Programmable Anisotropic Hydrogels for Biomedicine: From Precise Design to Advanced Applications.

Constructing anisotropic and strong polysaccharide-based hydrogels with stretching-dehydration strategy: Effect of sodium alginate, pectin, gellan gum, and curdlan.

Anisotropic biomaterials containing oriented collagen fibers have shown great potential for various biomedical research areas, such as wound dressing, corneal grafting, and the study of cancer cell invasion in biomimetic microenvironments. To fabricate such anisotropic biomaterials, previous studies have used electric, microfluidic, magnetic, and mechanical methods to align collagen fibers during the fabrication process. In this study, we put forward traveling and standing acoustic wave-based approaches that enable the rapid in-Petri-dish fabrication of anisotropic biomaterials containing acoustically arranged collagen fibers. To develop these approaches, we investigated the effects of traveling and standing acoustic waves on collagen self-assembly and the micro/nanoscale architectures of the fabricated collagen-based biomaterials. Our results reveal that traveling acoustic wave-induced fluid streaming can transport collagen molecules, thereby influencing the collagen self-assembly process, while standing acoustic waves can accumulate self-assembled collagen fibers, increasing their concentrations in acoustic potential valleys periodically distributed. Using our acoustics-assisted approach, we successfully manufactured anisotropic collagen hydrogels containing aligned collagen fibers, which provide anisotropic microenvironments for cell growth and development. Notably, we demonstrated the functionality of these fabricated anisotropic collagen hydrogels in facilitating cell elongation along the acoustically aligned collagen fibers. Compared to previous methods, our acoustics-based approaches are easy to operate without requiring customized chambers for loading collagen and are capable of rapidly fabricating anisotropic collagen hydrogels directly in commercial Petri dishes, thus allowing our approaches to be readily integrated into existing laboratory workflows and combined with other test protocols. In the long run, we expect this work to inspire the development of useful tools that will benefit biomedical researchers working in tissue engineering, regenerative medicine, biomaterials, and bioprinting.

Integrating structural anisotropy, excellent mechanical properties, and superior sensing capability into conductive hydrogels is of great importance to wearable flexible electronics yet challenging. Herein, inspired from the aligned structure of human muscle, we proposed a facile and universal method to construct an anisotropic hydrogel composed of polyacrylamide and sodium alginate by pre-stretching in a confined geometry and subsequent ionic cross-linking. The designed hydrogels showed extraordinary mechanical performances, such as ultrahigh stretchability, a comparable modulus to that of human tissues, and good toughness, ascribed to their anisotropically aligned polymer networks. Additionally, the hydrogel possessed anisotropic conductivity due to the anisotropy in ion transport channels. The hydrogel along the vertical direction was further cut and assembled into a flexible strain sensor, exhibiting a low detection limit (0.1%), wide strain range (1585%), rapid response (123 ms), distinct resilience, good stability, and repeatability, thereby being capable of monitoring and discriminating different human movements. In addition, the relatively high ionic conductivity and superior sensitivity enabled the anisotropic hydrogel sensor to be used for wireless human-machine interaction. More interestingly, the Ca2+-cross-linking strategy also endowed the hydrogel sensor with antifreezing ability, further broadening their working temperature. This work is expected to speed up the development of hydrogel sensors in the emerging wearable soft electronics.

Electrically induced anisotropic assembly of chitosan with different molecular weights

Anisotropic biological tissues contain hierarchical complexity from the nano to macro length scales. While novel fabrication strategies have advanced the creation of biomimetic architectures, most rely on biologically derived polymers that possess inherent batch-to-batch variability. Here, we fabricate omnidirectional anisotropic nanofibrous hydrogels using synthetic, self-assembling MultiDomain Peptides (MDPs). Using support bath-assisted extrusion 3D printing, MDP hydrogels are created with control over nanometer-scale fibrous alignment, ~150 μm-scale print resolution, and centimeter-scale 3D architecture. Further, scaffold anisotropy is tuned by adjusting the ionic strength of the support bath, allowing fiber alignment to be decoupled from extrusion shear force and the ink used. Applying these hydrogels to in vitro tissue engineering, fabricated anisotropic hydrogels are shown to guide the alignment of multiple cell types within complex 3D prints. Furthermore, the gels are demonstrated to support the growth of human embryonic stem cell-derived cardiomyocytes into functional tissue. Collectively, this work introduces a platform for engineering anisotropic peptide hydrogels with hierarchical complexity, offering broad potential for bottom-up fabrication of functional human tissues in vitro.

Magnet-oriented hydrogels with mechanical–electrical anisotropy and photothermal antibacterial properties for wound repair and monitoring

Extrusion-based 3D printing is a facile technology to construct complex structures of hydrogels, especially for tough hydrogels that have shown demonstrated potential in load-bearing materials and tissue engineering. However, 3D-printed hydrogels often possess mechanical properties that do not guarantee their usage in tissue-mimicking, load-bearing components, and motion sensors. This study proposes a novel strategy to construct high-strength and anisotropic Fe3+ cross-linked poly(acrylamide-co-acrylic acid)/sodium alginate double network hydrogels. The semi-flexible sodium alginate chains act as a "conformation regulator" to promote the formation of strong intermolecular interactions between polymer chains and lock the more extended conformation exerted by the pre-stretch, enabling the construction of 3D-printed hydrogel structures with high orientation. The equilibrated anisotropic hydrogel filaments with a water content of 50-60 wt.% exhibit outstanding mechanical properties (tensile strength: 9-44MPa; elongation at break: 120-668%; Young's modulus: 7-62MPa; toughness: 26-52MJm- 3). 3D-printed anisotropic hydrogel structures with high mechanical performance show demonstrated potential as loading-bearing structures and electrodes of flexible triboelectric nanogenerators for versatile human motion sensing.

Anisotropic hydrogels are promising candidates as load-bearing materials for tissue engineering, while huge challenges remain in exploring effective and scalable methods for the preparation of anisotropic hydrogels with simultaneous high tensile strength, large toughness, good fracture strain, excellent fatigue and swelling resistances. Inspired by the brick-and-mortar layered structure of nacre and the hierarchical fibril strucure of soft tissues (e.g., tendon and ligament), a facile organogel-assissted calendering strategy is reported to design anisotropic hydrogels with a highly oriented and dense fiber lamellar strucure. The synergy of shearing and annealing promotes macromolecular chain alignment and crystallinity along the calendering direction while forming a nacre-like lamellar morphology in the thickness direction. The tensile strength, elastic modulus, toughness and fracture energy of the anisotropic hydrogels can reach as high as 41.0 ± 6.4MPa, 67.0 ± 5.1MPa, 46.2 ± 3.3MJ m-3, and 62.20 ± 8.55kJ m-2, respectively. More importantly, the hydrogels show excellent crack growth and swelling resistances with the fatigue threshold increased to 2170 J m-2. This study provides a promising approach for fabrication of large-sized biomimetic anisotropic hydrogels with outstanding mechanical properties for biomedical and engineering applications.

Cytocompatible chitosan based multi-network hydrogels with antimicrobial, cell anti-adhesive and mechanical properties

The development of effective wound dressings is critical for enhancing patient outcomes in both acute and chronic wound care scenarios. In this research, electrospun nanofibrous scaffolds were fabricated from poly(ε-caprolactone) (PCL), enhanced with curcumin and reduced graphene oxide (RGO) to optimize their biomedical applications, particularly in wound healing. The resulting scaffolds were rigorously characterized through scanning electron microscopy, contact angle measurements, water uptake capacity, and water vapor transmission rate assays. The biocompatibility of these novel nanofibers was affirmed through MTT assays. Antibacterial tests confirmed the scaffolds’ ability to inhibit both Gram-negative and Gram-positive bacteria, with inhibition zones measuring up to 9.9 mm for S. aureus and 9.2 mm for E. coli. Additionally, scaffolds containing curcumin exhibited significant antioxidant activity, achieving up to 40% radical scavenging efficiency. The study further revealed the scaffolds’ capability for sustained drug release, with an initial burst release within the first 12 hours followed by a gradual release over 168 hours. Overall, the PCL-curcumin-RGO electrospun mats demonstrated considerable potential for biomedical applications, notably in the field of wound dressings, due to their enhanced antibacterial, antioxidant, and biocompatible properties.

Bone extracellular matrix comprises a unique composite compound including the mineral and organic components. Therefore, use of biomimetic approach to the formation of tissue-engineered constructions for bone defects replacement based on composite materials containing biopolymers and calcium phosphates, as expected, can significantly improve their cyto-, biocompatibility and osteoplastic properties. The aim of the work was to study the structural features, biocompatibility and osteoplastic properties of 3D-constructions based on sodium alginate, gelatin, and two types of calcium phosphates (tricalcium phosphate and octacalcium phosphate) obtained by three-dimensional printing. The method of 3D-constructions fabrication comprised inkjet 3D-printing with hydrogel, consisted of alginate and gelatin with the addition of calcium phosphate granules, followed by freezing, freeze-drying and sterilization by y-irradiation. The structure of 3D-constructions, porosity and strength characteristics were evaluated. After the subcutaneous implantation in mice we investigated the biocompatibility of 3D-constructions during the period of up to 12 weeks. Also the osteoplastic properties of the constructions were estimated in vivo in a rat model of tibial defects. 3D printed constructions had irregular lamellar structure of sodium alginate with inclusions of spherical calcium phosphates granules. Addition of gelatin to the composite increased the porosity of constructs and significantly increased the compressive strength meanwhile practically had no effect on the ultimate strain value. In results of subcutaneous in vivo tests 3D printed constructions demonstrated perfect prolonged biocompatibility. The highest rate of biodegradation was noticed for implants containing octacalcium phosphate. All of the studied 3D-scaffolds had osteoconductive potential, more pronounced according to the number of examined histological parameters in those, made from sodium alginate, gelatin and octacalcium phosphate. The data showed the feasibility and prospect of using three-component mineral polymer composite materials based on alginate, gelatin and octacalcium phosphate as an “ink” for 3D printing of bone grafting constructions intended for implantation in bone defects.

To enhance cell adhesion and cell interactions for diverse tissue engineering applications, polycaprolactone (PCL) has been integrated with few biomaterials such as ceramic (i.e. tricalcium phosphate - TCP), hydrogel (i.e. sodium alginate - SA), and synthetic polymer materials (i.e. polyethylene glycol - PEG). Each type of additive material presents typical characteristics, the comparison among these three biomaterial types is currently inadequate. In this study, a 3D printer using direct powder screw extrusion technique was applied for fabricating three types of PCL-based composite scaffolds (namely, PCL-PEG, PCL-SA, and PCL-TCP) which are representative of each type of additive material. The experimental evaluation on the printability, scaffold morphology, surface roughness, hydrophobicity, and cell proliferation of these PCL-based composite scaffolds were compared under the same conditions. The results demonstrated that the additive materials with an amount from 20 wt% have a notable effect on the printability of PCL matrix material and significant enhancement of cell proliferation. The incorporation of PEG with PCL is the most effective choice to increase the hydrophilicity of the scaffold surface. The PCL-SA scaffold provided a more favorable environment for cells at the initial stage, whereas the PCL-TCP scaffold demonstrated superior cell proliferation over time. These findings also demonstrate the feasibility of a direct powder screw extrusion printhead on 3D printing for composite scaffolds in tissue engineering applications.

Controlled fabrication of anisotropic materials has become a hotspot in materials science, particularly biomaterials, since the next generation of tissue engineering is based on the application of heterogeneous structures that can simulate the original biological complexity of the body. The current fabrication method of producing anisotropic materials involves expensive and highly specialized equipment, and not every conventional method can be applied to preparing anisotropic materials for corresponding tissue engineering. Anisotropic materials can be easily applied to a problem in tissue engineering: cartilage injury repairing. The articular cartilage consists of four spatially distinct regions: superficial, transitional, deep, and calcified. Each region has a specific extracellular matrix composition, mechanical properties, and cellular organization; this calls for the application of an anisotropic hydrogel. Controlled diffusion, under the assistance of buoyancy, has been considered a generalized method to prepare materials using a gradient. The diffusion of two solutions can be controlled through the difference in their densities. In addition to providing anisotropy, this method realizes the in situ formation of an anisotropic hydrogel, and simplifies the preparation process, freeing it from the need for expensive equipment such as 3D printing and microfluidics. Herein, an anisotropic hydrogel based on a decellularized extracellular matrix is fabricated and characterized. The as-prepared scaffold possessed specific chemical composition, physical properties, and physiological factor gradient. In vitro experiments ensured its biocompatibility and biological effectiveness; further in vivo experiments confirmed its application in the effective regeneration of cartilage injury.

Fabrication of tissue-engineered tympanic membrane patches using 3D-Printing technology

Additive-free 3D-printed nanostructured carboxymethyl cellulose aerogels.