Chrome-Free Sheep Leathers with Antimicrobiological Protection for Medical and Therapeutic Applications

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:

Sample No. 1 - sheep leather with wool fleece - control sample

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 Staphylococcus aureus ATCC 6538 (gram positive), Staphylococcus aureus may cause purulent changes on the skin, contributing to bacterial infections of the skin [14,15,16];

Escherichia coli ATCC 11229 (gram negative) can colonize the skin and mucous membranes of the mouth and respiratory system, causing urinary tract infections and meningitis in newborns, and is one of the most common gram negative bacterium causing sepsis, especially among hospital patients, especially connected with nosocomial infections [17];

Pseudomonas aeruginosa ATCC9721 (gram negative), also known as blue oil rod, causes infections of the respiratory system, burn wounds, bones and soft tissues [18,19,20]

The fungi used were Candida albicans ATCC 90028 (pathogenic yeast, belonging to the etiological factors of skin mycosis; it infects wounds) [21], the filamentous fungi Aspergillus brasiliensis (niger) ATCC 16404 (mould, pathogenic species, causing lung aspergillosis, ear infections; easily colonises materials) [22], and Trichophyton mentagrophytes ATCC 18748 (pathogenic fungus, dermatophyte, which is the etiological factor of mycosis of the skin and nails of the feet and hands, difficult to treat) [23,24,25,26].

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: 1)

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.

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].

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]:

good effect - no growth;

Fungal cultures were cultivated at 27 ± 1°C for 3 days (A. brasiliensis) and 5 days (T. mentagrophytes). For yeast-like fungi, deep inoculation was used. A 1.5 McF suspension of C. albicans was prepared. Then, 2 ml of the suspension was transferred to 300 ml of liquid SGA at about 45°C and it was mixed thoroughly. 15 ml of liquid medium was poured into sterile Petri dishes with a diameter of 90 mm and allowed to solidify. Samples were placed on the solidified substrate and pressed with sterile tweezers, similarly as in the method for filamentous fungi. The samples were incubated for 24 hours at 35 ± 1°C. During and after the cultivation, the plates were observed with the unaided eye and under a stereoscopic microscope. Due to the specific nature of the samples (height of fleece layer), microscopic evaluation of the fleece was not performed. The fungal growth was evaluated on the basis of observations, according to the scale included in the standard [37]:

0 - no visible growth assessed under a microscope (magnification 50×)

Results of the tests of physical and chemical parameters for sheep leathers antimicrobially treated are presented in Table 1.

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 S. aureus, E. coli and P. aeruginosa are presented in Table 2 and Figure 1.

Fig. 1.

Results of tests of the antifungal activity of leather samples against C. albicans, A. brasiliensis and T. mentagrophytes are shown in Table 3 and Figures 2–3.

Fig. 2.

Fig. 3.

Figures 4 and 5 visually demonstrate the tested samples on microbiological media on the day of the microbial growth reading.

Fig. 4.

Fig. 5.

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.