[Todos] Seminario departamental DQIAyQF/ INQUIMAE Lunes 16 de diciembre

[andrea en qi.fcen.uba.ar]

Lunes 16 de diciembre de 2013, 13 hs
Aula de seminarios 3er piso, INQUIMAE

Título de la charla:
What is the pH of a soft material? Hydrogels as a case study

Igal Szleifer
Department of Biomedical Engineering
Department of Chemistry
Department of Chemical and Biological Engineering
Department of Medicine
Chemistry of Life Processes Institute
Northwestern University


The application of synthetic materials for biorelated, and other,
applications requires exquisite control of the physical and chemical
environment within the materials. In this talk we discuss the problem of
pH within hydrogels. In particular we attempt to answer the question what
is the pH within a hydrogel and how it relates to the conditions in which
it is synthesized and stored. The physical and chemical properties of
pH-responsive gels are found to depend on the coupling between acid-base
equilibrium, molecular organization and physical interactions. For
example, the network’s degree of protonation is not only determined by
chemical composition of the bath solution but also by the ability of the
polymeric structure to modify the local environment. This coupling results
in swelling (or shrinking) that depends on the bath pH and salt
concentration. In this presentation I will describe results obtained from
a recently developed molecular theory that describes the behavior of a
variety of stimuli-responsive hydrogels. Our approach explicitly accounts
for all of the physicochemical interactions that determine the
thermodynamic equilibrium of these intelligent soft materials, and
incorporates molecular details and the conformations of the polymer
network.  We will discuss examples of three types of hydrogels: bulk
systems, thin gel films and block copolymer gels. For bulk systems we
predict that the gel pH can be several units smaller than the bath pH
depending on the salt concentration. In thin films we will discuss the
gradients of protonation state and pH that results from the inhomogeneous
distribution of species within the film and how this effect has
implications on the effective interactions between proteins (and
nanoparticles) and the film as well as the possibility of protein
denaturation within the film due to the changes in pH as compared to the
bulk solution in contact with it. Finally, we will discuss nanodomain
formation in amphiphilic gels driven by pH and ionic strength. The
theoretical predictions can be used as guidelines for the design of
responsive gels in a variety of applications ranging from drug delivery
systems to tissue engineering scaffolds and they provide for fundamental
understanding on the non-trivial behavior of these gels. Moreover, our
predictions demonstrate that the chemical state within soft materials may
be dramatically different from that of the environment solutions in
contact with them.