Bioinspired Anti-digestive Hydrogels Selected by a Simulated Gut Microfluidic Chip for Closing Gastrointestinal Fistula

In situ bioprinting of double network anti-digestive xanthan gum derived hydrogel scaffolds for the treatment of enterocutaneous fistulas

The clinical treatment of enterocutaneous fistula is challenging and causes significant patient discomfort. Fibrin gel can be used to seal tubular enterocutaneous fistulas, but it has low strength and poor digestion resistance. Based on in situ bioprinting and the anti-digestive properties of xanthan gum (XG), we used carboxymethyl chitosan (CMC) and xanthan gum modified by grafted glycidyl methacrylate (GMA) and aldehyde (GCX) as the ink to print a double network hydrogel that exhibited high strength and an excellent anti-digestive performance. In addition, in vitro studies confirmed the biocompatibility, degradability, and self-healing of hydrogels. In our rabbit tubular enterocutaneous fistula model, the in situ printed hydrogel resisted corrosion due to the intestinal fluid and acted as a scaffold for intestinal mucosal cells to proliferate on its surface. To summarize, in situ bioprinting GCX/CMC double network hydrogel can effectively block tubular enterocutaneous fistulas and provide a stable scaffold for intestinal mucosal regeneration.

Microfluidic intestinal organoid-on-a-chip uncovers therapeutic targets by recapitulating oxygen dynamics of intestinal IR injury

Increasing evidence demonstrates that mammals have different reactions to hypoxia with varied oxygen dynamic patterns. It takes ∼24 h for tri-gas incubator to achieve steady cell hypoxia, which fails to recapitulate ultrafast oxygen dynamics of intestinal ischemia/reperfusion (IR) injury. Inspired from the structure of native intestinal villi, we engineered an intestinal organoid chip embedded with engineered artificial microvessels based on co-axial microfluidic technology by using pH-responsive ZIF-8/sodium alginate scaffold. The chip was featured on: (i) eight times the oxygen exchange efficiency compared with the conventional device, tri-gas incubator, (ii) implantation of intestinal organoid reproducing all types of intestinal epithelial cells, and (iii) bio-responsiveness to hypoxia and reoxygenation (HR) by presenting metabolism disorder, inflammatory reaction, and cell apoptosis. Strikingly, it was found for the first time that Olfactomedin 4 (Olfm4) was the most significantly down-regulated gene under a rapid HR condition by sequencing the RNA from the organoids. Mechanistically, OLFM4 played protective functions on HR-induced cell inflammation and tissue damage by inhibiting the NF-kappa B signaling activation, thus it could be used as a therapeutic target. Altogether, this study overcomes the issue of mismatched oxygen dynamics between in vitro and in vivo, and sets an example of next-generation multisystem-interactive organoid chip for finding precise therapeutic targets of IR injury.

Nanocomposite hydrogel based on chitosan/laponite for sealing and repairing tracheoesophageal fistula

Tracheoesophageal fistula (TEF) is an abnormal connection between the trachea and esophagus that severely impairs quality of life. Current treatment options have limitations, including conservative treatment, surgical repair, and esophageal stent implantation. Here, we introduced laponite (LP) nano-clay to improve chitosan-based hydrogels' rheological properties and mechanical properties and developed an endoscopically injectable nanocomposite shear-thinning hydrogel to seal and repair fistulas as an innovative material for the treatment of TEF. Excellent injectability, rheological properties, mechanical strength, self-healing, biodegradability, biocompatibility, and tissue repair characterize the new hydrogel. The introduction of LP nano-clay improves the gel kinetics problem of hydrogels to realize the sol-gel transition immediately after injection, avoiding gel flow to non-target sites. The addition of LA nano-clay can significantly improve the rheological properties and mechanical strength of hydrogels, and hydrogel with LP content of 3 % shows better comprehensive performance. The nanocomposite hydrogel also shows good cytocompatibility and can promote wound repair by promoting the migration of HEEC cells and the secretion of VEGF and FGF. These findings suggest that this nanocomposite hydrogel is a promising biomaterial for TEF treatment.

Injectable Zn2+ and Paeoniflorin Release Hydrogel for Promoting Wound Healing

As more and more superbugs emerge, wounds are struggling to heal due to the inflammation that accompanies infection. Therefore, there is an urgent need to reduce the abuse of antibiotics and find nonantibiotic antimicrobial methods to counter infections to accelerate wound healing. In addition, common wound dressings struggle to cover irregular wounds, causing bacterial invasion or poor drug release, which reduces the wound healing rate. In this study, Chinese medicinal monomer paeoniflorin which can inhibit inflammation is loaded in mesoporous zinc oxide nanoparticles (mZnO), while Zn²⁺ released from mZnO degradation can kill bacteria and facilitate wound healing. The drug-loaded mZnO was encapsulated by a hydrogel formed from oxidized konjac glucomannan and carboxymethyl chitosan via rapid Schiff base reaction to obtain an injectable drug-releasing hydrogel wound dressing. The immediate-formation hydrogel allows the dressing to cover any wound shape. In vitro and in vivo studies have demonstrated that the dressing has good biocompatibility and superior antibacterial properties, which can promote wound healing and tissue regeneration by promoting angiogenesis and collagen production, providing a promising perspective for the further development of multifunctional wound dressings.

Bioinspired Hydrogels as Platforms for Life-Science Applications: Challenges and Opportunities

Hydrogels, as interconnected networks (polymer mesh; physically, chemically, or dynamic crosslinked networks) incorporating a high amount of water, present structural characteristics similar to soft natural tissue. They enable the diffusion of different molecules (ions, drugs, and grow factors) and have the ability to take over the action of external factors. Their nature provides a wide variety of raw materials and inspiration for functional soft matter obtained by complex mechanisms and hierarchical self-assembly. Over the last decade, many studies focused on developing innovative and high-performance materials, with new or improved functions, by mimicking biological structures at different length scales. Hydrogels with natural or synthetic origin can be engineered as bulk materials, micro- or nanoparticles, patches, membranes, supramolecular pathways, bio-inks, etc. The specific features of hydrogels make them suitable for a wide variety of applications, including tissue engineering scaffolds (repair/regeneration), wound healing, drug delivery carriers, bio-inks, soft robotics, sensors, actuators, catalysis, food safety, and hygiene products. This review is focused on recent advances in the field of bioinspired hydrogels that can serve as platforms for life-science applications. A brief outlook on the actual trends and future directions is also presented.

Tissue engineering of the gastrointestinal tract: the historic path to translation

The gastrointestinal (GI) tract is imperative for multiple functions including digestion, nutrient absorption, and timely waste disposal. The central feature of the gut is peristalsis, intestinal motility, which facilitates all of its functions. Disruptions in GI motility lead to sub-optimal GI function, resulting in a lower quality of life in many functional GI disorders. Over the last two decades, tissue engineering research directed towards the intestine has progressed rapidly due to advances in cell and stem-cell biology, integrative physiology, bioengineering and biomaterials. Newer biomedical tools (including optical tools, machine learning, and nuanced regenerative engineering approaches) have expanded our understanding of the complex cellular communication within the GI tract that lead to its orchestrated physiological function. Bioengineering therefore can be utilized towards several translational aspects: (i) regenerative medicine to remedy/restore GI physiological function; (ii) in vitro model building to mimic the complex physiology for drug and pharmacology testing; (iii) tool development to continue to unravel multi-cell communication networks to integrate cell and organ-level physiology. Despite the significant strides made historically in GI tissue engineering, fundamental challenges remain including the quest for identifying autologous human cell sources, enhanced scaffolding biomaterials to increase biocompatibility while matching viscoelastic properties of the underlying tissue, and overall biomanufacturing. This review provides historic perspectives for how bioengineering has advanced over time, highlights newer advances in bioengineering strategies, and provides a realistic perspective on the path to translation.

Recent Development of Drug Delivery Systems through Microfluidics: From Synthesis to Evaluation

Conventional drug administration usually faces the problems of degradation and rapid excretion when crossing many biological barriers, leading to only a small amount of drugs arriving at pathological sites. Therapeutic drugs delivered by drug delivery systems to the target sites in a controlled manner greatly enhance drug efficacy, bioavailability, and pharmacokinetics with minimal side effects. Due to the distinct advantages of microfluidic techniques, microfluidic setups provide a powerful tool for controlled synthesis of drug delivery systems, precisely controlled drug release, and real-time observation of drug delivery to the desired location at the desired rate. In this review, we present an overview of recent advances in the preparation of nano drug delivery systems and carrier-free drug delivery microfluidic systems, as well as the construction of in vitro models on-a-chip for drug efficiency evaluation of drug delivery systems. We firstly introduce the synthesis of nano drug delivery systems, including liposomes, polymers, and inorganic compounds, followed by detailed descriptions of the carrier-free drug delivery system, including micro-reservoir and microneedle drug delivery systems. Finally, we discuss in vitro models developed on microfluidic devices for the evaluation of drug delivery systems, such as the blood–brain barrier model, vascular model, small intestine model, and so on. The opportunities and challenges of the applications of microfluidic platforms in drug delivery systems, as well as their clinical applications, are also discussed.

Bioinstructive Layer-by-Layer-Coated Customizable 3D Printed Perfusable Microchannels Embedded in Photocrosslinkable Hydrogels for Vascular Tissue Engineering

The development of complex and large 3D vascularized tissue constructs remains the major goal of tissue engineering and regenerative medicine (TERM). To date, several strategies have been proposed to build functional and perfusable vascular networks in 3D tissue-engineered constructs to ensure the long-term cell survival and the functionality of the assembled tissues after implantation. However, none of them have been entirely successful in attaining a fully functional vascular network. Herein, we report an alternative approach to bioengineer 3D vascularized constructs by embedding bioinstructive 3D multilayered microchannels, developed by combining 3D printing with the layer-by-layer (LbL) assembly technology, in photopolymerizable hydrogels. Alginate (ALG) was chosen as the ink to produce customizable 3D sacrificial microstructures owing to its biocompatibility and structural similarity to the extracellular matrices of native tissues. ALG structures were further LbL coated with bioinstructive chitosan and arginine–glycine–aspartic acid-coupled ALG multilayers, embedded in shear-thinning photocrosslinkable xanthan gum hydrogels and exposed to a calcium-chelating solution to form perfusable multilayered microchannels, mimicking the biological barriers, such as the basement membrane, in which the endothelial cells were seeded, denoting an enhanced cell adhesion. The 3D constructs hold great promise for engineering a wide array of large-scale 3D vascularized tissue constructs for modular TERM strategies.

Preclinical evaluation of a regenerative immiscible bioglue for vesico-vaginal fistula

Currently, there are no clinically available tissue adhesives that work effectively in the fluid-rich and highly dynamic environments of the human body, such as the urinary system. This is especially relevant to the management of vesico-vaginal fistula, and developing a high-performance tissue adhesive for this purpose could vastly expand urologists' surgical repertoire and dramatically reduce patient discomfort. Herein, we developed a water-immiscible mussel protein-based bioadhesive (imWIMBA) with significantly improved properties in all clinical respects, allowing it to achieve rapid and strong underwater adhesion with tunable rheological properties. We evaluated in vivo potential of imWIMBA for sealing thermally injured fistula tracts between the bladder and vagina. Importantly, the use of imWIMBA in the presence of prolonged bladder drainage resulted in perfect closure of the vesico-vaginal fistula in operated pigs. Thus, imWIMBA could be successfully used for many surgical applications and improve treatment efficacy when combined with conventional surgical methods. STATEMENT OF SIGNIFICANCE: Vesico-vaginal fistula (VVF) is an abnormal opening between the bladder and the vagina, which is a stigmatized disease in many developing countries. Leakage of urine into internal organs can induce serious complications and delay wound repair. Conventional VVF treatment requires skillful suturing to provide a tension-free and watertight closure. In addition, there is no clinically approved surgical glue that works in wet and highly dynamic environments such as the urinary system. In this work, for potential clinical VVF closure and regeneration, we developed an advanced immiscible mussel protein-based bioglue with fast, strong, wet adhesion and tunable rheological properties. This regenerative immiscible bioglue could be successfully used for sealing fistulas and further diverse surgical applications as an adjuvant for conventional suture methods.

Technique Advances in Enteroatmospheric Fistula Isolation After Open Abdomen: A Review and Outlook

Enteroatmospheric fistula (EAF) after open abdomen adds difficulties to the management and increases the morbidity and mortality of patients. As an effective measurement, reconstructing gastrointestinal tract integrity not only reduces digestive juice wasting and wound contamination, but also allows expedient restoration of enteral nutrition and intestinal homeostasis. In this review, we introduce several technologies for the temporary isolation of EAF, including negative pressure wound therapy, fistuloclysis, fistula patch, surgical covered stent, three-dimensional (3D) printing stent, and injection molding stent. The manufacture and implantation procedures of each technique with their pros and cons are described in detail. Moreover, the approach in combination with finger measurement, x-ray imaging, and computerized tomography is used to measure anatomic parameters of fistula and design appropriate 3D printer-recognizable stereolithography files for production of isolation devices. Given the active roles that engineers playing in the technology development, we call on the cooperation between clinicians and engineers and the organization of clinical trials on these techniques.

Photocross-linkable Methacrylated Polypeptides and Polysaccharides for Casting, Injecting, and 3D Fabrication

For modern tissue engineering, we need not only develop new hydrogels but also suitable processing methods for them. Polypeptides and polysaccharides are potential candidates because they can be methacrylated, processed before photocross-linking, and yielded into hydrogels with given shape and form. In this study, we successfully methacrylated collagen, gelatin, hyaluronan, and alginate to 30 and 60% degree of modification. We studied methacrylated compositions (i.e., precursors) to investigate their processability. The precursors of collagen and gelatin with 60% methacrylation exhibited suitable yield stress, shear-thinning properties, and fiber-forming capability for injecting and 3D bioprinting. On the contrary, the 30% methacrylated precursors had properties suitable for casting purposes. Our study also showed that the mechanical properties of hydrogels corresponded to the used photocross-linking conditions and the degree of modification. These results underline the importance of tunability of the precursors and resulting hydrogels according to the specific fabrication method and tissue engineering application.

Freeform 3D printing using a continuous viscoelastic supporting matrix

Embedded bio-printing has fostered significant advances toward the fabrication of soft complex tissue-like constructs, by providing a physical support that allows the freeform shape maintenance within the prescribed spatial arrangement, even under gravity force. Current supporting materials still present major drawbacks for up-scaling embedded 3D bio-printing technology towards tissue-like constructs with clinically relevant dimensions. Herein, we report a a cost-effective and widely available supporting material for embedded bio-printing consisting on a continuous pseudo-plastic matrix of xanthan-gum (XG). This natural polisaccharide exhibits peculiar rheological properties that have enabled the rapid generation of complex volumetric 3D constructs with out-of-plane features. The freedom of design within the three orthogonal axes through the independent and controlled bio-printing process opens new opportunities to produce on demand large arbitrary shapes for personalized medicine. Additionally, we have demonstrated the versatile functionality of XG as a photocurable gel reservoir to engineer perfused cell-laden hydrogel constructs, addressing other practical biomedical applications such as in vitro models and organ-on-chip platforms.

Biomaterials and biosensors in intestinal organoid culture, a progress review

As an emerging technology, intestinal organoids are promising new tools for basic and translational research in gastroenterology. Currently, culture of intestinal organoids relies mostly on a type of tumor-derived scaffolds, namely Matrigel, which may pose tumorigenic risks to organoid implantation. Apart from the traditional detection methods, such as tissue slicing and fluorescence staining, the monitoring of intestinal organoids requires real-time biosensors that can adapt to their three-dimensional dynamic growth patterns. In this review, we summarized the recent advances in developing definite hydrogel scaffolds for intestinal organoid culture and identified key parameters for scaffold design. In addition, classified by different substrate compositions like pH, electrolytes, and functional proteins, we concluded the existing live-imaging biosensors and elucidated their underlying mechanisms. We hope this review enhances the understanding of intestinal organoid culture and provides more practical approaches to investigate them.

Controlled release of silver ions from AgNPs using a hydrogel based on konjac glucomannan and chitosan for infected wounds

Konjac glucomannan is a biocompatible polysaccharide with high medicinal potential. In this study, we prepared a hydrogel using an optimized crosslinking konjac glucomannan and chitosan. Silver nanoparticles (AgNPs) were incorporated into the hydrogel to enhance its antimicrobial property. This nanocomposite hydrogel could absorb wound exudates due to its swelling ability, and showed self-healing property that enabled structure stability. Moreover, as a carrier, the hydrogel could modulate the release of silver ions burst, thereby reducing AgNPs cytotoxicity. Rats models with infected skin defects were used to assess wound healing. The results indicated that AgNPs hydrogels dressing could promote wound healing and reduce inflammatory response, exhibiting great clinical application potentials.

Engineering an adhesive based on photosensitive polymer hydrogels and silver nanoparticles for wound healing

Adhesives developed possess a good hemostatic effect. Attractively, agents loaded into the adhesives could exert sustained excellent antibacterial properties.

A polypropylene mesh coated with interpenetrating double network hydrogel for local drug delivery in temporary closure of open abdomen

Prosthetic materials are widely used for temporary abdominal closure after open abdomen (OA), but local adhesion, erosion and fistula formation caused by current materials seriously affect the quality of life of patients. Recently, a three-dimensional porous network structure hydrogel has been used to simulate cell extracellular matrix that can support cell growth and tissue regeneration. In this study, we prepared an interpenetrating double-network hydrogel by photoinitiating glycidyl methacrylate-conjugated xanthan (XG) and 4-arm polyethylene glycol thiol (TPEG). This double-network hydrogel combined stiffness and deformation ability as well as in situ forming property, which could coat polypropylene (PP) mesh to reduce friction to wound tissues. Moreover, this double-network hydrogel exhibited a denser porous structure that controlled drug release without initial outburst. When testing the hydrogel-coated growth factor-loaded PP mesh on a rat model of OA, it was found that this composite material could reduce inflammation and promote granulation tissue growth. Therefore, our design provides a new strategy of material-assisted wound protection of OA and shows potential clinical applications.

Prosthetic materials are widely used for temporary abdominal closure after open abdomen (OA), but local adhesion, erosion and fistula formation caused by current materials seriously affect the quality of life of patients.

Sandwich-structure hydrogels implement on-demand release of multiple therapeutic drugs for infected wounds

Wound infections bring huge challenges to clinical practice. A series of approaches are involved in the management of infected wounds including use of antibacterial agents, granulation tissue regeneration and scar prevention. In this study, we fabricated a sandwich-structure hydrogel dressing through layer-by-layer assembly of films and hydrogels. By pre-loading silver nanoparticles (AgNPs), vascular endothelial growth factors (VEGF) and ginsenoside Rg3 (Rg3) into each layer of the sandwich compound, this hydrogel could realize the sequential release of these drugs onto infected wound beds as demanded. Moreover, altering the thickness of middle layer could further change the drug delivery patterns characterized by delay at the initial releasing timepoint. When applying this dressing on infected wounds of rabbit ears, we found it could alleviate infection-induced inflammation, promote granulation tissue regeneration and inhibit scar formation. Collectively, the design of sandwich-structure hydrogels was facilitated to deliver specific drugs sequentially during their therapeutic time window for complicated diseases and has shown potential applications in infected wounds.

Wound infections bring huge challenges to clinical practice.

Hybrid material for open abdomen: saving the wound from intestinal fistula

Treatment of an open abdomen (OA) wound combined with an intestinal fistula is a challenge in the clinic. Here, inspired by the antibacterial activity of graphene (G) and its derivatives, we present a hybrid patch based on the ability of graphene and polycaprolactone (PCL) to kill bacteria and save the cells in a wound. Benefiting from the antibacterial ability of graphene oxide (GO), cells could survive in the presence of bacteria. With the increased ability to protect cells, this patch accelerated wound healing in an OA and intestinal fistula wound model. Additionally, the sub-acute toxicity score showed no extra damage to organs. In conclusion, the employment of the hybrid material for an OA and an intestinal fistula wound healing is encouraging. A hybrid patch based on graphene oxide and polycaprolactone electrospun was generated for open abdomen and fistula wound. The application of the hybrid patch could save the cells from bacteria which contribute to accelerating wound healing.

Gut bioengineering promotes gut repair and pharmaceutical research: a review

The gastrointestinal (GI) tract has a diverse set of physiological functions, including peristalsis, immune defense, and nutrient absorptions. These functions are mediated by various intestinal cells such as epithelial cells, interstitial cells, smooth muscle cells, and neurocytes. The loss or dysfunction of specific cells directly results in GI disease, while supplementation of normal cells promotes gut healing. Gut bioengineering has been developing for this purpose to reconstruct the damaged tissues. Moreover, GI tract provides an accessible route for drug delivery, but the collateral damages induced by side effects cannot be ignored. Bioengineered intestinal tissues provide three-dimensional platforms that mimic the in vivo environment to study drug functions. Given the importance of gut bioengineering in current research, in this review, we summarize the advances in the technologies of gut bioengineering and their applications. We were able to identify several ground-breaking discoveries in our review, while more work is needed to promote the clinical translation of gut bioengineering.

Application of a 3D-printed ”fistula stent” in plugging enteroatmospheric fistula with open abdomen: A case report

BACKGROUND

Open abdomen (OA) has been generally accepted for its magnificent superiority and effectiveness in patients with severe trauma, severe intra-abdominal infection, and abdominal compartment syndrome. In the meantime, OA calls for a mass of nursing and the subsequent enteroatomospheric fistula (EAF), which is one of the most common complications of OA therapy, remains a thorny challenge.

CASE SUMMARY

Our team applied thermoplastic polyurethane as a befitting material for producing a 3D-printed “fistula stent” in the management of an EAF patient, who was initially admitted to local hospital because of abdominal pain and distension and diagnosed with bowel obstruction. After a series of operations and OA therapy, the patient developed an EAF.

CONCLUSION

Application of this novel “fistula stent” resulted in a drastic reduction in the amount of lost enteric effluent and greatly accelerated rehabilitation processes.

Early Active Drainage by Fine Tube Bundles Improves the Clinical Outcome of Anastomotic Leak after Abdominal Surgery: A Pilot Randomized, Controlled Trial in Two Tertiary Hospitals in China

BACKGROUND

Post-operative anastomotic leak (PAL) is the most feared complication after abdominal surgery. Timely drainage of enteric effluent is beneficial in the healing of PAL.

METHODS

We introduced a new and feasible approach for early active drainage of PAL using fine tube bundles (FTBs). The therapeutic effects of FTBs were observed prospectively and compared with the traditional drainage tube without FTBs in a non-blinded randomized controlled trial.

RESULTS

Sixty patients with PAL in two tertiary hospitals in China from 2010 to 2016 were included in this study. Of these patients, 30 received FTBs and 30 were treated with a traditional drainage tube. The implantation failure rate was zero in the FTB group. No statistical difference was observed between the two groups in terms of demographic data. After these interventions, patients in the FTB group showed a faster decline in infection-related indictors, a higher ratio of spontaneous PAL closure, and shorter treatment duration of antibacterial agents compared with those in the traditional drainage tube group. Fatal complications and financial cost were also reduced in the FTB group.

CONCLUSION

Fine tube bundles may contribute to the healing of PAL through active drainage. This method should be validated by further clinical trials for wider use.