Sol-gel/Ag coating and oxygen plasma treatment eff ect on synthetic wound fl uid sorption by non-woven cellulose material Učinek prevleke sol-gel/Ag in obdelave s kisikovo plazmo na absorpcijo sintetičnih izločkov iz ran pri netkanem celuloznem materialu

Non-woven cellulose material was functionalized using two techniques, i.e. the coating with AgCl via sol-gel and oxygen plasma. The treatment eﬀ ects were studied regarding the wound ﬂ uid adsorption potential using physiological saline, synthetic exudate and synthetic blood. Plasma treatment was most eﬃ cient since a signiﬁ cant improvement by absorbency rate and capacity was evident, less pronounced in case of synthetic blood. The combination of both treatments showed a similar trend, while the eﬀ ects were less prominent, but still suﬃ cient by managing ﬂ uid-associated as well as infected wounds.


Introduction
A wound dressing, designed for optimal healing, should provide antimicrobial protection along with wound drainage and toxic components removal [1,2].Silver is known as an excellent antimicrobial agent [2][3][4][5], applied in many wound dressing products [2].Plasma treatment is one of the most versatile techniques in polymer surface modifi cations [6] used for increasing wettability [7] and adhesion [8], while the best results are observed when using oxygen gas [9].In our previous studies [10], we combined safe silver binding on cellulose substrate and oxygen plasma modifi cation aiming at achieving simultaneously antimicrobial properties along with improved hydrophilicity.Th e silver-containing samples showed minimal silver release while providing safe antimicrobial activity towards four most common present bacteria in wounds.Hydrophilicity was signifi cantly improved when plasma was applied, as

Materials
A non-woven fabric composed of regenerated cellulose fi bers with surface mass 175 g/m 2 and the thickness 1.7 mm (purchased from KEMEX, Th e Netherlands) was sol-gel coated and oxygen plasma treated.

Preparation procedure
Th e samples studied are denoted as N-for nontreated cellulose non-woven, S -for sol-gel silver coated, P -for oxygen plasma modifi ed and SPfor sol-gel silver coated and aft er that oxygen plasma treated.

Sol-gel silver binding
Silver nano-particles in silver chloride form, iSys Ag (CHT, Germany) in combination with iSys LTX (CHT, Germany) as organic-inorganic binders, were used to achieve an antimicrobial eff ect of the used materials.Kollasol CDO (CHT, Germany) was used as a wetting agent.Kollasol is a hydrophilic silicone surface-active substance mixed with higher alcohols.Firstly, the water solution of iSys LTX (5 g/L), iSys Ag (5 g/L) and Kollasol (0.7 g/L) was prepared.Viscose non-woven samples were impregnated in solution with bath ratio 1:30 at room temperature for 1 h.Aft er treatment, viscose was wrung-out with a foulard (Werner Mathis Ag, Switzerland) with a pressure of 4 bar between cylinders and their speed of rotation at 0.5 m/min, oven dried in a stretched state at 80 °C, and additionally condensed for 1 min at 150 °C (Werner Mathis Ag, Switzerland).

Oxygen plasma treatment
Before plasma treatment, the samples were air-conditioned at 20 °C and 65% RH for 24 h.Th e samples were treated with oxygen plasma in a discharge chamber.Th e discharge chamber was a spherical cylinder with an inner diameter of 36 cm and the height of 30 cm.Plasma was created with an inductively coupled RF (radio frequency) generator, operating at a frequency of 27.12 MHz and output power of about 500 W.During the experiment, the pressure was fi xed at 75 Pa.A more detailed description of the treatment procedure is written elsewhere [11,12].Th e samples were exposed to oxygen gas for 10 min.

Capillary rise method
To simulate real wound fl uid-handling, three test liquids were used, i.e. physiological saline solution, synthetic exudate and blood.Th e composition and physical properties of used liquids are described in our previous study [13].Th e capillary rise method was used as a modifi ed experimental procedure based on Washburn equation [14].It enables the characterization of porous solid and also fabric with regard to their wettability.Th e samples in circular shape (2.5 cm in diameter; 0.087 g) were placed in the Krüss K12 Tensiometer (Krüss GmbH, Germany).All measurements were performed at constant temperature of 20 °C.For a more detailed description of the experimental technique, the readers are referred to [13].As an experimental result, the weight increase (m) as a function of time (t) is observed.Th e amount of liquid uptake in equilibrium represents the absorbency capacity.By determining the slope of the linear part of these plots, the quantity m 2 /t is obtained indicating the absorbency rate.At least ten single measurements were performed for each sample with each test liquid.

Results and discussion
Fig. 1 presents the absorbency rate of physiological saline, synthetic exudate, and blood solution in nontreated (N), oxygen plasma (P), sol -gel/Ag (S), and sol -gel/Ag and plasma (SP) treated samples.Th e curves in Fig. 1 are presented only for 100 s of monitoring the wetting process.Th e slowest absorbency rate was evident by nontreated sample (N) irrespective of used wound relevant fl uids.Th e complete wetting for physiological saline and synthetic exudate solutions occurred only aft er 300 s and the amount of liquids' uptake in equilibrium amounted 1.2 g and 1.3 g for saline and exudate solutions, respectively.Th e blood rise curve reached the plateau only just aft er 1200 s and the equilibrium uptake amounted 1 g.synthetic wound fl uid sorption by non-woven cellulose material Tekstilec, 2017, 60 (1), 25-28 Plasma treatment signifi cantly improved the hydrophilicity since the equilibrium was obtained in a much shorter time, i.e. 10 s for saline and exudate and 66 s for blood.Th e plasma treated sample (P) was able to uptake above 1 g of all tested wound relevant fl uids.Among treated materials, the sol-gel/Ag sample showed the lowest wetting rise curves by all tested liquids.By saline solution the complete wetting occurred within 20 s, by exudate the plateau was obtained within 40 s, while for blood the equilibrium was established no sooner than within 300 s.Th e sol-gel/Ag sample (S) was able to absorb about 1 g of tested liquids in equilibrium.Th e absorbency rate for antimicrobial and plasma modifi ed sample (SP) was slightly lower compared to the plasma treated sample (P).Th e complete wetting for all used liquids occurred within the same time as by the plasma treated samples, while the equilibrium uptake amount was up to 1 g.Th e results presented in Fig. 1 demonstrated the eff ects of the used treatments on the absorbency rate and capacity using wound relevant fl uids.Plasma treatment evidenced the biggest eff ect due to incorporation of polar functional groups and/ or cleaning and/or etching.Th e sol-gel/Ag treated sample showed the lowest absorbency rate and capacity due to organic-inorganic origin of sol-gel components infl uencing the inter-molecular interactions between liquid probes and solid surfaces.Absorbency properties aft er applied plasma treatment onto the sol-gel/Ag samples (SP) was also signifi cantly noticeable, but the eff ect on the rate and capacity was less evident compared to the plasma treated sample (P).A faster absorbency rate by physiological saline and synthetic exudate solutions compared to synthetic blood for all tested samples raised due to diff erent liquids' physical (e.g.viscosity and surface tension) and chemical (e.g.composition, size and shape of molecules) properties.

Conclusions
A non-woven cellulose material was modifi ed using two processes, i.e. sol-gel/Ag and oxygen plasma treatment to simultaneously gain both desired properties for a dressing appropriate for healing infected and exudating wounds.Sorption properties were evaluated using synthetic solutions simulating wound fl uids.Plasma treatment, when applied as single procedure as well as in two-step procedure signifi cantly improved the absorbency rate and capacity for all tested liquids.Although the plasma eff ect was less evident when using synthetic blood, the obtained results indicate the importance of testing in a simulated real environment before being suitable for application.

Figure 1 :
Figure 1: Th e square mass data of physiological saline (a), synthetic exudate (b), and blood solution (c) rise on non-treated (N), oxygen plasma (P), sol -gel /Ag (S), and sol -gel/Ag and plasma (SP) treated samples