Endothelium-Mimicking Materials: A "Rising Star" for Antithrombosis

The advancement of antithrombotic materials has significantly mitigated the thrombosis issue in clinical applications involving various medical implants. Extensive research has been dedicated over the past few decades to developing blood-contacting materials with complete resistance to thrombosis. However, despite these advancements, the risk of thrombosis and other complications persists when these materials are implanted in the human body. Consequently, the modification and enhancement of antithrombotic materials remain pivotal in 21st-century hemocompatibility studies. Previous research indicates that the healthy endothelial cells (ECs) layer is uniquely compatible with blood. Inspired by bionics, scientists have initiated the development of materials that emulate the hemocompatible properties of ECs by replicating their diverse antithrombotic mechanisms. This review elucidates the antithrombotic mechanisms of ECs and examines the endothelium-mimicking materials developed through single, dual-functional and multifunctional strategies, focusing on nitric oxide release, fibrinolytic function, glycosaminoglycan modification, and surface topography modification. These materials have demonstrated outstanding antithrombotic performance. Finally, the review outlines potential future research directions in this dynamic field, aiming to advance the development of antithrombotic materials.

Glycan Modifications as Regulators of Stem Cell Fate

Glycosylation is a process where proteins or lipids are modified with glycans. The presence of glycans determines the structure, stability, and localization of glycoproteins, thereby impacting various biological processes, including embryogenesis, intercellular communication, and disease progression. Glycans can influence stem cell behavior by modulating signaling molecules that govern the critical aspects of self-renewal and differentiation. Furthermore, being located at the cell surface, glycans are utilized as markers for stem cell pluripotency and differentiation state determination. This review aims to provide a comprehensive overview of the current literature, focusing on the effect of glycans on stem cells with a reflection on the application of synthetic glycans in directing stem cell differentiation. Additionally, this review will serve as a primer for researchers seeking a deeper understanding of how synthetic glycans can be used to control stem cell differentiation, which may help establish new approaches to guide stem cell differentiation into specific lineages. Ultimately, this knowledge can facilitate the identification of efficient strategies for advancing stem cell-based therapeutic interventions.

Glycosaminoglycan Mimetic Precision Glycomacromolecules with Sequence-Defined Sulfation and Rigidity Patterns

Sulfated glycosaminoglycans (sGAGs) such as heparan sulfate (HS) are structurally diverse linear polysaccharides that are involved in many biological processes and have gained interest as antiviral compounds. Their recognition is driven by a complex orchestra of structural parameters that are still under intense investigation. One distinct characteristic is the incorporation of sulfation patterns including highly sulfated and non-sulfated sequences that provide variations in flexibility and conformation, which in turn impact the biological function of sGAGs. However, these distinct features have not yet been fully realized in the synthetic preparation of sGAG mimetics. Here, we present the synthesis of three groups of sulfated glycomacromolecules as sGAG mimetics: (i) globally sulfated glycooligomers, (ii) glycooligomers with sequence-defined sulfation patterns, and (iii) a globally sulfated glycooligomer-oligo-L-proline hybrid structure. The complete synthesis, including chemical sulfation, was conducted on solid support, enabled by the introduction of a commercially available photocleavable linker allowing for the preservation of sensitive sulfates during cleavage of the products. Structures were obtained in good purity and with high degrees of sulfation demonstrating the wide applicability of this methodology to prepare tailor-made sulfated glycomacromolecules and similar sGAG mimetics. Structures were tested for their anticoagulant properties showing activity similar to their natural HS counterpart and significantly lower than HP.

Cyclic and dimeric fibroblast growth factor 2 variants with high biomedical potential

Fibroblast growth factor 2 (FGF2) is a pleiotropic protein engaged in the regulation of key cellular processes in a wide spectrum of cells. FGF2 is an important object of basic research as well as a molecule used in regenerative medicine, in vitro cell culture maintenance, and as an anticancer drug carrier. However, the unsatisfactory stability and pleiotropic activities of the wild-type FGF2 largely limit its use as a medical product. To overcome these limitations, we have designed a set of FGF2-based macromolecules via sortase A-mediated cyclization and oligomerization. We obtained heparin-switchable FGF2 variants with enhanced stability and improved ability to stimulate cell proliferation and migration. We have shown that stimulation of glucose uptake by adipocytes is modulated by the architecture of FGF2 oligomers. Moreover, we used hyper-stable FGF2 variants for the construction of highly effective drug carriers for selective killing of FGFR1-overproducing cancer cells. The strategy for FGF2 engineering presented in this work provides novel insights into the design of growth factor variants for regenerative and anti-cancer precise medicine.

Recycling protein selective adsorption on fluorine-modified surface through fluorine-fluorine interaction

Low surface energy materials with micro-nano structures have been widely developed to prevent non-specific adhesion of biomolecules. Herein we put forward a new approach based on the antifouling and self-assembly properties of fluorine components, to construct a non-specific protein resistance surface with selective protein adsorption property. Briefly, the antifouling surface (SN-F) was obtained by a simple one-step modification on silicon nanowire arrays (SiNWAs) with fluorine coupling agent 1 H,1 H,2 H,2 H-perfluorodecyltrimethoxysilane (FAS). And protein was fluorinated by conjugation with an amphiphilic fluoro-copolymer, produced from 2-methacrylamido glucopyranose (MAG) and trifluoroethyl methacrylate (TFEMA) via RAFT polymerization. The properties of the materials were characterized by ¹H nuclear magnetic resonance (¹H NMR), infrared spectroscopy (FTIR), water contact angle, and X-ray photoelectron spectroscopy (XPS) etc., and protein adsorption was investigated by protein content measurement, fluorescence detection, and electrophoresis. It was observed that the adsorption for native proteins on SN-F was at an extremely low level, while the adsorption for the fluoro-copolymer conjugated protein (PFG-BSA) was significantly increased. When the percentage of TFEMA in the fluoro-copolymer was as high as 52.0%, the fluorinated protein adsorbed on SN-F was more than 35 times of native proteins on the surface. Moreover, the platform could resist IgG adhesion in serum after the adsorption of fluorinated protein, and it could be recycled three times after 75% ethanol treatment. In conclusion, SN-F showed non-specific protein resistance through low surface energy and specific protein adsorption by fluorine-fluorine self-assembly. The fluorinated nanostructured platform has a great potential in controlling protein adsorption and release.

Self-Assembling Hydrogel Structures for Neural Tissue Repair

Hydrogel materials have been employed as biological scaffolds for tissue regeneration across a wide range of applications. Their versatility and biomimetic properties make them an optimal choice for treating the complex and delicate milieu of neural tissue damage. Aside from finely tailored hydrogel properties, which aim to mimic healthy physiological tissue, a minimally invasive delivery method is essential to prevent off-target and surgery-related complications. The specific class of injectable hydrogels termed self-assembling peptides (SAPs), provide an ideal combination of in situ polymerization combined with versatility for biofunctionlization, tunable physicochemical properties, and high cytocompatibility. This review identifies design criteria for neural scaffolds based upon key cellular interactions with the neural extracellular matrix (ECM), with emphasis on aspects that are reproducible in a biomaterial environment. Examples of the most recent SAPs and modification methods are presented, with a focus on biological, mechanical, and topographical cues. Furthermore, SAP electrical properties and methods to provide appropriate electrical and electrochemical cues are widely discussed, in light of the endogenous electrical activity of neural tissue as well as the clinical effectiveness of stimulation treatments. Recent applications of SAP materials in neural repair and electrical stimulation therapies are highlighted, identifying research gaps in the field of hydrogels for neural regeneration.

The role of carboxylic groups in heparin-mimicking polymer-functionalized surfaces for blood compatibility: Enhanced vascular cell selectivity

Blood compatibility is an eternal topic of biomedical materials. The effect of heparin-mimicking polymers (HMPs) on blood compatibility has been well studied, especially the synergistic effect of sugar unit and sulfonate/sulfate unit. However, carboxylic groups also play an important role in HMPs. In this work, copolymers of sodium 4-vinyl-benzenesulfonate (SS) and 2-methacrylamido glucopyranose (MAG) (poly(SS-co-MAG)) and poly(acrylate acid) (PAA) were self-assembled on Au surfaces with different feed ratios. When self-assembly of poly(SS-co-MAG) alone, the optimized feed ratio of SS and MAG for vascular cell selectivity was 1:1 (PS1M1); at this ratio the Au-PS1M1 surface showed the highest human umbilical vein endothelial cells (HUVECs) density and the lowest human umbilical vein smooth muscle cells (HUVSMCs) density. When self-assembly of PAA alone (surface designated as Au-PAA), the proliferation of both HUVECs and HUVSMCs was inhibited. Compared with either PS1M1 or PAA alone, the surfaces modified with both PAA and PS1M1 at the feed ratio of 1:1 (material designated as Au-PSM/PAA-2) showed enhanced promoting effect on HUVECs as well as enhanced inhibiting effect on HUVSMCs, indicating stronger vascular cell selectivity of carboxylic groups in the presence of sugar and sulfonate units.

Hyaluronic acid bioinspired polymers for the regulation of cell chondrogenic and osteogenic differentiation

As the simplest glycosaminoglycan (GAG) in extracellular matrix, hyaluronic acid (HA) takes part in several important biological processes, such as regulating cell proliferation, differentiation, and migration. In this work, a series of HA-inspired polymers with different saccharide and carboxylate units (HA-analogue polymers) are synthesized by free radical polymerization, and characterized using Fourier transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC) and nuclear magnetic resonance spectrometer (NMR), Moreover, cell experiments demonstrate that HA-analogue polymers with a certain proportion of saccharide and carboxylate (PM₁G₁) units shows a positive effect on the proliferation and differentiation of bone marrow mesenchymal stem cells (BMSCs). Furthermore, HA-analogue polymers have prominent cartilage inductive capacity in chondrogenic induction medium (CIM) and brilliant bone inductive capacity in osteogenic induction medium (OIM) toward BMSCs. Therefore, it is confirmed that the HA-analogue polymers can effectively mimic the functions of HA and have broad potential application prospects in the biomedical and clinical fields.

Vascular cell responses to silicone surfaces grafted with heparin-like polymers: surface chemical composition vs. topographic patterning

Heparin-like polymers are promising synthetic materials with biological functionalities, such as anticoagulant ability, growth factor binding to regulate cellular functions, and inflammation mediation, similar to heparin. The biocompatibility of heparin-like polymers with well-defined chemical structures has inspired many researchers to design heparin-like surfaces to explore their biological applications. The concept of the recombination of functional heparin structural units (sulfonate- and glyco-containing units) was proven to be successful in designing heparin-mimicking surfaces. However, besides surface structural units, topographic patterning is also an important contributor to the biological activity of the surfaces modified with heparin-like polymers. In this work, both surface structural units and topographic patterning were taken into account to investigate the vascular cell behaviors on the silicone surfaces. A facile method for the production of patterned bromine-containing polydimethylsiloxane surface (PDMS-Br) was developed from a one-step multicomponent thermocuring procedure and replica molding using a nanohole-arrayed silicon template. Different structural units of heparin-like polymers, i.e. homopolymer of sulfonate-containing sodium 4-vinylbenzenesulfonate (pSS), homopolymer of glyco-containing 2-(methacrylamido)glucopyranose (pMAG), and copolymers of MAG and SS (pSG), were then introduced on the flat and patterned PDMS-Br surface using visible light-induced graft polymerization. For the flat surfaces, compared with the PDMS-Br surface, pSS-grafted and pSG-grafted surfaces significantly increased cell densities of both human umbilical vein endothelial cells (HUVECs) and human umbilical vein smooth muscle cells (HUVSMCs), indicating that they are "vascular cell-friendly". In contrast, the pMAG-grafted surface showed decreased cell attachment of both HUVECs and HUVSMCs, indicating that the pMAG-grafted surface is "vascular cell-resistant". Moreover, surface topographic patterning enhanced the cell responses to the corresponding flat surfaces. That is to say, surface patterning can make the "vascular cell-friendly" surface still friendly, and the "vascular cell-resistant" surface much more resistant. The combination of surface structural units and topographic patterning shows promise in the preparation of new heparin-like surfaces with improved cell compatibility that is suitable for blood-compatible biomaterials.

Heparin mimics and fibroblast growth factor-2 fabricated nanogold composite in promoting neural differentiation of mouse embryonic stem cells

The replacement therapy or transplantation using neural cells, which differentiated from stem cells, has emerged as a promising strategy for repairing damaged neural tissues and helping functional recovery in the treatment of neural system diseases. The challenge, however, is how to control embryonic stem cell fate so that neural differentiation can be efficiently directed to enrich a neuron cell population, and meanwhile to maintain their bioactivities. This is a key question and has a very significant impact in regenerative medicine. Here we proposed a new neural-differentiation inductive nanocomposite, containing gold nanoparticles (AuNPs), poly(2-methacrylamido glucopyranose-co-3-sulfopropyl acrylate) (PMS), and basic fibroblast growth factor (FGF2), for the high efficient directional neural-specific differentiation of mouse embryonic stem cells (mESCs). In this AuNP-PMS/FGF2 composite, PMS, playing as the high-active mimic of heparin/heparan sulfate (HS), is covalently anchored to AuNPs and bound with FGF2 on the surface of nanoparticles, forming a HS/FGF2 complex nanomimics to facilitate its binding to FGF receptor (FGFR) and promote high neural-inductive activity of mESCs. The stability, bioactivity and biocompatibility of the composite are investigated in this study. The results showed that the AuNP-PMS/FGF2 composite could maintain a long-term stability at room temperature for at least 8 days, and greatly promote the neural differentiation of mESCs. Compared with the other materials, the AuNP-PMS/FGF2 composite could significantly stimulate the expression of the specific neural differentiation markers (nestin and β3-tubulin), while obviously down-regulate the mRNA production of pluripotency marker Oct-4 in mESCs. Moreover, the promotion effect of the composite on neuronal maturation marker β3-tubulin expression achieved maximally at the low concentration of FGF2 (4 ng/mL), which suggested the high efficiency of AuNP-PMS/FGF2 composite in neural differentiation of mESCs. Meanwhile, both mESCs and L929 cells showed desirable growth during the incubation with AuNP-PMS/FGF2 composite. The AuNP-PMS/FGF2 system presents a new way to achieve HS/FGF2 complex nanomimics efficiently for the neural differentiation of mESCs.

Dual Pathway for Promotion of Stem Cell Neural Differentiation Mediated by Gold Nanocomposites

The neural differentiation of embryonic stem cells (ESCs) is of great value in the treatment of neurodegenerative diseases. On the basis of the two related signaling pathways that direct the neural differentiation of ESCs, we used gold nanoparticles (GNP) as a means of combining chemical and physical cues to trigger the neurogenic differentiation of stem cells. Neural differentiation-related functional units (glyco and sulfonate units on glycosaminoglycans, GAG) were anchored on the GNP surface and were then transferred to the cell membrane surface via GNP-membrane interactions. The functional units were able to activate the GAG-related signaling pathway, in turn promoting differentiation and maturation of stem cells into neuronal lineages. In addition, using the photothermal effect of GNP, the differentiation-inducing factor retinoic acid (RA), could be actively delivered into cells via laser irradiation. The RA-related intracellular signaling pathway was thereby further triggered, resulting in strong promotion of neurogenesis with a 300-fold increase in mature neural marker expression. The gold nanocomposites developed in this work provide the basis for a new strategy directing ESCs differentiation into nerve cells with high efficiency and high purity by acting on two related signaling pathways.

Advances in biomolecule inspired polymeric material decorated interfaces for biological applications

With the development of surface modification technology, interface properties have great effects on the interaction between biomedical materials and cells and biomolecules, which significantly affects the biocompatibility and functionality of materials. As an orderly and perfect system, biological organisms in nature effectively integrate all kinds of bio-interfaces with physiological functions, which shed light on the importance of biomolecules in organisms. It gives birth to a bio-inspiration strategy to design and fabricate smart materials with specific functionalities, e.g. osteogenic and chondrocytic induced materials inspired by bone sialoprotein and chondroitin sulfate. Through this mimicking approach, various functional materials were utilized to decorate the interfaces and further optimize the performance of biomedical materials, which would widely expand their applications. In this review, followed by a summary and brief introduction of surface modification methods, we highlight recent advances in the fabrication of functional polymeric materials inspired by a range of biomolecules for decorating interfaces. Then, the other applications of biomolecule inspired materials including tissue engineering, diagnosis and treatment of diseases and physiological function regulation are presented and the future outlook is discussed as well.

Glycosaminoglycan-Inspired Biomaterials for the Development of Bioactive Hydrogel Networks

Glycosaminoglycans (GAG) are long, linear polysaccharides that display a wide range of relevant biological roles. Particularly, in the extracellular matrix (ECM) GAG specifically interact with other biological molecules, such as growth factors, protecting them from proteolysis or inhibiting factors. Additionally, ECM GAG are partially responsible for the mechanical stability of tissues due to their capacity to retain high amounts of water, enabling hydration of the ECM and rendering it resistant to compressive forces. In this review, the use of GAG for developing hydrogel networks with improved biological activity and/or mechanical properties is discussed. Greater focus is given to strategies involving the production of hydrogels that are composed of GAG alone or in combination with other materials. Additionally, approaches used to introduce GAG-inspired features in biomaterials of different sources will also be presented.

Modular Polymers as a Platform for Cell Surface Engineering: Promoting Neural Differentiation and Enhancing the Immune Response

Regulating cell behavior and cell fate are of great significance for basic biological research and cell therapy. Carbohydrates, as the key biomacromolecules, play a crucial role in regulating cell behavior. Herein, "modular" glycopolymers were synthesized by reversible addition-fragmentation chain transfer polymerization. These glycopolymers contain sugar units (glucose), anchoring units (cholesterol), "guest" units (adamantane) for host-guest interaction, and fluorescent labeling units (fluorescein). It was demonstrated that these glycopolymers can insert into cell membranes with high efficiency and their residence time on the membranes can be regulated by controlling their cholesterol content. Furthermore, the behavior of the engineered cells can be controlled by modifying with different functional β-cyclodextrins (CD-X) via host-guest interactions with the adamantane units. Host-guest interactions with the modular polymers were demonstrated using CD-RBITC (X = a rhodamine B isothiocyanate). The glycopolymers were modified with CD-S (X = seven sulfonate groups) and CD-M (X = seven mannose groups) and were then attached, respectively, to the surfaces of mouse embryonic stem cells for the promotion of neural differentiation and to the surfaces of cancer cells for the enhancement of the immune response. The combination of multiple anchors and host-guest interactions provides a widely applicable cell membrane modification platform for a variety of applications.

The First Synthesis of Periodic and Alternating Glycopolymers by RAFT Polymerization: A Novel Synthetic Pathway for Glycosaminoglycan Mimics

This study concerned the controlled synthesis of periodic glycopolymers by reversible addition-fragmentation chain transfer (RAFT) copolymerization. To this end, maltose- and lactose-substituted vinyl ethers (MalVE and LacVE, respectively) and maltose-substituted maleimide (MalMI) were newly synthesized. RAFT copolymerization of MalVE and ethyl maleimide (EtMI) (monomer feed ratio: MalVE:EtMI = 1:1) afforded periodic glycopolymers (poly(MalVE-co-EtMI)) consisting of major parts of alternating structure (-(MalVE-EtMI)n-) and a small part of consecutive sequences of EtMI (⁻EtMI-EtMI-). Occurrence of the latter sequences was caused by the homopolymerizability of maleimide under the present polymerization condition, and the formation of the consecutive sequences of EtMI was successfully suppressed by varying the monomer feed ratio. RAFT copolymerization of LacVE and EtMI was also found to proceed and similarly yielded periodic glycopolymers (poly(LacVE-co-EtMI)). Moreover, RAFT copolymerization of LacVE and MalMI (monomer feed ratio: LacVE:MalMI = 1:1) was performed to give copolymers (poly(LacVE-co-MalMI)) having composition ratio of LacVE/MalMI ≈ 36/64. The resultant periodic glycopolymers poly(MalVE-co-EtMI) and poly(LacVE-co-EtMI) were subjected to lectin binding assay using concanavalin A and peanut agglutinin, exhibiting the glycocluster effect. Moreover, these glycopolymers obtained from the copolymerization of VE and MI were found to be non-cytotoxic.

Chondroitin-analogue decorated magnetic nanoparticles via a click reaction for selective adsorption of low-density lipoprotein

Chondroitin-analogue polymers are synthesized to anchor on Fe₃O₄ nanoparticle surfaces to achieve efficient, selective and reusable adsorption of low-density lipoprotein.

Sustained release of a synthetic structurally-tailored glycopolymer modulates endothelial cells for enhanced endothelialization of materials

GAG-mimicking polymers were prepared by a novel method allowing close control of structure and can be used as potent synthetic bioactive modifiers to promote endothelialization of materials.

Chemical synthesis of glycosaminoglycan-mimetic polymers

This review describes several general chemical approaches for the preparation of glycosaminoglycan (GAG)-mimetic polymers based on different backbones and sidechains, and highlights the importance of these synthetic GAG-mimetic polymers in controlling key biofunctions.

Heparin-Mimicking Sulfonated Polymer Nanoparticles via RAFT Polymerization-Induced Self-Assembly

Heparin plays a significant role in wound healing and tissue regeneration applications, through stabilization of fibroblast growth factors (FGF). Risks associated with batch-to-batch variability and contamination from its biological sources have led to the development of synthetic, highly sulfonated polymers as promising heparin mimics. In this work, a systematic study of an aqueous polymerization-induced self-assembly (PISA) of styrene from poly(2-acrylamido-2-methylpropane sodium sulfonate) (P(AMPS)) macro reversible addition-fragmentation chain transfer (macro-RAFT) agents produced a variety of spherical heparin-mimicking nanoparticles, which were further characterized with light scattering and electron microscopy techniques. None of the nanoparticles tested showed toxicity against mammalian cells; however, significant hemolytic activity was observed. Nonetheless, the heparin-mimicking nanoparticles outperformed both heparin and linear P(AMPS) in cellular proliferation assays, suggesting increased bFGF stabilization efficiencies, possibly due to the high density of sulfonated moieties at the particle surface.

Sulfonate Groups and Saccharides as Essential Structural Elements in Heparin-Mimicking Polymers Used as Surface Modifiers: Optimization of Relative Contents for Antithrombogenic Properties

Blood compatibility is a long sought-after goal in biomaterials research, but remains an elusive one, and in spite of extensive work in this area, there is still no definitive information on the relationship between material properties and blood responses such as coagulation and thrombus formation. Materials modified with heparin-mimicking polymers have shown promise and indeed may be seen as comparable to materials modified with heparin itself. In this work, heparin was conceptualized as consisting of two major structural elements: saccharide- and sulfonate-containing units, and polymers based on this concept were developed. Copolymers of 2-methacrylamido glucopyranose, containing saccharide groups, and sodium 4-vinylbenzenesulfonate, containing sulfonate groups, were graft-polymerized on vinyl-functionalized polyurethane (PU) surfaces by free radical polymerization. This graft polymerization method is simple, and the saccharide and sulfonate contents are tunable by regulating the feed ratio of the monomers. Homopolymer-grafted materials, containing only sulfonate or saccharide groups, showed different effects on cell-surface interactions including platelet adhesion, adhesion and proliferation of vascular endothelial cells, and adhesion and proliferation of smooth muscle cells. The copolymer-grafted materials showed effects due to both sulfonate and saccharide elements with respect to blood responses, and the optimum composition was obtained at a 2:1 ratio of sulfonate to saccharide units (material designated as PU-PS1M1). In cell adhesion experiments, this material showed the lowest platelet and human umbilical vein smooth muscle cell density and the highest human umbilical vein endothelial cell density. Among the materials investigated, PU-PS1M1 also had the longest plasma clotting time. This material was thus shown to be multifunctional with a combination of properties, suggesting thromboresistant behavior in blood contact.

Exploiting Heparan Sulfate Proteoglycans in Human Neurogenesis-Controlling Lineage Specification and Fate

Unspecialized, self-renewing stem cells have extraordinary application to regenerative medicine due to their multilineage differentiation potential. Stem cell therapies through replenishing damaged or lost cells in the injured area is an attractive treatment of brain trauma and neurodegenerative neurological disorders. Several stem cell types have neurogenic potential including neural stem cells (NSCs), embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and mesenchymal stem cells (MSCs). Currently, effective use of these cells is limited by our lack of understanding and ability to direct lineage commitment and differentiation of neural lineages. Heparan sulfate proteoglycans (HSPGs) are ubiquitous proteins within the stem cell microenvironment or niche and are found localized on the cell surface and in the extracellular matrix (ECM), where they interact with numerous signaling molecules. The glycosaminoglycan (GAG) chains carried by HSPGs are heterogeneous carbohydrates comprised of repeating disaccharides with specific sulfation patterns that govern ligand interactions to numerous factors including the fibroblast growth factors (FGFs) and wingless-type MMTV integration site family (Wnts). As such, HSPGs are plausible targets for guiding and controlling neural stem cell lineage fate. In this review, we provide an overview of HSPG family members syndecans and glypicans, and perlecan and their role in neurogenesis. We summarize the structural changes and subsequent functional implications of heparan sulfate as cells undergo neural lineage differentiation as well as outline the role of HSPG core protein expression throughout mammalian neural development and their function as cell receptors and co-receptors. Finally, we highlight suitable biomimetic approaches for exploiting the role of HSPGs in mammalian neurogenesis to control and tailor cell differentiation into specific lineages. An improved ability to control stem cell specific neural lineage fate and produce abundant cells of lineage specificity will further advance stem cell therapy for the development of improved repair of neurological disorders. We propose a deeper understanding of HSPG-mediated neurogenesis can potentially provide novel therapeutic targets of neurogenesis.

Deciphering the Role of Sulfonated Unit in Heparin-Mimicking Polymer to Promote Neural Differentiation of Embryonic Stem Cells

Glycosaminoglycans (GAGs), especially heparin and heparan sulfate (HS), hold great potential for inducing the neural differentiation of embryonic stem cells (ESCs) and have brought new hope for the treatment of neurological diseases. However, the disadvantages of natural heparin/HS, such as difficulty in isolating them with a sufficient amount, highly heterogeneous structure, and the risk of immune responses, have limited their further therapeutic applications. Thus, there is a great demand for stable, controllable, and well-defined synthetic alternatives of heparin/HS with more effective biological functions. In this study, based upon a previously proposed unit-recombination strategy, several heparin-mimicking polymers were synthesized by integrating glucosamine-like 2-methacrylamido glucopyranose monomers (MAG) with three sulfonated units in different structural forms, and their effects on cell proliferation, the pluripotency, and the differentiation of ESCs were carefully studied. The results showed that all the copolymers had good cytocompatibility and displayed much better bioactivity in promoting the neural differentiation of ESCs as compared to natural heparin; copolymers with different sulfonated units exhibited different levels of promoting ability; among them, copolymer with 3-sulfopropyl acrylate (SPA) as a sulfonated unit was the most potent in promoting the neural differentiation of ESCs; the promoting effect is dependent on the molecular weight and concentration of P(MAG-co-SPA), with the highest levels occurring at the intermediate molecular weight and concentration. These results clearly demonstrated that the sulfonated unit in the copolymers played an important role in determining the promoting effect on ESCs' neural differentiation; SPA was identified as the most potent sulfonated unit for copolymer with the strongest promoting ability. The possible reason for sulfonated unit structure as a vital factor influencing the ability of the copolymers may be attributed to the difference in electrostatic and steric hindrance effect. The synthetic heparin-mimicking polymers obtained here can offer an effective alternative to heparin/HS and have great therapeutic potential for nervous system diseases.

Structure Activity Relationship of Heparin Mimicking Polymer p(SS-co-PEGMA): Effect of Sulfonation and Polymer Size on FGF2-Receptor Binding

Fibroblast growth factor-2 (FGF2) is a heparin binding protein that plays a role in a range of biological functions such as wound healing and bone regeneration. Heparin, a highly sulfated glycosaminoglycan, is required for FGF2 to bind to its receptor. Therefore, polymeric mimics of heparin are widely studied for their ability to manipulate FGF2-induced biological interactions. It is known that altering the degree of sulfonated monomer incorporation and size of heparin-mimicking polymers can affect protein-receptor binding. To elucidate the relationship between degree of sulfonation and receptor binding for the heparin-mimicking polymer, poly(styrene sulfonate-co-poly(ethylene glycol) methyl ether methacrylate) (p(SS-co-PEGMA)) a library was synthesized to contain nine polymers with degrees of sulfonation ranging from 0-100%. Kinetics of the polymerization was evaluated and reactivity ratios compared to literature results. These polymers were then tested for their ability to enhance FGF2 binding with its receptor as both covalent conjugates and as excipients. In a receptor based enzyme-linked immunosorbant assay (ELISA), as well as a cell-based study, the polymer with 81% SS incorporation enhanced receptor binding compared to FGF2 alone, and to a greater extent than the other polymers. Therefore, another library of polymers was prepared maintaining the degree of sulfonation at 81% and changing the size from 41 to 390 monomer repeat units. The polymers were again tested in receptor based ELISA and cell studies, and all of the different sizes performed similarly, except for degree of polymerization 295 and 390, which had reduced response in the cellular assay. These results provide important information for the use of pSS-co-PEGMA as a potential heparin-mimicking therapeutic.

Synthetic Glycopolymers for Highly Efficient Differentiation of Embryonic Stem Cells into Neurons: Lipo- or Not?

To realize the potential application of embryonic stem cells (ESCs) for the treatment of neurodegenerative diseases, it is a prerequisite to develop an effective strategy for the neural differentiation of ESCs so as to obtain adequate amount of neurons. Considering the efficacy of glycosaminoglycans (GAG) and their disadvantages (e.g., structure heterogeneity and impurity), GAG-mimicking glycopolymers (designed polymers containing functional units similar to natural GAG) with or without phospholipid groups were synthesized in the present work and their ability to promote neural differentiation of mouse ESCs (mESCs) was investigated. It was found that the lipid-anchored GAG-mimicking glycopolymers (lipo-pSGF) retained on the membrane of mESCs rather than being internalized by cells after 1 h of incubation. Besides, lipo-pSGF showed better activity in promoting neural differentiation. The expression of the neural-specific maker β3-tubulin in lipo-pSGF-treated cells was ∼3.8- and ∼1.9-fold higher compared to natural heparin- and pSGF-treated cells at day 14. The likely mechanism involved in lipo-pSGF-mediated neural differentiation was further investigated by analyzing its effect on fibroblast growth factor 2 (FGF2)-mediated extracellular signal-regulated kinases 1 and 2 (ERK1/2) signaling pathway which is important for neural differentiation of ESCs. Lipo-pSGF was found to efficiently bind FGF2 and enhance the phosphorylation of ERK1/2, thus promoting neural differentiation. These findings demonstrated that engineering of cell surface glycan using our synthetic lipo-glycopolymer is a highly efficient approach for neural differentiation of ESCs and this strategy can be applied for the regulation of other cellular activities mediated by cell membrane receptors.

Promoting neural differentiation of embryonic stem cells using β-cyclodextrin sulfonate

Promoting neural differentiation of embryonic stem cells using inclusion complexes formed between β-cyclodextrin sulfonate and all-trans retinoic acid.

Heparin-Mimicking Polymers: Synthesis and Biological Applications

Heparin is a naturally occurring, highly sulfated polysaccharide that plays a critical role in a range of different biological processes. Therapeutically, it is mostly commonly used as an injectable solution as an anticoagulant for a variety of indications, although it has also been employed in other forms such as coatings on various biomedical devices. Due to the diverse functions of this polysaccharide in the body, including anticoagulation, tissue regeneration, anti-inflammation, and protein stabilization, and drawbacks of its use, analogous heparin-mimicking materials are also widely studied for therapeutic applications. This review focuses on one type of these materials, namely, synthetic heparin-mimicking polymers. Utilization of these polymers provides significant benefits compared to heparin, including enhancing therapeutic efficacy and reducing side effects as a result of fine-tuning heparin-binding motifs and other molecular characteristics. The major types of the various polymers are summarized, as well as their applications. Because development of a broader range of heparin-mimicking materials would further expand the impact of these polymers in the treatment of various diseases, future directions are also discussed.

Recyclable Escherichia coli-Specific-Killing AuNP-Polymer (ESKAP) Nanocomposites

Escherichia coli plays a crucial role in various inflammatory diseases and infections that pose significant threats to both human health and the global environment. Specifically inhibiting the growth of pathogenic E. coli is of great and urgent concern. By modifying gold nanoparticles (AuNPs) with both poly[2-(methacrylamido)glucopyranose] (pMAG) and poly[2-(methacryloyloxy)ethyl trimethylammonium iodide] (pMETAI), a novel recyclable E. coli-specific-killing AuNP-polymer (ESKAP) nanocomposite is proposed in this study, which based on both the high affinity of glycopolymers toward E. coli pili and the merits of antibacterial quaternized polymers attached to gold nanoparticles. The properties of nanocomposites with different ratios of pMAG to pMETAI grafted onto AuNPs are studied. With a pMAG:pMETAI feed ratio of 1:3, the nanocomposite appeared to specifically adhere to E. coli and highly inhibit the bacterial cells. After addition of mannose, which possesses higher affinity for the lectin on bacterial pili and has a competitive advantage over pMAG for adhesion to pili, the nanocomposite was able to escape from dead E. coli cells, becoming available for repeat use. The recycled nanocomposite retained good antibacterial activity for at least three cycles. Thus, this novel ESKAP nanocomposite is a promising, highly effective, and readily recyclable antibacterial agent that specifically kills E. coli. This nanocomposite has potential applications in biological sensing, biomedical diagnostics, biomedical imaging, drug delivery, and therapeutics.

Synthesis of lipo-glycopolymers for cell surface engineering

A novel synthetic lipo-glycopolymer was inserted into cell membranes for cell surface engineering.

Highly hemo-compatible, mechanically strong, and conductive dual cross-linked polymer hydrogels

Novel hydrogels with highly hemo-compatible, mechanically strong and conductive properties are developed as promising candidates for a wide range of biomedical applications.

One-step synthesis of glycoprotein mimics in vitro: improvement of protein activity, stability and application in CPP hydrolysis

Glycoprotein mimics produced in vitro by one-step conjugation of glycopolymer and pyrophosphatase have improved bioactivity and stability for potential biomedical applications.

Biomaterials for in situ tissue regeneration: development and perspectives

Biomaterials are of fundamental importance to in situ tissue regeneration, which has emerged as a powerful method to treat tissue defects. The development and perspectives of biomaterials for in situ tissue regeneration were summarized.