Injectable Hybrid Hydrogels, with Cell-Responsive Degradation, for Tumor Resection

A review of hydrogels used in endoscopic submucosal dissection for intraoperative submucosal cushions and postoperative management

Endoscopic submucosal dissection (ESD) has been clinically proved to have prominent advantages in the treatment of early gastrointestinal cancers over traditional surgery, including less trauma, fewer complications, a quicker recovery and lower costs. During the procedure of ESD, appropriate and multifunctional submucosal injected materials (SIMs) as submucosal cushions play an important role, however, even with many advances in design strategies of SIMs over the past decades, the performance of the submucosal cushions with postoperative management function seems to be still unsatisfactory. In this review, we gave a brief historical recount about the clinical development of SIMs, then some common applications of hydrogels used as SIMs in ESD were summarized, while an account of the universal challenges during ESD procedure was also outlined. Going one step further, some cutting-edge functional strategies of hydrogels for novel applications in ESD were exhibited. Finally, we concluded the advantages of hydrogels as SIMs for ESD as well as the treatment dilemma clinicians faced when it comes to deeply infiltrated lesions, some technical perspectives about linking the clinical demand with commercial supply were also proposed. Encompassing the basic elements of SIMs used in ESD surgery and the corresponding postoperative management requirements, this review could be a good reference for relevant practitioners in expanding the research horizon and improving the well-being index of patients.

Rheology of Pseudomonas fluorescens biofilms: From experiments to predictive DPD mesoscopic modeling

Bacterial biofilms mechanically behave as viscoelastic media consisting of micron-sized bacteria cross-linked to a self-produced network of extracellular polymeric substances (EPSs) embedded in water. Structural principles for numerical modeling aim at describing mesoscopic viscoelasticity without losing details on the underlying interactions existing in wide regimes of deformation under hydrodynamic stress. Here, we approach the computational challenge to model bacterial biofilms for predictive mechanics in silico under variable stress conditions. Up-to-date models are not entirely satisfactory due to the plethora of parameters required to make them functioning under the effects of stress. As guided by the structural depiction gained in a previous work with Pseudomonas fluorescens [Jara et al., Front. Microbiol. 11, 588884 (2021)], we propose a mechanical modeling by means of Dissipative Particle Dynamics (DPD), which captures the essentials of topological and compositional interactions between bacterial particles and cross-linked EPS-embedding under imposed shear. The P. fluorescens biofilms have been modeled under mechanical stress mimicking shear stresses as undergone in vitro. The predictive capacity for mechanical features in DPD-simulated biofilms has been investigated by varying the externally imposed field of shear strain at variable amplitude and frequency. The parametric map of essential biofilm ingredients has been explored by making the rheological responses to emerge among conservative mesoscopic interactions and frictional dissipation in the underlying microscale. The proposed coarse grained DPD simulation qualitatively catches the rheology of the P. fluorescens biofilm over several decades of dynamic scaling.

Injectable shear-thinning sodium alginate hydrogels with sustained submucosal lift for endoscopic submucosal dissection

Endoscopic submucosal dissection (ESD) is one of the most effective approaches for the minimally invasive treatment of early gastrointestinal cancers. Submucosal injections help safely and successfully remove lesions during ESD by elevating the mucosa and separating the submucosal muscle layer. Herein, we report dynamic injectable sodium alginate hydrogels (ISAHs) with shear-thinning for ESD surgery, which were easily fabricated by the sulfhydryl group of GSH-modified sodium alginate (SA-GSH) reacting with the aldehyde group of oxidized sodium alginate (OSA) at room temperature. ISAHs have advantageous self-healing abilities and antioxidant activity. Additionally, according to an in vitro test on porcine colorectal submucosal lifting, the submucosal elevation heights created by ISAHs were 13 % -18 % greater than those created by commercial ESD solutions (0.4 w/v% sodium hyaluronate). These properties and biocompatibility were confirmed in vitro and in vivo experiments. ISAHs will hopefully become a novel submucosal injectable hydrogel to assist ESD surgery.

Redox-Responsive Hydrogels with Decoupled Initial Stiffness and Degradation

Disulfide-cross-linked hydrogels have been widely used for biological applications because of their degradability in response to redox stimuli. However, degradability often depends on polymer concentration, which also influences the hydrogel mechanical properties such as the initial stiffness. Here, we describe a one-pot cross-linking approach utilizing both a thiol-ene reaction through a Michael pathway with divinyl sulfone (DVS) to form non-reducible thioether bonds and thiol oxidation promoted by ferric ethylenediaminetetraacetic acid (Fe-EDTA) to form reducible disulfide bonds. The ratio between these two bonds was modulated by varying the DVS concentration used, and the initial shear or elastic modulus and degradation rate of the hydrogels were decoupled. These gels had tunable release rates of encapsulated dextran when exposed to 10 μM glutathione. Fibroblast encapsulation results suggested good cytocompatibility of the cross-linking reactions. This work shows the potential of combining DVS and Fe-EDTA to create thiol-cross-linked hydrogels as redox-responsive drug delivery vehicles and tissue engineering scaffolds with variable degradability.

Image-Guided Surgical Simulation in Minimally Invasive Liver Procedures: Development of a Liver Tumor Porcine Model Using a Multimodality Imaging Assessment

Background: Image-guided liver surgery and interventions are growing as part of the current trend to translate liver procedures into minimally invasive approaches. Hands-on surgical training in such techniques is required. Consequently, a meaningful and realistic liver tumor model using multi-imaging modalities, such as ultrasound (US), computed tomography (CT), magnetic resonance (MR), cone beam-CT (CBCT), is mandatory. The first aim of this study is to develop a novel tumor-mimic model and assess it with multi-imaging modalities. The second aim is to evaluate the usefulness of the model during image-guided liver procedures. Materials and Methods: The tumor-mimic model is made of a composition of hydrogel, smashed muscle, and gadolinium contrast solution. Five ex vivo livers and three pigs were included in the study. Procedures were performed in an experimental hybrid operating room. Under general anesthesia, US guidance was required to inject the biotumor formula into the pig's liver. US, CT, CBCT, and MR acquisitions were then performed after the initial injection. In vivo models were then used to perform liver procedures, including US-guided biopsy, radiofrequency ablation, and laparoscopic resection. Results: The formula developed is easily injected generating a tissue-like material. Visualization using multi-imaging modalities was appropriate, thereby allowing to perform image-guided techniques. Conclusion: A novel design of an in vivo and ex vivo tissue-like tumor liver model is presented. Due to the multimodality imaging appraisal, it may provide a realistic and meaningful model allowing to perform image-guided liver procedures.

Injectable Self-Healing Adhesive pH-Responsive Hydrogels Accelerate Gastric Hemostasis and Wound Healing

Endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD) are well-established therapeutics for gastrointestinal neoplasias, but complications after EMR/ESD, including bleeding and perforation, result in additional treatment morbidity and even threaten the lives of patients. Thus, designing biomaterials to treat gastric bleeding and wound healing after endoscopic treatment is highly desired and remains a challenge. Herein, a series of injectable pH-responsive self-healing adhesive hydrogels based on acryloyl-6-aminocaproic acid (AA) and AA-g-N-hydroxysuccinimide (AA-NHS) were developed, and their great potential as endoscopic sprayable bioadhesive materials to efficiently stop hemorrhage and promote the wound healing process was further demonstrated in a swine gastric hemorrhage/wound model. The hydrogels showed a suitable gelation time, an autonomous and efficient self-healing capacity, hemostatic properties, and good biocompatibility. With the introduction of AA-NHS as a micro-cross-linker, the hydrogels exhibited enhanced adhesive strength. A swine gastric hemorrhage in vivo model demonstrated that the hydrogels showed good hemostatic performance by stopping acute arterial bleeding and preventing delayed bleeding. A gastric wound model indicated that the hydrogels showed excellent treatment effects with significantly enhanced wound healing with type I collagen deposition, α-SMA expression, and blood vessel formation. These injectable self-healing adhesive hydrogels exhibited great potential to treat gastric wounds after endoscopic treatment.

Development of Spirulina sea-weed raw extract/polyamidoamine hydrogel system as novel platform in photodynamic therapy: Photostability and photoactivity of chlorophyll a

The aim of this paper is to present and characterize Polyamidoamine-based hydrogels (PAA) as scaffolds to host photoactive Chlorophyll a (Chl a) from Spirulina (Arthrospira platensis) sea-weed Extract (SE), for potential applications in Photodynamic Therapy (PDT). The pigment extracted from SE was blended inside PAA without further purification, according to Green Chemistry principles. A comprehensive investigation of this hybrid platform, PAA/SE-based, was thus performed in our laboratory and, by means of Visible absorption and emission spectroscopies, the Chl a features, stability and photoactivity were studied. The obtained results evidenced the presence of two main Chl a forms, monomeric and dimeric, interacting with hydrogel polyamidoamines network. To better understand the nature of this interaction, the spectroscopic investigation of this system was performed both before and after the solidification of the hydrogel, that occurred at least in 24 h. Then, focusing the attention on solid scaffold, the ¹Chl a^⁎ fluorescence lifetime and FTIR-ATR analyses of PAA/SE were carried out, confirming the findings. The swelling and Point Zero Charge (PZC) measurements of solid PAA and PAA/SE were additionally performed to investigate the hydrogel behavior in water. Chl a molecules blended in PAA were (photo) stable and photoactive, and this latter feature was demonstrated showing that the pigment induced, when swelled in water and under irradiation, the formation of singlet oxygen (¹O₂), measured by direct and indirect methods.

Injectable, self-healing mesoporous silica nanocomposite hydrogels with improved mechanical properties

Self-healing hydrogels have emerged as promising biomaterials in regenerative medicine applications. However, an ongoing challenge is to create hydrogels that combine rapid self-healing with high mechanical strength to make them applicable to a wider range of organs/tissues. Incorporating nanoparticles within hydrogels is a popular strategy to improve the mechanical properties as well as to provide additional functionalities such as stimuli responsiveness or controlled drug delivery, further optimizing their use. In this context, mesoporous silica nanoparticles (MSNs) are promising candidates as they are bioactive, improve mechanical properties, and can controllably release various types of cargo. While commonly nanoparticles are added to hydrogels as filler component, in the current study we developed thiol surface-functionalized MSNs capable of acting as chemical crosslinkers with a known hydrophilic polymer, polyethylene glycol (PEG), through dynamic thiol-disulfide covalent interactions. Due to these dynamic exchange reactions, mechanically strong nanocomposites with a storage modulus of up to 32 ± 5 kPa compared to 1.3 ± 0.3 kPa for PEG hydrogels alone, with rapid self-healing capabilities, could be formed. When non-surface modified MSNs were used, the increase in storage modulus of the hydrogels was significantly lower (3.4 ± 0.7 kPa). In addition, the nanocomposites were shown to degrade slowly over 6 weeks upon exposure to glutathione while remaining intact at physiological conditions. Together, the data argue that creating nanocomposites using MSNs as dynamic crosslinkers is a promising strategy to confer mechanical strength and rapid self-healing capabilities to hydrogels. This approach offers new possibilities for creating multifunctional self-healing biomaterials for a wider range of applications in regenerative medicine.

In Situ Forming, Silanized Hyaluronic Acid Hydrogels with Fine Control Over Mechanical Properties and In Vivo Degradation for Tissue Engineering Applications

In situ forming hydrogels that can be injected into tissues in a minimally-invasive fashion are appealing as delivery vehicles for tissue engineering applications. Ideally, these hydrogels should have mechanical properties matching those of the host tissue, and a rate of degradation adapted for neo-tissue formation. Here, the development of in situ forming hyaluronic acid hydrogels based on the pH-triggered condensation of silicon alkoxide precursors into siloxanes is reported. Upon solubilization and pH adjustment, the low-viscosity precursor solutions are easily injectable through fine-gauge needles prior to in situ gelation. Tunable mechanical properties (stiffness from 1 to 40 kPa) and associated tunable degradability (from 4 days to more than 3 weeks in vivo) are obtained by varying the degree of silanization (from 4.3% to 57.7%) and molecular weight (120 and 267 kDa) of the hyaluronic acid component. Following cell encapsulation, high cell viability (> 80%) is obtained for at least 7 days. Finally, the in vivo biocompatibility of silanized hyaluronic acid gels is verified in a subcutaneous mouse model and a relationship between the inflammatory response and the crosslink density is observed. Silanized hyaluronic acid hydrogels constitute a tunable hydrogel platform for material-assisted cell therapies and tissue engineering applications.

Novel Polymeric Formulation for Removal of Gastrointestinal Polyps by Digestive Endoscopy

Endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD) are two techniques used in the resection of gastrointestinal mucosal polyps. The aim of this work is the development and evaluation of an innovative polymeric solution containing sodium carboxymethylcellulose and hyaluronic acid. For this purpose, several mixtures of these two main components, as well as other components such as fructose, citric acid, and zinc, are evaluated in terms of physicochemical and microbiological properties, rheological behavior, extensibility, syringeability, and stability at different storage conditions. Furthermore, the potential production of mucosal elevation and duration is also studied by an ex vivo model using porcine stomach and colon. Results show that the developed polymeric solutions possess optimal values of pH, from 4.58 to 6.63, for their use in the gastrointestinal tract. The formulations exhibit both Newtonian and pseudoplastic behaviors with different viscosity values as a function of their composition. All formulations exhibit high stability properties and no bacterial or fungal growth is detected. MCS01 and MCS05 are the polymeric solutions with the best syringeability results. In this line, MCS05 is the formulation that provides the highest, 2.20 ± 0.18 cm and 1.40 ± 0.11 cm, and longest-lasting, for more than 120 min, elevation effect on porcine submucosal stomach and colon tissues, respectively. Thus, it can be concluded that polymeric solution MCS05 might be considered as a promising tool for use in human EMR and ESD.

Design of Nanocomposite Injectable Hydrogels for Minimally Invasive Surgery

Biocompatible hydrogels are materials that hold great promise in medicine and biology since the porous structure, the ability to entrap a large amount of water, and the tunability of their mechanical and tissue adhesive properties make them suitable for several applications, including wound healing, drug and cell delivery, cancer treatment, bioelectronics, and tissue regeneration. Among the possible developed systems, injectable hydrogels, owing to their properties, are optimal candidates for in vivo minimally invasive procedures. To be injectable, a hydrogel must be liquid before and during the injection, but it must quickly jellify after injection to form a soft, self-standing, solid material. The possibility to work with a liquid precursor encoding the functions that will be available after gelation allows the development of biocompatible materials that can be employed in surgery and, in particular, in noninvasive procedures. The underlying idea is to reach the target tissue by using just a needle, or by exploiting the natural body orifices, reducing surgery procedure time, induced pain, and risk of infections. Hydrogels with different properties can be obtained by changing the type of cross-linking, the cross-linking density or the molecular weight of the polymer, or by introducing pending functional groups. The introduction of a nanofiller in the hydrogel network allows for expanding the suite of the structural and functional properties and for better mimicking native tissues. In this Account, we discuss how to provide a hydrogel network with designed properties by playing with both the polymeric chains and the fillers. We present selected examples from the literature that show how to introduce stiffness, stretchability, adhesiveness, self-healing, anisotropy, antimicrobial activity, biodegradability, and conductivity in injectable hydrogels. We further describe how the chemical composition, the mechanical properties, and the microarchitecture of the hydrogel influence cell adhesion, proliferation, and differentiation. Examples of injectable hydrogels for innovative minimally invasive procedures are then discussed in detail; in particular, we showcase the use of hydrogels for tumor resection and as vascular chemoembolization agents. We further discuss how one can improve the rheological properties of injectable hydrogels to exploit them in osteochondral tissue engineering. The effect of the introduction of a conductive filler is then presented in relation to the development of electroactive scaffolds for cardiac-tissue engineering and neural and nerve repair. We believe that the rational design of biocompatible, injectable hybrid hydrogels with tunable properties will likely play a crucial role in reducing the invasiveness and improving the outcome of several clinical and surgical setups.