Hydrogen-Bonded Multifunctional Supramolecular Copolymers in Water

Tubular supramolecular alternating copolymers fabricated by cyclic peptide-polymer conjugates

Supramolecular copolymers are an emerging class of materials, which bring together different properties and functionalities of multiple components via noncovalent interactions. While it is widely acknowledged that the repeating unit sequence plays an essential role on the performance of these materials, mastering and tuning the supramolecular copolymer sequence is still an open challenge. To date, only statistical supramolecular copolymers have been reported using cyclic peptide-polymer conjugates as building blocks. To enrich the diversity of tubular supramolecular copolymers, we report here a strategy of controlling their sequences by introducing an extra complementary noncovalent interaction. Hence, two conjugates bearing one electron donor and one electron acceptor, respectively, are designed. The two conjugates can individually assemble into tubular supramolecular homopolymers driven by the multiple hydrogen bonding interactions between cyclic peptides. However, the complementary charge transfer interaction between the electron donor and acceptor makes each conjugate more favorable for complexing with its counterpart, resulting in an alternating sequence of the supramolecular copolymer. Following the same principle, more functional supramolecular alternating copolymers are expected to be designed and constructed via other complementary noncovalent interactions (electrostatic interactions, metal coordination interactions, and host-guest interactions, etc.).

Biomaterial screening of protein coatings and peptide additives: towards a simple synthetic mimic of a complex natural coating for a bio-artificial kidney

Bio-artificial kidneys require conveniently synthesized membranes providing signals that regulate renal epithelial cell function. Therefore, we aimed to find synthetic analogues for natural extracellular matrix (ECM) protein coatings traditionally used for epithelial cell culturing. Two biomaterial libraries, based on natural ECM-coatings and on synthetic supramolecular small molecule additives, were developed. The base material consisted of a bisurea (BU) containing polymer, providing supramolecular BU-additives to be incorporated via specific hydrogen bonding interactions. This system allows for a modular approach and therefore easy fractional factorial based screening. A natural coating on the BU-polymer material with basement membrane proteins, laminin and collagen IV, combined with catechols was shown to induce renal epithelial monolayer formation. Modification of the BU-polymer material with synthetic BU-modified ECM peptide additives did not result in monolayer formation. Unexpectedly, simple BU-catechol additives induced monolayer formation and presented similar levels of epithelial markers and apical transporter function as on the laminin, collagen IV and catechol natural coating. Importantly, when this BU-polymer material was processed into fibrous e-spun membranes the natural coating and the BU-catechol additive were shown to perfectly function. This study clearly indicates that complex natural ECM-coatings can be replaced by simple synthetic additives, and displays the potency of material libraries based on design of experiments in combination with modular, supramolecular chemistry.

Development of Poor Cell Adhesive Immersion Precipitation Membranes Based on Supramolecular Bis-Urea Polymers

A variety of biomedical applications requires tailored membranes; fabrication through a mix-and-match approach is simple and desired. Polymers based on supramolecular bis-urea (BU) moieties are capable of modular integration through directed non-covalent stacking. Here, it is proposed that non-cell adhesive properties can be introduced in polycaprolactone-BU-based membranes by the addition of poly(ethylene glycol) (PEG)-BU during immersion precipitation membrane fabrication, while unmodified PEG is not retained in the membrane. PEG-BU addition results in denser membranes with a similar pore size compared to pristine membranes, while PEG addition induces defect formation. Infrared spectroscopy and surface hydrophobicity measurements indicate that PEG-BU is retained during membrane processing. Additionally, PEG-BU incorporation successfully leads to poor cell adhesive surfaces. No evidence is observed to indicate PEG retention. The results obtained indicate that the BU system enables intimate mixing of BU-modified polymers after processing. Collectively, the results provide the first steps toward BU-based immersion precipitated supramolecular membranes for biomedical applications.

Future of Supramolecular Copolymers Unveiled by Reflecting on Covalent Copolymerization

Supramolecular copolymers are an emerging class of materials, and in the last years their potential has been demonstrated on a broad scale. Implementing noncovalent polymers with multiple components can bring together useful features such as dynamicity and new functionalities. However, mastering and tuning the microstructure of these systems is still an open challenge. In this Perspective, we aim to trace the general principles of supramolecular copolymerization by analyzing them through the lens of the well-established field of covalent copolymerization. Our goal is to delineate guidelines to classify and analyze supramolecular copolymers in order to create a fruitful platform to design and investigate new multicomponent systems.

Carboxymethyl Starch Excipients for Drug Chronodelivery

Carboxymethyl starch (CMS) is a pH-responsive excipient exhibiting also interesting properties for applications in delayed drug delivery systems. This work was aimed to investigate the release properties of monolithic and dry-coated tablets based on ionic sodium CMS and on protonated CMS, formulated with three model tracers: acetaminophen, acetylsalicylic acid (ASA), and sodium diclofenac. The sodium or protonated CMS were obtained from the same CMS synthesis by controlling the final pH of reaction media. The two forms of CMS were confirmed by the Fourier transform infrared spectroscopy. The in vitro dissolution profiles for monolithic and double core tablets were different and allowed a better understanding of characteristics of the two excipient forms. It was found that the protonated CMS exhibited a better stability in simulated gastric fluid in comparison to its sodium salt in monolithic dosage forms, whereas both excipients afforded a complete gastric protection of drugs when formulated as dry-coated dosages. Determination of water uptake and erosion rate of monolithic matrices based on the two CMS forms showed different mechanisms involved in the delivery of the three model active molecules in simulated intestinal media. When pancreatic enzymes were added in dissolution media, the drug release was accelerated showing that CMS is still a substrate for alpha-amylase. Both sodium and protonated starch excipients, formulated as dry-coated dosages, afforded a good gastro-protection and allowed a drug chronodelivery at various intervals up to 4-5 h. They could be considered as an alternative for delayed delivery and a solvent-free coating procedure.