Hydrogels for Engineering of Perfusable Vascular Networks

Injectable hydrogels for treating skin injuries in diabetic animal models: a systematic review

Purpose

One of the main causes of chronic wounds is diabetes mellitus (DM), a metabolic disease characterized by chronic hyperglycemia. In this context, hydrogels have been used as a promising treatment for stimulating tissue ingrowth and healing in these injuries. This systematic review aimed to evaluate the findings of studies that investigated the effects of injectable hydrogels of various origins on skin wound healing using in vivo experimental models in diabetic rats.

Methods

This review was conducted in March 2023 using two databases, PubMed and Scopus, following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) guidelines and the SYRCLE (Systematic Review Centre for Laboratory Animal Experimentation). The following Medical Subject Headings (MeSH) descriptors were used: "hydrogels," "injectable," "in vivo," "diabetes mellitus," and "skin wound dressing."

Results

After the eligibility assessment, 12 studies were selected and analyzed from an initial 95 articles identified across databases. The studies demonstrated that a variety of injectable hydrogels showed biocompatibility and bioactivity, effectively interacting with skin tissue in diabetic wound models. These hydrogels were assessed for their compositions, structural properties, and in vivo effects on wound closure, inflammation reduction, and collagen deposition. Also, immunofluorescence analyses revealed increased expression of neoangiogenesis markers and reduced inflammatory factors in treated groups, highlighting the hydrogels potential for enhancing skin healing in diabetic wounds.

Conclusion

Injectable hydrogels show significant potential as an effective treatment for diabetic skin wounds, though further clinical studies are needed to fully assess their biological performance.

Ascending aorta over-angulation is a risk factor for acute type A aortic dissection: evidence from advanced finite element simulations

OBJECTIVES

To assess whether ascending aorta over-angulation, a morphological feature recently found to be associated with acute type A aortic dissection, precedes dissection and how it affects wall stress distribution.

METHODS

A baseline finite element model, previously created by a neural network tool from end-diastolic computed tomography angiography measurements in 124 healthy subjects, was modified to simulate the over-angulation accompanying aortic elongation, obtaining paradigmatic models with different ascending angulations (ascending-arch angle 145°-110°). The models were discretized and embedded in a deformable continuum representing surrounding tissues, aortic wall anisotropy and nonlinearity were accounted for, pre-tensioning at diastolic pressures was applied and peak systolic stresses were computed. Then, from 15 patients' pre-dissection geometries, patient-specific finite element models of pre-dissection aorta were created through the same framework. The sites of maximum longitudinal stress were compared with the respective sites of dissection entry tear in post-dissection imaging.

RESULTS

Paradigmatic models showed that progressive narrowing of the ascending-arch angle was associated with increasing longitudinal stress (becoming significant for angles <130°), whereas the impact on circumferential stress was less consistent. In pre-dissection patient-specific models, the ascending-arch angle was narrowed (113°±11°), and the region of peak longitudinal stresses corresponded to the entry tear location in the respective post-dissection computed tomography angiography.

CONCLUSIONS

This study strongly supports the hypothesis that the ascending-arch angle, as quantifier of aorta over-angulation, can be a good predictor of aortic dissection, since its narrowing below 130° increases longitudinal wall stress, and the dissection entry tears develop in the aortic wall in areas of highest longitudinal stress.

Intrinsic fluorescence hydrogels for ON/OFF screening of antidiabetic drugs: assessing α-glucosidase inhibition by acarbose

Diabetes remains one of the most prevalent chronic diseases globally, significantly impacting mortality ratetables. The development of effective treatments for controlling glucose level in blood is critical to improve the quality of life of patients with diabetes. In this sense, smart optical sensors using hydrogels, responsive to external stimuli, have emerged as a revolutionary approach to diabetes care. In this study, changes in the optical properties of a hydrogel are employed for monitoring α-glucosidase activity, a critical enzyme involved in diabetes mellitus type II due to its role in breaking terminal α-glycosidic bonds, releasing α-glucose. The enzyme is encapsulated within a triazine-based hydrogel that exhibits intrinsic blue fluorescence. Upon hydrolysis of the substrate p-nitrophenyl-α-D-glucopyranoside (p-NPG) by α-glucosidase, the fluorescence is quenched due to the release of p-nitrophenol (PNP). However, when exposed to potential antidiabetic drugs, the enzyme's activity is inhibited, and the hydrogel's fluorescence remains intact. This ON/OFF fluorescence-based assay enables rapid screening of drug candidates by evaluating their ability to inhibit α-glucosidase enzymatic activity. Sensor optimization involves conducting swelling studies, fluorescent assays, reusability tests and a trial with a real antidiabetic drug. This innovative approach holds potential for enhancing antidiabetic drug screening and management, offering a more accessible and efficient solution compared to traditional biosensors.

High Internal Phase Emulsion-Templated Hydrophilic Polyphosphoester Scaffolds: Tailoring the Porosity and Degradation for Soft Tissue Engineering

Synthetic porous scaffolds are key elements in tissue engineering (TE), requiring controlled porosity for cell colonization, along with a degradation rate aligned with tissue growth. While biodegradable polyester scaffolds are widely used in TE, they are primarily hydrophobic and suited for semirigid to hard tissue applications. This work broadens the scope of TE by introducing porous scaffolds made of polyphosphoesters (PPEs), degradable polymers with adaptable physicochemical properties. PPE hydrogels were shaped into 3D scaffolds using an emulsion templating method, yielding hydrophilic matrices with controlled porosity and tunable Young's moduli for soft tissues. Degradation assays at physiological pH confirmed the scaffolds' biodegradability. Cytotoxicity tests with PPE scaffolds showed excellent cell viability, while RGD functionalization further enhanced cell adhesion. Scaffold colonization, low inflammation, and angiogenesis were demonstrated in vivo through subcutaneous implantation of the scaffolds in mice and histological analysis. These results highlight PPE-based scaffolds as promising candidates for regenerative medicine.

Heparinized collagen-based hydrogels for tissue engineering: physical, mechanical and biological properties

As the main protein forming the vascular extracellular matrix, collagen has a weak antigenicity, making it an attractive candidate for coatings of vascular grafts. In order to bring antithrombotic properties to collagen for obtaining suitable blood compatibility of surfaces and further bioactive molecule carrying capacity, heparinization appears as a method of choice. Thus, in this article, pH-driven self-assembly was used to form collagen-based hydrogels with physical incorporation of heparins, especially low molecular weight heparin or unfractionated heparin at 1 IU/mL and 6 IU/mL. These heparinized hydrogels were evaluated for their physicochemical properties including gelation kinetic, spreading, viscoelasticity, microstructure and heparin quantification, and their biocompatibility such as cytocompatibility and their capacity to release bioactive heparins with antithrombotic properties. The loading capacity of collagen-based hydrogels was higher for unfractionated heparin (60 to 80 %) than for low molecular weight heparin (20 %). Interestingly, the highest concentration (6 IU/mL) of heparin used to form collagen-based hydrogels resulted in the formation of a softer hydrogel owning a better spreadability compared to 1 IU/mL and non heparinized collagen-based hydrogel. The 3D structure observation showed a layered formation with visible pores or spaces between the layers in all types of collagen-based hydrogels. These layers are interconnected by fibrous structures, suggesting a networked architecture. Moreover, the amount of heparin released from collagen-based hydrogel prepared with 6 IU /mL was higher than from those heparinized with 1 IU/mL attested by a delay in blood coagulation (activated partial thromboplastin time and thrombin time) and the abolishment of thrombin generation. Those hydrogels were also biocompatible, with low albumin adsorption and no impact on cell viability. Finally, heparin is retained in these hydrogels for at least seven days after cell seeding, providing the possibility of long-term antithrombotic properties. Thus, we succeeded in develop/obtain coatings with antithrombogenic properties, biocompatible and able to retain heparins at least seven days, making them good candidates with a great potential for the development and application of efficient blood-contacting materials.

Multisensory Extended Reality Applications Offer Benefits for Volumetric Biomedical Image Analysis in Research and Medicine

3D data from high-resolution volumetric imaging is a central resource for diagnosis and treatment in modern medicine. While the fast development of AI enhances imaging and analysis, commonly used visualization methods lag far behind. Recent research used extended reality (XR) for perceiving 3D images with visual depth perception and touch but used restrictive haptic devices. While unrestricted touch benefits volumetric data examination, implementing natural haptic interaction with XR is challenging. The research question is whether a multisensory XR application with intuitive haptic interaction adds value and should be pursued. In a study, 24 experts for biomedical images in research and medicine explored 3D medical shapes with 3 applications: a multisensory virtual reality (VR) prototype using haptic gloves, a simple VR prototype using controllers, and a standard PC application. Results of standardized questionnaires showed no significant differences between all application types regarding usability and no significant difference between both VR applications regarding presence. Participants agreed to statements that VR visualizations provide better depth information, using the hands instead of controllers simplifies data exploration, the multisensory VR prototype allows intuitive data exploration, and it is beneficial over traditional data examination methods. While most participants mentioned manual interaction as the best aspect, they also found it the most improvable. We conclude that a multisensory XR application with improved manual interaction adds value for volumetric biomedical data examination. We will proceed with our open-source research project ISH3DE (Intuitive Stereoptic Haptic 3D Data Exploration) to serve medical education, therapeutic decisions, surgery preparations, or research data analysis.

Human Chorionic Membrane-derived Tunable Hydrogels for Vascular Tissue Engineering Strategies

One of the foremost targets in the advancement of biomaterials to engineer vascularized tissues is not only to replicate the composition of the intended tissue but also to create thicker structures incorporating a vascular network for adequate nutrients and oxygen supply. For the first time, to the best of current knowledge, a clinically relevant biomaterial is developed, demonstrating that hydrogels made from the human decellularized extracellular matrix can exhibit robust mechanical properties (in the kPa range) and angiogenic capabilities simultaneously. These properties enable the culture and organization of human umbilical vein endothelial cells into tubular structures, maintaining their integrity for 14 days in vitro without the need for additional polymers or angiogenesis-related factors. This is achieved by repurposing the placenta chorionic membrane (CM), a medical waste with an exceptional biochemical composition, into a valuable resource for bioengineering purposes. After decellularization, the CM underwent chemical modification with methacryloyl groups, giving rise to methacrylated CM (CMMA). CMMA preserved key proteins, as well as glycosaminoglycans. The resulting hydrogels rapidly photopolymerize and have enhanced strength and customizable mechanical properties. Furthermore, they demonstrate angio-vasculogenic competence in vitro and in vivo, holding significant promise as a humanized platform for the engineering of vascularized tissues.

Dynamic Hydrogel-Based Strategy for Traumatic Brain Injury Modeling and Therapy

Traumatic brain injury (TBI) is one of the most traumatizing and poses serious health risks to people's bodies due to its unique pathophysiological characteristics. The investigations on the pathological mechanism and valid interventions of TBI have attracted widespread attention worldwide. With bio-mimic mechanic cues, the dynamic hydrogels with dynamic stiffness changes or reversible crosslinking have been suggested to construct the in vitro disease models or novel therapeutic agents for TBI. However, there is a lack of clarification on the dynamic hydrogels currently reported and their biomedical applications on TBI. Our review starts with introducing the native mechanical characters and changes in TBI and then summarizes the common chemical strategies of the dynamic hydrogels with dynamically tunable stiffness and reversible networks for in vitro modeling and therapy. Finally, we prospect the future development of dynamic hydrogels in the mechanical modeling of TBI, providing new mechanical insights for TBI and guidance for tailored brain-targeted biomaterials.

3D Printing of a Chitosan and Tamarind Gum Ink: a Two-Step Approach

3D bioprinting stands out as one of the most promising innovations in the field of high technologies for personalized biomedicine, enabling the fabrication of biomaterial-based scaffolds designed to repair, restore, or regenerate tissues and organs in the body. Among the various materials used as inks, hydrogels play a critical role due to their unique characteristics, including excellent biocompatibility, adjustable mechanical properties, and high solvent retention. This versatility makes them ideal for various applications such as biomedical devices, drug delivery, or flexible electronics. Although chitosan is a promising material for such applications, when used alone, it does not possess the necessary strength and stiffness for creating high-resolution 3D bioprinted structures. In this study, we propose a combined method for the fabrication of self-supporting 3D printed objects with an ink made of chitosan and tamarind gum. Our approach involves two key techniques. The first one is a controlled evaporation of the solvent, aiming to increase the concentration of the components of the ink. The second one relies on printing in a gelling bath composed of sodium hydroxide and ethanol, allowing for improved printability and long-term stability of the scaffolds. The results obtained revealed the possibility of modulating the concentration of the components based on the heating time. The latter positively influences not only the ink printability but also the properties of the resulting scaffolds such as their biodegradability and mechanical properties.

Characterizing Microbubble-Mediated Permeabilization in a Vessel-on-a-Chip Model

Drug transport from blood to extravascular tissue can locally be achieved by increasing the vascular permeability through ultrasound-activated microbubbles. However, the mechanism remains unknown, including whether short and long cycles of ultrasound induce the same onset rate, spatial distribution, and amount of vascular permeability increase. Accurate models are necessary for insights into the mechanism so a microvessel-on-a-chip is developed with a membrane-free extravascular space. Using these microvessels-on-a-chip, distinct differences between 2 MHz ultrasound treatments are shown with 10 or 1000 cycles. The onset rate is slower for 10 than 1000 cycles, while both cycle lengths increase the permeability in spot-wise patterns without affecting microvessel viability. Significantly less vascular permeability increase and sonoporation are induced for 10 versus 1000 cycles at 750 kPa (i.e., the highest studied peak negative acoustic pressure (PNP)). The PNP threshold for vascular permeability increases is 750 versus 550 kPa for 10 versus 1000 cycles, while this is 750 versus 220 kPa for sonoporation. Vascular permeability increases do not correlate with αvβ3-targeted microbubble behavior, while sonoporation correlates with αvβ3-targeted microbubble clustering. In conclusion, the further mechanistic unraveling of vascular permeability increase by ultrasound-activated microbubbles in a developed microvessel-on-a-chip model aids the safe and efficient development of microbubble-mediated drug transport.

Ag quantum dots-doped poly (vinyl alcohol)/chitosan hydrogel coatings to prevent catheter-associated urinary tract infections

The prevention of catheter-associated urinary tract infections (CAUTIs) significantly impacts the reduction of morbidity and mortality associated with the use of indwelling urinary catheters. This study focused on developing an antibacterial double network hydrogel coating for latex urinary catheters, which incorporated Ag quantum dots (Ag QDs) in a polyvinyl alcohol (PVA)-chitosan (CS) double network hydrogel matrix. The PVA-CS-Ag QDs, referred to as the PCA hydrogel coating exhibited excellent mechanical and physiochemical properties with controlled release of Ag QDs. The antibacterial properties of the PCA hydrogel-coated urinary catheters were studied against both gram-negative Escherichia coli (E. coli, ATCC25922) and gram-positive Staphylococcus aureus (S. aureus, ATCC29213). The continuous release of CS oligomers and Ag QDs from the hydrogel coating contributed to the synergistic antibacterial and antiadhesion effects. Measurements of the Ag release rate revealed that even after 30 days, the concentration of Ag QDs from the PCA hydrogel-coated urinary catheters remained significantly higher than the effective antibacterial concentration of the total Ag (0.1 μg·L-1). These results indicated that the PCA hydrogel coating not only efficiently prevented bacteria attachment, but also exhibited long-term antibacterial activity, thereby inhibiting biofilm formation. Furthermore, the PCA hydrogel-coated urinary catheter demonstrated excellent biocompatibility and hemocompatibility. Overall, this novel PCA hydrogel-coated urinary catheter, with its exceptional antibacterial properties, holds great potential in reducing the incidence of CAUTIs.

Physicochemical Properties, Drug Release and In Situ Depot-Forming Behaviors of Alginate Hydrogel Containing Poorly Water-Soluble Aripiprazole

The objective of this study was to investigate the physicochemical properties, drug release and in situ depot-forming behavior of alginate hydrogel containing poorly water-soluble aripiprazole (ARP) for achieving free-flowing injectability, clinically accessible gelation time and sustained drug release. The balanced ratio of pyridoxal phosphate (PLP) and glucono-delta-lactone (GDL) was crucial to modulate gelation time of the alginate solution in the presence of calcium carbonate. Our results demonstrated that the sol state alginate hydrogel before gelation was free-flowing, stable and readily injectable using a small 23 G needle. In addition, the ratio (w/w) of PLP and GDL altered the gelation time, which was longer as the PLP content increased but shorter as the GDL content increased. The alginate hydrogel with a ratio of PLP to GDL of 15:9 had the optimal physicochemical properties in terms of a clinically acceptable gelation time (9.1 min), in situ-depot formation with muscle-mimicking stiffness (3.55 kPa) and sustained release over a two-week period. The alginate hydrogel, which is tunable by varying the ratio of PLP and GDL, could provide a controllable pharmaceutical preparation to meet the need for long-acting performance of antipsychotic drugs like ARP.

Mechanics-Switchable and Antiswelling Colloidal Hydrogels Inspired by the Cononsolvency Effect

Stiffness switching hydrogels have been in high demand for intelligent devices, adhesion science, soft robotics, and flexible electronics. However, it is challenging to post-tune the mechanical properties of a hydrogel once the polymer network structure is formed. Inspired by the cononsolvency effect, we prepared a mechanics-switching colloidal hydrogel through the precipitation polymerization of methacrylamide in mixed dimethyl sulfoxide and water solvents. The colloidal network enables the hydrogels to simultaneously strengthen, stiffen, and toughen. The colloidal hydrogels not only display a broad spectrum of adjustable mechanical properties (ranging from 0.08 to 57.1 MPa) via solvent response but also accomplish reversible stiffness conversion through the solvent-tuned conformational adjustment of colloidal polymer networks, with the maximum modulus conversion reaching 1427, and exhibit solvent-responsive shape memory. Based on the stable and tight colloidal network, the hydrogels exhibit antiswelling properties in various aqueous solutions and solvents. The colloidal hydrogel would provide more possibilities in various applications, such as antiimpact protection, shape memory, electronic switches, and intelligent engineering materials. It is envisioned that this work will provide key opportunities in developing mechanics-switching and on-demand tuning of soft materials for tissue engineering, flexible electronics, and biomedical science.

Lowest gelation concentration in a complex-coacervate-driven self-assembly system, achieved by redox-RAFT synthesis of high molecular weight block polyelectrolytes

The objective of this work was to synthesize high molecular weight polyelectrolyte complex (PEC) micelles that are effective in controlling the rheology of aqueous solutions at low concentrations, paving the way for industrial applications of thickeners based on the principle of electrostatic self-assembly. Redox-initiated RAFT (reversible addition-fragmentation chain-transfer) polymerization was used to obtain anionic block polyelectrolytes based on poly(sodium 2-acrylamido-2-methylpropane sulfonate) and poly(acrylamide)-poly(AMPS)-block-poly(AM) (di-block) and poly(AMPS)-block-poly(AM)-block-poly(AMPS) (tri-block), with molecular weights of 237 kDa and 289 kDa and polydispersities of 1.29 and 1.34, respectively. A random poly(AMPS)-co-poly(AM) copolymer was also synthesized for comparison. PEC micelles were obtained upon mixing with cationic poly(N-[3-(dimethylamino)propyl]methacrylamide hydrochloride) - poly(DMAPMA), forming viscoelastic gels at unprecedented low concentrations of <3 wt% for the di-block and <1 wt% for the tri-block, which to date is the lowest demonstrated gelation concentration for a synthetic PEC micelle system. Differences between tri-block and di-block architectures are discussed, with the former being more affected by the addition of salt, which is attributed to percolated network breakdown. The random co-polymer was shown not to be an effective thickener but displayed a surprising lack of phase separation upon coacervation. The assemblies were characterized using dynamic light scattering (DLS) and cryo transmission electron microscopy (cryoTEM), revealing spherical micelles with a diameter of approximately 200 nm for the diblock and a mixture of spherical micelles and network particles for the tri-block PEC micelles. The micelles were not affected by dilution down to a polymer concentration of 7.8 × 10-4% (approx. 0.03 μM). Responsiveness to salinity, pH, and temperature was studied using DLS, revealing a critical NaCl concentration of 1.1 M for the block copolymer micelles.

Use of Hydrogels in Regenerative Medicine: Focus on Mechanical Properties

Bioengineered materials represent an innovative option to support the regenerative processes of damaged tissues, with the final objective of creating a functional environment closely mimicking the native tissue. Among the different available biomaterials, hydrogels represent the solution of choice for tissue regeneration, thanks to the easy synthesis process and the highly tunable physical and mechanical properties. Moreover, hydrogels are biocompatible and biodegradable, able to integrate in biological environments and to support cellular interactions in order to restore damaged tissues' functionality. This review offers an overview of the current knowledge concerning hydrogel synthesis and characterization and of the recent achievements in their experimental use in supporting skin, bone, cartilage, and muscle regeneration. The currently available in vitro and in vivo results are of great interest, highlighting the need for carefully designed and controlled preclinical studies and clinical trials to support the transition of these innovative biomaterials from the bench to the bedside.

A Polyvinyl Alcohol (PVA)-Based Phantom for Prostate Cancer Detection Using Multiparametric Ultrasound: A Validation Study

Multiparametric ultrasound (mpUS) enhances prostate cancer (PCa) diagnosis by using multiple imaging modalities. Tissue-mimicking materials (TMM) phantoms, favoured over animal models for ethical and consistency reasons, were created using polyvinyl alcohol (PVA) with varying molecular weights (Mw).

METHODS

Four PVA samples, varying in Mw with constant concertation, were mixed with glycerol, silicon carbide (SiC), and aluminium oxide (Al2O3). Phantoms with varying depth and inclusion sizes were created and tested using shear-wave elastography (SWE). An mpUS phantom was developed to mimic prostate tissue, including isoechoic and hypoechoic inclusions and vessels. The phantom was scanned using supersonic ultrasound, strain elastography, and Doppler ultrasound. Validation was performed using radical prostatectomy data and shear-wave elastography.

RESULTS

The acoustic properties varied with enhancers like glycerol and Al2O3. Low Mw PVA samples had a speed of sound ranging from 1547.50 ± 2 to 1553.70 ± 2.2 m/s and attenuation of 0.61 ± 0.062 to 0.63 ± 0.05 dB/cm/MHz. High Mw PVA samples ranged from 1555 ± 2.82 to 1566 ± 4.5 m/s and 0.71 ± 0.02 to 0.73 ± 0.046 dB/cm/MHz. Young's modulus ranged from 11 ± 2 to 82.3 ± 0.5 kPa across 1 to 10 freeze-thaw cycles. Inclusion size, depth, and interaction statistically affect the SWE measurements with p-value = 0.056327, p-value = 8.0039 × 10-8, and p-value = 0.057089, respectively. SWE showed isoechoic inclusions, prostate tissue, and surrounding tissue only. The Doppler velocity was measured in three different inner diameters.

CONCLUSION

PVA mixed with enhancer materials creates an mpUS phantom with properties that mimic normal and abnormal prostate tissue, blood vessels, and soft tissue, facilitating advanced diagnostic training and validation.

Hydrogel System with Independent Tailoring of Mechanics, CT, and US Contrasts for Affordable Medical Phantoms

Medical phantoms mimic aspects of procedures like computed tomography (CT), ultrasound (US) imaging, and surgical practices. However, the materials for current commercial phantoms are expensive and the fabrication with these is complex and lacks versatility. Therefore, existing material solutions are not suitable for creating patient-specific phantoms. We present a novel and cost-effective material system (utilizing ubiquitous sodium alginate hydrogel and coconut fat) with independently and accurately tailorable CT, US, and mechanical properties. By varying the concentration of alginate, cross-linker, and coconut fat, the radiological parameters and the elastic modulus were adjusted independently in a wide range. The independence was demonstrated by creating phantoms with features hidden in US, while visible in CT imaging and vice versa. This system is particularly beneficial in resource-scarce areas since the materials are cheap (<$ 1 USD/kg) and easy to obtain, offering realistic and versatile phantoms to practice surgeries and ultimately enhance patient care.

Remote-Controlled Gene Delivery in Coaxial 3D-Bioprinted Constructs using Ultrasound-Responsive Bioinks

Introduction

Coaxial 3D bioprinting has advanced the formation of tissue constructs that recapitulate key architectures and biophysical parameters for in-vitro disease modeling and tissue-engineered therapies. Controlling gene expression within these structures is critical for modulating cell signaling and probing cell behavior. However, current transfection strategies are limited in spatiotemporal control because dense 3D scaffolds hinder diffusion of traditional vectors. To address this, we developed a coaxial extrusion 3D bioprinting technique using ultrasound-responsive gene delivery bioinks. These bioink materials incorporate echogenic microbubble gene delivery particles that upon ultrasound exposure can sonoporate cells within the construct, facilitating controllable transfection.

Methods

Phospholipid-coated gas-core microbubbles were electrostatically coupled to reporter transgene plasmid payloads and incorporated into cell-laden alginate bioinks at varying particle concentrations. These bioinks were loaded into the coaxial nozzle core for extrusion bioprinting with CaCl2 crosslinker in the outer sheath. Resulting bioprints were exposed to 2.25 MHz focused ultrasound and evaluated for microbubble activation and subsequent DNA delivery and transgene expression.

Results

Coaxial printing parameters were established that preserved the stability of ultrasound-responsive gene delivery particles for at least 48 h in bioprinted alginate filaments while maintaining high cell viability. Successful sonoporation of embedded cells resulted in DNA delivery and robust ultrasound-controlled transgene expression. The number of transfected cells was modulated by varying the number of focused ultrasound pulses applied. The size region over which DNA was delivered was modulated by varying the concentration of microbubbles in the printed filaments.

Conclusions

Our results present a successful coaxial 3D bioprinting technique designed to facilitate ultrasound-controlled gene delivery. This platform enables remote, spatiotemporally-defined genetic manipulation in coaxially bioprinted tissue constructs with important applications for disease modeling and regenerative medicine.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-024-00818-x.

Microdissection tools to generate organoids for modeling the tumor immune microenvironment

Patient-derived tumor organoids have emerged as promising models for predicting personalized drug responses in cancer therapy, but they typically lack immune components. Preserving the in vivo association between tumor cells and endogenous immune cells is critical for accurate testing of cancer immunotherapies. Mechanical dissection of tumor specimens into tumor fragments, as opposed to enzymatic digestion into single cells, is essential for maintaining these native tumor-immune cell spatial relationships. However, conventional mechanical dissection relying on manual mincing is time-consuming and irreproducible. This study describes two microdissection devices, the µDicer and µGrater, to facilitate the generation of intact tumor fragments from mouse B16 melanoma, a common model of human melanoma. The µDicer- and µGrater-cut tumor fragments were used to generate air‒liquid interface (ALI) organoids that copreserve tumor cells with infiltrating immune subsets without artificial reconstitution. The µDicer, consisting of a hexagonal array of silicon microblades, was employed to investigate the effect of organoid size. The viability of ALI organoid immune cells appeared insensitive to organoid sizes exceeding ~400 µm but diminished in organoids ~200 µm in size. The µGrater, consisting of an array of submillimeter holes in stainless steel, was employed to accelerate dissection. For the samples studied, the µGrater was 4.5 times faster than manual mincing. Compared with those generated by manual mincing, ALI organoids generated by the µGrater demonstrated similar viability, immune cell composition, and responses to anti-PD-1 immunotherapy. With further optimization, the µGrater holds potential for integration into clinical workflows to support the advancement of personalized cancer immunotherapy.

Integrated processes (HPSE+scCO2) to prepare sterilized alginate-gelatine-based aerogel

Biopolymers application in biomedical areas has been limited due to the physicochemical degradation that occurs using conventional processing/sterilization methods (e.g., steam heat, γ-radiation, ethylene oxide). Aiming to avoid/minimize degradation and preserve their properties, supercritical carbon dioxide (scCO2) has been proposed as an alternative sterilization method for such materials. ScCO2 can simultaneously be used as a drying method to produce aerogels (i) and sterilize them (ii). However, a solvent exchange is required to prepare the alcogel from hydrogel, achievable through high-pressure solvent exchange (HPSE) (iii). This study integrated three processes: HPSE, scCO2 drying, and sterilization to prepare alginate-gelatine sterilized aerogels. Two scCO2 sterilization methods were tested. Results showed that sterilization did not compromise the aerogels' chemical, thermal and swelling properties. Conversely, Young's Modulus increased, and BET surface area decreased, due to the structural changes caused by the fast pressurization/depressurization rates applied during sterilization. Regarding the sterilization efficiency, results showed a reduction in contamination throughout the process, achieving a SAL of 10-4. The sterilized aerogels were non-cytotoxic in vitro and showed improved wound-healing properties. The innovative integrated process produced decontaminated/sterile and ready-to-use aerogels reducing process time by 75 %, from 2 days up to 12 h without compromising the aerogel's properties.

Vascularized platforms for investigating cell communication via extracellular vesicles

The vascular network plays an essential role in the maintenance of all organs in the body via the regulated delivery of oxygen and nutrients, as well as tissue communication via the transfer of various biological signaling molecules. It also serves as a route for drug administration and affects pharmacokinetics. Due to this importance, engineers have sought to create physiologically relevant and reproducible vascular systems in tissue, considering cell-cell and extracellular matrix interaction with structural and physical conditions in the microenvironment. Extracellular vesicles (EVs) have recently emerged as important carriers for transferring proteins and genetic material between cells and organs, as well as for drug delivery. Vascularized platforms can be an ideal system for studying interactions between blood vessels and EVs, which are crucial for understanding EV-mediated substance transfer in various biological situations. This review summarizes recent advances in vascularized platforms, standard and microfluidic-based techniques for EV isolation and characterization, and studies of EVs in vascularized platforms. It provides insights into EV-related (patho)physiological regulations and facilitates the development of EV-based therapeutics.

Engineering Tough and Elastic Polyvinyl Alcohol-Based Hydrogel with Antimicrobial Properties

Hydrogels have been extensively used for tissue engineering applications due to their versatility in structure and physical properties, which can mimic native tissues. Although significant progress has been made towards designing hydrogels for soft tissue repair, engineering hydrogels that resemble load-bearing tissues is still considered a great challenge due to their specific mechano-physical demands. Here, we report microporous, tough, yet highly compressible poly(vinyl alcohol) (PVA)-based hydrogels for potential applications in repairing or replacing different load-bearing tissues. The synergy of freeze-thawing and the Hofmeister effect, which controlled the spatial arrangement and aggregation of polymer chains, facilitated the formation of micro-structured frameworks with tunable porosity. While the maximum mechanical strength, toughness, and stretchability of the engineered hydrogel were ~390 kPa, ~388 kJ/m3, and ~170%, respectively, the Young's modulus based on compression testing was found to be in the range of ~0.02 - 0.30 MPa, highlighting the all-in-one mechanically enriched nature of the hydrogel system. Furthermore, the minimal swelling and degradation rate of the engineered hydrogel met the specific requirements of load-bearing tissues. Finally, excellent antibacterial resistance as well as in vitro biocompatibility of the hydrogel demonstrated its potential for the replacement of load-bearing tissues.

Droplet-based microfluidics for engineering shape-controlled hydrogels with stiffness gradient

Current biofabrication strategies are limited in their ability to replicate native shape-to-function relationships, that are dependent on adequate biomimicry of macroscale shape as well as size and microscale spatial heterogeneity, within cell-laden hydrogels. In this study, a novel diffusion-based microfluidics platform is presented that meets these needs in a two-step process. In the first step, a hydrogel-precursor solution is dispersed into a continuous oil phase within the microfluidics tubing. By adjusting the dispersed and oil phase flow rates, the physical architecture of hydrogel-precursor phases can be adjusted to generate spherical and plug-like structures, as well as continuous meter-long hydrogel-precursor phases (up to 1.75 m). The second step involves the controlled introduction a small molecule-containing aqueous phase through a T-shaped tube connector to enable controlled small molecule diffusion across the interface of the aqueous phase and hydrogel-precursor. Application of this system is demonstrated by diffusing co-initiator sodium persulfate (SPS) into hydrogel-precursor solutions, where the controlled SPS diffusion into the hydrogel-precursor and subsequent photo-polymerization allows for the formation of unique radial stiffness patterns across the shape- and size-controlled hydrogels, as well as allowing the formation of hollow hydrogels with controllable internal architectures. Mesenchymal stromal cells are successfully encapsulated within hollow hydrogels and hydrogels containing radial stiffness gradient and found to respond to the heterogeneity in stiffness through the yes-associated protein mechano-regulator. Finally, breast cancer cells are found to phenotypically switch in response to stiffness gradients, causing a shift in their ability to aggregate, which may have implications for metastasis. The diffusion-based microfluidics thus finds application mimicking native shape-to-function relationship in the context of tissue engineering and provides a platform to further study the roles of micro- and macroscale architectural features that exist within native tissues.

A Review on the Rheological Properties of Single Amino Acids and Short Dipeptide Gels

Self-assembled peptide-based hydrogels have attracted considerable interest from the research community. Particularly, low molecular weight gelators (LMWGs) consisting of amino acids and short peptides are highly suitable for biological applications owing to their facile synthesis and scalability, as well as their biocompatibility, biodegradability, and stability in physiological conditions. However, challenges in understanding the structure-property relationship and lack of design rules hinder the development of new gelators with the required properties for several applications. Hereby, in the plethora of peptide-based gelators, this review discusses the mechanical properties of single amino acid and dipeptide-based hydrogels. A mutual analysis of these systems allows us to highlight the relationship between the gel mechanical properties and amino acid sequence, preparation methods, or N capping groups. Additionally, recent advancements in the tuning of the gels' rheological properties are reviewed. In this way, the present review aims to help bridge the knowledge gap between structure and mechanical properties, easing the selection or design of peptides with the required properties for biological applications.

Engineered Regenerative and Adhesive Hydrogel for Concurrent Sealing and Healing of Enterocutaneous Fistulas

In addressing the intricate challenges of enterocutaneous fistula (ECF) treatment, such as internal bleeding, effluent leakage, inflammation, and infection, our research is dedicated to introducing a regenerative adhesive hydrogel that can seal and expedite the healing process. A double syringe setup was utilized, with dopagelatin and platelet-rich plasma (PRP) in one syringe and Laponite and sodium periodate in another. The hydrogel begins to cross-link immediately after passing through a mixing tip and exhibits tissue adhesive properties. Results demonstrated that PRP deposits within the pores of the cross-linked hydrogel and releases sustainably, enhancing its regenerative capabilities. The addition of PRP further improved the mechanical properties and slowed down the degradation of the hydrogel. Furthermore, the hydrogel demonstrated cytocompatibility, hemostatic properties, and time-dependent macrophage M1 to M2 phase transition, suggesting the anti-inflammatory response of the material. In an in vitro bench test simulating high-pressure fistula conditions, the hydrogel effectively occluded pressures up to 300 mmHg. In conclusion, this innovative hydrogel holds promise for ECF treatment and diverse fistula cases, marking a significant advancement in its therapeutic approaches.

FRESH-based 3D bioprinting of complex biological geometries using chitosan bioink

Traditional three-dimensional (3D) bioprinting has always been associated with the challenge of print fidelity of complex geometries due to the gel-like nature of the bioinks. Embedded 3D bioprinting has emerged as a potential solution to print complex geometries using proteins and polysaccharides-based bioinks. This study demonstrated the Freeform Reversible Embedding of Suspended Hydrogels (FRESH) 3D bioprinting method of chitosan bioink to 3D bioprint complex geometries. 4.5% chitosan was dissolved in an alkali solvent to prepare the bioink. Rheological evaluation of the bioink described its shear-thinning nature. The power law equation was fitted to the shear rate-viscosity plot. The flow index value was found to be less than 1, categorizing the material as pseudo-plastic. The chitosan bioink was extruded into another medium, a thermo-responsive 4.5% gelatin hydrogel. This hydrogel supports the growing print structures while printing. After this, the 3D bioprinted structure was crosslinked with hot water to stabilize the structure. Using this method, we have 3D bioprinted complex biological structures like the human tri-leaflet heart valve, a section of a human right coronary arterial tree, a scale-down outer structure of the human kidney, and a human ear. Additionally, we have shown the mechanical tunability and suturability of the 3D bioprinted structures. This study demonstrates the capability of the chitosan bioink and FRESH method for 3D bioprinting of complex biological models for biomedical applications.

Exploiting light-based 3D-printing for the fabrication of mechanically enhanced, patient-specific aortic grafts

Despite polyester vascular grafts being routinely used in life-saving aortic aneurysm surgeries, they are less compliant than the healthy, native human aorta. This mismatch in mechanical behaviour has been associated with disruption of haemodynamics contributing to several long-term cardiovascular complications. Moreover, current fabrication approaches mean that opportunities to personalise grafts to the individual anatomical features are limited. Various modifications to graft design have been investigated to overcome such limitations; yet optimal graft functionality remains to be achieved. This study reports on the development and characterisation of an alternative vascular graft material. An alginate:PEGDA (AL:PE) interpenetrating polymer network (IPN) hydrogel has been produced with uniaxial tensile tests revealing similar strength and stiffness (0.39 ± 0.05 MPa and 1.61 ± 0.19 MPa, respectively) to the human aorta. Moreover, AL:PE tubular conduits of similar geometrical dimensions to segments of the aorta were produced, either via conventional moulding methods or stereolithography (SLA) 3D-printing. While both fabrication methods successfully demonstrated AL:PE hydrogel production, SLA 3D-printing was more easily adaptable to the fabrication of complex structures without the need of specific moulds or further post-processing. Additionally, most 3D-printed AL:PE hydrogel tubular conduits sustained, without failure, compression up to 50% their outer diameter and returned to their original shape upon load removal, thereby exhibiting promising behaviour that could withstand pulsatile pressure in vivo. Overall, these results suggest that this AL:PE IPN hydrogel formulation in combination with 3D-printing, has great potential for accelerating progress towards personalised and mechanically-matched aortic grafts.

Human muscle stem cell responses to mechanical stress into tunable 3D alginate matrices

Preclinical data acquired for human muscle stem (hMuStem) cells indicate their great repair capacity in the context of muscle injury. However, their clinical potential is limited by their moderate ability to survive after transplantation. To overcome these limitations, their encapsulation within protective environment would be beneficial. In this study, tunable calcium-alginate hydrogels obtained through molding method using external or internal gelation were investigated as a new strategy for hMuStem cell encapsulation. The mechanical properties of these hydrogels were characterized in their fully hydrated state by compression experiments using Atomic Force Microscopy. Measured elastic moduli strongly depended on the gelation mode and calcium/alginate concentrations. Values ranged from 1 to 12.5 kPa and 3.9 to 25 kPa were obtained for hydrogels prepared following internal and external gelation, respectively. Also, differences in mechanical properties of hydrogels resulted from their internal organization, with an isotropic structure for internal gelation, while external mode led to anisotropic one. It was further shown that viability, morphological and myogenic differentiation characteristics of hMuStem cells incorporated within alginate hydrogels were preserved after their release. These results highlight that hMuStem cells encapsulated in calcium-alginate hydrogels maintain their functionality, thus allowing to develop muscle regeneration protocols to improve their therapeutic efficacy.

An injectable polyacrylamide/chitosan-based hydrogel with highly adhesive, stretchable and electroconductive properties loaded with irbesartan for treatment of myocardial ischemia-reperfusion injury

Myocardial ischemia-reperfusion injury (MIRI) significantly contributes to the high incidence of complications and mortality associated with acute myocardial infarction. Recently, injectable electroconductive hydrogels (IECHs) have emerged as promising tools for replicating the mechanical, electroconductive, and physiological characteristics of cardiac tissue. Herein, we aimed to develop a novel IECH by incorporating irbesartan as a drug delivery system (DDS) for cardiac repair. Our approach involved merging a conductive poly-thiophene derivative (PEDOT: PSS) with an injectable dual-network adhesive hydrogel (DNAH) comprising a catechol-branched polyacrylamide network and a chitosan-hyaluronic acid covalent network. The resulting P-DNAH hydrogel, benefitting from a high conducting polymer content, a chemically crosslinked network, a robust dissipative matrix, and dynamic oxidation of catechol to quinone exhibited superior mechanical strength, desirable conductivity, and robust wet-adhesiveness. In vitro experiments with the P-DNAH hydrogel carrying irbesartan (P-DNAH-I) demonstrated excellent biocompatibility by cck-8 kit on H9C2 cells and a rapid initial release of irbesartan. Upon injection into the infarcted hearts of MIRI mouse models, the P-DNAH-I hydrogel effectively inhibited the inflammatory response and reduced the infarct size. In conclusion, our results suggest that the P-DNAH hydrogel, possessing suitable mechanical properties and electroconductivity, serves as an ideal IECH for DDS, delivering irbesartan to promote heart repair.

Bioengineering vascularized liver tissue for biomedical research and application

The liver performs a wide range of biological functions that are essential to body homeostasis. Damage to liver tissue can result in reduced organ function, and if chronic in nature can lead to organ scarring and progressive disease. Currently, donor liver transplantation is the only longterm treatment for end-stage liver disease. However, orthotopic organ transplantation suffers from several drawbacks that include organ scarcity and lifelong immunosuppression. Therefore, new therapeutic strategies are required. One promising strategy is the engineering of implantable and vascularized liver tissue. This resource could also be used to build the next generation of liver tissue models to better understand human health, disease and aging in vitro. This article reviews recent progress in the field of liver tissue bioengineering, including microfluidic-based systems, bio-printed vascularized tissue, liver spheroids and organoid models, and the induction of angiogenesis in vivo.

Degradable, anti-swelling, high-strength cellulosic hydrogels via salting-out and ionic coordination

Cellulosic hydrogels are widely used in various applications, as they are natural raw materials and have excellent degradability. However, their poor mechanical properties restrict their practical application. This study presents a facile approach for fabricating cellulosic hydrogels with high strength by synergistically utilizing salting-out and ionic coordination, thereby inducing the collapse and aggregation of cellulose chains to form a cross-linked network structure. Cellulosic hydrogels are prepared by soaking cellulose in an Al2(SO4)3 solution, which is both strong (compressive strength of up to 16.99 MPa) and tough (compressive toughness of up to 2.86 MJ/m3). The prepared cellulosic hydrogels exhibit resistance to swelling in different solutions and good biodegradability in soil. The cellulosic hydrogels are incorporated into strain sensors for human-motion monitoring by introducing AgNWs. Thus, the study offers a promising, simple, and scalable approach for preparing strong, degradable, and anti-swelling hydrogels using common biomass resources with considerable potential for various applications.

A Spontaneous In Situ Thiol-Ene Crosslinking Hydrogel with Thermo-Responsive Mechanical Properties

The thermo-responsive behavior of Poly(N-isopropylacrylamide) makes it an ideal candidate to easily embed cells and allows the polymer mixture to be injected. However, P(NiPAAm) hydrogels possess minor mechanical properties. To increase the mechanical properties, a covalent bond is introduced into the P(NIPAAm) network through a biocompatible thiol-ene click-reaction by mixing two polymer solutions. Co-polymers with variable thiol or acrylate groups to thermo-responsive co-monomer ratios, ranging from 1% to 10%, were synthesized. Precise control of the crosslink density allowed customization of the hydrogel's mechanical properties to match different tissue stiffness levels. Increasing the temperature of the hydrogel above its transition temperature of 31 °C induced the formation of additional physical interactions. These additional interactions both further increased the stiffness of the material and impacted its relaxation behavior. The developed optimized hydrogels reach stiffnesses more than ten times higher compared to the state of the art using similar polymers. Furthermore, when adding cells to the precursor polymer solutions, homogeneous thermo-responsive hydrogels with good cell viability were created upon mixing. In future work, the influence of the mechanical micro-environment on the cell's behavior can be studied in vitro in a continuous manner by changing the incubation temperature.

Vascular network-inspired fluidic system (VasFluidics) with spatially functionalizable membranous walls

In vascular networks, the transport across different vessel walls regulates chemical compositions in blood over space and time. Replicating such trans-wall transport with spatial heterogeneity can empower synthetic fluidic systems to program fluid compositions spatiotemporally. However, it remains challenging as existing synthetic channel walls are typically impermeable or composed of homogeneous materials without functional heterogeneity. This work presents a vascular network-inspired fluidic system (VasFluidics), which is functionalizable for spatially different trans-wall transport. Facilitated by embedded three-dimensional (3D) printing, elastic, ultrathin, and semipermeable walls self-assemble electrostatically. Physicochemical reactions between fluids and walls are localized to vary the trans-wall molecules among separate regions, for instance, by confining solutions or locally immobilizing enzymes on the outside of channels. Therefore, fluid compositions can be regulated spatiotemporally, for example, to mimic blood changes during glucose absorption and metabolism. Our VasFluidics expands opportunities to replicate biofluid processing in nature, providing an alternative to traditional fluidics.

Electrochemical and Electrical Biosensors for Wearable and Implantable Electronics Based on Conducting Polymers and Carbon-Based Materials

Bioelectronic devices are designed to translate biological information into electrical signals and vice versa, thereby bridging the gap between the living biological world and electronic systems. Among different types of bioelectronics devices, wearable and implantable biosensors are particularly important as they offer access to the physiological and biochemical activities of tissues and organs, which is significant in diagnosing and researching various medical conditions. Organic conducting and semiconducting materials, including conducting polymers (CPs) and graphene and carbon nanotubes (CNTs), are some of the most promising candidates for wearable and implantable biosensors. Their unique electrical, electrochemical, and mechanical properties bring new possibilities to bioelectronics that could not be realized by utilizing metals- or silicon-based analogues. The use of organic- and carbon-based conductors in the development of wearable and implantable biosensors has emerged as a rapidly growing research field, with remarkable progress being made in recent years. The use of such materials addresses the issue of mismatched properties between biological tissues and electronic devices, as well as the improvement in the accuracy and fidelity of the transferred information. In this review, we highlight the most recent advances in this field and provide insights into organic and carbon-based (semi)conducting materials' properties and relate these to their applications in wearable/implantable biosensors. We also provide a perspective on the promising potential and exciting future developments of wearable/implantable biosensors.

Bioactive Polyurethane-Poly(ethylene Glycol) Diacrylate Hydrogels for Applications in Tissue Engineering

Polyurethanes (PUs) are a highly adaptable class of biomaterials that are among some of the most researched materials for various biomedical applications. However, engineered tissue scaffolds composed of PU have not found their way into clinical application, mainly due to the difficulty of balancing the control of material properties with the desired cellular response. A simple method for the synthesis of tunable bioactive poly(ethylene glycol) diacrylate (PEGDA) hydrogels containing photocurable PU is described. These hydrogels may be modified with PEGylated peptides or proteins to impart variable biological functions, and the mechanical properties of the hydrogels can be tuned based on the ratios of PU and PEGDA. Studies with human cells revealed that PU-PEG blended hydrogels support cell adhesion and viability when cell adhesion peptides are crosslinked within the hydrogel matrix. These hydrogels represent a unique and highly tailorable system for synthesizing PU-based synthetic extracellular matrices for tissue engineering applications.

Self-assembled and perfusable microvasculature-on-chip for modeling leukocyte trafficking

Leukocyte recruitment from blood to tissue is a process that occurs at the level of capillary vessels during both physiological and pathological conditions. This process is also relevant for evaluating novel adoptive cell therapies, in which the trafficking of therapeutic cells such as chimeric antigen receptor (CAR)-T cells throughout the capillaries of solid tumors is important. Local variations in blood flow, mural cell concentration, and tissue stiffness contribute to the regulation of capillary vascular permeability and leukocyte trafficking throughout the capillary microvasculature. We developed a platform to mimic a biologically functional human arteriole-venule microcirculation system consisting of pericytes (PCs) and arterial and venous primary endothelial cells (ECs) embedded within a hydrogel, which self-assembles into a perfusable, heterogeneous microvasculature. Our device shows a preferential association of PCs with arterial ECs that drives the flow-dependent formation of microvasculature networks. We show that PCs stimulate basement membrane matrix synthesis, which affects both vessel diameter and permeability in a manner correlating with the ratio of ECs to PCs. Moreover, we demonstrate that hydrogel concentration can affect capillary morphology but has no observed effect on vascular permeability. The biological function of our capillary network was demonstrated using an inflammation model, where significantly higher expression of cytokines, chemokines, and adhesion molecules was observed after tumor necrosis factor-alpha (TNF-α) treatment. Accordingly, T cell adherence and transendothelial migration were significantly increased in the immune-activated state. Taken together, our platform allows the generation of a perfusable microvasculature that recapitulates the structure and function of an in vivo capillary bed that can be used as a model for developing potential immunotherapies.

Mussel-inspired adhesive and anti-swelling hydrogels for underwater strain sensing

The application of hydrogels in an underwater environment is limited due to their swelling behavior and the existence of a hydration layer. In this study, a hydrogel based on poly(sulfobetaine methacrylate) (PSBMA), tannic acid (TA) and montmorillonite (MMT) was prepared with excellent anti-swelling properties and underwater self-adhesion properties. The PSBMA hydrogel has excellent anti-swelling properties due to the strong electrostatic interaction between charged groups of PSBMA chains. Inspired by marine mussels, tannic acid modified montmorillonite (TA@MMT) was introduced. Natural polyphenol tannic acid, as a catechol donor, provides a large number of catechol groups for hydrogels. Montmorillonite acts as the physical cross-linking point of PSBMA chains through electrostatic interaction to improve the cohesion of the hydrogel. By combining the adhesion mechanism of zwitterions and catechol, the hydrogel maintains adhesion in air and underwater environments. In addition, a strain sensor was prepared based on the PSBMA/TA@MMT hydrogel, which can closely fit the human skin and stably monitor different movements in air and in underwater environments. Through a Bluetooth communication system, long-distance information transmission can be achieved. Therefore, the PSBMA/TA@MMT hydrogel broadens the application prospect of wearable devices in the underwater environment.

Biomaterials and Cell Therapy Combination in Central Nervous System Treatments

Current pharmacological and surgical therapies for the central nervous system (CNS) show a limited capacity to reduce the damage progression; that together with the intrinsic limited capability of the CNS to regenerate greatly reduces the hopes of recovery. Among all the therapies proposed, the tissue engineering strategies supplemented with therapeutic stem cells remain the most promising. Neural tissue engineering strategies are based on the development of devices presenting optimal physical, chemical, and mechanical properties which, once inserted in the injured site, can support therapeutic cells, limiting the effect of a hostile environment and supporting regenerative processes. Thus, this review focuses on the employment of hydrogel and nanofibrous scaffolds supplemented with stem cells as promising therapeutic tools for the central and peripheral nervous systems in preclinical and clinical applications.

Influence of Dopamine Methacrylamide on Swelling Behavior and Nanomechanical Properties of PNIPAM Microgels

The combination of the catechol-containing comonomer dopamine methacrylamide (DMA) with stimuli-responsive poly(N-isopropylacrylamide) (PNIPAM) microgels bears a huge potential in research and for applications due to the versatile properties of catechols. This research gives the first detailed insights into the influence of DMA on the swelling of PNIPAM microgels and their nanomechanical properties. Dynamic light scattering measurements showed that DMA decreases the volume phase transition temperature and completion temperature due to its higher hydrophobicity when compared to NIPAM, while sharpening the transition. The cross-linking ability of DMA decreases the swelling ratios and mesh sizes of the microgels. Microgels adsorbed at the solid surface are characterized by atomic force microscopy─as the DMA content increases, microgels protrude more from the surface. Force spectroscopy measurements below and above the volume phase transition temperature display a stiffening of the microgels with the incorporation of DMA and upon heating across its entire cross section as evidenced by an increase in the E modulus. This confirms the cross-linking ability of DMA. The affine network factor β, derived from the Flory-Rehner theory, is linearly correlated with the E moduli of both pure PNIPAM and P(NIPAM-co-DMA) microgels. However, large DMA amounts hinder the microgel shrinking while maintaining mechanical stiffness, possibly due to catechol interactions within the microgel network.

Optimization of 3D Synthetic Scaffolds for Neuronal Tissue Engineering Applications

The increasing prevalence of neurodegenerative diseases has spurred researchers to develop advanced 3D models that accurately mimic neural tissues. Hydrogels stand out as ideal candidates as their properties closely resemble those of the extracellular matrix. A critical challenge in this regard is to comprehend the influence of the scaffold's mechanical properties on cell growth and differentiation, thus enabling targeted modifications. In light of this, a synthesis and comprehensive analysis of acrylamide-based hydrogels incorporating a peptide has been conducted. Adequate cell adhesion and development is achieved due to their bioactive nature and specific interactions with cellular receptors. The integration of a precisely controlled physicochemical hydrogel matrix and inclusion of the arginine-glycine-aspartic acid peptide sequence has endowed this system with an optimal structure, thus providing a unique ability to interact effectively with biomolecules. The analysis fully examined essential properties governing cell behavior, including pore size, mechanical characteristics, and swelling ability. Cell-viability experiments were performed to assess the hydrogel's biocompatibility, while the incorporation of grow factors aimed to promote the differentiation of neuroblastoma cells. The results underscore the hydrogel's ability to stimulate cell viability and differentiation in the presence of the peptide within the matrix.

Sacrificial biomaterials in 3D fabrication of scaffolds for tissue engineering applications

Three-dimensional (3D) printing technology has progressed exceedingly in the area of tissue engineering. Despite the tremendous potential of 3D printing, building scaffolds with complex 3D structure, especially with soft materials, still exist as a challenge due to the low mechanical strength of the materials. Recently, sacrificial materials have emerged as a possible solution to address this issue, as they could serve as temporary support or templates to fabricate scaffolds with intricate geometries, porous structures, and interconnected channels without deformation or collapse. Here, we outline the various types of scaffold biomaterials with sacrificial materials, their pros and cons, and mechanisms behind the sacrificial material removal, compare the manufacturing methods such as salt leaching, electrospinning, injection-molding, bioprinting with advantages and disadvantages, and discuss how sacrificial materials could be applied in tissue-specific applications to achieve desired structures. We finally conclude with future challenges and potential research directions.

Advances in Wireless, Batteryless, Implantable Electronics for Real-Time, Continuous Physiological Monitoring

This review summarizes recent progress in developing wireless, batteryless, fully implantable biomedical devices for real-time continuous physiological signal monitoring, focusing on advancing human health care. Design considerations, such as biological constraints, energy sourcing, and wireless communication, are discussed in achieving the desired performance of the devices and enhanced interface with human tissues. In addition, we review the recent achievements in materials used for developing implantable systems, emphasizing their importance in achieving multi-functionalities, biocompatibility, and hemocompatibility. The wireless, batteryless devices offer minimally invasive device insertion to the body, enabling portable health monitoring and advanced disease diagnosis. Lastly, we summarize the most recent practical applications of advanced implantable devices for human health care, highlighting their potential for immediate commercialization and clinical uses.

Bioadhesives with Antimicrobial Properties

Bioadhesives with antimicrobial properties enable easier and safer treatment of wounds as compared to the traditional methods such as suturing and stapling. Composed of natural or synthetic polymers, these bioadhesives seal wounds and facilitate healing while preventing infections through the activity of locally released antimicrobial drugs, nanocomponents, or inherently antimicrobial polers. Although many different materials and strategies are employed to develop antimicrobial bioadhesives, the design of these biomaterials necessitates a prudent approach as achieving all the required properties including optimal adhesive and cohesive properties, biocompatibility, and antimicrobial activity can be challenging. Designing antimicrobial bioadhesives with tunable physical, chemical, and biological properties will shed light on the path for future advancement of bioadhesives with antimicrobial properties. In this review, the requirements and commonly used strategies for developing bioadhesives with antimicrobial properties are discussed. In particular, different methods for their synthesis and their experimental and clinical applications on a variety of organs are reviewed. Advances in the design of bioadhesives with antimicrobial properties will pave the way for a better management of wounds to increase positive clinical outcomes.

Metal Organic Framework-Incorporated Three-Dimensional (3D) Bio-Printable Hydrogels to Facilitate Bone Repair: Preparation and In Vitro Bioactivity Analysis

Hydrogels are three-dimensional (3D) water-swellable polymeric matrices that are used extensively in tissue engineering and drug delivery. Hydrogels can be conformed into any desirable shape using 3D bio-printing, making them suitable for personalized treatment. Among the different 3D bio-printing techniques, digital light processing (DLP)-based printing offers the advantage of quickly fabricating high resolution structures, reducing the chances of cell damage during the printing process. Here, we have used DLP to 3D bio-print biocompatible gelatin methacrylate (GelMA) scaffolds intended for bone repair. GelMA is biocompatible, biodegradable, has integrin binding motifs that promote cell adhesion, and can be crosslinked easily to form hydrogels. However, GelMA on its own is incapable of promoting bone repair and must be supplemented with pharmaceutical molecules or growth factors, which can be toxic or expensive. To overcome this limitation, we introduced zinc-based metal-organic framework (MOF) nanoparticles into GelMA that can promote osteogenic differentiation, providing safer and more affordable alternatives to traditional methods. Incorporation of this nanoparticle into GelMA hydrogel has demonstrated significant improvement across multiple aspects, including bio-printability, and favorable mechanical properties (showing a significant increase in the compressive modulus from 52.14 ± 19.42 kPa to 128.13 ± 19.46 kPa with the addition of ZIF-8 nanoparticles). The designed nanocomposite hydrogels can also sustain drug (vancomycin) release (maximum 87.52 ± 1.6% cumulative amount) and exhibit a remarkable ability to differentiate human adipose-derived mesenchymal stem cells toward the osteogenic lineage. Furthermore, the formulated MOF-integrated nanocomposite hydrogel offers the unique capability to coat metallic implants intended for bone healing. Overall, the remarkable printability and coating ability displayed by the nanocomposite hydrogel presents itself as a promising candidate for drug delivery, cell delivery and bone tissue engineering applications.

Stacking thick perfusable human microvascular grafts enables dense vascularity and rapid integration into infarcted rat hearts

Fabrication of large-scale engineered tissues requires extensive vascularization to support tissue survival and function. Here, we report a modular fabrication approach, by stacking of patterned collagen membranes, to generate thick (2 mm and beyond), large, three-dimensional, perfusable networks of endothelialized vasculature. In vitro, these perfusable vascular networks exhibit remodeling and evenly distributed perfusion among layers, while maintaining their patterned, open-lumen architecture. Compared to non-perfusable, self-assembled vasculature, constructs with perfusable vasculature demonstrated increased gene expression indicative of vascular development and angiogenesis. Upon implantation onto infarcted rat hearts, perfusable vascular networks attain greater host vascular integration than self-assembled controls, indicated by 2.5-fold greater perfused vascular density measured by histological analysis and 5-fold greater perfusion rate measured by optical microangiography. Together, the success of fabricating thick, perfusable tissues with dense vascularity and rapid anastomoses represents an important step forward for vascular bioengineering, and paves the way towards more complex, large scale, highly metabolic engineered tissues.

Triaxial bioprinting large-size vascularized constructs with nutrient channels

Bioprinting has demonstrated great advantages in tissue and organ regeneration. However, constructing large-scale tissue and organsin vitrois still a huge challenge due to the lack of some strategies for loading multiple types of cells precisely while maintaining nutrient channels. Here, a new 3D bioprinting strategy was proposed to construct large-scale vascularized tissue. A mixture of gelatin methacrylate (GelMA) and sodium alginate (Alg) was used as a bioink, serving as the outer and middle layers of a single filament in the triaxial printing process, and loaded with human bone marrow mesenchymal stem cells and human umbilical vein endothelial cells, respectively, while a calcium chloride (CaCl2) solution was used as the inner layer. The CaCl2solution crosslinked with the middle layer bioink during the printing process to form and maintain hollow nutrient channels, then a stable large-scale construct was obtained through photopolymerization and ion crosslinking after printing. The feasibility of this strategy was verified by investigating the properties of the bioink and construct, and the biological performance of the vascularized construct. The results showed that a mixture of 5% (w/v) GelMA and 1% (w/v) Alg bioink could be printed at room temperature with good printability and perfusion capacity. Then, the construct with and without channels was fabricated and characterized, and the results revealed that the construct with channels had a similar degradation profile to that without channels, but lower compressive modulus and higher swelling rate. Biological investigation showed that the construct with channels was more favorable for cell survival, proliferation, diffusion, migration, and vascular network formation. In summary, it was demonstrated that constructing large-scale vascularized tissue by triaxial printing that can precisely encapsulate multiple types of cells and form nutrient channels simultaneously was feasible, and this technology could be used to prepare large-scale vascularized constructs.

A dual stimuli-responsive smart soft carrier using multi-material 4D printing

This paper proposes a 4D printed smart soft carrier with a hemispherical hollow and openable lid. The soft carrier is composed of a lid with a slot (with a shape of 4 legs), a border, and a hemisphere. The soft carrier is fabricated by 4D printing using smart hydrogels. Specifically, the lid, border, and hemisphere are fabricated using a thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel, a non-responsive polyethylene glycol (PEG) hydrogel with superparamagnetic iron oxide nanoparticles (SPIONs), and a PEG hydrogel, respectively. Since the SPIONs are included in the border, the slot in the center of the lid is opened and closed according to the temperature change caused by near-infrared (NIR) irradiation, and the proposed soft carrier is magnetically driven by an external magnetic field. The hemisphere enables the storage and transport of cargo. The proposed soft carrier can control the opening and closing of the slot and movement to a desired position in water. Several cargo delivery experiments were conducted using various shapes and numbers of cargo. In addition, the proposed soft carrier can successfully handle small living marine organisms. This soft carrier can be manufactured by 4D printing and operated by dual stimuli (NIR and magnetic field) and can safely deliver various types of cargo and delicate organisms without leakage or damage. The flexibility of 4D printing enables the size of the soft carrier to be tailored to the specific physical attributes of various objects, making it an adaptable and versatile delivery approach.

A Flexible Conductive Electrode Using Boronic-Acid Modified Carbon Dots

Flexible electrodes are becoming a topic of interest for a range of applications including implantation. They can be used for neural signal recording and for electrical stimulation of atrophying muscles. Unlike the traditionally used metal electrodes that are harsh to the body's tissues, flexible electrodes conduct electricity while preserving the delicate tissues. Polydimethylsiloxane (PDMS), a non-conductive synthetic polymer characterized by its flexibility, low cost, biocompatibility, and durability during implantation, has been explored as a matrix for flexible electrodes. This study reports the synthesis of composite boronic acid-modified carbon dots (BA-CDs)/PDMS electrode materials. The performance of the composite electrode is evaluated electrochemically (for its conductivity and charge storage capacity) and mechanically (Young's modulus). Furthermore, the effect of increasing the PDMS crosslinking density on the electrode's performance is studied based on the hypothesis that a higher crosslinking will bring the BA-CDs closer together, thereby facilitating the movement of electrons. Results of this study showed that incorporating 10% BA-CDs dispersed with 16% glycerol in 74% PDMS with a higher crosslinking density resulted in a bulk impedance of 47.7 Ω and a conductivity of 2.68×10-3 S/cm, both of which surpassed that of the same composition with lower crosslinking. The synthesized flexible electrode material was capable of charge storage although the charge storage capacity (0.00365 mC/cm2) was lower than the safe limit for some tissue activation. Furthermore, the electrode maintained a modulus of elasticity (0.2322 MPa) that is compatible with biological soft tissues.Clinical Relevance- This study reports a conductive electrode that has a flexibility compatible with that of biological tissues for future purposes such as neural signal recording and tissue electrical stimulation (e.g. atrophying muscles). The reported BA-CD/PDMS electrode overcomes the limitations of the harsh metals previously used as implantable electrodes that harm the biological tissues due to their high rigidity.

Leveraging peptide-cellulose interactions to tailor the hierarchy and mechanics of peptide-polymer hybrids

Inspired by spider silk's hierarchical diversity, we leveraged peptide motifs with the capability to tune structural arrangement for controlling the mechanical properties of a conventional polymer framework. The addition of nanofiller with hydrogen bonding sites was used as another pathway towards hierarchical tuning via matrix-filler interactions. Specifically, peptide-polyurea hybrids (PPUs) were combined with cellulose nanocrystals (CNCs) to develop mechanically-tunable nanocomposites via tailored matrix-filler interactions (or peptide-cellulose interactions). In this material platform, we explored the effect of these matrix-filler interactions on the secondary structure, hierarchical ordering, and mechanical properties of the peptide hybrid nanocomposites. Interactions between the peptide matrix and CNCs occur in all of the PPU/CNC nanocomposites, preventing α-helical ordering, but promoting inter-molecular hydrogen bonded β-sheet formation. Depending on peptide and CNC content, the Young's modulus varies from 10 to 150 MPa. Unlike conventional cellulose-reinforced polymer nanocomposites, the mechanical properties of these composite materials are dictated by a balance of CNC reinforcement, peptidic ordering, and microphase-separated morphology. This research highlights that leveraging peptide-cellulose interactions is a strategy to create materials with targeted mechanical properties for a specific application using a limited selection of building blocks.

Hydrogel electrodes with conductive and substrate-adhesive layers for noninvasive long-term EEG acquisition

Noninvasive brain-computer interfaces (BCIs) show great potential in applications including sleep monitoring, fatigue alerts, neurofeedback training, etc. While noninvasive BCIs do not impose any procedural risk to users (as opposed to invasive BCIs), the acquisition of high-quality electroencephalograms (EEGs) in the long term has been challenging due to the limitations of current electrodes. Herein, we developed a semidry double-layer hydrogel electrode that not only records EEG signals at a resolution comparable to that of wet electrodes but is also able to withstand up to 12 h of continuous EEG acquisition. The electrode comprises dual hydrogel layers: a conductive layer that features high conductivity, low skin-contact impedance, and high robustness; and an adhesive layer that can bond to glass or plastic substrates to reduce motion artifacts in wearing conditions. Water retention in the hydrogel is stable, and the measured skin-contact impedance of the hydrogel electrode is comparable to that of wet electrodes (conductive paste) and drastically lower than that of dry electrodes (metal pin). Cytotoxicity and skin irritation tests show that the hydrogel electrode has excellent biocompatibility. Finally, the developed hydrogel electrode was evaluated in both N170 and P300 event-related potential (ERP) tests on human volunteers. The hydrogel electrode captured the expected ERP waveforms in both the N170 and P300 tests, showing similarities in the waveforms generated by wet electrodes. In contrast, dry electrodes fail to detect the triggered potential due to low signal quality. In addition, our hydrogel electrode can acquire EEG for up to 12 h and is ready for recycled use (7-day tests). Altogether, the results suggest that our semidry double-layer hydrogel electrodes are able to detect ERPs in the long term in an easy-to-use fashion, potentially opening up numerous applications in real-life scenarios for noninvasive BCI.