Cynara cardunculus in Wound Dressing Films: Lab Data

‍Introduction

Chronic wound dressings remain a formulation challenge across pharmaceutical and biomedical sectors.

Cynara cardunculus leaves—a source of cynaropicrin, a sesquiterpene lactone—have drawn attention in bioactive film research for their potential anti-inflammatory properties. A 2020 study published in the International Journal of Biological Macromolecules examined how ethanolic extracts from these leaves perform when incorporated into chitosan-based wound dressing films.

This article breaks down the physical, mechanical, and biological characterization data from this lab-based study, along with key considerations for formulators working with bioactive chitosan systems.

Key Takeaways

• Researchers prepared chitosan films loaded with 1%, 5%, and 10% (w/w) ethanolic ultrasound-assisted extracts from Cynara cardunculus var. scolymus leaves.
• Cynaropicrin was identified as the key bioactive compound in the extract used for film formulation.
• Films containing 1% and 5% extract showed no cytotoxicity on normal human skin fibroblasts (BJ5-ta cell line) at concentrations below the cynaropicrin IC50 threshold.
• Chitosan films with 5% extract reduced IL-6 cytokine levels by 86% in lipopolysaccharide-stimulated fibroblast cultures—a marker relevant to inflammation research.
• Extract incorporation influenced swelling capacity and mechanical properties, reducing fluid absorption and increasing fragility, but did not alter thermal stability or film microstructure.
• This is preclinical in vitro data. Clinical performance, stability in real-world wound environments, and long-term safety were not evaluated.

What the Research Examined

Researchers at the LAQV-REQUIMTE and NOVA University in Portugal prepared chitosan-based films doped with different concentrations of Cynara cardunculus leaves extract obtained through pulsed ultrasound-assisted ethanolic extraction (EtPUAE). The extract was incorporated at 1%, 5%, and 10% (w/w) relative to chitosan polymer.

Films were conditioned at various relative humidity levels and characterized for structure, swelling behavior, thermal properties, and mechanical performance. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and tensile testing were employed.

Biological screening focused on cytotoxicity (using BJ5-ta normal human skin fibroblasts), anti-inflammatory activity (measuring IL-6 cytokine levels in lipopolysaccharide-stimulated cells), and scratch wound closure assays to assess cell migration.

Key Findings from Film Characterization

Physical and Structural Properties

SEM analysis revealed that all films—regardless of extract loading—maintained a dense, homogeneous structure with no visible phase separation. This suggests the extract integrated uniformly into the chitosan matrix at the concentrations tested.

FTIR spectroscopy confirmed the presence of characteristic chitosan peaks and did not detect significant chemical interactions between extract components and the polymer backbone. The structure remained intact across all formulations.

Swelling and Mechanical Performance

Extract incorporation reduced the films' volumetric swelling capacity. Chitosan control films absorbed more fluid than extract-loaded films, with swelling decreasing as extract concentration increased. This effect was attributed to reduced polymer chain mobility and altered hydrogen bonding patterns caused by the extract components.

Mechanical testing showed that extract-loaded films became more fragile. Tensile strength and elongation at break both decreased with higher extract concentrations. Researchers noted that the 10% extract film was significantly weaker than the control, which has direct implications for handling and application.

Thermal Stability

TGA analysis showed no meaningful differences in thermal degradation profiles between control and extract-loaded films. All formulations exhibited similar decomposition temperatures, indicating that Cynara cardunculus extract incorporation does not compromise the thermal stability of chitosan films within the tested range.

Biological Activity: Cytotoxicity and Anti-Inflammatory Response

Cynaropicrin Content and Cytotoxicity Testing

The research team quantified cynaropicrin content in each film formulation. Films containing 1% and 5% extract delivered cynaropicrin at concentrations below the compound's IC50 value (the concentration that inhibits 50% of cell viability), as determined in preliminary dose-response experiments.

When tested on BJ5-ta normal human skin fibroblasts, the 1% and 5% extract films did not induce cytotoxicity over the exposure period. Cell viability remained above 70%, the threshold defined in ISO 10993-5 guidelines for cytotoxicity testing of medical materials, indicating that the 1% and 5% extract films were considered non-cytotoxic under the tested conditions. The 10% extract film, however, showed reduced cell viability, likely due to cynaropicrin concentration exceeding the tolerable threshold for this cell line.

IL-6 Reduction in Lipopolysaccharide-Stimulated Cells

To model inflammatory conditions, researchers stimulated BJ5-ta fibroblasts with lipopolysaccharide (LPS), a bacterial endotoxin known to trigger cytokine release. They then exposed these cells to film extracts and measured interleukin-6 (IL-6) levels, a pro-inflammatory cytokine.

Chitosan films containing 5% Cynara cardunculus extract reduced IL-6 levels by 86% compared to LPS-stimulated controls. This suggests the extract components—primarily cynaropicrin—were associated with reduced inflammatory signaling in this in vitro model. Chitosan alone showed moderate anti-inflammatory activity, but the addition of extract significantly enhanced the effect.

Importantly, this was a cell culture experiment. It measured cytokine levels in a controlled lab setting using a specific cell line and inflammatory stimulus. It does not provide information about how these films would perform in actual wound environments.

Scratch Wound Closure Assay

In the scratch wound closure assay, researchers evaluated fibroblast migration in the presence of chitosan films with and without plant extract. After 24 hours, films containing 1% Cynara cardunculus extract showed a higher wound closure rate compared with untreated controls, suggesting that low concentrations of cynaropicrin may support fibroblast migration and early wound repair processes. Films with higher extract loading were not further evaluated in this assay due to concerns about cytotoxicity.

What This Means for Wound Dressing Formulators

This study provides early-stage data for formulators considering Cynara cardunculus extract as a bioactive ingredient in chitosan wound dressing systems. Several practical considerations emerge from the findings.

Formulation Concentration Trade-offs

The 5% extract loading appears to be a functional sweet spot in this system. It delivered measurable anti-inflammatory activity in cell culture without triggering cytotoxicity. The 10% loading, while potentially more bioactive, compromised both cell viability and mechanical integrity—two critical factors for wound dressing performance.

Formulators will need to balance bioactive compound delivery against mechanical performance. The reduction in tensile strength and swelling capacity at higher extract concentrations may limit film durability and fluid management in practical applications.

Extract Standardization and Cynaropicrin Quantification

This study used ultrasound-assisted ethanolic extraction with specific parameters (detailed in the research team's prior optimization work). Extract composition—and therefore bioactivity—will vary based on extraction method, solvent, plant material source, and processing conditions.

For reproducible formulation outcomes, cynaropicrin content should be quantified and standardized. The researchers used HPLC analysis to confirm cynaropicrin levels in each film batch. This level of analytical characterization would be necessary for quality control in commercial development.

Biological Activity Context

The IL-6 reduction observed in LPS-stimulated fibroblasts is relevant for inflammation research but does not translate directly to wound healing efficacy. IL-6 is one of many cytokines involved in wound inflammation, and LPS stimulation is a simplified model that does not replicate the complex biochemical environment of a chronic wound.

The absence of enhanced cell migration in the scratch assay suggests that any potential benefit from these films would likely stem from their ability to help manage inflammatory signaling rather than actively promoting tissue regeneration. This distinction matters for product positioning and claim substantiation.

Physical Performance Considerations

The reduced fluid absorption capacity of extract-loaded films could be beneficial or limiting depending on the target wound type. Because extract-loaded films absorb less fluid, they may be particularly suitable for wounds with lower exudate levels, where excessive fluid absorption is not required and maintaining film stability is beneficial.

The increased fragility of extract-loaded films raises handling and application concerns. Films that tear easily during application or removal could complicate clinical use, particularly in settings where dressing changes are frequent.

Limitations and What We Don't Know Yet

This study provides useful preliminary data but leaves several critical questions unanswered.

First, all biological testing was conducted in cell culture using a single cell line (BJ5-ta normal human skin fibroblasts). These are not primary wound-derived cells, and the LPS inflammatory model does not replicate the microenvironment of a chronic wound. Animal models or ex vivo human tissue studies would be needed to assess how these films perform in more complex biological systems.

Second, the study did not examine antimicrobial activity, even though bacterial infection is a major concern in chronic wound management. Chitosan has known antimicrobial properties, and sesquiterpene lactones have been studied for antibacterial effects in other contexts, but this was not measured here.

Third, no stability data was provided. It's unclear how cynaropicrin degrades over time in the chitosan matrix, how storage conditions affect bioactivity, or whether the extract components remain stable during sterilization processes required for medical device manufacturing.

Fourth, the study did not address bioavailability or release kinetics. How rapidly does cynaropicrin diffuse out of the film? What concentration reaches the wound bed? How long does bioactivity persist after application? These are essential questions for translating lab data into functional wound dressing performance.

Finally, regulatory and safety considerations for wound dressings were not discussed. Demonstrating cytotoxicity below IC50 in a single cell line is a starting point, but comprehensive safety assessment—including sensitization, irritation, and systemic exposure studies—would be required for product development.

Frequently Asked Questions

What is cynaropicrin?

Cynaropicrin is a sesquiterpene lactone compound found in Cynara cardunculus (cardoon) leaves. It was identified as the primary bioactive component in the extract used in this study.

How was the Cynara cardunculus extract prepared for these films?

The researchers used pulsed ultrasound-assisted extraction with ethanol as the solvent. This method was previously optimized by the same research team in earlier studies focused on cynaropicrin recovery.

Did the chitosan films without extract show any biological activity?

Yes. Chitosan alone exhibited moderate IL-6 reduction in LPS-stimulated cells, consistent with known anti-inflammatory properties of chitosan. However, the addition of 5% Cynara cardunculus extract significantly enhanced this effect.

Why did the 10% extract film show cytotoxicity while lower concentrations did not?

The researchers attribute this to cynaropicrin concentration exceeding the compound's IC50 value (the concentration that reduces cell viability by 50%) in the 10% formulation. The 1% and 5% films delivered cynaropicrin below this threshold.

How does extract incorporation affect the mechanical strength of chitosan films?

Films became more fragile as extract concentration increased. Both tensile strength and elongation at break decreased, with the 10% extract film showing significantly reduced mechanical performance compared to the control.

Was any antimicrobial testing performed on these films?

No. The study focused on cytotoxicity, anti-inflammatory activity (IL-6 measurement), and cell migration. Antimicrobial testing was not included in this characterization.

What type of wound dressings could these films be developed for?

The researchers suggest these films could be explored for chronic wound applications where managing inflammatory signaling is relevant. However, this remains speculative—no clinical or in vivo wound healing data was generated in this study.

How stable is cynaropicrin in the chitosan film matrix over time?

This was not evaluated. Stability testing would be necessary to understand how storage conditions and time affect cynaropicrin content and bioactivity.

Research Summary

• Research focus: Development and characterization of chitosan films loaded with ethanolic Cynara cardunculus leaves extract for potential wound dressing applications
• Study type: In vitro material characterization and cell culture biological screening
• Extract concentrations tested: 1%, 5%, and 10% (w/w) relative to chitosan
• Key bioactive compound: Cynaropicrin, a sesquiterpene lactone
• Cell line used: BJ5-ta normal human skin fibroblasts
• Key findings: 5% extract films reduced IL-6 levels by 86% in LPS-stimulated cells without cytotoxicity; extract incorporation reduced swelling capacity and mechanical strength; thermal stability was unaffected
• Key limitations: No animal or human data; no antimicrobial testing; no stability or release kinetics data; mechanical fragility increased with extract loading; scratch wound closure was not accelerated
• Professional applications as studied: Formulation research for bioactive chitosan wound dressing systems; extract standardization considerations; mechanical property optimization; cytotoxicity threshold determination for cynaropicrin in chitosan matrices

This article is based on published scientific research: Brás T, Rosa D, Gonçalves AC, Gomes AC, Alves VD, Crespo JG, Duarte MF, Neves LA. Development of bioactive films based on chitosan and Cynara cardunculus leaves extracts for wound dressings. International Journal of Biological Macromolecules. 2020;163:1707-1718.

Content reviewed for scientific accuracy.