Development of a Supramolecular Hydrogel for Intraperitoneal Injections

Local intraperitoneal drug administration is considered a challenging drug delivery route. The therapeutic efficiency is low, mainly due to rapid clearance of drugs. To increase the intraperitoneal retention time of specific drugs, a pH-sensitive supramolecular hydrogel that can act as a drug delivery vehicle is developed. To establish the optimal formulation of the hydrogel and to study its feasibility, safety, and tissue compatibility, in vitro, postmortem, and in vivo experiments are performed. In vitro tests reveal that a hydrogelator formulation with pH ≥ 9 results in a constant viscosity of 0.1 Pa·s. After administration postmortem, the hydrogel covers the parietal and visceral peritoneum with a thin, soft layer. In the subsequent in vivo experiments, 14 healthy rats are subjected to intraperitoneal injection with the hydrogel. Fourteen and 28 days after implantation, the animals are euthanized. Intraperitoneal exposure to the hydrogel is not resulted in significant weight loss or discomfort. Moreover, no macroscopic adverse effects or signs of organ damage are detected. In several intra-abdominal tissues, vacuolated macrophages are found indicating a physiological degradation of the synthetic hydrogel. This study demonstrates that the supramolecular hydrogel is safe for intraperitoneal application and that the hydrogel shows good tissue compatibility in rats.

Iron Oxide Nanoparticles with Supramolecular Ureido-Pyrimidinone Coating for Antimicrobial Peptide Delivery

Antimicrobial peptides (AMPs) can kill bacteria by disrupting their cytoplasmic membrane, which reduces the tendency of antibacterial resistance compared to conventional antibiotics. Their possible toxicity to human cells, however, limits their applicability. The combination of magnetically controlled drug delivery and supramolecular engineering can help to reduce the dosage of AMPs, control the delivery, and improve their cytocompatibility. Lasioglossin III (LL) is a natural AMP form bee venom that is highly antimicrobial. Here, superparamagnetic iron oxide nanoparticles (IONs) with a supramolecular ureido-pyrimidinone (UPy) coating were investigated as a drug carrier for LL for a controlled delivery to a specific target. Binding to IONs can improve the antimicrobial activity of the peptide. Different transmission electron microscopy (TEM) techniques showed that the particles have a crystalline iron oxide core with a UPy shell and UPy fibers. Cytocompatibility and internalization experiments were carried out with two different cell types, phagocytic and nonphagocytic cells. The drug carrier system showed good cytocompatibility (>70%) with human kidney cells (HK-2) and concentration-dependent toxicity to macrophagic cells (THP-1). The particles were internalized by both cell types, giving them the potential for effective delivery of AMPs into mammalian cells. By self-assembly, the UPy-coated nanoparticles can bind UPy-functionalized LL (UPy-LL) highly efficiently (99%), leading to a drug loading of 0.68 g g-1. The binding of UPy-LL on the supramolecular nanoparticle system increased its antimicrobial activity against E. coli (MIC 3.53 µM to 1.77 µM) and improved its cytocompatible dosage for HK-2 cells from 5.40 µM to 10.6 µM. The system showed higher cytotoxicity (5.4 µM) to the macrophages. The high drug loading, efficient binding, enhanced antimicrobial behavior, and reduced cytotoxicity makes ION@UPy-NH2 an interesting drug carrier for AMPs. The combination with superparamagnetic IONs allows potential magnetically controlled drug delivery and reduced drug amount of the system to address intracellular infections or improve cancer treatment.

Complementary Supramolecular Functionalization Enhances Antifouling Surfaces: A Ureidopyrimidinone-Functionalized Phosphorylcholine Polymer

Fibrosis of implants remains a significant challenge in the use of biomedical devices and tissue engineering materials. Antifouling coatings, including synthetic zwitterionic coatings, have been developed to prevent fouling and cell adhesion to several implantable biomaterials. While many of these coatings need covalent attachment, a conceptually simpler approach is to use a spontaneous self-assembly event to anchor the coating to a surface. This could simplify material processing through highly specific molecular recognition. Herein, we investigate the ability to utilize directional supramolecular interactions to anchor an antifouling coating to a polymer surface containing a complementary supramolecular unit. A library of controlled copolymerization of ureidopyrimidinone methacrylate (UPyMA) and 2-methacryloyloxyethyl phosphorylcholine (MPC) was prepared and their UPy composition was assessed. The MPC-UPy copolymers were characterized by 1H NMR, Fourier transform infrared (FTIR), and gel permeation chromatography (GPC) and found to exhibit similar mol % of UPy as compared to feed ratios and low dispersities. The copolymers were then coated on an UPy elastomer and the surfaces were assessed for hydrophilicity, protein absorption, and cell adhesion. By challenging the coatings, we found that the antifouling properties of the MPC-UPy copolymers with more UPy mol % lasted longer than the MPC homopolymer or low UPy mol % copolymers. As a result, the bioantifouling nature could be tuned to exhibit spatio-temporal control, namely, the longevity of a coating increased with UPy composition. In addition, these coatings showed nontoxicity and biocompatibility, indicating their potential use in biomaterials as antifouling coatings. Surface modification employing supramolecular interactions provided an approach that merges the simplicity and scalability of nonspecific coating methodology with the specific anchoring capacity found when using conventional covalent grafting with longevity that could be engineered by the supramolecular composition itself.

The effect of chronic kidney disease on tissue formation of in situ tissue-engineered vascular grafts

Vascular in situ tissue engineering encompasses a single-step approach with a wide adaptive potential and true off-the-shelf availability for vascular grafts. However, a synchronized balance between breakdown of the scaffold material and neo-tissue formation is essential. Chronic kidney disease (CKD) may influence this balance, lowering the usability of these grafts for vascular access in end-stage CKD patients on dialysis. We aimed to investigate the effects of CKD on in vivo scaffold breakdown and tissue formation in grafts made of electrospun, modular, supramolecular polycarbonate with ureido-pyrimidinone moieties (PC-UPy). We implanted PC-UPy aortic interposition grafts (n = 40) in a rat 5/6th nephrectomy model that mimics systemic conditions in human CKD patients. We studied patency, mechanical stability, extracellular matrix (ECM) components, total cellularity, vascular tissue formation, and vascular calcification in CKD and healthy rats at 2, 4, 8, and 12 weeks post-implantation. Our study shows successful in vivo application of a slow-degrading small-diameter vascular graft that supports adequate in situ vascular tissue formation. Despite systemic inflammation associated with CKD, no influence of CKD on patency (Sham: 95% vs CKD: 100%), mechanical stability, ECM formation (Sirius red⁺, Sham 16.5% vs CKD 25.0%-p:0.83), tissue composition, and immune cell infiltration was found. We did find a limited increase in vascular calcification at 12 weeks (Sham 0.08% vs CKD 0.80%-p:0.02) in grafts implanted in CKD animals. However, this was not associated with increased stiffness in the explants. Our findings suggest that disease-specific graft design may not be necessary for use in CKD patients on dialysis.

Marker-Independent Monitoring of in vitro and in vivo Degradation of Supramolecular Polymers Applied in Cardiovascular in situ Tissue Engineering

The equilibrium between scaffold degradation and neotissue formation, is highly essential for in situ tissue engineering. Herein, biodegradable grafts function as temporal roadmap to guide regeneration. The ability to monitor and understand the dynamics of degradation and tissue deposition in in situ cardiovascular graft materials is therefore of great value to accelerate the implementation of safe and sustainable tissue-engineered vascular grafts (TEVGs) as a substitute for conventional prosthetic grafts. In this study, we investigated the potential of Raman microspectroscopy and Raman imaging to monitor degradation kinetics of supramolecular polymers, which are employed as degradable scaffolds in in situ tissue engineering. Raman imaging was applied on in vitro degraded polymers, investigating two different polymer materials, subjected to oxidative and enzymatically-induced degradation. Furthermore, the method was transferred to analyze in vivo degradation of tissue-engineered carotid grafts after 6 and 12 months in a sheep model. Multivariate data analysis allowed to trace degradation and to compare the data from in vitro and in vivo degradation, indicating similar molecular observations in spectral signatures between implants and oxidative in vitro degradation. In vivo degradation appeared to be dominated by oxidative pathways. Furthermore, information on collagen deposition and composition could simultaneously be obtained from the same image scans. Our results demonstrate the sensitivity of Raman microspectroscopy to determine degradation stages and the assigned molecular changes non-destructively, encouraging future exploration of this techniques for time-resolved quality assessment of in situ tissue engineering processes.

Supramolecular Hydrogels: Design Strategies and Contemporary Biomedical Applications

Self-assembly of supramolecular hydrogels is driven by dynamic, non-covalent interactions between molecules. Considerable research effort has been exerted to fabricate and optimise supramolecular hydrogels that display shear-thinning, self-healing, and reversibility, in order to develop materials for biomedical applications. This review provides a detailed overview of the chemistry behind the dynamic physicochemical interactions that sustain hydrogel formation (hydrogen bonding, hydrophobic interactions, ionic interactions, metal-ligand coordination, and host-guest interactions). Novel design strategies and methodologies to create supramolecular hydrogels are highlighted, which offer promise for a wide range of applications, specifically drug delivery, wound healing, tissue engineering and 3D bioprinting. To conclude, future prospects are briefly discussed, and consideration given to the steps required to ultimately bring these biomaterials into clinical settings.

Soft Self-Healing Fluidic Tactile Sensors with Damage Detection and Localization Abilities

Self-healing sensors have the potential to increase the lifespan of existing sensing technologies, especially in soft robotic and wearable applications. Furthermore, they could bestow additional functionality to the sensing system because of their self-healing ability. This paper presents the design for a self-healing sensor that can be used for damage detection and localization in a continuous manner. The soft sensor can recover full functionality almost instantaneously at room temperature, making the healing process fully autonomous. The working principle of the sensor is based on the measurement of air pressure inside enclosed chambers, making the fabrication and the modeling of the sensors easy. We characterize the force sensing abilities of the proposed sensor and perform damage detection and localization over a one-dimensional and two-dimensional surface using multilateration techniques. The proposed solution is highly scalable, easy-to-build, cheap and even applicable for multi-damage detection.