Biofunctionality with a twist: the importance of molecular organisation, handedness and configuration in synthetic biomaterial design

The building blocks of life – nucleotides, amino acids and saccharides – give rise to a large variety of components and make up the hierarchical structures found in Nature. Driven by chirality and non-covalent interactions, helical and highly organised structures are formed and the way in which they fold correlates with specific recognition and hence function. A great amount of effort is being put into mimicking these highly specialised biosystems as biomaterials for biomedical applications, ranging from drug discovery to regenerative medicine. However, as well as lacking the complexity found in Nature, their bio-activity is sometimes low and hierarchical ordering is missing or underdeveloped. Moreover, small differences in folding in natural biomolecules (e.g., caused by mutations) can have a catastrophic effect on the function they perform. In order to develop biomaterials that are more efficient in interacting with biomolecules, such as proteins, DNA and cells, we speculate that incorporating order and handedness into biomaterial design is necessary. In this review, we first focus on order and handedness found in Nature in peptides, nucleotides and saccharides, followed by selected examples of synthetic biomimetic systems based on these components that aim to capture some aspects of these ordered features. Computational simulations are very helpful in predicting atomic orientation and molecular organisation, and can provide invaluable information on how to further improve on biomaterial designs. In the last part of the review, a critical perspective is provided along with considerations that can be implemented in next-generation biomaterial designs

A supramolecular platform stabilizing growth factors

High concentrations of supplemented growth factors can cause oversaturation and adverse effects in in vitro and in vivo studies. Though, these supraphysiological concentrations are often required due to the low stability of growth factors. Here we demonstrate the stabilization of TGF-β1 and BMP4 using supramolecular polymers. Inspired by heparan sulfate, sulfonated peptides were presented on a supramolecular polymer to allow for non-covalent binding to growth factors in solution. After mixing with excipient molecules, both TGF-β1 and BMP4 were shown to have a prolonged half-life compared to the growth factors free in solution. Moreover, high cellular response was measured by a luciferase assay, indicating that TGF-β1 remained highly active upon binding to the supramolecular assembly. The results demonstrate that significant lower concentrations of growth factors can be used when supramolecular polymers bearing growth factor binding moieties are implemented. This approach can also be exploited in hydrogel systems to control growth factor release

Importance of Molecular and Bulk Dynamics in Supramolecular Hydrogels in Dictating Cellular Spreading

Cellular spreading is affected not only by the stiffness of the matrix but also by its dynamics. Synthetic hydrogels, formed by the assembly of supramolecular monomers, are intrinsically dynamic and tunable in their stiffness. However, the importance of molecular dynamics resulting in differences in bulk dynamics and stiffness remains elusive. Here, we present two different hydrogel systems employing slow-exchanging ureidopyrimidinone monomers and fast-exchanging benzene-1,3,5-tricarboxamide monomers to decipher design rules for supramolecular hydrogel-cell interactions. To achieve cell spreading, both robust incorporation of cell-binding ligands, reflected in slow molecular dynamics (monomer exchange), and sufficient material resistance, reflected in slow bulk dynamics (stress relaxation), are crucial. Epithelial cells respond to gel dynamics as cells remain round on fast-relaxing gels, independent of gel stiffness. Fibroblasts respond to gel dynamics on soft gels (∼100-200 Pa), but gel stiffness overrules gel dynamics on stiffer gels (∼1 kPa). Together, our results disclose that (1) molecular dynamics at the supramolecular fiber level is translated to bulk dynamics on the hydrogel level, (2) gel dynamics is the dominant factor in dictating cellular spreading in soft gels, and (3) design rules for supramolecular hydrogel-cell interaction are cell-type-dependent.</p

Engineering the Dynamics of Cell Adhesion Cues in Supramolecular Hydrogels for Facile Control over Cell Encapsulation and Behavior

The extracellular matrix (ECM) forms through hierarchical assembly of small and larger polymeric molecules into a transient, hydrogel-like fibrous network that provides mechanical support and biochemical cues to cells. Synthetic, fibrous supramolecular networks formed via non-covalent assembly of various molecules are therefore potential candidates as synthetic mimics of the natural ECM, provided that functionalization with biochemical cues is effective. Here, combinations of slow and fast exchanging molecules that self-assemble into supramolecular fibers are employed to form transient hydrogel networks with tunable dynamic behavior. Obtained results prove that modulating the ratio between these molecules dictates the extent of dynamic behavior of the hydrogels at both the molecular and the network level, which is proposed to enable effective incorporation of cell-adhesive functionalities in these materials. Excitingly, the dynamic nature of the supramolecular components in this system can be conveniently employed to formulate multicomponent supramolecular hydrogels for easy culturing and encapsulation of single cells, spheroids, and organoids. Importantly, these findings highlight the significance of molecular design and exchange dynamics for the application of supramolecular hydrogels as synthetic ECM mimics