Binary polymer brush patterns from facile initiator stickiness for cell culturing.

We report a new initiator stickiness method to fabricate micropatterned binary polymer brush surfaces, which are ideal platforms for studying cell adhesion behavior. The atom transfer radical polymerization (ATRP) initiator, ω-mercaptoundecyl bromoisobutyrate (MUDBr), is found to adsorb on several hosting polymer brushes, including poly[oligo(ethylene glycol)methyl ether methacrylate] (POEGMA), poly(2-hydroxyethyl methacrylate) (PHEMA), and poly(glycidyl methacrylate) (PGMA) brushes. Based on the initiator stickiness, micropatterned initiator molecules are printed onto a layer of homogenous hosting polymer brushes via microcontact printing (µCP), and then, vertically, a patterned second layer of polymer brushes is grown from the initiator areas. With this simple, fast, and additive method, we demonstrate the fabrication of various binary polymer brushes, and show their applications for patterning cell microarrays and controlling cell orientation. This new approach to generating binary polymer brushes shows great potential for the manipulation of interfacial phenomena, facilitating a range of applications from semiconductors and lubrication to fundamental cell biology studies.

Development of poly(hydroxyethyl methacrylate) nanogel for effective oral insulin delivery.

Because of uncomfortable, painful and even deleterious effects of daily injection of insulin, extensive efforts are being made worldwide for developing noninvasive drug delivery systems, especially via the oral route. In this study, we synthesized hydroxyethyl methacrylate (HEMA) nanogel via emulsion polymerization method. The morphology and stability of the nanogel were characterized by scanning electronic microscope and dynamic light scattering. In vivo results showed the soft HEMA nanogel had longer half-live in the body circulation and exhibited almost negligible uptake by the macrophage cells as compared with blank cells. For the FITC-dextran tracking for intestinal penetration, the results indicated that the FITC-dextran in the soft nanogel penetrated faster from the inner side of the abdominal segment, which explained why the soft HEMA nanogel could promote intestinal absorption of encapsulated insulin. In vivo delivery of insulin encapsulated in the soft HEMA nanogel sustained blood glucose control for 12 h, and the overall bioavailability of administrated insulin was much higher than free insulin. Our results showed that the insulin-loaded HEMA nanogel was able to efficiently control blood glucose as a delivery system, suggesting the HEMA nanogel using emulsion polymerization could be an alternative carrier for oral insulin delivery.

Increasing the Bile Acid Sequestration Performance of Cationic Hydrogels by Using an Advanced/Controlled Polymerization Technique.

PURPOSE: To investigate the influence of the polymerization technique and the content of hydroxyl groups on the performance of new bile acid sequestrants based on PAMPMTA-co-PHEA (PAMPTMA: poly((3-acrylamidopropyl)trimethylammonium chloride); PHEA: poly(2-hydroxyethyl acrylate)) hydrogels. METHODS: PAMPMTA-co-PHEA hydrogels were prepared using either free radical polymerization or supplemental activator and reducing agent atom transfer radical polymerization. The chemical structure and composition of the hydrogels was confirmed by both FTIR and ssNMR. The binding of sodium cholate as the model bile salt was evaluated in simulated intestinal fluid using HPLC. The degradation of the polymers was evaluated in vitro in solutions mimicking the gastrointestinal tract environment. RESULTS: The binding showed that an increase of the amount of HEA in the hydrogel lead to a decrease of the binding capacity. In addition, it was demonstrated for the first time that the hydrogels produced by SARA ATRP presented a higher binding capacity than similar ones produced by FRP. Finally, it was observed that copolymers of PAMPTMA-co-PHEA showed no sign of degradation in solutions mimicking both the stomach and the intestine environment. CONCLUSIONS: The use of an advanced polymerization technique, such as the SARA ATRP, could be beneficial for the preparation of BAS with enhanced performance.

Fabrication of carbohydrate microarrays on a poly(2-hydroxyethyl methacrylate)-based photoactive substrate.

We report the fabrication of carbohydrate microarrays on a photoactive polymer, poly(HEMA-co-HEMA-PFPA), synthesized by RAFT copolymerization of 2-hydroxyethyl methacrylate (HEMA) and perfluorophenyl azide (PFPA)-derivatized HEMA (HEMA-PFPA). PFPA allows the covalent immobilization of carbohydrates whereas the HEMA polymer provides an antifouling surface, thus the microarrays can be used directly without pretreating the array with a blocking agent. The microarrays were prepared by spin-coating the polymer followed by printing the carbohydrates. Subsequent irradiation simultaneously immobilized the carbohydrates and crosslinked the polymer matrix. The obtained 3D carbohydrate microarrays showed enhanced fluorescence signals upon treating with a fluorescent lectin in comparison with a 2D microarray. The signals were acquired at a lower lectin concentration and a shorter incubation time. When treated with E. coli bacteria, the carbohydrate microarray showed results that were consistent with their binding patterns.

Hydrogel thin film with swelling-induced wrinkling patterns for high-throughput generation of multicellular spheroids.

Three-dimensional (3D) multicellular spheroids (MCSs) mimic the structure and function of real tissue much better than the conventional 2D cell monolayers, however, their application was severely hindered by difficulties in their generation. An ideal method for MCS fabrication should produce spheroids with narrow size distribution and allow for control over their size. The method should also be simple, cheap, and scalable. Here, we use patterned nonadhesive poly(2-hydroxyethyl methacrylate) hydrogel films to guide the self-assembly of cells. The films were fabricated directly in the wells of cell culture plates. They were patterned spontaneously by swelling in water, without the use of any template or specialized facilities. When cell suspension is added, the cells settle down by gravity to the bottom. Because of the presence of the wrinkling pattern composed of uniformed microcaves, the cells accumulate to the center of the microcaves and gradually self-assemble into MCSs. Using this method, monodisperse MCSs were generated. The size of the spheroids can be facilely controlled by the number of cells seeded. The method is compatible with the conventional monolayer cell culture method. Thousands of spheroids can be generated in a single well. We expect this method will pave the way for the application of MCSs in various biomedical areas.

(Ultra)fast catalyst-free macromolecular conjugation in aqueous environment at ambient temperature.

Tailor-made water-soluble macromolecules, including a glycopolymer, obtained by living/controlled RAFT-mediated polymerization are demonstrated to react in water with diene-functionalized poly(ethylene glycol)s without pre- or post-functionalization steps or the need for a catalyst at ambient temperature. As previously observed in organic solvents, hetero-Diels-Alder (HDA) conjugations reached quantitative conversion within minutes when cyclopentadienyl moieties were involved. However, while catalysts and elevated temperatures were previously necessary for open-chain diene conjugation, additive-free HDA cycloadditions occur in water within a few hours at ambient temperature. Experimental evidence for efficient conjugations is provided via unambiguous ESI-MS, UV/vis, NMR, and SEC data.

An innovative approach to molecularly imprinted capillaries for polar templates by grafting polymerization.

Molecularly imprinted polymers have been successfully used as selective stationary phases in capillary electrophoresis. Notwithstanding, this technique suffers from several drawbacks as the loss of molecular recognition properties in aqueous media and the lack of feasibility for imprinted systems directed towards highly polar templates soluble in aqueous environments only. Thus, the preparation of imprinted polymers for highly polar, water-soluble analytes, represents a challenge. In this work, we present an innovative approach to overcome these drawbacks. It is based on a surface molecular imprinting technique that uses preformed macromonomers as both functional recognition elements and cross-linking agents. A poly-2-hydroxyethyl-co-methacrylic acid linear polymer was grafted from the surface of silica capillaries. The grafted polymer was exhaustively esterified with methacrylic anhydride to obtain polyethylendimethacrylate-co-methacrylic acid linear chains. Then, as a proof of concept, an adequate amount of a very polar template like penicillin V was added in a hydro-organic mixture, and a thin layer of imprinted polymer was obtained by cross-linking the polymer linear chains. The binding behaviour of the imprinted and non-imprinted capillaries was evaluated in different separation conditions in order to assess the presence of template selectivity and molecular recognition effects. The experimental results clearly show that this innovative kind of imprinted material can be easily obtained in very polar polymerization environments and that it is characterized by enhanced molecular recognition properties in aqueous buffers and good selectivity towards the template and strictly related molecules.

Diazonium salt-derived 4-(dimethylamino)phenyl groups as hydrogen donors in surface-confined radical photopolymerization for bioactive poly(2-hydroxyethyl methacrylate) grafts.

In this paper we describe a novel methodology for grafting polymers via radical photopolymerization initiated on gold surfaces by aryl layers from diazonium salt precursors. The parent 4-(dimethylamino)benzenediazonium salt was electroreduced on a gold surface to provide 4-(dimethylamino)phenyl (DMA) hydrogen donor layers; free benzophenone in solution was used as a photosensitizer to strip hydrogen from the grafted DMA. This system permitted efficient surface initiation of photopolymerization of 2-hydroxyethyl methacrylate. The resulting poly(2-hydroxyethyl methacrylate) (PHEMA) grafts were found to be very adherent to the surface as they resist total failure after being soaked in the well-known paint stripper methyl ethyl ketone. The PHEMA grafts were reacted with 1,1'-carbonyldiimidazole to yield carbamate groups that are able to react readily with amino groups from proteins. The final surface consisted of protein-functionalized PHEMA grafts where bovine serum albumin (BSA) protein is specifically linked to the grafts by covalent bonds. We used X-ray photoelectron spectroscopy to monitor the chemical changes at the gold surface all along the process from the neat gold to the end-protein-functionalized polymer grafts: the PHEMA graft thickness ranged from 7 to 27 nm, and the activation by 1,1'-carbonyldiimidazole reached 37% of the OH groups, which was sufficient for 90% surface coverage of the grafts by BSA. This work conclusively provides a new approach for bridging reactive and functional polymers to surfaces via aryl diazonium salts in a simple, fast, and efficient approach of importance in biomedical and other applications.

Poly(2-hydroxyethyl methacrylate) brush surface for specific and oriented adsorption of glycosidases.

We present a detailed picture to screen general ligands from simple chemicals for fabricating affinity surface to glycosidase enzymes. The surface was constructed by grafting poly(2-hydroxyethyl methacrylate) (PHEMA) brush on SPR gold chip via surface-initiated atom-transfer radical polymerization, after which poly(methoxyethyl methacrylate) (PMEMA) and poly(oligo(ethylene glycol) methacrylate) (POEGMA) brushes were also prepared for comparison. SPR measurements were adopted to monitor the early-stage adsorption of two glycosidases and three other typical proteins. PHEMA resists the adsorption of lysozyme, bovine serum albumin, and fibrinogen, while it is capable of specifically adsorbing ß-glucosidase (GLU) and ß-galactosidase (GAL). These are quite different from the nonspecific adsorption of PMEMA and the anti-nonspecific adsorption of POEGMA to the studied proteins, because PHEMA is the acceptor substrate of the glycosidases. About 69.6 and 93.7 ng/cm(2) of GAL and GLU are adsorbed on the PHEMA brush surface, of which more than 49.6 ng/cm(2) is remained after washing with PBS. The specific adsorption process is appropriately described by Freundlich isothermal model rather than Langmuir one, and is also indicated to be spontaneous, endothermic, and entropy driven through thermodynamic studies. Taking into account all stated results above, we propose that molecular recognition takes place between the hydroxyl groups of PHEMA and the active sites of glycosidases, which subsequently enables the oriented adsorption of glycosidases on the brush surface. The adsorbed enzyme can be effectively eluted with 1.0 M aqueous solution of ethanol. Our findings open the door to the further development in the design of novel acceptor substrate-ligand affinity chromatography for enzyme purification.

Polymer brush-modified magnetic nanoparticles for His-tagged protein purification.

Growth of poly(2-hydroxyethyl methacrylate) brushes on magnetic nanoparticles and subsequent brush functionalization with nitrilotriacetate-Ni(2+) yield magnetic beads that selectively capture polyhistidine-tagged (His-tagged) protein directly from cell extracts. Transmission electron microscopy, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis, and magnetization measurements confirm and quantify the formation of the brushes on magnetic particles, and multilayer protein adsorption to these brushes results in binding capacities (220 mg BSA/g of beads and 245 mg His-tagged ubiquitin/g of beads) that are an order of magnitude greater than those of commercial magnetic beads. Moreover, the functionalized beads selectively capture His-tagged protein within 5 min. The high binding capacity and protein purity along with efficient protein capture in a short incubation time make brush-modified particles attractive for purification of recombinant proteins.

Molecularly imprinted supermacroporous cryogels for cytochrome c recognition.

Molecular imprinting is an attractive biomimetic approach that creates specific recognition sites for the shape and functional group arrangement to template molecules. The purpose of this study is to prepare cytochrome c-imprinted poly(hydroxyethyl methacrylate) (PHEMA)-based supermacroporous cryogel which can be used for the separation of cytochrome c from protein mixtures. N-Methacryloyl-(L)-histidinemethylester (MAH) was used as the metal-coordinating monomer. In the first step, Cu(2+) was complexed with MAH, and the cytochrome c imprinted PHEMA (MIP) cryogel was prepared by free radical cryopolymerization initiated by N,N,N',N'-tetramethylene diamine at -12°C. After polymerization is completed, the template cytochrome c molecules were removed from the MIP cryogel using 0.5 M NaCl solution. The maximum cytochrome c binding amount was 126 mg/g polymer. Selective binding studies were performed in the presence of lysozyme and bovine serum albumin. The relative selectivity coefficients of MIP cryogel for cytochrome c/lysozyme and cytochrome c/bovine serum albumin were 1.7 and 5.2 times greater than those of the non-imprinted PHEMA cryogel, respectively. The selectivity of MIP cryogel for cytochrome c was also confirmed with fast protein liquid chromatography. The MIP cryogel could be used many times with no remarkable decrease in cytochrome c binding capacity.

Dual-Functional Surfaces Based on an Antifouling Polymer and a Natural Antibiofilm Molecule: Prevention of Biofilm Formation without Using Biocides.

Pathogenic biofilms formed on the surfaces of implantable medical devices and materials pose an urgent global healthcare problem. Although conventional antibacterial surfaces based on bacteria-repelling or bacteria-killing strategies can delay biofilm formation to some extent, they usually fail in long-term applications, and it remains challenging to eradicate recalcitrant biofilms once they are established and mature. From the viewpoint of microbiology, a promising strategy may be to target the middle stage of biofilm formation including the main biological processes involved in biofilm development. In this work, a dual-functional antibiofilm surface is developed based on copolymer brushes of 2-hydroxyethyl methacrylate (HEMA) and 3-(acrylamido)phenylboronic acid (APBA), with quercetin (Qe, a natural antibiofilm molecule) incorporated via acid-responsive boronate ester bonds. Due to the antifouling properties of the hydrophilic poly(HEMA) component, the resulting surface is able to suppress bacterial adhesion and aggregation in the early stages of contact. A few bacteria are eventually able to break through the protection of the anti-adhesion layer leading to bacterial colonization. In response to the resulting decrease in the pH of the microenvironment, the surface could then release Qe to interfere with the microbiological processes related to biofilm formation. Compared to bactericidal and anti-adhesive surfaces, this dual-functional surface showed significantly improved antibiofilm performance to prevent biofilm formation involving both Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus for up to 3 days. In addition, both the copolymer and Qe are negligibly cytotoxic, thereby avoiding possible harmful effects on adjacent normal cells and the risk of bacterial resistance. This dual-functional design approach addresses the different stages of biofilm formation, and (in accordance with the growth process of the biofilm) allows sequential activation of the functions without compromising the viability of adjacent normal cells. A simple and reliable solution may thus be provided to the problems associated with biofilms on surfaces in various biomedical applications.

Immobilization of type-I collagen and basic fibroblast growth factor (bFGF) onto poly (HEMA-co-MMA) hydrogel surface and its cytotoxicity study.

Type-I collagen and bFGF were immobilized onto the surface of poly (HEMA-co-MMA) hydrogel by grafting and coating methods to improve its cytotoxicity. The multi-layered structure of the biocompatible layer was confirmed by FTIR, AFM and static water contact angles. The layers were stable in body-like environment (pH 7.4). Human skin fibroblast cells (HSFC) were seeded onto Col/bFGF-poly (HEMA-co-MMA), Col-poly (HEMA-co-MMA) and poly (HEMA-co-MMA) films for 1, 3 and 5 day. MTT assay was performed to evaluate the extraction toxicity of the materials. Results showed that the cell attachment, proliferation and differentiation on Col/bFGF-poly (HEMA-co-MMA) film were higher than those of the control group, which indicated the improvement of cell-material interaction. The extraction toxicity of the modified materials was also lower than that of the unmodified group. The protein and bFGF immobilized poly (HEMA-co-MMA) hydrogel might hold great promise to be a biocompatible material.

Synthesis of Poly(2-Hydroxyethyl Methacrylate) (PHEMA)-Based Superparamagnetic Nanoparticles for Biomedical and Pharmaceutical Applications.

The performance of polymeric nanomaterials relies greatly upon their properties which are intimately related to the methods of fabrication of their materials. Among various synthetic polymers the polymers of 2-hydroxyethyl methacrylate (PHEMA) maintains a prime position in the biomedical field due to their useful physicochemical properties and suitability for controlled drug delivery applications. Furthermore, the addition of iron oxide to PHEMA nanoparticles imparts superparamagnetism to the nanoparticles and expands the range of their uses to include magnetic drug targeting applications. Here we focus on three methods for preparation of PHEMA nanoparticles, one by suspension polymerization, a second by emulsion polymerization without the use of any surfactants, and the final one with the incorporation of iron oxide into PHEMA nanoparticles.

[Preparation and properties of poly (acrylic ester) hydrogel as basic materials for intraocular lens].

Poly (acrylic ester) hydrogel materials were widely used in intraocular lens and contact lens because of their excellent optical performance and biocompatibility. In this paper, the bulk copolymerization behavior of hydrophilic hydroxyethyl methacrylat with hydrophobic methyl metharylate was studied; and the optical performance, calcium deposits, equilibrium water content of polymers and its hydrogels obtained by different ratios of monomers were systematically investigated. The experimental results showed that the average light transmittance and the equilibrium water content of the obtained hydrogels increased with the increasing of the hydrophilic monomer content from 0 to 100%; however, the hardness decreased. The highest light transmittance reached 97% and the hardness of Shore A fell from 92 to 25, the equilibrium water content of hydrogel increased from 16% to 64%. The absorbent capacity of copolymers reduced with the adding of cross-linking monomer. When m(hydrophilic monomer): m(hydrophobic monomer) = 90 : 10, the combination property of the polymer and its hydrogel obtained is optimum.

Nanoscale Characteristics and Antimicrobial Properties of (SI-ATRP)-Seeded Polymer Brush Surfaces.

Microbial resistant coatings have raised considerable interest in the biotechnological industry and clinical scenarios to combat the spreading of infections, in particular in implanted medical devices. Polymer brushes covalently attached to surfaces represent a useful platform to identify ideal compositions for preventing bacterial settlement by quantifying bacteria-surface interactions. In this work, a series of polymer brushes with different charges, positively charged poly[2-(methacryloyloxy)ethyl trimethylammonium chloride] (PMETAC), negatively charged poly(3-sulfopropyl methacrylate potassium salt) (PSPMA), and neutral poly(2-hydroxyethyl methacrylate) (PHEMA) were grafted onto glass surfaces by surface-initiated atom transfer radical polymerization in aqueous conditions. The antimicrobial activity of the polymer brushes against Gram-negative Escherichia coli was tested at the nano- and microscopic level on different time scales, that is, from nm to 100 µm, and ms to 24 h, respectively. The interaction between the polymer brushes and E. coli was studied by single-cell force spectroscopy (SCFS) and by quantification of the bacterial density on surfaces incubated with bacterial suspensions. E. coli firmly attached to positive PMETAC brushes with high work required for de-adhesion of 28 ± 9 nN·nm, but did not significantly bind to negatively charged PSPMA and neutral PHEMA brushes. Our studies of bacterial adhesion using polymer brushes with controllable chemistry provide essential insights into bacterial surface interactions and the origins of bacterial adhesion.

A novel radiolabeled graft polymer: Investigation of the radiopharmaceutical potential using Albino Wistar rats.

Fe3O4 magnetic graft-Lys-poly(HEMA) was synthesized, labeled with 99mTc for the first time and its radiopharmaceutical potential was investigated using animal models in this study. Quality control procedures were carried out using thin layer radiochromatography. The labeling yield of radiolabeled polymer was found to be about 100%. Then, stability and lipophilicity were determined. The lipophilicity of 99mTc labeled Fe3O4 graft-Lys-poly(HEMA) was found to be 3.77. The serum stability experiments demonstrated that approximately 100% of radiolabeled polymer existed as an intact complex in the rat serum within 240 min. Biodistribution of radiolabeled magnetic graft-Lys-poly(HEMA) was performed on female Albino Wistar rats by scintigraphy and biodistribution studies. High uptake was seen in the stomach, the pancreas, brain, ovarian, intestines and the breast.

Toxicity and photosensitizing assessment of gelatin methacryloyl-based hydrogels photoinitiated with lithium phenyl-2,4,6-trimethylbenzoylphosphinate in human primary renal proximal tubule epithelial cells.

Gelatin methacryloyl (GelMA) and lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) photoinitiator are commonly used in combination to produce a photosensitive polymer but there are concerns that must be addressed: the presence of unreacted monomer is well known to be cytotoxic, and lithium salts are known to cause acute kidney injury. In this study, acellular 10% GelMA hydrogels cross-linked with different LAP concentrations and cross-linking illumination times were evaluated for their cytotoxicity, photosensitizing potential, and elastic moduli. Alamar Blue and CyQuant Direct Cell viability assays were performed on human primary renal proximal tubule epithelial cells (hRPTECs) exposed to extracts of each formulation. UV exposure during cross-linking was not found to affect extract cytotoxicity in either assay. LAP concentration did not affect extract cytotoxicity as determined by the Alamar Blue assay but reduced hRPTEC viability in the CyQuant Direct cell assay. Photocatalytic activity of formulation extracts toward NADH oxidation was used as a screening method for photosensitizing potential; longer UV exposure durations yielded extracts with less photocatalytic activity. Finally, elastic moduli determined using nanoindentation was found to plateau to approximately 20-25 kPa after exposure to 342 mJ/cm2 at 2.87 mW of UV-A exposure regardless of LAP concentration. LAP at concentrations commonly used in bioprinting (<0.5% w/w) was not found to be cytotoxic although the differences in cytotoxicity evaluation determined from the two viability assays imply cell membrane damage and should be investigated further. Complete cross-linking of all formulations decreased photocatalytic activity while maintaining predictable final elastic moduli.

Preparation and properties of cryogel based on poly(hydroxypropyl methacrylate).

A novel supermacroporous poly(hydroxypropyl methacrylate) (p(HPMA)) cryogel was synthesized by cryogelation method at -16 °C. In this synthesis process, HPMA was used as a monomer, and N,N'-methylenebisacrylamide (MBAAm) was used as cross-linker; the reaction was carried out in the presence of redox initiator pair N,N,N',N'-tetramethylene diamine (TEMED) and ammonium persulfate (APS). The effect of monomer concentration, cross-linker content, cooling rate, and dioxane co-solvent were determined with respect to the pore structure, mechanical behavior, swelling degree, and porosity of cryogel. The ESEM images indicate that the pore wall structure of cryogels was rough; moreover, small holes were present in the pore walls of cryogels. The result of compression test indicates that cryogels can be compressed by at least 80% without any breakdown. The result of swelling kinetics indicates that cryogels attain swelling equilibrium in 10 s. Furthermore, p(HPMA)-Cu2+ cryogel was prepared by loading Cu2+ ions on functionalized poly(hydroxypropyl methacrylate)-iminodiacetic acid (p(HPMA)-IDA) cryogel. We investigated the adsorption of bovine serum albumin (BSA) on cryogels. The results indicate that compared to Freundlich isotherm, Langmuir isotherm could more suitably describe the adsorption process of BSA on cryogels. Meanwhile, the adsorption capacity of p(HPMA)-Cu2+ cryogel was significantly greater than that of p(HPMA) cryogel. The maximum adsorption capacity of BSA on p(HPMA)-Cu2+ cryogel, which was treated with 1 M Cu2+ ions, was as high as 196.87 mg/g cryogel (equivalent to 20.48 mg/mL cryogel) at 25 °C and pH = 7.8; therefore, the maximum adsorption capacity of BSA on p(HPMA)-Cu2+ cryogel was 4.35 times higher than that of p(HPMA) cryogel. Thus, the adsorption capacity of cryogels was strongly influenced by Cu2+ concentration, moreover, temperature changes clearly affected the adsorption capacity of p(HPMA)-Cu2+cryogel. The adsorption capacity at 25 °C was twice as that at 15 °C. By calculating Gibbs free energy change (∆G) of adsorption, we found that the adsorption process was spontaneous; moreover, adsorption process occurred better at higher temperature.

Synthesis and characterization of degradable p(HEMA) microgels: use of acid-labile crosslinkers.

New divinyl-functionalized acetal-based crosslinkers were synthesized as building elements to form acid-labile microgel particles for controlled-release applications. The synthesized crosslinkers underwent hydrolysis at slightly acidic pHs in less than 1 h while they were stable at neutral pHs for longer times. HEMA was copolymerized with the crosslinkers via an inverse emulsion polymerization technique using a redox initiator system at room temperature to form crosslinked, colloidal p(HEMA) microgels. Microgels in diameters ranging from 150 to 475 nm with narrow distribution could be produced. The crosslinking density and the diameter of the microgels were found to be controlled by monomer/crosslinker feed ratio. The microgels demonstrated a pH-dependent cleavage behavior that mimicked the pH-dependent hydrolysis profile of the acid-labile crosslinkers. Model biomacromolecules, i.e., Rhodamine B-labeled dextran and BSA were efficiently loaded into the microgels. The release of the biomolecules from p(HEMA) microgels was also found to be controllable by the pH of the environment similar to the particle degradation. The protein released from the microgels was observed to retain its structural stability.