Batch-fabricated hydrogel/polymeric-magnet bilayer for wireless chemical sensing

Abstract

This paper introduces a fabrication and wireless chemical sensing scheme using a hydrogel/ polymeric-magnet bilayer. The swelling/deswelling of the hydrogel in response to chemical stimuli (e.g. pH, glucose etc.) results in vertical movement of the polymeric permanent magnet located on top of the hydrogel film. The hydrogel volume change is wirelessly detected by a giant magnetoresistance (GMR) sensor. A pH-sensitive hydrogel magnet bilayer is fabricated and tested as proof of the concept. The sensor shows a sensitivity of 0.01 Oe/pH, a resolution of 0.05 pH unit between pH 4 and pH 6, and a response time of 30 minutes. The described device is the first integrated wireless hydrogel/polymeric-magnet transducer with potential applications in biomedical and environmental sensing areas.

Target-Specific Superparamagnetic Hydrogel with Excellent pH Sensitivity and Reversibility: A Promising Platform for Biomedical Applications

“… 21 Moreover, pH-sensitive hydrogels are particularly attractive for implantable devices/applications, since they do not require an on-board power source and/or electronic circuitry. 22 In particular, hydrogels that are sensitive to pH have become increasingly important for use in chemical microsensor technology. 23 Such sensors usually consist of a stimulus-responsive hydrogel, which is used as a sensing element and a transducer to convert the response of the hydrogel to the optical or electrical domain.…”

“…Among these stimulus-responsive magnetic nanocomposite hydrogels, pH-sensitive hydrogels have received immense interest in biomedical applications, such as in disease diagnosis, as polymeric drug carriers, and as biosensors, because pH is an important environmental factor in the body and some disease states manifest themselves by a change in pH value. , For example, they can be used in the delivery of therapeutic agents to the tumor site and/or to diagnose the disease because the extracellular pH of the tumor site is lower (pH 5) than the extracellular pH of normal tissue (pH 7.4); , in the drug delivery to the intestine (pH 6.8), but protecting the drugs, especially protein drugs, from getting destroyed by gastric acid or decreasing the harm of irritant drugs on gastric mucosa in stomach (pH 1.2); , for diagnosis of kidney stone patients with type II diabetes, who are reported to have lower pH urine than normal individuals; and for diagnosis of skin diseases related to skin disorders such as dermatitis (pH 6.6), ichthyosis (pH 4.6 and 5.3), and fungal infections (pH 5.1–5.7) . Moreover, pH-sensitive hydrogels are particularly attractive for implantable devices/applications, since they do not require an on-board power source and/or electronic circuitry . In particular, hydrogels that are sensitive to pH have become increasingly important for use in chemical microsensor technology .…”

Magnetic actuated pH-responsive hydrogel-based soft micro-robot for targeted drug delivery

“…In general, hydrogels [8] have three-dimensional polymer networks strongly imbibed with water, where the amount of water can reach up to 90% of the hydrogel's mass. Because of this property, hydrogels are able to swell and shrink considerably (>10 times in volume) when the amount of water in the polymer network changes [7,9]. Therefore, many hydrogel actuators and drug-delivery devices were proposed as microrobots and micro-grippers for biomedical applications using biodegradable and biocompatible stimuli-responsive hydrogels.…”