Shaoyi Jiang

Ultralow‐Fouling, Functionalizable, and Hydrolyzable Zwitterionic Materials and Their Derivatives for Biological Applications

In recent years, zwitterionic materials such as poly(carboxybetaine) (pCB) and poly(sulfobetaine) (pSB) have been applied to a broad range of biomedical and engineering materials. Due to electrostatically induced hydration, surfaces coated with zwitterionic groups are highly resistant to nonspecific protein adsorption, bacterial adhesion, and biofilm formation. Among zwitterionic materials, pCB is unique due to its abundant functional groups for the convenient immobilization of biomolecules. pCB can also be prepared in a hydrolyzable form as cationic pCB esters, which can kill bacteria or condense DNA. The hydrolysis of cationic pCB esters into nonfouling zwitterionic groups will lead to the release of killed microbes or the irreversible unpackaging of DNA. Furthermore, mixed-charge materials have been shown to be equivalent to zwitterionic materials in resisting nonspecific protein adsorption when they are uniformly mixed at the molecular scale.

Zwitterionic Polymers Exhibiting High Resistance to Nonspecific Protein Adsorption from Human Serum and Plasma

This study examined six different polymer and self-assembled monolayer (SAM) surface modifications for their interactions with human serum and plasma. It was demonstrated that zwitterionic polymer surfaces are viable alternatives to more traditional surfaces based on poly(ethylene glycol) (PEG) as nonfouling surfaces. All polymer surfaces were formed using atom transfer radical polymerization (ATRP) and they showed an increased resistance to nonspecific protein adsorption compared to SAMs. This improvement is due to an increase in the surface packing density of nonfouling groups on the surface, as well as a steric repulsion from the flexible polymer brush surfaces. The zwitterionic polymer surface based on carboxybetaine methacrylate (CBMA) also incorporates functional groups for protein immobilization in the nonfouling background, making it a strong candidate for many applications such as in diagnostics and drug delivery.

Poly(zwitterionic)protein conjugates offer increased stability without sacrificing binding affinity or bioactivity

Treatment with therapeutic proteins is an attractive approach to targeting a number of challenging diseases. Unfortunately, the native proteins themselves are often unstable in physiological conditions, reducing bioavailability and therefore increasing the dose that is required. Conjugation with poly(ethylene glycol) (PEG) is often used to increase stability, but this has a detrimental effect on bioactivity. Here, we introduce conjugation with zwitterionic polymers such as poly(carboxybetaine). We show that poly(carboxybetaine) conjugation improves stability in a manner similar to PEGylation, but that the new conjugates retain or even improve the binding affinity as a result of enhanced protein-substrate hydrophobic interactions. This chemistry opens a new avenue for the development of protein therapeutics by avoiding the need to compromise between stability and affinity.

Zwitterionic carboxybetaine polymer surfaces and their resistance to long-term biofilm formation

In this work, we report a systematic study of zwitterionic poly(carboxybetaine methacrylate) (pCBMA) grafted from glass surfaces via atom transfer radical polymerization (ATRP) for their resistance to long-term bacterial biofilm formation. Results show that pCBMA-grafted surfaces are highly resistant to non-specific protein adsorption (fibrinogen and undiluted blood plasma) at 25, 30 and 37 degrees C. Long-term (over 24 h) colonization of two bacterial strains (Pseudomonas aeruginosa PAO1 and Pseudomonas putida strain 239) on pCBMA surface was studied using a parallel flow cell at 25, 30 and 37 degrees C. Uncoated glass cover slips were chosen as the positive reference. Results show that pCBMA coatings reduced long-term biofilm formation of P. aeruginosa up to 240 h by 95% at 25 degrees C and for 64 h by 93% at 37 degrees C, and suppressed P. putida biofilm accumulation up to 192 h by 95% at 30 degrees C, with respect to the glass reference. The ability of pCBMA coatings to resist non-specific protein adsorption and significantly retard bacterial biofilm formation makes it a very promising material for biomedical and industrial applications.

Zwitterionic hydrogels implanted in mice resist the foreign-body reaction

The performance of implantable biomedical devices is impeded by the foreign-body reaction, which results in formation of a dense collagenous capsule that blocks mass transport and/or electric communication between the implant and the body. No known materials or coatings can completely prevent capsule formation. Here we demonstrate that ultra-low-fouling zwitterionic hydrogels can resist the formation of a capsule for at least 3 months after subcutaneous implantation in mice. Zwitterionic hydrogels also promote angiogenesis in surrounding tissue, perhaps owing to the presence of macrophages exhibiting phenotypes associated with anti-inflammatory, pro-healing functions. Thus, zwitterionic hydrogels may be useful in a broad range of applications, including generation of biocompatible implantable medical devices and tissue scaffolds.

Ultralow fouling and functionalizable surface chemistry based on a zwitterionic polymer enabling sensitive and specific protein detection in undiluted blood plasma.

A crucial step in the development of implanted medical devices, in vivo diagnostics, and microarrays is the effective prevention of nonspecific protein adsorption from real-world complex media such as blood plasma or serum. In this work, a zwitterionic poly(carboxybetaine acrylamide) (polyCBAA) biomimetic material was employed to create a unique biorecognition coating with an ultralow fouling background, enabling the sensitive and specific detection of proteins in blood plasma. Conditions for surface activation, protein immobilization, and surface deactivation of the carboxylate groups in the polyCBAA coating were determined. An antibody-functionalized polyCBAA surface platform was used to detect a target protein in blood plasma using a sensitive surface plasmon resonance (SPR) sensor. A selective protein was directly detected from 100% human blood plasma with extraordinary specificity and sensitivity. The total nonspecific protein adsorption on the functionalized polyCBAA surface was very low (<3 ng/cm (2) for undiluted blood plasma). Because of the significant reduction of nonspecific protein adsorption, it was possible to monitor the kinetics of antigen-antibody interactions in undiluted blood plasma. The functionalization effectiveness and detection characteristics using a cancer protein marker candidate of polyCBAA were compared with those of the conventional nonfouling oligo(ethylene glycol)-based surface chemistry.

Spectral surface plasmon resonance biosensor for detection of staphylococcal enterotoxin B in milk

This work evaluates a newly developed wavelength modulation-based SPR biosensor for the detection of staphylococcal enterotoxin B (SEB) in milk. Two modes of operation of the SPR biosensor are described: direct detection of SEB and sandwich assay. In the sandwich assay detection mode, secondary antibodies are bound to the already captured toxin to amplify sensor response. Samples including SEB in buffer and SEB in milk were analyzed in this work. The SPR biosensor has been shown to be capable of directly detecting concentrations of SEB in buffer as low as 5 ng/ml. In sandwich detection mode, the lowest detection limit was determined to be 0.5 ng/ml for both buffer and milk samples. The reported wavelength modulation-based SPR sensor provides a generic platform which can be tailored for detection of various foodborne pathogens and agents for food analysis and testing.

Integrated Antimicrobial and Nonfouling Zwitterionic Polymers

Zwitterionic polymers are generally viewed as a new class of nonfouling materials. Unlike their poly(ethylene glycol) (PEG) counterparts, zwitterionic polymers have a broader chemical diversity and greater freedom for molecular design. In this Minireview, we highlight recent microbiological applications of zwitterionic polymers and their derivatives, with an emphasis on several unique molecular strategies to integrate antimicrobial and nonfouling properties. We will also discuss our insights into the bacterial nonfouling performance of zwitterionic polymers and one example of engineering zwitterionic polymer derivatives for antimicrobial wound-dressing applications.

Molecular Simulation Studies of Protein Interactions with Zwitterionic Phosphorylcholine Self-Assembled Monolayers in the Presence of Water

Molecular simulations were performed to study the interactions between a protein (lysozyme, LYZ) and phosphorylcholine-terminated self-assembled monolayers (PC-SAMs) in the presence of explicit water molecules and ions. The results show that the water molecules above the PC-SAM surface create a strong repulsive force on the protein as it approaches the surface. The structural and dynamic properties of the water molecules above the PC-SAM surface were analyzed to provide information regarding the role of hydration in surface resistance to protein adsorption. It can be seen from residence time dynamics that the water molecules immediately above the PC-SAM surface are significantly slowed down as compared to bulk water, suggesting that the PC-SAM surface generates a tightly bound, structured water layer around its head groups. Moreover, the orientational distribution and reorientational dynamics of the interfacial water molecules near the PC-SAM surface were found to have the ionic solvation nature of the PC head groups. These properties were also compared to those obtained previously for an oligo(ethylene glycol) (OEG) SAM system and bulk water.

Polysulfobetaine-Grafted Surfaces as Environmentally Benign Ultralow Fouling Marine Coatings

Coatings based on polysulfobetaine polymers are being developed as environmentally benign, fouling-resistant marine coatings. Poly(sulfobetaine methacrylate) (polySBMA) brushes were grafted onto glass surfaces using surface-initiated atom transfer radical polymerization (ATRP). The settlement, growth, and attachment strength of marine algae were investigated on polySBMA-coated surfaces. Results showed that few spores of the green marine alga, Ulva, settled (attached) on the polySMBA surfaces, and the adhesion strength of both spores and sporelings (young plants) was low. Diatoms were also mostly unable to adhere to the polySMBA surfaces. Assays demonstrated that SBMA polymers in solution were not toxic. The data are discussed in terms of the interfacial properties presented by the polySMBA surfaces. Zwitterionic polymers and coatings exhibit great advantages for their effectiveness to resist marine fouling while being environmentally benign and are promising as ultralow fouling marine coatings.