11 research outputs found
Temperature-Controlled Masking/Unmasking of Cell-Adhesive Cues with Poly(ethylene glycol) Methacrylate Based Brushes
Thin,
thermoresponsive polymer coatings that allow to reversibly
modulate cell adhesion and detachment are attractive substrates for
cell sheet engineering. Usually, this is accomplished by applying
thin polyÂ(<i>N</i>-isopropylacrylamide) (PNIPAM) coatings,
which allow cell adhesion via nonspecific interactions above the collapse
temperature (<i>T</i><sub>T</sub>) of the surface-attached
polymer and cell detachment upon cooling below <i>T</i><sub>T</sub>. This Article presents an alternative, thermoresponsive polymer
platform that is based on 2-(2-methoxyethoxy)Âethyl methacrylate (MEO<sub>2</sub>MA) containing copolymer brushes prepared via surface-initiated
atom transfer radical polymerization (SI-ATRP). These brushes are
interesting as they gradually collapse and dehydrate upon increasing
the temperature from 10 to 40 °C, yet resist nonspecific adhesion
of cells over this entire temperature window. The MEO<sub>2</sub>MA
based brushes presented here were modified via a two-step postpolymerization
modification protocol to introduce cell-adhesive RGD containing peptide
ligands. The possibility to reversibly control the swelling and collapse
of these brush films by varying temperature allows to modulate the
effectively available surface concentration of these cell-adhesive
cues and thus provides a way to mask/unmask their biological activity.
As a first proof of concept, this Article demonstrates that these
MEO<sub>2</sub>MA brush copolymer films enable integrin-mediated adhesion
of 3T3 fibroblasts at 37 °C and allow release of these cells
by cooling to 23 °C. The use of cell-adhesive ligands, which
can be thermoreversibly masked/unmasked, is attractive as it enables
the use of serum-free cell culture conditions. This is advantageous
since it avoids possible concerns regarding eventual toxicity and
immunological side effects of serum proteins and also provides opportunities
to select for particular cell types and for enhanced control over
cell stimulation and differentiation
Aqueous Fabrication of pH-Gated, Polymer-Brush-Modified Alumina Hybrid Membranes
In
this Article, we studied the surface immobilization of five
organic-acid-modified atom-transfer radical polymerization (ATRP)
initiators based on salicylic acid, catechol, phthalic acid, and <i>m</i>- and <i>p</i>-benzoic acid on alumina, and we
also investigated the growth of hydrophilic polyÂ(2-hydroxyethyl methacrylate)
(PHEMA) and polyÂ(polyÂ(ethylene glycol)Âmethycrylate) (PPEGMA<sub>6</sub>) brushes from the resulting initiator-modified substrates. Whereas
the surface immobilization of phthalic acid- and benzoic acid-based
initiators results in only very thin brushes or no brush growth at
all, SI-ATRP of HEMA and PEGMA<sub>6</sub> from alumina surfaces modified
with salicylate or catechol generates brushes with thicknesses comparable
to those obtained using organosilane-based initiators. Most interestingly,
the surface immobilization of the catechol- and salicylate based-initiators
was found to be pH-dependent, which allowed facile variation of the
ATRP initiator surface concentration and, concomitantly, the polymer
brush grafting density by adjusting the pH of the aqueous solution
that was used to immobilize the initiator. This is in contrast to
organosilane-based initiators, where the variation of the grafting
density is usually accomplished using mixtures of the ATRP initiator
and an ATRP inactive âdummyâ. Another difference between
the organosilane-based initiators and the organic acid analogues is
the stability of hydrophilic brushes grown from alumina. After a certain
threshold thickness was exceeded, organosilane-tethered PPEGMA<sub>6</sub> brushes were observed to detach from the substrate, in contrast
to brushes grown from catechol or salicylate initiators, which did
not show signs of degradation. Finally, as a first proof-of-concept,
the salicylate-based initiator was used to develop an all-aqueous
protocol for the modification of alumina membranes with hydrophilic
PHEMA and succinic anhydride post-modified polymer brushes. The water
permeation properties of these hybrid membranes can be controlled
by adjusting the brush thickness in the case of the neutral PHEMA
brush coating or can be pH-gated after post-polymerization modification
to introduce carboxylic acid groups
Polymer Brush Gradients Grafted from Plasma-Polymerized Surfaces
A new method for generating a surface
density gradient of polymer
chains is presented. A substrate-independent polymer deposition technique
was used to coat materials with a chemical gradient based on plasma copolymerization of 1,7-octadiene
and allylamine. This provided a uniform chemical gradient to which
initiators for atom transfer radical polymerization (ATRP) were immobilized.
After surface-initiated atom transfer radical polymerization (SI-ATRP),
polyÂ(2-hydroxyethyl methacrylate) (PHEMA) chains were grafted from
the surface and the measured thickness profiles provided direct evidence
for how surface crowding provides an entropic driving force resulting
in chain extension away from the surface. Film thicknesses were found
to increase with the position along the gradient surface, reflecting
the gradual transition from collapsed to more extended surface-tethered
polymer chains as the grafting density increased. The method described
is novel in that the approach provides covalent linkages from the
polymer coating to the substrate and is not limited to a particular
surface chemistry of the starting material
Squaric Acid Mediated Synthesis and Biological Activity of a Library of Linear and Hyperbranched Poly(Glycerol)âProtein Conjugates
Polymerâprotein conjugates generated from side
chain functional
synthetic polymers are attractive because they can be easily further
modified with, for example, labeling groups or targeting ligands.
The residue specific modification of proteins with side chain functional
synthetic polymers using the traditional coupling strategies may be
compromised due to the nonorthogonality of the side-chain and chain-end
functional groups of the synthetic polymer, which may lead to side
reactions. This study explores the feasibility of the squaric acid
diethyl ester mediated coupling as an amine selective, hydroxyl tolerant,
and hydrolysis insensitive route for the preparation of side-chain
functional, hydroxyl-containing, polymerâprotein conjugates.
The hydroxyl side chain functional polymers selected for this study
are a library of amine end-functional, linear, midfunctional, hyperbranched,
and linear-block-hyperbranched polyglycerol (PG) copolymers. These
synthetic polymers have been used to prepare a diverse library of
BSA and lysozyme polymer conjugates. In addition to exploring the
scope and limitations of the squaric acid diethylester-mediated coupling
strategy, the use of the library of polyglycerol copolymers also allows
to systematically study the influence of molecular weight and architecture
of the synthetic polymer on the biological activity of the protein.
Comparison of the activity of PGâlysozyme conjugates generated
from relatively low molecular weight PG copolymers did not reveal
any obvious structureâactivity relationships. Evaluation of
the activity of conjugates composed of PG copolymers with molecular
weights of 10000 or 20000 g/mol, however, indicated significantly
higher activities of conjugates prepared from midfunctional synthetic
polymers as compared to linear polymers of similar molecular weight
pH-Sensitive Coiled-Coil Peptide-Cross-Linked Hyaluronic Acid Nanogels: Synthesis and Targeted Intracellular Protein Delivery to CD44 Positive Cancer Cells
The
clinical translation of protein drugs that act intracellularly
is limited by the absence of safe and efficient intracellular protein
delivery vehicles. Here, pH-sensitive coiled-coil peptide-cross-linked
hyaluronic acid nanogels (HA-cNGs) were designed and investigated
for targeted intracellular protein delivery to CD44 overexpressing
MCF-7 breast cancer cells. HA-cNGs were obtained with a small size
of 176 nm from an equivalent mixture of hyaluronic acid conjugates
with GYÂ(EIAALEK)<sub>3</sub>GC (E3) and GYÂ(KIAALKE)<sub>3</sub>GC
(K3) peptides, respectively, at pH 7.4 by nanoprecipitation. Circular
dichroism (CD) proved the formation of coiled-coil structures between
E3 and K3 peptides at pH 7.4 while fast uncoiling at pH 5.0. HA-cNGs
showed facile loading of cytochrome C (CC) and greatly accelerated
CC release under mild acidic conditions (18.4%, 76.8%, and 91.4% protein
release in 24 h at pH 7.4, 6.0, and 5.0, respectively). Confocal microscopy
and flow cytometry displayed efficient internalization of CC-loaded
HA-cNGs and effective endosomal escape of CC in MCF-7 cancer cells.
Remarkably, HA-cNGs loaded with saporin, a ribosome inactivating protein,
exhibited significantly enhanced apoptotic activity to MCF-7 cells
with a low IC<sub>50</sub> of 12.2 nM. These coiled-coil peptide-cross-linked
hyaluronic acid nanogels have appeared as a simple and multifunctional
platform for efficient intracellular protein delivery
Comparative Study on the In Vitro Cytotoxicity of Linear, Dendritic, and Hyperbranched Polylysine Analogues
Lysine-based polycations are widely used as nonviral
carriers for
gene delivery. This manuscript reports the results of a comparative
study on the in vitro cytotoxicity of a library of three structural
polylysine variants, namely, linear polylysine (LPL), dendritic polylysine
(DPL), and hyperbranched polylysine (HBPL). The aim of this study
was to identify possible effects of polymer molecular weight and architecture
on both immediate and delayed cytotoxicity and also to provide a mechanistic
understanding for possible differences. Acute cytotoxicities were
evaluated using cell viability assays with CHO DG44 cells. At comparable
molecular weights, the EC<sub>50</sub> values for the LPL analogues
were âŒ5â250 times higher as compared to the DPL and
HBPL samples. For low molecular weight polycations, osmotic shock
was found to be an important contributor to immediate cell death,
whereas for the higher molecular weight analogues, direct cell membrane
disruption was identified to play a role. Delayed cytotoxicity (â„3
h) was assessed by identifying several of the hallmark events that
characterize apoptosis, including phosphatidyl serine translocation,
mitochondrial membrane depolarization, cytoplasmic cytochrome C release,
and caspase 3 activation. At comparable molecular weights, apoptosis
was found to be more pronounced for DPL and HBPL as compared to LPL.
This difference was ascribed to the fact that LPL is completely enzymatically
degradable, in contrast to DPL and HBPL, which also contain Δ-peptidic
bonds and are only partially degradable. Because their toxicity profiles
are similar, HBPL is an interesting (i.e., synthetically easily accessible
and inexpensive) alternative to DPL for the nonviral delivery of DNA
Polymer-Brush-Templated Three-Dimensional Molybdenum Sulfide Catalyst for Hydrogen Evolution
Earth-abundant hydrogen
evolution catalysts are essential for high-efficiency solar-driven
water splitting. Although a significant amount of studies have been
dedicated to the development of new catalytic materials, the microscopic
assembly of these materials has not been widely investigated. Here,
we describe an approach to control the three-dimensional (3D) assembly
of amorphous molybdenum sulfide using polymer brushes as a template.
To this end, polyÂ(dimethylaminoethyl methacrylate) brushes were grown
from highly oriented pyrolytic graphite. These cationic polymer films
bind anionic MoS<sub>4</sub><sup>2â</sup> through an anion-exchange
reaction. In a final oxidation step, the polymer-bound MoS<sub>4</sub><sup>2â</sup> is converted into the amorphous MoS<sub><i>x</i></sub> catalyst. The flexibility of the assembly design
allowed systematic optimization of the 3D catalyst. The best system
exhibited turnover frequencies up to 1.3 and 4.9 s<sup>â1</sup> at overpotentials of 200 and 250 mV, respectively. This turnover
frequency stands out among various molybdenum sulfide catalysts. The
work demonstrates a novel strategy to control the assembly of hydrogen
evolution reaction catalysts
Ductile, High-Lignin-Content Thermoset Films and Coatings
In the context of
transitioning toward a more sustainable use of
natural resources, the application of lignin to substitute commonly
utilized petroleum-based plastics can play a key role. Although lignin
is highly available at low cost and presents interesting properties,
such as antioxidant and UV barrier activities, its application is
limited by its low reactivity, which is a consequence of harsh conditions
normally used to extract lignin from biomass. In this work, the use
of glyoxylic acid lignin (GA lignin), rich in carboxylic acid groups
and hence highly reactive toward epoxy cross-linkers, is presented.
GA lignin, which is directly extracted from biomass via a one-step
aldehyde-assisted fractionation process, allowed the preparation of
thermoset films and coatings via a simple reaction with sustainable
poly(ethylene glycol) diglycidyl ether and glycerol diglycidyl ether
cross-linkers. This allows one to prepare freestanding films containing
up to 70 wt % lignin with tunable mechanical properties and covalently
surface-attached coatings containing up to 90 wt % lignin with high
solvent resistance. Both films and coatings display antioxidant properties
and combine excellent UV barrier activity with high visible transparency,
which is attractive for applications in sustainable food packaging