Lysozyme was inkjet printed on two different polyester fabrics considering several challenges of printing enzymes on synthetic fabric surfaces. Wettability of both the fabrics were improved by alkaline pre-treatment resulting reduction in water contact angle to 60±2 from 95°±3 and to 80°±2 from 115°±2 for thinner and coarser fabric respectively. Activity of lysozyme in the prepared ink was 9240±34 units/ml and reduced to 5946±23 units/ml as of collected after jetting process (before printing on fabric). The formulated ink was effectively inkjet printed on alkali treated polyester fabric for antimicrobial applications. Retention of higher activity of the printed fabric requires further studies on enzyme-fibre binding mechanisms and understanding protein orientation on fabric surface after printing

Enzymes immobilized on synthetic polyethylene terephthalate (PET) textile surface by resource‐efficient inkjet printing technology can promote developments for various novel applications. Synthetic fabrics often require adequate pretreatments to facilitate such printing process. This work discusses PET–woven fabric pretreatment routes to improve wettability by alkaline, enzymatic, and plasma processes for effective printing of lysozyme using an industrial piezoelectric printhead. Results indicate that all pretreated samples contain a similar amount of enzymes upon printing. Plasma treated fabrics show relatively more hydrophilic surface characteristics, better protein binding stability, and lower retained activity. Alkali and cutinase‐treated samples possess relatively higher activity due to the greater amount of enzyme desorption to substrate solution. Depending on respective enzyme‐binding stability, a combination of a well-pretreated surface and inkjet as preferential placement technology, the approach of this study can be used as a facile enzyme immobilization method for suitable applications, for example, controlled‐release and bio‐sensing.

Inkjet printing of enzymes can facilitate many novel applications where a small amount of materials need to be deposited in a precise and flexible manner. However, maintaining the satisfactory activity of inkjet printed enzyme is a challenging task due to the requirements of ink rheology and printhead parameters. Thus to find optimum inkjetting conditions we studied the effects of several ink formulation and jetting parameters on lysozyme activity using a piezoelectric printhead. Within linear activity range of protein concentrations ink containing 50 µg/mL lysozyme showed a satisfactory activity retention of 85%. An acceptable activity of jetted ink was found at pH 6.2 and ionic strength of 0.06 molar. Glycerol was found to be an effective viscosity modifier (10–15 mPa.s), humectant and protein structure stabilizer for the prepared ink. A non-ionic surfactant when used just below critical micelle concentration was found to be favourable for the jetted inks. An increase in activity retention was observed for inks jetted after 24 hours of room temperature incubation. However, no additional activity was seen for inkjetting above the room temperature. Findings of this study would be useful for formulating other protein-based inks and setting their inkjet printing parameters without highly compromising the functionality.

Immobilization of enzymes on textiles can impart a range of advanced applications e.g. anti-microbial, controlled release, drug delivery and bio-sensing (Wehrschütz-Sigl et al., 2010). Such applications enable minimal consumption, recovery, and reusability of these valuable bio-materials compared to their conventional textile applications in surface cleaning and finishing (Araujo et al., 2008). Methods used for immobilization can play important roles to ensure precise, flexible and contamination free application. Compared to many of the conventional methods of textile immobilization such as coating and screen-printing, digital inkjet technology offers many benefits for such advanced applications (Kan and Yuen, 2012). Among various inkjet technologies, drop-on-demand piezoelectric printing is a promising resource-efficient technology for enzyme immobilization. 

The enzymes should retain high activity after the immobilization process. Various factors involved during inkjet printing (Saunders and Derby, 2014) and fabric characteristics (Mohamed et al., 2008) can influence this enzymatic activity. Factors concerning the inkjet procedure include rheology and ionic nature of ink along with the shear force and waveform generated inside a piezoelectric printhead (Magdassi, 2010). Factors dependent upon fabric characteristics include surface structure, pore size distribution, and binding mechanism (Nierstrasz and Warmoeskerken, 2003). In this work, we have studied the effects of inkjet procedures on enzymatic activity. Lysozyme being a stable and well-studied enzyme was chosen for our experiments. A Xennia Carnelian printer with a Dimatix QS10 industrial printhead was used for inkjetting. Lytic activity of lysozyme was studied by a UV-Vis spectrophotometer against decrease of Micrococcus lysodeikticus cell concentration at 450 nm. Results showed ca. 10-15% activity reduction of the jetted lysozyme ink. As all the ink and printer parameters were optimized, the probable reason for such reduction could be the effect of shear forces inside the printhead on three-dimensional conformation of lysozyme. In conclusion, our formulated lysozyme ink showed potential for printing textiles with probable activity reduction that require further investigation. 

The catalytic activity of the enzymes can be introduced to textile surfaces for bio-sensing applications by immobilizing them through a resource-efficient deposition method such as inkjet printing [1]. Contrary to conventional dispensing methods, drop-on-demand inkjet printing can provide with high precision deposition of these enzymes along with flexibility for small-scale production [2]. To the best of our knowledge, studies on the inkjetting of enzymes are limited and often uses a modified/adapted commercial paper printer for jetting [3]. Additionally, the effect of ink formulation and printing condition variables on the activity of enzyme are not well explored. Many of such variables suggested for jetting of proteins [4] includes e.g. ink rheology, operating temperature, drop size retention, and the shear force acting on the ink. In our research effect of these variables are studied using a digital inkjet printer (Xennia Carnelian) with a Sapphire QS10 piezo-electric print head (Fujifilm Dimatix, USA). Lysozyme is used as a model enzyme for printing due to its well-known structure and catalytic mechanism. Effect of temperature and shear force development within the print head on lysozyme activity is investigated. Additionally, pre-treatment of the fabric to improve ink adhesion through various surface activation processes are studied. Finally, remaining activity of the printed enzymes over washing is evaluated to ensure the fastness property.

Acknowledgment

This research project is funded by University of Borås, Sweden.

References

[1]     Li J, Rossignol F, Macdonald J. Inkjet printing for biosensor fabrication: combining chemistry and technology for advanced manufacturing. Lab on a Chip 2015;15(12):2538-2558.

[2]     Nierstrasz V, Yu J, Seipel S. Towards more flexible, sustainable and energy-efficient textile functionalization processes: Digital inkjet in functional and smart textile production. In: 9th Aachen-Dresden International Textile Conference 2015; 2015.

[3]     Yamazoe H. Fabrication of protein micropatterns using a functional substrate with convertible protein-adsorption surface properties. J Biomed Mater Res A 2012;100(2):362-9.

[4]     Delaney JT, Smith PJ, Schubert US. Inkjet printing of proteins. Soft Matter 2009;5(24):4866-4877.

Enzymes can be immobilized on textiles to impart anti-microbial properties in a more environment-friendly manner compared to conventional biocide-based solutions. Such application requires ensuring precise, flexible and contamination-free immobilization methods that can be offered by digital printing compared to coating or screen-printing techniques. Drop-on-demand inkjet printing is a resource-efficient technology that can ensure these requirements. The use of polyester and polyamide-based fabrics is rising for applications ranging from apparel and home furnishing to hygiene and medical textiles. These fibers offer superior chemical, physical, and mechanical properties due to their inert nature but challenge the printing process due to hydrophobicity and lack of functional groups. Lysozyme and tyrosinase are two enzymes showing great potential for grafting on synthetic fabrics paving the way to use them for inkjet printing as well.

Challenges for inkjet printing of enzymes on synthetic fabric surfaces come in multiple forms i.e. ink recipe formation, printer mechanics and fabric surface characteristics. The ink must maintain a suitable viscosity and surface tension for effective drop ejection and a feasible ionic nature for enzyme activity. Then, the enzyme must be able to sustain the temperature and shear stress generated inside an inkjet printhead. Finally, influential fabric characteristics include surface structure, pore size distribution, evaporation rate and binding mechanism. By considering these parameters, lysozyme and tyrosinase were successfully printed on variously modified synthetic fabrics using a combination of sustainable technologies.

Tyrosinase enzyme was digitally printed on plasma pretreated polyamide-6,6 fabric using several sustainable technologies. Ink containing carboxymethyl cellulose was found to be the most suitable viscosity modifier for this enzyme. Before and after being deposited on the fabric surface, the printed inks retained enzyme activity of 69% and 60%, respectively, compared to activity prior printing process. A good number of the printed enzyme was found to be strongly adsorbed on the fabric surface even after several rinsing cycles due to surface activation by plasma treatment. Rinsed out fabrics retained a maximum activity of 34% resulting from the well-adsorbed enzymes. The activity of tyrosinase on printed fabrics was more stable than ink solution for at least 60 days. Effects of pH, temperature and enzyme kinetics on ink solution and printed fabrics were assessed. Tyrosinase printed synthetic fabrics can be utilized for a range of applications from biosensing and wastewater treatment to cultural heritage works.

An ink containing tyrosinase catalyzes the tyrosine residues on lysozyme protein to bind it on a plasma-treated polyamide-6,6 (PA) fabric. Inkjet printing enables controlled and sequential deposition of two enzymes on PA which is necessary for proper binding. The effect of different printing sequences on crosslinking stability and enzymatic activity is presented. The lysozyme bound on the fabric shows satisfactory antimicrobial activity. The printed fabric retains about 68% of the ink activity when tyrosinase is printed before lysozyme. Further, this fabric retains about 24% of the initial activity up to four reuses. The fabric shows acceptable inhibition of bacterial growth and retains almost half of its initial activity when cold stored for a month. This work shows the potential of protein binding on textile surface using various means of sustainable technologies, namely enzyme, inkjet, and plasma. 

The inherent flammability of cellulosic fibers limits their use in some advanced applications. This work demonstrates for the first time the production of flame-retardant macroscopic fibers from wood-derived cellulose nanofibrils (CNF) and silica nanoparticles (SNP). The fibers are made by extrusion of aqueous suspensions of anionic CNF into a coagulation bath of cationic SNP at an acidic pH. As a result, the fibers with a CNF core and a SNP thin shell are produced through interfacial complexation. Silica-modified nanocellulose fibers with a diameter of ca. 15 μm, a titer of ca. 3 dtex and a tenacity of ca. 13 cN tex–1 are shown. The flame retardancy of the fibers is demonstrated, which is attributed to the capacity of SNP to promote char forming and heat insulation on the fiber surface.

Conventional textile dyeing and finishing processes typically utilize large quantities of water, energy and chemicals. Despite many efforts to improve resource efficiency textile industry still needs to find radical solutions to substantially reduce its ecological footprint. The objective of the research is to enable textile industry to introduce more effective processes avoiding unnecessary use of water, energy, chemicals and minimization of waste.Digital inkjet technology is a technology with large potential in resource effective production of high end products such as functional and smart textiles in addition to colour printing on textiles. Moreover, digital inkjet technology stimulates innovation through the possibility of small batches, enables novel production strategies (digitalisation of the value chain) and it effectively bridges design and technology. The technology offers strong potential in made-to-measure smart textiles with e.g. applications in health-care and sports.Our research projects in digital inkjet technology focus on the development of stable functional inks, in order to produce textiles with e.g. superhydrophobic, antistatic, conductive, UV sensing or antimicrobial properties as well as inks for color printing.

Conventional textile processes are characterized by large scale production runs and typically utilize large quantities of water, energy and chemicals, making them less suitable for the production of functional and smart textiles. Key objective of the research initiative is to introduce flexible, more resource effective textile functionalization processes.

Digital inkjet technology is a technology with large potential in resource effective production of high end products such as functional and smart textiles in addition to colour printing on textiles. The challenge is to make the potential of digital inkjet technology in high end products an opportunity for the European textile industry.

Digital inkjet technology stimulates innovation through the possibility of small production runs, enables novel production strategies (digitalisation of the value chain) and it effectively bridges design and technology. The technology offers strong potential in made-to-measure smart textiles with e.g. applications in health-care and sports.

The general objective of our research is to develop smart textiles using novel production techniques like digital inkjet printing. Digital inkjet printing enables a sustainable and integrated textile production where less energy, water and chemicals are used, as well as less waste is produced. Inkjet printing can typically be used for the production of small batches, which benefits the production of technical and smart high end products. The advantage compared to traditional textile production techniques is that functionalizing chemicals are applied only where needed and complex designs can easily be changed.

Smart textiles are capable of interacting with the environment and are therewith ideal, flexible lightweight sensors [1]. A wearable and integrated sensor technology can among others be developed through the functionalization of textiles with chromic materials. By showing a reversible colour change a photochromic textile can make the user aware of an environmental danger such as augmented UV-radiation coupled with certain temperature conditions [2,3].

Our research focus on the sustainable production of a UV-sensing smart textile leads to the exploration of minimized water and energy consumption in textile production. In specific, a radiation curable matrix as carrier for the functional material is investigated. The challenge in our work is to consider the role of radiation as curer and activator, as well as the effect of temperature in order to optimize the functionality range of the sensor. Furthermore, storage tests of photochromic prints are conducted to determine the storage stability of the UV-sensor. 

Health concerns as a result of harmful UV-rays drive the development of UV-sensors of different kinds. In this research, a UV-responsive smart textile is produced by inkjet printing and UV-LED curing of a specifically designed photochromic ink on PET fabric. This paper focuses on tuning and characterizing the colour performance of a photochromic dye embedded in a UV-curable ink resin. The influence of industrial fabrication parameters on the crosslinking density of the UV-resin and hence on the colour kinetics is investigated. A lower crosslinking density of the UV-resin increases the kinetic switching speed of the photochromic dye molecules upon isomerization. By introducing an extended kinetic model, which defines rate constants kcolouration, kdecayand kdecolouration, the colour performance of photochromic textiles can be predicted. Fabrication parameters present a flexible and fast alternative to polymer conjugation to control kinetics of photochromic dyes in a resin. In particular, industrial fabrication parameters during printing and curing of the photochromic ink are used to set the colour yield, colouration/decolouration rates and the durability, which are important characteristics towards the development of a UV-sensor for smart textile applications.

Although resource-efficient processes like inkjet printing have a large potential to foster the development of smart and functional textiles, one bottleneck still is the development of functional inks. To make inkjet printing and UV curing given production techniques for smart and functional specialty products, e.g. photochromic textiles, deepened knowledge about the development, rheological behavior and jetting behavior of functional ink is needed. This paper focuses on the formulation and performance of UV-responsive and UV-curable inkjet inks, which are based on photochromic dyes and their application to produce UV-responsive textiles. Two commercial photochromic dyes—Reversacol Ruby Red (RR) and Sea Green (SG), which represent dyes of the naphthopyran and spirooxazine class, respectively, have been used to develop the inks. The photochromic inks are characterized according to their physical–chemical and rheological properties in respect to temperature. The influence of temperature on the drop formation of the inks in an industrial print head is analyzed using a high-speed camera, which reveals important information regarding challenges in ink jettability. It was found that the dye structure and type used in the ink can influence the jetting behavior of photochromic UV-curable ink. More pronounced temperature sensitivity of dyes can increase the temperature-related effects of drop formation as was observed for SG ink. The printability of the RR and SG inks is framed and underpinned by theoretical calculations of the Z number. Discrepancies are observed and discussed between existing theory of ink jettability and visual evaluation of the photochromic ink.

For the development of niche products like smart textiles and other functional high-end products, resource-saving production processes are needed. Niche products only require small batches, which makes their production with traditional textile production techniques time-consuming and costly. To achieve a profitable production, as well as to further foster innovation, flexible and integrated production techniques are a requirement. Both digital inkjet printing and UV-light curing contribute to a flexible, resource-efficient, energy-saving and therewith economic production of smart textiles. In this article, a smart textile UV-sensor is printed using a piezoelectric drop-on-demand printhead and cured with a UV-LED lamp. The UVcurable ink system is based on free radical polymerization and the integrated UVsensing material is a photochromic dye, Reversacol Ruby Red. The combination of two photoactive compounds, for which UV-light is both the curer and the activator, challenges two processes: polymer crosslinking of the resin and color performance of the photochromic dye. Differential scanning calorimetry (DSC) is used to characterize the curing efficiency of the prints. Color measurements are made to determine the influence of degree of polymer crosslinking on the developed color intensities, as well as coloration and decoloration rates of the photochromic prints. Optimized functionality of the textile UV-sensor is found using different belt speeds and lamp intensities during the curing process.

The development and design of novel functional and smart textile materials such as textile sensors and multicolored systems based on photochromic dyes necessitate controls of color intensities, switching speeds, and material durability. Precise control and synchronization of dye kinetics are important for multi-colored photochromic applications especially. However, durability towards abrasion and washing should not be compromised on if we aim to design reliable future textile products. In this study, two different commercial photochromic dyes — a naphthopyran and a spirooxazine-based dye — have been applied on PET fabric by inkjet printing and UV-LED curing. The photochromic textiles’ color behavior, fastness to abrasion and washing, and handle are evaluated using spectrophotometry, scanning electron microscopy, and Kawabata evaluation system. Despite a decrease in color performance after washing, the photochromic inkjet print is effective and barely influences the textile structure. Reduced rigidity of the host matrix promoted higher color yields and faster dye kinetics, but also improved durability towards abrasion and washing. In order to synchronize kinetics of the different dye types for multi-colored applications, distinct curing conditions are preferable, which, however, result in varying print durability. In the design of multi-colored photochromic textiles, dye kinetics, and durability have to be balanced.

Photochromic molecules are well-established colourants in the manufacturing of niche products, providing reversible colour change effects when irradiated with ultraviolet (UV) light. The high material cost of such speciality dyes along with the general high carbon footprint and extensive water consumption of textile products necessitates resource-efficient production processes. The use of supercritical CO2 (scCO(2)) dyeing technique enables the economic production of textile high-end products, where a uniform through colouration is desired. This study investigates the potential application of two commercial photochromic dyes based on spirooxazine (Sea Green - SO-SG) and naphthopyran (Ruby Red - NP-RR) to polyester fabric using scCO(2) dyeing technique and examines their photochromic behaviour. The dyeing was carried out at 120 degrees C and 25 MPa for 1 h. The photochromic performance was evaluated using a specially designed online colour measurement system capable of simultaneous UV irradiation and continuous measurement of photochromic colour change even after the shutdown of the UV source. The colour yields (K/S values), photoswitching rates and durability against washing were the main parameters examined. The results showed that scCO(2) dyed photochromic polyester fabrics exhibited reversible colour changing properties upon UV exposure and removal. The samples dyed with SO-SG demonstrated a comparable degree of photo-colouration, lower background colour, faster colouration and decolouration speeds, but inferior wash fastness compared with NP-RR dyed samples. Particularly, the same class of dyes applied by scCO(2) dyeing showed faster fading rates compared with conventionally dyed and screen printed samples. This study shows that scCO(2) dyeing method is a potential alternative to develop uniformly coloured photochromic textiles providing excellent photochromic performance with additional economic and environmental benefits.

Viscosity and surface tension are the fundamental rheological property of an ink for inkjet printing. In this work, we optimized the viscosity and surface tension of inkjet inks by varying the concentration of glycerol with water, PEDOT-PSS with glycerol and water, finally by adding the surfactant. The surface resistance of the sample was characterized by four-probe measurement principle. The change in volume of PEDOT-PSS in water, as well as the change in weight of glycerol in water has got a great influence on the viscosity on both temperature dependence and shear dependence behaviour of the ink solution. The surface tension of the solution changed from 37 to 28mN/m due to the addition of Triton. Varying the volume of PEDOT-PSS and the volume of glycerol in water has a great influence on the viscosity of the ink solution for inkjet printing. Viscosity drops from 12.5 to 9.5 mPa s with the addition of Triton at 25 ^oC. The PEDOT-PSS solution was found to be temperature dependence but not shear dependence as it is a Newtonian fluid. The sample was used to connect the light emitting diode (LED), and hence the electrical conductivity, with a surface resistance of 0.158 KΩ/square, was sufficient enough to give transfer current for LED lamp. The rheology of the inkjet ink is very critical for the successful droplet formation of the inkjet printing.

Digital inkjet printing is a production technology with high potential in resource efficient processes, which features both flexibility and productivity. In this research, waterborne, fluorocarbon-free ink containing polysiloxane in the form of micro-emulsion is formulated for the application of water-repellent sports- and work wear. The physicochemical properties of the ink such as surface tension, rheological properties and particle size are characterized, and thereafter inkjet printed as solid square pattern (10 × 10 cm) on polyester and polyamide 66 fabrics. The water contact angle (WCA) of the functional surfaces is increased from < 90° to ca. 140° after 10 inkjet printing passes. Moreover, the functional surface shows resistance to wash and abrasion. The WCA of functional surfaces is between 130° and 140° after 10 wash cycles, and is ca. 140° after 20000 revolutions of rubbing. The differences in construction of the textile as well as ink–filament interaction attribute to the different transportation behaviors of the ink on the textile, reflected in the durability of the functional layer on the textile. The functionalized textile preserves its key textile feature such as softness and breathability. Inkjet printing shows large potential in high-end applications such as customized functionalization of textiles in the domain of smart textiles.

Digital inkjet printing of functional layer on textiles is a resource efficient and flexible manufacturing process, with reduced ecological footprint. This technology has large potential in high-end applications such as in the domain of smart textiles. The purpose of our research is to develop a waterborne, fluorocarbon free ink for water-repellent sports- and work- wear. The novel ink formulation was characterized by measuring surface tension and rheology and thereafter inkjet printed as solid block pattern (10×10 cm) on polyester fabrics. The hydrophobicity of the functional surface was characterized by water contact angle measurements. The wash fastness and abrasion properties of functional surface were investigated. The inkjet printed functional surface shows promising hydrophobicity compared to commercial available products.

Digital inkjet printing is a resource effective and flexible manufacturing method, which has great potential to replace the large-scale conventional textile processes, and stimulates innovation in small and flexible production such as in the domain of smart textiles. Water-repellent textile has great importance in the application of sport- and work- wear. In this research, a hydrophobic ink free from fluorocarbon is formulated. The rheological properties, surface tension and particle size were characterized in order to fit the jetting parameter of the print head. In order to improve the adhesion between the deposited ink and substrate, plasma and alkaline pre-treatment were performed on polyester substrate. The novel formulation was inkjet printed as the solid bock on polyester and polyamide 6,6. The hydrophobicity of the fabrics was measured by water contract angle measurement. The effect of pre-treatment on the adhesion of ink to substrate as well as on functional property of textile was evaluated after washing and abrasion tests.   

Fluorocarbon-free, water-repellent inks for sports- and work- wear were developed and inkjet printed. The inkjet printed samples show promising hydrophobicity and fastness properties. The result indicates that it can be possible to combine inkjet printing and functional ink as resource efficient production method for customization in the domain of smart textile.