Towards industry-ready additive manufacturing: AI-enabled closed-loop control for 3D melt electrowriting.

Melt electrowriting (MEW) is an emerging high-resolution 3D printing technology used in biomedical engineering, regenerative medicine, and soft robotics. Its transition from academia to industry faces challenges such as slow experimentation, low printing throughput, poor reproducibility, and user-dependent operation, largely due to the nonlinear and multiparametric nature of the MEW process. To address these challenges, we applied computer vision and machine learning to monitor and analyze the process in real-time through imaging of the MEW jet between the nozzle-collector gap.

Understanding the Significance of Layer Bonding in Melt Electrowriting.

Melt electrowriting (MEW) is a high-resolution additive manufacturing technology capable of depositing micrometric fibers onto a moving collector to form 3D scaffolds of controlled mechanical properties. While the critical role of layer bonding to achieve mechanical integrity in fused deposition modeling has been widely reported, it remains largely unknown in MEW, in part due to a lack of methods to assess it. Here, a systematic framework is developed to unravel the significance of layer bonding in MEW scaffolds and its ultimate effect on their mechanical properties.

Electrowriting of SU-8 Microfibers.

As microfiber-based additive manufacturing (AM) technologies, melt electrowriting (MEW) and solution electrowriting (SEW) have demonstrated efficacy with more biomedically relevant materials. By processing SU-8 resin using MEW and SEW techniques, a material with substantially different mechanical, thermal, and optical properties than that typically processed is introduced. SU-8 polymer is temperature sensitive and requires the devising of a specific heating protocol to be properly processed.

[n]Cycloparaphenylenes as Compatible Fluorophores for Melt Electrowriting.

Fluorescent probes are an indispensable tool in the realm of bioimaging technologies, providing valuable insights into the assessment of biomaterial integrity and structural properties. However, incorporating fluorophores into scaffolds made from melt electrowriting (MEW) poses a challenge due to the sustained, elevated temperatures that this processing technique requires. In this context, [n]cycloparaphenylenes ([n]CPPs) serve as excellent fluorophores for MEW processing with the additional benefit of customizable emissions profiles with the same excitation wavelength.

Why bioprinting in regenerative medicine should adopt a rational technology readiness assessment.

Bioprinting is an annex of additive manufacturing, as defined by the American Society for Testing and Materials (ASTM) and International Organization for Standardization (ISO) standards, characterized by the automated deposition of living cells and biomaterials. The tissue engineering and regenerative medicine (TE&RM) community has eagerly adopted bioprinting, while review articles regularly herald its imminent translation to the clinic as functional tissues and organs. Here we argue that such proclamations are premature and counterproductive; they place emphasis on technological progress while typically ignoring the critical stage-gates that must be passed through to bring a technology to market.

Materials and Strategies to Enhance Melt Electrowriting Potential.

Melt electrowriting (MEW) is an emerging additive manufacturing (AM) technology that enables the precise deposition of continuous polymeric microfibers, allowing for the creation of high-resolution constructs. In recent years, MEW has undergone a revolution, with the introduction of active properties or additional functionalities through novel polymer processing strategies, the incorporation of functional fillers, postprocessing, or the combination with other techniques. While extensively explored in biomedical applications, MEW's potential in other fields remains untapped.

Bioassembly of hemoglobin-loaded photopolymerizable spheroids alleviates hypoxia-induced cell death.

The delivery of oxygen within tissue engineered constructs is essential for cell survivability; however, achieving this within larger biofabricated constructs poses a significant challenge. Efforts to overcome this limitation often involve the delivery of synthetic oxygen generating compounds. The application of some of these compounds is problematic for the biofabrication of living tissues due to inherent issues such as cytotoxicity, hyperoxia and limited structural stability due to oxygen inhibition of radical-based crosslinking processes.

Cryo-Electrohydrodynamic Jetting of Aqueous Silk Fibroin Solutions.

The incorporation of 3D-printing principles with electrohydrodynamic (EHD) jetting provides a harmonious balance between resolution and processing speed, allowing for the creation of high-resolution centimeter-scale constructs. Typically, EHD jetting of polymer melts offers the advantage of rapid solidification, while processing polymer solutions requires solvent evaporation to transition into solid fibers, creating challenges for reliable printing. This study navigates a hybrid approach aimed at minimizing printing instabilities by combining viscous solutions and achieving rapid solidification through freezing.

Melt Electrowriting of Nylon-12 Microfibers with an Open-Source 3D Printer.

This study demonstrates how either a heated flat or cylindrical collector enables defect-free melt electrowriting (MEW) of complex geometries from high melting temperature polymers. The open-source "MEWron" printer uses nylon-12 filament and combined with a heated flat or cylindrical collector, produces well-defined fibers with diameters ranging from 33 ± 4 to 95 ± 3 µm. Processing parameters for stable jet formation and minimal defects based on COMSOL thermal modeling for hardware design are optimized.

Technical improvements in preparing 3D printed anatomical models for comminuted fracture preoperative planning.

Preoperative planning of comminuted fracture repair using 3D printed anatomical models is enabling surgeons to visualize and simulate the fracture reduction processes before surgery. However, the preparation of such models can be challenging due to the complexity of certain fractures, particularly in preserving fine detail in bone fragments, maintaining the positioning of displaced fragments, and accurate positioning of multiple bones. This study described several key technical considerations for preparing 3D printed anatomical models for comminuted fracture preoperative planning.

Function Follows Form: Oriented Substrate Nanotopography Overrides Neurite-Repulsive Schwann Cell-Astrocyte Barrier Formation in an Model of Glial Scarring.

Schwann cell (SC) transplantation represents a promising therapeutic approach for traumatic spinal cord injury but is frustrated by barrier formation, preventing cell migration, and axonal regeneration at the interface between grafted SCs and reactive resident astrocytes (ACs). Although regenerating axons successfully extend into SC grafts, only a few cross the SC-AC interface to re-enter lesioned neuropil. To date, research has focused on identifying and modifying the molecular mechanisms underlying such scarring cell-cell interactions, while the influence of substrate topography remains largely unexplored.

A Decade of Melt Electrowriting.

Over the past decade, melt electrowriting (MEW) has established the fundamental understanding of processing (and printer) requirements. Iterative work on parametric development and dissemination of this recent additive manufacturing technology has been performed across many systems and polymers (mainly poly-(ε-caprolactone)), showing similarities and trends. However, the software and hardware ecosystems of MEW are not mature.

Primary Glial Cell and Glioblastoma Morphology in Cocultures Depends on Scaffold Design and Hydrogel Composition.

3D cell cultures better replicate the in vivo environment compared to 2D models. Glioblastoma multiforme, a malignant brain tumor, highly profits from its cellular environment. Here, the U87 glioblastoma cell line in the presence/absence of primary astrocytes is studied.

Electrohydrodynamic 3D Printing of Aqueous Solutions.

Among the various electrohydrodynamic (EHD) processing techniques, electrowriting (EW) produces the most complex 3D structures. Aqueous solution EW similarly retains the potential for additive manufacturing well-resolved 3D structures, while providing new opportunities for processing biologically derived polymers and eschewing organic solvents. However, research on aqueous-based EHD processing is still limited.

Reinforced Hyaluronic Acid-Based Matrices Promote 3D Neuronal Network Formation.

3D neuronal cultures attempt to better replicate the in vivo environment to study neurological/neurodegenerative diseases compared to 2D models. A challenge to establish 3D neuron culture models is the low elastic modulus (30-500 Pa) of the native brain. Here, an ultra-soft matrix based on thiolated hyaluronic acid (HA-SH) reinforced with a microfiber frame is formulated and used.

The Multiweek Thermal Stability of Medical-Grade Poly(ε-caprolactone) During Melt Electrowriting.

Melt electrowriting (MEW) is a high-resolution additive manufacturing technology that places unique constraints on the processing of thermally degradable polymers. With a single nozzle, MEW operates at low throughput and in this study, medical-grade poly(ε-caprolactone) (PCL) is heated for 25 d at three different temperatures (75, 85, and 95 °C), collecting daily samples. There is an initial increase in the fiber diameter and decrease in the jet speed over the first 5 d, then the MEW process remains stable for the 75 and 85 °C groups.

Brain and Breast Cancer Cells with PTEN Loss of Function Reveal Enhanced Durotaxis and RHOB Dependent Amoeboid Migration Utilizing 3D Scaffolds and Aligned Microfiber Tracts.

Background: Glioblastoma multiforme (GBM) and metastatic triple-negative breast cancer (TNBC) with mutations often lead to brain dissemination with poor patient outcome, thus new therapeutic targets are needed. To understand signaling, controlling the dynamics and mechanics of brain tumor cell migration, we implemented GBM and TNBC cell lines and designed 3D aligned microfibers and scaffolds mimicking brain structures.

Methods: 3D microfibers and scaffolds were printed using melt electrowriting.

An initiator- and catalyst-free hydrogel coating process for 3D printed medical-grade poly(ε-caprolactone).

Additive manufacturing or 3D printing as an umbrella term for various materials processing methods has distinct advantages over many other processing methods, including the ability to generate highly complex shapes and designs. However, the performance of any produced part not only depends on the material used and its shape, but is also critically dependent on its surface properties. Important features, such as wetting or fouling, critically depend mainly on the immediate surface energy.

Spinal Cord Neuronal Network Formation in a 3D Printed Reinforced Matrix-A Model System to Study Disease Mechanisms.

3D cell cultures allow a better mimicry of the biological and mechanical environment of cells in vivo compared to 2D cultures. However, 3D cell cultures have been challenging for ultrasoft tissues such as the brain. The present study uses a microfiber reinforcement approach combining mouse primary spinal cord neurons in Matrigel with melt electrowritten (MEW) frames.

A novel in vitro assay for peripheral nerve-related cell migration that preserves both extracellular matrix-derived molecular cues and nanofiber-derived topography.

Background: Molecular composition and topography of the extracellular matrix (ECM) influence regenerative cell migration following peripheral nerve injury (PNI). Advanced tissue engineering strategies for the repair of neurotmesis-type PNI include the development of nanofiber-containing implantable scaffolds that mimic features of the ECM to orchestrate regenerative growth. Reliable and quantifiable in vitro assays are required to assess the ability of such substrates to influence migration of the cell types of interest.

Convergence of Machine Vision and Melt Electrowriting.

Melt electrowriting (MEW) is a high-resolution additive manufacturing technology that balances multiple parametric variables to arrive at a stable fabrication process. The better understanding of this balance is underscored here using high-resolution camera vision of jet stability profiles in different electrical fields. Complementing this visual information are fiber-diameter measurements obtained at precise points, allowing the correlation to electrified jet properties.

Design of Suspended Melt Electrowritten Fiber Arrays for Schwann Cell Migration and Neurite Outgrowth.

In this study, well-defined, 3D arrays of air-suspended melt electrowritten fibers are made from medical grade poly(ɛ-caprolactone) (PCL). Low processing temperatures, lower voltages, lower ambient temperature, increased collector distance, and high collector speeds all aid to direct-write suspended fibers that can span gaps of several millimeters between support structures. Such processing parameters are quantitatively determined using a "wedge-design" melt electrowritten test frame to identify the conditions that increase the suspension probability of long-distance fibers.

Prevascularized Retrievable Hybrid Implant to Enhance Function of Subcutaneous Encapsulated Islets.

Replacement of pancreatic β-cells is one of the most promising treatment options for treatment of type 1 diabetes (T1D), even though, toxic immunosuppressive drugs are required. In this study, we aim to deliver allogeneic β-cell therapies without antirejection drugs using a bioengineered hybrid device that contains microencapsulated β-cells inside 3D polycaprolactone (PCL) scaffolds printed using melt electrospin writing (MEW). Mouse β-cell (MIN6) pseudoislets and QS mouse islets are encapsulated in alginate microcapsules, without affecting viability and insulin secretion.

Melt Electrospinning of Nanofibers from Medical-Grade Poly(ε-Caprolactone) with a Modified Nozzle.

Melt electrospun fibers, in general, have larger diameters than normally achieved with solution electrospinning. This study uses a modified nozzle to direct-write melt electrospun medical-grade poly(ε-caprolactone) onto a collector resulting in fibers with the smallest average diameter being 275 ± 86 nm under certain processing conditions. Within a flat-tipped nozzle is a small acupuncture needle positioned so that reduces the flow rate to ≈0.

Polymers for Melt Electrowriting.

Melt electrowriting (MEW) is an emerging high-resolution additive manufacturing technique based on the electrohydrodynamic processing of polymers. MEW is predominantly used to fabricate scaffolds for biomedical applications, where the microscale fiber positioning has substantial implications in its macroscopic mechanical properties. This review gives an update on the increasing number of polymers processed via MEW and different commercial sources of the gold standard poly(ε-caprolactone) (PCL).