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Glucose-responsive shape-memory cryogels Marc Behl1,2, Qian Zhao1,2, Andreas Lendlein1,2,3,a) 1

Institute of Biomaterial Science, Helmholtz-Zentrum Geesthacht, Teltow 14513, Germany Tianjin University − Helmholtz-Zentrum Geesthacht Joint Laboratory for Biomaterials and Regenerative Medicine, Teltow 14513, Germany Institute of Chemistry, University of Potsdam, Potsdam 14476, Germany a) Address all correspondence to this author. e-mail: [email protected] 2 3

Received: 30 April 2020; accepted: 23 July 2020

Boronic ester bonds can be reversibly formed between phenylboronic acid (PBA) and triol moieties. Here, we aim at a glucose-induced shape-memory effect by implementing such bonds as temporary netpoints, which are cleavable by glucose and by minimizing the volume change upon stimulation by a porous cryogel structure. The polymer system consisted of a semi-interpenetrating network (semi-IPN) architecture, in which the triol moieties were part of the permanent network and the PBA moieties were located in the linear polymer diffused into the semi-IPN. In an alkaline medium (pH = 10), the swelling ratio was approximately 35, independent of Cglu varied between 0 and 300 mg/dL. In bending experiments, shape fixity Rf ≈ 80% and shape recovery Rr ≈ 100% from five programming/recovery cycles could be determined. Rr was a function of Cglu in the range from 0 to 300 mg/ dL, which accords with the fluctuation range of Cglu in human blood. In this way, the shape-memory hydrogels could play a role in future diabetes treatment options.

Introduction Glucose is a representative in the group of most important biomolecules, as it is the primary source of energy and a metabolic intermediate for living cells [1]. For a healthy human, blood glucose should maintain at a concentration level ranging from 70 to 100 mg/dL, otherwise diseases like hypoglycemia or diabetes would be caused [2]. Accordingly, there is strong interest in monitoring the glucose level. Recently, glucose-responsive polymer systems, which are capable to show physical or chemical changes in response to glucose, have been designed [3, 4]. The systems are, for example, expected to automatically detect the blood glucose level and further control the release of insulin in response to the glucose level, which potentially provides a painless treatment for diabetes compared to insulin injection. Three different categories of glucose-responsive systems can be differentiated: glucose oxidase (GOD), lectin, and phenylboronic acid (PBA) based systems [3, 5]. Applications of these systems are focused on either diagnosis of glucose concentration or controlled release of insulin [6]. As monitoring of the blood sugar level requires access to the blood system, which is typically realized by painful injection, other less painful methods have been developed to determine the glucose level. Among them, microneedle systems, in which a microarray of needles, typically fabricated

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from silicone is used to pass the transdermal barrier [7]. Microneedl