Active ingredients in cosmetic or dermatological products provide specific benefits to the skin, such as moisturization, anti-ageing effects, sun protection, or treatment of any skin disease conditions. These actives can be delivered to the skin using topical or transdermal manners. Topical or transdermal delivery of cosmeceutical products and transdermal drugs offers a painless alternative to other routes of administration like injections. This is particularly beneficial for delivering compounds that do not need to reach the bloodstream at high concentrations or for those that are better suited for localized effects on the skin.

In-vitro permeation testing (IVPT) and In-vitro release testing (IVRT) are the most commonly used tests during formulation development and optimization for transdermal and topical formulations. It allows researchers to assess how well active ingredients penetrate the skin barrier and how effectively they are delivered to the desired target within the skin. The goal of skincare product development is to create formulations that are safe, effective, and beneficial to the skin. IVPT and IVRT assist in identifying the most suitable formulation that delivers the desired results. Once a promising formulation is identified through IVPT, IVRT, and other testing, it can be advanced to clinical trials for further evaluation on human subjects.

Overview of Franz Diffusion Cells Method for IVRT & IVPT

Franz diffusion cells are commonly used for IVPT and IVRT. They are used in cosmetic research for the development and optimisation of formulations. These cells are designed to mimic the physiological conditions of transdermal drug delivery and are widely used in cosmetic research to evaluate the permeability, absorption, and release rates of actives through biological membranes, typically through the skin.

A Franz diffusion cell consists of two chambers, a donor chamber, and a receptor chamber, separated by a barrier membrane. The sample to be tested is introduced through the donor chamber (top chamber), separated from the receptor compartment by the membrane. The membrane serves as a barrier that simulates the skin layer through which the substance is intended to permeate. It simulates the diffusion characteristics and permeability of the actual biological membrane. For skin absorption studies, this could be synthetic or natural skin membranes. The membrane’s properties are crucial for mimicking real-life conditions and interactions. The receptor chamber (bottom chamber) contains a suitable medium maintained at 32 or 37 °C with constant stirring, that simulates the environment on the other side of the barrier. It collects the substance that permeates through the membrane. Samples are collected from the receptor compartment at regular intervals to determine the amount of actives that permeate through the membrane.

What are the advantages of using Franz diffusion cells for cosmetic research?

Franz diffusion cells offer a controlled and standardized method to assess the penetration and absorption of cosmetic ingredients through the skin. This information is essential for product development, safety evaluation, and regulatory compliance in the cosmetic industry. Below are some applications for using Franz diffusion cells in cosmetic research.

• Skin Permeation Studies: Cosmetic products, such as creams, lotions, and serums, are designed to be applied to the skin. Franz cells allow researchers to study the permeation of active cosmetic ingredients through the skin barrier, helping to assess their effectiveness and potential for skin absorption.

• Formulation Optimization: Cosmetic formulations can be complex, with various ingredients interacting with each other and the skin. Franz cells enable researchers to optimize cosmetic formulations by evaluating how different ingredients affect skin permeation and absorption rates.

• Safety Assessment: Cosmetic products are intended to enhance skin health and appearance. Franz cells can be used to assess the safety of cosmetic ingredients by studying their potential to penetrate the skin and evaluating any potential irritations or adverse reactions.

• Comparative Studies: Franz cells allow for direct comparisons between different cosmetic formulations or products. Researchers can assess which formulation leads to better penetration and absorption of active ingredients, aiding in the selection of the most effective product.

• Claim Substantiation: Cosmetics often make specific claims about their effects on the skin, such as moisturization, wrinkle reduction, or skin brightening. Franz cells can help substantiate these claims by providing scientific data on the penetration and permeation of active ingredients that contribute to the claimed effects.

• Regulatory Compliance: Cosmetic products are subject to regulatory requirements regarding ingredient safety and labelling claims. Franz diffusion cell studies can provide the scientific data needed to comply with regulatory standards and substantiate product claims.

• Non-Invasive Testing: Franz diffusion cell studies are non-invasive and do not require human volunteers initially. This can save time and resources in the early stages of cosmetic product development, allowing for preliminary testing before moving on to more extensive clinical trials.

• Ethical Considerations: Using Franz cells can reduce the need for animal testing, aligning with the growing demand for alternative testing methods that are more ethically and environmentally responsible.

• Customized Research: Researchers can tailor Franz cell experiments to mimic specific skin types, conditions, or demographics, ensuring that the cosmetic product’s performance is assessed accurately for the intended target audience.

Comparison between traditional and automated Franz Cell Diffusion

The method for in vitro transdermal diffusion was developed by T.J. Franz in 1975. Since then, automated Franz Cells have been developed to fully automate and overcome tiresome manual operations of traditional Franz cells, providing a more realistic, reliable, and cost-effective solution for in vitro & ex vivo testing of active compounds & products.

	Traditional Franz Cell	Automated Franz Cell
Experimental Throughput	Low throughput due to the need for manual handling and limited sample capacity.	High throughput due to the ability to run multiple experiments simultaneously and collect more data and time points efficiently.
Experimental Control	Limited control over experimental parameters and conditions.	Precise control over factors such as temperature, agitation, and sample collection, leading to more reliable results.
Data Collection	Manual sampling can introduce variability and requires constant monitoring.	Continuous data collection with minimal human intervention, reducing the risk of human errors and contamination.
Data Quality and Reproducibility	More prone to human errors and inconsistencies.	Improved data quality and reproducibility due to reduced human involvement and standardized protocols.
Labour Requirements	Requires more manual labour and continuous monitoring.	Requires less manual intervention, freeing up researchers’ time for other tasks.
Sample Handling	More hands-on sample handling, increasing the risk of contamination.	Minimized risk of contamination due to reduced need for direct sample handling.
Real-time Monitoring	Limited ability to monitor experiments in real-time.	Real-time monitoring and remote control capabilities provide insights and enable adjustments during experiments.
Setup Complexity	Simpler setup but may lack precise control and data collection capabilities.	More complex setup due to equipment requirements, but offers advanced functionalities and experimental customization.
Standardization	Protocols and conditions might vary between experiments.	Standardized protocols and conditions, leading to greater consistency and comparability between studies.
Cost	Generally less expensive to set up and maintain.	Higher initial and maintenance costs due to specialized equipment and technology.
Flexibility	Limited flexibility in terms of experimental conditions and parameter control.	Greater flexibility to tailor experiments to specific research needs.

Modern Transdermal Franz Diffusion Cell Method

Automation & Better Control of Testing Conditions

Logan Instruments has developed an automated transdermal Franz diffusion cell sampling system designed for testing IVRT and IVPT of semi-sold dosage and topical drug formulation, as well as for cosmetic products, such as ointment, gels, transdermal patches, face masks, lotion, sunscreen, etc.

Their automated diffusion cell sampling system contains two vertical transdermal diffusers (which use either the water jacket heating system to ensure temperature accuracy or the dry heat method to provide even temperature), a sample collector, dual syringe pumps, and a system controller.

With their updated design and technology, Logan’s transdermal Franz diffusion cell system allows simultaneous permeation tests for 12 samples. With the availability of data audit tracking function and its compliance with FDA 21 CFR Part 11 requirements, it is trusted by researchers and formulators at most major pharmaceutical manufacturers worldwide.

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References

• Salamanca CH, Barrera-Ocampo A, Lasso JC, Camacho N, Yarce CJ. Franz Diffusion Cell Approach for Pre-Formulation Characterisation of Ketoprofen Semi-Solid Dosage Forms. Pharmaceutics. 2018;10(3):148. Published 2018 Sep 5. doi:10.3390/pharmaceutics10030148