Surface-functionalization mediated through “grafting from” methods is of considerable interest as means to tailor the chemical and physical properties of functional substrates in a reliable way. The ...resulting polymer brushes, obtained by a “grafting from” strategy, are composed of grafted polymer chains tethered from one of their extremities to a surface by a covalent bond. Tuning the molecular parameters of these polymeric brushes such as the nature of monomer, the grafting density, and the chain length as well as the design of micropatterned structures enables delicate modification of the properties of these substrates, paving the way to the development of functional surfaces. In this review, we highlight recent and most important approaches to form monolayers and to subsequently elaborate homogeneous and heterogeneous coatings of polymer brushes by surface-initiated polymerization. The control of initiator molecule assembly is particularly important for the final configuration of polymer brushes. We report the creation of homopolymers and block copolymers using major controlled polymerization techniques as well as lithographic techniques aiming at the design of polymeric (micro- or nano-) patterns.
This paper report the synthesis of binary-patterned brushes, combining two distinctive surface initiated-polymerizations (SIP) on the basis of different propagating species: the SI Ring Opening ...Polymerization (ROP) of L-Lactide (LLA) and SI atom transfer radical polymerization (ATRP) of N,N’-dimethylaminoethyl methacrylate (DMAEMA) on gold surface. First of all, a careful study of surfaceinitiated ROP of L-Lactide from hydroxyl end-group of thiol monolayer on gold surface as catalyzed by metal-free catalyst was carried out. The PLLA brushes synthesis was evaluated using two types of thiol monolayer and revealed the influence of ROP initiator chain length on the final thickness of the PLLA film. Combining the soft lithographic technique, microcontact printing, and the liquid phase deposition, the deposition onto specific micro-domains of both initiators was performed. The growth of PDMAEMA brushes and PLLA brushes was conducted by successive ATRP and ROP.
Ring opening polymerization of epsilon caprolactone from the hydroxyl end-group of thiol monolayer was carried out on gold surface. The crystal morphology of the grafted chains was studied in detail.
...This paper is the first report about the morphology of semi-crystalline poly(ε-caprolactone) (PCL) brushes studied by Atomic Force Microscopy (AFM) in tapping mode. This represents a convenient way to observe how the growth of a polymer proceeds from a thiol monolayer on gold substrate in terms of grafting density and thiol monolayer stability. The synthesis of semi-crystalline PCL brushes was carried out by Ring-Opening Polymerization (ROP) of ε-caprolactone (ε-CL) from hydroxyl end-group of thiol monolayer on gold surface as catalyzed with tin octoate (Sn(Oct)
2) at 50
°C. Addition of a sacrificial initiator was also attempted in order to get a finer control over PCL crystals. For a sake of comparison, triazabicyclo4.4.0dec-5-ene (TBD) was also investigated as another ROP catalyst active at ambient temperature. The composition and the morphology of resulting semi-crystalline PCL brushes were characterized using X-ray Photoelectron Spectroscopy (XPS) and AFM. In the case of Sn(Oct)
2-promoted ROP of CL with or without free (sacrificial) initiator (i.e., benzyl alcohol), different types of morphologies were observed on the gold substrate, due to the thermal instability of thiol-gold bond under the experimental conditions. When TBD was used at ambient temperature, a regular and homogeneous crystalline morphology, i.e., compact PCL crystals, could be observed.
The selective adsorption of carbon nanotubes (CNTs) on a pH-reversible PDMAEMA patterned gold surface is presented. In acidic conditions, a selective CNTs adsorption onto the polymer brushes is ...obtained due to ammonium-π interactions. The reversible behavior was shown by successive treatments in both alkaline and acidic solutions with CNTs.
Imidazolium end‐functionalized poly(butyl acrylate) and polystyrene (co)polymers (Im‐PnBuA, Im‐PSty, and Im‐PnBuA‐b‐PSty are synthesized via ATRP. The controlled character of the polymerization ...reactions is highlighted by SEC and MALDI‐TOF MS analyses. Subsequently, the polymers are tested as dispersing/compatibilizing agents for CNTs in polymer matrices. When CNTs are challenged with a mixture of Im‐PnBuA and Im‐PSty, the CNTs are mainly located in the PnBuA phase. In contrast, the Im‐PnBuA‐b‐PSty block copolymer enables CNT confinement in the PSty phase. By selecting the proper ω‐imidazolium polymer, it is possible to direct the CNT confinement toward a specific polymer phase within polymer mixtures.
Imidazolium end‐functionalized (co)polymers are synthesized via ATRP. In solution, the polymers demonstrate a high binding ability toward CNTs. Careful selection of the ω‐imidazolium polymer allows to control the CNT confinement toward a specific polymer phase within polymer mixtures.
This paper report the synthesis of binary-patterned brushes, combining two distinctive surface initiated-polymerizations (SIP) on the basis of different propagating species: the SI Ring Opening ...Polymerization (ROP) of L-Lactide (LLA) and SI atom transfer radical polymerization (ATRP) of N,N’-dimethylaminoethyl methacrylate (DMAEMA) on gold surface. First of all, a careful study of surfaceinitiated ROP of L-Lactide from hydroxyl end-group of thiol monolayer on gold surface as catalyzed by metal-free catalyst was carried out. The PLLA brushes synthesis was evaluated using two types of thiol monolayer and revealed the influence of ROP initiator chain length on the final thickness of the PLLA film. Combining the soft lithographic technique, microcontact printing, and the liquid phase deposition, the deposition onto specific micro-domains of both initiators was performed. The growth of PDMAEMA brushes and PLLA brushes was conducted by successive ATRP and ROP.
This paper report the synthesis of binary-patterned brushes, combining two distinctive surface initiated-polymerizations (SIP) on the basis of different propagating species: the SI Ring Opening ...Polymerization (ROP) of L-Lactide (LLA) and SI atom transfer radical polymerization (ATRP) of N,N’-dimethylaminoethyl methacrylate (DMAEMA) on gold surface. First of all, a careful study of surfaceinitiated ROP of L-Lactide from hydroxyl end-group of thiol monolayer on gold surface as catalyzed by metal-free catalyst was carried out. The PLLA brushes synthesis was evaluated using two types of thiol monolayer and revealed the influence of ROP initiator chain length on the final thickness of the PLLA film. Combining the soft lithographic technique, microcontact printing, and the liquid phase deposition, the deposition onto specific micro-domains of both initiators was performed. The growth of PDMAEMA brushes and PLLA brushes was conducted by successive ATRP and ROP.
Polymer brushes represent a relatively new class of materials and are referred to an assembly of polymer chains tethered by one of their extremities to a surface by a chemical bond. Different ...techniques to produce polymer brushes exist but our privileged choice was about the ¡§grafting from¡¨ method due to the better control over the types of grafted polymer, the surface-grafting density, and the chain-lengths. In our project, we focused on polymerizations from self-assembled monolayers of thiol chemisorbed on gold surface, bearing end-group functions as anchoring sites. The main objective of this work is to develop multifunctional polymeric surfaces composed by micro-domains of diverse compounds, which contain opposite features. Poly(ƓÕ-caprolactone) and poly(L,L-lactide)-based brushes both known for their high degree of crystallinity and hydrophobicity, and poly(dimethylamino ethyl methacrylate) (PDMAEMA)-based brushes for their hydrophilicity and external stimuli responsive characteristics were investigated. Moreover, the design of these advanced materials can be achieved with patterning technique such as micro-contact printing, leading to a spatial confinement of the polymer brushes.
In order to reach our objective, the thesis was decomposed in different parts. First, the preparation of homogeneous and heterogeneous monolayers derived from thiols on gold surface will be investigated. Secondly, the ¡§grafting from¡¨ synthesis of homo-polymers from thiol end group will be carried out. This part required the development of synthesis conditions for both types of homopolymer brushes. Subsequently, these parameters were applied to the creation of a binary system by the growth of two different macromolecular chains on the same substrate. Finally, upon the ¡§smart¡¨ behavior of PDMAEMA, the potential of the polymer as chemical sensor was evaluated with single walled and multi walled-carbon nanotubes (SW- and MW-CNTs) as interesting conductive (nano)fillers.
Progress toward finding a cure for muscle diseases has been slow because of the absence of relevant cellular models and the lack of a reliable source of muscle progenitors for biomedical ...investigation. Here we report an optimized serum-free differentiation protocol to efficiently produce striated, millimeter-long muscle fibers together with satellite-like cells from human pluripotent stem cells (hPSCs) in vitro. By mimicking key signaling events leading to muscle formation in the embryo, in particular the dual modulation of Wnt and bone morphogenetic protein (BMP) pathway signaling, this directed differentiation protocol avoids the requirement for genetic modifications or cell sorting. Robust myogenesis can be achieved in vitro within 1 month by personnel experienced in hPSC culture. The differentiating culture can be subcultured to produce large amounts of myogenic progenitors amenable to numerous downstream applications. Beyond the study of myogenesis, this differentiation method offers an attractive platform for the development of relevant in vitro models of muscle dystrophies and drug screening strategies, as well as providing a source of cells for tissue engineering and cell therapy approaches.
Background
Data on the prevalence of bacterial and viral co-infections among patients admitted to the ICU for acute respiratory failure related to SARS-CoV-2 pneumonia are lacking. We aimed to assess ...the rate of bacterial and viral co-infections, as well as to report the most common micro-organisms involved in patients admitted to the ICU for severe SARS-CoV-2 pneumonia.
Patients and methods
In this monocenter retrospective study, we reviewed all the respiratory microbiological investigations performed within the first 48 h of ICU admission of COVID-19 patients (RT-PCR positive for SARS-CoV-2) admitted for acute respiratory failure.
Results
From March 13th to April 16th 2020, a total of 92 adult patients (median age: 61 years, 1st–3rd quartiles 55–70; males:
n
= 73/92, 79%; baseline SOFA: 4 3–7 and SAPS II: 31 21–40; invasive mechanical ventilation:
n
= 83/92, 90%; ICU mortality:
n
= 45/92, 49%) were admitted to our 40-bed ICU for acute respiratory failure due to SARS-CoV-2 pneumonia. Among them, 26 (28%) were considered as co-infected with a pathogenic bacterium at ICU admission with no co-infection related to atypical bacteria or viruses. The distribution of the 32 bacteria isolated from culture and/or respiratory PCRs was as follows: methicillin-sensitive
Staphylococcus aureus
(
n
= 10/32, 31%),
Haemophilus influenzae
(
n
= 7/32, 22%),
Streptococcus pneumoniae
(
n
= 6/32, 19%), Enterobacteriaceae (
n
= 5/32, 16%),
Pseudomonas aeruginosa
(
n
= 2/32, 6%),
Moraxella catarrhalis
(
n
= 1/32, 3%) and
Acinetobacter baumannii
(
n
= 1/32, 3%). Among the 24 pathogenic bacteria isolated from culture, 2 (8%) and 5 (21%) were resistant to 3rd generation cephalosporin and to amoxicillin–clavulanate combination, respectively.
Conclusions
We report on a 28% rate of bacterial co-infection at ICU admission of patients with severe SARSCoV-2 pneumonia, mostly related to
Staphylococcus aureus, Haemophilus influenzae
,
Streptococcus pneumoniae
and Enterobacteriaceae. In French patients with confirmed severe SARSCoV-2 pneumonia requiring ICU admission, our results encourage the systematic administration of an empiric antibiotic monotherapy with a 3rd generation cephalosporin, with a prompt de-escalation as soon as possible. Further larger studies are needed to assess the real prevalence and the predictors of co-infection together with its prognostic impact on critically ill patients with severe SARS-CoV-2 pneumonia.
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