Sensors and Actuators B: Chemical - Smart...آ  Kassal et al. / Sensors and Actuators B 246

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    Sensors and Actuators B 246 (2017) 455–460

    Contents lists available at ScienceDirect

    Sensors and Actuators B: Chemical

    jo ur nal home page: www.elsev ier .com/ locate /snb

    mart bandage with wireless connectivity for optical monitoring of pH

    etar Kassala, Marko Zubaka, Gregor Scheiplb, Gerhard J. Mohrb, Matthew D. Steinbergc, vana Murković Steinberga,∗

    Faculty of Chemical Engineering & Technology, University of Zagreb, Marulićev Trg 19, HR-10000 Zagreb, Croatia Joanneum Research Forschungsgesellschaft mbH – Materials, Franz-Pichler-Straße 30, Weiz A-8160, Austria GoSense Wireless Ltd.,Moorfield Road, Duxford, Cambridge CB22 4PP, UK

    r t i c l e i n f o

    rticle history: eceived 16 November 2016 eceived in revised form 14 February 2017 ccepted 15 February 2017 vailable online 20 February 2017


    a b s t r a c t

    Wound care technologies need to adapt in order to cope with the growing socio-economic burden of chronic wounds. Non-invasive analytical systems which monitor important wound status biomarkers such as pH of wound fluid, are needed. In this work, a wireless smart bandage for optical determination of pH, as an indicator of wound status, is demonstrated and characterised. The bandage is constructed by immobilising cellulose particles, covalently modified with a pH indicator dye, within a biocompatible hydrogel. Thin layers of the pH sensitive hydrogel are cast onto a conventional dressing and interfaced to

    mart bandage ound monitoring

    ptical pH sensor ireless chemical sensor

    adio-frequency identification

    a wireless platform via a miniaturised optoelectronic probe. The smart bandage can detect pH changes in the physiologically relevant range with high accuracy and precision, and communicate this information with an external readout unit using radio-frequency identification (RFID). The new system could provide insight into temporal changes in wound status in a convenient and non-invasive manner, and prompt an appropriate response from a healthcare provider.

    © 2017 Elsevier B.V. All rights reserved.

    . Introduction

    Wound management is a significant socio-economic burden for odern society. Two percent of the population in the developed orld will suffer a chronic wound during their lifetime [1]. The nited States spends $25bn a year on chronic wound care [2], and omparable amounts are spent in other major economies [3,4]. arly identification of non-healing wounds and wound infection s thus of paramount importance in preventing deterioration of a atient’s condition, hospitalisation of the patient, or even limb or

    ife-threatening consequences [4,5]. There is a clear need for smart ound care dressings – dressings equipped with physical and or

    bio)chemical sensors or indicators – that can determine and com- unicate wound status in a clinically relevant and cost effective anner [6]. Smart dressings should be simple, effective and provide

    ctionable data, thus enabling truly non-invasive wound assess-

    ent that will guide treatment decisions [6]. A strategy typically

    dopted by healthcare providers in managing chronic wounds is to ttempt to reduce the total cost of patient treatment by focusing

    Abbreviations: RFID, radio-frequency identification; NFC, near field communi- ation. ∗ Corresponding author.

    E-mail address: (I. Murković Steinberg).

    ttp:// 925-4005/© 2017 Elsevier B.V. All rights reserved.

    on reducing the incidence of complications (infection), the num- ber and duration of patient hospitalisations, and on reducing the total time to heal. Nurse time and community/home visits thus tend to dominate the real cost of patient treatment when compared to the baseline material costs incurred (dressings, bandages, antisep- tics) which account for only a small percentage of the overall cost [7]. Therefore smart dressings may generate significant savings if they reduce the frequency of nursing home visits, reduce the sever- ity of infections – by facilitating early detection and treatment – and, by implication, reduce the frequency and duration of patient hospitalisations.

    The pH of wound fluid is known to affect wound healing and is recognised as an important biomarker of wound status [4,8]. Gen- erally after an acute cutaneous wound has occurred, acidosis of the underlying tissue – regulated at around pH 7.4 – follows. This is a natural response to injury that aims to prevent infection and bac- terial growth [9]. Colonising bacteria seek to increase the pH to create a more favourable microenvironment, and thus an increase in wound fluid pH may indicate infection [9,10]. The pH of chronic wounds is more complex, but seems to oscillate between pH 7–8 as the wound fails to heal [9].

    Different electrochemical methods have been used to determine the pH of wound fluids [11,12]. Examples of such include potentio- metric sensing with screen-printed electrodes [13] and monitoring the pH-dependent oxidation current of endogenous biomarkers

  • 456 P. Kassal et al. / Sensors and Actua

    Fig. 1. Schematic showing operation of the wireless smart bandage. The pH-induced colour change of cellulose particles with covalently linked GJM 534 is measured and s

    – e a p t b i fl u e e w I o l m a s p u c a l c c a

    n o b w w l T s d t a D w c

    components by automated pick and place followed by reflow solder ˇ

    ent by contactless readout to a remote unit.

    such as uric acid – during voltammetric scans [14]. Wireless lectrochemical platforms which enable potentiometric [15] and mperometric [16] sensing have been developed in parallel to sup- ort these electrochemical measurement methodologies, although o the best of our knowledge a fully wireless electrochemical smart andage for pH sensing has not yet been devised. Optical chem-

    cal sensors that sense pH through the change in absorbance or uorescence of an (immobilised) indicator dye are simple to man- facture in high volume, are easily miniaturised, do not suffer from lectromagnetic interference and do not require a separate ref- rence electrode [17]. Optical sensors are therefore attractive for ound pH sensing and in the imaging and mapping of wounds.

    n the simplest case optical readout is by naked eye of the colour f an indicator dye [18]. In practice however this simple approach imits the level of quantification of the wound. By addition of instru-

    entation the optical quantification and accuracy can be improved, lthough this in turn can impact the price and complexity, and in ome cases may impair the mobility of the patient [19,20]. Smart hones and mobile computing devices, such as tablets, are near biquitous in the developed world, and combine high-resolution ameras with powerful computational ability [21]. As such, they re popularly used as instruments for mobile diagnostics. Nonethe- ess, accurate determination of true colour even with high-quality onsumer products is non-trivial and requires complex image pro- essing, as well as auxiliary (often ‘phone-specific) coupling devices nd/or light sources [22,23].

    In this paper we provide a viable solution to the challenge set for ext generation wound dressings – a quantitative optical indicator f wound pH status with non-contact electronic readout. This has een achieved by immobilising a pH indicator dye on a commercial ound dressing, and integrating the pH sensing film thus formed ith a novel radio-frequency identification (RFID)-based contact-

    ess readout platform via a low-cost optoelectronic interface, Fig. 1. he proposed dye immobilisation technique enables low-cost and calable fabrication (e.g. by screen printing) of pH sensitive films on ifferent kinds of materials commonly used in dressings. The elec- ronics autonomously measures and stores quantitative pH data, nd upon request, transfers it wirelessly by RFID to a computer. evelopment of an appropriate Android application in the future

    ould allow the electronics to directly communicate by near field

    ommunication (NFC) with a Smartphone or tablet.

    tors B 246 (2017) 455–460

    2. Materials & methods

    2.1. Chemicals and reagents

    The pH indicator dye 4-[4-(2-hydroxyethanesulfonyl)- phenylazo]-2,6-dimethoxyphenol (GJM-534) [24,25] was from Joanneum Research Forschungsgesellschaft mbH (Austria). Sig- macell Cellulose Type 20 particles were from Aldrich (Austria). Hydromed D4 polyurethane-based hydrogel was from Cardiotech (USA). Wide range pH buffer solutions were prepared by weighing boric acid (Sigma–Aldrich,St. Louis, MO,USA), citric acid and sodium hydroxide (Kemika d.d., Zagreb, Croatia), dissolving them in deionised water and mixing with phosphoric acid (Kemika d.d., Zagreb, Croatia). pH was adjusted with 0.1 M solution of hydrochloric acid (Carlo Erba Reagenti, Arese, Italy).

    2.2. Preparation of coloured cellulose particles and sensor layers

    In a typical immobilisation procedure, 100 mg of GJM-534 was treated with 1.0 g of concentrated sulfuric acid for 30 min at room temperat