5 research outputs found
Consequences of Water between Two Hydrophobic Surfaces on Adhesion and Wetting
The contact of two hydrophobic surfaces
in water is of importance
in biology, catalysis, material science, and geology. A tenet of hydrophobic
attraction is the release of an ordered water layer, leading to a
dry contact between two hydrophobic surfaces. Although the water-free
contact has been inferred from numerous experimental and theoretical
studies, this has not been directly measured. Here, we use surface
sensitive sum frequency generation spectroscopy to directly probe
the contact interface between hydrophobic polyÂ(dimethylsiloxane) (PDMS)
and two hydrophobic surfaces (a self-assembled monolayer, OTS, and
a polymer coating, PVNODC). We show that the interfacial structures
for OTS and PVNODC are identical in dry contact but that they differ
dramatically in wet contact. In water, the PVNODC surface partially
rearranges at grain boundaries, trapping water at the contact interface
leading to a 50% reduction in adhesion energy compared to OTSâPDMS
contact. The YoungâDupreĚ equation, used extensively
to calculate the thermodynamic work of adhesion, predicts no differences
between the adhesion energy for these two hydrophobic surfaces, indicating
a failure of this well-known equation when there is a heterogeneous
contact. This study exemplifies the importance of interstitial water
in controlling adhesion and wetting
Peptide-Functionalized Oxime Hydrogels with Tunable Mechanical Properties and Gelation Behavior
We demonstrate the formation of polyethylene
glycol (PEG) based
hydrogels via oxime ligation and the photoinitiated thiolâene
3D patterning of peptides within the hydrogel matrix postgelation.
The gelation process and final mechanical strength of the hydrogels
can be tuned using pH and the catalyst concentration. The time scale
to reach the gel point and complete gelation can be shortened from
hours to seconds using both pH and aniline catalyst, which facilitates
the tuning of the storage modulus from 0.3 to over 15 kPa. Azide-
and alkene-functionalized hydrogels were also synthesized, and we
have shown the post gelation âclickâ-type Huisgen 1,3
cycloaddition and thiolene-based radical reactions for spatially defined
peptide incorporation. These materials are the initial demonstration
for translationally relevant hydrogel materials that possess tunable
mechanical regimes attractive to soft tissue engineering and possess
atom neutral chemistries attractive for post gelation patterning in
the presence or absence of cells
Adhesion Properties of Catechol-Based Biodegradable Amino Acid-Based Poly(ester urea) Copolymers Inspired from Mussel Proteins
Amino acid-based polyÂ(ester urea)
(PEU) copolymers functionalized
with pendant catechol groups that address the need for strongly adhesive
yet degradable biomaterials have been developed. Lap-shear tests with
aluminum adherends demonstrated that these polymers have lap-shear
adhesion strengths near 1 MPa. An increase in lap-shear adhesive strength
to 2.4 MPa was achieved upon the addition of an oxidative cross-linker.
The adhesive strength on porcine skin adherends was comparable with
commercial fibrin glue. Interfacial energies of the polymeric materials
were investigated via contact angle measurements and JohnsonâKendallâRoberts
(JKR) technique. The JKR work of adhesion was consistent with contact
angle measurements. The chemical and physical properties of PEUs can
be controlled using different diols and amino acids, making the polymers
candidates for the development of biological glues for use in clinical
applications