Cationic amphiphilic model networks based on symmetrical ABCBA pentablock terpolymers: synthesis, characterization, and modeling

Eight isomeric networks based on equimolar terpolymers were synthesized using group transfer polymerization (GTP) and were characterized in terms of their swelling properties. Two hydrophilic monomers, the nonionic methoxy hexa(ethylene glycol) methacrylate (HEGMA) and the ionizable 2-(dimethylamino)ethyl methacrylate (DMAEMA), and a hydrophobic (nonionic) monomer, methyl methacrylate (MMA), were employed for the syntheses. 1,4-Bis(methoxytrimethylsiloxymethylene)cyclohexane (MTSMC) was used as the bifunctional GTP initiator, while ethylene glycol dimethacrylate (EGDMA) served as the cross-linker. Seven of the networks were model networks, six of which were based on the symmetrical pentablock terpolymers ABCBA, ACBCA, BACAB, BCACB, CBABC, and CABAC, whereas the seventh model network was based on the statistical terpolymer. The eighth network was a randomly cross-linked network based on the statistical terpolymer, prepared by the simultaneous quaterpolymerization of the three monomers and the cross-linker. The molecular weights and molecular weight distributions of the linear pentablock terpolymer precursors, as well as those of their homopolymer and ABA triblock copolymer precursors, were characterized by gel permeation chromatography (GPC) in tetrahydrofuran. The sol fraction of each network was measured and found to be relatively low. The aqueous degrees of swelling of all networks were found to increase at acidic pH due to the ionization of the DMAEMA tertiary amine units. The acidic degrees of swelling of the pentablock terpolymer networks were lower than those of their statistical counterparts due to microphase separation in the former type of networks, also confirmed by thermodynamic calculations and small-angle neutron scattering experiments.     

Synthesis, characterization, and DNA adsorption studies of ampholytic model conetworks based on cross-linked star copolymers

Five model conetworks based on cross-linked star ampholytic copolymers were synthesized by group transfer polymerization. The ampholytic copolymers were based on two hydrophilic monomers: the positively ionizable 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the negatively ionizable methacrylic acid (MAA). Ethylene glycol dimethacrylate was used as the cross-linker. These five ampholytic model conetworks were isomers based on equimolar DMAEMA-MAA copolymer stars of different architectures: heteroarm (two), star block (two), and statistical. The two networks based on the homopolymer stars were also synthesized. The MAA units were introduced via the polymerization of tetrahydropyranyl methacrylate and the acid hydrolysis of the latter after network formation. All the precursors to the (co)networks were characterized in terms of their molecular weights using gel permeation chromatography (GPC). The mass of the extractables from the (co)networks was measured and characterized in terms of molecular weight and composition using GPC and proton nuclear magnetic resonance (1H NMR) spectroscopy, respectively. The degrees of swelling (DS) of all the ampholytic conetworks were measured as a function of pH and were found to present a minimum at a pH value which was taken as the isoelectric point, pI. The DS and the pI values did not present a dependence on conetwork architecture. Finally, DNA adsorption studies onto the ampholyte conetworks indicated that DNA binding was governed by electrostatics.     

Amphiphilic model conetworks based on cross-linked star copolymers of benzyl methacrylate and 2-(dimethylamino)ethyl methacrylate: synthesis, characterization, and DNA adsorption studies

Six amphiphilic model conetworks of a new structure, that of cross-linked "in-out" star copolymers, were synthesized by the group transfer polymerization (GTP) of the hydrophobic monomer benzyl methacrylate (BzMA) and the ionizable hydrophilic monomer 2-(dimethylamino)ethyl methacrylate (DMAEMA) in a one-pot preparation. The synthesis took place in tetrahydrofuran (THF) using tetrabutylammonium bibenzoate (TBABB) as the catalyst, 1-methoxy-1-(trimethylsiloxy)-2-methyl-propene (MTS) as the initiator, and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. Three heteroarm star-, two star block-, one statistical copolymer star-, and one homopolymer star-based networks were prepared. The synthesis of these star-based networks involved four to six steps, including the preparation of the linear (co)polymers, the "arm-first" and the "in-out" star copolymers, and finally the network. The precursors and the extractables were characterized using gel permeation chromatography (GPC) and proton nuclear magnetic resonance (1H NMR) spectroscopy. The degrees of swelling (DSs) of all the networks were measured in THF, while the aqueous DSs were measured as a function of pH. The DSs at low pH were higher than those at neutral or high pH because of the protonation of the DMAEMA units and were found to be dependent on the structure of the network. The DSs in THF were higher than those in neutral water and were independent of the structure. Finally, DNA adsorption studies onto the networks indicated that the DNA binding was governed by electrostatics.     

Synthesis, characterization, and evaluation as transfection reagents of ampholytic star copolymers: effect of star architecture

Five star polymers based on the positively ionizable hydrophilic 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the hydrophobic but hydrolyzable tetrahydropyranyl methacrylate (THPMA) were prepared by group-transfer polymerization (GTP) using ethylene glycol dimethacrylate (EGDMA) as the coupling agent. In particular, four isomeric star copolymers (one heteroarm, two star block, and the statistical star), all with a 3:1 DMAEMA:THPMA molar ratio, plus one star homopolymer of DMAEMA, with degrees of polymerization of the arms equal to 15, were synthesized. After star polymer preparation and preliminary characterization, the THPMA units were hydrolyzed to negatively ionizable hydrophilic methacrylic acid (MAA) untis, thus yielding star polyampholytes. All the star polyampholytes as well as the commercially available transfection reagent SuperFect were evaluated for their ability to transfect human cervical HeLa cancer cells with the modified plasmid pRLSV40 bearing the enhanced green fluorescent protein (EGFP) as the reporter gene. The transfection efficiency was affected by star architecture. The DMAEMA15-star-MAA5 polyampholyte presented the highest transfection efficiency of all the star polymers tested but lower than that of SuperFect at its optimum conditions. All four star copolymers showed decreased toxicity compared to the DMAEMA star homopolymer for the same amounts of star polymer tested and also compared to the SuperFect at its optimum conditions.     

Synthesis, characterization, and evaluation as transfection reagents of double-hydrophilic star copolymers: effect of star architecture

Five star polymers of the ionizable hydrophilic 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the nonionic hydrophilic methoxy hexa(ethylene glycol) methacrylate (HEGMA) were prepared by group transfer polymerization (GTP) using ethylene glycol dimethacrylate (EGDMA) as coupling agent. In particular, four isomeric star copolymers, one heteroarm, two star block and one statistical star, with 90% mol DMAEMA and 10% mol HEGMA, plus one star homopolymer of DMAEMA with degrees of polymerization of the arms equal to 20 were synthesized. The polymers were characterized in terms of their molar masses (MMs) and compositions using gel permeation chromatography (GPC) and proton nuclear magnetic resonance (1H NMR) spectroscopy, respectively. The hydrodynamic diameters in water indicated some aggregation for all the star polymers except for the statistical copolymer star, while the pK values of the DMAEMA units were around 7 for all star polymers. All the star polymers were evaluated for their ability to transfect human cervical HeLa cancer cells with the modified plasmid pRLSV40 bearing the enhanced green fluorescent protein (EGFP) as the reporter gene. All four star copolymers showed decreased toxicity compared to that of the DMAEMA star homopolymer for the same amounts of star polymer tested. The star block copolymer with outer DMAEMA blocks exhibited the highest overall transfection efficiency, 11%, compared to that of all the star polymers examined in this study. This efficiency was the same as that of the commercially available transfection reagent SuperFect.     

Synthesis and hydration properties of pH-sensitive p(HEMA)-based hydrogels containing 3-(trimethoxysilyl)propyl methacrylate

An amphiphilic hydrogel network was synthesized from a cross-linked poly(2-hydroxyethyl methacrylate) backbone copolymerized with the monomers 3-(trimethoxysilyl)propyl methacrylate (PMA) and dimethylaminoethyl methacrylate (DMAEMA) using tetraethylene glycol diacrylate (TEGDA) as cross-linker and using the radical initiator system comprising N,N,N',N'-tetramethylethylenediamine and ammonium peroxydisulfate. The degree of hydration of hydrogel slabs was investigated as functions of varying monomer compositions and cross-link density and as a function of pH and ionic strength of the bathing medium. As much as a 45% increase in hydration was observed for hydrogels containing 15 mol % DMAEMA upon reducing the pH of the bathing medium from 8.0 to 2.0. This confirms the pH-modulated swelling of amine-containing hydrogels. Increasing the concentration of TEGDA cross-linker from 3 to 12 mol % in a 10 mol % DMAEMA-containing hydrogel resulted in only a 10% reduction in the degree of hydration of the gel. There was, however, a 40-50% reduction in the degree of hydration of a 15 mol % DMAEMA hydrogel upon increasing the molar composition of PMA from 0 up to 20 mol %. The presence of PMA confers hydrophobic character that reduces hydration and introduces additional cross-links that reduce network mesh size. The water content of the hydrogel was consistently higher in buffers of lower ionic strength. The reversible pH-dependent swelling observed in these studies, along with the control of cross-link density afforded by the PMA component, endows these biocompatible materials with potential for use in pH-controlled drug delivery of more hydrophobic drugs and present new compositions for in vitro and in vivo biocompatibility studies.     

Synthesis of biocompatible PEG-Based star polymers with cationic and degradable core for siRNA delivery

Star polymers with poly(ethylene glycol) (PEG) arms and a degradable cationic core were synthesized by the atom transfer radical copolymerization (ATRP) of poly(ethylene glycol) methyl ether methacrylate macromonomer (PEGMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA), and a disulfide dimethacrylate (cross-linker, SS) via an "arm-first" approach. The star polymers had a diameter ~15 nm and were degraded under redox conditions by glutathione treatment into individual polymeric chains due to cleavage of the disulfide cross-linker, as confirmed by dynamic light scattering. The star polymers were cultured with mouse calvarial preosteoblast-like cells, embryonic day 1, subclone 4 (MC3T3-E1.4) to determine biocompatibility. Data suggest star polymers were biocompatible, with ≥ 80% cell viability after 48 h of incubation even at high concentration (800 μg/mL). Zeta potential values varied with N/P ratio confirming complexation with siRNA. Successful cellular uptake of the star polymers in MC3T3-E1.4 cells was observed by confocal microscopy and flow cytometry after 24 h of incubation.     

ATRP synthesis of amphiphilic random,gradient, and block copolymers of 2-(dimethylamino)ethyl methacrylate and n-butyl methacrylate in aqueous media

Amphiphilic random, gradient, and block copolymers of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and n-butyl methacrylate (BMA) were synthesized by atom transfer radical polymerization (ATRP) in water/2-propanol mixtures using a methoxy-poly(ethylene glycol) (MPEG) (M(n) = 2000) macroinitiator. Kinetic studies indicate that the copolymerization is well controlled with molecular weights increasing linearly with conversion. Copolymers with molecular weights up to M(n) = 34000 and low polydispersities (M(w)/M(n) = 1.11-1.47) were prepared. The reactivity ratios were calculated for the copolymerizations catalyzed by CuBr/bpy, (r(DMAEMA) = 1.07, r(BMA) = 1.24). The thermosensitivity and aggregation properties of the random, gradient, and block copolymers significantly depended on the architecture of the copolymers. The lower critical solution temperature of MPEG-b-PDMAEMA(84) was 38 degrees C (5 wt % in water).     

Preparation and characterization of UV-curable polymeric support for covalent immobilization of xylanase enzyme

The hydroxyl group of poly(ethylene glycol) monoacrylate (PEGMA) was activated by 1,1′-carbonyldiimidazole (CDI) and then a xylanase enzyme was immobilized to amine active PEGMA. UV-curable polymeric support formulation was prepared by mixing the xylanase bonded PEGMA, aliphatic polyester, 2-hydroxyethyl methacrylate (HEMA), poly(ethylene glycol) diacrylate (PEGDA) and photoinitiator. After UV irradiation, the enzymatic activity of the polymeric matrix was evaluated and compared with the corresponding free enzyme. By immobilization, the temperature resistance of the enzyme was improved and showed maximum activity at 60 °C. pH dependent activities of the free and immobilized enzymes were also investigated, and it was found that the pH of maximum activity for the free enzyme was 6.0, while for the optimal pH of the immobilized enzyme was 6.5. The immobilized enzyme retained 75% of its activity after 33 runs. The morphology of the polymeric support was characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) coupled with SEM was used to explore the chemical composition. The results have confirmed the evidence of enzyme in the structure of the polymeric material.     

Thermocontrol of solute permeation across polymer membrane composed of poly(N,N-dimethylaminoethyl methacrylate) and its copolymers

Polymer membranes composed ofN,N-dimethylaminoethyl methacrylate (DMAEMA) and acrylamide (AAm) (or ethyl acrylamide (EAAm)) were prepared to demonstrate the thermocontrol of solute permeation. Poly DMEMA has a lower critical solution temperature (LCST) at around 50°C in water. With the copolymerization of DMAEMA with AAm (or EAAm), a shift in the LCST to a lower temperature was observed, probably due to the formation of hydrogen bonds between the amide andN,N-dimethylamino groups. However, the temperature-induced phase transition of poly (DMAEMA-co-EAAm) did not show a similar trend to that of poly (DMAEMA-co-AAm) in the gel state. The hydrogen bonds in poly (DMAEMA-co-EAAm) were significantly disrupted with the formation of a gel network, which led to a difference in the swelling behavior of polymer gels in response to temperature. To apply these polymers to temperature-sensitive solute permeation, polymer membranes were prepared. The permeation pattern of hydrocortisone, used as the model solute, was explained based on the temperature-sensitive swelling behavior of the polymer membranes.     

Enhancement of fibrinolytic enzyme production from Bacillus subtilis via immobilization process onto radiation synthesized starch/dimethylaminoethyl methacrylate hydrogel

Hydrogel matrices based on starch and dimethylaminoethyl methacrylate (Starch/DMAEMA) were synthesized including γ-irradiation as a clean initiator. The prepared hydrogels were characterized in terms of their gel fraction yield, degree of equilibrium swelling. The prepared hydrogels were examined as carriers for immobilization of Bacillus subtilis that has the ability to secrete an extracellular fibrinolytic enzyme that degrades fibrin. Scanning electron microscope (SEM) analysis showed proliferation of the bacterial cells entrapped inside the polymeric matrix. The immobilization process increases the production time of fibrinolytic enzyme up to 120 h instead of 96 h for the free cells. The optimum temperature of activity broadened and a significant shift in the pH optima was observed upon immobilization. The reusability of immobilized cells under repeated batch fermentation conditions was also investigated. At the optimum production conditions, immobilization of B. subtilis cells onto Starch/DMAEMA resulted in a four fold increase in enzyme activity.     

Spatially well-defined binary brushes of poly(ethylene glycol)s for micropatterning of active proteins on anti-fouling surfaces

We report a novel method for micropatterning of active proteins on anti-fouling surfaces via spatially well-defined and dense binary poly(ethylene glycol)s (PEGs) brushes with controllable protein-docking sites. Binary brushes of poly(poly(ethylene glycol) methacrylate-co-poly(ethylene glycol)methyl ether methacrylate), or P(PEGMA-co-PEGMEMA), and poly(poly(ethylene glycol)methyl ether methacrylate), or P(PEGMEMA), were prepared via consecutive surface-initiated atom transfer radical polymerizations (SI-ATRPs) from a resist-micropatterned Si(100) wafer surface. The terminal hydroxyl groups on the side chains of PEGMA units in the P(PEGMA-co-PEGMEMA) microdomains were activated directly by 1,1'-carbonyldiimidazole (CDI) for the covalent coupling of human immunoglobulin (IgG) (as a model active protein). The resulting IgG-coupled PEG microdomains interact only and specifically with target anti-IgG, while the other PEG microregions effectively prevent specific and non-specific protein fouling. When extended to other active biomolecules, microarrays for specific and non-specific analyte interactions with a high signal-to-noise ratio could be readily tailored.     

Hydrophilic cationic star homopolymers based on a novel diethanol-N-methylamine dimethacrylate cross-linker for siRNA transfection: synthesis, characterization, and evaluation

Four cationic hydrophilic star homopolymers based on the novel hydrophilic, positively ionizable cross-linker bis(methacryloyloxyethyl)methylamine (BMEMA) were synthesized using sequential group transfer polymerization (GTP) and were, subsequently, evaluated for their ability to deliver siRNA to mouse myoblast cells. The nominal degrees of polymerization (DP) of the arms were varied from 10 to 50. For the polymerizations, 2-(dimethylamino)ethyl methacrylate (DMAEMA) was employed as the hydrophilic, positively ionizable monomer. For comparison, four linear DMAEMA homopolymers were also synthesized, whose nominal DPs were the same as those of the arms of the stars. The numbers of arms of the star homopolymers were determined using gel permeation chromatography with static light scattering detection, and found to range from 7 to 19, whereas the hydrodynamic diameters of the star homopolymers in aqueous solution were measured using dynamic light scattering and found to increase with the arm DP from 13 to 26 nm. The presence of the hydrophilic BMEMA cross-linker enabled the solubility of all star homopolymers in pure water. The cloud points of the star homopolymers in aqueous solution increased with the arm DP from 23 to 29 °C, while the cloud points of the linear homopolymers were found to decrease with their DP, from 42 to 32 °C. The effective pK values of the DMAEMA units were in the range of 6.9 to 7.3 for the star homopolymers, whereas they ranged between 7.3 and 7.4 for the linear homopolymers. Subsequently, all star and linear homopolymers were evaluated for their ability to deliver siRNA to the C2C12 mouse myoblast cell line, expressing the reporter enhanced green fluorescent protein (EGFP). All star homopolymers and the largest linear homopolymer presented significant EGFP suppression, whereas the smaller linear homopolymers were much less efficient. For all star homopolymers and the largest linear homopolymer both the EGFP suppression and the cell toxicity increased with polymer loading. The siRNA-specific EGFP suppression, calculated by subtracting the effect of cell toxicity on EGFP suppression, slightly increased with star polymer loading for the two smaller stars, whereas it presented a shallow maximum and a decrease for the other two stars. Moreover, the siRNA-specific EGFP suppression also increased slightly with the DP of the arms of the DMAEMA star homopolymers. Overall, the EGFP suppression efficiencies with the present star homopolymers were at levels comparable to that of the commercially available transfection reagent Lipofectamine.     

Protein fouling resistant membrane prepared by amphiphilic pegylated polyethersulfone

A mild and facile grafting of poly(ether glycol) methyl ether methacrylate (PEGMA) monomers onto polyethersulfone (PES) was carried out. Then, the PES-g-PEGMA membranes with integrally anisotropic morphology were fabricated through the coupling of non-solvent induced phase inversion and surface segregation. Compared with PES control membrane, the surface hydrophilicity of PES-g-PEGMA membranes was remarkably enhanced due to the drastic enrichment of poly(ethylene glycol) (PEG) segments on the membrane surface; protein adsorption was significantly inhibited due to the hydrogen bonding interactions between hydrophilic groups and water molecules. Ultrafiltration experiments were used to assess the permeability and protein fouling resistance of the PES-g-PEGMA membranes. It was found that the PES-g-PEGMA membranes with higher surface coverage of PEG segments displayed stronger antibiofouling property. Moreover, the stable antibiofouling property for PES-g-PEGMA membranes was acquired due to covalent bonding interactions between hydrophilic PEGMA side chains and PES main chains.     

The effect of temperature on the impedimetric response of bioreceptor hosting hydrogels

Biocompatible hydrogels that serve as the hosting membrane for various bioreceptors contribute to the response of impedimetric biosensors. The temperature response of poly(2-hydroxymethacrylate) [p(HEMA)]-based hydrogel networks prepared with poly(ethylene glycol) methacrylate (PEGMA) for enhanced biocompatibility and with N-[tris(hydroxymethyl)methyl] acrylamide (HMMA) was studied. Hydrogels were cross-linked with tetraethyleneglycol diacrylate (TEGDA) and synthesized by UV initiation (2M% DMPA photoinitiator). The p(HEMA-co-PEGMA-co-HMMA) based hydrogels were fabricated as discrete gel pads (D=2.5 mm, H=2 mm and V=9.82 μL) on top of 250 μm diameter cysteamine modified and acryloyl (polyethylene glycol)(110) N-hydroxy succinamide ester (acryloyl-PEG-NHS) derivatized gold microelectrodes set within 8-well (8W1E) cell culture biochips. Gel pads were fabricated with cross-link densities corresponding to 1, 3, 5, 7, 9 and 12 M% TEGDA and were studied by frequency dependent 3-electrode electrochemical impedance spectroscopy (1 mHz to 100 kHz; 50 mV p-t-p) and by temporal 2-electrode impedimetry (64 kHz; 50 mV p-t-p) over the temperature range 30-45°C at 90% RH or in aqueous 0.1 M Tris/KCl at pH 7.2 buffer. The p(HEMA-co-PEGMA-co-HMMA) hydrogels showed an increase in the real component of impedance with increasing cross-link density and demonstrated activation energies for impedimetric transport that ranged from 15 kJ/mol (3 M%) to 20 kJ/mol (12 M%) confirming the dominance of proton migration in the impedance of the hydrogels.     

Synthesis and characterization of methacrylic derivatives of 5-amino salicylic acid with pH-sensitive swelling properties

The purpose of this study is to develop novel colon-specific drug delivery systems with pH-sensitive swelling and drug release properties. Methacrylic-type polymeric prodrugs with different content levels of 5-amino salicylic acid (5-ASA) were synthesized by free radical copolymerization of metacrylic acid (MAA), polyethylene glycol monomethacrylate (PEGMA), and a methacrylic derivative of 5-ASA (methacryloyloxyethyl 5-amino salicylate [MOES]). The copolymers were characterized, and the drug content of the copolymers was determined. The effect of copolymer composition on the swelling behavior and hydrolytic degradation was studied in simulated gastric fluid (SGF, pH 1.2) and simulated intestinal fluid (SIF, pH 7.2). The swelling and hydrolytic behavior of the copolymers was dependent on the content of MAA groups and caused a decrease in gel swelling in SGF or an increase in gel swelling in SIF. Drug release studies showed that increasing content of MAA in the copolymer enhances the hydrolysis in SIF but has no effect in SGF. The results suggest that hydrogen-bonded complexes are formed between MAA and PEG pendant groups and that these pH-sensitive systems could be useful for preparation of a controlled-release formulation of 5-ASA.     

Synthesis and characterization of chitosan-based hydrogels

Biocompatible hydrogels based on water-soluble chitosan–ethylene glycol acrylate methacrylate (CS–EGAMA) and polyethylene glycol diamethacrylate (PEGDMA) were synthesized by photopolymerization. Characterization of morphology, weight loss, water state of hydrogel, pH-sensitivity and cytotoxicity were investigated by scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), swelling test and methylthiazolydiphenyl-tetrazolium bromide (MTT) assay. The results indicated that the hydrogels were sensitive to pH of the medium, no cytotoxicity for L929 and SW1353, satisfactory for the composite to be used in bioapplications.     

An acid-labile block copolymer of PDMAEMA and PEG as potential carrier for intelligent gene delivery systems

Intelligent gene delivery systems based on physiologically triggered reversible shielding technology have evinced enormous interest due to their potential in vivo applications. In the present work, an acid-labile block copolymer consisting of poly(ethylene glycol) and poly(2-(dimethylamino)ethyl methacrylate) segments connected through a cyclic ortho ester linkage (PEG- a-PDMAEMA) was synthesized by atom transfer radical polymerization of DMAEMA using a PEG macroinitiator with an acid-cleavable end group. PEG- a-PDMAEMA condensed with plasmid DNA formed polyplex nanoparticles with an acid-triggered reversible PEG shield. The pH-dependent shielding/deshielding effect of PEG chains on the polyplex particles were evaluated by zeta potential and size measurements. At pH 7.4, polyplexes generated from PEG- a-PDMAEMA exhibited smaller particle size, lower surface charge, reduced interaction with erythrocytes, and less cytotoxicity compared to PDMAEMA-derived polyplexes. At pH 5.0, zeta potential of polyplexes formed from PEG- a-PDMAEMA increased, leveled up after 2 h of incubation and gradual aggregation occurred in the presence of bovine serum albumin (BSA). In contrast, the stably shielded polyplexes formed by DNA and an acid-stable block copolymer, PEG- b-PDMAEMA, did not change in size and zeta potential in 6 h. In vitro transfection efficiency of the acid-labile copolymer greatly increased after 6 h incubation at pH 5.0, approaching the same level of PDMAEMA, whereas there was only slight increase in efficiency for the stable copolymer, PEG- b-PDMAEMA.     

Release characteristics of novel pH-sensitive p(HEMA-DMAEMA) hydrogels containing 3-(trimethoxy-silyl) propyl methacrylate

An amphiphilic hydrogel of poly(2-hydroxyethyl methacrylate) cross-linked with tetraethyleneglycol diacrylate (TEGDA) was synthesized to contain the hydrophobic monomer 3-(trimethoxy-silyl) propyl methacrylate (PMA) and the pH-responsive, hydrophilic monomer N',N'-dimethylaminoethyl methacrylate (DMAEMA). The gels were separately loaded with two biomolecular probes, insulin and protamine, via both physical entrapment and equilibrium imbibition methods. The release profiles for these biomolecular probes, possessing similar MW (5.7 and 4-6 kDa, respectively) but different pI's (5.3 and 10.0, respectively), were investigated with respect to variation in the pH of the bathing medium as well as the DMAEMA content, and the cross-link density of the hydrogel. Gels exhibited classical Fickian diffusion release profiles. For a typical gel composition 66:15:10:09 mol % (HEMA:DMAEMA:PMA:TEGDA), as the pH of the release media decreased from 7.3 to 4.0, the rate of release of both biomolecular probes increased. When loaded via entrapment, the insulin release rate increased ca. 4-fold (1.0-3.7 x 10(-7) cm(2) s(-1)), whereas that of protamine increased 10-fold (0.3-3.3 x 10(-7) cm(2) s(-1)). When loaded by imbibition, the insulin diffusion coefficient increased 2-fold (3.8-7.2 x 10(-7) cm(2) s(-1)), whereas that of protamine increased 3-fold (1.9-5.5 x 10(-7) cm(2) s(-1)). The reduction of pH, through its protonation of the gel network, has a more dramatic influence on protamine release, the result of its higher pI (10.0) compared to that of insulin (5.3). As the DMAEMA content of the hydrogel was increased from 0 to 20 mol %, the diffusion coefficient of protamine increased by ca. 7-fold (1.7-12.2 x 10(-7) cm(2) s(-1)), whereas that of insulin increased only ca. 2-fold (1.7-4.0 x 10(-7) cm(2) s(-1)). This differential release confirms the role of internal protonation in effecting the greater release of the protonated drug molecule. Increasing the TEGDA content from 3 to 15 mol % reduced the diffusion coefficient ca. 3-fold for insulin (1.6-0.5 x 10(-7) cm(2) s(-1)) and 5-fold for protamine (4.0-0.8 x 10(-7) cm(2) s(-1)). The final D(ip) at 15 mol % TEGDA suggests that the smaller mesh size offsets any differential release that arises from protonation. The presence of PMA in the hydrogel formulation, which contributes additional cross-links by reason of the formation of siloxane macromers, did not change the usually observed Fickian diffusion mechanism.     

Surface-active and stimuli-responsive polymer--Si(100) hybrids from surface-initiated atom transfer radical polymerization for control of cell adhesion

A simple two-step method was developed for the covalent immobilization of atom-transfer radical polymerization (ATRP) initiators on the hydrogen-terminated Si(100) (Si-H) surface. Well-defined functional polymer-Si hybrids, consisting of covalently tethered brushes of poly(ethylene glycol) monomethacrylate (PEGMA) polymer, N-isopropylacrylamide (NIPAAm) polymer, and NIPAAm-PEGMA copolymers and block copolymers on Si-H surfaces, were prepared via surface-initiated ATRP. Kinetics study revealed that the chain growth from the silicon surface was consistent with a "controlled" process. Surface cultures of the cell line 3T3-Swiss albino on the hybrids were evaluated. The PEGMA graft-polymerized silicon [Si-g-P(PEGMA)] surface is very effective in preventing cell attachment and growth. At 37 degrees C [above the lower critical solution temperature (LCST, approximately 32 degrees C) of NIPAAm], the seeded cells adhered, spread, and proliferated on the NIPAAm graft polymerized silicon [Si-g-P(NIPAAm)] surface. Below the LCST, the cells detached from the Si-g-P(NIPAAm) surface spontaneously. Incorporation of PEGMA units into the NIPAAm chains of the Si-g-P(NIPAAm) surface via copolymerization resulted in more rapid cell detachment during the temperature transition. The "active" chain ends on the Si-g-P(PEGMA) and Si-g-P(NIPAAm) hybrids were also used as the macroinitiators for the synthesis of diblock copolymer brushes. Thus, not only are the hybrids potentially useful as stimuli-responsive adhesion modifiers for cells in silicon-based biomedical microdevices but also the active chain ends on the hybrid surfaces offer opportunities for further surface functionalization and molecular design.