristic of the membrane should be considered in analyzing the corneal adhesion. The modified JKR model successfully described the adhesion characteristics of the cornea from solid to membrane.