Biomaterial with chemically engineered surface for protein immobilization.

The last 3 decades have been a revolution in the area of sol-gel-derived materials. They can be used to encapsulate biomolecules such as enzymes, antibodies, hormones, and proteins retaining their functional state. Proteins can be immobilized in many ways but it is crucial that they retain their native conformational structure and, therefore, bioactivity. Porous silica gel matrixes with modified surfaces offer unlimited possibilities to control the protein-solid interaction behavior. The bioimmobilization process on sol-gel biomaterials with chemically engineered surface has driven applications on solid-phase materials, affinity chromatography, biosensors and many others. In the present work, we have aimed to produce surface-modified silica glass materials obtained via sol-gel route to be used as solid support on drug delivery systems and as solid-phase in immunodiagnostic. The functionalization process was carried out by reacting alkoxysilanes with 5 different silane surface modifying chemical groups: tetraethoxysilane (TEOS), 3-mercaptopropyltrimethoxysilane (MPTMS) and 3-aminopropyltriethoxysilane (APTES), 3-glycidoxypropyltrimethoxysilane (GPTMS) and 3-isocyanatopropyltriethoxysilane (ICPES). The bioactivity assays were based on two main tests: (a) An in vivo bioresponse of rats with sol-gel disk implants with insulin protein incorporated. In vivo tests with adult male rats were used to verify the immobilized insulin bioactivity after implantation of different biomaterial with functionalized surfaces. All surface modified materials have presented hypoglycemic peak response associated with the insulin bioactivity. (b) The produced solid-phase sol-gel disks with protein substrates were tested through Enzyme Linked Immuno Sorbent Assay (ELISA). The immunoassay results have showed that glasses with chemically functionalized surfaces regulated the extent of bioimmobilization of protein. The amine, thiol and hydroxyl terminated porous gels have showed significant interaction with the antibody-antigen, during the coupling process. We believe that it is due to balance of forces associated with Van der Waals interaction, hydrophilic and hydrophobic forces and steric hindrance acting at the surface. Therefore, such novel biomaterial could be advantageously used in drug delivery systems and in immunoassays of diagnostic kits.

Surface functionalization of porous glass networks: effects on bovine serum albumin and porcine insulin immobilization.

Biomolecules can be immobolized in many different ways. They can also be entrapped or tightly adsorbed within porous gels, clays, membranes, resins, and several other materials, but it is crucial that they retain their active conformation after the incorporation procedure. Porous gel matrixes with functionalized surfaces offer unlimited possibilities to control the protein-substrate interaction behavior. In the present work, we have studied the adsorption and the relative stability of bovine serum albumin (BSA) and porcine insulin(PI) incorporated in gels of SiO2 glass matrixes. The porous gel matrixes were obtained using tetramethoxysilane (TMOS)/metanol and functionalized with (3-mercaptopropyl) trimethoxysilane and (3-aminopropyl) triethoxysilane. The relative adsorption kinetics and stability of BSA and PI incorporated in glass networks were evaluated by immersion in phosphate buffer saline (PBS) and alkaline elution media for different periods of time. The kinetics of protein release from the gel matrix was monitored by UV-visible spectroscopy. A significantly larger PI release was observed compared to BSA in PBS solutions. We believe this is mainly associated with the difference on protein interactions with the modified surface, according to the characterization results of porosity, surface area, and contact angle of different functionalized gel matrixes. We could not observe any evidence of denaturation with either proteins after their desorption from gel matrixes using the ultraviolet spectroscopy technique. These results have also been confirmed with the strong bioactivity response from "in vivo" test conducted in rats, where porous gels with PI incorporated were implanted, showing that released proteins retained their native conformation.