Additive manufacturing of tissues and organs

Low-temperature extrusion-based 3D printing of icariin-laden scaffolds for osteogenesis enrichment

Despite the accessibility to porous architectures through various biofabrication approaches for tissue engineering, incorporating various active growth regulators within their matrices that act as biochemical cues is also an essential attribute for effective tissue growth. To address these facts, icariin (ICA)-encapsulated polymeric scaffolds are fabricated using a low-temperature extrusion-based three-dimensional (3D) printing technology for efficiently promoting osteogenesis. This approach not only resulted in the generation of porous architectures but also substantially maintained the bio-efficacy of the encapsulated ICA. Moreover, these composite scaffolds based on poly(ε-caprolactone) (PCL) and tricalcium phosphate (β-TCP) encapsulated with ICA (ITP scaffolds) are systematically characterized using various techniques before and after printing. Furthermore, various investigations relevant to biodegradability, biocompatibility, ICA release, and osteogenic ability of the ITP scaffolds are explored. The intact physiochemical properties of the materials, sustained release of ICA from the scaffolds, and high biosafety at various levels ranging from cellular to animal efficiently promoted the proliferation of mouse bone marrow mesenchymal stem cells (BMSCs) and their differentiation to osteoblasts. Together, the utilization of low-temperature extrusion approach provides a convenient and eco-friendly means of fabricating highly porous 3D architectures that supply the required growth regulators in their active form for tissue regeneration.

A Review of 3-Dimensional Skin Bioprinting Techniques: Applications, Approaches, and Trends

BACKGROUND

Tissue engineering is used to fabricate 3-dimensional (3D) artificial scaffolds to create a microenvironment that mimics human tissue. Bioprinting uses biomaterials, cells, and/or bioink to fabricate prospective scaffolds to mirror the structural, compositional, and functional aspects of the skin. Various bioprinting methods (inkjet-based bioprinting, pressure-assisted bioprinting, and laser-assisted bioprinting) have been used for regenerative wound repair and have been characterized based on biocompatibility, cellular microenvironment, cell proliferation, vitality, and morphology.

OBJECTIVE

This article reviews the basic principles of 3D printing, current 3D skin bioprinting applications and approaches, and future directions for regenerative medical skin constructs.

METHODS

A comprehensive literature review was conducted using PubMed with keywords "three-dimensional printing," "dermatologic surgery," "bioprinting," "reconstructive surgical procedures," "wound healing," "skin grafts," "skin scaffolds," "tissue reconstruction," and "tissue engineering."

RESULTS

A summary of the different applications and 3-dimensional skin bioprinting techniques is presented. In addition, synthetic, natural, and combination polymers are reviewed. Advantages, disadvantages, indications, and approaches are discussed in depth.

CONCLUSION

Skin grafting is a dynamic technique of dermal reconstruction that can be successful with comprehensive knowledge of skin bioprinting methods.

Current Status in the Utilization of Biobased Polymers for 3D Printing Process: A Systematic Review of the Materials, Processes, and Challenges

Three-dimensional (3D) printing is a revolutionary additive manufacturing technique that allows rapid prototyping of objects with intricate architectures. This Review covers the recent state-of-the-art of biopolymers (protein and carbohydrate-based materials) application in pharmaceutical, bioengineering, and food printing and main reinforcement approaches of biomacromolecular structure for the development of 3D constructs. Some perspectives and main important limitations with the biomaterials utilization for advanced 3D printing procedures are also provided. Because of the improved the ink's flow behavior and enhance the mechanical strength of resulting printed architectures, biopolymers are the most used materials for 3D printing applications. Biobased polymers by taking advantage of modifying the ink viscosity could improve the resolution of deposited layers, printing precision, and consequently, develop well-defined geometries. In this regard, the rheological properties of printable biopolymeric-based inks and factors affecting ink flow behavior related to structural properties of printed constructs are discussed. On the basis of successful applications of biopolymers in 3D printing, it is suggested that other biomacromolecules and nanoparticles combined with the matrix can be introduced into the ink dispersions to enhance the multifunctionality of 3D structures. Furthermore, tuning the biopolymer's structural properties offers the most common and essential approach to attain the printed architectures with precisely tailored geometry. We finish the Review by giving a viewpoint of the upcoming 3D printing process and recognize some of the existing bottlenecks facing the blossoming 3D pharmaceutical, bioengineering, and food printing applications.

New prospects in skin regeneration and repair using nanophased hydroxyapatite embedded in collagen nanofibers

This study reflects an exploitation of a composite matrix produced by electrospinning of collagen and electrospraying of nanophased hydroxyapatite (nanoHA), for skin regeneration applications. The main goal was to evaluate the effect of nanoHA, as source of localized calcium delivery, on human dermal fibroblasts, keratinocytes, and human mesenchymal stem cells (hMSCs) growth, proliferation, differentiation, and extracellular matrix production. This study revealed that calcium ions provided by nanoHA significantly enhanced cellular growth and proliferation rates and prevented adhesion of pathogenic bacteria strains typically found in human skin flora. Moreover, hMSCs were able to differentiate in both osteogenic and adipogenic lineages. Rat subcutaneous implantation of the membranes also revealed that no adverse reaction occurred. Therefore, the mechanically fit composite membrane presents a great potential to be used either as cell transplantation scaffold for skin wound regeneration or as wound dressing material in plastic surgery, burns treatment or skin diseases.

In vivo study of conductive 3D printed PCL/MWCNTs scaffolds with electrical stimulation for bone tissue engineering

Critical bone defects are considered one of the major clinical challenges in reconstructive bone surgery. The combination of 3D printed conductive scaffolds and exogenous electrical stimulation (ES) is a potential favorable approach for bone tissue repair. In this study, 3D conductive scaffolds made with biocompatible and biodegradable polycaprolactone (PCL) and multi-walled carbon nanotubes (MWCNTs) were produced using the extrusion-based additive manufacturing to treat large calvary bone defects in rats. Histology results show that the use of PCL/MWCNTs scaffolds and ES contributes to thicker and increased bone tissue formation within the bone defect. Angiogenesis and mineralization are also significantly promoted using high concentration of MWCNTs (3 wt%) and ES. Moreover, scaffolds favor the tartrate-resistant acid phosphatase (TRAP) positive cell formation, while the addition of MWCNTs seems to inhibit the osteoclastogenesis but present limited effects on the osteoclast functionalities (receptor activator of nuclear factor κβ ligand (RANKL) and osteoprotegerin (OPG) expressions). The use of ES promotes the osteoclastogenesis and RANKL expressions, showing a dominant effect in the bone remodeling process. These results indicate that the combination of 3D printed conductive PCL/MWCNTs scaffold and ES is a promising strategy to treat critical bone defects and provide a cue to establish an optimal protocol to use conductive scaffolds and ES for bone tissue engineering.

A Combined Strategy of Additive Manufacturing to Support Multidisciplinary Education in Arts, Biology, and Engineering

This research presents results for the design and creation of supporting teaching materials using additive manufacturing. The materials are inspired by selected artwork of four animal species, which belong to a collection from the museum of the University of Antioquia. The topic selected was fauna in Colombia, and the animals in question were chosen based on important roles they have in areas like health, the environment, and food. These animals will complement science education given to several age groups visiting the museum. In addition to the 3D-manufactured objects, a study was conducted using several age groups that are very relevant to the museum: children, teenagers, and first year undergraduate students. A video showing technical information cards about the manufacturing process was also developed. This project was multidisciplinary, involving collaboration between the engineering school, the museum, and a local high school. The results showed that young visitors want complete information on the animals and to have interaction with the animal models, which is not always possible. This project serves as a local strategy not only for taking arts and knowledge out of the museum but also for planning first year courses in the university and thus reducing problems like school dropout, low motivation, and poor performance in national exams.

A 3D Printed Composite Scaffold Loaded with Clodronate to Regenerate Osteoporotic Bone: In Vitro Characterization

Additive manufacturing (AM) is changing our current approach to the clinical treatment of bone diseases, providing new opportunities to fabricate customized, complex 3D structures with bioactive materials. Among several AM techniques, the BioCell Printing is an advanced, integrated system for material manufacture, sterilization, direct cell seeding and growth, which allows for the production of high-resolution micro-architectures. This work proposes the use of the BioCell Printing to fabricate polymer-based scaffolds reinforced with ceramics and loaded with bisphosphonates for the treatment of osteoporotic bone fractures. In particular, biodegradable poly(ε-caprolactone) was blended with hydroxyapatite particles and clodronate, a bisphosphonate with known efficacy against several bone diseases. The scaffolds' morphology was investigated by means of Scanning Electron Microscopy (SEM) and micro-Computed Tomography (micro-CT) while Energy Dispersive X-ray Spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS) revealed the scaffolds' elemental composition. A thermal characterization of the composites was accomplished by Thermogravimetric analyses (TGA). The mechanical performance of printed scaffolds was investigated under static compression and compared against that of native human bone. The designed 3D scaffolds promoted the attachment and proliferation of human MSCs. In addition, the presence of clodronate supported cell differentiation, as demonstrated by the normalized alkaline phosphatase activity. The obtained results show that the BioCell Printing can easily be employed to generate 3D constructs with pre-defined internal/external shapes capable of acting as a temporary physical template for regeneration of cancellous bone tissues.

Biomimetic Mineralization on 3D Printed PLA Scaffolds: On the Response of Human Primary Osteoblasts Spheroids and In Vivo Implantation

This study aimed to assess the response of 3D printed polylactic acid (PLA) scaffolds biomimetically coated with apatite on human primary osteoblast (HOb) spheroids and evaluate the biological response to its association with Bone Morphogenetic Protein 2 (rhBMP-2) in rat calvaria. PLA scaffolds were produced via 3D printing, soaked in simulated body fluid (SBF) solution to promote apatite deposition, and characterized by physical-chemical, morphological, and mechanical properties. PLA-CaP scaffolds with interconnected porous and mechanical properties suitable for bone repairing were produced with reproducibility. The in vitro biological response was assessed with human primary osteoblast spheroids. Increased cell adhesion and the rise of in vitro release of growth factors (Platelet-Derived Growth Factor (PDGF), Basic Fibroblast Growth Factor (bFGF), Vascular Endothelial Growth Factor (VEGF) was observed for PLA-CaP scaffolds, when pre-treated with fetal bovine serum (FBS). This pre-treatment with FBS was done in a way to enhance the adsorption of serum proteins, increasing the number of bioactive sites on the surface of scaffolds, and to partially mimic in vivo interactions. The in vivo analysis was conducted through the implantation of 3D printed PLA scaffolds either alone, coated with apatite (PLA-CaP) or PLA-CaP loaded with rhBMP-2 on critical-sized defects (8 mm) of rat calvaria. PLA-CaP+rhBMP2 presented higher values of newly formed bone (NFB) than other groups at all in vivo experimental periods (p < 0.05), attaining 44.85% of NFB after six months. These findings indicated two new potential candidates as alternatives to autogenous bone grafts for long-term treatment: (i) 3D-printed PLA-CaP scaffold associated with spheroids, since it can reduce the time of repair in situ by expression of biomolecules and growth factors; and (ii) 3D-printed PLA-CaP functionalized rhBMP2 scaffold, a biocompatible, bioactive biomaterial, with osteoconductivity and osteoinductivity.

The Potential of Polyethylene Terephthalate Glycol as Biomaterial for Bone Tissue Engineering

The search for materials with improved mechanical and biological properties is a major challenge in tissue engineering. This paper investigates, for the first time, the use of Polyethylene Terephthalate Glycol (PETG), a glycol-modified class of Polyethylene Terephthalate (PET), as a potential material for the fabrication of bone scaffolds. PETG scaffolds with a 0/90 lay-dawn pattern and different pore sizes (300, 350 and 450 µm) were produced using a filament-based extrusion additive manufacturing system and mechanically and biologically characterized. The performance of PETG scaffolds with 300 µm of pore size was compared with polycaprolactone (PCL). Results show that PETG scaffolds present significantly higher mechanical properties than PCL scaffolds, providing a biomechanical environment that promotes high cell attachment and proliferation.

Current Advances in 3D Bioprinting Technology and Its Applications for Tissue Engineering

Three-dimensional (3D) bioprinting technology has emerged as a powerful biofabrication platform for tissue engineering because of its ability to engineer living cells and biomaterial-based 3D objects. Over the last few decades, droplet-based, extrusion-based, and laser-assisted bioprinters have been developed to fulfill certain requirements in terms of resolution, cell viability, cell density, etc. Simultaneously, various bio-inks based on natural-synthetic biomaterials have been developed and applied for successful tissue regeneration. To engineer more realistic artificial tissues/organs, mixtures of bio-inks with various recipes have also been developed. Taken together, this review describes the fundamental characteristics of the existing bioprinters and bio-inks that have been currently developed, followed by their advantages and disadvantages. Finally, various tissue engineering applications using 3D bioprinting are briefly introduced.

Nano-CT scans in the optimisation of purposeful experimental procedures: A study on metallic fibre networks

Motive Metallic fibre networks and their mechanical behaviour are only insufficiently understood. In this particular field of research, the use of nano-CT scans offers advanced opportunities for the optimised planning of experimental work and component design. Several novel applications will benefit from this research; in particular, tissue engineering applications where a controlled and reproducible mechanical stimulus on cells is required can make use of these components. MethodFor the present study, the geometry of metallic fibre network samples is measured and digitalised through the use of nano-CT scan protocols and adequate radiological post-processing steps. Fibre medial axes are transferred into finite element assemblies and are exposed to magnetic actuation models. Network displacement of input geometries is quantified by averaging of node displacement fields. Key resultsComplex 3D deformation fields with regions of tension, shear, and compression are obtained. Results from a previous study about matrix material deformation can be confirmed in this study for greater sample geometries. The strain magnitude is not uniform across the samples; several influencing parameters and deformation patterns are identified. A simple analytical model can be presented which quantifies the material deformation. ConclusionsNano-CT scans provide an efficient radiological tool in the planning of relevant experimental procedures. The present study confirms the general usability of fibre networks for the contactless creation of 3D strain fields in tissue engineering. Mechanical effects in tissue growth stimulation known from experimental work are obtained numerically for the investigated assemblies. Further work about the mechanical effects in tissue cultures appears highly worthwhile.

3D Printing of Bone-Mimetic Scaffold Composed of Gelatin/β-Tri-Calcium Phosphate for Bone Tissue Engineering

3D printed scaffolds composed of gelatin and β-tri-calcium phosphate (β-TCP) as a biomimetic bone material are fabricated, thereby providing an environment appropriate for bone regeneration. The Ca²⁺ in β-TCP and COO^- in gelatin form a stable electrostatic interaction, and the composite scaffold shows suitable rheological properties for bioprinting. The gelatin/β-TCP scaffold is crosslinked with glutaraldehyde vapor and unreacted aldehyde groups which can cause toxicity to cells is removed by a glycine washing. The stable binding of the hydrogel is revealed as a result of FTIR and degradation rate. It is confirmed that the composite scaffold has compressive strength similar to that of cancellous bone and 60 wt% β-TCP groups containing 40 wt% gelatin have good cellular activity with preosteoblasts. Also, in the animal experiments, the gelatin/β-TCP scaffold confirms to induce bone formation without any inflammatory responses. This study suggests that these fabricated scaffolds can serve as a potential bone substitute for bone regeneration.

Biofabrication of Hepatic Constructs by 3D Bioprinting of a Cell-Laden Thermogel: An Effective Tool to Assess Drug-Induced Hepatotoxic Response

A thermoresponsive Pluronic/alginate semisynthetic hydrogel is used to bioprint 3D hepatic constructs, with the aim to investigate liver-specific metabolic activity of the 3D constructs compared to traditional 2D adherent cultures. The bioprinting method relies on a bioinert hydrogel and is characterized by high-shape fidelity, mild depositing conditions and easily controllable gelation mechanism. Furthermore, the dissolution of the sacrificial Pluronic templating agent significantly ameliorates the diffusive properties of the printed hydrogel. The present findings demonstrate high viability and liver-specific metabolic activity, as assessed by synthesis of urea, albumin, and expression levels of the detoxifying CYP1A2 enzyme of cells embedded in the 3D hydrogel system. A markedly increased sensitivity to a well-known hepatotoxic drug (acetaminophen) is observed for cells in 3D constructs compared to 2D cultures. Therefore, the 3D model developed herein may represent an in vitro alternative to animal models for investigating drug-induced hepatotoxicity.

Assessing the Radiological Density and Accuracy of Mandible Polymer Anatomical Structures Manufactured Using 3D Printing Technologies

Nowadays, 3D printing technologies are among the rapidly developing technologies applied to manufacture even the most geometrically complex models, however no techniques dominate in the area of craniofacial applications. This study included 12 different anatomical structures of the mandible, which were obtained during the process of reconstructing data from the Siemens Somatom Sensation Open 40 system. The manufacturing process used for the 12 structures involved the use of 8 3D printers and 12 different polymer materials. Verification of the accuracy and radiological density was performed with the CT160Xi Benchtop tomography system. The most accurate results were obtained in the case of models manufactured using the following materials: E-Model (Standard Deviation (SD) = 0.145 mm), FullCure 830 (SD = 0.188 mm), VeroClear (SD = 0.128 mm), Digital ABS-Ivory (SD = 0.117 mm), and E-Partial (SD = 0.129 mm). In the case of radiological density, ABS-M30 was similar to spongious bone, PC-10 was similar to the liver, and Polylactic acid (PLA) and Polyethylene terephthalate (PET) were similar to the spleen. Acrylic resin materials were able to imitate the pancreas, kidney, brain, and heart. The presented results constitute valuable guidelines that may improve currently used radiological phantoms and may provide support to surgeons in the process of performing more precise treatments within the mandible area.

Process hybridization schemes for multiscale engineered tissue biofabrication

Recapitulation of multiscale structure-function properties of cells, cell-secreted extracellular matrix, and 3D architecture of natural tissues is central to engineering biomimetic tissue substitutes. Toward achieving biomimicry, a variety of biofabrication processes have been developed, which can be broadly classified into five categories-fiber and fabric formation, additive manufacturing, surface modification, remote fields, and other notable processes-each with specific advantages and limitations. The majority of biofabrication literature has focused on using a single process at a time, which often limits the range of tissues that could be created with relevant features that span nano to macro scales. With multiscale biomimicry as the goal, development of hybrid biofabrication strategies that synergistically unite two or more processes to complement each other's strengths and limitations has been steadily increasing. This work discusses recent literature in this domain and attempts to equip the reader with the understanding of selecting appropriate processes that can harmonize toward creating engineered tissues with appropriate multiscale structure-function properties. Opportunities related to various hybridization schemes and a future outlook on scale-up biofabrication have also been discussed. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement.

Three-Dimensional Bioprinting: Role in Craniomaxillary Surgery Ethics and Future

Three-dimensional (3D) printing and bioprinting is gaining lot of momentum, especially in surgical specialties. These two technologies have wide array of applications in presurgical, surgical, and in vitro scenarios. Bioprinting can generate customized patient specific tissue engineered from specialized cells. This technology can be a gold standard in reconstructive and regenerative surgeries, if used in regulated and ethical environment. This communication focuses on basics of these technologies, their role in surgical specialties, ethical issues specific to these technologies, and its future.

Emulating Human Tissues and Organs: A Bioprinting Perspective Toward Personalized Medicine

The lack of in vitro tissue and organ models capable of mimicking human physiology severely hinders the development and clinical translation of therapies and drugs with higher in vivo efficacy. Bioprinting allow us to fill this gap and generate 3D tissue analogues with complex functional and structural organization through the precise spatial positioning of multiple materials and cells. In this review, we report the latest developments in terms of bioprinting technologies for the manufacturing of cellular constructs with particular emphasis on material extrusion, jetting, and vat photopolymerization. We then describe the different base polymers employed in the formulation of bioinks for bioprinting and examine the strategies used to tailor their properties according to both processability and tissue maturation requirements. By relating function to organization in human development, we examine the potential of pluripotent stem cells in the context of bioprinting toward a new generation of tissue models for personalized medicine. We also highlight the most relevant attempts to engineer artificial models for the study of human organogenesis, disease, and drug screening. Finally, we discuss the most pressing challenges, opportunities, and future prospects in the field of bioprinting for tissue engineering (TE) and regenerative medicine (RM).

Three dimensional bioprinting technology: Applications in pharmaceutical and biomedical area

3D bioprinting is a technology based on the principle of three-dimensional printing of designed biological materials, which has been widely used recently. The production of biological materials, such as tissues, organs, cells and blood vessels with this technology is alternative and promising approach for organ and tissue transplantation. Apart from tissue and organ printing, it has a wide range of usage, such as in vitro/in vivo modeling, production of drug delivery systems and, drug screening. However, there are various restrictions on the use of this technology. In this review, the process steps, classification, advantages, limitations, usage and application areas of 3D bioprinting technology, materials and auxiliary materials used in this technology are discussed.

3D Printed Hydrogel-Based Sensors for Quantifying UV Exposure

Exposure to excessive ultraviolet (UV) radiation can have detrimental effects on human health. Inexpensive easy-to-use sensors for monitoring UV radiation can allow broad-scale assessment of UV exposure, but their implementation requires technology that enables rapid and affordable manufacturing of these sensors on a large scale. Herein, we report a novel three-dimensional (3D) printing procedure and printable ink composition that produce robust, flexible, and wearable UV sensors. To fabricate the sensors, a color-changing hydrogel ink was first developed from which standalone constructs were 3D printed. The ink contains alginate, gelatin, photoactive titanium dioxide nanoparticles, and dyes (methyl orange, methylene blue, and malachite green) in which the nanoparticles are used to initiate photocatalytic degradation of dyes, leading to discoloration of the dye. The sensors resemble a color-changing tattoo that loses color upon exposure to UV. The viscosity and ink composition were optimized to achieve printability and tune the mechanical properties (e.g., modulus, hardness) of the sensors. The optimized procedure enabled the one-step fabrication of mechanically stable sensors that can effectively measure outdoor sun exposure by quantifying the decrease in color, visible to the naked eye. Apart from being used as wearable sensors, these sensors have the potential to be used along with UV-based workspace sterilizing devices to ensure that surfaces have been efficiently exposed to UV. The sensors are inexpensive, stable, extremely robust, biodegradable, and easy to use. The tunability, biocompatibility, and printability of the ink offer excellent potential for developing advanced 3D printing methods that, in addition to UV sensors, can be applied more broadly to fabricate other sensing technologies for a variety of other applications.

Additive Manufacturing of Nerve Guidance Conduits for Regeneration of Injured Peripheral Nerves

As a common and frequent clinical disease, peripheral nerve defect has caused a serious social burden, which is characterized by poor curative effect, long course of treatment and high cost. Nerve autografting is first-line treatment of peripheral nerve injuries (PNIs) but can result in loss of function of the donor site, neuroma formation, and prolonged operative time. Nerve guidance conduit (NGC) serves as the most promising alternative to autologous transplantation, but its production process is complicated and it is difficult to effectively combine growth factors and bioactive substances. In recent years, additive manufacturing of NGCs has effectively solved the above problems due to its simple and efficient manufacturing method, and it can be used as the carrier of bioactive substances. This review examines recent advances in additive manufacture of NGCs for PNIs as well as insight into how these approaches could be improved in future studies.

3D Printing of Solid Oral Dosage Forms: Numerous Challenges With Unique Opportunities

Since the FDA approval of Spritam, there has been a growing interest in the application of 3D printing in pharmaceutical science. 3D printing is a method of manufacturing involving the layer-by-layer deposition of materials to create a final product according to a digital model. There are various techniques used to achieve this method of printing including the SLS, SLA, FDM, SSE and PB-inkjet printing. In biomanufacturing, bone and tissue engineering involving 3D printing to create scaffolds, while in pharmaceutics, 3D printing was applied in drug development, and the fabrication of drug delivery devices. This paper aims to review the use of some 3D printing techniques in the fabrication of oral solid dosage forms. FDM, SLA SLS, and PB-Inkjet printing processes were found suitable for the fabrication of oral solid dosage forms, though a great deal of the available research was focused on fused deposition modelling due to its availability and flexibility. Process parameters as well as strategies to control the characteristics of printed dosage forms are analysed and discussed. The review also presents the advantages and possible limitations of 3D printing of medicines.

Inkjet Printing of Synthesized Melanin Nanoparticles as a Biocompatible Matrix for Pharmacologic Agents

Melanin is a natural biopigment that is produced by melanocytes and can be found in most living organisms. The unique physical and chemical properties of melanin render it potentially useful for numerous applications, particularly those in which a biocompatible functional material is required. Herein, we introduce one important technology in which melanin can be utilized: a drug delivery system in terms of a biocompatible matrix. However, extracting melanin from different biological sources is costly and time-consuming and introduces variabilities in terms of chemical structure, properties, and functions. Hence, a functionally reproducible system is hard to achieve using biologically extracted melanin. Here we report the synthesis of melanin nanoparticles of controlled uniform sizes and chemical characteristics. The optical, chemical, and structural characteristics of synthesized nanoparticles were characterized by optical confocal photoluminescence (PL) imaging, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Zeta potentiometry. The melanin nanoparticles have 100 nm size and a narrow size distribution. The advantage of a nanoparticle structure is its enhanced surface-to-volume ratio compared to bulk pigments, which is important for applications in which controlling the microscopic surface area is essential. Using the inkjet printing technique, we developed melanin thin films with minimum ink waste and loaded them with methylene blue (our representative drug) to test the drug-loading ability of the melanin nanoparticles. Inkjet printing allowed us to create smooth uniform films with precise deposition and minimum ink-waste. The spectroscopic analysis confirmed the attachment of the "drug" onto the melanin nanoparticles as a matrix. Hence, our data identify melanin as a material system to integrate into drug release applications.

Peculiarities of Cell Seeding on Electroformed Polycaprolactone Scaffolds Modified with Surface-Active Agents Triton X-100 and Polyvinylpyrrolidone

We compared the capability of human fibroblasts to populate porous polycaprolactone (PCL) scaffolds modified during fabrication with surface-active agents Triton Х-100 (type 1 scaffold) and polyvinylpyrrolidone (type 2 scaffold). The mean fiber diameter in both scaffolds was almost the same: 3.90±2.19 and 2.46±2.15 μ, respectively. Type 1 scaffold had higher surface density and hydrophilicity, when type 2 scaffold was 1.6 times thicker. The cells were seeded on the scaffolds by the dynamic seeding technique and then cultured in Petri dishes with nutrient medium in a humid atmosphere. During 3-day culturing, no cell release from the matrix was noted. DAPI staining proved the presence of cells in both scaffolds. However, in type 1 scaffold the cells populated the whole thickness, while in type 2 scaffold, the cells were present only in the superficial layer. These findings suggest that PCL scaffolds modified with Triton Х-100 or polyvinylpyrrolidone are not cytotoxic, but the structure of the scaffold treated with Triton Х-100 is more favorable for population with cells.

Instant Gelation System as Self-Healable and Printable 3D Cell Culture Bioink Based on Dynamic Covalent Chemistry

The rapid development of additive manufacturing techniques in the field of tissue regeneration offers unprecedented success for artificial tissue and organ fabrication. However, some limitations still remain for current bioinks, such as the compromised cell viability after printing, the low cross-linking efficiency leading to poor printing resolution and speed due to the relatively slow gelation rate, and the requirement of external stimuli for gelation. To address these problems, herein, a biocompatible and printable instant gelation hydrogel system has been developed based on a designed hyperbranched poly(ethylene glycol) (PEG)-based multihydrazide macro-cross-linker (HB-PEG-HDZ) and an aldehyde-functionalized hyaluronic acid (HA-CHO). HB-PEG-HDZ is prepared by the postfunctionalization of hyperbranched PEG-based multivinyl macromer via thiol-ene chemistry. Owing to the high functional group density of HB-PEG-HDZ, the hydrogel can be formed instantly upon mixing the solutions of two components. The reversible cross-linking mechanism between the hydrazide and aldehyde groups endows the hydrogel with shear-thinning and self-healing properties. The minimally toxic components and cross-linking chemistry allow the resulting hydrogel to be a biocompatible niche. Moreover, the fast sol-to-gel transition of the hydrogel, combining all of the advanced characteristics of this platform, protects the cells during the printing procedure, avoids their damage during extrusion, and improves the transplanted cell survival.

Direct-Write Deposition of Thermogels

The use of biocompatible hydrogels has widely extended the potential of additive manufacturing (AM) in the biomedical field leading to the production of 3D tissue and organ analogs for in vitro and in vivo studies.In this work, the direct-write deposition of thermosensitive hydrogels is described as a facile route to obtain 3D cell-laden constructs with controlled 3D structure and stable behavior under physiological conditions.

3D printing of silk microparticle reinforced polycaprolactone scaffolds for tissue engineering applications

Polycaprolactone (PCL) scaffolds have been widely investigated for tissue engineering applications, however, they exhibit poor cell adhesion and mechanical properties. Subsequently, PCL composites have been produced to improve the material properties. This study utilises a natural material, Bombyx mori silk microparticles (SMP) prepared by milling silk fibre, to produce a composite to enhance the scaffolds properties. Silk is biocompatible and biodegradable with excellent mechanical properties. However, there are no studies using SMPs as a reinforcing agent in a 3D printed thermoplastic polymer scaffold. PCL/SMP (10, 20, 30 wt%) composites were prepared by melt blending. Rheological analysis showed that SMP loading increased the shear thinning and storage modulus of the material. Scaffolds were fabricated using a screw-assisted extrusion-based additive manufacturing system. Scanning electron microscopy and X-ray microtomography was used to determine scaffold morphology. The scaffolds had high interconnectivity with regular printed fibres and pore morphologies within the designed parameters. Compressive mechanical testing showed that the addition of SMP significantly improved the compressive Young's modulus of the scaffolds. The scaffolds were more hydrophobic with the inclusion of SMP which was linked to a decrease in total protein adsorption. Cell behaviour was assessed using human adipose derived mesenchymal stem cells. A cytotoxic effect was observed at higher particle loading (30 wt%) after 7 days of culture. By day 21, 10 wt% loading showed significantly higher cell metabolic activity and proliferation, high cell viability, and cell migration throughout the scaffold. Calcium mineral deposition was observed on the scaffolds during cell culture. Large calcium mineral deposits were observed at 30 wt% and smaller calcium deposits were observed at 10 wt%. This study demonstrates that SMPs incorporated into a PCL scaffold provided effective mechanical reinforcement, improved the rate of degradation, and increased cell proliferation, demonstrating potential suitability for bone tissue engineering applications.

Acrylated epoxidized soybean oil/hydroxyapatite-based nanocomposite scaffolds prepared by additive manufacturing for bone tissue engineering

The mechanical properties and biocompatibility of nanocomposites composed of Acrylated Epoxidized Soybean Oil (AESO), nano-Hydroxyapatite (nHA) rods and either 2-Hydroxyethyl Acrylate (HEA) or Polyethylene Glycol Diacrylate (PEGDA) and 3D printed using extrusion-based additive manufacturing methods were investigated. The effects of addition of HEA or PEGDA on the rheological, mechanical properties and cell-biomaterial interactions were studied. AESO, PEGDA (or HEA), and nHA were composited using an ultrasonic homogenizer and scaffolds were 3D printed using a metal syringe on an extrusion-based 3D printer while simultaneously UV cured during layer-by-layer deposition. Nanocomposite inks were characterized for their viscosity before curing, and dispersion of the nHA particles and tensile mechanical properties after curing. Proliferation and differentiation of human bone marrow-derived mesenchymal stem cells (BM-MSCs) were studied by seeding cells onto the scaffolds and culturing in osteogenic differentiation medium for 7, 14 and 21 days. Overall, each of the scaffolds types demonstrated controlled morphology resulting from the printability of nanocomposite inks, well-dispersed nHA particles within the polymer matrices, and were shown to support cell proliferation and osteogenic differentiation after 14 and 21 days of culture. However, the nature of the functional groups present in each ink detectably affected the mechanical properties and cytocompatibility of the scaffolds. For example, while the incorporation of HEA reduced nHA dispersion and tensile strength of the final nanocomposite, it successfully enhanced shear yield strength, and printability, as well as cell adhesion, proliferation and osteogenic differentiation, establishing a positive effect perhaps due to additional hydrogen bonding.

Process of Creating an Integrated Design and Manufacturing Environment as Part of the Structure of Industry 4.0

This paper presents the process for creating an integrated design and manufacturing environment supporting 3D printing as part of the structure of Industry 4.0. This process is based on a developed framework for the design of modern automated and computerized infrastructure. The task of the described system is to combine all the steps included in the operating range of incremental systems based on an IT platform by integrating data from individual areas, such as IT systems supporting remote 3D printing. The proposed framework for incremental processes is a universal solution that can be defined in detail by a single organizational unit running 3D printing, as well as by a cluster of entities related to 3D printing. In the initial phase, the framework design includes a set of guidelines for IT (Information Technology) systems that facilitate the construction of individual elements and the creation of communication interfaces. In subsequent stages, the framework may already implement elements of the access and communication program interface, as well as guidelines for the industrial components to be included. The proposed framework for additive technologies is based on modern IT tools that enable the creation of geographically and functionally possible prototyping systems that can be integrated into the structure of Industry 4.0. To create optimal processes and economic systems, the principles of the construction and integration of individual services and equipment were developed. This new comprehensive approach is proposed in the present paper as a coherent framework. Moreover, the proposed solution has great potential for use in the design and production processes of various industries, such as chemicals, materials and construction.

Natural 3D-Printed Bioinks for Skin Regeneration and Wound Healing: A Systematic Review

Three-dimensional bioprinting has rapidly paralleled many biomedical applications and assisted in advancing the printing of complex human organs for a better therapeutic practice. The objective of this systematic review is to highlight evidence from the existing studies and evaluate the effectiveness of using natural-based bioinks in skin regeneration and wound healing. A comprehensive search of all relevant original articles was performed based on prespecified eligibility criteria. The search was carried out using PubMed, Web of Science, Scopus, Medline Ovid, and ScienceDirect. Eighteen articles fulfilled the inclusion and exclusion criteria. The animal studies included a total of 151 animals with wound defects. A variety of natural bioinks and skin living cells were implanted in vitro to give insight into the technique through different assessments and findings. Collagen and gelatin hydrogels were most commonly used as bioinks. The follow-up period ranged between one day and six weeks. The majority of animal studies reported that full wound closure was achieved after 2–4 weeks. The results of both in vitro cell culture and in vivo animal studies showed the positive impact of natural bioinks in promoting wound healing. Future research should be focused more on direct the bioprinting of skin wound treatments on animal models to open doors for human clinical trials.

Constrained Window Design in Projection Stereolithography for Continuous Three-Dimensional Printing

Although continuous projection Stereolithography (SL) printing is one of the next-generation ultra-fast additive manufacturing (AM) processes, its current constrained window design of the resin vat is suffering from many challenges, such as the complex control mechanism and limited hardware lifetime. In this article, we investigate a novel constrained window design, namely Island Window (IW), for the continuous three-dimensional (3D) printing by using the projection SL process. The proposed IW window has a highly oxygen-permeable polydimethylsiloxane membrane onto the laser-machined acrylic vat frame, which allows the formation of an effective liquid interface (>200 μm oxygen inhibition layer) to enable the continuous projection SL process. Experimental results verified the feasibility of the window design for extending the maximum printing time (increased by up to 73%) due to the enhanced oxygen concentration. It was also found that the maximum printing speed for producing parts with a smooth surface (Rz <30 μm) can be as high as 90 mm/h, which is comparable to the speeds in recently reported continuous SL processes. In addition, a variety of parts were successfully fabricated through continuous 3D printing by using the proposed IW design, implying tremendous promise for future low-cost, high-resolution, easy-controlled, and ultra-fast AM processes.

Direct-write 3D printing and characterization of a GelMA-based biomaterial for intracorporeal tissue

We develop and characterize a biomaterial formulation and robotic methods tailored for intracorporeal tissue engineering (TE) via direct-write (DW) 3D printing. Intracorporeal TE is defined as the biofabrication of 3D TE scaffolds inside of a living patient, in a minimally invasive manner. A biomaterial for intracorporeal TE requires to be 3D printable and crosslinkable via mechanisms that are safe to native tissues and feasible at physiological temperature (37 °C). The cell-laden biomaterial (bioink) preparation and bioprinting methods must support cell viability. Additionally, the biomaterial and bioprinting method must enable the spatially accurate intracorporeal 3D delivery of the biomaterial, and the biomaterial must adhere to or integrate into the native tissue. Current biomaterial formulations do not meet all the presumed intracorporeal DW TE requirements. We demonstrate that a specific formulation of gelatin methacryloyl (GelMA)/Laponite^®/methylcellulose (GLM) biomaterial system can be 3D printed at physiological temperature and crosslinked using visible light to construct 3D TE scaffolds with clinically relevant dimensions and consistent structures. Cell viability of 71%-77% and consistent mechanical properties over 21 d are reported. Rheological modifiers, Laponite^® and methylcellulose, extend the degradation time of the scaffolds. The DW modality enables the piercing of the soft tissue and over-extrusion of the biomaterial into the tissue, creating a novel interlocking mechanism with soft, hydrated native tissue mimics and animal muscle with a 3.5-4 fold increase in the biomaterial/tissue adhesion strength compared to printing on top of the tissue. The developed GLM biomaterial and robotic interlocking mechanism pave the way towards intracorporeal TE.

FDM-Based 3D Printing of Polymer and Associated Composite: A Review on Mechanical Properties, Defects and Treatments

Fused deposition modelling (FDM) is one of the fastest-growing additive manufacturing methods used in printing fibre-reinforced composites (FRC). The performances of the resulting printed parts are limited compared to those by other manufacturing methods due to their inherent defects. Hence, the effort to develop treatment methods to overcome these drawbacks has accelerated during the past few years. The main focus of this study is to review the impact of those defects on the mechanical performance of FRC and therefore to discuss the available treatment methods to eliminate or minimize them in order to enhance the functional properties of the printed parts. As FRC is a combination of polymer matrix material and continuous or short reinforcing fibres, this review will thoroughly discuss both thermoplastic polymers and FRCs printed via FDM technology, including the effect of printing parameters such as layer thickness, infill pattern, raster angle and fibre orientation. The most common defects on printed parts, in particular, the void formation, surface roughness and poor bonding between fibre and matrix, are explored. An inclusive discussion on the effectiveness of chemical, laser, heat and ultrasound treatments to minimize these drawbacks is provided by this review.

Biological perspectives and current biofabrication strategies in osteochondral tissue engineering

Articular cartilage and the underlying subchondral bone are crucial in human movement and when damaged through disease or trauma impacts severely on quality of life. Cartilage has a limited regenerative capacity due to its avascular composition and current therapeutic interventions have limited efficacy. With a rapidly ageing population globally, the numbers of patients requiring therapy for osteochondral disorders is rising, leading to increasing pressures on healthcare systems. Research into novel therapies using tissue engineering has become a priority. However, rational design of biomimetic and clinically effective tissue constructs requires basic understanding of osteochondral biological composition, structure, and mechanical properties. Furthermore, consideration of material design, scaffold architecture, and biofabrication strategies, is needed to assist in the development of tissue engineering therapies enabling successful translation into the clinical arena. This review provides a starting point for any researcher investigating tissue engineering for osteochondral applications. An overview of biological properties of osteochondral tissue, current clinical practices, the role of tissue engineering and biofabrication, and key challenges associated with new treatments is provided. Developing precisely engineered tissue constructs with mechanical and phenotypic stability is the goal. Future work should focus on multi-stimulatory environments, long-term studies to determine phenotypic alterations and tissue formation, and the development of novel bioreactor systems that can more accurately resemble the in vivo environment.

Advances in Tissue Engineering and Innovative Fabrication Techniques for 3-D-Structures: Translational Applications in Neurodegenerative Diseases

In the field of regenerative medicine applied to neurodegenerative diseases, one of the most important challenges is the obtainment of innovative scaffolds aimed at improving the development of new frontiers in stem-cell therapy. In recent years, additive manufacturing techniques have gained more and more relevance proving the great potential of the fabrication of precision 3-D scaffolds. In this review, recent advances in additive manufacturing techniques are presented and discussed, with an overview on stimulus-triggered approaches, such as 3-D Printing and laser-based techniques, and deposition-based approaches. Innovative 3-D bioprinting techniques, which allow the production of cell/molecule-laden scaffolds, are becoming a promising frontier in disease modelling and therapy. In this context, the specific biomaterial, stiffness, precise geometrical patterns, and structural properties are to be considered of great relevance for their subsequent translational applications. Moreover, this work reports numerous recent advances in neural diseases modelling and specifically focuses on pre-clinical and clinical translation for scaffolding technology in multiple neurodegenerative diseases.

A Preliminary Evaluation of the Pro-Chondrogenic Potential of 3D-Bioprinted Poly(ester Urea) Scaffolds

Degeneration of articular cartilage (AC) is a common healthcare issue that can result in significantly impaired function and mobility for affected patients. The avascular nature of the tissue strongly burdens its regenerative capacity contributing to the development of more serious conditions such as osteoarthritis. Recent advances in bioprinting have prompted the development of alternative tissue engineering therapies for the generation of AC. Particular interest has been dedicated to scaffold-based strategies where 3D substrates are used to guide cellular function and tissue ingrowth. Despite its extensive use in bioprinting, the application of polycaprolactone (PCL) in AC is, however, restricted by properties that inhibit pro-chondrogenic cell phenotypes. This study proposes the use of a new bioprintable poly(ester urea) (PEU) material as an alternative to PCL for the generation of an in vitro model of early chondrogenesis. The polymer was successfully printed into 3D constructs displaying adequate substrate stiffness and increased hydrophilicity compared to PCL. Human chondrocytes cultured on the scaffolds exhibited higher cell viability and improved chondrogenic phenotype with upregulation of genes associated with type II collagen and aggrecan synthesis. Bioprinted PEU scaffolds could, therefore, provide a potential platform for the fabrication of bespoke, pro-chondrogenic tissue engineering constructs.

The Overview of Porous, Bioactive Scaffolds as Instructive Biomaterials for Tissue Regeneration and Their Clinical Translation

Porous scaffolds have been employed for decades in the biomedical field where researchers have been seeking to produce an environment which could approach one of the extracellular matrixes supporting cells in natural tissues. Such three-dimensional systems offer many degrees of freedom to modulate cell activity, ranging from the chemistry of the structure and the architectural properties such as the porosity, the pore, and interconnection size. All these features can be exploited synergistically to tailor the cell-material interactions, and further, the tissue growth within the voids of the scaffold. Herein, an overview of the materials employed to generate porous scaffolds as well as the various techniques that are used to process them is supplied. Furthermore, scaffold parameters which modulate cell behavior are identified under distinct aspects: the architecture of inert scaffolds (i.e., pore and interconnection size, porosity, mechanical properties, etc.) alone on cell functions followed by comparison with bioactive scaffolds to grasp the most relevant features driving tissue regeneration. Finally, in vivo outcomes are highlighted comparing the accordance between in vitro and in vivo results in order to tackle the future translational challenges in tissue repair and regeneration.

The emerging role of microfluidics in multi-material 3D bioprinting

To assist the transition of 3D bioprinting technology from simple lab-based tissue fabrication, to fully functional and implantable organs, the technology must not only provide shape control, but also functional control. This can be accomplished by replicating the cellular composition of the native tissue at the microscale, such that cell types interact to provide the desired function. There is therefore a need for precise, controllable, multi-material printing that could allow for high, possibly even single cell, resolution. This paper aims to draw attention to technological advancements made in 3D bioprinting that target the lack of multi-material, and/or multi cell-type, printing capabilities of most current devices. Unlike other reviews in the field, which largely focus on variations in single-material 3D bioprinting involving the standard methods of extrusion-based, droplet-based, laser-based, or stereolithographic methods; this review concentrates on sophisticated multi-material 3D bioprinting using multi-cartridge printheads, co-axial nozzles and microfluidic-enhanced printing nozzles.

Tapered Polymer Whiskers to Enable Three-Dimensional Tactile Feature Extraction

Many mammals use their vibrissae (whiskers) to tactually explore their surrounding environment. Vibrissae are thin tapered structures that transmit mechanical signals to a wealth of mechanical receptors (sensors) located in a follicle at each vibrissal base. A recent study has shown that-provided that the whisker is tapered-three mechanical signals at the base are sufficient to determine the three-dimensional location at which a whisker made contact with an object. However, creating biomimetic tapered whiskers has proved challenging from both materials and manufacturing standpoints. This study develops and characterizes an artificial whisker for use as part of a sensory input device that is a biomimic of the biological rat whisker neurosensory system. A novel manufacturing process termed surface conforming fiber drawing (SCFD) is developed to produce artificial whiskers that meet the requirements to be a successful mechanical and geometric mimic of the biological rat vibrissae. Testing the sensory capabilities of the artificial whisker shows improved performance over previous nontapered filaments. SCFD-manufactured tapered whiskers demonstrate the ability to predict contact point locations with a median distance error of 0.47 cm.

Microphysiological Systems: Design, Fabrication, and Applications

Microphysiological systems, including organoids, 3-D printed tissue constructs and organ-on-a-chips (organ chips), are physiologically relevant in vitro models and have experienced explosive growth in the past decades. Different from conventional, tissue culture plastic-based in vitro models or animal models, microphysiological systems recapitulate key microenvironmental characteristics of human organs and mimic their primary functions. The advent of microphysiological systems is attributed to evolving biomaterials, micro-/nanotechnologies and stem cell biology, which enable the precise control over the matrix properties and the interactions between cells, tissues and organs in physiological conditions. As such, microphysiological systems have been developed to model a broad spectrum of organs from microvasculature, eye, to lung and many others to understand human organ development and disease pathology and facilitate drug discovery. Multiorgans-on-a-chip systems have also been developed by integrating multiple associated organ chips in a single platform, which allows to study and employ the organ function in a systematic approach. Here we first discuss the design principles of microphysiological systems with a focus on the anatomy and physiology of organs, and then review the commonly used fabrication techniques and biomaterials for microphysiological systems. Subsequently, we discuss the recent development of microphysiological systems, and provide our perspectives on advancing microphysiological systems for preclinical investigation and drug discovery of human disease.

Investigations on the Processing of Ceramic Filled Inks for 3D InkJet Printing

3D inkjet printing is moving from a technology of rapid prototyping to rapid manufacturing. The introduction of ultraviolet curable composites filled with functional ceramics could expand the possibilities of this technology. In this work, a simple and scalable process was investigated as a template for the production of inkjet printable functional ceramics. Pyrogenic alumina particles with an average size of 13 nm, 35 nm and 100 nm were used as fillers in an acrylate mixture. The physical coating of the ceramics with 2-[2-(2-methoxyethoxy)ethoxy] acetic acid results in a low-viscosity dispersion with a ceramic content of up to 2 vol%, Newtonian behavior and surface tension within the limits allowed for inkjet printing. The material has sufficient stability for printing tensile specimens. Tensile tests have shown that modulus of elasticity, tensile strength and toughness can be kept constant despite the light scatter caused by the particles. The final production steps could be reduced to grinding and drying of the powders, their resuspension in the organic matrix and inkjet printing. The process can be used in an industrial-scale production of materials for abrasion-resistant components with adapted tribology.

Three-Dimensional Printing and Electrospinning Dual-Scale Polycaprolactone Scaffolds with Low-Density and Oriented Fibers to Promote Cell Alignment

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.