The subject of the research work was the development of a new glutaraldehyde tanning technology for sheep leathers with wool fleece. Chrome-free tanned leathers with antimicrobial protection were used for the production of anti-bedsore sheets in order to implement a new product for medical and therapeutic purposes. Rheumatologists and physiotherapists recommend such leathers as sheets for people with rheumatic diseases, as well as with problems with the spine, joints and sleep [1].
Sheep leathers gain silky, resilient and fluffy hair as a result of chrome-free tanning. Wool fiber has characteristic features such as excellent thermal insulation properties and high hygroscopicity, i.e. it has the ability to absorb and maintain a large amount of moisture available from the environment. Under normal climatic conditions, wool contains 17 % moisture, but can absorb up to about 50 % without feeling wet [2,3]. For this reason, wool products absorb human sweat well. Wool does not allow the person’s body to overheat, because it dissipates excess heat thanks to the properties of the hair. The dynamics of the hair, which consist in the contraction and relaxation of the hair under the influence of temperature, is of great importance. When the ambient temperature is elevated, the hair expands, allowing excess heat to pass through, and when it is cold, the hair shrinks, by which the wool begins to warm. This is one of the most important properties of wool, thanks to which woolen bedding maintains a constant body temperature. This feature is very important because it prevents colds, to which people lying for a long time are most vulnerable. Wool brings the relief of pain in the spine, joints and muscles through the constant action of mild heat, which reduces their tension; and also improves blood circulation. Wool works prophylactically by stimulating the endings of the nervous and circulatory systems, thus increasing the body’s resistance. It makes us feel rested, and we do not succumb to excessive excitability [4,5,6,7].
The anti-bedsore sheet developed in the project is intended for patients without bedsores or hard-to-heal wounds who require long-term therapy in the lying position; and in addition it will be offered for recreational purposes to people not in treatment. A method of preserving the product consisting in removing impurities and possibly regenerating the antimicrobial protection was developed as part of the project. Sheep leather sheets with wool fleece, chrome-free tanned, were used to support and improve the effectiveness of therapy, reduce side effects during therapy, and reduce the effects of functional limitations of the users. In many cases, reduction in therapy costs will be achieved by shortening the therapy period. Anti-bedsore sheets made of sheep leathers with antimicrobial treatment will protect their users against the development of infection as well as the reinfection of the skin and its appendages [8,9,10,11,12,13].
The aim of the project was to develop the chrome-free tanning of sheep leathers with antimicrobiological protection for medical and therapeutic applications, which will be used as anti-bedsore sheets. The thematic scope of the tasks carried out included works related to the modification of glutaraldehyde tanning technology for sheep leather with long, thick hair, as well as works on the selection of biocide preparations and methods of their application to leather with fleece. Qualitative tests of physico-chemical parameters and antimicrobial activity were carried out on leathers obtained according to the newly developed technology of aldehyde-syntane tanning and syntane-vegetable re-tanning.
The research paper presents the results of tests, as well as the assessment of the quality and effectiveness of microbiological treatment of sheep leathers with fleece, from which anti-bedsore sheets were made. These sheets were then used by immobilized persons who had been lying for a long time, in order to test them.
The research was carried out as part of the research project POIR.02.03.02.-12-0048/20.
Sheep leathers with fleece, chrome-free tanned, antimicrobially protected according to three different methods of application of a preparation containing a zinc pyrithione formulation were selected for qualitative and microbiological tests.
The following leather samples protected with the preparation were tested:
The microbial resistance of the leather samples was tested on six selected species of microorganisms. The tests were carried out in relation to pathogenic as well as environmental bacteria and fungi often inhabit wool and leather products. Three species of bacteria, one species of yeast-like fungi, two species of filamentous fungi: mould, and dermatophytes were included in the study.
The bacteria included in the studies were
The fungi used were
The microbiological treatment of the leathers was carried out using an agent containing an active substance in the form of a zinc pyrithione formulation. The dose of the selected preparation used to obtain an antibacterial finish depends on the type of material, weight of the final product, and method of application.
Three application methods of the preparation with antimicrobial activity were used in technological tests of the biostabilization of sheep leathers with fleece:
Bathing method - in this method, a biocide agent was introduced into the sheepskins in the rinsing bath after tanning in the amount of 1.0% by weight of the dry leather, drying conditions- time: 72 h and temperature: 20 ± 1°C. Spray method- the aqueous solution with an agent containing an active substance prepared was applied by spraying with a pneumatic gun in a chamber for applying finishing to the leather. The biocide preparation was applied by spraying on both sides of the skin, i.e. on the side of the fleshy leather and on the side of the wool fleece, in the amount of 1% to the weight of dry skin. The preparation was cross-applied in three stages for even distribution of the active substance and better penetration of the solution into the skin and into the dense and high (35 mm) wool fleece. Subsequent sprays were made after drying the sheep leathers. The leathers were dried at room temperature for 24 h. Mixed method of bathing and spraying – in this method, two previously described methods were used to apply the biocide. The agent was introduced in the rinsing bath after tanning in the amount of 1% to the weight of dry leather, and then cross-sprayed with a gun, also in the amount of 1% to the weight of dry leather. As a consequence, the preparation was applied at a dose of 2% to the weight of dry sheep leather with fleece.
Tests of physical and chemical parameters, including strength, shrinkage temperature, chromium and formaldehyde content, pH of leather and wool, and others, were performed in accordance with Polish standards [27,28,29,30,31,32,33,34,35].
The sheep leather samples after treatment with a preparation containing a zinc pyrithione formulation and a control sample without microbiological treatment underwent microbiological testing in the form of the following:
Evaluation of resistance to bacteria and determination of the antibacterial effect of antibacterial treatment according to PN-EN ISO 20645: 2006 Textile fabrics - Determination of antibacterial activity - Agar diffusion plate test [36]. Evaluation of resistance to fungi and determination of the antifungal effect according to the PN-EN 14119: 2005 standard. Testing of textiles - Evaluation of the action of microfungi [37]. Method B2: Working samples are placed on an inoculated, complete agar medium (the agar contains a carbon source and fungal spores).
The research methodology was adapted to the type of material tested and to the nature of the growth of microorganisms selected. The tests were performed separate in duplicate for each sample. The working samples were circular, with a diameter of 25 ± 0.5 mm and tested on both sides, placing the samples on the surface of the agar once on the leather flesh side and then on the wool fleece side. Only unsterilised samples of leather were used. Blind test samples of identical sheep leather, but without treatment with biocidal preparation, were used to control the growth of microorganisms.
Bacterial cultures were carried out for 24 hours at a temperature of 37 ± 1 °C. After cultivation, microbial growth around and under the samples was observed. The antimicrobial effect was assessed in accordance with the recommendations of the standard [36]:
Fungal cultures were cultivated at 27 ± 1°C for 3 days ( 0 - no visible growth assessed under a microscope (magnification 50×) 1 - no visible growth without magnifying devices, clearly visible under a microscope 2 - visible increase without magnifying devices, covering up to 25% of the examination surface 3 - visible increase without magnifying devices, covering up to 50% of the examination surface 4 - significant increase, covering more than 50% of the tested surface 5 - heavy growth covering the tested surface.
Salt-preserved sheep skins from a slaughterhouse in Great Britain were used for technological trials of chromium-free tanning. Sheep leathers with fleece obtained according to the newly developed technology of aldehyde-syntan tanning and syntan-vegetable tanned were the subject of research and evaluation. In technological tests, the leather was treated with an antimicrobial agent containing a zinc pyrithione formulation.
In relation to the bioactive substance (zinc pyrithione) introduced into the product developed, skin compatibility was tested by the cytotoxicity test DIN EN ISO (10993-5) Institute Hohenstein. The substance has been accepted for the Oeko-Tex Label, Standard 100, Class I-IV - EPA, registration No. 3090-221 - Allergy UK approved [38].
All leather samples were impregnated with the same antibacterial agent but by three different methods.
The leathers tanned according to the newly developed tanning technology were characterized by a dense, high wool fleece and a uniform natural dyeing of the wool fiber in écru color. Although they had a compact structure of collagen fibers, they were soft.
The qualitative tests of the leather included physico-chemical parameters and microbiological tests.
Results of the tests of physical and chemical parameters for sheep leathers antimicrobially treated are presented in Table 1.
Test results of physical and chemical parameters for sheep skins protected with an agent containing a zinc pyrithione formulation.
1. |
Tear strength - along - across |
N |
206,4 188,5 |
≥ 100 | PN –EN ISO 3376:2012 |
2. |
Max. elongation - along - across |
% |
59,6 58,8 |
≥ 50 | |
3. |
Temperature of shrink - along - across |
ºC |
86 85,5 |
> 70 | PN-EN ISO 3380:2015-11 |
4. |
Abrasion resistance load 9 kPa - dry - wet |
number of cycles |
25 600 in the middle part of the samples, the fleece was abrasion to a height of about 10 mm, full fleece was observed at the periphery of the samples; 12 800 fulling of wool hair |
≥ 25 600 without skin damage ≥ 12 800 without skin damage |
PN-EN ISO 20344:2012 p.6.12 |
5. |
pH / number of differences - wool - skin |
- |
3,5 4,3 |
3,5–7,0 For pH < 4,00 number of differences ≤0,7 |
PN-EN ISO 4045:2018-09 |
6. | Water vapour permeability | mg/(cm2 h) | 11,43 | ≥ 4 |
PN-EN ISO 14268:2013-03 (water vapor permeability for leather) PN-EN ISO 17229:2016-05 (water vapor absorption) |
Water vapour absorption | mg/cm2 | 7,74 | not normalized | ||
7. | Water vapour coefficient | mg/cm2 | 99,2 | min. 33 | |
8. |
Seam tearing force - along - across |
N |
111,7 113,5 |
≥ 70 | PN-EN ISO 23910 |
9. | Formaldehyde | mg/kg | (58,1 ±0,8) | ≤ 75,0 | PN-EN ISO 17226-2:2019-05 |
10. | Chrome(VI) | mg/kg | undetectable 1/ | undetectable | PN-EN ISO 5398-2:2010 |
The sheep leathers with fleece demonstrated high tensile strength (along: 206.4 N, across: 188.5 N) and correct elongation at break (59.6 ÷ 58.8%), as well as high seam tearing strength (along: 111.7 N, across: 113.5 N). The leathers are characterized by high water vapour permeability (11.43 mg/cm2 h) and also a high water vapour coefficient (99.2 mg/cm2). It should be noted that sheep leathers with fleece obtained a satisfactory temperature, at which shrinkage of the samples occurred, as the shrinkage parameter was at the level of 86°C for samples cut along the leather and 85.5°C for samples cut across. The correct pH was found in chemical tests; for leather at the level of 4.3, while for wool the score was 3.5, and the number of differences was 0.5.
In the case of testing the abrasion resistance of leather from the last technological trial of tanning, an improvement in properties in this respect was observed. After completing the test of rubbing the skin with a wool fabric on Martindal’a apparatus with 25600 cycles, noticeable abrasion of the wool fleece on the surface of the skin samples in the middle part was found. In this place, there was abrasion of the hair to a height of about 10 mm, while a full fleece of 35 mm remained on the edges of the samples. Peeling of the fleece was observed on the surface of the samples during the test. In the case of testing the abrasion resistance of wool fleece of sheep leathers in wet conditions, after 12800 rubbing cycles, the peeling and fulling of wool hair were found.
The aim of the study was to determine the antimicrobial effect for 4 samples of sheep leather with chrome-free tanning (3 samples with microbiological protection and 1 control sample) in relation to selected species of bacteria and fungi. The microbiological resistance of the leather samples to the action of six selected species of microorganisms was tested in relation to pathogenic and environmental bacteria and fungi. Three species of bacteria, one species of yeast-like fungi and two species of filamentous fungi (mould and dermatophyte), were included in the study.
The test was performed in two repetitions for each sample. The leather samples were examined from each side (left side-flesh on the agar surface, right side-fleece on the agar surface). After measuring the zone of inhibition, working samples were removed from the agar surface with tweezers. The assessment of bacterial growth on the medium under the working sample was performed using a microscope, at a 20-fold magnification and bottom illumination, in accordance with the guidelines of the PN-ENISO 20645:2006 standard, presented in Table 1. The growth of fungi on the samples and in the agar medium was visually assessed according to the criteria presented in the PN-EN ISO 14119:2005 standard in chapter 11. Due to the specificity of the samples (high layer of the fleece), a microscopic evaluation of the fleece was not performed.
Results of testing the antibacterial activity of the leather samples against
Determination of the antibacterial activity of leather samples against bacteria:
1 | 0/0 | heavy/none | insufficient effect/good effect | 0/0 | heavy/none | insufficient effect/good effect | 0/0 | heavy/none | insufficient effect/good effect |
0/0 | heavy/none | insufficient effect/good effect | 0/0 | heavy/none | insufficient effect/good effect | 0/0 | heavy/none | insufficient effect/good effect | |
0/6 | heavy/none | insufficient effect/good effect | 0/7 | heavy/none | insufficient effect/good effect | 0/7,5 | heavy/none | insufficient effect/good effect | |
1,5/5,5 | none/none | good effect/good effect | 1,5/7 | none/none | good effect/good effect | 0/2,5 | none/none | good effect/good effect |
Results of tests of the antifungal activity of leather samples against
Determination of antifungal activity of leather samples against fungi:
0/0 | 1*/1 | 5/5 | 0/0 | 4/3 | 5/3 | 0/0 | 3/3 | 4/2 | |
0/0 | 1*/1 | 5/4 | 0/0 | 4/2 | 4/3 | 0/0 | 3/2 | 4/1 | |
0/0 | 1*/0 | 5/0 | 0/53 | 3/0 | 4/0 | 0/62 | 3/0 | 4/0 | |
54/65 | 0/0 | 0/0 | 0/29 | 0/0 | 0/0 | 71/59 | 0/0 | 0/0 |
Figures 4 and 5 visually demonstrate the tested samples on microbiological media on the day of the microbial growth reading.
The way in which the antibacterial agent is introduced into the leather samples significantly affects the antibacterial properties of the tested sheep leather with wool fleece. Leathers impregnated in a rinsing bath after tanning showed a much better antibacterial effect. An insufficient effect was observed on leathers impregnated by spraying for both the flesh and fleece side. The side of the leather which had direct contact with the surface of the agar medium showed a different effect on the growth of the test microorganisms. In the case of the flesh side of the spray impregnated leather, growth inhibition was observed only under the sample, in the place of contact with the agar. The flesh side of the leather after the rinsing inhibited the growth of all bacteria. This was evidenced by both a zone of inhibition around the sample and no growth under the working sample. In the case of the wool fleece side, no such effect was found for all the microorganisms used. Growth under the surface of the fleece of the sample was noticeable in every case tested, regardless of the application method of the antibacterial agent.
In the case of the flesh side of the leather, which was filled with a biocide in the rinsing bath after tanning, followed by spraying the same medium, inhibition of growth was observed both under the sample, in the place of contact with the agar, and around the working sample for all test microorganisms used. In the case of fleece, a slightly smaller effect was found, but still satisfactory for all microorganisms used. There was no growth under the sample and a slight zone of inhibition around the working sample for
The antifungal effect was found in the case of the flesh of the leather marked as test no. 3, which was preserved in the rinsing bath after tanning. Growth inhibition zones of all micro-fungi used in the tests were observed for this sample on the flesh side.
In the case of chrome-free tanning sheep leather, marked as sample No. 4, which was protected with a 2% antibacterial preparation using two methods of application (in a rinsing bath after tanning and additionally by spraying), effective antifungal activity was obtained for all fungi species used. Both sides of the leathers samples, both the fleshy and fleece side, inhibited the growth of pathogenic fungi:
The research work included the development of two bed-sheet construction solutions, technology for making anti-bedsore sheets, and the production of prototype sheets.
In order to develop a technological solution for the prototype sheet, the authors focused their attention on the sheet’s construction, the quality of the fleece of chrome-free tanned sheep leather (even the density of hair in the hair cover of the leathers, determining the height of the sheep leather fleece), selection of the appropriate softness of the leathers, and protection against shifting of the sheet during use.
Anti-bedsore sheets made of sheep leather with fur with chrome-free tanning and microbiological treatment were handed over for trial use by people lying in bed due to their health condition. Sheet users took part in testing, reviewing, giving opinions, and identifying needs for a new solution.
One of the users was a man who had been immobilized for a long time due to spinal ailments, lower limb paresis and joint degeneration, lying at home. The second user was a patient of a home for the elderly who suffers from generalized atherosclerosis, hypertension and insomnia.
Assessment of the comfort, convenience and durability of the newly developed bed-sheet construction, as well as the use of sheep leathers with a fleece of 35 mm height, chrome-free tanned for their production, was the purpose of carrying out functional tests of the sheets.
Based on the surveys conducted, it was found that matching the appropriate size of the sheet to the size of the couch is beneficial for the patient. The solution for attaching the sheets to the bed was recognized as very good, because the sheet was stable and did not move during use. The sheets are characterized by high aesthetics, with their edges trimmed. The seams connecting the elements of the sheet were imperceptible to users during its use and received a very good opinion from them.
The users of the sheets found the height of the fleece of the sheep leathers used for the anti-bedsore sheet appropriate. The dense and resilient wool hair of the fleece was not crushed during the use of the sheet, which was usually about 20 hours a day at an ambient temperature of 18÷21°C, for 2 months. The sheets did not become soiled during the entire period of use. Users (sick people) and staff caring for the sick emphasized the high quality of the sheets and the preservation of the fresh appearance during use. The sheets’ users deemed them very comfortable with high usability. Bedsores and other changes were not created on the skin of the sheet users. Both patients reported high comfort in all respects and great satisfaction with the use of the sheets. Anti-bedsore sheets received a positive assessment in the opinion of the doctors who provided medical care to the patients who were the users of those sheets.
Sheep leathers with fleece, after chrome-free tanning, reached a shrinkage temperature of 86°C with the required ≥70°C; pH 4.3 for the leather and 3.5 for the wool fleece with the required 3.5 ÷ 7.0.
All leather samples are characterized by high tensile strength, seam tearing, adequate abrasion resistance, high water vapour permeability and water vapour coefficient, a formaldehyde content of 58 mg/kg with the required ≤75 mg/kg, undetectable chromium (VI).
The mixed method was the most advantageous of the three methods of application of the microbiologically active substance to sheep leathers with fleece. This method included surfacing the leathers in a rinsing bath after tanning and cross-spraying on both sides of the leather.
Sheep leather protected with a preparation at a concentration of 2% showed a good antibacterial effect on the side of the flesh and wool fleece in relation to pathogenic bacteria:
Tests of the sheets made of the newly developed sheep leathers showed their usefulness during the therapy of chronically ill people lying for a long time, because the sheets contributed to the improvement of their comfort and gave a feeling of relief of ailments and rest.
The great satisfaction and high comfort of using the anti-bedsore sheets as well as good quality and aesthetics of workmanship, reported by users lying in bed for a long time, including their medical caregivers, allow the sheet to be assessed as comfortable for use by bedridden patients, in the prevention of sores and the formation of other skin lesions.