Melt Electrowriting (MEW) is a continuously growing manufacturing platform. Its advantage is the consistent production of micro- to nanometer fibers, that stack intricately, forming complex geometrical shapes. MEW allows tuning of the mechanical properties of constructs via the geometry of deposited fibers. Due to this, MEW can create complex mechanics only seen in multi-material compounds and serve as guiding structures for cellular alignment. The advantage of MEW is also shown in combination with other biotechnological manufacturing methods to create multilayered constructs that increase mechanical approximation to native tissues, biocompatibility, and cellular response. These features make MEW constructs a perfect candidate for small-diameter vascular graft structures. Recently, studies have presented fascinating results in this regard, but is this truly the direction that tubular MEW will follow or are there also other options on the horizon? This perspective will explore the origins and developments of tubular MEW and present its growing importance in the field of artificial small-diameter vascular grafts with mechanical modulation and improved biomimicry and the impact of it in convergence with other manufacturing methods and how future technologies like AI may influence its progress.

Atherosclerosis is the primary cause of cardiovascular disease, resulting in mortality, elevated healthcare costs, diminished productivity, and reduced quality of life for individuals and their communities. This is exacerbated by the limited understanding of its underlying causes and limitations in current therapeutic interventions, highlighting the need for sophisticated models of atherosclerosis. This review critically evaluates the computational and biological models of atherosclerosis, focusing on the study of hemodynamics in atherosclerotic coronary arteries. Computational models account for the geometrical complexities and hemodynamics of the blood vessels and stenoses, but they fail to capture the complex biological processes involved in atherosclerosis. Different in vitro and in vivo biological models can capture aspects of the biological complexity of healthy and stenosed vessels, but rarely mimic the human anatomy and physiological hemodynamics, and require significantly more time, cost, and resources. Therefore, emerging strategies are examined that integrate computational and biological models, and the potential of advances in imaging, biofabrication, and machine learning is explored in developing more effective models of atherosclerosis.

The current barrier to clinical translation of small-caliber tissue-engineered vascular grafts (TEVGs) is the long-term patency upon implantation in vivo. Key contributors are thrombosis and stenosis caused by inadequate mechanical graft properties and mismatch of hemodynamic conditions. Herein, the authors report on an approach for the fabrication of a mechanically tunable bilayered composite TEVGs. Using a combination of solution electrospinning (SES) and melt electrowriting (MEW), it is shown that the mechanical properties can be tailored and the natural J-shape of the stress-strain relationship can be recapitulated. Upon cell seeding, the luminal surface of the composite SES layers permits the formation of a confluent mature endothelium. MEW fibers provide structural support to promote stacking and orientation of MSCs in a near-circumferential native vessel like direction. By adjusting the ratios of poly(epsilon-caprolactone) and poly(ester-urethane) during the SES process, TEVGs with a range of tunable mechanical properties can be manufactured. Notably, this hybrid approach permits modulation of the radial tensile properties of TEVGs to approximate different native vessels. Overall, a strategy for the fabrication of TEVGs with mechanical properties resembling those of native vessels which can help to accommodate long-term patency of TEVGs at various treatment sites in future applications is demonstrated. A barrier for clinical translation of small-caliber tissue-engineered vascular grafts (TEVGs) is long-term patency. An important limiting factor is inadequate graft mechanics. This manuscript reports the fabrication of mechanically tunable TEVGs using a combination of solution electrospinning and melt electrowriting. The radial tensile properties of the TEVGs approximate human vessels and will accommodate long-term patency of such TEVGs in future. image

A previously developed cellularized collagen-based vascular wall model showed promising results in mimicking the biological properties of a native vessel but lacked appropriate mechanical properties. In this work, we aim to improve this collagen-based model by reinforcing it using a tubular polymeric (reinforcement) scaffold. The polymeric reinforcements were fabricated exploiting commercial poly (ε-caprolactone) (PCL), a polymer already used to fabricate other FDA-approved and commercially available devices serving medical applications, through 1) solution electrospinning (SES), 2) 3D printing (3DP) and 3) melt electrowriting (MEW). The non-reinforced cellularized collagen-based model was used as a reference (COL). The effect of the scaffold’s architecture on the resulting mechanical and biological properties of the reinforced collagen-based model were evaluated. SEM imaging showed the differences in scaffolds’ architecture (fiber alignment, fiber diameter and pore size) at both the micro- and the macrolevel. The polymeric scaffold led to significantly improved mechanical properties for the reinforced collagen-based model (initial elastic moduli of 382.05 ± 132.01 kPa, 100.59 ± 31.15 kPa and 245.78 ± 33.54 kPa, respectively for SES, 3DP and MEW at day 7 of maturation) compared to the non-reinforced collagen-based model (16.63 ± 5.69 kPa). Moreover, on day 7, the developed collagen gels showed stresses (for strains between 20% and 55%) in the range of [5–15] kPa for COL, [80–350] kPa for SES, [20–70] kPa for 3DP and [100–190] kPa for MEW. In addition to the effect on the resulting mechanical properties, the polymeric tubes’ architecture influenced cell behavior, in terms of proliferation and attachment, along with collagen gel compaction and extracellular matrix protein expression. The MEW reinforcement resulted in a collagen gel compaction similar to the COL reference, whereas 3DP and SES led to thinner and longer collagen gels. Overall, it can be concluded that 1) the selected processing technique influences the scaffolds’ architecture, which in turn influences the resulting mechanical and biological properties, and 2) the incorporation of a polymeric reinforcement leads to mechanical properties closely matching those of native arteries.

Major challenges in biofabrication revolve around capturing the complex, hierarchical composition of native tissues. However, individual 3D printing techniques have limited capacity to produce composite biomaterials with multi-scale resolution. Volumetric bioprinting recently emerged as a paradigm-shift in biofabrication. This ultrafast, light-based technique sculpts cell-laden hydrogel bioresins into 3D structures in a layerless fashion, providing enhanced design freedom over conventional bioprinting. However, it yields prints with low mechanical stability, since soft, cell-friendly hydrogels are used. Herein, the possibility to converge volumetric bioprinting with melt electrowriting, which excels at patterning microfibers, is shown for the fabrication of tubular hydrogel-based composites with enhanced mechanical behavior. Despite including non-transparent melt electrowritten scaffolds in the volumetric printing process, high-resolution bioprinted structures are successfully achieved. Tensile, burst, and bending mechanical properties of printed tubes are tuned altering the electrowritten mesh design, resulting in complex, multi-material tubular constructs with customizable, anisotropic geometries that better mimic intricate biological tubular structures. As a proof-of-concept, engineered tubular structures are obtained by building trilayered cell-laden vessels, and features (valves, branches, fenestrations) that can be rapidly printed using this hybrid approach. This multi-technology convergence offers a new toolbox for manufacturing hierarchical and mechanically tunable multi-material living structures.

Recreating the intricate mechanical and functional gradients found in natural tissues through additive manufacturing poses significant challenges, including the need for precise control over time and space and the availability of versatile biomaterial inks. In this proof-of-concept study, we developed a new biomaterial ink for direct ink writing, allowing the creation of 3D structures with tailorable functional and mechanical gradients. Our ink formulation combined multifunctional cellulose nanofibrils (CNFs), allyl-functionalized gelatin (0.8-2.0 wt%), and polyethylene glycol dithiol (3.0-7.5 wt%). The CNF served as a rheology modifier, whereas a concentration of 1.8 w/v % in the inks was chosen for optimal printability and shape fidelity. In addition, CNFs were functionalized with azido groups, enabling the spatial distribution of functional moieties within a 3D structure. These functional groups were further modified using a spontaneous click chemistry reaction. Through additive manufacturing and a readily available static mixer, we successfully demonstrated the fabrication of mechanical gradients - ranging from 3 to 6 kPa in indentation strength - and functional gradients. Additionally, we introduced dual gradients by combining gradient printing with an anisotropic photocrosslinking step. The developed biomaterial ink opens up possibilities for printing intricate multigradient structures, resembling the complex hierarchical organization seen in living tissues.

Objectives Synthetic bone substitutes which can be adapted preoperatively and patient specific may be helpful in various bony defects in the field of oral- and maxillofacial surgery. For this purpose, composite grafts made of self-setting and oil-based calcium phosphate cement (CPC) pastes, which were reinforced with 3D-printed polycaprolactone (PCL) fiber mats were manufactured. Materials and methods Bone defect models were acquired using patient data from real defect situations of patients from our clinic. Using a mirror imaging technique, templates of the defect situation were fabricated via a commercially available 3D-printing system. The composite grafts were assembled layer by layer, aligned on top of these templates and fitted into the defect situation. Besides, PCL-reinforced CPC samples were evaluated regarding their structural and mechanical properties via X-ray diffraction (XRD), infrared (IR) spectroscopy, scanning electron microscopy (SEM), and 3-point-bending testing. Results The process sequence including data acquisition, template fabrication, and manufacturing of patient specific implants proved to be accurate and uncomplicated. The individual implants consisting mainly of hydroxyapatite and tetracalcium phosphate displayed good processability and a high precision of fit. The mechanical properties of the CPC cements in terms of maximum force and stress load to material fatigue were not negatively affected by the PCL fiber reinforcement, whereas clinical handling properties increased remarkably. Conclusion PCL fiber reinforcement of CPC cements enables the production of very freely modelable three-dimensional implants with adequate chemical and mechanical properties for bone replacement applications. Clinical relevance The complex bone morphology in the region of the facial skull often poses a great challenge for a sufficient reconstruction of bony defects. A full-fledged bone replacement here often requires the replication of filigree three-dimensional structures partly without support from the surrounding tissue. With regard to this problem, the combination of smooth 3D-printed fiber mats and oil-based CPC pastes represents a promising method for fabricating patient specific degradable implants for the treatment of various craniofacial bone defects.

Melt electrowriting (MEW) is an additive manufacturing process that produces highly defined constructs with elements in the micrometer range. A specific configuration of MEW enables printing tubular constructs to create small-diameter tubular structures. The small pool of processable materials poses a bottleneck for wider application in biomedicine. To alleviate this obstacle, an acrylate-endcapped urethane-based polymer (AUP), using a poly(epsilon-caprolactone) (PCL) (molar mass: 20 000 g mol(-1)) (AUP PCL20k) as backbone material, is synthesized and utilized for MEW. Spectroscopic analysis confirms the successful modification of the PCL backbone with photo-crosslinkable acrylate endgroups. Printing experiments of AUP PCL20k reveal limited printability but the photo-crosslinking ability is preserved post-printing. To improve printability and to tune the mechanical properties of printed constructs, the AUP-material is blended with commercially available PCL (AUP PCL20k:PCL in ratios 80:20, 60:40, 50:50). Print fidelity improves for 60:40 and 50:50 blends. Blending enables modification of the constructs' mechanical properties to approximate the range of blood vessels for transplantation surgeries. The crosslinking-ability of the material allows pure AUP to be manipulated post-printing and illustrates significant differences in mechanical properties of 80:20 blends after crosslinking. An in vitro cell compatibility assay using human umbilical vein endothelial cells also demonstrates the material's non-cytotoxicity.

In 3D bioprinting, bioinks with high concentrations of polymeric materials are frequently used to enable fabrication of 3D cell-hydrogel constructs with sufficient stability. However, this is often associated with restricted cell bioactivity and an inhomogeneous distribution of newly produced extracellular matrix (ECM). Therefore, this study investigates bioink compositions based on hyaluronic acid (HA), an attractive material for cartilage regeneration, which allow for reduction of polymer content. Thiolated HA and allyl-modified poly(glycidol) in varying concentrations are UV-crosslinked. To adapt bioinks to poly(ε-caprolactone) (PCL)-supported 3D bioprinting, the gels are further supplemented with 1 wt% unmodified high molecular weight HA (hmHA) and chondrogenic differentiation of incorporated human mesenchymal stromal cells is assessed. Strikingly, addition of hmHA to gels with a low polymer content (3 wt%) results in distinct increase of construct quality with a homogeneous ECM distribution throughout the constructs, independent of the printing process. Improved ECM distribution in those constructs is associated with increased construct stiffness after chondrogenic differentiation, as compared to higher concentrated constructs (10 wt%), which only show pericellular matrix deposition. The study contributes to effective bioink development, demonstrating dual function of a supplement enabling PCL-supported bioprinting and at the same time improving biological properties of the resulting constructs.

The therapeutic potential of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) is limited by immature functional features including low impulse propagation and reduced cell excitability. Key players regulating electrical activity are voltage-gated Na+ channels (Na(v)1.5) and gap junctions built from connexin-43 (Cx43). Here we tested the hypothesis that enhanced Cx43 expression increases intercellular coupling and influences excitability by modulating Na(v)1.5. Using transgenic approaches, Cx43 and Na(v)1.5 localization and cell coupling were studied by confocal imaging. Na(v)1.5 currents and action potentials (APs) were measured using the patch-clamp technique. Enhanced sarcolemmal Cx43 expression significantly improved intercellular coupling and accelerated dye transfer kinetics. Furthermore, Cx43 modulated Na(v)1.5 function leading to significantly higher current and enhanced AP upstroke velocities, thereby improving electrical activity as measured by microelectrode arrays. These findings suggest a mechanistic link between cell coupling and excitability controlled by Cx43 expression in iPSC-CMs. Therefore, we propose Cx43 as novel molecular target for improving electrical properties of iPSC-CMs to match the functional properties of native myocytes.