Digital skin: A smart solution and potential alternative to animal testing

A computational model that details and mimics characteristics of the human skin.

A digital twin of the skin is a virtual representation of every distinct layer of the human skin—one that considers all of the skin’s qualitative characteristics or physiochemical nature, be it composition and thickness, or the process of wrinkling. The twin uses a multiscale modeling framework and simulates the biophysical and biomechanical aspects of the largest human organ for research and experiments. It can also digitally analyze the effects of deformation on the skin—a feature that enhances cosmetic product design, particularly when formulating and understanding the interaction of anti-aging ingredients.

The digital replica offers an alternative to traditional testing, allowing developers to experiment and test drug and cosmetic formulations and permeation enhancers (molecules of substances that help with penetration into the skin), as well as their delivery mechanisms via medical devices.

Animal testing has previously been used for skin tests, but the biological characteristics of animal skin are significantly different than that of humans. Drugs that have been tested on animals may not pass clinical trials on humans. A digital model of the human skin eliminates this lack of certainty, making it an effective and even more humane substitute to animal testing.

Skin and skin formulations

How and why are biophysics and biomechanics of skin crucial to the design and testing of formulations and devices?

A formulation—a complex mix of solvents, active molecules, co-additives, and permeation enhancers—is the percentage or weight-based list of ingredients required to formulate a product. Several formulations need to be tried before a desired outcome is reached. The efficacy of a formulation is determined based on how the skin absorbs the former’s active molecule. This mechanism in skin exploration is the biophysics aspect.

In case of large-sized molecules like insulin, vaccines, and proteins, medical devices such as subcutaneous injections are used to deliver the formulation. Here, the efficacy of the device used to deliver the formulation to the skin depends not only on the transport properties of the formulation inside the skin, but also the mechanical interaction between the transporting device and the skin. These injections need to be designed with consideration, accounting for factors such as the length and size of the needle, drug formulation viscosity, and the injecting speed, all of which influence transport to the subcutaneous layer.

The digital skin model also helps study these parameters on the skin’s subcutaneous layer. For instance, it can predict the impact of injection flow rate on the drug’s transport to the skin.

There are, therefore, two aspects at play when it comes to skin research: biophysics, which has to do with the testing of permeation enhancers and cosmetic formulations; and biomechanics, which involves testing medical and personal-care devices. The multiscale modeling framework in the digital twin of skin emulates both the biomechanics and the biophysics involved in skin explorations.

Limitations in traditional testing

The digital skin model could be an alternative to consider given the physical and regulatory constraints in conventional testing. Here’s why.

The design and testing of clinical drugs and cosmetic products is a complex process—one that calls for detailed experiments along with an adherence to stringent regulatory standards before market launch. Not only does animal testing raise concerns around humaneness, the uncertainty in determining outcomes often means wasted time, effort, and resources, not to mention intellectual fatigue. It can also be limiting as multiple trials and experiments, even though needed, cannot always be carried out. Experiments sometimes have one type of outcome during an animal test and a different one when tested on humans. Trials are, therefore, often protracted processes that don’t always end favorably.

An in silico model of human skin can significantly accelerate the process of design and testing of human drugs by reducing the number of experiments needed. Though computational models are not always as accurate as experiments, they can provide critical insights that can drive successful experiments. It is here that a digitally recreated model of the human skin has proved most impactful for the biopharma and cosmetics industries.

The development of the twin for skin becomes even more pertinent given the ban across certain geographies such as Canada, European Union, and India, on the use of animals in the testing and development of cosmetic products. Around 10 states in the US have also passed regulations to ban cosmetic animal testing. Added to this is the push from regulatory bodies on the adoption of computational or in silico models as alternatives to animal testing.