Caffeine in cosmetics –
optimizing its release
into the body by means
of "MOFs”
Hybrid metal-organic frameworks or MOFs
are very promising candidates for societally
relevant applications in catalysis, separation
or, more recently, biomedicine. A group
from Institut Lavoisier de Versailles, pioneer
in the MOF biomedical field, has studied,
notably on the CRISTAL beamline, the
encapsulation and release of caffeine, which
is of great interest to the cosmetics industry
due to its lipolytic action.
MOFs or (metal-organic-frameworks)
typically consist of a regular assembly
of inorganic entities (clusters, chains,
planes…) and organic ligands combining
polycomplexing functions (carboxylates,
phosphonates…) [1]. These crystalline
solids possess a network of regular micro-
or meso-porous cavities and channels.
The versatility of their structures (porosity/
connectivity, topology, etc.) and their
chemical compositions (metal, ligand)
make MOFs very promising candidates
for applications in strategic areas such
as catalysis, separation [1] or, more
recently, biomedicine [2]. In particular,
their high and regular porosity, as well
as the presence of an amphiphilic
environment (having both hydrophilic
and hydrophobic parts, metal cation
and organic ligand), well-adapted
to the adsorption of different drugs,
have led to remarkable encapsulation
capabilities and progressive releases
under physiological conditions [3].
A thorough microscopic understanding
of both the encapsulation and release
of the active ingredient from MOF-type
carriers is however crucial for a better
control of these processes. This has
motivated the recent studies of the group
of Institut Lavoisier, pioneer in this field,
which are focused on streamlining
the encapsulation of therapeutic molecules
within a series of porous MOFs [4].
In this context, a systematic study of the
main factors governing the encapsulation
of active ingredients and their release
kinetics from MOFs with various topologies
and chemical compositions was performed
by combining experimental techniques
and numerical simulations performed
in collaboration with one group of Institut
Charles Gerhardt Montpellier (Figure
➊
).
The caffeine molecule, exhibiting a
remarkable lipolytic action highly suitable
for the cosmetics field, was selected.
Indeed, the current lack of effective
caffeine formulations on the market
is mainly due to its strong tendency
to crystallize, which leads to low
capacities (< 5 wt%) and uncontrolled
releases [5].
MOFs have proved to be very promising
candidates to overcome this technological
barrier in the cosmetics industry
(see related publication). In particular,
an exceptional encapsulation rate of 50
wt% was achieved using biocompatible
MOFs such as the mesoporous iron(III)
trimesate MIL-100(Fe). In addition,
the structures of flexible MOFs loaded
with caffeine has been analyzed through
a combination of high resolution X-ray
powder diffraction data on the CRISTAL
beamline, and numerical simulations
(density functional theory) to better
understand the conformation of caffeine
and its interactions with the pore walls.
For instance, the caffeine is not aligned
along the direction of the tunnel of the
microporous iron(III) terephthalate MIL-53
but adopts an orientation at a slight angle
to the channel axis, leading to interactions
through relatively strong hydrogen bonding
between the oxygen of the caffeine
carbonyl group and the hydroxy group
present at the MOF inner pore wall.
Furthermore, the release of caffeine
strongly depends on the nature of
the medium (Figure
➋
). Under serum
conditions (phosphate buffer solution
pH = 7.4, 37°C), caffeine is rapidly
released following on the whole the
degradation of the MOF, while in
a simulated skin physiological medium
(distilled water pH = 6.3, 37°C),
caffeine is progressively delivered,
as a consequence of the degree
of confinement and MOF-drug interactions.
Thus, considering a typical cosmetic
administration ranging between 8 and
24 h, the most promising porous MOFs
for the topical administration of caffeine
are the mesoporous iron(III) trimesate
MIL-100(Fe) and the microporous
zirconium(IV) terephthalate UiO-
66(Zr), which combine record caffeine
encapsulation rates and progressive
releases over 24 hours.
Introduction
Results
PHYSICS AND CHEMISTRY OF CONDENSED MATTER, EARTH SCIENCES
104
SOLEIL
HIGHLIGHTS
2013
