Construction Of Multistimulus Responsive Bioactive Surfaces

Stimuli-responsive bioactive surfaces are a class of surfaces that can undergo pronounced changes in properties and functions,e.g.wettability,roughness,adhesiveness,in response to the change of external stimuli in the surrounding environment,thus achieving the regulation of specific biological functions.In previous work on the design of stimuli-responsive bioactive surfaces,two approaches have been adopted including(i)modification with stimuli-responsive polymers via layer-by-layer assembly or surface initiated polymerization,(ii)introduction of reversible interaction(e.g.,host-guest couples,dynamic covalent bonds)to control the presentation of bioactive ligands on the surface.Over the past decades,stimuli-responsive bioactive surfaces that can respond to a single stimulus such as temperature,pH,light,or electric field have been studied extensively.Given the fact that in real biological systems,several external signals may be present simultaneously.Therefore,it is clear that multistimulus responsive surfaces with switchable bioactivity would be better adapt to interaction in real biological systems,show potentials in a much broader range of applications.The main work of this thesis is to prepare a multistimulus responsive bioactive surface based on thermoresponsive poly(N-isopropylacrylamide)(PNIPAAm)and pH-/sugar-responsive phenylboronic acid(PBA)group to achieve regulation of bioadhesion and biological functions in response to change in temperature,pH,or sugar content.The detailed researches are as follows:(1)Combining surface-initiated polymerization and post-modification,a surface(Si-PNB)with switchable wettability and bioadhesion in response to temperature,pH,or sugar was developed.Firstly,surface-initiated copolymerization of N-isopropylacrylamide(NIPAAm)and 2-aminoethyl methacrylate hydrochloride(AMA)was carried out to graft copolymer poly(NIPAAm-co-AMA)(PNA)on Si surface,the NH2 groups on the side chains of PNA were then activated for conjugation of PBA groups via amidation.Surface wettability was determined using water contact angle(WCA)goniometer and the feed ratio of the monomer was screened,variations in WCA of the Si-PNB surface showed that significant change in WCA was observed in response to any of the stimuli(temperature,pH,or sugar content)with monomer feed ratio,NIPAAm/AMA=80/20.Also,the responsiveness of wettability to all three stimuli was reversible over at least three cycles.Furthermore,quartz crystal microbalance was adopted to investigate the interaction between Si-PNB surface and proteins.It was found that change in either temperature,pH,or fructose concentration caused release of ovalbumin(OVA),and a much higher OVA release ratio was achieved under all three stimuli applied simultaneously.(2)The attachment and release of bacteria and mammalian cells on Si-PNB surface was investigated,and a multi-stimulus responsive antibacterial surfaces with switchable killing bacteria and releasing bacteria functions was developed via the introduction of bactericidal molecule.Specifically,Escherichia coli(E.coli)and Hela cells,which also present cis-diol structures on the surfaces,were chosen as model bacterium/cell.Results of fluorescent staining assays showed that compared to unmodified Si,the Si-PNB surface exhibited a significant enhancement in E.coli attachment and Hela cell attachment,and significant release of bacteria or cells occurred under all three stimuli.Also,no significant decrease in release ability was observed over three cycles.Moreover,The Si-PNB surface with only a single function(attachment/detachment)was "upgraded" to a bioactive surface with two different functions(killing bacteria/releasing bacteria),after incorporation of a ?-cyclodextrin(?-CD)derivative having seven quaternary ammonium host(QAS)groups(CD-QAS)into the Si-PNB surface(Si-PNB@CD-QAS)via the formation of boronate ester bond.Fluorescent staining assays and scanning electron microscope indicated that the killing efficiency of the Si-PNB@CD-QAS surface was nearly 100%,and the killed bacteria could be removed from the surface in response to three different external stimuli.In addition,no significant decreases in biocidal activity or bacterial release ability were observed over three cycles.In summary,a multistimulus responsive surface with switchable bioactivity was developed based on a copolymer containing a thermoresponsive PNIPAAm component and a pH-/sugar-responsive PBA component.The surface not only showed a reversible responsiveness of wettability to all three stimuli,but also achieve a multistimulus responsive regulation of bioadhesion behavior such as protein adsorption,bacteria attachment,and cell attachment.Furthermore,this multistimulus responsive system was "upgraded" as a "smart"bioactive surface having the ability to switch between two different functions,namely bacteria killing and bacteria release,by introduction of a diol-containing biocidal compound CD-QAS.Compared to a switchable bioactive surface that responds to only a single stimulus,our multistimulus responsive surface is better adapted to the complex conditions of real biological environments,showing potential for use in various biomedical and biotechnology applications.