Construction of Tough Hydrogel Cross-Linked via Ionic Interaction by Protection Effect of Hydrophobic Domains.

Most hydrogels have poor mechanical properties, severely limiting their potential applications, and numerous approaches have been introduced to fabricate more robust and durable examples. However, these systems consist of nonbiodegradable polymers which limit their application in tissue engineering. Herein, we focus on the fabrication and investigate the influence of hydrophobic segments on ionic cross-linking properties for the construction of a tough, biodegradable hydrogel. A biodegradable, poly(γ-glutamic acid) polymer conjugated with a hydrophobic amino acid, l-phenylalanine ethyl ester (Phe), together with an ionic cross-linking group, alendronic acid (Aln) resulting in γ-PGA-Aln-Phe, was initially synthesized. Rheological assessments through time sweep oscillation testing revealed that the presence of hydrophobic domains accelerated gelation. Comparing gels with and without hydrophobic domains, the compressive strength of γ-PGA-Aln-Phe was found to be six times higher and exhibited longer stability properties in ethylenediaminetetraacetic acid solution, lasting for up to a month. Significantly, the contribution of the hydrophobic domains to the mechanical strength and stability of ionic cross-linking properties of the gel was found to be the dominant factor for the fabrication of a tough hydrogel. As a result, this study provides a new strategy for mechanical enhancement and preserves ionic cross-linked sites by the addition of hydrophobic domains. The development of tough, biodegradable hydrogels reported herein will open up new possibilities for applications in the field of biomaterials.

Functionalizable bacterial cellulose composite membrane for guided tissue regeneration.

This research aims to develop guided tissue regeneration (GTR) membranes from bacterial cellulose (BC), a natural polysaccharide-based biopolymer. A double-layered BC composite membrane was prepared by coating the BC membrane with mixed carboxymethyl cellulose/poly(ethylene oxide) (CMC/PEO) fibers via electrospinning. The CMC/PEO-BC membranes were then characterized for their chemical and physical characteristics. The 8 % (wt/v) CMC/PEO (1:1) aqueous solution yielded well-defined electrospun CMC/PEO nanofibers (125 ± 10 nm) without beads. The CMC/PEO-BC membranes exhibited good mechanical and swelling properties as well as good cytocompatibility against human periodontal ligament cells (hPDLs). Its functionalizability via carboxyl entities in CMC was tested using the calcium-binding domain of plant-derived recombinant human osteopontin (p-rhOPN-C122). As evaluated by enzyme-linked immunosorbent assay, a 98-99 % immobilization efficiency was achieved in a concentration-dependent manner over an applied p-rhOPN-C122 concentration range of 7.5-30 ng/mL. The biological function of the membrane was assessed by determining the expression levels of osteogenic-related gene transcripts using quantitative real-time reverse-transcriptase polymerase chain reaction. Mineralization assay indicated that the p-rhOPN-C122 immobilized CMC/PEO-BC membrane promoted hPDLs osteogenic differentiation. These results suggested that the developed membrane could serve as a promising GTR membrane for application in bone tissue regeneration.

Current significance and future perspective of 3D-printed bio-based polymers for applications in energy conversion and storage system.

The increasing global population has led to a surge in energy demand and the production of environmentally harmful products, highlighting the urgent need for renewable and clean energy sources. In this context, sustainable and eco-friendly energy production strategies have been explored to mitigate the adverse effects of fossil fuel consumption to the environment. Additionally, efficient energy storage devices with a long lifespan are also crucial. Tailoring the components of energy conversion and storage devices can improve overall performance. Three-dimensional (3D) printing provides the flexibility to create and optimize geometrical structure in order to obtain preferable features to elevate energy conversion yield and storage capacitance. It also serves the potential for rapid and cost-efficient manufacturing. Besides that, bio-based polymers with potential mechanical and rheological properties have been exploited as material feedstocks for 3D printing. The use of these polymers promoted carbon neutrality and environmentally benign processes. In this perspective, this review provides an overview of various 3D printing techniques and processing parameters for bio-based polymers applicable for energy-relevant applications. It also explores the advances and current significance on the integration of 3D-printed bio-based polymers in several energy conversion and storage components from the recently published studies. Finally, the future perspective is elaborated for the development of bio-based polymers via 3D printing techniques as powerful tools for clean energy supplies towards the sustainable development goals (SDGs) with respect to environmental protection and green energy conversion.

Zwitterionic hydrogel for preserving stability and activity of oxidase enzyme for electrochemical biosensor.

Enzymatic electrochemical biosensor is the most common analytical platform for medical diagnosis. To mimic the biological environment of the enzyme for maintaining the function of biosensor, zwitterionic hydrogels have been recognized as effective matrices for enzymatic immobilization. Herein, a zwitterionic hydrogel derived from a copolymer, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-N-methacryloyloxyethyl tyrosine methylester (MAT)] (PMM) was firstly applied as versatile coating to preserve stability and activity of oxidase enzymes, glucose oxidase (GOx) and lactate oxidase (LOx) for enzymatic electrochemical sensor. A screen-printed carbon electrode (SPCE) was sequentially coated with nitrogen-doped graphene (NDG), oxidase enzyme, and PMM mixed with Ru(II)bpy32+ and (NH4)2S2O8 followed by visible light irradiation for 3 min to induce PMM gelation. Electrochemical detection of glucose and lactate using the modified SPCE was performed via amperometry in the presence of hydrogen peroxide. The activity of both GOx and LOx immobilized on the modified SPCE was well maintained for 49 days at 87 and 80 %, respectively. Additionally, two different electrodes, a screen-printed graphene electrode (SPGE), and a screen-printed silver electrode (SPAgE), similarly modified gave the same satisfactory detection of spiked glucose and lactate in human plasma and sweat with 93-118 % recovery. This indicates the potential of the PMM hydrogel as a universal platform for preservation of enzymes which can be easily fabricated without the need for specific chemical modification of the electrode.

Zwitterionic Polymer-Decorated Lipid Nanoparticles for mRNA Delivery in Mammalian Cells.

Lipid nanoparticles (LNPs) play a key role in the effective transport of mRNA into cells for protein translation. Despite the stealthiness of poly(ethylene glycol) (PEG) that helps protect LNPs from protein absorption and blood clearance, the generation of anti-PEG antibodies resulting in PEG allergies remains a challenge for the development of an mRNA vaccine. Herein, a non-PEG lipid was developed by conjugating 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) with an antifouling zwitterionic polymer, poly(2-methyacryloyloxyethyl phosphorylcholine) (PMPC), of different chain lengths. The PMPC-LNPs formulated from DPPE-PMPC were spherical (diameter ≈ 144-255 nm), neutral in charge, and stable at 4 °C for up to 28 days. Their fraction of stealthiness being close to 1 emphasized the antifouling characteristics of PMPC decorated on LNPs. The PMPC-LNPs were nontoxic to HEK293T cells, did not induce inflammatory responses in THP-1 cells, and exhibited an mRNA transfection efficiency superior to that of PEG-LNPs. This work demonstrated the potential of the developed zwitterionic polymer-conjugated LNPs as promising mRNA carriers.

Bacterial cellulose composite hydrogel for pre-concentration and mass spectrometric detection of thiol-containing biomarker.

Simple soaking of bacterial cellulose (BC) membrane in carboxymethyl cellulose (CMC) solution yielded BC/CMC hydrogel having re-swellable property. Then, gold nanoparticles (AuNPs) were embedded in the BC/CMC hydrogel via in situ chemical reduction to form BC/CMC/AuNPs composite hydrogel. It was found that the composite hydrogel exhibited physical/chemical characteristics similar to those of BC. The AuNPs with an average diameter of 13 nm distributed uniformly within the BC/CMC matrix as verified by transmission electron microscopy. The novelty of this work is the application of the BC/CMC/AuNPs composite hydrogel for selective adsorption of an important thiol-containing biomarker of Alzheimer's disease, glutathione (GSH), prior to direct laser desorption/ionization mass spectrometric (LDI-MS) detection. GSH adsorbed in the BC/CMC/AuNPs composite hydrogel showed the high ionization signal in LDI-MS providing a linear range of 50-10,000 nM with a limit of detection as low as 54.1 nM, which is a cut-off level for distinguishing between normal individuals and Alzheimer's patients. It should be emphasized that an additional matrix was not necessary as AuNPs can act as self-matrix for LDI-MS analysis. Furthermore, the BC/CMC/AuNPs composite hydrogel can effectively preconcentrate GSH approximately 10 times upon adsorption allowing for ultrasensitive detection of GSH required for disease diagnosis.

Pyrene-Labeled and Quaternized Chitosan: Synthesis, Characterization, and Its Potential Application for Fluorescently Trackable Nucleic Acid Delivery into Cells.

A chitosan derivative (Pyr-CS-HTAP) having pyrene (Pyr) and N-[(2-hydroxyl-3-trimethylammonium)] propyl (HTAP) units conjugated at C6 and C2 positions, respectively, was synthesized and characterized. Dynamic light scattering and scanning electron microscopy revealed that Pyr-CS-HTAP self-assembled into spherical nanoparticles with a hydrodynamic diameter of 211 ± 5 nm and a ζ-potential of +49 mV. The successful binding of Pyr-CS-HTAP with nucleic acid was ascertained by fluorescence resonance energy-transfer analysis and gel electrophoresis. Pyr-CS-HTAP facilitated the cellular uptake of nucleic acid up to 99%. Co-localization analysis using fluorescence microscopy revealed the endosomal escape of the Pyr-CS-HTAP/nucleic acid complexes and the successful release of the nucleic acid cargoes from the polyplexes into the nucleus. It is strongly believed that Pyr-CS-HTAP can potentially be developed into a fluorescently trackable gene delivery system in the future.

Introduction of an Ambient 3D-Printable Hydrogel Ink to Fabricate an Enzyme-Immobilized Platform with Tunable Geometry for Heterogeneous Biocatalysis.

An enzyme-immobilized platform for biocatalysis was developed through 3D printing of a hydrogel ink comprising dimethacrylate-functionalized Pluronic F127 (F127-DMA) and sodium alginate (Alg) with laccase that can be done at ambient temperature, followed by UV-induced cross-linking. Laccase is an enzyme that can degrade azo dyes and various toxic organic pollutants. The fiber diameter, pore distance, and surface-to-volume ratio of the laccase-immobilized and 3D-printed hydrogel constructs were varied to determine their effects on the catalytic activity of the immobilized enzyme. Among the three geometrical designs investigated, the 3D-printed hydrogel constructs with flower-like geometry exhibited better catalytic performance than those with cubic and cylindrical geometries. Once tested against Orange II degradation in a flow-based format, they can be reused for up to four cycles. This research demonstrates that the developed hydrogel ink can be used to fabricate other enzyme-based catalytic platforms that can potentially increase their industrial usage in the future.

Amphiphilic Chitosan Bearing Double Palmitoyl Chains and Quaternary Ammonium Moieties as a Nanocarrier for Plasmid DNA.

Amphiphilic chitosan, bPalm-CS-HTAP, having N-(2-((2,3-bis(palmitoyloxy)propyl)amino)-2-oxoethyl) (bPalm) groups as double hydrophobic tails and O-[(2-hydroxyl-3-trimethylammonium)] propyl (HTAP) groups as hydrophilic heads was synthesized and evaluated for its self-assembly properties and potential as a gene carrier. The degree of bis-palmitoyl group substitution (DS bPalm) and the degree of quaternization (DQ) were approximately 2 and 56%, respectively. bPalm-CS-HTAP was found to assemble into nanosized spherical particles with a hydrodynamic diameter (D H) of 265.5 ± 7.40 nm (PDI = 0.5) and a surface charge potential of 40.1 ± 0.04 mV. bPalm-CS-HTAP condensed the plasmid pVAX1.CoV2RBDme completely at a bPalm-CS-HTAP:pDNA ratio of 2:1. The self-assembled bPalm-CS-HTAP/pDNA complexes could enter HEK 293A and CHO cells and enabled gene expression at negligible cytotoxicity compared to commercial PEI (20 kDa). These results suggested that bPalm-CS-HTAP can be used as a promising nonviral gene carrier.

Conductive electrospun composite fibers based on solid-state polymerized Poly(3,4-ethylenedioxythiophene) for simultaneous electrochemical detection of metal ions.

Conductive composite fibers containing poly (3,4-ethylenedioxythiophene) (PEDOT) and silver nanoparticles (AgNPs) were fabricated by emulsion electrospinning of 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) in toluene together with aqueous solution of poly (vinyl alcohol) (PVA) and silver nanoparticles (AgNPs) in the presence of sodium dodecylsulfate followed by heat treatment at 70 °C to convert DBEDOT to conductive PEDOT via solid state polymerization (SSP). The composite fibers were characterized by scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy and thermogravimetric analysis. The PEDOT/PVA/AgNPs composite fibers deposited on a screen-printed carbon electrode (SPCE) surface exhibited good electrochemical response and was applied for simultaneous detection of heavy metal ions in a mixture, namely Zn(II), Cd(II), and Pb(II) via square wave anodic stripping voltammetry (SWASV). With added Bi+3 into the detection system, the bismuth film formed on the electrode allows effective alloy formation with the deposited heavy metals obtained upon reduction of the heavy metal ions, the detection of heavy metal ions after stripping was successfully accomplished with a linear range of 10-80 ppb and limits of detections (LOD) of 6, 3 and 8 ppb for Zn(II), Cd(II), and Pb(II), respectively.

Amphiphilic quaternized chitosan: Synthesis, characterization, and anti-cariogenic biofilm property.

Hydrophobized chitosan derivatives, hexyl chitosan (HCS), dodecyl chitosan (DCS), and phthaloyl chitosan (PhCS) of approximately 30 and 50% degree of substitution (%DS) reacted with glycidyltrimethylammonium chloride (GTMAC) to incorporate hydrophilic positively charged groups of N-[(2-hydroxyl-3-trimethylammonium)propyl] and yielded amphiphilic quaternized chitosan derivatives. They can assemble into spherical nanoparticles with a hydrodynamic diameter of ~100-300 nm and positive ζ-potential values (+15 to +56). Their anti-biofilm efficacy was evaluated against the dental caries pathogen, Streptococcus mutans. Among all derivatives, the one having 30%DS of hexyl group and prepared by reacting with 1 mol equivalent of GTMAC (H30CS-GTMAC) showed the best performance in terms of its aqueous solubility, the lowest minimum inhibitory concentration (138 µg/mL) and the minimum bactericidal concentration (275 µg/mL) which are superior to the unmodified chitosan. Its equivalent anti-biofilm efficacy to that of chlorhexidine suggests that it can be a greener antibacterial agent for oral care formulations.

Upper Critical Solution Temperature Behavior of pH-Responsive Amphoteric Statistical Copolymers in Aqueous Solutions.

Amphoteric statistical equivalent copolymers (P(2VP/NaSS) n ) composed of 2-vinylpyridine (2VP) and anionic sodium p-styrenesulfonate (NaSS) were prepared via reversible addition-fragmentation chain transfer polymerization. The degrees of polymerization (n) were 19 and 95. The monomer reactivity ratio, time conversion profile, and 1H nuclear magnetic resonance diffusion-ordered spectra suggested that the copolymerization of 2VP and NaSS provided statistical or near to random copolymers. P(2VP/NaSS) n exhibited an upper critical solution temperature (UCST) in acidic aqueous solutions on the basis of the charge interactions between the protonated cationic 2VP and anionic NaSS units. With an increase in pH value, the interaction was weakened because of the deprotonation of the 2VP units, thus reducing the UCST. At high [NaCl], the electrostatic interactions among the polymers were weakened because of the screening effect, and again, the UCST was reduced. With an increase in polymer concentration, the intra- and interpolymer interactions increased because of some entanglement, and the UCST consequently increased. Electrostatic interactions among the polymer chains with high molecular weight occurred easier than those among the low-molecular-weight polymer chains, which increased the UCST. The UCST also increased when deuterium oxide was used instead of hydrogen oxide, which was due to the isotopic effect. Hence, the UCST of P(2VP/NaSS) n can be adjusted according to the desired application.

Bacterial cellulose-based re-swellable hydrogel: Facile preparation and its potential application as colorimetric sensor of sweat pH and glucose.

Direct deposition of the negatively charged polyelectrolyte, carboxymethyl cellulose (CMC), into a bacterial cellulose (BC) matrix was used as a simple route to fabricate a re-swellable and biocompatible cellulose-based hydrogel. As a result of this non-destructive approach, the physical and mechanical property of the original BC were well-preserved within the resulting BC/CMC hydrogel. As a BC/CMC-based colorimetric pH sensor, it exhibited a rapid response with an easy color differentiation between each pH by the naked eye, and wide linear range of pH 4.0-9.0 with good linearity. For the detection of glucose in sweat, the BC/CMC-based colorimetric glucose sensor provided a low limit of detection (25 µM) with a wide linear detection range (0.0-0.5 mM) and high accuracy. These BC/CMC based sensors could potentially be applied as non-invasive semi-quantitative sensors for on-skin health monitoring.

Simple Colorimetric Assay for Vibrio parahaemolyticus Detection Using Aptamer-Functionalized Nanoparticles.

Simple, rapid, and sensitive screening methods are the key to prevent and control the spread of foodborne diseases. In this study, a simple visual colorimetric assay using magnetic nanoparticles (MNPs) and gold nanoparticles (AuNPs) was developed for the detection of Vibrio parahaemolyticus. First, the aptamer responding to V. parahaemolyticus was conjugated onto the surface of MNPs and used as a specific magnetic separator. In addition, the aptamer was also immobilized on the surface of AuNPs and used as a colorimetric detector. In the presence of V. parahaemolyticus, a sandwich structure of MNP-aptamer-bacteria-aptamer-AuNPs is formed through specific recognition of the aptamer and V. parahaemolyticus. The magnetic separation technique was then applied to generate a detection signal. Owing to the optical properties of AuNPs, a visual signal could be observed, resulting in an instrument-free colorimetric detection. Under optimal conditions, this assay shows a linear response toward V. parahaemolyticus concentration through the range of 10-106 cfu/mL, with a limit of detection of 2.4 cfu/mL. This method was also successfully applied for V. parahaemolyticus detection in spiked raw shrimp samples.

Protein patterning with antifouling polymer gel platforms generated using visible light irradiation.

Visible light-assisted protein patterning on a solid surface was performed with phosphorylcholine (PC) polymers bearing tyrosine residues. Because of the antifouling nature of PC polymers, protein immobilisation was regiospecifically controlled, thus enabling the microfabricated surfaces to be used as immunoassay platforms.

Bacterial cellulose membrane conjugated with plant-derived osteopontin: Preparation and its potential for bone tissue regeneration.

Bacterial cellulose membrane (BCM) has been recently recognized as a new generation of carbohydrate-based nanomaterial that possesses a great potential in tissue engineering applications. This research aims to develop an active non-resorbable guided tissue regeneration (GTR) membrane from BCM by conjugating with plant-derived recombinant human osteopontin (p-rhOPN), an economically produced and RGD-containing biomolecule. The BCM was initially grafted with poly(acrylic acid) (PAA) brushes to form poly(acrylic acid)-grafted BCM. Multiple carboxyl groups introduced to the BCM by PAA can serve as active anchoring points for p-rhOPN conjugation and yielded p-rhOPN-BCM. All chemically modified BCMs were characterized by attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, while their surface morphology was evaluated by field emission-scanning electron microscopy and atomic force microscopy analyses. The amount of p-rhOPN adhered on the membrane was quantified by enzyme-linked immunosorbent assay. The immunocytochemistry, two-stage quantitative real-time reverse transcriptase polymerase chain reaction and in vitro mineralization analyses strongly suggested that p-rhOPN-BCM could elicit biological functions leading to the enhancement of osteogenic differentiation of human periodontal ligament stem cells as effective as BCM conjugated with commercially available rhOPN from mammalian cells (rhOPN-BCM), suggesting its potential to be used as GTR membrane to promote bone tissue regeneration.

Sequential post-polymerization modification of a pentafluorophenyl ester-containing homopolymer: a convenient route to effective pH-responsive nanocarriers for anticancer drugs.

Recently, pH-responsive polymeric micelles have gained significant attention as effective carriers for anti-cancer drug delivery. Herein, pH-responsive polymeric micelles were constructed by a simple post-polymerization modification of a single homopolymer, poly(pentafluorophenyl acrylate) (PPFPA). The PPFPA was first subjected to modification with 1-amino-2-propanol yielding the amphiphilic copolymer of poly(pentafluorophenyl acrylate)-ran-poly(N-(2-hydroxypropyl acrylamide)). A series of amphiphilic random copolymers of different compositions could self-assemble into spherical micelles with a unimodal size distribution in aqueous solution. Then, 1-(3-aminopropyl)imidazole (API), a reagent to introduce charge conversional entities, was reacted with the remaining PPFPA segment in the micellar core resulting in API-modified micelles which can encapsulate doxorubicin (DOX), a hydrophobic anti-cancer drug. As monitored by dynamic light scattering, the API-modified micelles underwent disintegration upon pH switching from 7.4 to 5.0, presumably due to imidazolyl group protonation. This pH-responsiveness of the API-modified micelles was responsible for the faster and greater in vitro DOX release in an acidic environment than neutral pH. Cellular uptake studies revealed that the developed carriers were internalized into MDA-MB-231 cells within 30 min via endocytosis and exhibited cytotoxicity in a dose-dependent manner.

Disposable paper-based electrochemical sensor using thiol-terminated poly(2-methacryloyloxyethyl phosphorylcholine) for the label-free detection of C-reactive protein.

A paper-based electrochemical sensor is described that is based on the use of thiol-terminated poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC-SH) that was self-assembled on a gold nanoparticle-modified screen-printed electrode (SPE). The SPE sensor was used for label-free detection of C-reactive protein (CRP). Gold nanoparticles (AuNPs) were first electrodeposited on the SPCE, followed by the self-assembly of PMPC-SH on gold. The electrochemical response of the modified SPE to CRP was measured by differential pulse voltammetry (DPV). If the CRP on the paper device is contacted with Ca (II) ions, the current (measured by using hexacyanoferrate as the electrochemical probe) decreases. The signal drops in the 5 to 5000 ng·mL-1 CRP concentration range, and the lower detection limit (at 3 SD/slope) is 1.6 ng·mL-1. The use of a PMPC-modified surface also reduces the nonspecific adsorption of proteins. The sensor is not interfered by bilirubin, myoglobin and albumin. It was successfully applied to CRP detection in certified human serum. This sensor is applicable as an attractive protocol for an inexpensive, highly sensitive, and disposable material for electrochemical detection of CRP. Graphical abstract Schematic presentation of highly sensitive and disposable paper-based electrochemical sensor using thiol-terminated poly(2-methacryloyloxyethyl phosphorylcholine) in the presence of Ca2+ for the label-free C-reactive protein detection. The current was measured by differential pulse voltammetry.

Surface-immobilized plant-derived osteopontin as an effective platform to promote osteoblast adhesion and differentiation.

In this report, recombinant human osteopontin synthesized in tobacco plants (p-rhOPN) is introduced as a potential bioactive molecule that can promote osteoblast adhesion and differentiation. A glass substrate (SiO2/Si-OH) grafted with poly(acrylic acid) (SiO2/Si-PAA) was prepared by surface-initiated reversible addition-fragmentation chain transfer polymerization and used as a carboxyl-rich platform for the chemical conjugation of p-rhOPN. The PAA grafting and subsequent p-rhOPN immobilization were confirmed by water contact angle, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy analyses. Indirect ELISA quantification revealed that the p-rhOPN immobilization efficiency was above 95% and the surface coverage was a function of the p-rhOPN concentration. MC-3T3-E1 cells cultured on the SiO2/Si-PAA substrate immobilized with various concentrations (0.6-30 ng/mL) of p-rhOPN (SiO2/Si-p-rhOPN) exhibited superior cell spreading compared to those cultured on SiO2/Si-OH or gelatin-modified glass substrate (SiO2/Si-gelatin). Polymerase chain reaction analysis indicated that the SiO2/Si-p-rhOPN substrates with high level of immobilized p-rhOPN promoted MC-3T3-E1 cell differentiation, as demonstrated by the higher transcript expression levels of the osteogenic differentiation regulatory gene, Runt-related transcription factor 2, compared to cells cultured on SiO2/Si-OH or SiO2/Si-gelatin. Given that p-rhOPN can be more economically produced than the commercially available OPN derived from human or mammalian sources, then, together with its well-preserved biological function in spite of being chemically conjugated to the substrates, it is likely that p-rhOPN could be more broadly applied for the development of materials for bone tissue engineering with a promising medical and commercial value.

Filter paper grafted with epoxide-based copolymer brushes for activation-free peptide nucleic acid conjugation and its application for colorimetric DNA detection.

Epoxide-bearing filter paper was first prepared by surface-initiated reversible addition-fragmentation chain transfer (RAFT) copolymerization of glycidyl methacrylate (GMA) and poly(ethylene glycol)methacrylate (PEGMA). Without the need for activation step, the capture peptide nucleic acid (PNA) probes carrying a C-terminal lysine modification can be directly immobilized on the surface-grafted poly[glycidyl methacrylate-ran-poly(ethylene glycol)methacrylate] (P(GMA-ran-PEGMA)) through ring-opening of epoxide groups in the GMA repeating units by amino groups in the PNA's structure. The success of P(GMA-ran-PEGMA) grafting on the filter paper and subsequent PNA immobilization was confirmed by fluorescence microscopy, Fourier transform-infrared spectroscopy and X-ray photoelectron spectroscopy. Colorimetric detection with signal amplification upon DNA hybridization relies on sandwich-hybridization assay employing another biotinylated PNA strand as a reporter probe together with streptavidin-horseradish peroxidase conjugate (SA-HRP) and o-phenylenediamine (OPD) substrate. It was found that increasing ionic strength during the DNA hybridization step by addition of NaCl can increase the signal intensity, which can be visualized by naked eye. The sensing platform showed the best performance in preventing non-specific adsorption from the non-complementary DNA and discriminating between complementary and single-mismatched targets of at least 50 fmol without the requirement for stringent hybridization or washing condition. This superior ability to suppress non-specific adsorption of non-target DNA as well as other non-DNA components may be explained as a result of hydrophilic PEGMA repeating units in the surface-grafted copolymer.