Synthesis and properties of vinyl monomer/enzyme conjugates. Conjugation of L-asparaginase with N-succinimidyl acrylate

Thermoresponsive Metallo-protein-based Hybrid Hydro-gels for Reversible and Highly Selective Removal of Lead(II) from Water

It is interesting to develop biomaterials for easily removing ultra-trace toxic metal ions from the environment. Herein, we have synthesized a thermoresponsive hybrid hydrogel PNIPAM-co-PbrRP by incorporating a reconstituted lead-binding...

Temperature-Driven Metalloprotein-Based Hybrid Hydrogels for Selective and Reversible Removal of Cadmium(II) from Water

To develop biomaterials that easily and reversibly remove trace amounts of metal ions, we synthesized PNIPAM-co-CadRP, a thermally sensitive hybrid hydrogel by immobilizing a reconstituted cadmium binding peptide (CadRP) derived from the metalloregulatory protein CadR in a poly(N-isopropylacrylamide) (PNIPAM) gel network. The hybrid hydrogel retains the properties of the immobilized peptide and highly sensitively and selectively binds Cd(II) ions. The thermally sensitive properties of the hybrid hydrogel, which swells at low temperatures (<34 °C) and shrinks at high temperatures, provides a driving force sufficient to alternate the conformation of the immobilized CadRP such that the peptide captures and releases metal ions at high and low temperatures, respectively. Using this novel hybrid gel, we captured nanomolar Cd(II) from samples of environmental water in a highly efficient manner, leading to a practical and repeatedly reusable material to remediate our environment.

Biofabrication Using Pyrrole Electropolymerization for the Immobilization of Glucose Oxidase and Lactate Oxidase on Implanted Microfabricated Biotransducers

The dual responsive Electrochemical Cell-on-a-Chip Microdisc Electrode Array (ECC MDEA 5037) is a recently developed electrochemical transducer for use in a wireless, implantable biosensor system for the continuous measurement of interstitial glucose and lactate. Fabrication of the biorecognition membrane via pyrrole electropolymerization and both in vitro and in vivo characterization of the resulting biotransducer is described. The influence of EDC-NHS covalent conjugation of glucose oxidase with 4-(3-pyrrolyl) butyric acid (monomerization) and with 4-sulfobenzoic acid (sulfonization) on biosensor performance was examined. As the extent of enzyme conjugation was increased sensitivity decreased for monomerized enzymes but increased for sulfonized enzymes. Implanted biotransducers were examined in a Sprague-Dawley rat hemorrhage model. Resection after 4 h and subsequent in vitro re-characterization showed a decreased sensitivity from 0.68 (±0.40) to 0.22 (±0.17) µA·cm^-2·mM^-1, an increase in the limit of detection from 0.05 (±0.03) to 0.27 (±0.27) mM and a six-fold increase in the response time from 41 (±18) to 244 (±193) s. This evidence reconfirms the importance of biofouling at the bio-abio interface and the need for mitigation strategies to address the foreign body response.

Aptamer-functionalized hydrogel diffraction gratings for the human thrombin detection

The aptamer-functionalized hydrogel diffraction gratings were successfully fabricated by incorporating an aptamer and its complementary sequence as crosslinking junctions in the network structure. The gratings showed a sensitive response to human thrombin as read out from the diffracted light.

Tumor marker-responsive behavior of gels prepared by biomolecular imprinting

We report dynamic glycoprotein recognition of gels prepared by biomolecular imprinting using lectin and antibody molecules as ligands for tumor-specific marker glycoproteins. The glycoprotein-imprinted gels prepared with minute amounts of cross-linkers could dynamically recognize tumor-specific marker glycoproteins by lectin and antibody ligands and induce volume changes according to the glycoprotein concentration. The glycoprotein-imprinted gel shrank in response to a target glycoprotein but nonimprinted gel swelled a little. The glycoprotein-responsive shrinking of the imprinted gel was caused by formation of lectin-glycoprotein-antibody complexes that acted as reversible cross-linking points. Glycoprotein-imprinted gels only shrank when both lectin and antibody in the gels simultaneously recognized the saccharide and peptide chains of the target glycoprotein. As shrinking behavior of biomolecularly imprinted gels in response to glycoproteins enables the accurate detection and recognition of tumor-specific marker glycoproteins, they have many potential applications as smart devices in sensing systems and for molecular diagnostics.

Surface grafted antibodies: controlled architecture permits enhanced antigen detection

The attachment of antibodies to substrate surfaces is useful for achieving specific detection of antigens and toxins associated with clinical and field diagnostics. Here, acrylated whole antibodies were produced through conjugation chemistry, with the goal of covalently photografting these proteins from surfaces in a controlled fashion, to facilitate rapid and sensitive antigenic detection. A living radical photopolymerization chemistry was used to graft the acrylated whole antibodies on polymer surfaces at controlled densities and spatial locations by controlling the exposure time and area, respectively. Copolymer grafts containing these antibodies were synthesized to demonstrate two principles. First, PEG functionalities were introduced to prevent nonspecific protein interactions and improve the reaction kinetics by increasing solvation and mobility of the antibody-containing chains. Both of these properties lead to sensitive (pM) and rapid (<20 min) detection of antigens with this surface modification technique. Second, graft composition was tailored to include multiple antibodies on the same grafted chains, establishing a means for simultaneously detecting multiple antigens on one grafted surface area. Finally, the addition of PEG spacers between the acrylate functionality and the pendant detection antibodies was tuned to enhance the detection of a short-half-life molecule, glucagon, in a complex biological environment, plasma.

Drug release from hydrogel containing albumin as crosslinker

Albumin is the major plasma protein and acts as a physiological carrier for various compounds including drugs. To take advantage of the drug-binding ability of albumin for a drug delivery system, we have prepared hydrogels consisting of acrylamide (AAm) and bovine serum albumin (BSA) by introducing three to four vinyl groups into one BSA molecule and subsequently copolymerizing it with AAm. The resultant hydrogel was solubilized by trypsin treatment, since BSA served as a crosslinker in the hydrogel. The BSA-crosslinked hydrogel (BSA-AAm hydrogel) was loaded with salicylic acid or sodium benzoate and their release was investigated. The BSA-AAm hydrogel released much more salicylic acid than sodium benzoate. In addition, the amount of released salicylic acid increased with the BSA content of the hydrogel, despite a decrease in the swelling ratio of the hydrogel. On the other hand, the amount of released sodium benzoate increased with the swelling ratio. When a hydrogel crosslinked with N,N'-methylenebis (acrylamide) was used as a control, both drugs showed release tendencies similar to that of sodium benzoate from the BSA-AAm hydrogel. Furthermore, the salicylic acid release was sustained longer on the BSA-AAm hydrogel than the sodium benzoate release. Taken together, it is thought that albumin in the BSA-AAm hydrogel preferentially adsorbs salicylic acid and contributes to the high drug loading and the sustained release of salicylic acid.

Conjugation of penicillin acylase with the reactive copolymer of N-isopropylacrylamide: a step toward a thermosensitive industrial biocatalyst

Conjugation of penicillin acylase (PA) to poly-N-isopropylacrylamide (polyNIPAM) was studied as a way to prepare a thermosensitive biocatalyst for industrial applications to antibiotic synthesis. Condensation of PA with the copolymer of NIPAM containing active ester groups resulted in higher coupling yields of the enzyme (37%) compared to its chemical modification and copolymerization with the monomer (9% coupling yield) at the same NIPAM:enzyme weight ratio of ca. 35. A 10-fold increase of the enzyme loading on the copolymer resulted in 24% coupling yield and increased by 4-fold the specific PA activity of the conjugate. Two molecular forms of the conjugate were found by gel filtration on Sepharose CL 4B: the lower molecular weight fraction of ca. 10(6) and, presumably, cross-linked protein-polymer aggregates of MW > 10(7). Michaelis constant for 5-nitro-3-phenylacetamidobenzoic acid hydrolysis by the PA conjugate (20 microM) was found to be slightly higher than that of the free enzyme (12 microM), and evaluation of V(max) testifies to the high catalytic efficiency of the conjugated enzyme. PolyNIPAM-cross-linked PA retained its capacity to synthesize cephalexin from d-phenylglycin amide and 7-aminodeacetoxycephalosporanic acid. The synthesis-hydrolysis ratios of free and polyNIPAM-cross-linked enzyme in cephalexin synthesis were 7.46 and 7.49, respectively. Thus, diffusional limitation, which is a problem in the industrial production of beta-lactam antibiotics, can be successfully eliminated by cross-linking penicillin acylase to a smart polymer (i.e., polyNIPAM).

Chemically modified polysulfone hollow fibers with vinylpyrrolidone having improved blood compatibility

Hydrophilic polysulfone membranes (PVP-PSf) were prepared from polysulfone membranes covalently conjugated with polyvinylpyrrolidone (PVP) on the surface. The immobilized amount of vinylpyrrolidone on PVP-PSf membranes was controlled by the amount of vinylpyrrolidone monomer in the reaction solution and the reaction time. The PVP-PSf membranes were found to be the most hydrophilic membranes among the polysulfone and surface-modified polysulfone membranes prepared in this study. This is explained by the long hydrophilic side chain of polyvinylpyrrolidone on the PVP-PSf membranes which contributes to the hydrophilic wiper on the hydrophobic PSf membranes. It was found that PVP-PSf membranes gave lower protein adsorption from a plasma solution than polysulfone and other surface-modified membranes (p < 0.01). This is attributed to the hydrophilic surface of the PVP-PSf membranes, because the hydrophilic surface is known to reduce the protein adsorption on the membranes. The PVP-PSf membranes showed a much suppressed number of adhering platelets on the surface than polysulfone and other surface-modified membranes (p < 0.01). It is suggested that the hydrophilic surface of the PVP-PSf membranes without ionic groups causes the suppression of platelet adhesion on the PVP-PSf membranes and that the long hydrophilic side chain of polyvinylpyrrolidone on PVP-PSf membranes contributes to the hydrophilic and hemocompatible wipers on the surface of the hydrophobic PSf membranes.

A reversibly antigen-responsive hydrogel

Stimuli-responsive hydrogels that undergo abrupt changes in volume in response to external stimuli such as pH, temperature and solvent composition have potential applications in biomedicine and the creation of 'intelligent' materials systems, for example as media for drug delivery, separation processes and protein immobilization. Hydrogels have been reported that respond to pH, temperature, electric fields and saccharides. For some biomedical applications it would be very useful to have a material whose swelling response was dictated by a specific protein. Here we report such a material, which swells reversibly in a buffer solution in response to a specific antigen. The hydrogel was prepared by grafting the antigen and corresponding antibody to the polymer network, so that binding between the two introduces crosslinks in the network. Competitive binding of the free antigen triggers a change in gel volume owing to breaking of these non-covalent crosslinks. In addition, we show that the hydrogel displays shape-memory behaviour, and that stepwise changes in antigen concentration can induce pulsatile permeation of a protein through the network.

Unusual properties of thermally sensitive oligomer-enzyme conjugates of poly(N-isopropylacrylamide)-trypsin

Reversible soluble-insoluble oligomer-enzyme conjugates have been prepared by conjugating a thermally sensitive oligomer, poly(N-isopropylacrylamide) [poly(NIPAAm)] to trypsin. The conjugates can catalyze enzymatic reactions in solution and then may be separated from the solution by thermal precipitation. One special feature of the conjugates is that every poly(NIPAAm) chain has only one end attachment to the enzyme, so that the loss of enzymatic activity due to steric hindrance should be minimized. Conjugates with various numbers of oligomer chains per trypsin molecule were prepared. Surprisingly, the conjugates increased in enzymatic activity with increasing oligomer conjugation to the native trypsin. The trypsin active sites in the conjugates were accessible to large molecules, such as soybean trypsin inhibitor (MW = 21,500). The enzyme conjugates were more stable than native trypsin, both in solution and in the precipitated phase. On the other hand, the conjugates lost enzymatic activity faster than native trypsin when the temperature was repeatedly cycled through the lower critical solution temperature (LCST) of the poly(NIPAAm). The recovery of the conjugates by thermal precipitation in each cycle was over 95% even after 14 cycles through the LCST.