Carbohydrate-specific, boronate-containing copolymers: from sugar-sensing to cell adhesion

Sammanfattning: Carbohydrates play a major role in many cell recognition events and metabolic pathways of living organisms. Synthetic carbohydrate receptors are of great interest for the chemical design of sugar sensors, materials for cell separation, cell immobilization, drug delivery and other biomedical/biotechnological applications. These receptors are more stable under harsh conditions and have lower cost as compared to natural carbohydrate-binding proteins, such as lectins, antibodies or enzymes. Phenylboronic acid (PBA) is a highly stable, well-studied synthetic ligand that exhibits specificity to carbohydrates and has been employed for the molecular recognition of sugars, nucleotides, nucleosides, glycoproteins, and other biological molecules containing diol or polyol moieties. Water-soluble boronate-containing copolymers (BCCs) are extremely attractive for preparing glucose-responsive materials that can be used for both sugarsensing and drug delivery. Another important property of BCCs is their reversible multivalent binding to the carbohydrates present on the surfaces of living cells, thus enabling the cell adhesion to artificial BCC-grafted surfaces. This thesis presents a study of several BCCs and their applications to sugar-sensing and the reversible adhesion of carbohydrate particles and cells. Novel BCC-containing polymer brushes were prepared on glass slides by graft copolymerization, and these BCC brushes were characterized by time-of-flight secondary ion mass-spectrometry, atomic force microscopy and contact angle measurements. The brushes were able to interact strongly with carbohydrates of living mammalian cells surfaces and cause cell adhesion. It was possible to detach the adhered living cells on demand by competitive elution with an aqueous fructose solution under mild conditions. Thus, a promising technique for manipulation of mammalian cells was discovered. A boronate-containing hydrogel was used for quantitative sugar assays based on the optical detection of PBA-sugar binding. The interaction of sugar molecules with the boronate groups of the gels provided changes in the gel turbidity, which were detected by a spectrophotometer. BCC gels gave linear and reversible optical response to sugars in a broad concentration range at physiological pH. Scanning electron microscopy revealed the existence of micrometer-sized pores in the gels, which explained the good gel permeability and accessibility of the PBA ligands to the analytes. Moreover, the gel was able to maintain its properties after autoclaving, which allows for sterilization and repeated use of the sensor for sugar monitoring during fermentation processes.