Synthesis and characterization of UV photocrosslinkable hydrogels with poly(N-vinyl-2-pyrrolidone): Determination of the network mesh size distribution

Swift Covalent Gelation Coupled with Robust Wet Adhesive Powder: A Novel Approach for Acute Massive Hemorrhage Control in Dynamic and High-Pressure Wound Environments

The quest for efficient hemostatic agents in emergency medicine is critical, particularly for managing massive hemorrhages in dynamic and high-pressure wound environments. Traditional self-gelling powders, while beneficial due to their ease of application and rapid action, fall short in such challenging conditions. To bridge this gap, the research introduces a novel self-gelling powder that combines ultrafast covalent gelation and robust wet adhesion, presenting a significant advancement in acute hemorrhage control. This ternary system comprises ε-polylysine (ε-PLL) and 4-arm polyethylene glycol succinyl succinate (4-arm-PEG-NHS) forming the hydrogel framework. Na2HPO4 functions as the "H+ sucker" to expedite the amidation reaction, slashing gelation time to under 10 s, crucial for immediate blood loss restriction. Moreover, PEG chains' hydrophilicity facilitates efficient absorption of interfacial blood, increasing the generated hydrogel's cross-linking density and strengthens its tissue bonding, thereby resulting in excellent mechanical and wet adhesion properties. In vitro experiments reveal the optimized formulation's exceptional tissue compliance, procoagulant activity, biocompatibility and antibacterial efficacy. In porcine models of heart injuries and arterial punctures, it outperforms commercial hemostatic agent Celox, confirming its rapid and effective hemostasis. Conclusively, this study presents a transformative approach to hemostasis, offering a reliable and potent solution for the emergency management of massive hemorrhage.

Photocrosslinkable natural polymers in tissue engineering

Natural polymers have been widely used in scaffolds for tissue engineering due to their superior biocompatibility, biodegradability, and low cytotoxicity compared to synthetic polymers. Despite these advantages, there remain drawbacks such as unsatisfying mechanical properties or low processability, which hinder natural tissue substitution. Several non-covalent or covalent crosslinking methods induced by chemicals, temperatures, pH, or light sources have been suggested to overcome these limitations. Among them, light-assisted crosslinking has been considered as a promising strategy for fabricating microstructures of scaffolds. This is due to the merits of non-invasiveness, relatively high crosslinking efficiency via light penetration, and easily controllable parameters, including light intensity or exposure time. This review focuses on photo-reactive moieties and their reaction mechanisms, which are widely exploited along with natural polymer and its tissue engineering applications.

Polysaccharide-based hydrogels crosslink density equation: A rheological and LF-NMR study of polymer-polymer interactions

A simple relation between pendant groups of polymers in hydrogels is introduced to determine the crosslink density of (complex) hydrogel systems (mixtures of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) modified nanocellulose, alginate, scleroglucan and Laponite in addition of crosslinking agents). Furthermore, the rheological properties and their great potential connection to design complex hydrogel systems with desired properties have been thoroughly investigated. Hydrogel structures governing internal friction and flow resistance were described by the predominant effect of ionic, hydrogen, and electrostatic interactions. The relationship between rheological properties and polymer-polymer interactions in the hydrogel network is explained and expressed in a new mathematical model for determining the crosslink density of (crosslinked) hydrogels based on single or mixture of polymer systems. In the end, the combined used of rheology and low field nuclear magnetic resonance spectroscopy (LF-NMR) for the characterization of hydrogel networks is developed.

Dual stimuli-responsive polyurethane-based hydrogels as smart drug delivery carriers for the advanced treatment of chronic skin wounds

The design of multi-stimuli-responsive vehicles for the controlled and localized release of drugs is a challenging issue increasingly catching the attention of many research groups working on the advanced treatment of hard-to-close wounds. In this work, a thermo- and pH-responsive hydrogel (P-CHP407) was prepared from an ad hoc synthesized amphiphilic poly(ether urethane) (CHP407) exposing a significant amount of –COOH groups (8.8 ± 0.9 nmol/g_polymer). The exposure of acid moieties in P-CHP407 hydrogel led to slightly lower initial gelation temperature (12.1 °C vs. 14.6 °C, respectively) and gelation rate than CHP407 hydrogel, as rheologically assessed. Nanoscale hydrogel characterization by Low Field NMR (LF-NMR) spectroscopy suggested that the presence of carboxylic groups in P-CHP407 caused the formation of bigger micelles with a thicker hydrated shell than CHP407 hydrogels, as further proved by Dynamic Light Scattering analyses. In addition, P-CHP407 hydrogel showed improved capability to change its internal pH compared to CHP407 one when incubated with an alkaline buffer (pH 8) (e.g., pH_{change_5min} = 3.76 and 1.32, respectively). Moreover, LF-NMR characterization suggested a stronger alkaline-pH-induced interaction of water molecules with micelles exposing –COOH groups. Lastly, the hydrogels were found biocompatible according to ISO 10993 and able to load and release Ibuprofen: delivery kinetics of Ibuprofen was enhanced by P-CHP407 hydrogels at alkaline pH, suggesting their potential use as smart delivery systems in the treatment of chronic infected wounds.

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Chronic infected wounds are characterized by the production of alkaline exudate.

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Multi-stimuli-responsive hydrogels are powerful tools to design smart drug carriers.

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Alkaline wound exudate can successfully guide drug release kinetics.

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Hydrogel thermosensitivity allows easy injectability in the wound site.

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LF-NMR describes nano-scale hydrogel structural changes in an alkaline environment.

Thin Film Analysis by Nanomechanical Infrared Spectroscopy

There is a fundamental need for techniques for thin film characterization. The current options for obtaining infrared (IR) spectra typically suffer from low signal-to-noise-ratios (SNRs) for sample thicknesses confined to a few nanometers. We present nanomechanical infrared spectroscopy (NAM-IR), which enables the measurement of a complete infrared fingerprint of a polyvinylpyrrolidone (PVP) layer as thin as 20 nm with an SNR of 307. Based on the characterization of the given NAM-IR setup, a minimum film thickness of only 160 pm of PVP can be analyzed with an SNR of 2. Compared to a conventional attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) system, NAM-IR yields an SNR that is 43 times larger for a 20 nm-thick PVP layer and requires only a fraction of the acquisition time. These results pave the way for NAM-IR as a highly sensitive, fast, and practical tool for IR analysis of polymer thin films.

Theoretical Importance of PVP-Alginate Hydrogels Structure on Drug Release Kinetics

BACKGROUND

The new concepts of personalized and precision medicine require the design of more and more refined delivery systems. In this frame, hydrogels can play a very important role as they represent the best surrogate of soft living tissues for what concerns rheological properties. Thus, this paper focusses on a global theoretical approach able to describe how hydrogel polymeric networks can affect the release kinetics of drugs characterized by different sizes. The attention is focused on a case study dealing with an interpenetrated hydrogel made up by alginate and poly(N-vinyl-2-pyrrolidone).

METHODS

Information about polymeric network characteristics (mesh size distribution and polymer volume fraction) is deduced from the theoretical interpretation of the rheological and the low field Nuclear Magnetic Resonance (NMR) characterization of hydrogels. This information is then, embodied in the mass balance equation whose resolution provides the release kinetics.

RESULTS

Our simulations indicate the influence of network characteristics on release kinetics. In addition, the reliability of the proposed approach is supported by the comparison of the model outcome with experimental release data.

CONCLUSIONS

This study underlines the necessity of a global theoretical approach in order to design reliable delivery systems based on hydrogels.

Combined Used of Rheology and LF-NMR for the Characterization of PVP-Alginates Gels Containing Liposomes

PURPOSE

This paper is based on the characterization of the rheological and Low Field NMR (LF-NMR) properties of an interpenetrated hydrogel made up by poly(N-vinyl-2-pyrrolidone) and sodium alginate. The final aim is to use the hydrogel as a delivery matrix for liposomes, widely used tools in the drug delivery field.

METHODS

Rheology, LF-NMR, TEM, cryo-TEM, confocal laser scanning microscopy and release test were employed to characterize the interpenetrated hydrogel. Different theoretical approaches such as Flory, Chui, Scherer and Schurz theories were used to interpret the experimental results.

RESULTS

We found that the crosslinking mechanisms of the two polymers produced an anti-synergistic effect on the final mechanical properties of the interpenetrated hydrogel. Instead of creating a continuous network, alginate formed isolated, cross-linked, clusters embedded in a continuous network of poly(N-vinyl-2-pyrrolidone). Additionally, gel structure significantly influenced liposome delivery.

CONCLUSIONS

The rheological and LF-NMR characterization were confirmed and supported by the independent techniques TEM, cryo-TEM and release tests Thus, our findings reiterate the potentiality of both rheology and LF-NMR for the characterisation of soft materials such as interpenetrated polymeric networks.

Oxidized Nanocarbons-Tripeptide Supramolecular Hydrogels: Shape Matters!

Short peptide hydrogels are attractive biomaterials but typically suffer from limited mechanical properties. Inclusion of other nanomaterials can serve the dual purpose of hydrogel reinforcement and of conferring additional physicochemical properties ( e. g., self-healing, conductivity), as long as they do not hamper peptide self-assembly. In particular, nanocarbons are ideal candidates, and their physicochemical properties have demonstrated great potential in nanocarbon-polymer gel biomaterials for tissue engineering or drug delivery. Recently, increasing interest in supramolecular hydrogels drove research also on their enhancement with nanocarbons. However, little is known on the effect of nanocarbon morphology on the self-assembly of short peptides, which are among the most popular hydrogel building blocks. In this work, three different oxidized nanocarbons ( i. e., carbon nanotube or CNT as 1D material, graphene oxide sheet or GO as 2D material, and carbon nanohorn or CNH as 3D material) were evaluated for their effects on the self-assembly of the unprotected tripeptide Leu-^DPhe-^DPhe at physiological conditions. Supramolecular hydrogels were obtained in all cases, and viscoelastic properties were clearly affected by the nanocarbons, which increased stiffness and resistance to applied stress. Notably, self-healing behavior was observed only in the case of CNTs. Tripeptide-nanotube interaction was noted already in solution prior to self-assembly, with the tripeptide acting as a dispersing agent in phosphate buffer. Experimental and in silico investigation of the interaction between peptide and CNTs suggests that the latter acts as nucleation templates for self-assembly and reassembly. Overall, we provide useful insights for the future design of composite biomaterials with acquired properties.

A novel approach based on low-field NMR for the detection of the pathological components of sputum in cystic fibrosis patients

PURPOSE

Development of a reliable, simple method to monitor lung condition in cystic fibrosis (CF) patients. Lung functionality assessment in CF patients is relevant, as most of them still die of respiratory failure. In lung mucus (sputum) of CF patients, components such as proteins, biopolymers, DNA, bacteria, and mucin are pathologically increased. As lung functionality is related to the amount of the pathological components in the sputum, their determination can help clinicians in monitoring lung condition and planning therapy.

METHODS

Low-field NMR was used to evaluate the variation of the relaxation time (T_2m ) of the water hydrogens present in CF sputum in relation to the amounts of the pathological components. Low-field NMR was tested in artificial samples (mucin or alginates), then in conditional sputum (saliva from healthy volunteers, added by different amounts of the pathological components), and finally in 12 patients' sputums, in which T_2m was correlated to a commonly used lung monitoring test (i.e., forced expiratory volume in the first second).

RESULTS

T_2m significantly (P < 0.05) differed between samples with and without pathological components and between healthy and CF patients (P < 0.05), in which T_2m correlated (r = 0.87) with FEV₁ .

CONCLUSIONS

The presented method can potentially become a valuable lung-monitoring tool in CF patients. Magn Reson Med 79:2323-2331, 2018. © 2017 International Society for Magnetic Resonance in Medicine.