Materials and Strategies to Enhance Melt Electrowriting Potential

Structurally defined cartilaginous MEW-assembloids for critical-size long bone healing

Bone defects exceeding a critical size pose significant clinical challenges due to their inability to heal spontaneously. Traditional treatments including autografts and synthetic implants, are often suffer from limitations such as donor site morbidity, infection risk, and poor integration. This study explores a novel approach using MEW-assembloid which combine Melt electrowriting (MEW) scaffolds with cartilaginous microtissues to enhance bone healing. Here, we fabricated bucket-shaped MEW scaffolds (OMesh and CMesh) to optimize microtissue retention and integration, with the OMesh design showing effective shape retention after microtissue seeding. To adapt the scaffold dimensions for in vivo implantation, we introduced elongated MEW (EMesh) based on the OMesh design, forming EMesh-assembloid. These constructs were evaluated for their ability to undergo endochondral ossification and mineralization in subcutaneous implants. Additionally, tubular MEW scaffolds were also created as stabilizers around EMesh-assembloid for orthotopic implantation and showed substantial new bone formation and nearly full defect bridging in a critical-sized mouse tibia defect model after 8 weeks. Our results indicates that MEW-assembloid offer a robust strategy for tissue engineering, enhancing the structural and functional integration of implants, and providing an innovation solution for the repair and regeneration of critical bone defects, potentially advancing clinical treatments for bone regeneration.

High resolution melt electro-written scaffolds promote alignment of human skeletal muscle cells

Advanced tissue engineering (TE) strategies are vital to address challenging musculoskeletal conditions, such as volumetric muscle loss. These disorders impose a considerable economic burden and affect individuals' quality of life, highlighting the need for innovative treatments, such as TE, to address these challenges. Here, we examine how scaffold fibre orientation influences mechanical properties and cellular behaviour by utilising melt electrowriting (MEW) as a high-resolution 3D printing technique that combines aspects of electrospinning and melt based polymer deposition. In this work, we investigated the effects of fibre orientation in MEW scaffolds, and its effect on the scaffold mechanical properties as well as cell orientation and alignment. MEW scaffolds were mechanically characterised through uniaxial strain testing to determine critical parameters, including strain at failure, ultimate tensile strength, Young's modulus (E), fatigue rate, recovery time, and yield strain. These mechanical properties were analysed to define an optimal strain regime for transitioning from static to dynamic culture conditions under muscle-like cyclic loading, relevant to muscle's viscoelastic behaviour. In parallel, static cultures of primary human skeletal muscle myoblasts and normal human dermal fibroblasts (NHDFs) were grown on MEW scaffolds, with varying architectures, to study the effects of fibre aspect ratio on cell alignment. Cell alignment was visualised using DAPI/phalloidin staining and quantified with the ImageJ directionality plugin, enabling a systematic comparison of scaffold designs. This approach evaluates the potential of supportive scaffold architectures to promote aligned cell growth, offering insights into designing effective scaffolds for tissue regeneration.

Fiber-reinforced gelatin-based hydrogel biocomposite tubular scaffolds with programmable mechanical properties

Tissue-engineered tubular scaffolds (TETS) provide an effective repair solution for human tubular tissue loss and damage caused by congenital defects, disease, or mechanical trauma. However, there are still major challenges to developing TETS with excellent mechanical properties and biocompatibility for human tubular tissue repair. Gelatin-based hydrogels are suitable candidates for tissue-engineered scaffolds because they are hydrolyzed collagen products and have excellent biocompatibility and degradability. However, the mechanical properties of gelatin-based hydrogels are relatively poor and do not align well with the mechanical properties of human tubular tissues. Inspired by the extracellular matrix architecture of human tubular tissues, this study utilizes high-precision 3D printing to fabricate ultrafine fiber network tubular scaffolds (UFNTS) that mimic the arrangement of collagen fibers, which are then embedded in a cell-compatible gelatin-based hydrogel, resulting in the preparation of a fiber/hydrogel biocomposite tubular scaffold (BCTS) with tunable mechanical properties and a J-shaped stress-strain response. Finite element analysis was employed to predict the mechanical behavior of the UFNTS and BCTS. Experimental results indicate that by modifying the structural parameters of the UFNTS, the mechanical properties of the BCTS can be effectively tuned, achieving a programmable range of tensile modulus (0.2-4.35 MPa) and burst pressure (1580-7850 mmHg), which broadly covers the mechanical properties of most human tubular tissues. The design and fabrication of BCTS offer a new approach for the development of TETS while also providing a personalized strategy for such scaffolds in tissue engineering.

Advancements in manufacturing technologies in the small-diameter artificial blood vessels field

Cardiovascular diseases (CVD) can cause narrowing or blockage in small diameter blood vessels (less than 6 millimeters in diameter). Bypass surgery, which involves replacing damaged native blood vessels, can address various CVD. Recent advancements in manufacturing techniques and the application of new materials have led to the creation of artificial blood vessels that more closely resemble native vessels. By combining different materials and manufacturing methods, it is possible to mimic the structure and function of native blood vessels. Surface coating technologies are also employed in the production of artificial blood vessels to replicate certain vascular functions, such as regulating thrombosis and dissolution. Although most products are not yet ready for clinical use, research and development in artificial blood vessels are progressing faster than ever before (figure1).

Melt Electrowriting of Polyhydroxyalkanoates for Enzymatically Degradable Scaffolds

Melt electrowriting (MEW) enables precise scaffold fabrication for biomedical applications. With a limited number of processable materials with short and tunable degradation times, polyhydroxyalkanoates (PHAs) present an interesting option. Here, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and a blend of PHBV and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (PHBV+P34HB) are successfully melt electrowritten into scaffolds with various architectures. PHBV+P34HB exhibits greater thermal stability, making it a superior printing material compared to PHBV in MEW. The PHBV+P34HB scaffolds subjected to enzymatic degradation show tunable degradation times, governed by enzyme dilution, incubation time, and scaffold surface area. PHBV+P34HB scaffolds seeded with human dermal fibroblasts (HDFs), demonstrate enhanced cell adherence, proliferation, and spreading. The HDFs, when exposed to the enzyme solutions and enzymatic degradation residues, show good viability and proliferation rates. Additionally, HDFs grown on enzymatically pre-incubated scaffolds do not show any difference in behavior compared those grown on control scaffolds. It is concluded that PHAs, as biobased materials with enzymatically tunable degradability rates, are an important addition to the already limited set of materials available for MEW technology.

Redesigning FDM Platforms for Bio-Printing Applications

Fused Deposition Modeling (FDM) is a prominent additive manufacturing technique known for its ability to provide cost-effective and fast printing solutions. FDM enables the production of computer-aided 3D designs as solid objects at macro scales with high-precision alignment while sacrificing excellent surface smoothness compared to other 3D printing techniques such as SLA (Stereolithography) and SLS (Selective Laser Sintering). Electro-Spinning (ES) is another technique for producing soft-structured nonwoven micro-scale materials, such as nanofibers. However, compared to the FDM technique, it has limited accuracy and sensitivity regarding high-precision alignment. The need for high-precision alignment of micro-scaled soft structures during the printing process raises the question of whether FDM and ES techniques can be combined. Today, the printing technique with such capability is called Melt Electro Writing (MEW), and in practice, it refers to the basic working principle on which bio-printers are based. This paper aims to examine how these two techniques can be combined affordably. Comparatively, it presents output production processes, design components, parameters, and materials used in output production. It discusses the limitations and advantages of such a hybrid platform, specifically from the perspective of engineering design and its biomedical applications.

Biofabricated tissue model for determining biocompatibility of metallic coatings

Metallic biomaterials are extensively used in orthopedics and dentistry, either as implants or coatings. In both cases, metal ions come into contact with surrounding tissues causing a particular cell response. Here, we present a biofabricated in vitro tissue model, consisting of a hydrogel reinforced with a melt electrowritten mesh, to study the effects of bound and released metal ions on surrounding cells embedded in a hydrogel matrix. We evaluate the biocompatibility, bioactivity, and antibacterial properties of these metal coatings. Our approach involves integrating physical vapour deposition coating technology with 3D bioprinting methods. To produce tissue models, melt electrowritten (MEW) meshes composed of polycaprolactone (PCL) were printed and integrated into cell-laden methacrylated galatin (GelMa). The mouse embryonic fibroblast cell line (NIH3T3) was used. GelMa concentration and printing parameters for MEW were adjusted and mechanical analysis of the models was performed to find the optimal material composition. Optimized models were placed on the glass slide surfaces coated with typically non-toxic metals, i.e. titanium (Ti), tantalum (Ta), zirconium (Zr), silver (Ag), tungsten (W), and niobium (Nb). Except for W, all other coatings were stable in a physiological wet environment, as studied by SEM. The viability of the cells at different distances from the coated surface was analyzed. Antibacterial tests against pathogens Staphylococcus aureus and Escherichia coli were used to assess the models' resistance, important for infection control. While Ag coatings showed toxicity, Nb, Ta, Ti, and Zr coatings promoted fibroblast growth, with the highest cell viability after 14 days of culture revealed for Ta and Nb. The strongest antimicrobial effect against E. coli and S. aureus was observed for Ag and W, while Ta exhibited antibacterial activity only against S. aureus. From a broader perspective, our work offers an effective 3D in vitro model for an in-depth characterization of the biocompatibility of metals and metal coatings.

An Integrated Dual-Layer Heterogeneous Polycaprolactone Scaffold Promotes Oral Mucosal Wound Healing through Inhibiting Bacterial Adhesion and Mediating HGF-1 Behavior

Recently, the high incidence of oral mucosal defects and the subsequent functional impairments have attracted widespread attention. Controlling scaffold geometry pattern has been proposed as a strategy to promote cell behavior and facilitate soft tissue repair. In this study, we innovatively construct an integrated dual-layer heterogeneous polycaprolactone (PCL) scaffold using melt electrowriting (MEW) technology. The outer layer was disordered, while the inner layer featured oriented fiber patterns: parallel (P-par), rhombic (P-rhomb), and square (P-sq). Our findings revealed that the P-rhomb and P-sq scaffolds exhibited superior surface wettability, roughness, and tensile strength compared to the pure disordered PCL scaffolds (P) and P-par. Compared to the commercial collagen membranes, the outer layer of PCL can effectively inhibit bacterial adhesion and biofilm formation. Furthermore, the P-rhomb and P-sq groups demonstrated higher gene and protein expression levels related to cell adhesion and cell migration rates than did the P and P-par groups. Among them, P-sq plays an important role in inducing the differentiation of gingival fibroblasts into myofibroblasts rich in α-smooth muscle actin (α-SMA). Additionally, P-sq could reduce inflammation, promote epithelial regeneration, and accelerate wound healing when used in full-thickness oral mucosal defects in rabbits. Overall, the integrated dual-layer heterogeneous PCL scaffold fabricated by MEW technology effectively inhibited bacterial adhesion and guided tissue regeneration, offering advantages for clinical translation and large-scale production. This promising material holds important potential for treating full-thickness mucosal defects in a bacteria-rich oral environments.

Advances in melt electrowriting for cardiovascular applications

Melt electrowriting (MEW) is an electric-field-assisted additive biofabrication technique that has brought significant advancements to bioinspired scaffold design for soft tissue engineering and beyond. Owing to its targeted microfiber placement, MEW has become a powerful platform technology for the fabrication of in vitro disease models up to functional biohybrid constructs that are investigated in vivo to reach clinical translation soon. This work provides a concise overview of this rapidly evolving field by highlighting the key contributions of MEW to cardiovascular tissue engineering. Specifically, we i) pinpoint the methods to introduce microvascular networks in thick 3D constructs benefitting from (sacrificial) MEW microfibers, ii) report MEW-based concepts for small-diameter vascular grafts and stents, iii) showcase how contracting cardiac tissues can profit from the tunable structure-property relationship of MEW scaffolds, and iv) address how complete regenerative heart valves can be built on complex fiber scaffold architectures that recapitulate J-shaped tensile properties and tissue heterogeneity. Lastly, we touch on novel biomaterial advancements and discuss the technological challenges of MEW to unlock the full potential of this transformative technology.

The Past, Present, and Future of Tubular Melt Electrowritten Constructs to Mimic Small Diameter Blood Vessels - A Stable Process?

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.