27 research outputs found
Designs of Zwitterionic Interfaces and Membranes
Zwitterionic materials are the latest
generation of materials for
nonfouling interfaces and membranes. They outperform poly(ethylene
glycol) derivatives because they form tighter bonds with water molecules
and can trap more water molecules. This feature article summarizes
our laboratory’s fundamental developments related to the functionalization
of interfaces and membranes using zwitterionic materials. Our molecular
designs of zwitterionic polymers and copolymers, sulfobetaine-based,
carboxybetaine-based, or phosphobetaine-based, are first reviewed.
Then, the strategies used to functionalize surfaces/membranes by coating,
grafting onto, grafting from, or in situ modification are examined
and discussed, and the third part of this article shifts the focus
to key applications of zwitterionic materials. Finally, some potential
future directions for molecular designs, functionalization processes,
and applications are presented
Zwitterionic Polyhydroxybutyrate Electrospun Fibrous Membranes with a Compromise of Bioinert Control and Tissue-Cell Growth
We
present a method for surface modification by thermal-evaporation
self-assembling of poly(3-hydroxybutyrate) (PHB) fibrous membranes
with a copolymer of hydrophobic octadecyl acrylate repeat units and
hydrophilic zwitterionic 4-vinylpyridine blocks, zP(4VP-<i>r</i>-ODA), in view of controlling biofoulant–fiber interactions.
PHB is of interest as a material for bioscaffolding, but its disadvantage
is its hydrophobicity, which leads to unwanted interactions with proteins,
blood cells, or bacteria. Surface modification
of electrospun PHB fibers addresses this issue because the hydrophilicity
of the membranes is improved, leading to a significant reduction in
bovine serum albumin (92%), lysozyme (73%), and fibrinogen (50%) adsorption.
From a coating density of 0.78 mg/cm<sup>2</sup>, no bacteria interacted
with the fibers, and from 1.13 mg/cm<sup>2</sup>, excellent hemocompatibility
of membranes was measured from thrombocytes, erythrocytes, leukocytes,
and whole blood attachment tests. Additionally, HT-1080 fibroblasts
were observed to develop in contact with the fibers after 3–7
days of incubation (cell density up to 329 ± 16 cells/mm<sup>2</sup>), suggesting that zP(4VP-<i>r</i>-ODA) provides
an adequate humid environment for their growth. Providing an effective
control of the surface chemistry and of the coating density, the association
of PHB and zP(4VP-<i>r</i>-ODA) can promote the growth of
fibroblasts, still maintaining resistance to unwanted biofoulants,
and appears to be a promising composite material for tissue engineering
Counterion-Activated Nanoactuator: Reversibly Switchable Killing/Releasing Bacteria on Polycation Brushes
A strategy to release attached bacteria
from surface-grafted bactericidal
poly((trimethylamino)ethyl methacrylate chloride) (pTMAEMA) brushes
has been proposed. The pTMAEMA brushes were fabricated via the surface-initiated
atom transfer radical polymerization for contact killing of bacteria,
including Escherichia coli, Staphylococcus epidermidis and Stenotrophomonas
maltophilia. The bacteria-conditioning surfaces, afterward,
were washed with electrolyte solutions containing anions with different
lipophilic characteristic, charge
density, polarity and adsorbility to quaternary ammonium groups in
polymers. Because of the special ion-pairing interactions, the interfacial
properties, including wettability and ζ-potential, can be manipulated
in a controlled manner. Therefore, the counterion-assisted modulation
of pTMAEMA brushes facilitates the bacterial release and regeneration
of antimicrobial polymer films. The physicochemical properties of
polymer brushes and their interactions with counterions were characterized
using an ellipsometer, contact angle goniometer, X-ray photoelectron
spectroscopy and an electrokinetic analyzer. The repetitive killing
and releasing actions of pTMAEMA through unlocking and locking counterions
were demonstrated, showing the robust effectiveness of the pTMAEMA-based
nanoactuator in controlling the physical action by the chemical stimuli.
The real-world implementation of the nanoactuator was demonstrated
with a surgical scalpel by repelling killed bacteria and retaining
reusability
Reduced Blood Cell Adhesion on Polypropylene Substrates through a Simple Surface Zwitterionization
To
overcome the thrombogenic reactions of hydrocarbon-based biomaterials
in clinical blood treatment, we introduce a model study of surface
zwitterionization of a polypropylene (PP) substrate using a set of
well-defined copolymers for controlling the adhesion of blood cells
in vitro. Random and block copolymers containing zwitterionic units
of 2-methacryloyloxyethyl phosphorylcholine (MPC), [3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonium
hydroxide inner salt (SBAA), or nonionic units of 2-hydroxyethyl methacrylate
(HEMA) with a controlled hydrophobic segment of 70% <i>n</i>-butyl methacrylate (BMA) units in these polymers were synthesized
through reversible addition–fragmentation chain transfer polymerization.
A systematic study of how zwitterionic and nonionic copolymer architectures
associated with controlled chain orientation via hydration processes
affect blood
compatibility is reported. The surface wettability of PP substrates
coated with the block copolymer with poly(MPC) (PMPC) segments was
higher than that of the random copolymer poly(MPC-random-BMA). However,
only the random copolymers with SBAA units demonstrate a higher surface
wettability. The PP substrate coated with nonionic copolymers containing
HEMA units showed relatively lower hydration capability associated
with higher protein adsorption, platelet adhesion, and leukocyte attachment
than those with zwitterionic copolymers. The random copolymer poly(SBAA-random-BMA)
coated on the PP substrates exhibited resistance to cell adhesion
in human whole blood at a level comparable to that of MPC copolymers.
An ideal zwitterionic PP substrate could be obtained by coating it
with a block copolymer composed of PMPC and poly(BMA) (PBMA) segments,
PMPC-<i>block</i>-PBMA. The water contact angle decreased
dramatically from approximately 100° on the original PP substrate
to 11° within 30 s. The number of blood cells attached on PMPC-<i>block</i>-PBMA decreased significantly to less than 2.5% of
that on original PP. These results prove that the rational design
of zwitterionic polymers incorporated with a hydrophobic anchoring
portion provides a promising approach to reduce blood cell adhesion
and protein adsorption of hydrocarbon-based biomaterials applied in
direct contact with human whole blood
RNA Origami Functions as a Self-Adjuvanted Nanovaccine Platform for Cancer Immunotherapy
Peptide-based vaccines have been widely investigated
in cancer
immunotherapy. Despite their high specificity, safety, and low production
cost, these vaccines have shown limited success in clinical studies,
owing to their poor immunogenicity. Extensive efforts have been devoted
to increasing the immunogenicity of peptide vaccines by mixing peptides
with adjuvants and/or promoting their delivery to tumor-draining lymph
nodes (TdLNs) for better antigen presentation by and maturation of
dendritic cells. Among these efforts, the exploration of various nanoparticles
has been at the forefront of the rational design and construction
of peptide-based vaccines. Here, we present a nanovaccine platform
that is built on a self-assembled RNA origami (RNA-OG) nanostructure.
As previously reported, this RNA-OG nanostructure is a potent toll-like
receptor (TLR)3 agonist. In addition, due to its robust synthesis
and versatility in modification, RNA-OG could be readily linked to
peptides of interest. Thus, these RNA-OG nanostructures function as
adjuvanted nanocarriers to construct RNA-OG-peptide nanovaccines that
are uniform in size, consistent in peptide loading, and highly stable.
Here, we demonstrate that the assembled RNA-OG-peptide nanovaccines
induced dendritic cell maturation, reduced tumor-mediated immunosuppression,
and mobilized tumor-specific CD8+ T cell responses at the
tumor site. Together, these actions led to the elicitation of an effective
antitumor immunity that increased the survival of tumor-bearing mice.
The combination of RNA-OG-based nanovaccines with the α-PD-1
immune checkpoint blockade further enhanced the immunity. Hence, our
RNA-OG nanostructures represent a robust, simple, and highly effective
platform to empower peptide-based vaccines for cancer immunotherapy
Applying Thermosettable Zwitterionic Copolymers as General Fouling-Resistant and Thermal-Tolerant Biomaterial Interfaces
We
introduced a thermosettable zwitterionic copolymer to design
a high temperature tolerance biomaterial as a general antifouling
polymer interface. The original synthetic fouling-resistant copolymer,
poly(vinylpyrrolidone)-<i>co</i>-poly(sulfobetaine methacrylate)
(poly(VP-<i>co</i>-SBMA)), is both thermal-tolerant and
fouling-resistant, and the antifouling stability of copolymer coated
interfaces can be effectively controlled by regulating the VP/SBMA
composition ratio. We studied poly(VP-<i>co</i>-SBMA) copolymer
gels and networks with a focus on their general resistance to protein,
cell, and bacterial bioadhesion, as influenced by the thermosetting
process. Interestingly, we found that the shape of the poly(VP-<i>co</i>-SBMA) copolymer material can be set at a high annealing
temperature of 200 °C while maintaining good antifouling properties.
However, while the zwitterionic PSBMA polymer gels were bioinert as
expected, control of the fouling resistance of the PSBMA polymer networks
was lost in the high temperature annealing process. A poly(VP-<i>co</i>-SBMA) copolymer network composed of PSBMA segments at
32 mol % showed reduced fibrinogen adsorption, tissue cell adhesion,
and bacterial attachment, but a relatively higher PSBMA content of
61 mol % was required to optimize resistance to platelet adhesion
and erythrocyte attachment to confer hemocompatibility to human blood.
We suggest that poly(VP-<i>co</i>-SBMA) copolymers capable
of retaining stable fouling resistance after high temperature shaping
have a potential application as thermosettable materials in a bioinert
interface for medical devices, such as the thermosettable coating
on a stainless steel blood-compatible metal stent investigated in
this study
Expression duration of <i>in vivo</i> transfected plasmid DNA.
<p>DNA (10 µg) was gently mixed with PEI at an N/P ratios of 0.5 or PDMAEMA at weight ratios of 0.25, 0.5 and 1. DNA/PEI and PDMAEMA complexes were then injected into the thigh muscle of mice and transfected by sonoporation. Luciferase activity in Balb/C mice was measured by an IVIS system on gene transfection with (right leg) or without (left leg) US exposure. (A) Quantification of the signal produced in mice muscle after transfection of each formulation (B) without and (C) with US exposure. All results are expressed as the mean ± SEM for five independent measurements (n = 5). <i>*P</i><0.05 vs. PDMAEAM 1.</p
Probing the Structural Dependence of Carbon Space Lengths of Poly(<i>N</i>‑hydroxyalkyl acrylamide)-Based Brushes on Antifouling Performance
Numerous
biocompatible antifouling polymers have been developed
for a wide variety of fundamental and practical applications in drug
delivery, biosensors, marine coatings, and many other areas. Several
antifouling mechanisms have been proposed, but the exact relationship
among molecular structure, surface hydration property, and antifouling
performance of antifouling polymers still remains elusive. Here this
work strives to provide a better understanding of the structure–property
relationship of poly(<i>N</i>-hydroxyalkyl acrylamide)-based
materials. We have designed, synthesized, and characterized a series
of polyHAAA brushes of various carbon spacer lengths (CSLs), that
is, poly(<i>N</i>-hydroxymethyl acrylamide) (polyHMAA),
poly(<i>N</i>-(2-hydroxyethyl)acrylamide) (polyHEAA), poly(<i>N</i>-(3-hydroxypropyl)acrylamide) (polyHPAA), and poly(<i>N</i>-(5-hydroxypentyl)acrylamide) (polyHPenAA), to study the
structural dependence of CSLs on their antifouling performance. HMAA,
HEAA, HPAA, and HPenAA monomers contained one, two, three, and five
methylene groups between hydroxyl and amide groups, while the other
groups in polymer backbones were the same as each other. The relation
of such small structural differences of polymer brushes to their surface
hydration and antifouling performance was studied by combined experimental
and computational methods including surface plasmon resonance sensors,
sum frequency generation (SFG) vibrational spectroscopy, cell adhesion
assay, and molecular simulations. Antifouling results showed that
all polyHAAA-based brushes were highly surface resistant to protein
adsorption from single protein solutions, undiluted blood serum and
plasma, as well as cell adhesion up to 7 days. In particular, polyHMAA
and polyHEAA with the shorter CSLs exhibited higher surface hydration
and better antifouling ability than polyHPMA and polyHPenAA. SFG and
molecular simulations further revealed that the variation of CSLs
changed the ratio of hydrophobicity/hydrophilicity of polymers, resulting
in different hydration characteristics. Among them, polyHMAA and polyHEAA
with the shorter CSLs showed the highest potency for surface hydration
and antifouling abilities, while polyHPenAA showed the lowest potency.
The combination of both hydroxyl and amide groups in the same polymer
chain provides a promising structural motif for the design of new
effective antifouling materials
Effect of PEI and PDMAEMA on intracellular uptake of DNA monitored by flow cytometry 24 h following exposures.
<p>Fluorescence labeled DNA was mixed with PEI or PDMAEMA in culture cell plates before being treated with US. (B) The overall fluorescence intensities of cultured cells and (C) the percentage of cells with fluorescence are also shown. All results are expressed as the mean ± SEM for four independent measurements. *<i>P</i><0.05 vs. PEI group (regardless of US exposure).</p
Schematic of <i>in-vivo</i> and <i>in-vitro</i> experimental setup.
<p>Schematic of <i>in-vivo</i> and <i>in-vitro</i> experimental setup.</p