Cartilage is an avascular tissue with a limited capacity for self-regeneration. Traditional autologous cartilage transplantation is incapable of fulfilling the increasing demand for repair of various cartilage tissue lesions. The advent of 3D bioprinting technology provides an opportunity to repair articular cartilage defects through the construction of organized living structures composed of biomaterials and cells. This technology can mimic natural cartilage by allowing control of cell distribution, and the modulation of mechanical and chemical properties with high precision. This review provides insight into the current developments in 3D bioprinting for cartilage tissue engineering. Recent studies on 3D-bioprinted cartilage tissue constructs and various bioinks are highlighted. The advantages and limitations of commonly used natural, synthetic, and composite bioinks in terms of printability, mechanical properties, and biological performance in bioprinting of anatomically shaped constructs (nasal, auricle, knee, and tracheal cartilage) are discussed. Furthermore, outlooks and challenges of 3D bioprinting of complex constructs with variable mechanical and biological properties are provided. Based on recent progress, it is expected that 3D bioprinting will lead to improved 3D tissue-engineered constructs for regeneration and repair of cartilage tissue.

Electrospun poly(ε-caprolactone) (PCL) meshes are widely studied in biomedical applications due to their biocompatibility and biodegradability. However, limited ability to modify their mechanical properties and degradation parameters restrict broader biomedical applications. In this study, we explore the development of electrospun PCL meshes incorporating low concentrations of poly(ethylene oxide) (PEO, 0-0.5 wt %) into PCL fiber development with varied molecular weight (25-80 kDa). Under consistent fabrication conditions, minimal PEO incorporation enabled electrospinning of uniform fibers at all PCL molecular weights, including those that do not form uniform fibers within the range of normal electrospinning parameters. A decrease in specific surface area was observed with increasing PEO content, suggesting a role for PEO in surface smoothing and filling of morphological features in the electrospinning process. Mechanical testing on fibrous scaffolds revealed that stiffness and ultimate tensile strength increased with PEO concentration, likely due to changes in scaffold architecture. Mass loss under accelerated degradation conditions was governed primarily by scaffold architecture rather than composition. These findings establish a simple formulation-based strategy to modify electrospun scaffold properties through coupled morphological and compositional effects without altering processing conditions.

Advanced bioelectronics require soft materials that mechanically mimic tissues by exhibiting nonlinear mechanics and seamlessly bridge ionic signals in tissues and electronic signals in circuits. Creating conductive hydrogels with percolative electronic pathways that show tissue-mimetic strain-stiffening behavior represents a promising strategy to potentially address this need. Here, we report a composite hydrogel of poly(vinyl alcohol) (PVA) and poly(aniline boronic acid) (PABA) that exhibits strain-stiffening mechanical behavior with mixed ionic and electronic conduction. Dynamic self-healing boronic-ester crosslinks that impart strain-stiffening also facilitate the formation of a percolative network of conjugated conductive polymers during gelation, providing a continuous pathway for electronic transport (σe ∼ 10-5-10-3 S m-1) alongside ionic conductivity (σi ∼ 1-10 S m-1). As a result, deformation directly modulates the electronic resistance, displaying a distinct resistance-stabilization plateau that coincides with the onset of strain-stiffening, suggesting a transition from geometry-limited to alignment-assisted charge transport within the network. By unifying adaptive tissue-like mechanics with dual conduction, this system offers a promising avenue for developing soft, mechanically resilient materials capable of continuous electromechanical transduction.

Spider silks are renowned for exceptional mechanical properties and as promising biomaterials. Here, we introduce a recombinant chimeric protein (W2Cma2ap-55) composed of two aciniform silk repetitive units (W2), a major ampullate silk non-repetitive C-terminal domain (Cma2), and the human peptidic G-protein-coupled receptor (GPCR) ligand apelin-55 (ap-55). Ap-55 is an endogenous apelin receptor (AR) ligand, regulating various natural and pathological processes and with noted potential for therapeutic targeting. W2Cma2ap-55 expressed in Escherichia coli proved amenable to both film and fiber formation, with the protein lacking ap-55 (W2Cma2) used as a control throughout. Films and fibers formed from W2Cma2ap-55 were recognized by an anti-apelin antibody, in contrast to W2Cma2, confirming ap-55 accessibility and intactness. Compared to W2Cma2 fibers, W2Cma2ap-55 fibers exhibited comparable extensibility alongside enhanced strength and toughness. Films prepared from both W2Cma2ap-55 and W2Cma2 were non-cytotoxic to HEK 293A cells stably transfected with the AR. Growth of these cells on W2Cma2ap-55 films increased ERK phosphorylation relative to either W2Cma2 or non-silk substrate conditions, consistent with ap-55-induced AR activation. Cell attachment was also observed on the surface of W2Cma2ap-55 fibers. W2Cma2ap-55 is thus a promising engineered protein capable of supporting cell growth and eliciting GPCR signaling. Statement of Significance : Spider silks form protein-based fibers renowned for withstanding high force and extension before breaking and for potential in biomedical application, with use of natural spider silks as sutures dating back thousands of years. Here, we introduce an engineered spider silk protein with an extension targeting a specific human cell surface receptor, the apelin receptor. This protein forms transparent films and strong and flexible fibers, supporting growth and attachment of human cells. The functionalized silk also promotes signaling in cells with the apelin receptor, while cells without it are unaffected. These new silk materials thus have enhanced functionality, allowing targeted cell signaling in the laboratory setting with potential for future application in tissue culture or biomedical device development.

Repair of osteochondral defects remains a great challenge because of the complex interplay between cartilage and subchondral bone, each of which has distinct structural, biological, and mechanical properties. Here, the fabrication and of a novel 3D printed biphasic osteochondral scaffold composed of polycaprolactone/laponite (PL) is demonstrated for the bone layer and methylsulfonylmethane (MSM)-loaded polycaprolactone/chitosan (PC) for the cartilage layer. Comprehensive characterization of the scaffold revealed gradient mechanical properties, high biocompatibility, and hydrophilicity, replicating the structural requirements of native osteochondral tissue. In vitro biological assays demonstrated enhanced cell adhesion, proliferation, and differentiation of bone marrow-derived mesenchymal stem cells for both cartilage and bone layers. The PL layer exhibited osteogenic capacity, while the MSM-loaded PC layer facilitated chondrogenesis. Additionally, the scaffold displayed controlled degradation and sustained release of MSM, further promoting extracellular matrix production. Altogether, the results suggest that the designed biphasic scaffold represents a promising platform for osteochondral tissue regeneration.

Peripheral nerve injuries often result in incomplete regeneration and significant functional impairments, necessitating innovative approaches for effective repair. This review explores recent advancements in bioengineered in vitro models with the potential to aid in the development of peripheral nerve regeneration therapies; while, reducing reliance on animal models. The potential of 2D and 3D bioengineered platforms ranging from patterned cell cultures and hydrogels to fibrous scaffolds and microfluidic systems is critically assessed, highlighting how these systems replicate the complex cellular and biochemical environments essential for nerve repair. In addition, the challenges associated with these models, such as balancing complexity with throughput, and the need for scalable solutions that can be translated into clinical settings are discussed. Finally, future perspectives on the field are provided, advocating for the use of advanced technologies to develop next‐generation nerve repair models with enhanced precision and clinical applicability.

The development of effective wound dressings is critical for accelerating tissue repair and minimizing complications in skin injuries. In this study, we designed and fabricated a multifunctional, sandwich-structured wound dressing using 3D bioprinting technology. The construct comprises an alginate/chitosan hydrogel inner layer loaded with gentamicin sulfate (GS), a middle layer containing L-arginine (Arg) to enhance angiogenesis, and a commercial non-woven tape as the outer protective layer. The physicochemical characterization confirmed appropriate printability, interconnected macro and microporous structure, and incorporation of bioactive agents. The scaffold exhibited hydrophilic properties with rapid moisture uptake and retention, and showed controlled degradation and dual drug release kinetics with pH-dependent release of GS and controlled delivery of Arg. In vitro assays indicated that the scaffold supports BMSCs viability, proliferation, and angiogenic genes expression (VEGF, CD31, FGF) along with effective antibacterial activity and blood clotting capacity. This 3D bioprinted multilayer scaffold represents a promising novel wound dressing for skin regeneration applications.

Bioink composition is a key consideration for the 3D-bioprinting of complex and stable structures used to model tissues and as tissue constructs for regenerative medicine. An emerging and industrially important area of research is the use of micro- and nanofillers to improve bioink performance without dramatically altering the physicochemical properties of the polymeric material that forms the bulk of the printed structure. The purpose of this review is to provide a comprehensive overview of emerging nanomaterial fillers designed to create heterogeneous and composite bioinks for 3D-bioprinting of complex functional tissues. We outline the criteria that must be considered when developing such a bioink and discuss applications where the fillers impart stimuli responsiveness, e.g., when exposed to magnetic fields, electrical fields, and light. We further highlight how the use of such fillers can enable non-destructive imaging to monitor scaffold placement and integrity following implantation.

Developing a simple and cost-effective wastewater concentration method using powdered activated charcoal sodium alginate (PAC-NaA) hydrogel beads, enhanced for capturing viruses.

Magnesium (Mg) and its alloys have gained attention for use in orthopedic implants and bone tissue engineering. However, the corrosion of these materials, which results in toxic by-products, reduces their mechanical strength and limits their use. Here, fused deposition modeling 3D printing was used to fabricate polycaprolactone (PCL)/ chitosan composite scaffolds on the surface of AZ31 Mg alloy to improve its corrosion resistance and bioactivity. Physiochemical characterization of the composite scaffold was performed. Corrosion behavior of the coatings was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy, indicating higher corrosion resistance of 3D-printed PCL/chitosan scaffold-coated AZ31 Mg alloy than that of the uncoated alloy with coating efficiency of 98.89 %. The resulting materials possessed antibacterial activity against Grampositive and Gram-negative bacteria. Cell viability, alkaline phosphatase, alizarin red, real-time PCR, and flow cytometry assays were performed to assess the response of MC3T3 cells to the materials over the course of 14 days in culture. Of the composite scaffolds examined, AZ31 surfaces coated with 4wt%PCL/ 3 wt% chitosan provided the best performance in adhesion, proliferation and osteogenic differentiation of cell, which was attributed to the presence of amine groups in the chitosan used in the PCL/chitosan blend. Thus, AZ31 modified by 3D printing of PCL/chitosan represents a promising strategy for regeneration and repair of bone defects.

The apelinergic system encompasses two peptide ligand families, apelin and apela, along with the apelin receptor (AR or APJ), a class A G-protein-coupled receptor. This system has diverse physiological effects, including modulating heart contraction, vasodilation/constriction, glucose regulation, and vascular development, with involvement in a variety of pathological conditions. Apelin peptides have been previously shown to interact with and become structured upon binding to anionic micelles, consistent with a membrane-catalyzed mechanism of ligand-receptor binding. To overcome the challenges of observing nuclear magnetic resonance (NMR) spectroscopy signals of a dilute peptide in biological environments, 19F NMR spectroscopy, including diffusion ordered spectroscopy (DOSY) and saturation transfer difference (STD) experiments, was used herein to explore the membrane-interactive behaviour of apelin. NMR-optimized apelin-17 analogues with 4-trifluoromethyl-phenylalanine at various positions were designed and tested for bioactivity through ERK activation in stably-AR transfected HEK 293 T cells. Far-UV circular dichroism (CD) spectropolarimetry and 19F NMR spectroscopy were used to compare the membrane interactions of these analogues with unlabelled apelin-17 in both zwitterionic/neutral and net-negative bicelle conditions. Each analogue binds to bicelles with relatively weak affinity (i.e., in fast exchange on the NMR timescale), with preferential interactions observed at the cationic residue-rich N-terminal and mid-length regions of the peptide leaving the C-terminal end unencumbered for receptor recognition, enabling a membrane-anchored fly-casting mechanism of peptide search for the receptor. In all, this study provides further insight into the membrane-interactive behaviour of an important bioactive peptide, demonstrating interactions and biophysical behaviour that cannot be neglected in therapeutic design.

Sarcopenia, the progressive loss of muscle mass and strength with age, is associated with many adverse health outcomes in aging populations decreasing greatly health span. Early detection of sarcopenia is critical for initiating preventative strategies to stop muscle deterioration. Current methods for detecting the onset of sarcopenia are inaccessible and costly, creating a barrier to routine screening. Here, we examine serum samples from a group of 360 community-dwelling individuals aged 50 to 70 who previously completed the international physical activity questionnaire (IPAQ). We further analyze urine samples from a group of 60 individuals, who completed standard physical performance battery (SPPB) tests, dual-energy x-ray absorptiometry (DEXA), IPAQ, and an additional questionnaire. We demonstrated for the first time that a panel of biomarkers composed by glutamate, xanthine, taurine, succinate, and carnitine are linked to early alterations in muscle metabolism and can be used to monitor muscle degeneration. These metabolites are detectable in urine and are predictive of sarcopenia as compared to DEXA and physical assessments. This panel serves as a sensitive and objective monitoring tool for assessing muscle metabolism, enabling more effective and accessible management of muscle-wasting conditions such as sarcopenia.

Crosslinking is usually required to improve the mechanical properties and stability of collagen-based scaffolds. Introducing exogenous crosslinks into collagen may however affect the collagen structure. Since the architecture of collagen is tied to its functionality, it is important to study the effect of crosslinking and to select a crosslinking method that preserves both the collagen structure and mechanical properties. The objective of this study is to compare the effect of various crosslinking methods on the structure and mechanical properties of bioartificial tendon-like materials (collagen multifilament bundles) fabricated by contact drawing. We examine both physical (ultraviolet light, UVC) and chemical (genipin, carbodiimide (EDC), and glutaraldehyde) crosslinking methods. The presence of collagen and the formation of well-ordered collagen structures are confirmed by attenuated total reflectance Fourier-transform infrared spectromicroscopy and wide-angle X-ray scattering for all crosslinking methods. The morphology of the collagen multifilament bundles is similar across crosslinking methods. Swelling of the multifilament bundles is dramatically reduced following crosslinking and varies by crosslinking method, with genipin- and carbodiimide-crosslinked specimens swelling the least. Ultimate tensile strength (UTS) and Young's modulus significantly improve for all crosslinked specimens compared to non-crosslinked specimens. Glutaraldehyde crosslinked collagen multifilament bundles display the highest UTS values ranging from 33.82±0.0 MPa to 45.59±0.76 MPa.

Transparent hydrogels have numerous applications in materials science and tissue engineering, particularly as materials for corneal repair. In this study, we developed a three-dimensional (3D)-bioprinted betamethasone sodium phosphate-loaded gellan gum (GG)-polyethyleneimine (PEI) composite hydrogel and assessed its performance in vitro. The bioinks used for 3D bioprinting were optimized based on their transparency and gelation properties. In the presence of an ionic crosslinker (citric acid), the GG-PEI blend transformed from a liquid precursor to an extrudable hydrogel with good printability and shape fidelity. The 2.5% GG-3% PEI hydrogel formulation had a transparency of 80%, a suitable degradation rate, and sufficient mechanical strength for application in corneal repair. The GG-PEI composite hydrogel displayed controlled and sustained release of betamethasone sodium phosphate. Moreover, the 3D-bioprinted composite hydrogel was biocompatible, as evidenced by the attachment, growth, and proliferation of corneal fibroblasts. Taken together, these findings suggest that the 3D-bioprinted GG-PEI composite hydrogel scaffold has the potential to control ocular inflammation and aid in corneal tissue healing.

Alginate is among the most popular bioinks for 3D bioprinting because it is biocompatible, biodegradable, and is easily crosslinked using divalent cations. Here, we investigate the addition of cellulose nanocrystals (CNCs) to an alginate-based bioink to strengthen bioprinted structures. Using coaxial 3D bioprinting, alginate strands were constructed with a core-sheath structure reinforced by CNCs within the core. The addition of CNCs resulted in an increase in the storage modulus. Formulations containing CNCs resulted in more stable strands with uniformity factors and printability numbers close to 1. Based on the uniformity factor, the formulations containing 1.5 wt% CNCs deviated the least from a theoretically flawless strand. The alginate strands displayed microporous internal structures that were evident by scanning electron microscopy of the strand cross-sections. The addition of CNCs to the core compartment doubled both the modulus and the tensile strength, and the material was able to resist a strain above 50% before failure, thus demonstrating that the addition of the CNCs to the core of the strand leads to resilient printed structures.

Collagen multifilament bundles comprised of thousands of monofilaments are prepared by multipin contact drawing of an entangled polymer solution consisting of collagen and poly(ethylene oxide) (PEO). The multifilament bundles are hydrated in graded concentrations of PEO and phosphate buffered saline (PBS) to promote assembly of collagen fibrils within each monofilament while preserving the structure of the multifilament bundle. Multiscale structural characterization reveals that the hydrated multifilament bundle contains properly folded collagen molecules packed in collagen fibrils containing microfibrils, staggered by exactly one-sixth of the microfibril D-band spacing to produce a periodicity of 11 nm. Sequence analysis predicts that in this structure, phenylalanine residues are close enough within and between microfibrils to become ultraviolet C (UVC) crosslinked. In agreement with this analysis, the ultimate tensile strength (UTS) and Young's modulus of the hydrated collagen multifilament bundles crosslinked by UVC radiation increase nonlinearly with total UVC energy to reach values in the range of native tendons without damage to the collagen molecules. This fabrication method recapitulates the structure of a tendon across multiple length scales and offers tunability in tensile properties using only collagen molecules and no other chemical additives in addition to PEO, which is almost entirely removed during the hydration process.

Textiles containing interposed layers of polyethylene oxide (PEO)-fibrinogen and PEO-thrombin fibers are explored as biomaterials for hemostasis. The PEO-fibrinogen and PEO-thrombin fibers are formed by contact drawing, an approach that uses an entangled polymer solution and a pin array to form fibers by extension of liquid bridges. The interposition of the PEO-fibrinogen and PEO-thrombin fibers results in polymerization of a fibrin hydrogel mesh once the textile is hydrated. This fibrin hydrogel mesh displays the expected bands and diffraction peaks by Fourier-transform infrared spectromicroscopy and X-ray diffraction, respectively. The functionality of the hemostatic textiles formed from the interposed PEO-fibrinogen and PEO-thrombin fibers is demonstrated by analyzing human blood hemolysis, complement activation, protein adsorption, and platelet and leukocyte adhesion, indicating compatibility with human blood (hemolysis ratio <5%), with minimal inflammatory response (levels of terminal complement complex equivalent to plasma). The cytocompatibility and potential for cell remodeling of the fibrin hydrogel mesh formed by this process is evaluated with human dermal fibroblasts and human keratinocytes and it is found that both cell types attach and grow on the fibrin mesh. Finally, a whole blood clotting time of less than 30 s suggests a potential use of this material in hemorrhage control.

The blood–brain barrier (BBB) surrounds brain cells and prevents external substances from entering the brain through blood vessels. This complicates drug delivery to brain cells, but drugs that can cross the BBB have been developed recently, expanding the scope of treatment for brain diseases. However, traditional biological research typically relies on simple monolayer cell cultures that do not reflect the complex functional properties of human tissues and organs or their responses to external stimuli. Bioprinting technology is gradually overcoming the drawbacks of in vitro models by applying techniques, such as simulating 3D structures, which cannot be realized by biological models, utilizing biocompatible materials and mass cell culture at the tissue level; however, it has been limited to printing microstructural patterns. The in vitro model presented here printed the BBB microstructure in a liquid state, eliminating many defects inherent to printing on a flat surface in air. The aqueous two-phase printing (ATPP) material consisted of a composite matrix capable of phase separation, where three different cell types could be cultured to create a BBB model. The ATPP model will help in central nervous system disease research, drug screening, and drug discovery, because it provides an environment where the nutrient supply and drug concentration of cells can be controlled.

Microtissues in the shape of toroidal rings provide an ideal geometry to better represent the structure and function of the airway smooth muscle present in the small airways, and to better understand diseases such as asthma. Here, polydimethylsiloxane devices consisting of a series of circular channels surrounding central mandrels are used to form microtissues in the shape of toroidal rings by way of the self-aggregation and -assembly of airway smooth muscle cell (ASMC) suspensions. Over time, the ASMCs present in the rings become spindle-shaped and axially align along the ring circumference. Ring strength and elastic modulus increase over 14 d in culture, without significant changes in ring size. Gene expression analysis indicates stable expression of mRNA for extracellular matrix-associated proteins, including collagen I and laminins α 1 and α 4 over 21 d in culture. Cells within the rings respond to TGF- β 1 treatment, leading to dramatic decreases in ring circumference, with increases in mRNA and protein levels for extracellular matrix and contraction-associated markers. These data demonstrate the utility of ASMC rings as a platform for modeling diseases of the small airways such as asthma.

With structural similarities to biological tissues, hydrogels offer many potential applications in biomedicine. To improve hydrogel perfusion, simple microchannels can be fabricated using a variety of templating and printing approaches, but the formation of interconnected, winding, and branching channels remains a significant challenge. The cavitation‐mediated etching of microchannels in agarose hydrogels is demonstrated. An ultrasonic cavitation transducer coupled with a motorized control system is used to enable the formation of consistent microchannels within the agarose hydrogels with ellipsoid cross‐sectional areas and uniform widths on the order of 244 ± 19.5 μm. With increasing transducer voltage, the average microchannel width increases, while higher positional translation speed results in shorter dwell times and, therefore, smaller microchannels. Infusion of fluorescent dyes indicates little turbulence within the microchannels formed by the cavitation etching process. This technique can fabricate branched and complex microchannel paths. Furthermore, the mechanical and swelling properties of hydrogels with internal microchannels formed by cavitation at varying pH support future development in diverse applications including tissue engineering, drug delivery, and biomimetic lab‐on‐a‐chip systems.