RESOURCES

Abstract
The meniscus is characterised by an anisotropic collagen fibre network which is integral to its biomechanical functionality. The engineering of structurally organized meniscal grafts that mimic the anisotropy of the native tissue remains a significant challenge. In this study, inkjet bioprinting was used to deposit a cell-laden bioink into additively manufactured scaffolds of differing architectures to engineer fibrocartilage grafts with user defined collagen architectures. Polymeric scaffolds consisting of guiding fibre networks with varying aspect ratios (1:1; 1:4; 1:16) were produced using either fused deposition modelling (FDM) or melt electrowriting (MEW), resulting in scaffolds with different internal architectures and fibre diameters. Scaffold architecture was found to influence the spatial organization of the collagen network laid down by the jetted cells, with higher aspect ratios (1:4 and 1:16) supporting the formation of structurally anisotropic tissues. The MEW scaffolds supported the development of a fibrocartilaginous tissue with compressive mechanical properties similar to that of native meniscus, while the anisotropic tensile properties of these constructs could be tuned by altering the fibre network aspect ratio. This MEW framework was then used to generate scaffolds with spatially distinct fibre patterns, which in turn supported the development of heterogenous tissues consisting of isotropic and anisotropic collagen networks. Such bioprinted tissues could potentially form the basis of new treatment options for damaged and diseased meniscal tissue.
Statement of significance
This study describes a multiple tool biofabrication strategy which enables the engineering of spatially organized fibrocartilage tissues. The architecture of MEW scaffolds can be tailored to not only modulate the directionality of the collagen fibres laid down by cells, but also to tune the anisotropic tensile mechanical properties of the resulting constructs, thereby enabling the engineering of biomimetic meniscal-like tissues. Furthermore, the inherent flexibility of MEW enables the development of zonally defined and potentially patient-specific implants.

Abstract
To progress cardiac tissue engineering strategies closer to the clinic, thicker constructs are required to meet the functional need following a cardiac event. Consequently, pre-vascularization of these constructs needs to be investigated to ensure survival and optimal performance of implantable engineered heart tissue. The aim of this research is to investigate the potential of combining extrusion-based bioprinting (EBB) and melt electrowriting for the fabrication of a myocardial construct with a precisely patterned pre-vascular pathway. Gelatin methacryloyl (GelMA) was investigated as a base hydrogel for the respective myocardial and vascular bioinks with collagen, Matrigel and fibrinogen as interpenetrating polymers to support myocardial functionality. Subsequently, extrusion-based printability and viability were investigated to determine the optimal processing parameters for printing into melt electrowritten meshes. Finally, an anatomically inspired vascular pathway was implemented in a dual EBB set-up into melt electrowritten meshes, creating a patterned pre-vascularized myocardial construct. It was determined that a blend of 5% GelMA and 0.8 mg·ml−1 collagen with a low crosslinked density was optimal for myocardial cellular arrangement and alignment within the constructs. For the vascular fraction, the optimized formulation consisted of 5% GelMA, 0.8 mg·ml−1 collagen and 1 mg·ml−1 fibrinogen with a higher crosslinked density, which led to enhanced vascular cell connectivity. Printability assessment confirmed that the optimized bioinks could effectively fill the microfiber mesh while supporting cell viability (∼70%). Finally, the two bioinks were applied using a dual EBB system for the fabrication of a pre-vascular pathway with the shape of a left anterior descending artery within a myocardial construct, whereby the distinct cell populations could be visualized in their respective patterns up to D14. This research investigated the first step towards developing a thick engineered cardiac tissue construct in which a pre-vascularization pathway is fabricated within a myocardial construct.

Abstract
Periodontitis is a chronic inflammatory condition that often causes serious damage to tooth-supporting tissues. The limited successful outcomes of clinically available approaches underscore the need for therapeutics that cannot only provide structural guidance to cells but can also modulate the local immune response. Here, three-dimensional melt electrowritten (i.e., poly(ε-caprolactone)) scaffolds with tissue-specific attributes were engineered to guide differentiation of human-derived periodontal ligament stem cells (hPDLSCs) and mediate macrophage polarization. The investigated tissue-specific scaffold attributes comprised fiber morphology (aligned vs. random) and highly-ordered architectures with distinct strand spacings (small 250 μm and large 500 μm). Macrophages exhibited an elongated morphology in aligned and highly-ordered scaffolds, while maintaining their round-shape on randomly-oriented fibrous scaffolds. Expressions of periostin and IL-10 were more pronounced on the aligned and highly-ordered scaffolds. While hPDLSCs on the scaffolds with 500 μm strand spacing show higher expression of osteogenic marker (Runx2) over 21 days, cells on randomly-oriented fibrous scaffolds showed upregulation of M1 markers. In an orthotopic mandibular fenestration defect model, findings revealed that the tissue-specific scaffolds (i.e., aligned fibers for periodontal ligament and highly-ordered 500 μm strand spacing fluorinated calcium phosphate [F/CaP]-coated fibers for bone) could enhance the mimicking of regeneration of natural periodontal tissues.

Abstract
Periodontitis is a chronic inflammatory condition that often causes serious damage to tooth-supporting tissues. The limited successful outcomes of clinically available approaches underscore the need for therapeutics that cannot only provide structural guidance to cells but can also modulate the local immune response. Here, three-dimensional melt electrowritten (i.e., poly(ε-caprolactone)) scaffolds with tissue-specific attributes were engineered to guide differentiation of human-derived periodontal ligament stem cells (hPDLSCs) and mediate macrophage polarization. The investigated tissue-specific scaffold attributes comprised fiber morphology (aligned vs. random) and highly-ordered architectures with distinct strand spacings (small 250 μm and large 500 μm). Macrophages exhibited an elongated morphology in aligned and highly-ordered scaffolds, while maintaining their round-shape on randomly-oriented fibrous scaffolds. Expressions of periostin and IL-10 were more pronounced on the aligned and highly-ordered scaffolds. While hPDLSCs on the scaffolds with 500 μm strand spacing show higher expression of osteogenic marker (Runx2) over 21 days, cells on randomly-oriented fibrous scaffolds showed upregulation of M1 markers. In an orthotopic mandibular fenestration defect model, findings revealed that the tissue-specific scaffolds (i.e., aligned fibers for periodontal ligament and highly-ordered 500 μm strand spacing fluorinated calcium phosphate [F/CaP]-coated fibers for bone) could enhance the mimicking of regeneration of natural periodontal tissues.

Abstract
Periodontitis is a chronic inflammatory condition that often causes serious damage to tooth-supporting tissues. The limited successful outcomes of clinically available approaches underscore the need for therapeutics that cannot only provide structural guidance to cells but can also modulate the local immune response. Here, three-dimensional melt electrowritten (i.e., poly(ε-caprolactone)) scaffolds with tissue-specific attributes were engineered to guide differentiation of human-derived periodontal ligament stem cells (hPDLSCs) and mediate macrophage polarization. The investigated tissue-specific scaffold attributes comprised fiber morphology (aligned vs. random) and highly-ordered architectures with distinct strand spacings (small 250 μm and large 500 μm). Macrophages exhibited an elongated morphology in aligned and highly-ordered scaffolds, while maintaining their round-shape on randomly-oriented fibrous scaffolds. Expressions of periostin and IL-10 were more pronounced on the aligned and highly-ordered scaffolds. While hPDLSCs on the scaffolds with 500 μm strand spacing show higher expression of osteogenic marker (Runx2) over 21 days, cells on randomly-oriented fibrous scaffolds showed upregulation of M1 markers. In an orthotopic mandibular fenestration defect model, findings revealed that the tissue-specific scaffolds (i.e., aligned fibers for periodontal ligament and highly-ordered 500 μm strand spacing fluorinated calcium phosphate [F/CaP]-coated fibers for bone) could enhance the mimicking of regeneration of natural periodontal tissues.

Abstract
Periodontitis is a chronic inflammatory condition that often causes serious damage to tooth-supporting tissues. The limited successful outcomes of clinically available approaches underscore the need for therapeutics that cannot only provide structural guidance to cells but can also modulate the local immune response. Here, three-dimensional melt electrowritten (i.e., poly(ε-caprolactone)) scaffolds with tissue-specific attributes were engineered to guide differentiation of human-derived periodontal ligament stem cells (hPDLSCs) and mediate macrophage polarization. The investigated tissue-specific scaffold attributes comprised fiber morphology (aligned vs. random) and highly-ordered architectures with distinct strand spacings (small 250 μm and large 500 μm). Macrophages exhibited an elongated morphology in aligned and highly-ordered scaffolds, while maintaining their round-shape on randomly-oriented fibrous scaffolds. Expressions of periostin and IL-10 were more pronounced on the aligned and highly-ordered scaffolds. While hPDLSCs on the scaffolds with 500 μm strand spacing show higher expression of osteogenic marker (Runx2) over 21 days, cells on randomly-oriented fibrous scaffolds showed upregulation of M1 markers. In an orthotopic mandibular fenestration defect model, findings revealed that the tissue-specific scaffolds (i.e., aligned fibers for periodontal ligament and highly-ordered 500 μm strand spacing fluorinated calcium phosphate [F/CaP]-coated fibers for bone) could enhance the mimicking of regeneration of natural periodontal tissues.

Abstract
Successful cartilage engineering requires the generation of biological grafts mimicking the structure, composition and mechanical behaviour of the native tissue. Here melt electrowriting (MEW) was used to produce arrays of polymeric structures whose function was to orient the growth of cellular aggregates spontaneously generated within these structures, and to provide tensile reinforcement to the resulting tissues. Inkjet printing was used to deposit defined numbers of cells into MEW structures, which self-assembled into an organized array of spheroids within hours, ultimately generating a hybrid tissue that was hyaline-like in composition. Structurally, the engineered cartilage mimicked the histotypical organization observed in skeletally immature synovial joints. This biofabrication framework was then used to generate scaled-up (50 mm × 50 mm) cartilage implants containing over 3,500 cellular aggregates in under 15 min. After 8 weeks in culture, a 50-fold increase in the compressive stiffness of these MEW reinforced tissues were observed, while the tensile properties were still dominated by the polymer network, resulting in a composite construct demonstrating tension-compression nonlinearity mimetic of the native tissue. Helium ion microscopy further demonstrated the development of an arcading collagen network within the engineered tissue. This hybrid bioprinting strategy provides a versatile and scalable approach to engineer cartilage biomimetic grafts for biological joint resurfacing.

Abstract
Abstract Periodontitis is a chronic inflammatory, bacteria-triggered disorder affecting nearly half of American adults. Although some level of tissue regeneration is realized, its low success in complex cases demands superior strategies to amplify regenerative capacity. Herein, highly ordered scaffolds are engineered via Melt ElectroWriting (MEW), and the effects of strand spacing, as well as the presence of a nanostructured fluorinated calcium phosphate (F/CaP) coating on the adhesion/proliferation, and osteogenic differentiation of human-derived periodontal ligament stem cells, are investigated. Upon initial cell-scaffold interaction screening aimed at defining the most suitable design, MEW poly(ε-caprolactone) scaffolds with 500 µm strand spacing are chosen. Following an alkali treatment, scaffolds are immersed in a pre-established solution to allow for coating formation. The presence of a nanostructured F/CaP coating leads to a marked upregulation of osteogenic genes and attenuated bacterial growth. In vivo findings confirm that the F/CaP-coated scaffolds are biocompatible and lead to periodontal regeneration when implanted in a rat mandibular periodontal fenestration defect model. In aggregate, it is considered that this work can contribute to the development of personalized scaffolds capable of enabling tissue-specific differentiation of progenitor cells, and thus guide simultaneous and coordinated regeneration of soft and hard periodontal tissues, while providing antimicrobial protection.

Abstract
One of the most damaging pathologies that affects the health of both soft and hard tissues around the tooth is periodontitis. Clinically, periodontal tissue destruction has been managed by an integrated approach involving elimination of injured tissues followed by regenerative strategies with bone substitutes and/or barrier membranes. Regrettably, a barrier membrane with predictable mechanical integrity and multifunctional therapeutic features has yet to be established. Herein, we report a fiber-reinforced hydrogel with unprecedented tunability in terms of mechanical competence and therapeutic features by integration of highly porous poly(ε-caprolactone) fibrous mesh(es) with well-controlled 3D architecture into bioactive amorphous magnesium phosphate-laden gelatin methacryloyl hydrogels. The presence of amorphous magnesium phosphate and PCL mesh in the hydrogel can control the mechanical properties and improve the osteogenic ability, opening a tremendous opportunity in guided bone regeneration (GBR). Results demonstrate that the presence of PCL meshes fabricated via melt electrowriting can delay hydrogel degradation preventing soft tissue invasion and providing the mechanical barrier to allow time for slower migrating progenitor cells to participate in bone regeneration due to their ability to differentiate into bone-forming cells. Altogether, our approach offers a platform technology for the development of the next-generation of GBR membranes with tunable mechanical and therapeutic properties to amplify bone regeneration in compromised sites.

Abstract
Three-dimensional printed hydrogel constructs with well-organized melt electrowritten (MEW) fibre-reinforcing scaffolds have been demonstrated as a promising regenerative approach to treat small cartilage defects. Here, we investige how to translate the fabrication of small fibre-reinforced structures on flat surfaces to anatomically relevant structures. In particular, the accurate deposition of MEW-fibres onto curved surfaces of conductive and non-conductive regenerative biomaterials is studied. This study reveals that clinically relevant materials with low conductivities are compatible with resurfacing with organized MEW fibres. Importantly, accurate patterning on non-flat surfaces was successfully shown, provided that a constant electrical field strength and an electrical force normal to the substrate material is maintained. Furthermore, the application of resurfacing the geometry of the medial human femoral condyle is confirmed by the fabrication of a personalised osteochondral implant. The implant composed of an articular cartilage-resident chondroprogenitor cells (ACPCs)-laden hydrogel reinforced with a well-organized MEW scaffold retained its personalised shape, improved its compressive properties and supported neocartilage formation after 28 days in vitro culture. Overall, this study establishes the groundwork for translating MEW from planar and non-resorbable material substrates to anatomically relevant geometries and regenerative materials that the regenerative medicine field aims to create.

Abstract
Abstract Fabrication of biomimetic tissues holds much promise for the regeneration of cells or organs that are lost or damaged due to injury or disease. To enable the generation of complex, multicellular tissues on demand, the ability to design and incorporate different materials and cell types needs to be improved. Two techniques are combined: extrusion-based bioprinting, which enables printing of cell-encapsulated hydrogels; and melt electrowriting (MEW), which enables fabrication of aligned (sub)-micrometer fibers into a single-step biofabrication process. Composite structures generated by infusion of MEW fiber structures with hydrogels have resulted in mechanically and biologically competent constructs; however, their preparation involves a two-step fabrication procedure that limits freedom of design of microfiber architectures and the use of multiple materials and cell types. How convergence of MEW and extrusion-based bioprinting allows fabrication of mechanically stable constructs with the spatial distributions of different cell types without compromising cell viability and chondrogenic differentiation of mesenchymal stromal cells is demonstrated for the first time. Moreover, this converged printing approach improves freedom of design of the MEW fibers, enabling 3D fiber deposition. This is an important step toward biofabrication of voluminous and complex hierarchical structures that can better resemble the characteristics of functional biological tissues.

Abstract
Successful periodontal repair and regeneration requires the coordinated responses from soft and hard tissues as well as the soft tissue–to–bone interfaces. Inspired by the hierarchical structure of native periodontal tissues, tissue engineering technology provides unique opportunities to coordinate multiple cell types into scaffolds that mimic the natural periodontal structure in vitro. In this study, we designed and fabricated highly ordered multicompartmental scaffolds by melt electrowriting, an advanced 3-dimensional (3D) printing technique. This strategy attempted to mimic the characteristic periodontal microenvironment through multicompartmental constructs comprising 3 tissue-specific regions: 1) a bone compartment with dense mesh structure, 2) a ligament compartment mimicking the highly aligned periodontal ligaments (PDLs), and 3) a transition region that bridges the bone and ligament, a critical feature that differentiates this system from mono- or bicompartmental alternatives. The multicompartmental constructs successfully achieved coordinated proliferation and differentiation of multiple cell types in vitro within short time, including both ligamentous- and bone-derived cells. Long-term 3D coculture of primary human osteoblasts and PDL fibroblasts led to a mineral gradient from calcified to uncalcified regions with PDL-like insertions within the transition region, an effect that is challenging to achieve with mono- or bicompartmental platforms. This process effectively recapitulates the key feature of interfacial tissues in periodontium. Collectively, this tissue-engineered approach offers a fundament for engineering periodontal tissue constructs with characteristic 3D microenvironments similar to native tissues. This multicompartmental 3D printing approach is also highly compatible with the design of next-generation scaffolds, with both highly adjustable compartmentalization properties and patient-specific shapes, for multitissue engineering in complex periodontal defects.

Abstract
Abstract Current biomaterial-based strategies explored to treat articular cartilage defects have failed to provide adequate physico-chemical cues in order to guide functional tissue regeneration. Here, it is hypothesized that atmospheric-pressure plasma (APPJ) treatment and melt electrowriting (MEW) will produce microfiber support structures with covalently-immobilized transforming growth factor beta-1 (TGFβ1) that can stimulate the generation of functional cartilage tissue. The effect of APPJ operational speeds to activate MEW polycaprolactone meshes for immobilization of TGFβ1 is first investigated and chondrogenic differentiation and neo-cartilage production are assessed in vitro. All APPJ speeds test enhanced hydrophilicity of the meshes, with the slow treatment speed having significantly less CC/CH and more COOH than the untreated meshes. APPJ treatment increases TGFβ1 loading efficiency. Additionally, in vitro experiments highlight that APPJ-based TGFβ1 attachment to the scaffolds is more advantageous than direct supplementation within the medium. After 28 days of culture, the group with immobilized TGFβ1 has significantly increased compressive modulus (more than threefold) and higher glycosaminoglycan production (more than fivefold) than when TGFβ1 is supplied through the medium. These results demonstrate that APPJ activation allows reagent-free, covalent immobilization of TGFβ1 on microfiber meshes and, importantly, that the biofunctionalized meshes can stimulate neo-cartilage matrix formation. This opens new perspectives for guided tissue regeneration.

Abstract
Herein, the fabrication of light-sensitive high-aspect ratio surfaces with switchable topography using melt-electrowriting of shape-memory polymers and deposition of light-to-heat converting black ink on it by dip coating is reported on. The lamellae exposed to low temperatures are hard and cannot be deformed by water droplets. The temperature reached upon illumination of surfaces is close to the melting point of the soft segment of the polyurethane that leads to softening of the polymer. Due to this, it is possible to locally deform and recover the light-softened surface structures by water droplets deposited on lamellae. The deformed state can be fixed by cooling down resulting in the crystallization of the polymer. Thus, the reversibility of local deformation can be achieved. Finally, the application of the developed approach and materials for the fabrication of smart light-controlled valves is demonstrated, which can be used for the controlled mixing of fluids in microfluidic devices.

Abstract
Summary
Acinetobacter baumannii causes a wide range of infections, including wound infections. Multidrug-resistant A. baumannii is a major healthcare concern and the development of novel treatments against these infections is needed. Fosmidomycin is a repurposed antimalarial drug targeting the non-mevalonate pathway, and several derivatives show activity towards A. baumannii. We evaluated the antimicrobial activity of CC366, a fosmidomycin prodrug, against a collection of A. baumannii strains, using various in vitro and in vivo models; emphasis was placed on the evaluation of its anti-biofilm activity. We also developed a 3D-printed wound dressing containing CC366, using melt electrowriting technology. Minimal inhibitory concentrations of CC366 ranged from 1 to 64 μg/mL, and CC366 showed good biofilm inhibitory and moderate biofilm eradicating activity in vitro. CC366 successfully eluted from a 3D-printed dressing, the dressings prevented the formation of A. baumannnii wound biofilms in vitro and reduced A. baumannii infection in an in vivo mouse model.

Abstract
The demand for high-throughput and scalable cell expansion platforms that can accommodate diverse cell types remains a critical requirement across various biomedical fields. Fibronectin (Fn), an essential component of the extracellular matrix (ECM), has been used as a conformal surface coating for two-dimensional (2D) cell culture systems. However, the soluble, globular Fn used for 2D coatings differs structurally from the native Fn, which possesses a three-dimensional (3D) fibrillar structure. Herein, a large-scale engineered ECM (EECM) cell expansion platform based on a 3D fibrillar Fn network spanning over centimeters is presented. Extended fibrillar networks are formed by shearing dilute Fn solutions over tessellated polymeric scaffolds, which are conveniently prepared by 3D printing. The structure and size of the Fn-based 3D EECM scaffold are optimized by evaluating the proliferation of a colorectal tumor cell line, CT26, commonly used in the in vivo tumor immunotherapy models. The 3D EECM scaffolds support a fourfold more efficient tumor cell expansion than a conventional 2D culture system, demonstrating the potential efficacy in supporting the robust expansion of cancer cells ex vivo with an eye on cancer immunotherapy.

Abstract
The meniscus is a fibrocartilage tissue that is integral to the correct functioning of the knee joint. The tissue possesses a unique collagen fiber architecture that is integral to its biomechanical functionality. In particular, a network of circumferentially aligned collagen fibers function to bear the high tensile forces generated in the tissue during normal daily activities. The limited regenerative capacity of the meniscus has motivated increased interest in meniscus tissue engineering; however, the in vitro generation of structurally organized meniscal grafts with a collagen architecture mimetic of the native meniscus remains a significant challenge. Here we used melt electrowriting (MEW) to produce scaffolds with defined pore architectures to impose physical boundaries upon cell growth and extracellular matrix production. This enabled the bioprinting of anisotropic tissues with collagen fibers preferentially oriented parallel to the long axis of the scaffold pores. Furthermore, temporally removing glycosaminoglycans (sGAGs) during the early stages of in vitro tissue development using chondroitinase ABC (cABC) was found to positively impact collagen network maturation. Specially we found that temporal depletion of sGAGs is associated with an increase in collagen fiber diameter without any detrimental effect on the development of a meniscal tissue phenotype or subsequent extracellular matrix production. Moreover, temporal cABC treatment supported the development of engineered tissues with superior tensile mechanical properties compared to empty MEW scaffolds. These findings demonstrate the benefit of temporal enzymatic treatments when engineering structurally anisotropic tissues using emerging biofabrication technologies such as MEW and inkjet bioprinting.

Abstract
Traumatic injury to the spinal cord (SCI) causes the transection of neurons, formation of a lesion cavity, and remodeling of the microenvironment by excessive extracellular matrix (ECM) deposition and scar formation leading to a regeneration-prohibiting environment. Electrospun fiber scaffolds have been shown to simulate the ECM and increase neural alignment and neurite outgrowth contributing to a growth-permissive matrix. In this work, electrospun ECM-like fibers providing biochemical and topological cues are implemented into a scaffold to represent an oriented biomaterial suitable for the alignment and migration of neural cells in order to improve spinal cord regeneration. The successfully decellularized spinal cord ECM (dECM), with no visible cell nuclei and dsDNA content < 50 ng/mg tissue, showed preserved ECM components, such as glycosaminoglycans and collagens. Serving as the biomaterial for 3D printer-assisted electrospinning, highly aligned and randomly distributed dECM fiber scaffolds (< 1 µm fiber diameter) were fabricated. The scaffolds were cytocompatible and supported the viability of a human neural cell line (SH-SY5Y) for 14 days. Cells were selectively differentiated into neurons, as confirmed by immunolabeling of specific cell markers (ChAT, Tubulin ß), and followed the orientation given by the dECM scaffolds. After generating a lesion site on the cell-scaffold model, cell migration was observed and compared to reference poly-ε-caprolactone fiber scaffolds. The aligned dECM fiber scaffold promoted the fastest and most efficient lesion closure, indicating superior cell guiding capabilities of dECM-based scaffolds. The strategy of combining decellularized tissues with controlled deposition of fibers to optimize biochemical and topographical cues opens the way for clinically relevant central nervous system scaffolding solutions.

Abstract
This work reports the construction of a bicomponent scaffold co-loaded with both a prodrug and a drug (BiFp@Ht) as an efficient platform for wound dressing, by combining the electrospinning and 3D-printing technologies. The outer component consisted of a chitosan/polyethylene oxide-electrospun membrane loaded with the indomethacin–polyethylene glycol–indomethacin prodrug (Fp) and served as a support for printing the inner component, a gelatin methacryloyl/sodium alginate hydrogel loaded with tetracycline hydrochloride (Ht). The different architectural characteristics of the electrospun and 3D-printed layers were very well highlighted in a morphological analysis performed by Scanning Electron Microscopy (SEM). In vitro release profile studies demonstrated that both Fp and Ht layers were capable to release the loaded therapeutics in a controlled and sustained manner. According to a quantitative in vitro biological assessment, the bicomponent BiFp@Ht scaffold showed a good biocompatibility and no cytotoxic effect on HeLa cell cultures, while the highest proliferation level was noted in the case of HeLa cells seeded onto an Fp nanofibrous membrane. Furthermore, the BiFp@Ht scaffold presented an excellent antimicrobial activity against the E. coli and S. aureus bacterial strains, along with promising anti-inflammatory and proangiogenic activities, proving its potential to be used for wound dressing.

Abstract
Fluid pressure develops transiently within mechanically-loaded, cell-embedding hydrogels, but its magnitude depends on the intrinsic material properties of the hydrogel and cannot be easily altered. The recently developed melt-electrowriting (MEW) technique enables three-dimensional printing of structured fibrous mesh with small fibre diameter (20 μm). The MEW mesh with 20 μm fibre diameter can synergistically increase the instantaneous mechanical stiffness of soft hydrogels. However, the reinforcing mechanism of the MEW meshes is not well understood, and may involve load-induced fluid pressurisation. Here, we examined the reinforcing effect of MEW meshes in three hydrogels: gelatin methcryloyl (GelMA), agarose and alginate, and the role of load-induced fluid pressurisation in the MEW reinforcement. We tested the hydrogels with and without MEW mesh (i.e., hydrogel alone, and MEW-hydrogel composite) using micro-indentation and unconfined compression, and analysed the mechanical data using biphasic Hertz and mixture models. We found that the MEW mesh altered the tension-to-compression modulus ratio differently for hydrogels that are cross-linked differently, which led to a variable change to their load-induced fluid pressurisation. MEW meshes only enhanced the fluid pressurisation for GelMA, but not for agarose or alginate. We speculate that only covalently cross-linked hydrogels (GelMA) can effectively tense the MEW meshes, thereby enhancing the fluid pressure developed during compressive loading. In conclusion, load-induced fluid pressurisation in selected hydrogels was enhanced by MEW fibrous mesh, and may be controlled by MEW mesh of different designs in the future, thereby making fluid pressure a tunable cell growth stimulus for tissue engineering involving mechanical stimulation.

Abstract
The global health emergency posed by the outbreak of Zika virus (ZIKV), an arthropod-borne flavivirus causing severe neonatal neurological conditions, has subsided, but there continues to be transmission of ZIKV in endemic regions. As such, there is still a medical need for discovering and developing therapeutical interventions against ZIKV. To identify small-molecule compounds that inhibit ZIKV disease and transmission, we screened multiple small-molecule collections, mostly derived from natural products, for their ability to inhibit wild-type ZIKV. As a primary high-throughput screen, we used a viral cytopathic effect (CPE) inhibition assay conducted in Vero cells that was optimized and miniaturized to a 1536-well format. Suitably active compounds identified from the primary screen were tested in a panel of orthogonal assays using recombinant Zika viruses, including a ZIKV Renilla luciferase reporter assay and a ZIKV mCherry reporter system. Compounds that were active in the wild-type ZIKV inhibition and ZIKV reporter assays were further evaluated for their inhibitory effects against other flaviviruses. Lastly, we demonstrated that wild-type ZIKV is able to infect a 3D-bioprinted outer-blood-retina barrier tissue model and disrupt its barrier function, as measured by electrical resistance. One of the identified compounds (3-Acetyl-13-deoxyphomenone, NCGC00380955) was able to prevent the pathological effects of the viral infection on this clinically relevant ZIKV infection model.

Abstract
The Foreign body response (FBR) is a major unresolved challenge that compromises medical implant integration and function by inflammation and fibrotic encapsulation. Mice implanted with polymeric scaffolds coupled to intravital non-linear multiphoton microscopy acquisition enable multiparametric, longitudinal investigation of the FBR evolution and interference strategies. However, follow-up analyses based on visual localization and manual segmentation are extremely time-consuming, subject to human error, and do not allow for automated parameter extraction. We developed an integrated computational pipeline based on an innovative and versatile variant of the U-Net neural network to segment and quantify cellular and extracellular structures of interest, which is maintained across different objectives without impairing accuracy. This software for automatically detecting the elements of the FBR shows promise to unravel the complexity of this pathophysiological process.

Abstract
The foreign body response (FBR) is a clinically relevant issue that can cause malfunction of implanted medical devices by fibrotic encapsulation. Whereas inflammatory aspects of the FBR have been established, underlying fibroblast-dependent mechanisms remain unclear. We here combine multiphoton microscopy with ad hoc reporter mice expressing α–smooth muscle actin (αSMA) protein to determine the locoregional fibroblast dynamics, activation, and fibrotic encapsulation of polymeric materials. Fibroblasts invaded as individual cells and established a multicellular network, which transited to a two-compartment fibrotic response displaying an αSMA cold external capsule and a long-lasting, inner αSMA hot environment. The recruitment of fibroblasts and extent of fibrosis were only incompletely inhibited after depletion of macrophages, implicating coexistence of macrophage-dependent and macrophage-independent mediators. Furthermore, neither altering material type or porosity modulated αSMA+ cell recruitment and distribution. This identifies fibroblast activation and network formation toward a two-compartment FBR as a conserved, self-organizing process partially independent of macrophages. Fibroblast recruitment in the foreign body response is a conserved, self-organizing process partially independent of macrophages.

Abstract
The permeability of the human trabecular meshwork (HTM) regulates eye pressure via a porosity gradient across its thickness modulated by stacked layers of matrix fibrils and cells. Changes in HTM porosity are associated with increases in intraocular pressure and the progress of diseases such as glaucoma. Engineered HTMs could help to understand the structure–function relation in natural tissues and lead to new regenerative solutions. Here, melt electrowriting (MEW) is explored as a biofabrication technique to produce fibrillar, porous scaffolds that mimic the multilayer, gradient structure of native HTM. Poly(caprolactone) constructs with a height of 125–500 μm and fiber diameters of 10–12 μm are printed. Scaffolds with a tensile modulus between 5.6 and 13 MPa and a static compression modulus in the range of 6–360 kPa are obtained by varying the scaffold design, that is, the density and orientation of the fibers and number of stacked layers. Primary HTM cells attach to the scaffolds, proliferate, and form a confluent layer within 8–14 days, depending on the scaffold design. High cell viability and cell morphology close to that in the native tissue are observed. The present work demonstrates the utility of MEW for reconstructing complex morphological features of natural tissues.

Abstract
Emerging 3D printing technologies can provide exquisite control over the external shape and internal architecture of scaffolds and tissue engineered constructs, enabling systematic studies to explore how geometric design features influence the regenerative process. Here we used fused deposition modelling (FDM) and melt electrowriting (MEW) to investigate how scaffold microarchitecture influences the healing of large bone defects. FDM was used to fabricate scaffolds with relatively large fibre diameters and low porosities, while MEW was used to fabricate scaffolds with smaller fibre diameters and higher porosities, with both scaffolds being designed to have comparable surface areas. Scaffold microarchitecture significantly influenced the healing response following implantation into critically sized femoral defects in rats, with the FDM scaffolds supporting the formation of larger bone spicules through its pores, while the MEW scaffolds supported the formation of a more round bone front during healing. After 12 weeks in vivo, both MEW and FDM scaffolds supported significantly higher levels of defect vascularisation compared to empty controls, while the MEW scaffolds supported higher levels of new bone formation. Somewhat surprisingly, this superior healing in the MEW group did not correlate with higher levels of angiogenesis, with the FDM scaffold supporting greater total vessel formation and the formation of larger vessels, while the MEW scaffold promoted the formation of a dense microvasculature with minimal evidence of larger vessels infiltrating the defect region. To conclude, the small fibre diameter, high porosity and high specific surface area of the MEW scaffold proved beneficial for osteogenesis and bone regeneration, demonstrating that changes in scaffold architecture enabled by this additive manufacturing technique can dramatically modulate angiogenesis and tissue regeneration without the need for complex exogenous growth factors. These results provide a valuable insight into the importance of 3D printed scaffold architecture when developing new bone tissue engineering strategies.

Abstract
This paper reports for the first time the fabrication and investigation of wetting properties of structured surfaces formed by lamellae with an exceptionally high aspect ratio of up to 57:1 and more. The lamellar surfaces were fabricated using a polymer with tunable mechanical properties and shape-memory behavior. It was found that wetting properties of such structured surfaces depend on temperature, and thermal treatment history-structured surfaces are wetted easier at elevated temperature or after cooling to room temperature when the polymer is soft because of the easier deformability of lamellae. The shape of lamellae deformed by droplets can be temporarily fixed at low temperature and remains fixed upon heating to room temperature. Heating above the transition temperature of the shape-memory polymer restores the original shape. The high aspect ratio allows tuning of geometry not only manually, as it is done in most works reported previously but can also be made by a liquid droplet and is controlled by temperature. This behavior opens new opportunities for the design of novel smart elements for microfluidic devices such as smart valves, whose state and behavior can be switched by thermal stimuli: valves that can or cannot be opened that are able to close or can be fixed in an open or closed states.

Abstract
Metastatic, castration-resistant prostate cancer (mCRPC) is an advanced prostate cancer with limited therapeutic options and poor patient outcomes. To investigate whether multitargeted kinase inhibitors (KIs) represent an opportunity for mCRPC drug development, we applied machine learning{textendash}based functional screening and identified two KIs, PP121 and SC-1, which demonstrated strong suppression of CRPC growth in vitro and in vivo. Furthermore, we show the marked ability of these KIs to improve on standard-of-care chemotherapy in both tumor response and survival, suggesting that combining multitargeted KIs with chemotherapy represents a promising avenue for mCRPC treatment. Overall, our findings demonstrate the application of a multidisciplinary strategy that blends bench science with machine-learning approaches for rapidly identifying KIs that result in desired phenotypic effects.Castration-resistant prostate cancer (CRPC) is an advanced subtype of prostate cancer with limited therapeutic options. Here, we applied a systems-based modeling approach called kinome regularization (KiR) to identify multitargeted kinase inhibitors (KIs) that abrogate CRPC growth. Two predicted KIs, PP121 and SC-1, suppressed CRPC growth in two-dimensional in vitro experiments and in vivo subcutaneous xenografts. An ex vivo bone mimetic environment and in vivo tibia xenografts revealed resistance to these KIs in bone. Combining PP121 or SC-1 with docetaxel, standard-of-care chemotherapy for late-stage CRPC, significantly reduced tibia tumor growth in vivo, decreased growth factor signaling, and vastly extended overall survival, compared to either docetaxel monotherapy. These results highlight the utility of computational modeling in forming physiologically relevant predictions and provide evidence for the role of multitargeted KIs as chemosensitizers for late-stage, metastatic CRPC.All study data are included in the article and/or supporting information.

Abstract
Radium 223 (223Ra) is an α-emitter approved for the treatment of bone metastatic prostate cancer (PCa), which exerts direct cytotoxicity towards PCa cells near the bone interface, whereas cells positioned in the core respond poorly, due to short α-particle penetrance. β1 integrin (β1I) interference has been shown to increase radiosensitivity and significantly enhance external beam radiation efficiency. We hypothesized that targeting β1I would improve 223Ra outcome. We tested the effect of combining 223Ra and anti-β1I antibody treatment in PC3 and C4-2B PCa cell models expressing high and low β1I levels, respectively. In vivo tumor growth was evaluated through bioluminescence. Cellular and molecular determinants of response were analyzed by ex vivo three-dimensional imaging of bone lesions, proteomic analysis and further confirmed by computational modeling and in vitro functional analysis in tissue-engineered bone mimetic systems. Interference with β1I combined with 223Ra reduced PC3 cell growth in bone and significantly improved overall mouse survival, while no change was achieved in C4-2B tumors. Anti-β1I treatment decreased PC3 tumor cell mitosis index and spatially expanded 223Ra lethal effects two-fold, in vivo and in silico. Regression was paralleled by decreased expression of radio-resistance mediators. Targeting β1I significantly improves 223Ra outcome and points towards combinatorial application in PCa tumors with high β1I expression.

Abstract
Near-field electrospinning (NFES) and melt electrowriting (MEW) are the process of extruding a fiber due to the force exerted by an electric field and collecting the fiber before bending instabilities occur. When paired with precise relative motion between the polymer source and the collector, a fiber can be directly written as dictated by preprogrammed geometry. As a result, this precise fiber control results in another dimension of scaffold tailorability for biomedical applications. In this review, biomedically relevant polymers that to date have manufactured fibers by NFES/MEW are explored and the present limitations in direct fiber writing of standardization in published setup details, fiber write throughput, and increased ease in the creation of complex scaffold geometries are discussed.

Abstract
Meniscus injury and meniscectomy are strongly related to osteoarthritis, thus there is a clinical need for meniscus replacement. The purpose of this study is to create a meniscus scaffold with micro-scale circumferential and radial fibres suitable for a one-stage cell-based treatment. Poly-caprolactone-based scaffolds with three different architectures were made using melt electrowriting (MEW) technology and their in vitro performance was compared with scaffolds made using fused-deposition modelling (FDM) and with the clinically used Collagen Meniscus Implants® (CMI®). The scaffolds were seeded with meniscus and mesenchymal stromal cells (MSCs) in fibrin gel and cultured for 28 d. A basal level of proteoglycan production was demonstrated in MEW scaffolds, the CMI®, and fibrin gel control, yet within the FDM scaffolds less proteoglycan production was observed. Compressive properties were assessed under uniaxial confined compression after 1 and 28 d of culture. The MEW scaffolds showed a higher Young’s modulus when compared to the CMI® scaffolds and a higher yield point compared to FDM scaffolds. This study demonstrates the feasibility of creating a wedge-shaped meniscus scaffold with MEW using medical-grade materials and seeding the scaffold with a clinically-feasible cell number and -type for potential translation as a one-stage treatment.

Abstract
Multi-material 3D printing technologies that resolve features at different lengths down to the microscale open new avenues for regenerative medicine, particularly in the engineering of tissue interfaces. Herein, extrusion printing of a bone-biomimetic ceramic ink and melt electrowriting (MEW) of spatially organized polymeric microfibres are integrated for the biofabrication of an osteochondral plug, with a mechanically reinforced bone-to-cartilage interface. A printable physiological temperature-setting bioceramic, based on α-tricalcium phosphate, nanohydroxyapatite and a custom-synthesized biodegradable and crosslinkable poloxamer, was developed as bone support. The mild setting reaction of the bone ink enabled us to print directly within melt electrowritten polycaprolactone meshes, preserving their micro-architecture. Ceramic-integrated MEW meshes protruded into the cartilage region of the composite plug, and were embedded with mechanically soft gelatin-based hydrogels, laden with articular cartilage chondroprogenitor cells. Such interlocking design enhanced the hydrogel-to-ceramic adhesion strength >6.5-fold, compared with non-interlocking fibre architectures, enabling structural stability during handling and surgical implantation in osteochondral defects ex vivo. Furthermore, the MEW meshes endowed the chondral compartment with compressive properties approaching those of native cartilage (20-fold reinforcement versus pristine hydrogel). The osteal and chondral compartment supported osteogenesis and cartilage matrix deposition in vitro, and the neo-synthesized cartilage matrix further contributed to the mechanical reinforcement at the ceramic-hydrogel interface. This multi-material, multi-scale 3D printing approach provides a promising strategy for engineering advanced composite constructs for the regeneration of musculoskeletal and connective tissue interfaces.

Abstract
Large bone defects due to trauma or disease present a significant clinical challenge with limited efficacy of current therapies. A key aim is to develop biomimetic scaffolds that reflect the native tissue structure with 3D printing being an important enabling technology. However, the incorporation of multiple length scales and anisotropic features, mimicking the native architecture, is difficult with current processes. In this study, we propose a simple and versatile hybrid printing process using a screw-assisted additive manufacturing technique combined with rotational electrospinning to fabricate dual-scale anisotropic scaffolds. 3D microscale porous polycaprolactone (PCL) structures with highly aligned nanoscale fibres were successfully produced layer-by-layer. The scaffolds were morphological, mechanical and biological characterised. Human adipose-derived stem cells (hADSCs) were seeded on the hybrid scaffold to evaluate the effects of structural and anisotropic topographic cues on cell attachment, proliferation and osteogenesis differentiation. Results show that the 3D printed microscale structures have uniform and well-defined geometries and the alignment of nanoscale electrospun fibres increases by increasing the electrospinning rotational velocity. Mechanical results show that there is no significant difference between 3D printed scaffolds with or without electrospun meshes. In vitro results show higher cell seeding efficiency and proliferation in dual-scale scaffolds with high density electrospun meshes. A more stretched and elongated cell morphology was observed in aligned nanofibre scaffolds showing higher anisotropic cytoskeletal organization than 3D printed PCL scaffolds without electrospun meshes. The dual-scale scaffolds present improved overall osteogenic markers expressions (COL-1, ALP and OCN). However, no statistical difference between normalised osteogenic marker expressions were observed between dual-scale scaffolds and 3D printed scaffolds. This might be attributed to the poor bioactivity of the substrate material, PCL, suggesting topographical cues might not be sufficient to stimulate cell fate towards to an osteogenic linage. The results suggest that the proposed fabrication strategy is a promising approach for the design of novel bone scaffolds to modulate cell fates by integrating the topographic cue reported in this paper with biochemical cues associated to the use of more bioactive materials.

Abstract
Abstract The immobilization of enzymes into polymer hydrogels is a versatile approach to improve their stability and utility in biotechnological and biomedical applications. However, these systems typically show limited enzyme activity, due to unfavorable pore dimensions and low enzyme accessibility. Here, 3D jet writing of water-based bioinks, which contain preloaded enzymes, is used to prepare hydrogel scaffolds with well-defined, tessellated micropores. After 3D jet writing, the scaffolds are chemically modified via photopolymerization to ensure mechanical stability. Enzyme loading and activity in the hydrogel scaffolds is fully retained over 3 d. Important structural parameters of the scaffolds such as pore size, pore geometry, and wall diameter are controlled with micrometer resolution to avoid mass-transport limitations. It is demonstrated that scaffold pore sizes between 120 µm and 1 mm can be created by 3D jet writing approaching the length scales of free diffusion in the hydrogels substrates and resulting in high levels of enzyme activity (21.2% activity relative to free enzyme). With further work, a broad range of applications for enzyme-laden hydrogel scaffolds including diagnostics and enzymatic cascade reactions is anticipated.

Abstract
Complex and hierarchically functionalized scaffolds composed of micro- and nanoscale structures are a key goal in tissue engineering. The combination of three-dimensional (3D) printing and electrospinning enables the fabrication of these multiscale structures. This study presents a polycaprolactone 3D-printed and electrospun scaffold with multiple mesh layers and fiber densities. The results show successful fabrication of a dual-scale scaffold with the 3D-printed scaffold acting as a gap collector with the printed microfibers as the electrodes and the pores a series of insulating gaps resulting in aligned nanofibers. The electrospun fibers are highly aligned perpendicular to the direction of the printed fiber and form aligned meshes within the pores of the scaffold. Mechanical testing showed no significant difference between the number of mesh layers whereas the hydrophobicity of the scaffold increased with increasing fiber density. Biological results indicate that increasing the number of mesh layers improves cell proliferation, migration, and adhesion. The aligned nanofibers within the microscale pores allowed enhanced cell bridging and cell alignment that was not observed in the 3D-printed only scaffold. These results demonstrate a facile method of incorporating low-density and aligned fibers within a 3D-printed scaffold that is a promising development in multiscale hierarchical scaffolds where alignment of cells can be desirable.

Abstract
In this study, a tissue-engineered trachea, consisting of multilevel structural electrospun polylactide (PLA) membranes enveloping 3D-printed thermoplastic polyurethane (TPU) skeletons, was developed to create a mechanically robust, antibacterial and bioresorbable graft for the tracheal reconstruction. The study design incorporated two distinct uses of stereocomplex PLA: patterned electrospun fibers to enhance tissue integration compared to the random layered fibers, meanwhile possessing good antibacterial property; and 3D-printed TPU scaffold with elasticity to provide external support and protection. Herein, ionic liquid (IL)-functioned graphene oxide (GO) was synthesized and presented enhanced mechanical and hydrophilicity properties. More interesting, antibacterial activity of the GO-g-IL modified PLA membranes were proved by Escherichia coli and Staphylococcus aureus, showing superior antibacterial effect compared to single GO or IL. The synergistic antibacterial effect could be related to that GO break cytomembrane of bacteria by its extremely sharp edges, while IL works by electrostatic interaction between its cationic structures and electronegative phosphate groups of bacteria membranes, leading to the loss of cell electrolyte and cell death. Hence, after L929 fibroblast cells were seeded on patterned fibrous membranes with phenotypic shape, further effective cell infiltration, cell proliferation and attachment were observed. In addition, the tissue-engineered trachea scaffolds were implanted into rabbit models. The in vivo result confirmed that the scaffolds with patterned membranes manifested favorable biocompatibility and promoted tissue regeneration.
In this study, a tissue-engineered trachea, consisting of multilevel structural electrospun polylactide (PLA) membranes enveloping 3D-printed thermoplastic polyurethane (TPU) skeletons, was developed to create a mechanically robust, antibacterial and bioresorbable graft for the tracheal reconstruction. The study design incorporated two distinct uses of stereocomplex PLA: patterned electrospun fibers to enhance tissue integration compared to the random layered fibers, meanwhile possessing good antibacterial property; and 3D-printed TPU scaffold with elasticity to provide external support and protection. Herein, ionic liquid (IL)-functioned graphene oxide (GO) was synthesized and presented enhanced mechanical and hydrophilicity properties. More interesting, antibacterial activity of the GO-g-IL modified PLA membranes were proved by Escherichia coli and Staphylococcus aureus, showing superior antibacterial effect compared to single GO or IL. The synergistic antibacterial effect could be related to that GO break cytomembrane of bacteria by its extremely sharp edges, while IL works by electrostatic interaction between its cationic structures and electronegative phosphate groups of bacteria membranes, leading to the loss of cell electrolyte and cell death. Hence, after L929 fibroblast cells were seeded on patterned fibrous membranes with phenotypic shape, further effective cell infiltration, cell proliferation and attachment were observed. In addition, the tissue-engineered trachea scaffolds were implanted into rabbit models. The in vivo result confirmed that the scaffolds with patterned membranes manifested favorable biocompatibility and promoted tissue regeneration.

Abstract
Abstract The recent development of electrostatic writing (electrowriting) with molten jets provides an opportunity to tackle some significant challenges within tissue engineering. The process uses an applied voltage to generate a stable fluid jet with a predictable path, that is continuously deposited onto a collector. The fiber diameter is variable during the process, and is applicable to polymers with a history of clinical use. Melt electrowriting therefore has potential for clinical translation if the biological efficacy of the implant can be improved over existing gold standards. It provides a unique opportunity for laboratories to perform low-cost, high resolution, additive manufacturing research that is well positioned for clinical translation, using existing regulatory frameworks.