CASE STUDY

Molecular dynamics
and coarse-grained
simulations facilitate thedesign of new eco-friendly
cosmetic formulations
L’Oreal and Schrödinger scientists gain a deeper understanding of the shearing behavior
differences between synthetic and polysaccharide polymers on biomimetic surfaces

Executive Summary• Gained novel insights into the aggregation
behavior of shampoo formulations with amodel hair surface• Demonstrated the impact of polymer
topology and related the observed polymer
interactions to experimental observables• Established a framework for studying
complex formulations in contact withbiomimetic surfaces using molecular
dynamics simulations• Accelerated rational design of eco-friendly
cosmetic formulations
A simplified representation of a typical molecular model system for shampoo
interacting with hair surfaces studied in this work.1

Challenges

Approach

Changes in consumer behaviors are driving
increased demand for green and eco-friendly
products in the cosmetic industry. Substitution ofnatural, bio-based polymers for petrochemicalderived ingredients in consumer formulations
has become an active area of research. However,the complexity of these formulations, typically
mixtures of surfactants, salt and polymers,
makes it non-trivial to replace an ingredient andanticipate its effect on product properties.

Scientists from L’Oreal and Schrödinger exploredthe behavioral differences of synthetic polymers
and eco-friendly polymers in hair formulations bybuilding realistic models of complex formulationand hair surfaces. All models and simulations wereperformed using the Schrödinger Materials Science
Suite and Desmond for molecular dynamics (MD)according to the following procedure:

Effective and efficient reformulation thatmaintains comparable performance to existingproducts requires a deep understanding of thedifferences in behavior between polymers, which
can be time and resource intensive using thetraditional experimental approach.

Build, parameterize andequilibrate coarse-grained
experiment-inspired bulk
formulations at dilute andconcentrated conditions

Introduce a model hair surface(healthy, extremely damagedand partially damaged) in contact
with the formulation and run
simulations

Apply shear to the model hairsurfaces and investigate theresponse of the formulations tothese drag forces

Figure 1. Structures of polymers used in this work: (a) Merquat M100TM, (b) Merquat M2003TM and (c) a polysaccharide, PS.1

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Results

What’s next

This work demonstrates an approach for studying
the interaction of complex polymer/surfactant
formulations with biological substrates via MD
simulations. Detailed, experiment-inspired allatom molecular models were used in order toparameterize coarse-grained simulations capableof portraying aggregation and adsorption behavior.
Continued progress in this area will establish
particle-based simulation as a viable technique fordesigning new eco-friendly formulations.

The exploratory measurements in this study
demonstrate that it is possible to quantify frictionalcoefficients of hair against complex formulations.
Large scale, systematic studies that allow for moredetailed comparisons between polymers of interest
are a clear next step in advancing this area of study.
In future work, we intend to examine friction as afunction of variations to formulation compositions,polymer chain lengths, model hair surface topology,
shear rate as well as distance between hair surfaces.

Summary• Distinct behaviors are observed among
polymers (M100, M2003 and PS) as a result of
their chemical architecture. The quaternaryammonium groups common to all threepolymers play an important role in bulk
aggregation, as well as in interactions withsurfactant-coated healthy hair surfaces• In M2003, the hydrophilic block does notincorporate into aggregates, but it does adhere
to the damaged surface, a quality not shown by
the other polymers• In PS, the highly branched carbohydrate
backbone offers a favorable environment forsurfactants, and may help increase surfactant
solubility. The 12-carbon alkane chains branching
off each monomer makes it the only polymer
that comes in direct contact with the healthy
hair surface• The data suggests that the length of the polymer
chain can play a role in lubrication properties

Figure 2. 100 ns moving averages of coefficient of friction, μk, versus time for systems undergoing shear. After about 400 ns of simulation,
the measured drag force in the PS system drops significantly. We can understand this visually by observing the detachment of a large
aggregate from the bottom layer.13

References
1. Shearing Friction Behaviour of Synthetic Polymers Compared to a
Functionalized Polysaccharide on Biomimetic Surfaces: Models for
the Prediction of Performance of Eco-designed Formulations
Benjamin J. Coscia, John C. Shelley, Andrea R. Browning, Jeffrey M.
Sanders, Robin Chaudret, Roger Rozot, Fabien Léonforte, Mathew
D. Halls, and Gustavo S. Luengo, Phys. Chem. Chem. Phys., 2023,
Advance Article, doi.org/10.1039/D2CP05465E

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