Abstract
The sulfobetaine (SB) moiety, which comprises a quaternary ammonium group linked to a negatively charged sulfonate ester, is known to impart nonfouling properties to interfaces coated with polysulfobetaines or grafted with SB-polymeric brushes. Increasingly, evidence emerges that the SB group is, overall, a better antifouling group than the phosphorylcholine (PC) moiety extensively used in the past. We report here the synthesis of a series of SB-modified chitosans (CH-SB) carrying between 20 and 40 mol % SB per monosaccharide unit. Chitosan (CH) itself is a naturally derived copolymer of glucosamine and N-acetyl-glucosamine linked with a β-1,4 bond. Analysis by quartz crystal microbalance with dissipation (QCM-D) indicates that CH-SB films (thickness ∼ 20 nm) resist adsorption of bovine serum albumin (BSA) with increasing efficiency as the SB content of the polymer augments (surface coverage ∼ 15 μg cm–2 for films of CH with 40 mol % SB). The cell adhesivity of CH-SB films coated on glass was assessed by determining the spreading dynamics of CT26 cell aggregates. When placed on chitosan films, known to be cell-adhesive, the CT26 cell aggregates spread by forming a cell monolayer around them. The spreading of CT26 cell aggregates on zwitterion-modified chitosans films is thwarted remarkably. In the cases of CH-SB30 and CH-SB40 films, only a few isolated cells escape from the aggregates. The extent of aggregate spreading, quantified based on the theory of liquid wetting, provides a simple in vitro assay of the nonfouling properties of substrates toward specific cell lines. This assay can be adopted to test and compare the fouling characteristics of substrates very different from the chemical viewpoint.
Highlights
Innovations in the synthesis and fabrication of biomaterials have enabled major advances in tissue engineering, treatment of cardiovascular diseases, cancer therapy, and development of long-lasting surgical implants
Since CT26 cell aggregates deposited on CH-SB30 and CHSB40 films do not form distinct precursor films, we present in an inset on Figure 4A, the changes with time of the normalized area, A/R0
Sulfobetaine-modified chitosans, as examples of polyzwitterions derived from natural resources, offer several advantages
Summary
Innovations in the synthesis and fabrication of biomaterials have enabled major advances in tissue engineering, treatment of cardiovascular diseases, cancer therapy, and development of long-lasting surgical implants. Some applications require platforms promoting cell adhesion,[2] directed cell migration,[3] or cell differentiation.[4] In contrast, in the context of cardiovascular implants, materials must resist cell adhesion to prevent stenosis.[5,6] Poly(ethylene glycols)[7] and zwitterionic polymers[8] are among the most successful nonfouling coatings currently available. The PC group comprises of a positively charged trimethylammonium group and a negatively charged phosphate ester.[13] In the SB and CB groups the anionic moieties are sulfonate esters and carbonate esters, respectively.[14,15] While all three families act as nonfouling agents, they show subtle differences in properties such as stability and resistance against oxidation.[16]
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