Gelation kinetics of hydrogels is closely linked to many applications such as the development of injectable and printable hydrogels. However, the control of gelation kinetics without compromising the structure and other properties of the hydrogels, remains a challenge. Here, we demonstrate a method to control the gelation kinetics of cucurbit[7]uril-adamantane (CB[7]-AD) cross-linked supramolecular hydrogels by using competing guest molecules. The association between CB[7] and AD moieties on the polymer backbone was impeded by pre-occupying the CB[7] cavity with competing guest molecules. By using various guest molecules and concentrations, the gelation of the hydrogels could be varied from seconds to hours. The strong interaction of CB[7]-AD pair endue the hydrogels good mechanical properties and stability. Moreover, the binding of functionalized guest molecules of CB[7] moieties offers a facile approach for tailoring of the hydrogels’ scaffold. Combined with hydrogel injection and printing technology, this method offers an approach for the development of hydrogels with advanced temporal and spatial complexity.

Cucurbiturils (CBs) are a family of macrocyclic molecules with high binding affinity and high binding selectivity. [1][2][3][4][5][6][7] They have been intensively researched for the past decade and have applications in a wide range of fields including molecular recognition, catalysis, drug delivery, bioassays, nanoparticle synthesis and modification, and molecular devices.1-3 Their anchoring onto macromolecules offers further opportunities to expand their applications, [8][9][10] however there are currently few examples of such reports.11-16 The relatively few reports are likely as a result of the difficulties encountered in the modification of CBs; this problem persisted until Kim's group reported the functionalization of CBs with a facile oxidation method in 2003.17 Through oxidization of CBs with persulfate, hydroxyl groups -which are suitable for further functionalization-could be introduced at their peripheries. Following that a series of polymer nanocapsules constructed with perallyloxy-CB[6] and dithiols have been reported. [11][12][13] The eminent binding properties of CB[6] allow these polymer nanocapsules to be decorated easily with targeting and labeling groups through host-guest interactions. Recently, allyl functionalized CB[6] and CB [7] were grafted on to hyaluronate through a thiol-ene click reaction, [14][15][16] and where employed for theranostic systems and tissue engineering applications. In addition of the oxidation method, Isaacs's group developed a different method to synthesize CB derivatives. In their works, CB [6] and CB [7] derivatives were synthesized by the condensation glycoluril hexamer with phthalaldehydes and glycoluril bis(cyclic ethers), respectively.18-20 Despite these, there is still an unmet need for new and facile methods for the construction of CB covalently linked polymers to broaden their portfolio of potential applications.The binding properties of the covalently linked macrocycle polymers are one of the key considerations in their design for specific applications. 21,22 Although their binding properties are usually determined by the binding properties of the macrocycle moieties; the structure of polymers also has a profound and sophisticated effect. Based on the research on polymeric cyclodextrins (CDs), if the CD moieties are spatially isolated, their binding affinity to guest molecules decreases slightly; 23-25 while if they are in close proximity, adjacent two CD moieties may have a cooperation effect and both the binding affinity and binding stoichiometry will be affected. [24][25][26][27][28] To the best of our knowledge, there have been no studies on the binding property of polymeric CBs prior to this work. Here, we present a universal method for the synthesis of linear CB [7] pendent copolymers through free radical polymerization (Scheme 1). The binding properties of the obtained copolymers were studied using turbidity measurement, isothermal titration calorimetry (ITC) and NMR.Free radical polymerization is a universal polymerization method which is suitable f...

Low pseudorotaxane content (≤3 mol%) endows N-isopropylacrylamide based cucurbit[7]uril polypseudorotaxanes unique aggregation and thermal gelation properties.

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A tetrahedron-like guest molecule (THV) with four ditopic arms, consisting of viologen (V) and hexylene moieties, was synthesized, and its interaction with cucurbit[8]uril (CB[8]) was investigated. As a reference, the interaction between CB[8] and an analogue of the arm of the linear ditopic guest (LHV) was first explored by H NMR and UV/Vis spectroscopy. In this case, CB[8] was located on the hexylene moiety and resulted in the formation of a binary complex. However, when THV interacted with CB[8], despite having four arms with four hexylene moieties, only two CB[8] molecules were identified as located on the hexylene moieties; the other two CB[8] molecules resided on the V moieties. Great steric hindrance among the arms played a dominant role in the interaction between THV and CB[8]. Regardless of whether the guest molecule was THV or LHV, CB[8] moved to its V moiety (electron-deficient part) to form the charge-transfer complex upon the addition of a stopper containing a naphthol residue (electron-rich part). Guests LHV and THV were reduced to LHV and THV upon the addition of sodium dithionite. Dimerization of LHV was enhanced when CB[8] was present in less than 0.5 equivalents. In contrast, dimerization was suppressed when CB[8] was present in more than 0.5 equivalents. However, the V units of THV stacked intramolecularly because of the tetrahedron-like molecular structure of THV. The influence of CB[8] on the dimerization of THV was weaker than that on LHV .