bm5b01026_si_001.pdf (2.01 MB)
Arrested Phase Separation of Elastin-like Polypeptide Solutions Yields Stiff, Thermoresponsive Gels
journal contribution
posted on 2015-12-14, 00:00 authored by Matthew
J. Glassman, Bradley D. OlsenThe preparation of new responsive
hydrogels is crucial for the
development of soft materials for various applications, including
additive manufacturing and biomedical implants. Here, we report the
discovery of a new mechanism for forming physical hydrogels by the
arrested phase separation of a subclass of responsively hydrophobic
elastin-like polypeptides (ELPs). When moderately concentrated solutions
of ELPs with the pentapeptide repeat (XPAVG)n (where X is either 20% or 60% valine with the remainder isoleucine)
are warmed above their inverse transition temperature, phase separation
becomes arrested, and hydrogels can be formed with shear moduli on
the order of 0.1–1 MPa at 20 wt % in water. The longest stress
relaxation times are well beyond 103 s. This result is
surprising because ELPs are classically known for thermoresponsive
coacervation that leads to macrophase separation, and solids are typically
formed in the bulk or by supplemental cross-linking strategies. This
new mechanism can form gels with remarkable mechanical behavior based
on simple macromolecules that can be easily engineered. Small angle
scattering experiments indicate that phase separation arrests to form
a network of nanoscale domains, exhibiting rheological and structural
features consistent with an arrested spinodal decomposition mechanism.
Gel nanostructure can be modeled as a disordered bicontinuous network
with interdomain, intradomain, and curvature length scales that can
be controlled by sequence design and assembly conditions. These studies
introduce a new class of reversible, responsive materials based on
a classic artificial biopolymer that is a versatile platform to address
critical challenges in industrial and medical applications.