UV-Cleavable Polyrotaxane Cross-Linker for Modulating Mechanical Strength of Photocurable Resin Plastics

Abstract

A UV-cleavable supramolecular cross-linker was designed to effectively control the mechanical strength of photocurable resin plastics. The resin monomer-soluble polyrotaxane (PRX) cross-linker was synthesized by introducing a hydrophobic n-butyl group and a cross-linkable methacrylate group in α-cyclodextrin threading to a polyethylene glycol containing UV-cleavable end groups. The UVcleavable PRX cross-linker was completely dissolved in 2-hydroxyethytl methacrylate (HEMA) and camphorquinone, representative photocurable resin components. The dumbbelllike stiff resin plastic was prepared by irradiating the mixture with 450 nm blue light. The stiffened resin plastic maintained its ultimate tensile strength (UTS) under visible light irradiation. However, the UTS of the resin plastic was remarkably decreased to 40% of the original value once the plastic was exposed to 254 nm UV light. This indicates that the suggested UVcleavable PRX cross-linker is effective in modulating the mechanical strength of photocurable resin plastics. P hotocurable resins are widely used in industry, commodities, and the biomedical field because they possess good formability, mechanical strength, and cost-effectiveness. 1,2 However, the irreversible stiffening of photocurable resins often causes significant problems in material applications in many engineering fields. For instance, photocurable resin plastic is essential to support prosthetic devices in the field of dentistry. 3 However, the irreversible stiffening of composite resins often causes significant damage to the dental tissue during removal after treatment. 4 Therefore, the development of stimuli-degradable resin plastic is highly desirable in dentistry.The use of photolabile groups, such as o-nitrobenzyl, has many advantages in the design of degradable materials. 5−7 Unlike other degradable chemical groups, photolabile groups can be accurately triggered to cause degradation in both dry and wet conditions without additives. 8,9 The most general designs for photocleavable polymers use some form of photocleavable cross-linker. Both end groups of o-nitrobenzylcontaining chemicals can be modified with (meth)acrylate groups, and the modified chemical can be used as a photocleavable cross-linker to reversibly reinforce the mechanical strength of (meth)acrylic resins. 10 Structural materials requiring temporary mechanical strength, such as hydrogels, scaffolds, and photoetching materials, are generally designed using this concept. 11−16 Although the strategy is useful for the design of functional photocleavable materials, the efficiency of cleavage remains a critical problem. Because each photolabile group is designed to connect two (meth)acrylate groups, equivalent amounts of photolabile groups with cross-linkable sites must be used to prepare the materials. For this reason, several minutes of irradiation with ultraviolet (UV) light is required to induce drastic degradation; the required time becomes much longer when the material is a rigid solid, such as a cross-linked resin. 17 Polyr...

A Guiding Principle for Strengthening Crosslinked Polymers: Synthesis and Application of Mobility‐Controlling Rotaxane Crosslinkers

“…Rotaxane‐crosslinked polymers (RCPs) have attracted great attention both from a fundamental and a practical perspective because of the extraordinary functionality based on the mechanically linked components with high mobility . Ito et al.…”

A Guiding Principle for Strengthening Crosslinked Polymers: Synthesis and Application of Mobility‐Controlling Rotaxane Crosslinkers

“…Rotaxane-crosslinkedpolymers(RCPs)have attracted great attention both from afundamental and apractical perspective because of the extraordinary functionality based on the mechanically linked components with high mobility. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Ito et al have reported that cyclodextrin-based polyrotaxane hydrogels with rotaxane crosslinks show excellent swelling ability and extensibility. [15] Related studies on such crosslinked cyclodextrin-based polyrotaxanes also revealed intriguing properties that cannot be attained by crosslinked polymers using covalent crosslinkers.…”

Polyrotaxanes as emerging biomaterials for tissue engineering applications: a brief review

“…Azo-substituted PRXs with PIPAAm exhibited responses to heat and UV stimuli [36]. Improving upon this, by introducing both a photo-initiator molecule and a photolabile group into the PRX crosslinker-based resin, it was shown that, upon exposure to 450-nm light, the PRX-based resin hardened, but when the hardened resin was irradiated with 250-300 nm UV light, the tensile strength of the resin reduced significantly indicating the photolabile nature [37]. Apart from these, functional group modifications such as acetylation, methoxylation or sulfonation, and conjugation of PRXs with peptides such as RGD, BMP2, and FGF2 have also been carried out on PRXs in order to improve cellular interactions [38][39][40].…”