Adhesion of dental materials on tooth surfaces is a fundamental technology in current dental treatments. In orthodontic treatment, the dental materials are temporarily adhered on tooth surfaces and detached after the treatments. The development of dismantlable dental resin adhesives is required to establish a technology that enables the detachment of the adhered dental materials easily and noninvasively. Polyrotaxane is a representative supramolecular polymer comprising multiple cyclic molecules threaded with a linear polymer chain, in which the terminal ends of the polymer axis are capped with bulky stopper molecules for mechanically interlocking cyclic molecules. When the stopper molecules are liberated from the polymer ends by external stimuli, the polyrotaxanes are readily dissociated into their constituent molecules. In this review, the development of dismantlable dental adhesives based on photodegradable polyrotaxanes is described.

For efficient control of surface properties of materials, the immobilization of functional molecules on a substrate surface can provide one effective pathway. Furthermore, stimulus-responsive molecules enable the realization of switchable surface/interface properties. In the field of adhesion, the surface treatment of adherends plays a critical role in ensuring sufficient adhesion strength, which is known as a primer treatment. This article introduces a new concept of a novel dismantling system inspired by our recent study into a photo/thermocleavable molecular layer comprising anthracene molecules. Several types of a cleavable molecular layer were applied at the adhesion interface as same as a conventional primer to investigate the effect of the chemical bond changes at the adhesion interface on the adhesion strength. The photoirradiation or heating process for just 1 min reduced the peel strength when compared with the sample without external stimuli, and changed the failure mode from cohesive to interfacial failure. Especially, the dismantling through a photocleavage process is low-energy: the energy required for this process is less than 10 ％ of that for other photo-triggered dismantlable adhesives. This stimulus-responsive, cleavable primers are expected to provide a new design approach for the development of dismantling adhesive technology.

Photoswitchable adhesives are expected to contribute to material recycling for a sustainable future as complex architectures composed of dissimilar materials are being developed in various fields, because they enable both robust bonding during use and on-demand photoinduced debonding after use with minimal damage to the adherends due to the advantages of light, i.e., high spatiotemporal resolution, easy and precise control of the wavelength and intensity, and no generation of chemical waste. In this review, we highlight photoswitchable adhesives of small molecules and polymers based on photoisomerization of molecular switches. It has been about a decade since the first paper was reported using azobenzene. Although a huge variety of photoswitches are known and widely used, only four of them, azobenezene, diarylethene, spiropyran, and donor–acceptor Stenhouse adducts, have been employed in photoswitchable adhesives. Here, we discuss them separately with respect to each photoswitch. We hope this review provides useful information, inspiration, and ideas for the development of the field.

Adhesive strengthening by light has been widely applied not only in the adhesion and coating fields but also in the medical and dental fields because of its high spatio-temporal resolution, control of various parameters, and low environmental impact. In recent years, easy-dismantlable adhesives are required for reuse and recycling, and research on light-triggered easy-dismantlable adhesives is underway to take advantage of the potential benefits of light. Among light-triggered easy-dismantlable adhesives, materials utilizing the change in physical properties of liquid crystals exhibit unique behavior based on orientation change. These materials incorporate photochromic molecules, and their adhesion changes based on changes in thermophysical properties associated with their photoisomerization and destabilization of the liquid crystal phase. In this paper, we will present recent studies on photo-disassemblable adhesives based on liquid crystals.

The development of tough, reusable adhesives is important but remains a major challenge, especially in water. A tough, reusable adhesive that fully returns to its original state when needed is reported using caffeic acid. Here, caffeic acid is used as an adhesive moiety to achieve these functions due to its dual properties: an adhesive moiety derived from mussel-inspired catechol and a photo-reversible crosslinking agent derived from cinnamic acid. Adhesion is a two-step process. First, the caffeic acid functionalised polymer is applied to the adherend, followed by UV irradiation at 365 nm to form a durable pre-applied adhesive（PAA）layer through cross-linking between the caffeic acid moieties. Secondly, thermal activation of the PAA layer ensures repeated adhesion to a variety of adherends（reuse-many mode）．The cyclic dimer of the caffeic acid moiety is decrosslinked by UV irradiation at 254 nm. This allows complete removal of adhesive residues from the adherends when the adhesive is no longer required（reset-on-demand mode）．Furthermore, the caffeic acid functionalised polymer can be remotely activated under water by magnetic induction heating using magnetic nanoparticles. This study paves the way for the rational design of bio-inspired adhesives that outperform nature using plant-based raw materials.