Proanthocyanidins from Vaccinium vitis-idaea L. Leaves: Perspectives in Wound Healing and Designing for Topical Delivery

The compositions and health-beneficial properties of lingonberry leaves (Vaccinium vitis-idaea L.) are well established; however, their proanthocyanidins are still heavily underutilized. Optimizing their delivery systems is key to enabling their wider applications. The present study investigates the phytochemical and ‘wound-healing’ properties of proanthocyanidin-rich fraction(s) (PRF) from lingonberry leaves as well as the development of optimal dermal film as a proanthocyanidin delivery system. The obtained PRF was subjected to HPLC-PDA and DMAC analyses to confirm the qualitative and quantitative profiles of different polymerization-degree proanthocyanidins. A ‘wound healing’ in vitro assay was performed to assess the ability of PRF to modulate the wound environment for better healing. Low concentrations of lingonberry proanthocyanidins were found to accelerate ‘wound‘ closures, while high levels inhibited human fibroblast migration. Fifteen dermal films containing PRF were prepared and evaluated based on their polymer (MC, HEC, PEG 400) compositions, and physical, mechanical, and biopharmaceutical properties using an experimental design. The composition containing 0.30 g of MC, 0.05 g of HEC, and 3.0 g of PEG 400 was selected as a promising formulation for PRF delivery and a potentially effective functional wound dressing material, supporting the need for further investigations.


Introduction
Lingonberry (Vaccinium vitis-idaea L.), a small evergreen shrub of the family Ericaceae, is among the best natural sources of bioactive compounds with beneficial health effects [1]. This plant is particularly valued for its content of proanthocyanidins, representing up to 71% of the total phenolic compounds [2]. Proanthocyanidins, also known as condensed tannins, are colorless flavonoids composed of flavan-3-ol units. These phenolic compounds are considered safe and effective natural antioxidants. Extensive research has indicated that proanthocyanidins exhibit anti-inflammatory, immunomodulatory, anticancer, antibacterial, and hypolipidemic activities [3][4][5][6][7]. They possess systemic as well as topical action. Skin care products with proanthocyanidins have anti-UV, anti-aging, brown spot-lightening, and anti-wrinkle effects [8,9]. Recently, proanthocyanidins were found to hasten the wound contractions and closure processes [10,11]; they are seen as promising candidates for the development of new dermal forms for wound healing.

'Wound-Healing' Properties of PRF
The additional cytotoxicity experiment by the MTT assay was performed on human foreskin fibroblast (HF) to evaluate the PRF effect on HF viability in the range of concentrations from 3.9 to 125 µg/mL ( Figure 2). It was found that PRF at a concentration of 20 µg/mL reduces HF viability up to~10% even after 72 h of incubation. Thus, the RPF effect on HF migration was tested at 20, 10, and 5 µg/mL concentrations, with expectations not to significantly reduce the cell proliferation.

'Wound-Healing' Properties of PRF
The additional cytotoxicity experiment by the MTT assay was performed on human foreskin fibroblast (HF) to evaluate the PRF effect on HF viability in the range of concentrations from 3.9 to 125 µg/mL ( Figure 2). It was found that PRF at a concentration of 20 µg/mL reduces HF viability up to ~10% even after 72 h of incubation. Thus, the RPF effect on HF migration was tested at 20, 10, and 5 µg/mL concentrations, with expectations not to significantly reduce the cell proliferation. The PRF showed a concentration-and time-dependent effect on HF migration by the 'wound healing' assay ( Figure 3). The stronger effect and smaller area of the 'wound'are seen after a longer incubation. The highest tested concentration of 20 µg/mL most efficiently (1.8-fold) inhibited the cell migration ('wound' area after 20 h was 39.5 ± 11.4%), while the lowest concentration of 5 µg/mL statistically significantly increased (1.6-fold) HF migration (the 'wound' area after 20 h was 13.3 ± 4.1%), compared to the control (the 'wound' area after 20 h was 21.8 ± 2.3%). The PRF showed a concentration-and time-dependent effect on HF migration by the 'wound healing' assay ( Figure 3). The stronger effect and smaller area of the 'wound'are seen after a longer incubation. The highest tested concentration of 20 µg/mL most efficiently (1.8-fold) inhibited the cell migration ('wound' area after 20 h was 39.5 ± 11.4%), while the lowest concentration of 5 µg/mL statistically significantly increased (1.6-fold) HF migration (the 'wound' area after 20 h was 13.3 ± 4.1%), compared to the control (the 'wound' area after 20 h was 21.8 ± 2.3%).

Thickness of Films
Quality parameters of experimental methylcellulose-hydroxyethyl cellulose (MC-HEC) films are given in Table 1. The thickness of the experimental polymeric films was in the range of 262-522 µm. The MH0.350-P2.0 film (No. 13) had the lowest thickness (262 ± 18 µm). This film did not differ statistically significantly (p ≥ 0.05) from MH0.400-P2.0 (No. 6) and MH0.400-P2.0 (No. 10) films with thicknesses of 285 ± 13 µm and 304 ± 6 µm, respectively. The MH0.425-P2.5 film (No. 9) had the highest thickness (522 ± 33 µm). This film differed statistically significantly (p < 0.05) from other experimental MC-HEC films. It appeared that, as the amount of PEG 400 in the film increased, its thickness increased. This was confirmed by a statistically significant (p < 0.05) moderate correlation (r = 0.624) between the amount of PEG 400 and film thickness. Note: *-MH is a mixture of polymers (MC, HEC), the number next to it indicates the total amount (g), P is PEG 400, and the number next to it indicates its amount (g).
It was found that as the amount of PEG 400 in the film increased, the moisture content in it decreased ( Figure 4). This was confirmed by a statistically significant (p < 0.01) and very strong correlation (r = −0.918) between the amount of PEG 400 and the moisture content.
It was found that as the amount of PEG 400 in the film increased, the moisture content in it decreased ( Figure 4). This was confirmed by a statistically significant (p < 0.01) and very strong correlation (r = −0.918) between the amount of PEG 400 and the moisture content.

Stickiness of Films
The stickiness of the experimental MC-HEC films ranged from 0.143 to 0.419 N ( Table  1)
The MH0.400-P3.0 film (No. 3), containing 0.30 g of methylcellulose, 0.10 g of hydroxyethyl cellulose, and 3.0 g of PEG 400, had the highest stickiness (0.419 ± 0.012 N). This film did not differ statistically significantly (p ≥ 0.05) from MH0.350-P3.0 (No. 14) and MH0.400-P3.0 (No. 5) films with a stickiness of 0.412 ± 0.027 N and 0.386 ± 0.024 N, respectively. It was found that by increasing the amount of PEG 400 and decreasing the amount of methylcellulose in the film, its stickiness increased ( Figure 5). However, only a statistically significant (p < 0.01) strong correlation (r = 0.851) was found between the amount of PEG 400 and film stickiness. Results showed that as the moisture content of the film decreased, its stickiness increased. This was confirmed by a statistically significant (p < 0.01) strong correlation (r = −0.751) between the moisture content and film stickiness.
Plants 2022, 11, x FOR PEER REVIEW 6 of 17 film did not differ statistically significantly (p ≥ 0.05) from MH0.350-P3.0 (No. 14) and MH0.400-P3.0 (No. 5) films with a stickiness of 0.412 ± 0.027 N and 0.386 ± 0.024 N, respectively. It was found that by increasing the amount of PEG 400 and decreasing the amount of methylcellulose in the film, its stickiness increased ( Figure 5). However, only a statistically significant (p < 0.01) strong correlation (r = 0.851) was found between the amount of PEG 400 and film stickiness. Results showed that as the moisture content of the film decreased, its stickiness increased. This was confirmed by a statistically significant (p < 0.01) strong correlation (r = −0.751) between the moisture content and film stickiness.

Proanthocyanidins Release from Films
The release kinetics of proanthocyanidins from experimental MC-HEC films are shown in Figure 6. The release profiles of these compounds corresponded to a zero-order model (R 2 = 0.9657-0.9942), which shows a linear relationship between the total released amount of proanthocyanidins (%) and the duration of the process (h).

Proanthocyanidins Release from Films
The release kinetics of proanthocyanidins from experimental MC-HEC films are shown in Figure 6. The release profiles of these compounds corresponded to a zero-order model (R 2 = 0.9657-0.9942), which shows a linear relationship between the total released amount of proanthocyanidins (%) and the duration of the process (h).
Experimental Statistical analysis showed a statistically significant (p < 0.01) moderate inverse correlation (r = −0.643) between the amount of hydroxyethyl cellulose in the films and the released amount of proanthocyanidins after 4 h.

Selection of the Film
After the analysis of the data on thickness, moisture, stickiness, and release (0.25, 0.5, 0.75, 1, 2, 3, and 4 h), only statistically significant linear models of moisture, stickiness, and release after 0.25 h were obtained (Section 4.6.1). These quality parameters were selected as optimization criteria. According to them, the composition of the polymeric films with the highest desirability value (0.869) was obtained, which shows the percentage compliance with the set criteria (in our case it would be 86.9%): 0.30 g of MC, 0.05 g of HEC, and 3.0 g of PEG 400. Table 2 shows theoretical and experimental values of the physical, mechanical, and biopharmaceutical properties of this film. Statistical analysis showed a statistically significant (p < 0.01) moderate inverse correlation (r = −0.643) between the amount of hydroxyethyl cellulose in the films and the released amount of proanthocyanidins after 4 h.

Selection of the Film
After the analysis of the data on thickness, moisture, stickiness, and release (0.25, 0.5, 0.75, 1, 2, 3, and 4 h), only statistically significant linear models of moisture, stickiness, and release after 0.25 h were obtained (Section 4.6.1). These quality parameters were selected as optimization criteria. According to them, the composition of the polymeric films with the highest desirability value (0.869) was obtained, which shows the percentage compliance with the set criteria (in our case it would be 86.9%): 0.30 g of MC, 0.05 g of HEC, and 3.0 g of PEG 400. Table 2 shows theoretical and experimental values of the physical, mechanical, and biopharmaceutical properties of this film. These selected compositions of the polymeric films corresponded to composition No. 14 of the experimental design; the practical values for the appropriate properties are given in Table 3. The experimental stickiness value of the optimal composition of the MC-HEC film was 4.6% lower than the theoretical value. The experimental values of moisture and release after 0.25 h were 2.3% and 20% higher than the theoretical values, respectively.  Note: *-MH is a mixture of polymers (MC, HEC), the number next to it indicates their total amount (g), P is PEG 400, and the number next to it indicates its amount (g).

Discussion
The interest in utilizing proanthocyanidins in the pharmaceutical industry has considerably increased over time with the discovery of their beneficial functions [27]. One possible approach is via skin application and incorporation into dermal formulations, such as polymeric films, which offer many advantages in terms of effective drug delivery and improved patient compliance [19,20]. However, to design an efficient thin film for the treatment of skin conditions, the following are needed: the purification of phytoconstituents, qualitative and quantitative analyses, biological property evaluations, and optimization of film formulations [24]. These steps were taken during the present study to model the polymeric film containing lingonberry proanthocyanidins with potential wound-healing properties.
Lingonberry fruits are highly valued in the food and nutraceuticals industry, while leaves, despite the considerable richness of proanthocyanidins and availability during all seasons, are still hardly used [28]. Due to the complexity of the matrix of lingonberry leaves, fractionation using Sephadex LH-20 was suggested, resulting in the proanthocyanidinsbounded fraction [29]. Present HPLC-PDA results showed that the PRF fraction was rich in different polymerization degree compounds: monomeric flavan-3-ols, and A-or B-type dimers and trimers. One primary problem with the analysis of proanthocyanidins is that due to the complexities of the structures and different linkages, the results of analytical procedures can often be erroneous, non-reproducible, non-selective, or not quantifiable [30]. Previously, PRF was additionally analyzed by our research group using the UPLC-PDA/ESI-QTOF-MS method to confirm the identity of proanthocyanidins and suggest more A-type procyanidin trimers [31]. Other studies indicated that oligomeric (mDP 4-10) and polymeric (mDP > 10) proanthocyanidins can be found in the lingonberry matrix as well [2,32], thus suggesting unidentified larger polymeric molecules in our tested sample. Nevertheless, liquid chromatography coupled to photodiode-array or mass detection may be useful for authentication, but it is not suitable for accurate quantification since not all analytical standards are available and response factors for the individual polymers are unknown [33,34]. Quantification problems are usually overcome by the DMAC spectrophotometric assay, which is regarded as a simple, rapid, robust, and relatively specific technique for the evaluation of the total amount of proanthocyanidins [34][35][36]. The DMAC analysis used in the present study revealed much more proanthocyanidins in the fraction of lingonberry leaves than determined with the HPLC-PDA method, showing that not all proanthocyanidins were identified. Therefore, the DMAC assay was chosen for further analysis of polymeric films containing proanthocyanidins. The literature pertaining to the biological activities of proanthocyanidins strongly suggests possible application in wound healing [10,37]. Wound healing comprises many processes, such as hemostasis, coagulation, inflammation, proliferation, epithelialization, contraction of the wound, and others, thus involving not only recovery of skin barrier integrity, but also suppression of inflammation and secondary complications [12,17,21]. Consequently, the main effects of plant secondary metabolites working toward wound healing can be addressed as cell migration and proliferation as well as antimicrobial, antiinflammatory, and antioxidant activities [17]. Previously, our group reported that PRF from lingonberry leaves surpassed all other phenolic fractions and crude extracts by the highest antioxidant, anti-inflammatory potential, and strongest antimicrobial properties [31]. In addition, cytotoxic PRF activity has been established in a previous experiment against human colon adenocarcinoma HT-29, renal carcinoma CaKi-1, and melanoma IGR39 cell lines, and was in the range from 30 to 50 µg/mL [29]. Thus, it was expected that PRF could also affect the viability of human fibroblasts, which serve pivotal roles in extracellular matrix reorganization during wound contractions. Fibroblast migration to (and proliferation within) the wound sites is critical for granulation and the end state of the wound [38,39].
A PRF fraction at 20 µg/mL and lower concentrations did not significantly reduce the viability of HF, indicating that proanthocyanidins do not decrease fibroblast proliferation and functions and do not delay epithelization. Obtained concentration-and time-dependent inter-relationships on HF migration by 'wound healing' assays correlate well with previous findings [40,41], wherein the effects of plant extracts on fibroblast migration were established. Similarly, the highest effects in most studies were established after longer incubations, e.g., 24 h [42]. Our study showed that only low concentrations (5 µg/mL) of proanthocyanidins significantly increased HF migration to the 'wound' bed. In line with these results, the study by Hemmati et al. [43] showed that the lowest tested concentration (2%) of grape seed extract rich in proanthocyanidins improved and accelerated the contraction and closure of wounds, shortening the healing time, while high concentrations (70%) had no promotive effect. This postulates that only small quantities of complex tannins can actively participate in and modulate the wound environment for faster healing. Han et al. [44] reported that low concentrations of proanthocyanidins are optimal for maximal cross-linking of collagen tissue and, thus, increasing the migration of fibroblasts. On the other hand, our obtained fibroblast migration inhibiting effects on high concentrations (20 µg/mL) of PRF can also be favorable in excessive fibroblast activity, which can be detrimental to wound healing, leading to complications, namely hypertrophic scarring, keloid formation, and contractures [45]. Some authors have also suggested that proanthocyanidinrich extracts may trigger the release of vascular endothelial growth factor [43], elevate the expression of collagen type 1 in fibroblast [42], or enhance 'wound healing' by mobilizing the fibroblast in the wound site [10]. Since proanthocyanidins work by multiple mechanisms and are involved in more than one phase of the wound healing process in a positive manner, the PRF could be used as a tool to promote tissue regeneration when incorporated into skin formulations, such as dermal films.
Thin films are receiving attention for drug delivery [46]. Pharmaceutical scientists throughout the world are working on the formulation and development of these dermal systems [24]. Ideal dermal films should have sufficient drug loading capacities, fast dissolution rates, long residence times at the sites of administration, adequate flexibility, thickness, moisture, stickiness, and acceptable physicochemical stability [24,46]. An additional important implication is the selection of polymers and plasticizers, which are defined as the backbone of dermal films and should be safe, non-irritant, and non-toxic [24,25]. Our study analyzed the impacts of polymers MC, HEC, and plasticizer PEG 400 on film thickness, moisture, stickiness, and release of the active substance. Methylcellulose and hydroxyethyl cellulose are excellent, non-toxic, and non-allergenic polymers used as film forming agents and drug carriers that produce moderate strength and good flexibility in thin films with less water vapor barriers due to their hydrophilic nature, which aids in water retention [47,48]. Additionally, polyethylene glycol as a plasticizer is commonly used to impart flexibility, reduce brittles, and enhance other mechanical properties of polymeric films [49]. However, to achieve these effects, the composition and ratio between different polymers, as well as plasticizers, have to be optimized [50].
Panchal et al. [51] pointed out that the amount of plasticizer is critical for film formation and separation properties. Our results indicated that as the concentration of PEG 400 increases, the thickness and stickiness of polymeric film increase as well, while the moisture content in it decreases. Lower moisture can decrease the bulkiness and risk of microbial attack [52], while too high of a film thickness may lead to decreased hardness and increased peeling degree of the film [53]. In other studies [25,54,55], polyethylene glycol appeared to have a direct relationship with adhesiveness, hardness, elasticity, and tensile strength. Contents of polymer MC and HEC were found to be more related to release and diffusion processes. Since most proanthocyanidins are water-soluble polyphenolics [56], the determination of their release properties is of great significance. Our obtained negative correlation between HEC content in films and the released amount of proanthocyanidins was partly in line with the study [25], wherein the authors concluded that HEC concentration should not exceed 2% for optimal release of active substances from HEC-based matrix films. Even though HEC is highly hydrophilic, and hydroxyethyl groups attached to the anhydroglucose units by ether linkages decrease the crystallinity of the active substance (increasing solubility in water) [57], it has sustained release and limited swelling properties [58,59]. The release mechanisms from swellable hydrophilic polymers, such as HEC or MC, are determined by the acceptor medium penetration throughout polymer chains, relaxation degree of hydrated polymers, diffusion of the active substance within swollen media, and possible erosion. When the hydrated viscous layer is formed around the polymers, it may act as a barrier, provoking water penetration from dissolving active substances [55,60].
In general, our selected composition of the polymeric film with the highest ratio between the polymer mixture and PEG 400 (1:8.6), when the polymer mixture was predominated by MC, provided acceptable moisture, stickiness, and 56.5% practical release of proanthocyanidins after 4 h and, therefore, could be regarded as a promising tool for PRF delivery. This and previous reports [10,61,62] indicate that topical application of proanthocyanidins may improve wound healing and histological reorganization of the injured tissues. Nevertheless, there are further concerns that have to be addressed, such as the penetration of proanthocyanidins into the skin, excessive hydrophilicity, high reactivity, safety, chemical instability, and ionizability [63][64][65]. Dermal films must be designed without forgetting that skin permeation is a key factor for effective formulation [64]. This may constitute the object of future studies.

Plant Material
The proanthocyanidin-rich fraction was obtained from the lingonberry (Vaccinium vitisidaea L.) leaves using column chromatography as described previously [29]. Lingonberry leaves for purification were collected from different natural sites in September 2019 in northeast Lithuania and then pooled. Briefly, a crude dry extract of lingonberry leaves was prepared by ultrasonic extraction using air-dried grounded leaves and 80% acetone (the sample/solvent ratio of 1:25), followed by vacuum evaporating and freeze-drying. The obtained light brown powder was dissolved in 50% methanol (1:40), applied to a glass column pre-loaded with Sephadex LH-20 (GE Healthcare Biosciences, Uppsala, Sweden), and washed with two columns of water to remove non-phenolic lingonberry constituents, phenolic acids, arbutin, and four columns of 50% ethanol to elute flavonols. The bound fraction, which was enriched in proanthocyanidins, was eluted with two volumes of 70% acetone. PRF was freeze-dried to obtain the yellowish powder, analyzed, and incorporated into experimental films.

Chemicals and Solvents
Analytical and chromatographic grade solvents were used for this study: acetonitrile, methanol, acetone, acetic acid, hydrochloric, and trifluoroacetic acid from Sigma-Aldrich (Steinheim, Germany), ethanol from Vilniaus degtine (Vilnius, Lithuania). Ultrapure water was obtained by a Milli-Q water purification system from Millipore (Bedford, MA, USA).

Cell Culture
The human foreskin fibroblasts (HF) CRL-4001 were originally obtained from the American Type Culture Collection (ATCC, Manassas, VA, USA) and kindly provided by Prof. Helder Santos (University of Helsinki, Finland). HF were cultured in Dulbecco's Modified Eagle's GlutaMAX medium (Gibco), supplemented with 1% of antibiotics (10,000 U/mL penicillin, 10 mg/mL streptomycin (Gibco)), and 10% fetal bovine serum (Gibco). Cell cultures were grown 25 cm 2 falcons at 37 • C in a humidified atmosphere containing 5% CO 2 , and were used until the passage of 10.

HPLC-PDA Method
Screening of individual proanthocyanidins and other tannins in the obtained fraction from lingonberry leaves was performed with HPLC-PDA (Waters e2695 Alliance system, Waters, Milford, MA, USA) system using ACE Super C18 (250 mm × 4.6 mm, 3 µm) column (ACT, Aberdeen, UK) and gradient elution consisting of 0.1% trifluoroacetic acid (eluent A) and acetonitrile (eluent B) [29]. Elution formed as follows: 0 min, 90% A; 0-40 min, 70% A; 40-60 min, 30% A; 60-64 min, 10% A; 64-70 min, 90% A at a flow rate of 0.5 mL/min. The injection volume of the sample was 10 µL, and the column temperature was maintained at 35 • C. The identification was made by comparison of retention times and spectra with those of commercially available proanthocyanidins.

DMAC Method
The total proanthocyanidin content in the PRF (before incorporating) and polymeric films (during in vitro release test) was evaluated using a DMAC assay with slight modifications [35]. Three milliliters of DMAC reagent (0.1% in acidified ethanol) were mixed with 20 µL of PRF or samples from in vitro release test and kept for 15 min. The absorbance was measured at 640 nm wavelength using a spectrophotometer (Spectronic CamSpec M550, Garforth, UK), when the reference solution was-3 mL of DMAC and 20 µL of distilled water. The total proanthocyanidin content is expressed as milligrams of procyanidin A2 equivalents per gram of dry weight of fraction (mg A2/g DW).

'Wound Healing' Assay
The PRF effect on human fibroblast migration was assessed using the 'wound healing' assay, as described elsewhere [66]. After trypsinization, HF cells were seeded in 24-well plates at a density of 4 × 10 4 cells/well and incubated for 48 h at 37 • C in a humidified atmosphere containing 5% CO 2 . Then the scratch was made using a 100 µL pipette tip. The cells were washed once with PBS, and the fresh medium containing different concentrations of PRF was added. The final extract concentrations were: 20, 10, and 5 µg/mL. For the selection of these PRF concentrations, the effect on HF cells was performed using a standard 4.6.5. Stickiness Measurement The stickiness of the experimental films (50.24 cm 2 ) was measured at several random locations (n = 4) using a texture analyzer (TA.XT plus, Godalming, UK) with a mucoadhesion rig (A/MUC) and expressed in N. Conditions for the texture analysis: (1) The pre-test speed was 1 mm/s. (2) The test speed was 0.5 mm/s. The experimental films (1.77 cm 2 , 0.099-0.187 g) were placed in Eppendorf ® centrifuge tubes (2 mL) and filled with 2 mL of purified water. The tubes were stored at 32 • C (normal skin surface temperature). Samples were taken after 0.25, 0.5, 0.75, 1, 2, 3, and 4 h by adding the same volume of fresh acceptor medium. Release samples were analyzed spectrophotometrically (Section 4.4.2). The amount of PRF released was calculated from the determined concentration of PRF in the samples and expressed in % and flux (µg/cm 2 ).

Statistical Analysis
The results of our studies are presented as mean ± standard deviation. Statistically significant differences were found using one-way ANOVA when the post hoc criterion was Tukey HSD. The correlation was assessed by Spearman's rank correlation coefficient. The significance level was α = 0.05.

Conclusions
The phytochemical profile and wound-healing properties of PRF from lingonberry leaves were evaluated and an optimal dermal film as a drug delivery system was developed. The considerable richness of proanthocyanidins was confirmed by HPLC-PDA and DMCA methods, while the 'wound healing' assay suggested that low concentrations of lingonberry proanthocyanidins may increase human fibroblast migration to the 'wound' bed. Fifteen compositions containing PRF and different concentrations of HEC, MC, and PEG 400 were formulated in order to develop dermal film for the possible wound-healing effect. The experimental design showed that the most appropriate composition was obtained with 0.30 g of MC, 0.05 g of HEC, and 3.0 g of PEG 400 (No. 14) in terms of quality parameters, such as thickness, moisture, stickiness, and ability to release proanthocyanidins. The above results provide firm evidence that topical application of lingonberry proanthocyanidin in the form of an MC-HEC film represents a feasible approach to support dermal wound healing. Future research could continue to elucidate the exact mechanisms of lingonberry proanthocyanidins in wound healing and assess the suitability of the developed polymeric films.  Data Availability Statement: All data generated during this study are included in this article.