Ureidopyrimidinone Research Articles

Injectable Supramolecular Ureidopyrimidinone Hydrogels Provide Sustained Release of Extracellular Vesicle Therapeutics.

Extracellular vesicles (EVs) are small vesicles secreted by cells and have gained increasing interest as both drug delivery vehicles or as cell-free therapeutics for regenerative medicine. To achieve optimal therapeutic effects, strategies are being developed to prolong EV exposure to target organs. One promising approach to achieve this is through EV-loaded injectable hydrogels. In this study, the use of a hydrogel based on ureido-pyrimidinone (UPy) units coupled to poly(ethylene glycol) chains (UPy-hydrogel) is examined as potential delivery platform for EVs. The UPy-hydrogel undergoes a solution-to-gel transition upon switching from a high to neutral pH, allowing immediate gelation upon administration into physiological systems. Here, sustained EV release from the UPy-hydrogel measured over a period of 4 d is shown. Importantly, EVs retain their functional capacity after release. Upon local administration of fluorescently labeled EVs incorporated in a UPy-hydrogel in vivo, EVs are still detected in the UPy-hydrogel after 3 d, whereas in the absence of a hydrogel, EVs are internalized by fat and skin tissue near the injection site. Together, these data demonstrate that UPy-hydrogels provide sustained EV release over time and enhance local EV retention in vivo, which could contribute to improved therapeutic efficacy upon local delivery and translation toward new applications.

Functional peptide presentation on different hydrogen bonding biomaterials using supramolecular additives

Supramolecular biomaterials based on hydrogen bonding units can be conveniently functionalized in a mix-and-match approach using supramolecular additives. The presentation of bioactive additives has been sparsely investigated in supramolecular-based elastomeric biomaterials. Here it was investigated how cell adhesive peptides are presented and affect the surface in supramolecular biomaterials based either on ureido-pyrimidinone (UPy) or bisurea (BU) moieties. Polycaprolactone modified with UPy or BU moieties served as the base material. RGD or cyclic (c)RGD were conjugated to complementary supramolecular motifs, and were mixed with the corresponding base materials as supramolecular additives. Biomaterial surface morphology changed upon bioactivation, resulting in the formation of random aggregates on UPy-based materials, and fibrous aggregates on BU-materials. Moreover, peptide type affected aggregation morphology, in which RGD led to larger cluster formation than cRGD. Increased cRGD concentrations led to reduced focal adhesion size and cell migration velocity, and increased focal adhesion numbers in both systems, yet most prominent on functionalized BU-biomaterials. In conclusion, both systems exhibited distinct peptide presenting properties, of which the BU-system most strongly affected cellular adhesive behavior on the biomaterial. This research provided deeper insights in the differences between supramolecular elastomeric platforms, and the level of peptide introduction for biomaterial applications.

Nonswellable and Tough Supramolecular Hydrogel Based on Strong Micelle Cross-Linkings.

Because of the difference in osmotic pressure, most tough hydrogels swell under physiological conditions, which seriously weakens their mechanical properties, limiting their applications in biomedicine. Herein, a novel strategy based on strong and high-density micelle cross-linkings is proposed to prepare nonswellable and tough hydrogel. To realize a strong micelle cross-linker, the synergetic effect of hydrophobic and quadruple hydrogen-bonding interactions is employed by introducing an alkyl chain-protected ureido pyrimidinone moiety into a segmented copolymer backbone. The length of the alkyl is the key factor in determining the strength of the hydrophobic interaction, which was carefully tailored to gain micelles with high strength and suitable solubility. A supramolecular hydrogel was formed in situ by simply linking micelle cross-linkers with poly(ethylene glycol) chains. The strong and high-density micelle cross-linkings restrain multiple effective chains outside the micelle from stretching during swelling, and the deformability of micelle cross-linkings disperses the local stress to maintain the network with high cross-linking density upon loading. Therefore, the hydrogel exhibited an outstanding nonswelling behavior under physiological conditions and excellent mechanical properties with a compressive strength of 4 MPa. The rapid in situ gelation also facilitated injection and cell encapsulation. Meanwhile, it also showed good tissue adhesion, cytocompatibility, and suitable degradability. This novel and facile strategy can offer new insights into the exploitation of cross-linkings to prepare nonswellable hydrogels for biomedical applications.

Aliphatic Polyester Thermoplastic Elastomers Containing Hydrogen-Bonding Ureidopyrimidinone Endgroups.

Polylactide- block-poly(γ-methyl-ε-caprolactone)- block-polylactide (LML) is a sustainable thermoplastic elastomer (TPE) candidate that exhibits competitive mechanical properties as compared to traditional styrenic TPEs. The relatively low glass transition temperature of the polylactide endblocks, however, results in stress relaxation and low levels of elastic recovery. We report the synthesis and characterization of poly(γ-methyl-ε-caprolactone) (PMCL) and LML end-functionalized with ureidopyrimidinone (UPy) hydrogen-bonding moieties to improve the elastic performance of these polymers. Although UPy-functionalized PMCL shows dynamical mechanical behavior that is distinct from the unfunctionalized homopolymer, it does not exhibit elastomeric behavior at room temperature. The addition of UPy endgroups to LML increases the ultimate tensile strength, elongation at break, and tensile toughness compared to unfunctionalized LML. Stress relaxation studies at a fixed strain show reduced levels of stress relaxation in LML with UPy endgroups. The stress relaxation was further reduced by including semicrystalline poly(( S, S)-lactide) as endblocks with UPy endgroups.

Supramolecular Modification of a Sequence-Controlled Collagen-Mimicking Polymer.

Structurally and functionally well-defined recombinant proteins are an interesting class of sequence-controlled macromolecules to which different crosslinking chemistries can be applied to tune their biological properties. Herein, we take advantage of a 571-residue recombinant peptide based on human collagen type I (RCPhC1), which we functionalized with supramolecular 4-fold hydrogen bonding ureido-pyrimidinone (UPy) moieties. By grafting supramolecular UPy moieties onto the backbone of RCPhC1 (UPy-RCPhC1), increased control over the polymer structure, assembly, gelation, and mechanical properties was achieved. In addition, by increasing the degree of UPy functionalization on RCPhC1, cardiomyocyte progenitor cells were cultured on “soft” (∼26 kPa) versus “stiff” (∼68–190 kPa) UPy-RCPhC1 hydrogels. Interestingly, increased stress fiber formation, focal adhesions, and proliferation were observed on stiffer compared to softer substrates, owing to the formation of stronger cell–material interactions. In conclusion, a bioinspired hydrogel material was designed by a combination of two well-known natural components, i.e., a protein as sequence-controlled polymer and UPy units inspired on nucleobases.

Influence of the Assembly State on the Functionality of a Supramolecular Jagged1-Mimicking Peptide Additive.

Expanding the bioactivation toolbox of supramolecular materials is of utmost relevance for their broad applicability in regenerative medicines. This study explores the functionality of a peptide mimic of the Notch ligand Jagged1 in a supramolecular system that is based on hydrogen bonding ureido-pyrimidinone (UPy) units. The functionality of the peptide is studied when formulated as an additive in a supramolecular solid material and as a self-assembled system in solution. UPy conjugation of the DSLJAG1 peptide sequence allows for the supramolecular functionalization of UPy-modified polycaprolactone, an elastomeric material, with UPy-DSLJAG1. Surface presentation of the UPy-DSLJAG1 peptide was confirmed by atomic force microscopy and X-ray photoelectron spectroscopy analyses, but no enhancement of Notch activity was detected in cells presenting Notch1 and Notch3 receptors. Nevertheless, a significant increase in Notch-signaling activity was observed when DSLJAG1 peptides were administered in the soluble form, indicating that the activity of DSLJAG1 is preserved after UPy functionalization but not after immobilization on a supramolecular solid material. Interestingly, an enhanced activity in solution of the UPy conjugate was detected compared with the unconjugated DSLJAG1 peptide, suggesting that the self-assembly of supramolecular aggregates in solution ameliorates the functionality of the molecules in a biological context.

Perturbation of Ureidopyrimidinone Polymerization Via Electrochemical Redox Reactions of Electro-Active Ureidopyrimidinones

The formation of supramolecular polymers is possible through directional and favorable intermolecular interactions that, unlike conventional covalent bonds, are weaker and purely electrostatic. The electrostatic nature of these interactions grants their respective systems reversibility in binding interactions, allowing molecular systems to achieve dynamic behavior. An important goal in supramolecular chemistry is the development of stimuli-responsive systems where the strengths of these binding interactions can be perturbed. Perturbation of these intermolecular forces is achieved through the use of external signals such as light absorption, changes in temperature and/or pH, etc. However, in an almost unexplored area, the use of an applied voltage as an external signal is expected to perturb intermolecular binding via electrochemical redox reactions. One such system known for self-complementary hydrogen bonding is the Ureidopyrimidinone (UPy). Introduced by Meijer, UPy can dimerize with another UPy along its complementary 4 hydrogen bond frame. Due to their directionality and strength of association, UPy’s have been utilized as cross-linkers in oligomerization and as capping agents in oligomer chain termination. In these cases, association and/or dissociation of UPy dimers can be influenced by external signals that were previously described. However, the use of voltage as a means of dimerization control of the UPy system and other H-bonded systems is virtually unheard of. Preliminary studies on electroactive UPy derivatives – UPy’s with substituents rendering them responsive to electrochemical stimuli – have been explored. One such UPy derivative is UPyFc, where a ferrocene substituent acts as an electrochemical redox center of the UPy derivative. Cyclic voltammetry and bulk electrolysis / steady-state voltammetry studies reveal that dimerization of UPyFc can be electrochemically controlled, and the mechanism of the electrochemical reaction indicates a square scheme for the UPyFc / UPyFc+ redox couple in dichloromethane. The fully reduced UPyFc exists as a dimer. Upon oxidation to UPyFc+, the dimer breaks apart to form the monomer. Furthermore, this process appears to be completely reversible in dichloromethane. Based off of these preliminary studies, electro-inactive UPy oligomers have been developed with the goal of altering the physical properties of bulk non-polar organic solutions containing these UPy oligomer units and electro-active UPy derivatives. It is expected that, in bulk solution, the formation of UPy hetero-dimers between UPyFc and electro-inactive UPy oligomer units will be observed and the bulk solution will show low viscosity. Oxidizing UPyFc to UPyFc+ will break these hetero-dimers apart and UPy oligomerization will be observed, in which the bulk solution should show an increase in viscosity. Based off of preliminary studies, this should be a reversible process in which physical properties of bulk solutions can be altered by controlling H-bonding interactions via electrochemical redox reactions.

Controlling Ureidopyrimidinone Polymerization Via Electrochemical Redox Reactions

The formation of supramolecular polymers is possible through directional and favorable intermolecular interactions that, unlike conventional covalent bonds, are weaker and purely electrostatic. The electrostatic nature of these interactions grants their respective systems reversibility in binding interactions, allowing molecular systems to achieve dynamic behavior. An important goal in supramolecular chemistry is the development of stimuli-responsive systems where the strengths of these binding interactions can be perturbed. Perturbation of these intermolecular forces is achieved through the use of external signals such as light absorption, changes in temperature and/or pH, etc. However, in an almost unexplored area, the use of an applied voltage as an external signal is expected to perturb intermolecular binding via electrochemical redox reactions. One such system known for self-complementary hydrogen bonding is the Ureidopyrimidinone (UPy). Introduced by Meijer, UPy can dimerize with another UPy along its complementary 4 hydrogen bond frame. Due to their directionality and strength of association, UPy’s have been utilized as cross-linkers in oligomerization and as capping agents in oligomer chain termination. In these cases, association and/or dissociation of UPy dimers can be influenced by external signals that were previously described. However, the use of voltage as a means of dimerization control of the UPy system and other H-bonded systems is virtually unheard of. Preliminary studies on electroactive UPy derivatives – UPy’s with substituents rendering them responsive to electrochemical stimuli – have been explored. One such UPy derivative is UPyFc, where a ferrocene substituent acts as an electrochemical redox center of the UPy derivative. Cyclic voltammetry and bulk electrolysis / steady-state voltammetry studies reveal that dimerization of UPyFc can be electrochemically controlled, and the mechanism of the electrochemical reaction indicates a square scheme for the UPyFc / UPyFc+ redox couple in dichloromethane. The fully reduced UPyFc exists as a dimer. Upon oxidation to UPyFc+, the dimer breaks apart to form the monomer. Furthermore, this process appears to be completely reversible in dichloromethane. Based off of these preliminary studies, electro-inactive UPy oligomers have been developed with the goal of altering the physical properties of bulk non-polar organic solutions containing these UPy oligomer units and electro-active UPy derivatives. It is expected that, in bulk solution, the formation of UPy hetero-dimers between UPyFc and electro-inactive UPy oligomer units will be observed and the bulk solution will show low viscosity. Oxidizing UPyFc to UPyFc+ will break these hetero-dimers apart and UPy oligomerization will be observed, in which the bulk solution should show an increase in viscosity. Based off of preliminary studies, this should be a reversible process in which physical properties of bulk solutions can be altered by controlling H-bonding interactions via electrochemical redox reactions.

A highly efficient flame retardant nacre-inspired nanocoating with ultrasensitive fire-warning and self-healing capabilities

Design and exploitation of flame retardant coatings with sensitive fire-warning response and self-healing capability are urgently needed to decrease the fire risk of combustible materials. Herein, we reported the fabrication of a novel multifunctional flame retardant nanocoating created by using graphene oxide (GO) and functional cellulose (FC) via one step self-assembly. The prepared nacre-like nanocoating endowed many kinds of combustible materials (including polypropylene, polyurethane foam and wood) with exceptional fire safety. All the coated substrates were self-extinguished in the flame retardant tests. More importantly, when being attacked by fire at the very early stage, it triggered the fire-warning in less than three seconds through the dramatic decrease of electrical resistance. Moreover, the nanocoating exhibited outstanding self-healing capability at room temperature. Due to the multiple hydrogen bondings between the ureido pyrimidinone groups on FC, the damaged coating could be healed successfully and almost recovered to its original integrated performance. Our work provides a new and effective route to remarkably improve the fire safety of the combustible materials, exhibiting an enticing prospect for its application in the fields of building, transportation and electrical equipment.

Physically cross-linked polyethyleneviareactive extrusion

Ureidopyrimidinone (UPy) is introduced into various polyethylenes (PEs) bearing hydroxyl groups by solution grafting, affording physically cross-linked PEviamultiple H-bonding.

Self-healing and recyclable photonic elastomers based on a water soluble supramolecular polymer

Photonic elastomers with angle-independent structural colors, self-healing, and recycling properties are prepared by incorporating isotropically arranged SiO2 nanoparticles into a water-soluble ureidopyrimidinone (UPy) cross-linked poly(ethylene glycol) (PEG) polymer matrix.

Exploring multiple functions of diarylsemipinacol linked to the saturated ethylene–propylene elastomer: from the dynamic covalent networks to tailoring its macroscopic performance

Through the multiple functions of diarylsemipinacol, we prepared a mechanically robust and healable EPM with shape memory properties, by integrating self-associating ureidopyrimidinone (UPy) into the dynamic covalent networks.

4D Printing of Smart Stimuli-Responsive Polymers

This paper starts with a short review of smart materials, which can be 4D printed and whose properties can be modified over time through specific stimuli such as heat, light, temperature, electric and magnetic fields. In the second part of the paper, a new polymer material for 4D printing was presented. The material was a thermally activated shape memory polymer (SPM), capable of memorizing a temporary shape and restoring the original one by means of a thermal stimulus. A self-healing behavior was introduced into the polymer, to enhance its durability and make it suitable for application in the fields of soft robotics and actuators. A polycaprolactone (PCL) was selected to provide a shape memory effect, taking into account its molecular weight and the possibility of chemically modifying it in order to make it photo-curable. Self-healing properties were provided by an ureidopyrimidinone (UPy) methacrylate monomer, capable of forming four hydrogen bonds with a self-complementary unit, favored by temperature. This new material was thus 4D printed by a digital liquid processing (DLP) printer. Both the shape memory effect and the self-healing feature were demonstrated, enabling this new material to be used as a raw material for new generation soft robotic actuators.

A supramolecular network derived by rotaxane tethering three ureido pyrimidinone groups.

A supramolecular network and its film were prepared via intermolecular hydrogen bonding of a [2]rotaxane with three ureido pyrimidinone groups. Adding less polar solvents such as CHCl3 to the rotaxane afforded a swollen rotaxane-cross-linked network. The properties of the film obtained by drying were evaluated to characterize it.

Self-Healing Polymer Electrolytes Formed via Dual-Networks: A New Strategy for Flexible Lithium Metal Batteries.

A novel polymer electrolyte with mechanically robust and self-healing properties was fabricated through a dual-network structure, crosslinked by quadruple hydrogen bonding and chemical bonding. The dynamic ureido-pyrimidinone (UPy) dimers were the first network in the polymer matrix. This group endows the polymer electrolyte with good self-healing capacity and improves the reliability and lifetime of the polymer lithium batteries. The crosslinked polyethylene glycol-bis-carbamate dimethacrylate (PEGBCDMA) is the second network and guarantees dimensional stability and good mechanical properties of the polymer electrolyte. The dual-network self-healing polymer electrolyte (DN-SHPE) exhibits improved ionic conductivity versus the polymer electrolyte fabricated by poly(ethylene glycol) diacrylate (PEGDA). It has high thermal stability (up to 350 °C) and excellent interfacial stability with the electrodes. When the DN-SHPE-based cells were fabricated with LiFePO4 and Li metal, the resulting cells show good reversible specific capacity and considerable rate capability. Moreover, the pouch cell could maintain electrochemical function even under deformation or folding conditions.

Quantifying Guest-Host Dynamics in Supramolecular Assemblies to Analyze Their Robustness.

The most basic function of synthetic microenvironments for tissue engineering is to act as a physical substrate for cell attachment, migration, and proliferation, similar to the natural cell environment. Functionalization of supramolecular materials with guest compounds that display the same recognition moieties is a common strategy to introduce biofunctionality. However, besides a robust interaction with the material, a certain level of dynamics needs to be conserved for an adaptive interface toward the living environment. A balance between robust material functionalization and dynamic cell interaction needs to be met. The detailed analysis hereof using a ureido-pyrimidinone (UPy) poly(ethylene glycol) system in dilute and transient network regime is demonstrated. Monovalent and bivalent UPy-functionalized guest molecules are designed and their interaction with UPy-host fibers is evaluated. Analysis of guest interaction in the dilute state by microfluidics, and in the gel state, by fluorescence recovery after photobleaching and fluorescence resonance energy transfer is proven to be suitable to quantify the local and ensemble guest mobility. The results demonstrate that the interaction of bioactive moieties through supramolecular host-guest chemistry yields a dynamic system, which is stronger for divalent guests but risks unintended leakage in the case of functional monomeric units.

Renal Epithelial Monolayer Formation on Monomeric and Polymeric Catechol Functionalized Supramolecular Biomaterials.

Induction of a functional, tight monolayer of renal epithelial cells on a synthetic membrane to be applied in a bioartificial kidney device requires for bio-activation of the membrane. The current golden standard in bio-activation is the combination of a random polymeric catechol (L-DOPA) coating and collagen type IV (Col IV). Here the possibility of replacing this with defined monomeric catechol functionalization on a biomaterial surface using supramolecular ureido-pyrimidinone (UPy)-moieties is investigated. Monomeric catechols modified with a UPy-unit are successfully incorporated and presented in supramolecular UPy-polymer films and membranes. Unfortunately, these UPy-catechols are unable to improve epithelial cell monolayer formation over time, solely or in combination with Col IV. L-DOPA combined with Col IV is able to induce a tight monolayer capable of transport on electrospun supramolecular UPy-membranes. This study shows that a random polymeric catechol coating cannot be simply mimicked by defined monomeric catechols as supramolecular additives. There is still a long way to go in order to synthetically mimic simple natural structures.

Morphology and mechanisms of a novel absorbable polymeric conduit in the pulmonary circulation of sheep

Right ventricular outflow tract (RVOT) conduits used in children with congenital heart disease often degenerate rapidly or develop other complications, and they do not grow with the patient. This leads to multiple surgeries until adult-sized conduits can be implanted. We report experimental in vivo experience with an entirely synthetic absorbable graft, designed to be replaced by tissue in-vivo by host cells, in a process termed Endogenous Tissue Restoration (ETR), and to grow commensurate with somatic growth. We characterized the structure, mechanical properties, biocompatibility, and in vivo remodelling of a bioabsorbable polyester based on the self-complementary ureido-pyrimidinone (UPy) quadruple hydrogen-bonding motif. Electrospinning was used to process the polymer into a tubular graft with a highly porous wall structure, which was implanted as a pulmonary artery interposition graft in 9 adult sheep with a maximum follow-up of 1 year, followed by pathologic and mechanical analysis. All grafts were patent by transthoracic echocardiography. Eight were intact at post-mortem examination. One graft had aneurysmal dilation. Graft polymer resorption in vivo was consistent among specimens. Histologic examination revealed progressive tissue replacement of graft polymer, ongoing at one year, with remodeling to a structure that had some key features of native vascular wall. Burst pressures for all explants at 8 weeks and beyond were higher than those of native pulmonary artery (PA) and largely determined by newly formed tissue. Preclinical studies of a new, absorbable polymeric graft for PA replacement showed remodelling by endogenous cells up to one-year follow-up. Our results show that ETR leads to progressive and substantial replacement of an off-the-shelf synthetic bioabsorbable conduit by functional host tissue to one year in sheep. Thus, further development of this novel concept is warranted.

Experimental reconstruction of an abdominal wall defect with electrospun polycaprolactone-ureidopyrimidinone mesh conserves compliance yet may have insufficient strength

PurposeElectrospun meshes mimic the extracellular matrix, which may improve their integration. We aimed to compare polycaprolactone (PCL) modified with ureidopyrimidinone (UPy) electrospun meshes with ultra-lightweight polypropylene (PP; Restorelle) reference textile meshes for in vivo compliance. We chose UPy-PCL because we have shown it does not compromise biomechanical properties of native tissue, and because it potentially can be bioactivated. MethodsWe performed ex vivo biomechanical cyclic loading in wet conditions and in vivo overlay of full-thickness abdominal wall defects in rats and rabbits. Animals were sacrificed at 7, 42 and 54 days (rats; n = 6/group) and 30 and 90 days (rabbits; n = 3/group). Outcomes were herniation, mesh degradation and mesh dimensions, explant compliance and histology. High failure rates prompted us to provide additional material strength by increasing fiber diameter and mesh thickness, which was further tested in rabbits as a biomechanically more challenging model. ResultsCompliance was tested in animals without herniation. In both species, UPy-PCL-explants were as compliant as native tissue. In rats, PP-explants were stiffer. Contraction was similar in UPy-PCL and PP-explants. However, UPy-PCL-meshes macroscopically degraded from 30 days onwards, coinciding with herniation in up to half of animals. Increased fiber and mesh thickness did not improve outcome. Degradation of UPy-PCL is associated with an abundance of foreign body giant cells until UPy-PCL disappears. ConclusionAbdominal wall reconstruction with electrospun UPy-PCL meshes failed in 50%. Degradation coincided with a transient vigorous foreign body reaction. Non-failing UPy-PCL-explants were as compliant as native tissue. Despite that, the high failure rate forces us to explore electrospun meshes based on other polymers.

Antimicrobial peptide modification of biomaterials using supramolecular additives.

ABSTRACTBiomaterials based on non‐active polymers functionalized with antimicrobial agents by covalent modification or mixing are currently regarded as high potential solutions to prevent biomaterial associated infections that are major causes of biomedical device failure. Herewith a strategy is proposed in which antimicrobial materials are prepared by simply mixing‐and‐matching of ureido‐pyrimidinone (UPy) based supramolecular polymers with antimicrobial peptides (AMPs) modified with the same UPy‐moiety. The N‐terminus of the AMPs was coupled in solution to an UPy‐carboxylic acid synthon resulting in formation of a new amidic bond. The UPy‐functionalization of the AMPs did not affect their secondary structure, as proved by circular dichroism spectroscopy. The antimicrobial activity of the UPy‐AMPs in solution was also retained. In addition, the incorporation of UPy‐AMPs into an UPy‐polymer was stable and the final material was biocompatible. The addition of 4 mol % of UPy‐AMPs in the UPy‐polymer material protected against colonization by Escherichia coli, and methicillin‐sensitive and ‐resistant strains of Staphylococcus aureus. This modular approach enables a stable but dynamic incorporation of the antimicrobial agents, allowing at the same time for the possibility to change the nature of the polymer, as well as the use of AMPs with different activity spectra. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1926–1934