Ismat Zerina, Johannes Wendlerb, Andreas Nockeb, Chokori Cherifb
a National Institute of Textile Engineering and Research (NITER)
b Institute Of Textile Machinery & High Performance Material Technology (ITM, TU DRESDEN)
The conventional textile products with new features are an innovative field of topic growing in potential. The goal consists in the integration of technical functions in textile materials. For example, Textile-based sensor for monitoring vital signs or other electrical impulses of an object such as construction of a Sensor Yarn for monitoring of chronic wound ensuring antibody and antigen reaction. Among different manners Electrochemical Impedance Spectroscopy (EIS) have been best suited for its easy adaptation . Due to its characteristics related to electrochemical behavior, it is able to miniaturize the system, i.e. cost effective without need of high-energy sources. The intention of this paper is to focus on the manufacturing of a sensor yarn by braiding. After having the required structure, it’s essential mechanical and electrical properties are tested regarding to the application on wound monitoring.
Wound care is the problem faced by nearly (1-1.5) % population of the industrial world. Therefore, wound treatment is costly included with personal and material costs. In Europe, wound management expenses 2 – 4 % of healthcare budgets . Wound healing is an intricate process whereby the skin (organ-tissue) repairs itself after injury by complex biochemical reactions. This process is fragile and susceptible to interruption by checking. Furthermore, the wound condition through dressing can enlarge the risk of a wound infection. To diminish the complication in the wound healing process, a continuous sensor-based monitoring of the healing area is essential where a persistent wound monitoring permits immediate detection of wound infections, working period of wound dressings and examination the wound condition without a removal of the wound dressing.
Manufacture of Sensor Yarn
Owing to the principle of wound monitoring, the sensor yarn is made by the combination of an electro-conductive component (Electrode) and a yarn from biocompatible fibre (Isolator) which can change its electrical properties due to environmental conditions, for example- swelling. Practically it can be constructed by Braiding, Twisting and Friction spinning machine. According to recent design approach and theoretical point of view, sensor yarn is produced by braiding because of its more stable geometry and covered multilayer production capability. Generally, braids are produced by the regular interlacement of three yarns, diagonally to the production direction. Additional reinforcement yarn can also be incorporated in a braid – in the axial direction which is shown in figure-1 .
For this project braiding machine-RU 2/12-80, Manufacturer: August Herzog Maschinenfabrik GmbH & Co. KG, shows in Figure-2, is used to produce sensor yarn. The most common technique, the is circular braiding is used here.
Here the sensor yarn is manufactured stepwise by copper wire of 120 µm diameter and chitosan filament yarn of 68 tex. Chitosan filament is sensitive for axial and lateral force. For this reason the demostrated braiding machine in Figure-2 is manually operated by cordless screwdriver to avoid the filament breakage rate due to high take up motion. The close view of sensor yarn fabrication is illustrated in figure-3.
Here a track plate is kept at the bottom of the machine. Packages which supply axial yarns are kept beneath the track plate. The braiding yarns are fed from the bobbins through the centre of horn gear. At first step the axial yarn-copper wire is supplied from the stationary creel through the centre of horn gear. Six chitosan yarns from six spool packages, are subdivided into two orbits. With the diphasic sinusoidal motion of spool package containing track plate, braid is produce through the thread crossing circle around the braiding point. At the second step the following braid is used as axial yarn and six spool packages of copper wire are acted as braiding yarn. Similarly the secondary layer of copper wire is produced above the copper-chitosan braid through the circular thread crossing around the braiding point and thus the sensor yarn is obtained, which is shown in the figure-4.
In figure-4, the two layers of copper wire are working as two electrode. Between the two electrodes a chitosan filament layer is presented as an isolator which is a functional layer. Owing to the parameter of the wound, for example – concentration of NET (Neutrophil Extracellular Traps), pH or Temperature i.e. according to the wound environment, change the properties of functional layer which ensures the wound infection or the healing stage. It is measured by Electrochemical Impedance Spectroscopy (EIS).
To ensure the parameter of the sensor yarn, its basic electrical and mechanical properties are tested by means of an electrical impedance and a bending stiffness test.
Electrical Impedance of sensor yarn
At first electrical impedance is practically measured. Here Electrical impedance is directly measured by a digital multimeter which is shown in figure-5.
The impedance values are as follows-
Average, X̅ = 12.3 pF
Standard deviation, S = 0.65 pF
Coefficient of variation, V = 5.33 %
Confidence interval, P = 11.84 <_ µ <_ 12.76
Again, the construction of sensor yarn is comparable to a coaxial cable which is illustrated in figure-6. Therefore, the impedance can be theoretically computed by the impedance calculation formula of coaxial cable.
C: Capacitance [F]
L: Length of the conductor (Sensor yarn) [m]
R₁: Outer radius of the inner conductor (axial copper wire) [mm]
R₂: Inner radius of the outer conductor (second layer of copper wire) [mm]
εᵣ: Permittivity of the capacitive medium [F/m]
ε₀: Vacuum permittivity [F/m]
Permittivity of chitosan according to 
From the direct reading of multimeter the average impedance value is 12.3 pF but after implementation of impedance calculation formula of coaxial cable, a value of 20.67 pF is obtained. The difference between the practical and theoretical impedance values is 8.37 pF. Owing to the partial covered layer of copper wire, the practical impedance value is differed.
Bending Stiffness of Sensor Yarn
Bending stiffness is defined as the resistance offered by sample against bending stress. Moreover, there is no standard procedure to measure the bending stiffness of such type of sensor yarn which is used for example in smart textiles, medical devices etc. As the sensor yarn is made by braiding and it is compared with a narrow fabric such as shoe lace, so the bending stiffness of the sensor yarn is tested by narrow fabric stiffness test .
Average, X̅ = 44.3 mN-cm2
Standard Deviation, S=10 mN-cm2
Coefficient of Variation = 22.57 %
Confidence limit, P = 37.15<_µ<_51.44
As it is the first approach of testing bending rigidity of sensor yarn where the yarn structure is incomparable with common yarns and as it is a narrow fabric, so it is tried sincerely to evaluate it’s bending stiffness by . From the result of bending rigidity it can say that this sensor yarn is stiffer than single yarn. The further evaluation of this result is in under research.
Because of stable geometry and advantage of multilayer production, the sensor yarn is manufactured by braiding with copper and chitosan filament. For accurate performance of sensor yarn in wound monitoring, it should be partially wrapped via 2nd electrode. Therefore, the impedance value differs from theoretical value. The test result of bending stiffness is showed relative higher bending rigidity of sensor yarn compared with single yarn. This simple advancement of sensor yarn manufacturing will be lead further to fabricate a textile-based biosensor which could be offer a superior flexible properties to access the wound condition. So on this article is recommended to carry on the sensor yarn construction in coming days.
References Prodromidis. M: Impedimetric Biosensors and Immunosensors. Pak. Anal. Environ. Chem. Vol. 8, No. 1 & 2 (2007). p. (69 – 71)  Gottrup. F.; Apelqvist, J.; Bjansholt, T.; Cooper, R; .Moore, Z; Peters, E.J.G; Probst, S: Antimicrobials and Non-healing Wounds – Evidence, controversies and suggestions. Journal of Wound Care 22(5) (May 2013), p. 4  Gong. R.H.; Specialist yarn and fabric structures- Development and applications. (2011). p (333-351)  Cherif. C.; Textile Werkstoffe für den Leichtbau. Techniken – Verfahren – Materialien – Eigenschaften. (2011). p (307-310)  Lima. CGA; de Olivira. RS; Figueiro. S.D; DC conductivity and dielectric permittivity of collagen- chitosan films. (2005). P (285)  Norm DIN 53362 Teil 7 2003-10. Bestimmung der Biegesteifigkeit – Verfahren nach Cantilever