Sulfated glycopeptide nanostructures for multipotent protein activation

Temperature-responsive supramolecular hydrogels

Hydrogels comprise a class of soft materials which are extremely useful in a number of contexts, for example as matrix-mimetic biomaterials for applications in regenerative medicine and drug delivery. One particular subclass of hydrogels consists of materials prepared through non-covalent physical crosslinking afforded by supramolecular recognition motifs. The dynamic, reversible, and equilibrium-governed features of these molecular-scale motifs often transcend length-scales to endow the resulting hydrogels with these same properties on the bulk scale. In efforts to engineer hydrogels of all types with more precise or application-specific uses, inclusion of stimuli-responsive sol-gel transformations has been broadly explored. In the context of biomedical uses, temperature is an interesting stimulus which has been the focus of numerous hydrogel designs, supramolecular or otherwise. Most supramolecular motifs are inherently temperature-sensitive, with elevated temperatures commonly disfavoring motif formation and/or accelerating its dissociation. In addition, supramolecular motifs have also been incorporated for physical crosslinking in conjunction with polymeric or macromeric building blocks which themselves exhibit temperature-responsive changes to their properties. Through molecular-scale engineering of supramolecular recognition, and selection of a particular motif or polymeric/macromeric backbone, it is thus possible to devise a number of supramolecular hydrogel materials to empower a variety of future biomedical applications.

Biological functions of supramolecular assemblies of small molecules in cellular environment

Like biomacromolecules, certain small molecules (e.g., aggregators) are able to self-assemble in aqueous phase to form nanoscale aggregates. Though it is well-established that the aggregates may interact with enzymes in vitro, the study of the biological activities of the assemblies of small molecules in cellular environment is only at its beginning. This review summarizes the recent progresses in exploring the biological functions of supramolecular assemblies of small molecules (SASMs). We first discuss the use of SASMs to inhibit pathogenic cells, such as cancer cells and bacteria. The use of SASMs to target different parts of cancer cells, such as pericellular space, cytosol, and subcellular organelles, and to combine with other bioactive entities (e.g., proteins and clinically used drugs), is particularly promising for addressing the challenge of acquired multidrug resistance in cancer therapy. Then, we describe the use of SASMs to sustain physiological functions of normal cells, that is, promoting cells proliferation and differentiation for tissue regeneration. After that, we show the use of SASMs as a basic tool to research cell behaviors, for instance, identifying the specific cells, improving enzyme probes, revealing membrane dynamics, enhancing molecular imaging, and mimicking context-dependent signaling. Finally, we give the outlook of the research of SASMs. We expect that this review, by highlighting the biological functions of SASMs, provides a starting point to explore the chemical biology of SASMs.

Superstructured Biomaterials Formed by Exchange Dynamics and Host-Guest Interactions in Supramolecular Polymers

Dynamic and reversible assembly of molecules is ubiquitous in the hierarchical superstructures of living systems and plays a key role in cellular functions. Recent work from the laboratory reported on the reversible formation of such superstructures in systems of peptide amphiphiles conjugated to oligonucleotides and electrostatically complimentary peptide sequences. Here, a supramolecular system is reported upon where exchange dynamics and host-guest interactions between β-cyclodextrin and adamantane on peptide amphiphiles lead to superstructure formation. Superstructure formation with bundled nanoribbons generates a mechanically robust hydrogel with a highly porous architecture that can be 3D printed. Functionalization of the porous superstructured material with a biological signal results in a matrix with significant in vitro bioactivity toward neurons that could be used as a supramolecular model to design novel biomaterials.

Assembly of Dynamic Supramolecular Polymers on a DNA Origami Platform

Biological processes rely on transient interactions that govern assembly of biomolecules into higher order, multi-component systems. A synthetic platform for the dynamic assembly of multicomponent complexes would provide novel entries to study and modulate the assembly of artificial systems into higher order topologies. Here, we establish a hybrid DNA origami-based approach as an assembly platform that enables dynamic templating of supramolecular architectures. It entails the site-selective recruitment of supramolecular polymers to the platform with preservation of the intrinsic dynamics and reversibility of the assembly process. The composition of the supramolecular assembly on the platform can be tuned dynamically, allowing for monomer rearrangement and inclusion of molecular cargo. This work should aid the study of supramolecular structures in their native environment in real-time and incites new strategies for controlled multicomponent self-assembly of synthetic building blocks.

Supramolecular polymerization of sulfated dendritic peptide amphiphiles into multivalent L-selectin binders

The synthesis of a sulfate-modified dendritic peptide amphiphile and its self-assembly into one-dimensional rod-like architectures in aqueous medium is reported. The influence of the ionic strength on the supramolecular polymerization was probed via circular dichroism spectroscopy and cryogenic transmission electron microscopy. Physiological salt concentrations efficiently screen the charges of the dendritic building block equipped with eight sulfate groups and trigger the formation of rigid supramolecular polymers. Since multivalent sulfated supramolecular structures mimic naturally occurring L-selectin ligands, the corresponding affinity was evaluated using a competitive SPR binding assay and benchmarked to an ethylene glycol-decorated supramolecular polymer.

Designing sub-20 nm self-assembled nanocarriers for small molecule delivery: Interplay among structural geometry, assembly energetics, and cargo release kinetics

Biological constraints in diseased tissues have motivated the need for small nanocarriers (10-30 nm) to achieve sufficient vascular extravasation and pervasive tumor penetration. This particle size limit is only an order of magnitude larger than small molecules, such that cargo loading is better described by co-assembly processes rather than simple encapsulation. Understanding the structural, kinetic, and energetic contributions of carrier-cargo co-assembly is thus critical to achieve molecular-level control towards predictable in vivo behavior. These interconnected set of properties were systematically examined using sub-20 nm self-assembled nanocarriers known as three-helix micelles (3HM). Both hydrophobicity and the "geometric packing parameter" dictate small molecule compatibility with 3HM's alkyl tail core. Planar obelisk-like apomorphine and doxorubicin (DOX) molecules intercalated well within the 3HM core and near the core-shell interface, forming an integral component to the co-assembly, as corroborated by small-angle X-ray and neutron-scattering structural studies. DOX promoted crystalline alkyl tail ordering, which significantly increased (+63%) the activation energy of 3HM subunit exchange. Subsequently, 3HM-DOX displayed slow-release kinetics (t_1/2 = 40 h) at physiological temperatures, with ~50× greater cargo preference for the micelle core as described by two drug partitioning coefficients (micellar core/shell K_p1 ~ 24, and shell/bulk solvent K_p2 ~ 2). The geometric and energetic insights between nanocarrier and their small molecule cargos developed here will aid in broader efforts to deconvolute the interconnected properties of carrier-drug co-assemblies. Adding this knowledge to pharmacological and immunological explorations will expand our understanding of nanomedicine behavior throughout all the physical and in vivo processes they are intended to encounter.

Multivalent Clustering of Adhesion Ligands in Nanofiber-Nanoparticle Composites

Because the positioning and clustering of biomolecules within the extracellular matrix dictates cell behaviors, the engineering of biomaterials incorporating bioactive epitopes with spatial organization tunable at the nanoscale is of primary importance. Here we used a highly modular composite approach combining peptide amphiphile (PA) nanofibers and silica nanoparticles, which are both easily functionalized with one or several bioactive signals. We show that the surface of silica nanoparticles allows the clustering of RGDS bioactive signals leading to improved adhesion and spreading of fibroblast cells on composite hydrogels at an epitope concentration much lower than in PA-only based matrices. Most importantly, by combining the two integrin-binding sequences RGDS and PHSRN on nanoparticle surfaces, we improved cell adhesion on the PA nanofiber/particle composite hydrogels, which is attributed to synergistic interactions known to be effective only for peptide intermolecular distance of ca. 5 nm. Such composites with soft and hard nanostructures offer a strategy for the design of advanced scaffolds to display multiple signals and control cell behavior.

Synthesis and self-assembly of amphiphilic precision glycomacromolecules

Amphiphilic precision glycomacromolecules (APG) are synthesized using solid-phase synthesis and studied for their self-assembly behavior and as inhibitors of bacterial adhesion.

Effect of C12H25O– substituent position on the self-assembly behaviour of C6H5COO–Ala–Ala dipeptide

Intramolecular hydrogen bonding and steric hindrance of side chain lead the different molecular packing of dipeptides and the morphological transformation of self-assemblies’ nanostructures.

Supramolecular self-assembling peptides to deliver bone morphogenetic proteins for skeletal regeneration

Recombinant human bone morphogenetic proteins (BMPs) have shown clinical success in promoting bone healing, but they are also associated with unwanted side effects. The development of improved BMP carriers that can retain BMP at the defect site and maximize its efficacy would decrease the therapeutic BMP dose and thus improve its safety profile. In this review, we discuss the advantages of using self-assembling peptides, a class of synthetic supramolecular biomaterials, to deliver recombinant BMPs. Peptide amphiphiles (PAs) are a broad class of self-assembling peptides, and the use of PAs for BMP delivery and bone regeneration has been explored extensively over the past decade. Like many self-assembling peptide systems, PAs can be designed to form nanofibrous supramolecular biomaterials in which molecules are held together by non-covalent bonds. Chemical and biological functionality can be added to PA nanofibers, through conjugation of chemical moieties or biological epitopes to PA molecules. For example, PA nanofibers have been designed to bind heparan sulfate, a natural polysaccharide that is known to bind BMPs and potentiate their signal. Alternatively, PA nanofibers have been designed to synthetically mimic the structure and function of heparan sulfate, or to directly bind BMP specifically. In small animal models, these bio-inspired PA materials have shown the capacity to promote bone regeneration using BMP at doses 10-100 times lower than established therapeutic doses. These promising results have motivated further evaluation of PAs in large animal models, where their safety and efficacy must be established before clinical translation. We conclude with a discussion on the possiblity of combining PAs with other materials used in orthopaedic surgery to maximize their utility for clinical translation.

Design of materials with supramolecular polymers

One hundred years ago Hermann Staudinger was strongly criticized by his scientific peers for his macromolecular hypothesis, but today it is hard to imagine a world without polymers. His hypothesis described polymers as macromolecules composed of large numbers of structural units connected by covalent bonds. In the 1990s the concept of supramolecular polymers emerged in the scientific literature as discrete entities of large molar mass comparable to that of classical polymers but built through non-covalent bonds among monomers. Supramolecular polymers exist in biological systems, and potentially blend the physical properties of covalent polymers with unique features such as high degrees of internal order within the polymeric structure, defined shapes, and novel dynamics. This trend article provides a summary of seminal contributions in supramolecular polymerization and provides recent examples from the Stupp laboratory to demonstrate the potential applications of an exciting class of materials composed fully or partially of supramolecular polymers. In closing, we provide our perspective on future opportunities provided by this field at the onset of a second century of polymers. It is our objective here to demonstrate that this second century could be as prosperous, if not more so, than the preceding one.

Multi-component peptide hydrogels - a systematic study incorporating biomolecules for the exploration of diverse, tuneable biomaterials

Peptide-based supramolecular gels can be designed to be functional "smart" materials that have applications in drug delivery, tissue engineering, and supramolecular chemistry. Although many multi-component gel systems have been designed and reported, many of these applications still rely solely on single-component gel systems which limits the functionalities of the materials. Multi-component self-assembly leads to the formation of highly ordered and complex architectures while offering the possibility to generate hydrogels with interesting properties including functional complexity and diverse morphologies. Being able to incorporate various classes of biomolecules can allow for tailoring the materials' functionalities to specific application needs. Here, a novel peptide amphiphile, myristyl-Phe-Phe (C14-FF), was synthesized and explored for hydrogel formation. The hydrogel possesses a nanofiber matrix morphology, composed of β-sheet aggregates, a record-low gelation concentration for this class of compounds, and a unique solvent-dependent helical switch. The C14-FF hydrogel was then explored with various classes of biomolecules (carbohydrates, vitamins, proteins, building blocks of HA) to generate a multi-component library of gels that have potential to represent the complex natural extracellular matrix. Selected multi-component gels exhibit an excellent compatibility with mesenchymal stem cells showing high cell viability percentages, which holds great promise for applications in regenerative therapy.

Nanostructured Biomaterials for Bone Regeneration

This review article addresses the various aspects of nano-biomaterials used in or being pursued for the purpose of promoting bone regeneration. In the last decade, significant growth in the fields of polymer sciences, nanotechnology, and biotechnology has resulted in the development of new nano-biomaterials. These are extensively explored as drug delivery carriers and as implantable devices. At the interface of nanomaterials and biological systems, the organic and synthetic worlds have merged over the past two decades, forming a new scientific field incorporating nano-material design for biological applications. For this field to evolve, there is a need to understand the dynamic forces and molecular components that shape these interactions and influence function, while also considering safety. While there is still much to learn about the bio-physicochemical interactions at the interface, we are at a point where pockets of accumulated knowledge can provide a conceptual framework to guide further exploration and inform future product development. This review is intended as a resource for academics, scientists, and physicians working in the field of orthopedics and bone repair.

Self-Assembling Glycopeptide Conjugate as a Versatile Platform for Mimicking Complex Polysaccharides

Polysaccharides are a class of carbohydrates that play pivotal roles in living systems such as being chemical messengers in many vital biological pathways. However, the complexity and heterogeneity of these natural structures have posed daunting challenges on their production, characterization, evaluation, and applications. While there have been various types of synthetic skeletons that could mimic some biological aspects of polysaccharides, a safer and more easily accessed system is still desired to avoid the unnatural components and difficulties in modifying the structures. In this work, conveniently accessible self-assembling glycopeptide conjugates are developed, where the natural O-glycosidic linkages and phosphoryl modifications assist the self-assembly and concurrently reduce the risk of toxicity. The generated nanoparticles in aqueous solution offer a multivalent display of structurally controllable carbohydrates as mimics of polysaccharides, among which a mannosylated version exhibits immunostimulatory effects in both cellular assays and vaccination of mice. The obtained results demonstrate the potential of this glycopeptide conjugate-derived platform in exploiting the intriguing properties of carbohydrates in a more structurally maneuverable fashion.

Artificial Intracellular Filaments

Intracellular protein filaments are ubiquitous for cellular functions, but forming bona fide biomimetic intracellular filaments of small molecules in living cells remains elusive. Here, we report the in situ formation of self-limiting intracellular filaments of a small peptide via enzymatic morphological transition of a phosphorylated and trimethylated heterochiral tetrapeptide. Enzymatic dephosphorylation reduces repulsive intermolecular electrostatic interactions and converts the peptidic nanoparticles into filaments, which exhibit distinct types of cross-β structures with either C7 or C2 symmetries, with the hydrophilic C-terminal residues at the periphery of the helix. Macromolecular crowding promotes the peptide filaments to form bundles, which extend from the plasma membrane to nuclear membrane and hardly interact with endogenous components, including cytoskeletons. Stereochemistry and post-translational modification (PTM) of peptides are critical for generating the intracellular bundles. This work may offer a way to gain lost functions or to provide molecular insights for understanding normal and aberrant intracellular filaments.

Glycosyltransferase-Induced Morphology Transition of Glycopeptide Self-Assemblies with Proteoglycan Residues

We previously proposed the deprotection-induced block copolymer self-assembly (DISA), that is, the deprotection of hydroxyl groups of saccharides resulted in self-assembly of glycopolymers (Qi et al. J. Am. Chem. Soc. 2018, 140 (28), 8851-8857 and Su et al. ACS Macro Lett. 2014, 3 (6), 534-539). In this study, we further combined glycochemistry and self-assembly strategy by introducing glycosyltransferase as the trigger, which constructs another glycosidic bonds and another carbohydrate building blocks in situ. Herein, we propose to utilize glycosyltransferase to induce the morphology transition of glycopeptide assemblies in the process of glycosidic bonds construction, which has never been reported in literature. This strategy provides us an alternative tool to construct proteoglycan-mimicking polymeric materials and deepens our understanding on the natural process of proteoglycan construction better in the future.

Synthetic Glycobiology: Parts, Systems, and Applications

Protein glycosylation, the attachment of sugars to amino acid side chains, can endow proteins with a wide variety of properties of great interest to the engineering biology community. However, natural glycosylation systems are limited in the diversity of glycoproteins they can synthesize, the scale at which they can be harnessed for biotechnology, and the homogeneity of glycoprotein structures they can produce. Here we provide an overview of the emerging field of synthetic glycobiology, the application of synthetic biology tools and design principles to better understand and engineer glycosylation. Specifically, we focus on how the biosynthetic and analytical tools of synthetic biology have been used to redesign glycosylation systems to obtain defined glycosylation structures on proteins for diverse applications in medicine, materials, and diagnostics. We review the key biological parts available to synthetic biologists interested in engineering glycoproteins to solve compelling problems in glycoscience, describe recent efforts to construct synthetic glycoprotein synthesis systems, and outline exemplary applications as well as new opportunities in this emerging space.

On Supramolecular Self-Assembly: Interview with Samuel Stupp

Ranging from 2D assemblies to peptide amphiphile-based biomaterials, Prof. Samuel Stupp and his team have enriched the scientific community with many breakthroughs in the field of supramolecular self-assembly. This Interview offers the unique possibility to share some highlights along his journey, providing also a glimpse to his vision of the future of supramolecular chemistry. Interdisciplinarity is an integral part of Prof. Stupp's research philosophy, and, using his own words, "it is the only way to understand the complex universe around us and help society along the way". What a great guideline to us all!

Supramolecular Energy Materials

Self-assembly is a bioinspired strategy to craft materials for renewable and clean energy technologies. In plants, the alignment and assembly of the light-harvesting protein machinery in the green leaf optimize the ability to efficiently convert light from the sun to form chemical bonds. In artificial systems, strategies based on self-assembly using noncovalent interactions offer the possibility to mimic this functional correlation among molecules to optimize photocatalysis, photovoltaics, and energy storage. One of the long-term objectives of the field described here as supramolecular energy materials is to learn how to design soft materials containing light-harvesting assemblies and catalysts to generate fuels and useful chemicals. Supramolecular energy materials also hold great potential in the design of systems for photovoltaics in which intermolecular interactions in self-assembled structures, for example, in electron donor and acceptor phases, maximize charge transport and avoid exciton recombination. Possible pathways to integrate organic and inorganic structures by templating strategies and electrodeposition to create materials relevant to energy challenges including photoconductors and supercapacitors are also described. The final topic discussed is the synthesis of hybrid perovskites in which organic molecules are used to modify both structure and functions, which may include chemical stability, photovoltaics, and light emission.

Transition of Nano-Architectures Through Self-Assembly of Lipidated β3-Tripeptide Foldamers

β³-peptides consisting exclusively of β³-amino acids adopt a variety of non-natural helical structures and can self-assemble into well-defined hierarchical structures by axial head-to-tail self-assembly resulting in fibrous materials of varying sizes and shapes. To allow control of fiber morphology, a lipid moiety was introduced within a tri-β³-peptide sequence at each of the three amino acid positions and the N-terminus to gain finer control over the lateral assembly of fibers. Depending on the position of the lipid, the self-assembled structures formed either twisted ribbon-like fibers or distinctive multilaminar nanobelts. The nanobelt structures were comprised of multiple layers of peptide fibrils as revealed by puncturing the surface of the nanobelts with an AFM probe. This stacking phenomenon was completely inhibited through changes in pH, indicating that the layer stacking was mediated by electrostatic interactions. Thus, the present study is the first to show controlled self-assembly of these fibrous structures, which is governed by the location of the acyl chain in combination with the 3-point H-bonding motif. Overall, the results demonstrate that the nanostructures formed by the β³-tripeptide foldamers can be tuned via sequential lipidation of N-acetyl β³-tripeptides which control the lateral interactions between peptide fibrils and provide defined structures with a greater homogeneous population.

Bone Morphogenetic Protein 4 Targeting Glioma Stem-Like Cells for Malignant Glioma Treatment: Latest Advances and Implications for Clinical Application

Malignant gliomas are heterogeneous neoplasms. Glioma stem-like cells (GSCs) are undifferentiated and self-renewing cells that develop and maintain these tumors. These cells are the main population that resist current therapies. Genomic and epigenomic analyses has identified various molecular subtypes. Bone morphogenetic protein 4 (BMP4) reduces the number of GSCs through differentiation and induction of apoptosis, thus increasing therapeutic sensitivity. However, the short half-life of BMP4 impedes its clinical application. We previously reviewed BMP4 signaling in central nervous system development and glioma tumorigenesis and its potential as a treatment target in human gliomas. Recent advances in understanding both adult and pediatric malignant gliomas highlight critical roles of BMP4 signaling pathways in the regulation of tumor biology, and indicates its potential as a therapeutic molecule. Furthermore, significant progress has been made on synthesizing BMP4 biocompatible delivery materials, which can bind to and markedly extend BMP4 half-life. Here, we review current research associated with BMP4 in brain tumors, with an emphasis on pediatric malignant gliomas. We also summarize BMP4 delivery strategies, highlighting biocompatible BMP4 binding peptide amphiphile nanostructures as promising novel delivery platforms for treatment of these devastating tumors.

Cellulose nanocrystals of variable sulfation degrees can sequester specific platelet lysate-derived biomolecules to modulate stem cell response

Cellulose nanocrystals can bind different patterns of platelet lysate-derived protein in a surface sulfation dependent manner. The potential to direct stem cell fate by solid-phase presentation of defined protein coronas is demonstrated.

Enhancement and orchestration of osteogenesis and angiogenesis by a dual-modular design of growth factors delivery scaffolds and 26SCS decoration

Preserving the bioactivity of growth factors (GFs) and mimicking their in vivo supply patterns are challenging in the development of GFs-based bone grafts. In this study, we develop a 2-N, 6-O-sulfated chitosan (26SCS) functionalized dual-modular scaffold composed of mesoporous bioactive glass (MBG) with hierarchical porous structures (module I) and GelMA hydrogel columns (module II) in situ fixed in hollowed channels of the module I, which is capable of realizing differentiated delivery modes for osteogenic rhBMP-2 and angiogenic VEGF. A combinational release profile consisting of a high concentration of VEGF initially followed by a decreasing concentration over time, and a slower/sustainable release of rhBMP-2 is realized by immobilizing rhBMP-2 in module I and embedding VEGF in module II. Systematic in vitro and in vivo studies prove that the two coupled processes of osteogenesis and angiogenesis are well-orchestrated and both enhanced ascribed to the specific GFs delivery modes and 26SCS decoration. 26SCS not only enhances the GFs' bioactivity but also decreases antagonism effects of noggin. This study highlights the importance of differentiating the delivery pattern of different GFs and likely sheds light on the future design of growth factor-based bone grafts.

C-Linked Glycomimetic Libraries Accessed by the Passerini Reaction

Carbohydrates and their conjugates are the most abundant natural products, with diverse and highly important biological roles. Synthetic glycoconjugates are versatile tools used to probe biological systems and interfere with them. In an endeavor to provide an efficient route to glycomimetics comprising structurally diverse carbohydrate units, we describe herein a robust, stereoselective, multicomponent approach. Isopropylidene-protected carbohydrate-derived aldehydes and ketones were utilized in the Passerini reaction, giving different glycosylated structures in high yields and diastereoselectivities up to 90:10 diastereomeric ratio (d.r). Access to highly valuable building blocks based on α-hydroxy C-glycosyl acids or more complex systems was elaborated by simple post-condensation methodologies.

Self-assembling peptide-based nanodrug delivery systems

Self-assembling peptide-based nanodrug delivery systems (NDDs), consisting of naturally occurring amino acids, not only share the advantages of traditional nanomedicine but also possess the unique properties of excellent biocompatibility, biodegradability, flexible responsiveness, specific biological function, and synthetic feasibility. Physical methods, enzymatic reaction, chemical reaction, and biosurface induction can yield versatile peptide-based NDDs; flexible responsiveness is their main advantage. Different functional peptides and abundant covalent modifications endow such systems with precise controllability and multifunctionality. Inspired by the above merits, researchers have taken advantage of the self-assembling peptide-based NDDs and achieved the accurate delivery of drugs to the lesion site. The present review outlines the methods for designing self-assembling peptide-based NDDs for small-molecule drugs, with an emphasis on the different drug delivery strategies and their applications in using peptides and peptide conjugates.

Synergistic Effect of NELL-1 and an Ultra-Low Dose of BMP-2 on Spinal Fusion

Bone morphogenetic protein 2 (BMP-2) is widely used in spinal fusion but it can cause adverse effects such as ectopic bone and adipose tissue in vivo. Neural epidermal growth factor like-like molecule-1 (NELL-1) has been shown to suppress BMP-2-induced adverse effects. However, no optimum carriers that control both NELL-1 and BMP-2 releases to elicit long-term bioactivity have been developed. In this study, we employed polyelectrolyte complex (PEC) as a control release carrier for NELL-1 and BMP-2. An ultra-low dose of BMP-2 synergistically functioned with NELL-1 on bone marrow mesenchymal stem cells osteogenic differentiation with greater mineralization in vitro. The osteoinductive ability of NELL-1 and an ultra-low dose of BMP-2 in PEC was investigated in rat posterolateral spinal fusion. Our results showed increased fusion rate, bone architecture, and improved bone stiffness at 8 weeks after surgery in the combination groups compared with NELL-1 or BMP-2 alone. Moreover, the formation of ectopic bone and adipose tissue was negligible in all the PEC groups. In summary, dual delivery of NELL-1 and an ultra-low dose of BMP-2 in the PEC control release carrier has greater fusion efficiency compared with BMP-2 alone and could potentially be a better alternative to the currently used BMP-2 treatments for spinal fusion. Impact Statement In this study, polyelectrolyte complex was used to absorb neural epidermal growth factor like-like molecule-1 (NELL-1) and bone morphogenetic protein 2 (BMP-2) to achieve controlled dual release. The addition of NELL-1 significantly reduced the effective dose of BMP-2 to 2.5% of its conventional dose in absorbable collagen sponge, to produce solid spinal fusion without significant adverse effects. This study was the first to identify the efficacy of combination NELL-1 and BMP-2 in a control release carrier in spinal fusion, which could be potentially used clinically to increase fusion rate and avoid the adverse effects commonly associated with conventional BMP-2.

Elucidating the Ordering in Self-Assembled Glycocalyx Mimicking Supramolecular Copolymers in Water

Polysaccharides present in the glycocalyx and extracellular matrix are highly important for a multitude of functions. Oligo- and polysaccharides-based biomaterials are being developed to mimic the glycocalyx, but the spatial functionalization of these polysaccharides represents a major challenge. In this paper, a series of benzene-1,3,5-tricarboxamide (BTA) based supramolecular monomers is designed and synthesized with mono- (BTA-β-d-glucose; BTA-Glc and BTA-α-d-mannose; BTA-Man) or disaccharides (BTA-β-d-cellobiose; BTA-Cel) at their periphery or a monosaccharide (BTA-OEG4-α-d-mannose; BTA-OEG4-Man) at the end of a tetraethylene glycol linker. These glycosylated BTAs have been used to generate supramolecular assemblies and it is shown that the nature of the carbohydrate appendage is crucial for the supramolecular (co)polymerization behavior. BTA-Glc and BTA-Man are shown to assemble into micrometers long 1D (bundled) fibers with opposite helicities, whereas BTA-Cel and BTA-OEG4-Man formed small spherical micelles. The latter two monomers are used in a copolymerization approach with BTA-Glc, BTA-Man, or ethylene glycol BTA (BTA-OEG4) to give 1D fibers with BTA-Cel or BTA-OEG4-Man incorporated. Consequently, the carbohydrate appendage influences both the assembly behavior and the internal order. Using this approach it is possible to create 1D-fibers with adjustable saccharide densities exhibiting tailored dynamic exchange profiles. Furthermore, hydrogels with tunable mechanical properties can be achieved, opening up possibilities for the development of multicomponent functional biomaterials.

The regulatory role of sulfated polysaccharides in facilitating rhBMP-2-induced osteogenesis

Sulfated polysaccharides have received much attention in recent years due to their special biological activities, especially the regulation of the biological activity of growth factors such as the representative inductive growth factor recombinant human bone morphogenetic protein-2 (rhBMP-2). However, the regulatory mechanisms from the aspect of the molecular chain structure have rarely been reported. In this article, we selected three kinds of sulfonates containing different backbone structures and functional groups, 2-N,6-O-sulfated chitosan (26 SCS), sulfated dextran (DSS) and poly(sodium-p-styrenesulfonate) (PSS), to explore the interaction between them and rhBMP-2. From in vivo and in vitro osteogenesis-related experiments, 26 SCS showed the best promoting effect on rhBMP-2 induced osteogenic differentiation and the sulfated amino group in 26 SCS could specifically bind to rhBMP-2. These findings indicated that the polysaccharide chain structure was a prerequisite for the synergy effect between 26 SCS and rhBMP-2; the effective combination of -SO₃^- and rhBMP-2 was an important factor in protecting the bioactivity of rhBMP-2. In addition, the presence of the sulfated amino group was the key factor in the specific binding between 26 SCS and rhBMP-2 and provided the possibility of capturing factors in vivo.

Stem and progenitor cell microenvironment for bone regeneration and repair

Stem cells reside in their native microenvironment, which provides dynamic physical and chemical cues essential to their survival, proliferation and function. A typical cell-based therapeutic approach requires the mesenchymal stem cells (MSC) to depart their native microenvironment, transplant to in-vivo environment, differentiate toward multiple lineages and participate in bone formation. The long-term survival, function and fate of MSC are dependent on the microenvironment in which they are transplanted. Transplantation of morselized autologous bone, which contains both stem cells and their native microenvironment, results in a good clinical outcome. However, implantation of bone graft substitutes does not provide the complete and dynamic microenvironment for MSC. Current bone graft therapeutics may need to be improved further to provide an optimal engineered MSC microenvironment.

Hyper-Crosslinked Carbohydrate Polymer for Repair of Critical-Sized Bone Defects

This study evaluated the safety and efficacy of a novel hyper-crosslinked carbohydrate polymer (HCCP) for the repair of critical-sized bone defects in comparison to two alternative treatments: autologous bone and poly(lactide-co-glycolide) with hyaluronic acid (PLGA/HA). Bilateral critical-sized defects were created in the lateral femoral condyles of skeletally mature New Zealand White rabbits, and they were subsequently implanted with HCCP, PLGA/HA, or autologous bone in a randomized manner. Clinical and behavioral observations were made daily, and radiological and histopathological evaluations were performed at 4, 10, and 16 weeks postimplantation. Defects implanted with HCCP showed progressive bone regeneration and bridging of the defect without adverse histological events. No signs of infection or inflammation associated with the implant material were observed in all animals that received HCCP implantation. A radiographic assessment performed at 16 weeks post-implantation showed significantly higher bone density and volume in defects implanted with HCCP compared to PLGA/HA. No statistically significant difference was observed in bone density and volume between HCCP and autologous bone. These findings demonstrate that HCCP is biocompatible, osteoconductive, and capable of promoting bone regeneration in vivo; therefore, it is suitable for both tissue engineering and the repair of critical-sized bone defects.

Biomacromolecules for Tissue Engineering: Emerging Biomimetic Strategies

Biomacromolecules used for tissue engineering must possess either inherent biochemical cues for tissue regeneration or be chemically modified to incorporate bioactive, tissue-specific moieties. To this end, many strategies have emerged recently in the field to both utilize novel bioinspired macromolecules for tissue engineering and apply bioconjugation strategies for the functionalization of biomacromolecules with tissue-specific cues and other biological properties of interest. Furthermore, biomacromolecules have been processed into more highly biomimetic and clinically deliverable scaffold and hydrogel systems using 3D printing and the fabrication of in situ forming hydrogels, respectively. To support these advances, tissue engineers have also pursued greater spatiotemporal control over macromolecular bioactivity and the modulation of scaffold and hydrogel properties in response to both physiological and external stimuli. This Perspective thus highlights a few notable advances and techniques in the usage of biomacromolecules for tissue engineering applications, including new bioinspired macromolecules, advanced hydrogel and scaffold fabrication techniques, and spatiotemporal control over biomacromolecule constructs.

DNA-Peptide Amphiphile Nanofibers Enhance Aptamer Function

The single stranded DNA oligonucleotides known as aptamers have the capacity to bind proteins and other molecules and offer great therapeutic potential. Further work is required to optimize their function and to diminish their susceptibility to nuclease degradation. We report here on the synthesis and supramolecular self-assembly of DNA-peptide amphiphiles that form high aspect ratio nanofibers and display aptamers for platelet-derived growth factor. The nanofibers were found to bind the growth factor with an affinity that was fivefold greater than the free aptamer. We also observed that the aptamer displayed by the supramolecular nanostructures was eight times more nuclease resistant than free aptamer. In order to highlight the therapeutic potential of these supramolecular systems, we demonstrated the improved inhibition of proliferation when the growth factor was bound to aptamers displayed by the nanofibers.

In-Situ Configuration Studies on Segmented DNA Origami Nanotubes

One-dimensional nanotubes are of considerable interest in materials and biochemical sciences. A particular desire is to create DNA nanotubes with user-defined structural features and biological relevance, which will facilitate the application of these nanotubes in the controlled release of drugs, templating of other materials into linear arrays and the construction of artificial membrane channels. However, little is known about the structures of assembled DNA nanotubes in solution. Here we report an in situ exploration of segmented DNA nanotubes, composed of multiple units with set length distributions, by using synchrotron small-angle X-ray scattering (SAXS). Through joint experimental and theoretical studies, we show that the SAXS data are highly informative in the context of heterogeneous mixtures of DNA nanotubes. The structural parameters obtained by SAXS are in good agreement with those determined by atomic force microscopy (AFM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). In particular, the SAXS data revealed important structural information on these DNA nanotubes, such as the in-solution diameters (≈25 nm), which could be obtained only with difficulty by use of other methods. Our results establish SAXS as a reliable structural analysis method for long DNA nanotubes and could assist in the rational design of these structures.

Antitumor Effects of Berberine on Gliomas via Inactivation of Caspase-1-Mediated IL-1β and IL-18 Release

Gliomas arise in the glial cells of the brain or spine and are the most prevalent and devastating type of brain tumors. Studies of tumor immunology have established the importance of the tumor micro-environment as a driver of oncogenesis. Inflammatory mediators such as IL-1β and IL-18 released by monocytes regulate transcriptional networks that are required for malignant cell growth. Berberine is a natural botanical alkaloid that is widely found in the Berberis species. Although it has been widely used as an anti-diarrheal treatment in North America for several decades, our study is the first to investigate berberine as an anti-tumor agent in glioma cells. In this study, we demonstrate that berberine significantly inhibits inflammatory cytokine Caspase-1 activation via ERK1/2 signaling and subsequent production of IL-1β and IL-18 by glioma cells. Moreover, we found that berberine treatment led to decreased motility and subsequently cell death in U251 and U87 cells. In addition, our study is the first to indicate that berberine can reverse the process of epithelial-mesenchymal transition, a marker of tumor invasion. Taken together, our work supports berberine as a putative anti-tumor agent targeting glioma cells.

Carbohydrate-based nanomaterials for biomedical applications

Carbohydrates are abundant biomolecules, with a strong tendency to form supramolecular networks. A host of carbohydrate-based nanomaterials have been exploited for biomedical applications. These structures are based on simple mono- or disaccharides, as well as on complex, polymeric systems. Chemical modifications serve to tune the shapes and properties of these materials. In particular, carbohydrate-based nanoparticles and nanogels were used for drug delivery, imaging, and tissue engineering applications. Due to the reversible nature of the assembly, often based on a combination of hydrogen bonding and hydrophobic interactions, carbohydrate-based materials are valuable substrates for the creations of responsive systems. Herein, we review the current research on carbohydrate-based nanomaterials, with a particular focus on carbohydrate assembly. We will discuss how these systems are formed and how their properties are tuned. Particular emphasis will be placed on the use of carbohydrates for biomedical applications. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Synthesis of a Fluorous-Tagged Hexasaccharide and Interaction with Growth Factors Using Sugar-Coated Microplates

Here, we report the synthesis of a sulfated, fully protected hexasaccharide as a glycosaminoglycan mimetic and the study of its interactions with different growth factors: midkine, basic fibroblast growth factor (FGF-2) and nerve growth factor (NGF). Following a fluorous-assisted approach, monosaccharide building blocks were successfully assembled and the target oligosaccharide was prepared in excellent yield. The use of more acid stable 4,6-O-silylidene protected glucosamine units was crucial for the efficiency of this strategy because harsh reaction conditions were needed in the glycosylations to avoid the formation of orthoester side products. Fluorescence polarization experiments demonstrated the strong interactions between the synthesized hexamer, and midkine and FGF-2. In addition, we have developed an alternative assay to analyse these molecular recognition events. The prepared oligosaccharide was non-covalently attached to a fluorous-functionalized microplate and the direct binding of the protein to the sugar-immobilized surface was measured, affording the corresponding K_D,surf value.

Biomimetic hydroxyapatite/collagen composite drives bone niche recapitulation in a rabbit orthotopic model

Synthetic osteoinductive materials that mimic the human osteogenic niche have emerged as ideal candidates to address this area of unmet clinical need. In this study, we evaluated the osteoinductive potential in a rabbit orthotopic model of a magnesium-doped hydroxyapatite/type I collagen ​(MHA/Coll) composite. The composite was fabricated to exhibit a highly fibrous structure of carbonated MHA with 70% (±2.1) porosity and a Ca/P ratio of 1.5 (±0.03) as well as a diverse range of elasticity separated to two distinct stiffness peaks of low (2.35 ​± ​1.16 ​MPa) and higher (9.52 ​± ​2.10 ​MPa) Young's Modulus. Data suggested that these specific compositional and nanomechanical material properties induced the deposition of de novo mineral phase, while modulating the expression of early and late osteogenic marker genes, in a 3D in vitro model using human bone marrow-derived mesenchymal stem cells (hBM-MSCs). When tested in the rabbit orthotopic model, MHA/Col1 scaffold induction of new trabecular bone mass was observed by DynaCT scan, only 2 weeks after implantation. Bone histomorphometry at 6 weeks revealed a significant amount of de novo bone matrix formation. qPCR demonstrated MHA/Coll scaffold full cellularization in vivo and the expression of both osteogenesis-associated genes (Spp1, Sparc, Col1a1, Runx2, Dlx5) as well as hematopoietic (Vcam1, Cd38, Sele, Kdr) and bone marrow stromal cell marker genes (Vim, Itgb1, Alcam). Altogether, these data provide ​evidence of the solid osteoinductive potential of MHA/Coll and its suitability for multiple approaches of bone regeneration.

Using Self-Assembling Peptides to Integrate Biomolecules into Functional Supramolecular Biomaterials

Throughout nature, self-assembly gives rise to functional supramolecular biomaterials that can perform complex tasks with extraordinary efficiency and specificity. Inspired by these examples, self-assembly is increasingly used to fabricate synthetic supramolecular biomaterials for diverse applications in biomedicine and biotechnology. Peptides are particularly attractive as building blocks for these materials because they are based on naturally derived amino acids that are biocompatible and biodegradable; they can be synthesized using scalable and cost-effective methods, and their sequence can be tailored to encode formation of diverse architectures. To endow synthetic supramolecular biomaterials with functional capabilities, it is now commonplace to conjugate self-assembling building blocks to molecules having a desired functional property, such as selective recognition of a cell surface receptor or soluble protein, antigenicity, or enzymatic activity. This review surveys recent advances in using self-assembling peptides as handles to incorporate biologically active molecules into supramolecular biomaterials. Particular emphasis is placed on examples of functional nanofibers, nanovesicles, and other nano-scale structures that are fabricated by linking self-assembling peptides to proteins and carbohydrates. Collectively, this review highlights the enormous potential of these approaches to create supramolecular biomaterials with sophisticated functional capabilities that can be finely tuned to meet the needs of downstream applications.