The Influence of Propolis Nonwoven Scaffolds on Burn Wound’s Heparan Sulfates and Hyaluronan

Abstract

Innovative types of dressings should manifest biodegradability and non-immunogenicity and prevent dehydration. The mentioned technological features are demonstrated by polymeric, nonwoven propolis dressings, which exhibit regenerative properties, produced with the implementation of the electrospinning method. These features are highly needed in the course of burn wound healing. To analyze the dynamics of the changes in content of glycosaminoglycans (GAGs), such as heparan sulfates and hyaluronan, a well-known protocol of burn wound healing (the Hoekstra model) was used. Burn wounds were subsequently treated with nonwoven dressings containing either 5% wt or 10% wt propolis. Control groups were treated with either a saline salt solution or nonwoven dressings without propolis. Statistical differences between groups were determined by a multivariate analysis of variance (ANOVA) and Tukey’s post hoc tests. Evaluation of the effectiveness of nonwoven dressings containing 5% wt and 10% wt propolis in healing burn wounds, based on the dynamics and concentration of GAGs, revealed apitherapeutic positive effects on injured tissue healing. This research underscores the advantageous impact of utilizing nonwoven dressings containing propolis for the treatment of burn wounds.

1. Introduction

The process of tissue repair, regardless of the stimulus of the damage, involves highly coordinated, physiological, time-stretched, systemic responses. Irregular progression of the regeneration process leads to the development of chronic wounds, necrosis, or exaggerated scarring. Some disorders necessitate the assistance of dressings, particularly those possessing biodegradable, non-immunogenic properties, in the course of damaged tissue recovery. The forementioned special type of dressing constitutes an indispensable component of healthcare, playing a vital role in burn injury treatment [1]. Electrospun polymer nanofiber dressings are intended not only to protect the wound against the influence of the external environment but also to support the process of regeneration of damaged tissue [2]. The dressings in question allow both air and body fluids to flow into the wound, while blocking the access of microorganisms. In order to shorten the regeneration time of the damaged tissues, nanofibers with the addition of active substances are used [3].

An example of a substance of natural origin used in apitherapy is bee glue, i.e., propolis, in addition to honey, pollen, bee bread or royal jelly [4]. Among bee products, propolis is the most biologically active substance. Most reports in the literature regarding the discussed apitherapeutic agent focus on determining its chemical composition, as well as describing the antibacterial, antiviral, antifungal, antioxidant and anticancer activities of its extracts [4,5,6,7].

The mentioned properties of propolis also include regenerative and reparative effects (also on post-burn wounds) through the influence on the components of the extracellular matrix (ECM), i.e., glycosaminoglycans (GAGs), collagen, fibronectin, laminin and vitronectin. The ECM plays a crucial role in tissue integrity restoration, involving the coordinated action of various cells, including neutrophils, macrophages, fibroblasts, and epithelial and endothelial cells. These cells interact with ECM components through integrin receptors and adhesion molecules. During the repair process, ECM components form a temporary matrix, facilitating cellular adhesion, migration, differentiation, and proliferation. Additionally, ECM components regulate the organization and metabolism of the matrix itself. GAGs and proteoglycans (PGs) within the ECM bind with high affinity to cytokines, growth factors, and chemokines, thus playing a significant role in signal transduction. Changes in ECM composition during repair can affect reepithelialization, basement membrane regeneration, and intercellular communication. Understanding these mechanisms is pivotal for developing new therapeutic strategies in wound healing processes [8,9,10,11,12,13].

The recovery of thermal tissue injuries encompasses four overlapping “events”, including the hemostasis stage, inflammatory stage, proliferation stage, and maturation stage. Hemostasis occurs immediately after injury, where blood vessels constrict and clotting mechanisms are activated to prevent excessive bleeding. This is followed by the inflammation phase, characterized by the infiltration of immune cells such as neutrophils and macrophages, which work to remove debris and pathogens from the wound site. The proliferation phase then ensues, marked by the formation of granulation tissue, angiogenesis, and re-epithelialization. During this stage, fibroblasts play a critical role by synthesizing ECM components like collagen, which provide structural support for new tissue formation. Finally, the remodeling phase involves the maturation and reorganization of collagen fibers, leading to increased tensile strength of the healed tissue and restoration of normal skin architecture. Throughout these stages, the ECM not only provides a scaffold for cellular activities but also regulates various signaling pathways crucial for effective wound healing [14].

The above mentioned process requires close cooperation of components of the ECM, including glycosaminoglycans, such as heparan sulfates (HS) and hyaluronan (HA), during all phases of the healing process [14,15,16,17].

GAGs—present in all mammalian tissues—representing negatively charged, unbranched, linear molecules, previously known as mucopolysaccharides, consist of repeating disaccharide units.

GAGs (excluding HA) co-create in animal tissue PGs, in the structure of which GAGs are covalently linked to PGs’ core proteins [18]. The molecules in question play key roles encompassing, among others, modulation of migratory activity of cells, cell proliferative activity, and cell differentiation activity and orchestrate ECM assembly by shaping its structure and mechanical properties as a result of interactions with fibrous proteins, such as collagen and elastin [18,19,20,21,22,23,24]. In addition, they play an important role in maintaining homeostasis, e.g., by controlling and participating in wound healing processes or cell–cell interactions [25]. Moreover, the heteropolysaccharides in question also actively participate in selected metabolic “phenomena”, such as bone tissue mineralization or blood coagulation. Both free GAGs and PGs are ubiquitously distributed throughout mammalian ECMs [20].

HS and heparin, co-creating the family of heparan sulfate proteoglycans (HSPGs), are expressed on cellular membranes within secretory structures as well as within the extracellular milieu. Degradation of HSPGs is responsible for the occurrence of free HS, mainly in lysosomes, in the cell nucleus while simultaneously contributing to the formation of fundamental elements of the ECM, such as basement membranes [17,18,21,26,27,28,29,30,31].

HSPGs take part in cell–cell interactions and cell–ECM interactions, resulting in migration and adhesion of cells to ECM components, such as fibronectin, laminin, collagen types I, III, V, XV, and XVIII [32,33]. PGs of the mentioned type modulate, among others, white blood cells’ infiltration of the damaged tissue, triggering the sequence of events contributing to wound healing [30].

Heparan sulfate GAGs, through their presence, protect the vascular endothelium against damage [18,34,35]. HS, moreover, demonstrates anticoagulant and antiproliferative effects and stimulates the activity of lipoprotein lipase [22]. HS glycans, through interactions with ECM glycoproteins and tissue growth influencing molecules, modulate cellular division, new blood vessel formation, embryogenesis, and cancer development [36,37].

Both heparan sulfate and heparin PGs play a role in the development of inflammation that occurs in the course of tissue damage. They are an indicator of the effectiveness of the wound healing process. In the initial phase of wound healing, their content increases, which is crucial in the early phase of repairing tissue damage [8].

HA is a naturally occurring, unbranched polysaccharide chain composed of repeating disaccharide units [18,38,39,40,41]. The mentioned glycan occurs in all human body fluids, as well as in tissues. The highest HA accumulation can be found, among others, in the inner skin layer (between epidermis and subcutaneous tissue), cartilaginous tissue, viscous fluid of a joint space, the largest intraocular component, the tube-like flexible compartment connecting the fetus and placenta, renal tissue, muscular tissue, the lymphoid system, mucosa, and cerebral tissue [18,21,38,40,42,43,44].

The basic function of HA is to bind and retain water in the intercellular spaces, which increases the tissues’ resistance to mechanical injuries. Together with chondroitin sulfate, HA provides tissues with strength and elasticity [27]. HA is also implicated in the regulation of cell adherence and movement and exhibits antiphlogistic and free radical scavenging activity [18,19,26,45,46,47]. It is also used as a marker of some diseases (including rheumatism and cancer) [18,26,47]. Moreover, HA is successfully implemented in general surgery, esthetic medicine, ophthalmology, dermatology, orthopedics, gynecology, urology, neurology, and tissue engineering [18,48,49].

Tissue healing is a dynamic process, synchronized in time. The discussed process involves components of the ECM, including GAGs. Although the participation of these macromolecules in the tissue repair process has been described, the influence of dressing burn wounds with modern biodegradable dressings, also containing a natural bee product—propolis—on the transformation of glycan macromolecules in the bed of a burned wound has not been studied so far [11]. The mentioned bee product has already been used in the treatment of wounds, although these were carried out using conventional methods.

Therefore, the primary aim of the study was to assess the dynamics of changes in the content of the individual types of GAGs, such as HS and HA, in the bed of experimental burn wounds, induced in domestic pigs, treated with nonwoven dressings containing 5% or 10% propolis.

The research task undertaken to achieve the primary goal of this work was to compare the therapeutic effectiveness of nonwoven dressings containing and not containing propolis.

2. Materials and Methods

2.1. Biological Material

The Local Ethical Committee for Animal Experiments in Katowice gave consent to conduct this research. The experimental protocol took into account the application of the Polish Landrace breed. The initial stage of the mentioned experimental plan, encompassing the infliction of thermal damages on laboratory animals was conducted in the unit of the Medical University of Silesia in Katowice, established to carry out tasks in the field of experimental medicine. Thermal damages of the skin integument were performed according to the procedure described by Hoekstra et al. [50] and Brans et al. [51].

Sections were taken—for the extraction and quantitative assessment of sulfated (HS) and non-sulphated (HA) GAGs—from the skin not exposed to the action of the burning factor (control samples) and from the skin three, five, ten, fifteen, and twenty-one days after the generation of the wounds and managed with a biodegradable apitherapeutic (5% or 10% bee glue) formulation or subjected to physiological saline.

2.2. Development of Experimental Dressings

Biodegradable, biocompatible, apitherapeutic dressings were designed and manufactured as a result of cooperation between the Department of Biopharmacy of the Medical University of Silesia and the Center of Polymer and Carbon Materials, Polish Academy of Sciences.

The polymer dosage forms representing the subject of this study are nonwoven dressings (with characteristics of programmable release of the active substance) containing poly(lactide-co-glycolide) fibers formed using an advanced electrospinning technique. The regeneratory formulation in question, performed by the implementation of the electrospinning method, is characterized by a high surface-to-volume ratio and porosity and the ability to absorb exudate without accumulating it directly at the site of damage, which ensures good gas exchange and protects the wound against infections and dehydration.

2.3. Heparan Sulfate and Hyaluronan Extraction

The extraction of heparan sulfate and HA from GAGs present in shredded, dewatered, and degreased burned skin sections was carried out involving Scott’s laboratory procedure [52], with the application of Van Amerongen et al.’s [53] transformation, at the Department of Clinical Chemistry and Laboratory Diagnostics, Faculty of Pharmaceutical Sciences in Sosnowiec, Medical University of Silesia in Katowice.

2.4. Heparan Sulfate and Hyaluronan Quantitative Assessment

At the Department of Community Pharmacy, Faculty of Pharmaceutical Sciences in Sosnowiec, Medical University of Silesia in Katowice, the heparan sulfate and HA quantitative assessment in the obtained isolates of GAGs was realized throughout the implementation of the technique of target antigen capture in the biological material with the application of specific antibodies:

• The competitive inhibition enzyme immunoassay kit for Heparan Sulfate (HS), no. CEA161Ge—from Cloud-Clone Corp.
• The competitive inhibition enzyme immunoassay kit for Hyaluronic Acid (HA), no. CEA182Ge—from Cloud-Clone Corp.

2.5. Statistical Analysis

Dissimilarities between the groups (included in the experiment) were verified using multivariate analysis of variance (ANOVA) and Tukey’s post hoc tests and subsequently considered significant.

The compliance of the distributions of individual groups of results with the normal distribution was verified upon implementation of the Shapiro–Wilk W test. The assumption of homogeneity of variance (sphericity) was checked using Mauchly’s test. Due to the deviation from sphericity, a multivariate approach was applied to compare the average results obtained on subsequent days of the experiment. The arithmetic mean and standard deviation were selected as descriptive statistics. The analysis was performed using Statistica v. 13 software (TIBCO Software Inc. (2017). Statistica (data analysis software system), version 13. http://statistica.io, accessed on 15 February 2024).

3. Results

The content of HS and HA in normal skin and in the bed of burn wounds treated on subsequent days with nonwoven dressings or saline solution was estimated on the basis of the concentration values of the discussed GAGs in tissue homogenates. The results showing the content of the tested GAG fractions in individual tissue samples are presented in

Table 1. Content of HS in homogenates of tissue samples obtained from healthy skin and from burned wound beds on subsequent days of the wound healing process.

Content of HS [mg/g of Dry Tissue] in the Burn Wound
Days of Experiment	NaCl (n = 3)	Nonwoven without Propolis (n = 3)	Nonwoven with 5% Propolis (n = 3)	Nonwoven with 10% Propolis (n = 3)
Day 0 (normal skin)	0.095 ± 0.01	0.092 ± 0.015	0.118 ± 0.018	0.11 ± 0.02
Day 3	0.118 ± 0.022	0.115 ± 0.015	0.26 ± 0.015	0.305 ± 0.008
Day 5	0.125 ± 0.029	0.116 ± 0.013	0.216 ± 0.009	0.254 ± 0.013
Day 10	0.122 ± 0.024	0.126 ± 0.012	0.135 ± 0.015	0.154 ± 0.021
Day 15	0.107 ± 0.022	0.11 ± 0.014	0.11 ± 0.01	0.14 ± 0.014
Day 21	0.092 ± 0.014	0.1 ± 0.016	0.106 ± 0.01	0.120 ± 0.021

The presented numerical values represent the arithmetic mean of three measurements made each day ± standard deviation, taking into account the method of wound dressing.

and

Table 2. The content of HA in homogenates of tissue samples obtained from healthy skin and from burned wound beds on subsequent days of the wound healing process.

Content of HA [mg/g of Dry Tissue] in a Burn Wound
Days of Experiment	NaCl (n = 3)	Nonwoven without Propolis (n = 3)	Nonwoven with 5% Propolis (n = 3)	Nonwoven with 10% Propolis (n = 3)
Day 0 (normal skin)	0.646 ± 0.036	0.575 ± 0.02	0.677 ± 0.029	0.680 ± 0.04
Day 3	0.716 ± 0.072	0.83 ± 0.055	1.464 ± 0.076	1.865 ± 0.087
Day 5	0.773 ± 0.04	1.187 ± 0.033	2.767 ± 0.09	3.261 ± 0.11
Day 10	0.903 ± 0.038	1.869 ± 0.125	3.371 ± 0.076	3.996 ± 0.222
Day 15	1.234 ± 0.041	1.842 ± 0.064	2.874 ± 0.094	3.199 ± 0.086
Day 21	1.275 ± 0.038	1.675 ± 0.042	2.746 ± 0.049	3.093 ± 0.104

The presented numerical values represent the arithmetic mean of three measurements made each day ± standard deviation, taking into account the method of wound dressing.

.

3.1. Heparan Sulfates

The dynamics of changes in the content of HS during the healing of experimental burn wounds on subsequent days of treatment with nonwoven dressings containing 5% and 10% propolis are illustrated in Figure 1.

Statistical analysis revealed significant differences in the content of HS during the healing progression of burn wounds treated with a nonwoven dressing infused with both 5% and 10% propolis. Specifically, on days 3 and 5 of the wound healing process, there was a substantial increase in heparan sulfate levels (p < 0.001) within the burnt tissue compared to those present in healthy skin.

Based on the obtained results, it was found that the content of HS in the wound bed differed significantly during the healing of the wound treated with a nonwoven dressing containing both 5% and 10% propolis between the 3rd and 5th and the 5th and 10th day of therapy (p < 0.001).

The research showed that on day 15 (p < 0.05) of the repair process, the content of HS in the wound treated with a biodegradable dressing enriched with 10% propolis was significantly higher than in normal skin.

The statistical evaluation revealed a significant increase in the content of HS in the wound bed compared to the control skin (p < 0.05) on the 10th day of post-burn wound treatment with a biodegradable dressing without propolis. Moreover, no statistically significant differences were found in the content of the tested compound in a wound post-burn treated with a nanofiber dressing without propolis, between each day of the repair process.

There are no statistically significant differences in the content of HS in the post-burn wound treated with saline solution, between individual days of wound healing, compared to the content of HS in normal skin. There were also no differences in the HS content in the wound treated with NaCl solution on subsequent days of its healing process.

Figure 1 also illustrates the dynamics of changes in the content of HS during the healing of experimental burn wounds, on subsequent days of treatment, depending on the method of wound dressing.

The analysis conducted as a part of this study regarding the therapeutic impact on heparan sulfate content during the wound repair process revealed significant effects of 5% and 10% nonwoven dressings. Specifically, on the 3rd and 5th day of wound healing, these dressings led to a notable increase in heparan sulfate levels within the wound bed compared to those observed when the wound was washed with NaCl solution on the same days (p < 0.001).

3.2. Hyaluronan

The dynamics of changes in the content of HA during the healing of experimental burn wounds on subsequent days of treatment with nonwoven dressings containing 5% and 10% propolis are illustrated in Figure 2.

It was found that the content of HA was significantly higher in post-burn wounds treated with polymer nanofibers containing both 5% and 10% propolis on subsequent days, i.e., 3, 5, 10, 15, and 21 of the experiment (p < 0.001), compared to the amount of HA characterizing normal skin.

Statistical analysis revealed that during the healing of a burn wound treated with a nonwoven dressing containing 5% and 10% propolis, the content of HA in the wound bed differed significantly between the 3rd and 5th, 5th and 10th and 10th and 15th day of the experiment (p < 0.001).

The statistical analyses allowed us to determine a significant increase in the content of HA in the burn wound treated with a nonwoven dressing without propolis, on day 3 (p < 0.05), 5 (p < 0.001), 10 (p < 0.001), 15 (p < 0.001), and 21 (p < 0.001) of the experiment, referring to healthy skin.

The content of this glycan during the healing of a burn wound differed significantly between the 3rd and 5th (p < 0.001) and the 5th and 10th (p < 0.001) days after the exposure to the thermal factor.

The saline solution treatment resulted in a significant increase in the content of HA on the 10th (p < 0.05), 15th (p < 0.001), and 21st (p < 0.001) day of the experiment, compared to healthy skin.

As a result of the conducted research, it was found that the difference in the content of HA in the bed of thermal damage between individual days of healing of the wound washed with NaCl solution was significantly higher only between days 10 and 15 (p < 0.01).

A graphical illustration of the changes describing the individual contents of hyaluronan isolated from samples treated with different experimental factors is presented in Figure 2.

Figure 2 also illustrates the dynamics of changes in the content of HA during the healing of experimental burn wounds, on subsequent days of treatment, depending on the method of wound dressing.

The statistical analysis examining the impact of post-burn wound treatment methods on HA content revealed consistent findings. Across all days of wound treatment, whether with nonwoven dressings containing 5% or 10% propolis, there was a substantial increase in HA content within the damaged tissue bed (p < 0.001), in contrast to wounds treated solely with saline solution. On day 3 of post-burn wound healing, there was a significant effect of treatment with a nonwoven dressing without propolis on the content of HA in the wound, compared to the content of HA at the site of damage washed with saline solution (p < 0.05). Moreover, it was shown that a biodegradable dressing without propolis significantly increases the HA content in the bed of the burn wound on days 5, 10, 15, and 21, compared to the values observed in the wound on the same days of NaCl solution therapy (p < 0.001).

4. Discussion

This study demonstrated that during the healing of burn wounds, the content of HS in the injured tissue changes with different intensities and different dynamics, although with a similar tendency in each of the four experimental systems. It was observed, as in the case of previous experimental achievements of the co-authors of this manuscript, that from the onset of the burn injury until the 3rd day of the healing process, there was a notable rise in the content of HS in tissues treated with nonwoven dressings containing 5% and 10% propolis [10,11]. However, this increase was followed by a rapid decline in the concentration of these particular GAGs, persisting until the conclusion of the experiment on day 21. Strong changes were caused by 10% propolis. Changes in the HS content in wounds treated with nonwoven dressings not containing propolis or treated with sodium chloride were characterized by convergent trends and dynamics.

The findings from this study regarding the fluctuation in heparan sulfate content, specifically a transient increase observed in the ECM of the wound, align with the phenomenon described by Belvedere et al. [54]. This phenomenon, characterized by a transient increase in HSPG (heparan sulfate proteoglycan) expression during tissue repair, was similarly noted in our study and was particularly evident when treating burn wounds with polymer nanofibers infused with 5% and 10% propolis.

The cited authors used mesoglycan—consisting of GAGs (including HS)—to examine its effect on the repair of tissue damage. The above-mentioned authors observed a significant relationship between the migration of keratinocytes and fibroblasts during the healing of venous ulcers and the content of GAGs in the wound bed. The described studies indicated the involvement of HS in the course of repair phenomenon, throughout the orchestration of the movement, growth, division and specialization of cells initiating inflammatory responses and cells synthesizing ECM particles, as well as those playing a key role in reepithelialisation [54,55].

Studies by Olczyk et al. [10] also showed (visible in the first three days after the burn) a short-term increase in the content of HS in the bed of burn wounds treated with propolis, which confirmed the beneficial effect of the mentioned compound of natural origin on the tissue repair process.

The initial increase in HS content is crucial in the early stages of wound healing. After injury, HSPGs are degraded by heparanases [10,56]. The increase in the content of the glycan in question in the burned wound bed may be due to the antioxidant properties of propolis, which stimulates the activity of superoxide dismutase. This enzyme weakens the action of heparanase. At a later stage of the healing process, the HS content in the wound bed decreases, which is related to the subsequent stages of wound healing. The discussed HSs have a significant impact on the wound healing process. HSPGs occur in the intracellular space and extracellular matrix. HSs, which are part of syndecans, interact with growth factors, proteolytic enzymes, and protease inhibitors [10,56]. HSPGs have the ability to bind adhesion molecules, contributing to the modulation of pro-angiogenic effects in tissues (by stimulating IL-1, IL-6, PGE2, and TGF-β) and stimulating matrix reorganization, which contributes to fibrosis and subsequent scar formation [54,57,58]. HSs are involved in the process of transformation of fibroblasts into myofibroblasts and wound closure [10]. Research by Keil et al. [59] confirmed the involvement of HSPG in tissue regeneration—the authors observed that the increased synthesis of HS in the body of freshwater fish promotes the regeneration of vertebrate limbs. Zhou et al. [59] presented conclusions suggesting that HS has a positive effect on the regulation of angiogenesis in vivo—mice, in which HSPG deficiency was found in an experimental model, showed significantly delayed wound healing as a result of impaired angiogenesis.

Not only the above-mentioned HSs demonstrate significant impact on new blood vessel formation but the non-sulfated glycan HA does also—the evaluation of which in the course of healing represents an equally important aspect of the experimental protocol described in this publication.

As shown in this study, the content of HA in the bed of burn wounds undergoes changes during healing, the trends of which depend on the method of wound dressing. It was found that dressing wounds with nonwovens enriched with propolis—5% and 10%—leads to an increase in the HA content, progressing until the 10th day of the experiment, and then to a decrease and stabilization of the content of this glycan. The use of nonwoven dressings without propolis also led to an increase in the HA content, followed by a progressive decrease in the content of this GAG, starting after day 10. An increasing tendency in changes in HA content was demonstrated during healing in tissues treated with physiologic salt.

In vivo studies conducted by Siméon et al. [60], examining the effects of the complex comprising the tripeptide (gly-his-lys)-Cu²⁺ on tissue repair processes, demonstrate parallels between changes in HA content observed during the healing of skin damage in rats and the healing process of post-burn wounds investigated in our study. The mentioned results illustrated an early intensification of HA isolation from rat skin tissue samples with a subsequent reduction in HA in the final phase of the experiment. Hamed et al. [61,62] described the effect of local applications of erythropoietin on the healing of post-burn wounds in animals with experimentally induced diabetes, which was reflected in the stimulation of an increase—by this renal hormone—in the HA content in the wound bed in the initial phase of the healing process. The consequence of this change was an accelerated wound healing process resulting from the stimulation of angiogenesis, reepithelialization, and collagen synthesis and, on the other hand, inhibition of the inflammatory response and apoptosis [61,62].

The analysis of HA’s extractability from the matrix of thermal skin injuries, performed and characterized in this manuscript, corresponds to the results previously described by Olczyk et al. [11]. The last mentioned experimental findings encompassing bee glue’s impact on glycosaminoglycan expression in the matrix of burn injuries indicated analogous insights into HA fluctuations during the repair phenomenon. The cited studies showed that in the initial phase of the experiment, there was an increase in the HA content in the wound bed treated with an ointment containing propolis and then—in the final phase—a decrease in the HA content. The observed tendency of HA content changes can be explained by the bee glue-stimulated enhanced biosynthesis of transforming growth factor-beta modulating the fibroblasts to produce the non-sulfated glycosaminoglycan [11].

The glycan in question is a compound abundantly present in the wound environment. It has been shown that HA is intensively synthesized by fibroblasts in the initial period of healing (for about 2 weeks from the moment of injury) and then—in the final phase of tissue healing—the content of this GAG in the wound bed is reduced [58].

HA can bind to specific proteins that are surface receptors of ECM cells. The most frequently described cell surface receptors include CD44, RHAMM (receptor for HA mediated motility), and ICAM-1. CD44 glycoprotein mediates the processes of migration, aggregation, cell adhesion and proliferation, angiogenesis, cell signaling, and the degradation of HA; RHAMM mediates cell migration and proliferation, while ICAM-1 is involved in the activation of inflammatory processes [63]. The nonsulfated glycan in question—functioning as a pivotal molecule in the course of connective tissue regeneration—modulates systemic reaction to infection/injury and formation of a provisional matrix (composed of fibroblasts, macrophages, and endothelial cells together with collagens and fibronectin) and resurface tissue injury by the novel epithelium formation [64,65,66,67]. HA is also involved in tissue repair and serves as an integral part of the extracellular matrix, also promoting the proliferation and migration of keratinocytes in the process of reepithelialization. Keratinocyte migration is necessary to re-epithelialize the wound and to restore the continuity of damaged skin [54,68].

Oksala et al. [65] found that HA and CD44 are localized in the same region of the epithelium (around mucosal keratinocytes) at all stages of human mucosal wound healing, participating in reepithelialization during the tissue repair process.

The research conducted in this study demonstrated a notable positive impact of nonwoven polymer dressings enriched with a natural active substance, namely propolis, particularly at a higher concentration (10%), on the healing mechanisms of burn wounds. The latter observation may potentially be explained by the significantly increased accumulation and intensity of extractability of molecules previously referred to as mucopolysaccharides, from the matrix of experimental thermal injuries. This contrasted with the biochemical profile observed in wounds treated solely with nonwoven dressings devoid of the incorporated active substance [69,70].

To minimize the risk of improper healing and excessive scarring, the best possible healing conditions should be ensured, which becomes possible as a result of the implementation of modern polymer dressings containing medicinal substances incorporated into therapeutic procedures [69]. As shown in this study, the use of PLGA nonwoven dressings containing propolis may prove to be an effective therapy for burn wounds [70].

5. Conclusions

Assessment of the regenerative effectiveness of a nonwoven dressing containing 5% or 10% propolis in the healing process of thermal damage, based on the examination of the dynamics and degree of increase in the content of HS and HA compared to the assessment of the dynamics of changes in the discussed glycans in wounds treated with the nonwoven polymer without bee glue, indicated the beneficial effect of the dressing incorporated with a natural bee product—propolis—on the process of tissue damage repair. The beneficial effect of a polymer nanofiber enriched with a pluripotent raw material on the burn wound healing process was the intensification and acceleration of these compounds’ accumulation in the matrix of the thermal injury, which supports the regeneration phenomenon.