Light‐Induced Swelling‐Responsive Conductive,Adhesive, and Stretchable Wireless Film Hydrogel as Electronic Artificial Skin

Light‐induced wireless soft electronic skin hydrogels with excellent mechanical and electronic properties are important for several applications, such as soft robotics and intelligent wearable devices. Precise control of reversible stretchability and capacitive properties depending on intermolecular interaction and surface characteristics remains a challenge. Here, a thin‐film hydrogel is designed based on titanium oxide (TiO₂) polydopamine–perfluorosilica carbon dot‐conjugated chitosan–polyvinyl alcohol‐loaded tannic acid with controllable hydrophobic–hydrophilic transition in the presence of UV–vis light irradiation. The shifting of surface wettability from hydrophobic to hydrophilic by irradiation affects thin‐film water permeability and swelling ratio. This allows the penetration of water into the matrix to change its mechanical strength, electronic properties, and adhesive behavior. Specifically, the hydrogel displays mechanical strain as high as 278% in response to light stimuli and demonstrates the ability to regain its initial state determining the elasticity of the fabricated material. Moreover, the thin‐film hydrogel shows an increase in conductivity to 1.096 × 10^?3 and 1.026 × 10^?3 S cm^?1 when irradiated with UV and visible light, respectively. The hydrogel exhibits capacitive reversibility that follows finger motion which can be identified directly or remotely using wireless connection, indicative of its possible applications as an artificial electronic skin.     

Inherent Photodegradability of Polymethacrylate Hydrogels: Straightforward Access to Biocompatible Soft Microstructures

Hydrogels are important functional materials useful for 3D cell culture, tissue engineering, 3D printing, drug delivery, sensors, or soft robotics. The ability to shape hydrogels into defined 3D structures, patterns, or particles is crucial for biomedical applications. Here, the rapid photodegradability of commonly used polymethacrylate hydrogels is demonstrated without the need to incorporate additional photolabile functionalities. Hydrogel degradation depths are quantified with respect to the irradiation time, light intensity, and chemical composition. It can be shown that these parameters can be utilized to control the photodegradation behavior of polymethacrylate hydrogels. The photodegradation kinetics, the change in mechanical properties of polymethacrylate hydrogels upon UV irradiation, as well as the photodegradation products are investigated. This approach is then exploited for microstructuring and patterning of hydrogels including hydrogel gradients as well as for the formation of hydrogel particles and hydrogel arrays of well‐defined shapes. Cell repellent but biocompatible hydrogel microwells are fabricated using this method and used to form arrays of cell spheroids. As this method is based on readily available and commonly used methacrylates and can be conducted using cheap UV light sources, it has vast potential to be applied by laboratories with various backgrounds and for diverse applications.     

Engineering Tridimensional Hydrogel Tissue and Organ Phantoms with Tunable Springiness

Biomimicking organ phantoms with vivid biological structures and soft and slippery features are essential for in vitro biomedical applications yet remain hither to unmet challenges in their fabrication such as balancing between spatial structural complexity and matchable mechanical properties. Herein, 3D printable tissue-mimicking elastomeric double network hydrogels with tailorable stiffness are evolved to idiosyncratically match diverse biological soft tissues by regulating the compositions of hydrogel matrix and the density of metal coordination bonds. Relying on digital light processing 3D printing, various mechanically tunable biomimetic volumetric hydrogel organ constructs with structural complexity and fidelity, including kidney, brain, heart, liver, stomach, lung, trachea, intestine, and even the intricate vascularized tissues, are fabricated faultlessly. Proof-of-concept 3D printed hydrogel heart and liver phantoms provide sophisticated internal channels and cavity structures and external realistic anatomical architectures that more closely mimic native organs. For the in vitro application demonstration, a 3D printed hydrogel brain phantom with tortuous cerebral arteries and slippery characters serves as an effective neurosurgical training platform for realistic simulation of endovascular interventions. This platform offers a means to construct mechanically precisely tunable hydrogel-based biomimetic organ phantoms that are expected to be used in surgical training, medical device testing, and organs-on-chips.     

Functional Nanomaterials on 2D Surfaces and in 3D Nanocomposite Hydrogels for Biomedical Applications

An emerging approach to improve the physicobiochemical properties and the multifunctionality of biomaterials is to incorporate functional nanomaterials (NMs) onto 2D surfaces and into 3D hydrogel networks. This approach is starting to generate promising advanced functional materials such as self‐assembled monolayers (SAMs) and nanocomposite (NC) hydrogels of NMs with remarkable properties and tailored functionalities that are beneficial for a variety of biomedical applications, including tissue engineering, drug delivery, and developing biosensors. A wide range of NMs, such as carbon‐, metal‐, and silica‐based NMs, can be integrated into 2D and 3D biomaterial formulations due to their unique characteristics, such as magnetic properties, electrical properties, stimuli responsiveness, hydrophobicity/hydrophilicity, and chemical composition. The highly ordered nano‐ or microscale assemblies of NMs on surfaces alter the original properties of the NMs and add enhanced and/or synergetic and novel features to the final SAMs of the NM constructs. Furthermore, the incorporation of NMs into polymeric hydrogel networks reinforces the (soft) polymer matrix such that the formed NC hydrogels show extraordinary mechanical properties with superior biological properties.     

Ascidian‐Inspired Fast‐Forming Hydrogel System for Versatile Biomedical Applications: Pyrogallol Chemistry for Dual Modes of Crosslinking Mechanism

Exploitation of unique biochemical and biophysical properties of marine organisms has led to the development of functional biomaterials for various biomedical applications. Recently, ascidians have received great attention, owing to their extraordinary properties such as strong underwater adhesion and rapid self‐regeneration. Specific polypeptides containing 3,4,5‐trihydroxyphenylalanine (TOPA) in the blood cells of ascidians are associated with such intrinsic properties generated through complex oxidative processes. In this study, a bioinspired hydrogel platform is developed, demonstrating versatile applicability for tissue engineering and drug delivery, by conjugating pyrogallol (PG) moiety resembling ascidian TOPA to hyaluronic acid (HA). The HA–PG conjugate can be rapidly crosslinked by dual modes of oxidative mechanisms using an oxidant or pH control, resulting in hydrogels with different mechanical and physical characteristics. The versatile utility of HA–PG hydrogels formed via different crosslinking mechanisms is tested for different biomedical platforms, including microparticles for sustained drug delivery and tissue adhesive for noninvasive cell transplantation. With extraordinarily fast and different routes of PG oxidation, ascidian‐inspired HA–PG hydrogel system may provide a promising biomaterial platform for a wide range of biomedical applications.     

Bioorthogonal Strategies for Engineering Extracellular Matrices

Hydrogels are commonly used as engineered extracellular matrix (ECM) mimics in applications ranging from tissue engineering to in vitro disease models. Ideal mechanisms used to crosslink ECM‐mimicking hydrogels do not interfere with the biology of the system. However, most common hydrogel crosslinking chemistries exhibit some form of crossreactivity. The field of bioorthogonal chemistry has arisen to address the need for highly specific and robust reactions in biological contexts. Accordingly, bioorthogonal crosslinking strategies are incorporated into hydrogel design, allowing for gentle and efficient encapsulation of cells in various hydrogel materials. Furthermore, the selective nature of bioorthogonal chemistries can permit dynamic modification of hydrogel materials in the presence of live cells and other biomolecules to alter matrix mechanical properties and biochemistry on demand. This review provides an overview of bioorthogonal strategies used to prepare cell‐encapsulating hydrogels and highlights the potential applications of bioorthogonal chemistries in the design of dynamic engineered ECMs.     

Injectable and Tunable Gelatin Hydrogels Enhance Stem Cell Retention and Improve Cutaneous Wound Healing

Stem cells have shown substantial promise for various diseases in preclinical and clinical trials. However, low cell engraftment rates significantly limit the clinical translation of stem cell therapeutics. Numerous injectable hydrogels have been developed to enhance cell retention. Yet, the design of an ideal material with tunable properties that can mimic different tissue niches and regulate stem cell behaviors remains an unfulfilled promise. Here, an injectable poly(ethylene glycol) (PEG)–gelatin hydrogel is designed with highly tunable properties, from a multifunctional PEG‐based hyperbranched polymer and a commercially available thiolated gelatin. Spontaneous gelation occurs within about 2 min under the physiological condition. Murine adipose‐derived stem cells (ASCs) can be easily encapsulated into the hydrogel, which supports ASC growth and maintains their stemness. The hydrogel mechanical properties, biodegradability, and cellular responses can be finely controlled by changing hydrogel formulation and cell seeding densities. An animal study shows that the in situ formed hydrogel significantly improves cell retention, enhances angiogenesis, and accelerates wound closure using a murine wound healing model. These data suggest that injectable PEG–gelatin hydrogel can be used for regulating stem cell behaviors in 3D culture, delivering cells for wound healing and other tissue regeneration applications.     

Rationally Designed Dynamic Protein Hydrogels with Reversibly Tunable Mechanical Properties

Protein hydrogels have attracted considerable interest due to their potential applications in biomedical engineering. Creating protein hydrogels with dynamic mechanical properties is challenging. Here, the engineering of a novel, rationally designed protein‐hydrogel is reported that translates molecular level protein folding‐unfolding conformational changes into macroscopic reversibly tunable mechanical properties based on a redox controlled protein folding‐unfolding switch. This novel protein folding switch is constructed from a designed mutually exclusive protein. Via oxidation and reduction of an engineered disulfide bond, the protein folding switch can switch its conformation between folded and unfolded states, leading to a drastic change of protein's effective chain length and mechanical compliance. This redox‐responsive protein can be readily photochemically crosslinked into solid hydrogels, in which molecular level conformational changes (folding‐unfolding) can result in significant macroscopic changes in hydrogel's physical and mechanical properties due to the change of the effective chain length between two crosslinking points in the protein hydrogel network. It is found that when reduced, the hydrogel swells and is mechanically compliant; when oxidized, it swells to a less extent and becomes resilient and stiffer, exhibiting an up to fivefold increase in its Young's modulus. The changes of the mechanical and physical properties of this hydrogel are fully reversible and can be cycled using redox potential. This novel protein hydrogel with dynamic mechanical and physical properties could find numerous applications in material sciences and tissue engineering.     

Bottom‐Up Preparation of Fully sp2‐Bonded Porous Carbons with High Photoactivities

Porous carbons, possessing exceptional stability, high surface area, and electric conductivity, are broadly used as superior adsorbent, supporter, or electrode material for environmental protection, industrial catalysis, and energy storage and conversion. The construction of such kinds of materials with designable structures and properties will extremely extend their potential applications, but remains a huge synthetic challenge. Herein, a bottom‐up approach is presented to synthesize one type of fully sp² carbon–bonded frameworks by transition metal–catalyzed cross‐coupling of different polyphenylenes with electron‐withdrawing 9,9′‐bifluorenylidene (9,9′‐BF) through its 2,7‐position. The resulting porous polymeric carbons exhibit substantial semiconducting properties, such as strong light‐harvesting capabilities in the visible light region, likely due to their π‐extended backbones with donor–acceptor characters. Their electronic and porous structures can be finely tuned via the polyphenylene spacers. The intriguing properties allow these porous carbons to efficiently catalyze dye degradation under visible light or even natural sunlight with high reusability. Meanwhile, associated with their intrinsic structures, these porous carbons also exhibit highly selective degradation activities toward different dyes. In particular, the photodegradation mechanism involving oxygen and electron is elucidated for the first time for such kinds of materials, related to the presence of specific 9,9′‐BF units in their π‐conjugated skeletons.     

Synthesizing Organo/Hydrogel Hybrids with Diverse Programmable Patterns and Ultrafast Self‐Actuating Ability via a Site‐Specific “In Situ” Transformation Strategy

A simple yet robust strategy called “‘in situ' transformation” is developed to prepare organo/hydro binary gels based on the aminolysis of poly(pentafluorophenyl acrylate) (pPFPA). Treated with desired hydrophilic, oleophilic alkylamines, and their mixtures, pPFPA‐based organogels can be thoroughly transformed to targeted hydrogels, organogels, and even organohydrogels with outstanding mechanical properties. Further, relying on programed aminolysis procedures, site‐specific “in situ” transformation can be realized, giving rise to organo/hydro binary gels with diverse patterns and morphologies, such as macroscopic layered organo/hydrogel with a smooth‐transitioned yet mechanically robust interface, reconfigurable microscale organo/hydrogel hybrids with a high spatial‐resolution pattern capable of reversibly transforming between 2D sheets and 3D helixes with controlled chirality in different solvents, and core–shell structured organo/hydrogel hybrids with readily adjustable core/shell dimensions, tunable internal stress, and transparency. Finally, an oscillator based on a bilayered organo/hydrogel hybrid is developed. Attributing to the synergistic effect of organogel expansion and hydrogel contraction, as well as the robust interfacial mechanical properties, this oscillator is capable of ultrafast self‐actuating through harvesting surrounding chemical and thermal energy. This work provides new design principles and highly efficient synthetic strategy for organo/hydro binary gels, and expands their potential applications in soft robotics.     

Engineering Natural Pollen Grains as Multifunctional 3D Printing Materials

The development of multifunctional 3D printing materials from sustainable natural resources is a high priority in additive manufacturing. Using an eco-friendly method to transform hard pollen grains into stimulus-responsive microgel particles, we engineered a pollen-derived microgel suspension that can serve as a functional reinforcement for composite hydrogel inks and as a supporting matrix for versatile freeform 3D printing systems. The pollen microgel particles enabled the printing of composite inks and improved the mechanical and physiological stabilities of alginate and hyaluronic acid hydrogel scaffolds for 3D cell culture applications. Moreover, the particles endowed the inks with stimulus-responsive controlled release properties. The suitability of the pollen microgel suspension as a supporting matrix for freeform 3D printing of alginate and silicone rubber inks was demonstrated and optimized by tuning the rheological properties of the microgel. Compared with other classes of natural materials, pollen grains have several compelling features, including natural abundance, renewability, affordability, processing ease, monodispersity, and tunable rheological features, which make them attractive candidates to engineer advanced materials for 3D printing applications.     

Magnetic Hydrogels and Their Potential Biomedical Applications

Hydrogels find widespread applications in biomedical engineering due to their hydrated environment and tunable properties (e.g., mechanical, chemical, biocompatible) similar to the native extracellular matrix (ECM). However, challenges still exist regarding utilizing hydrogels in applications such as engineering 3D tissue constructs and active targeting in drug delivery, due to the lack of controllability, actuation, and quick‐response properties. Recently, magnetic hydrogels have emerged as a novel biocomposite for their active response properties and extended applications. In this review, the state‐of‐the‐art methods for magnetic hydrogel preparation are presented and their advantages and drawbacks in applications are discussed. The applications of magnetic hydrogels in biomedical engineering are also reviewed, including tissue engineering, drug delivery and release, enzyme immobilization, cancer therapy, and soft actuators. Concluding remarks and perspectives for the future development of magnetic hydrogels are addressed.     

Multifunctional,Ultra-Tough Organohydrogel E-Skin Reinforced by Hierarchical Goatskin Fibers Skeleton for Energy Harvesting and Self-Powered Monitoring

E-skins based on conductive hydrogels are regarded as ideal candidates for sensing application. However, limited by the constructed materials and strategies, the current conductive hydrogels have poor mechanical properties, single function, and unsatisfactory conductivity, which seriously hinder their development and application. Herein, the natural goatskin with hierarchical 3D network structure weaved by collagen fibers is used as the substrate material for the construction of ultra-tough hydrogel through a “top-down” strategy, in which acrylic acid monomer is first vacuum-impregnated into the interstices of goatskin fibers skeleton and is then polymerized in situ to produce the skin-based hydrogel with unique 3D wrapping structure. Based on the skin-based hydrogel, a substrate with load-carrying capacity, after loaded with a new multifunctional nanoscale-conductive medium nanosilver particles (AgNPs) and 1,3-propanediol, a goatskin-derived multifunctional organohydrogel S@HCP is constructed with excellent mechanical properties, self-adhesion, transparency, ultraviolet shielding, antibacterial, biocompatibility, environmental stability, and conductivity. Notably, the stretchable S-TENG assembled using S@HCP can be perfectly suited for real-life applications including biomechanical energy harvesting, self-powered tactile-sensing, and motion monitoring. It is believed that, by combining natural animal skin with different functional materials, it is possible to reuse animal skin, “dead skin,” which provides a new platform for developing multifunctional flexible e-skin.     

2D Tellurium Based High‐Performance All‐Optical Nonlinear Photonic Devices

Tellurium (Te), as one of the rarest stable solid elements far more common in the universe than on earth, is a p‐type semiconductor with excellent optical properties. Herein, a novel two‐dimensional (2D) Te nanosheets (Ns)‐based air‐stable nonlinear photonic devices: all‐optical switcher and photonic diode, owing to its strong light–matter interaction in the visible‐to‐infrared band are reported. The findings validate that the proposed photonic diode can be utilized for the function of nonreciprocal light propagation in optical telecommunications or integrated photonics. Moreover, 2D Te‐based light‐modulate‐light system is successfully designed to realize “ON” and “OFF” modes for all‐optical switching operation. This work highlights a good promise of 2D Te in the field of nonlinear photonics, leading to an important step toward 2D Te‐based advanced photonics devices. The versatile solution process allows a universal access of 2D Te as a new 2D material in a wider range of photonics device applications such as, detector, modulator, switcher, etc.     

3D Fluorescent Hydrogel Origami for Multistage Data Security Protection

Current fluorescence‐based anti‐counterfeiting strategies primarily encode information onto single 2D planes and underutilize the possibility of encrypting data inside 3D structures to achieve multistage data security. Herein, a fluorescent‐hydrogel‐based 3D anti‐counterfeiting platform is demonstrated, which extends data encryption capability from single 2D planes to complex 3D hydrogel origami geometries. The materials are based on perylene‐tetracarboxylic‐acid‐functionalized gelatin/poly(vinyl alcohol) hydrogels, which simultaneously show Fe³⁺‐responsive fluorescence quenching, borax‐triggered shape memory, and self‐healing properties. By employing an origami technique, various complex 3D hydrogel geometries are facilely fabricated. On the basis of these results, a 3D anti‐counterfeiting platform is demonstrated, in which the data printed by using Fe³⁺ as the ink are safely protected inside complex 3D hydrogel origami structures. In this way, the encrypted data cannot be read until after specially predesigned procedures (both the shape recovery and UV light illumination actions), indicating higher‐level information security than the traditional 2D counterparts. This facile and general strategy opens up the possibility of utilizing 3D fluorescent hydrogel origami for data information encryption and protection.     

Complex Tuning of Physical Properties of Hyperbranched Polyglycerol‐Based Bioink for Microfabrication of Cell‐Laden Hydrogels

Microfabrication technology has emerged as a valuable tool for fabricating structures with high resolution and complex architecture for tissue engineering applications. For this purpose, it is imperative to develop “bioink” that can be readily converted to a solid structure by the modus operandi of a chosen apparatus, while optimally supporting the biological functions by tuning their physicochemical properties. Herein, a photocrosslinkable hyperbranched polyglycerol (acrylic hyperbranched glycerol (AHPG)) is developed as a crosslinker to fabricate cell‐laden hydrogels. Due to its hydrophilicity as well as numerous hydroxyl groups for the conjugation of reactive functional groups (e.g., acrylate), the mechanical properties of resulting hydrogels could be controlled in a wide range by tuning both molecular weight and degree of acrylate substitution of AHPG. The control of mechanical properties by AHPG is highly dependent on the type of monomer, due to the hydrophilic/hydrophobic balance of polyglycerol backbone and acrylate as well as the dynamic conformational flexibility based on the molecular weight of polyglycerol. The cell encapsulation studies demonstrate the biocompatibility of the AHPG‐linked hydrogels. Eventually, the AHPG‐based hydrogel precursor solution is employed as a bioink for a digital light processing based printing system to generate cell‐laden microgels with various shapes and sizes for tissue engineering applications.     

Chiral Nematic Polymer Mixture Containing Crosslinker and Photosensitive Chiral Dopant: New Type of Materials with Tunable Photo‐Optical Properties

A cholesteric mixture based on a menthyl‐containing copolymer, photosensitive chiral dopant, mesogenic diacrylate, and photoinitiating agent has been prepared. The mixture shows a selective light reflection in the visible light spectral region. The action of UV irradiation (313 or 365 nm) on the planar‐oriented films generates the occurrence of two parallel processes: E/Z (i.e., cis–trans) photoisomerization of the chiral dopant and photopolymerization of the diacrylate. The first process leads to the untwisting of the cholesteric helix and shifts the selective light‐reflection maximum to the long‐wavelength spectral region, whereas the second process leads to the development of a polymer network that fixes the helical supramolecular structure. As a result of a simultaneous occurrence of the two above‐mentioned processes, the shift in the selective light‐reflection maximum is thermally irreversible, even though the Z/E isomerization of the chiral dopant itself can be reversed by annealing. On irradiation with visible light (>450 nm), the dopant experiences the E/Z isomerization but photopolymerization is absent because the photoinitiator shows no absorption in this spectral region. In this case, the shift in the selective light‐reflection maximum can be reversed to its initial value by annealing, whereby the original helix pitch is recovered. The kinetic features of helix untwisting at different temperatures and light wavelengths were studied. The experimental data obtained in this work allow one to conclude that the as‐prepared mixture presents a new multifunctional material with “tunable” photo‐optical properties and may be used for recording and storage of optical information.     

Redox‐Active Iron‐Citrate Complex Regulated Robust Coating‐Free Hydrogel Microfiber Net with High Environmental Tolerance and Sensitivity

Stretchable hydrogel microfibers as a novel type of ionic conductors are promising in gaining skin‐like sensing applications in more diverse scenarios. However, it remains a great challenge to fabricate coating‐free but water‐retaining conductive hydrogel microfibers with a good balance of spinnability and mechanical strength. Here the old yet significant redox chemistry of Fe‐citrate complex is employed to solve this issue in the continuous draw‐spinning process of poly(acrylamide‐co‐sodium acrylate) hydrogel microfibers and microfiber nets from a water/glycerol solution. The resultant microfibers are ionically conductive, highly stretchable, and uniform with tunable diameters. Furthermore, the presence of redox‐reversible Fe‐citrate complex and glycerol endows the fibers with good anti‐freezing, water‐retaining, and environmentally intelligent properties. Humidity and UV light can finely mediate the stiffness of hydrogel microfibers; conversely, the ionic conductance of microfibers is also responsive to light, humidity, and strain, which enables the highly sensitive perception of environmental changes. The present draw‐spinning strategy provides more possibilities for coating‐free conductive hydrogel microfibers with a variety of responsive and sensing applications.     

Dopant‐Free Hydrogels with Intrinsic Photoluminescence and Biodegradable Properties

Photoluminescent hydrogels that function as both injectable scaffolds and fluorescent imaging probes hold great potential for therapeutics delivery and tissue engineering. Current fluorescent hydrogels are fabricated by either conjugating or doping a fluorescent dye, fluorescent protein, lanthanide chelate, or quantum dot into polymeric hydrogel matrix. Their biomedical applications are severely limited due to drawbacks such as photostability, carcinogenesis, and toxicity associated with the above‐mentioned dopants. Here, a successful development of dopant‐free photoluminescent hydrogels in situ formed by crosslinking of biocompatible polymer precursors is reported, which can be synthesized by incorporating an amino acid to a citric acid based polyester oligomer followed by functionalization of multivalent crosslinking group through a convenient transesterification reaction using Candida Antarctica Lipase B as a catalyst. It is demonstrated that the newly developed hydrogels possess tunable degradation, intrinsic photoluminescence, mechanical properties, and exhibit sustained release of various molecular weight dextrans. In vivo study shows that the hydrogels formed in situ following subcutaneous injection exhibit excellent biocompatibility and emit strong fluorescence under visible light excitation without the need of using any traditional organic dyes. Their in vivo degradation profiles are then depicted by noninvasively monitoring fluorescence intensity of the injected hydrogel implants.     

Composite Living Fibers for Creating Tissue Constructs Using Textile Techniques

The fabrication of cell‐laden structures with anisotropic mechanical properties while having a precise control over the distribution of different cell types within the constructs is important for many tissue engineering applications. Automated textile technologies for making fabrics allow simultaneous control over the color pattern and directional mechanical properties. The use of textile techniques in tissue engineering, however, demands the presence of cell‐laden fibers that can withstand the mechanical stresses during the assembly process. Here, the concept of composite living fibers (CLFs) in which a core of load bearing synthetic polymer is coated by a hydrogel layer containing cells or microparticles is introduced. The core thread is drawn sequentially through reservoirs containing a cell‐laden prepolymer and a crosslinking reagent. The thickness of the hydrogel layer increases linearly with to the drawing speed and the prepolymer viscosity. CLFs are fabricated and assembled using regular textile processes including weaving, knitting, braiding, winding, and embroidering, to form cell‐laden structures. Cellular viability and metabolic activity are preserved during CLF fabrication and assembly, demonstrating the feasibility of using these processes for engineering functional 3D tissue constructs.