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Microfluidic formation of pH responsive 5CB droplets decorated with PAA-<i>b</i>-LCP
Khan, Waliullah,Choi, Jin Ho,Kim, Gyu Man,Park, Soo-Young Royal Society of Chemistry 2011 Lab on a chip Vol.11 No.20
<P>We are reporting for the first time the pH responsiveness of liquid crystal (LC) microdroplets decorated with an amphiphilic block copolymer of PAA-<I>b</I>-LCP. We successfully demonstrated the adsorption of block copolymer on LC droplets by fluorescence microscopy and pH response to the radial-to-bipolar orientational change of the LC droplets by changing pH from 12 to 2 through the polarized optical microscope (POM). We believe that our results may pave the way for the generation of monodisperse droplets decorated by various amphiphilic block copolymers which respond to several kinds of the external stimuli. These developments may be important for potential applications of the LC droplets in sensing and encapsulation fields.</P> <P>Graphic Abstract</P><P>pH-responsive 5CB droplets coated with PAA-<I>b</I>-LCP are reported which have many potential applications based on LC droplets. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1lc20402e'> </P>
Khan, Waliullah,Seo, Jung-Min,Park, Soo-Young The Royal Society of Chemistry 2011 Soft matter Vol.7 No.2
<P>A novel diblock copolymer of poly(<I>N</I>-isopropylacrylamide)-<I>b</I>-poly(4-cyanobiphenyl-4-oxyundecylacrylate) (PNIPAM-<I>b</I>-LCP) was synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. PNIPAM-<I>b</I>-LCP was formed into the core–shell micelle in an aqueous solution, which consisted of the hydrophobic LCP block in the core and the hydrophilic PNIPAM block in the shell with a critical micelle concentration of 0.043 mg mL<SUP>−1</SUP>. The hydrophobic 4-cyano-4′-pentylbiphenyl (5CB, nematic liquid crystal (LC)) was added into the PNIPAM-<I>b</I>-LCP aqueous solution to incorporate hydrophobic LC monomers in the micelle core. The size of the micelles increased as the concentration of the 5CB increased, indicating that the 5CB was successfully loaded in the core. The size of the PNIPAM-<I>b</I>-LCP micelle in water also showed a step-wise decrease at ∼33 °C as temperature increased (or <I>vice versa</I>) due to the lower critical solution temperature (LCST) behavior of the PNIPAM. The combination of the LC properties in the core and the thermo-responsive behaviors in the shell might open new applications in the fields of smart windows, nanoactuation, controlled release, photonics, <I>etc.</I></P> <P>Graphic Abstract</P><P>The novel PNIPAM-<I>b</I>-LCP might work as a block copolymer surfactant of LC which makes the 5CB droplets stable and thermo-responsive. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0sm00758g'> </P>
Khan, Waliullah,Park, Soo-Young Royal Society of Chemistry 2012 Lab on a chip Vol.12 No.21
<P>4-cyano-4'-pentylbiphenyl (5CB) microdroplets coated with PAA-b-LCP were successfully made via microfluidics. Their functionalized interfaces were examined for lysozyme and bovine serum albumin detection, which could be easily visualized with an optical microscope under crossed polarizers by the radial-to-bipolar configurational change of the 5CB. This transition was strongly dependent on the electrostatic states of the proteins and PAA chains, which were controlled by the pH of the water. This study demonstrated a simple approach for the development of a liquid crystal-based sensor for label-free detection of proteins, which may have diverse applications in various biomedical fields.</P>
Seo, Jung-Min,Khan, Waliullah,Park, Soo-Young The Royal Society of Chemistry 2012 Soft matter Vol.8 No.1
<p>The interface between 5CB and water in a TEM grid by decoration of an amphiphilic block copolymer of PAA-<I>b</I>-LCP was examined for protein detection. Several proteins were detected at a few μM levels through homeotropic to planar orientational change (H–P change) of the 5CB. The H–P change became slow as the pH of water increased above the isoelectric point (pI) of the protein, and areal density of the monolayer and salt concentration increased. The TEM grid cell could detect proteins of human urine from a patient having albuminuria with a detection limit of as low as 0.032 mg mL<SUP>−1</SUP>.</p> <P>Graphic Abstract</P><P>The aqueous/LC interface decorated by PAA-<I>b</I>-LCP is examined for protein detection at μM levels through homeotropic to planar orientational change of the 5CB. <img src='http://pubs.rsc.org/ej/SM/2011/c1sm06616a/c1sm06616a-ga.gif'> </P>
Structural evolution of graphite oxide during heat treatment
Kim, Chan-Jun,Khan, Waliullah,Park, Soo-Young Elsevier 2011 Chemical physics letters Vol.511 No.1
<P><B>Graphical abstract</B></P><P><ce:figure id='f0025'></ce:figure></P><P><B>Highlights</B></P><P>► Effects of annealing on the removal of various functional groups from GO film. ► Annealing at higher temperatures might recover electrical conductivity. ► Dispersion of GOs provides a methodology for developing a composite system.</P> <P><B>Abstract</B></P><P>Structural evolution of graphite oxide (GO) during annealing was studied using different techniques. The oxygen containing groups were reduced step-wise at ∼220°C due to removal of the –OH and –COOH groups. These results suggest that the annealing at ∼220°C might recover partial electrical conductivity of the GO (from 10<SUP>−6</SUP> to 13S/cm within less than 10min) and provide a methodology for developing an electrically conducting composite system by first dispersing the GOs in the matrix, then exfoliation by sonication, and finally heating the composite system at desirable temperatures although complete recovery of the electrical conductivity may not be possible with moderate heat treatment.</P>
( Naiyer Asif ),( Mohammad Jesan Khan ),( K. P. Haris ),( Shah Waliullah ),( Anubhav Sharma ),( Danish Firoz ) 대한슬관절학회 2021 대한슬관절학회지 Vol.33 No.-
Purpose: Suspensory devices are extensively used in the management of anterior cruciate ligament (ACL) tear. They include fixed- and adjustable-loop devices. There are only a few studies comparing the efficacy of these two devices in the available literature. Therefore, the aim of this study is to compare clinical outcomes between the adjustableloop device (group I) and fixed-loop device (group II). Materials and methods: This was a prospective randomized study. Both groups were equivalent in demographic, preoperative, and intraoperative variables. Twenty-three patients underwent femoral side graft fixation with adjustable- loop and 20 with fixed-loop devices. Four patients were lost to follow-up. Assessment of clinical outcome was done with International Knee Documentation Committee (IKDC) score, Lysholm score, and knee stability tests (Lachman test and pivot shift test). Patient evaluation was performed preoperatively and finally postoperatively 2 years after surgery. Results: Postoperative IKDC scores of group I and II were 91.9 ± 3.6 and 91.5 ± 3.6, respectively, and Lysholm scores were 91.0 ± 3.6 and 91.4 ± 3.5, respectively, after 2 years; however, the difference in the outcomes was statistically insignificant (p > 0.05). Twenty patients (87%) in group I and 17 patients (85%) in group II had a negative Lachman test (p = 0.8). Twenty-two patients (95.7%) in group I and 19 patients (95%) in group II had a negative pivot shift test (p = 0.9). Conclusion: ACL reconstruction with fixed- and adjustable-loop suspensory devices for graft fixation gives equivalent and satisfactory clinical results. Level of evidence: 1.
pH-responsive aqueous/LC interfaces using SGLCP-<i>b</i>-polyacrylic acid block copolymers
Lee, Dong-Yul,Seo, Jung-Min,Khan, Waliullah,Kornfield, Julia A,Kurji, Zuleikha,Park, Soo-Young Royal Society of Chemistry 2010 SOFT MATTER Vol.6 No.9
<P>Block copolymers that combine a side-group liquid crystalline polymer (SGLCP) block and a pH-responsive hydrophilic block, poly(acrylic acid) (PAA), are shown to confer pH-dependent anchoring of the director orientation at the aqueous/LC interface. The SGLCP block, poly(4-cyanobiphenyl-4-oxyundecylacrylate), was chosen based on its ability to influence the director field of the 5CB (4-cyano-4′-pentylbiphenyl). At low pH the PAA block collapses and the inherent, planar alignment tendency of 5CB at a water interface prevails. As pH increases, the polyelectrolyte block becomes increasingly charged and expands, producing a change to homeotropic anchoring. The change in anchoring occurs as quickly as the buffer can be changed (within ∼2 s) and is reversible, with a response that is repeatable over as many cycles as were tested (approximately 20 cycles). The polymer-mediated anchoring persists for 6 days, indicating that the SGLCP block secures the self-assembled layer on the 5CB, even under conditions that cause repulsive interactions among the PAA blocks. Thus, SGLCP blocks can translate conformational changes of a responsive hydrophilic block into rapid, reversible changes in the director field.</P> <P>Graphic Abstract</P><P>A polyacrylic acid sensing domain changes from a collapsed conformation to an expanded one by variation of pH which changes the appearance from bright to dark when viewed between crossed polarizers. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b926461b'> </P>