Printing Of Scaffolds Research Articles

Development of a novel direct powder screw extruder for 3D scaffold printing of PCL-based composites

Development of a novel direct powder screw extruder for 3D scaffold printing of PCL-based composites

Non-planar bioprinting with molding assistance for irregular wound shape

Most human organs and tissues have different shapes, which vary per individual. When printing biomedical scaffolds using material extrusion-based additive manufacturing bioprinters, sacrificial layers are generally used to support the suspended parts of the scaffold. However, the in-process generation of sacrificial layers is time-consuming and the scaffold can be damaged when removing the sacrificial layers. In this study, a novel non-planar grid slicing (NPGS) process was proposed for printing irregularly shaped tissues with low aspect ratios (for example, skin wounds), where the required 3D shape is formed following the deposition of non-planar paths, layer-by-layer. By stacking layers of bioink onto a non-planar support base, the NPGS process considerably reduced the total length of the deposition paths and number of fragmented paths. Therefore, it can reduce the use of costly bioink and improve the success rate of the scaffold printing. The proposed NPGS process and traditional planar slicing (TPS) process were used to fabricate scaffolds that conform to the shape and depth of two clinical wounds. Compared to TPS, NPGS reduced the total length of the deposition paths and number of fragmented paths (paths shorter than 5 mm) by 49.2% and 59.6%, respectively. In animal testing, a large irregular wound was created on the rat's dorsal skin and treated with tri-cell-laden hydrogel printed by the NPGS process, demonstrating full repair after 28 days. The NPGS process shows great potential for customized biofabrication in tissue engineering.

3D printing of porous Ti6Al4V bone tissue engineering scaffold and surface anodization preparation of nanotubes to enhance its biological property

Abstract Porous structures and surface morphology of bone tissue scaffolds play an important role in improving the biocompatibility and antibacterial properties for bone repair. In this study, we investigated the effect of different anodic oxidation parameters on the nanotubes morphology in 3D printed porous titanium scaffolds. Micron-scale pores were fabricated by 3D printing first, and then the nano-scale tubes were obtained via anodizing treatments. The results demonstrated that the morphology of the nanotubes depended on the anodic oxidation time and voltage, respectively. Longer anodic oxidation led to the formation of circle-like nanotubes, and the diameter of the nanotubes increased with the voltage. The scaffolds anodized at 30 V showed the best cell proliferation potential. The presence of nanotubes on the surface of scaffold altered the adhesion of bacteria so that it improved the antibacterial properties of scaffold. The formation of nanotubes improved the drug-loading ability of the scaffold, which are used for loading of minocycline antibacterial drugs. The proposed 3D printed porous Ti6Al4V scaffold with nanotubes surface modification showed obvious antibacterial effect, which is expected to have a promising application in antibacterial bone prosthesis.

CBCT-Based Design of Patient-Specific 3D Bone Grafts for Periodontal Regeneration.

The purpose of this article is to define and implement a methodology for the 3D design of customized patient-specific scaffolds (bone grafts) for the regeneration of periodontal tissues. The prerequisite of the proposed workflow is the three-dimensional (3D) structure of the periodontal defect, i.e., the 3D model of the hard tissues (alveolar bone and teeth) around the periodontal damage, which is proposed to be generated via a segmentation and 3D editing methodology using cone beam computed tomography (CBCT) data. Two types of methodologies for 3D periodontal scaffold (graft) design are described: (i) The methodology of designing periodontal defect customized block grafts and (ii) the methodology of designing extraction socket preservation customized grafts. The application of the proposed methodology for the generation of a 3D model of the hard tissues around periodontal defects of a patient using a CBCT scan and the 3D design of the two aforementioned types of scaffolds for personalized periodontal regenerative treatment shows promising results. The outputs of this work will be used as the basis for the 3D printing of bioabsorbable scaffolds of personalized treatment against periodontitis, which will simultaneously be used as sustained-release drug carriers.

Direct Integration of 3D Printing and Cryogel Scaffolds for Bone Tissue Engineering.

Cryogels, known for their biocompatibility and porous structure, lack mechanical strength, while 3D-printed scaffolds have excellent mechanical properties but limited porosity resolution. By combining a 3D-printed plastic gyroid lattice scaffold with a chitosan-gelatin cryogel scaffold, a scaffold can be created that balances the advantages of both fabrication methods. This study compared the pore diameter, swelling potential, mechanical characteristics, and cellular infiltration capability of combined scaffolds and control cryogels. The incorporation of the 3D-printed lattice demonstrated patient-specific geometry capabilities and significantly improved mechanical strength compared to the control cryogel. The combined scaffolds exhibited similar porosity and relative swelling ratio to the control cryogels. However, they had reduced elasticity, reduced absolute swelling capacity, and are potentially cytotoxic, which may affect their performance. This paper presents a novel approach to combine two scaffold types to retain the advantages of each scaffold type while mitigating their shortcomings.

Calcium silicate/polyvinyl/chitosan/alginate-based bioceramic slurry for 3D printing of scaffolds: Interfacial interactions – Mechanical properties relationship

At present, there are few studies investigating the influence of mechanical properties of binders on bioceramic slurry at the micro- and macroscopic levels. In this work, we used molecular dynamics (MD) simulations and experiments to investigate the influence of mechanical properties of polyvinyl alcohol (PVA), chitosan (CS), and sodium alginate (SA) polymers on calcium silicate (CSi, CaSiO3)/binder bioceramic slurry and to choose the most suitable binders to prepare CSi/binder slurry. It was found that PVA demonstrated excellent stiffness, ductility, toughness, solubility, and low shear thinning. The formation of large number of hydrogen bonds (HBs) at the CSi/PVA interface results in strong interfacial bonding and higher compressive strength of CSi/PVA slurry while other binders suffer low solubility, higher shear thinning, poor stiffness, and ductility problems. From the calculated mechanical parameters, interfacial binding energy, and compressive tests, it was found that the slurry prepared by CSi and 10 PVA (mixing ratio: 1:0.9) demonstrate the best mechanical properties, a compressive strength of 7.3 MPa, thus, meeting the requirements of compressive properties of cancellous bone defects. The simulation results were supported by experiments. This study provides a theoretical and experimental guide for binder selection in bioceramic slurry and the design of future binder composites.

Effects of Six Processing Parameters on the Size of PCL Fibers Prepared by Melt Electrospinning Writing.

Melt electrospinning writing is a new and promising method for fabricating micro/nanofibers, which has shown great prospects in the biomedical fields such as 3D printing of porous scaffolds. The diameter of the melt electrospinning writing fiber can determine the resolution of the microstructure; thus, the controllability of the fiber diameter is of great significance to the whole fabrication process. In this paper, an orthogonal design experiment (six factors, three levels) was used to explore the impacts of six melt electrospinning parameters (melt temperature, collector speed, tip-to-collector distance, melt flow rate, voltage, and needle gauge) on the fiber diameter. In this experiment, the diameter of fibers obtained with the designed experimental parameters and conditions varied from 10.30 μm to 20.02 μm. The range analysis of orthogonal test results showed that the melt flow rate was the most important factor influencing the diameter of melt electrospinning writing fiber, while the voltage was the least influential factor. The variance analysis of orthogonal test results showed that melt temperature, collector velocity, tip-to-collector distance and melt flow rate had a significant influence on the diameter of melt electrospinning writing fiber. On the basis of the first-order regression equation, the fiber diameter of poly-ε-caprolactone can be accurately controlled, thus improving the engineering applications of poly-ε-caprolactone.

Embedded 3D Printing of Cryogel-Based Scaffolds.

Cryogel-based scaffolds have attracted great attention in tissue engineering due to their interconnected macroporous structures. However, three-dimensional (3D) printing of cryogels with a high degree of precision and complexity is a challenge, since the synthesis of cryogels occurs under cryogenic conditions. In this study, we demonstrated the fabrication of cryogel-based scaffolds for the first time by using an embedded printing technique. A photo-cross-linkable gelatin methacryloyl (GelMA)-based ink composition, including alginate and photoinitiator, was printed into a nanoclay-based support bath. The layer-by-layer extruded ink was held in complex and overhanging structures with the help of pre-cross-linking of alginate with Ca2+ present in the support bath. The printed 3D structures in the support bath were frozen, and then GelMA was cross-linked at a subzero temperature under UV light. The printed and cross-linked structures were successfully recovered from the support bath with an integrated shape complexity. SEM images showed the formation of a 3D printed scaffold where porous GelMA cryogel was integrated between the cross-linked alginate hydrogels. In addition, they showed excellent shape recovery under uniaxial compression cycles of up to 80% strain. In vitro studies showed that the human fibroblast cells attached to the 3D printed scaffold and displayed spread morphology with a high proliferation rate. The results revealed that the embedded 3D printing technique enables the fabrication of cytocompatible cryogel based scaffolds with desired morphology and mechanical behavior using photo-cross-linkable bioink composition. The properties of the cryogels can be modified by varying the GelMA concentration, whereby various shapes of scaffolds can be fabricated to meet the specific requirements of tissue engineering applications.

A 3D-printed micro-perfused culture device with embedded 3D fibrous scaffold for enhanced biomimicry

Additive manufacturing has rapidly revolutionized the medical sectors since it is a versatile, cost-effective, assembly free technique with the ability to replicate geometrically complicated features. Some of the widely reported applications include the printing of scaffolds, implants, or microfluidic devices. In this study, a 3D-printed micro-perfused culture (MPC) device embedded with a nanofibrous scaffold was designed to create an integrated micro-perfused 3D cell culture environment for living cells. The addition of 3D fibrous scaffold onto the microfluidic chip was to provide a more physiologically relevant microenvironment for cell culture studies. Stereolithography was adopted in this study as this technique obviates excessive preassembly and bonding steps, which would otherwise be needed in conventional microfluidic fabrication. Huh7.5 hepatocellular carcinoma cells were used as model cells for this platform since liver cells experience similar perfused microenvironment. Preliminary cell studies revealed that gene expressions of albumin (ALB) and cytochrome P450 isoform (CYP3A7) were found to be significantly upregulated on the 3D-printed MPC device as compared to the static counterpart. Taken together, the 3D-printed MPC device is shown to be a physiologically relevant platform for the maintenance of liver cells. The device and printing technique developed in this study is highly versatile and tailorable to mimic local in vivo microenvironment needs of various tissues, which could be studied in future.  

Developing a teriparatide-loaded calcium silicate biomaterial ink for 3D printing of scaffolds for bone tissue engineering

Critical-size bone defects of complex geometries are challenging to repair, making current approaches less satisfactory. Although calcium silicate (CaS) scaffolds prepared using 3D printing can be promising, these scaffolds are commonly treated with harsh conditions to reinforce their strength, significantly affecting the activity of biomolecules in the scaffolds. In this study, we developed a novel CaS biomaterial ink that did not require harsh post-treatments. It is shown that the printability was significantly improved using polyethylene glycol (PEG) and pluronic F-127 (PF), and the scaffolds showed excellent shape fidelity after printing. Moreover, the scaffolds demonstrated compatible mechanical strength with trabecular bone (∼7.07 MPa vs. 0.6 ∼ 16.8 MPa), and adding teriparatide (TP) in scaffolds could further improve the scaffold's potential for bone tissue engineering.

Stereolithographic printing of epithelial and mucosal scaffold

Stereolithography (SLA) is a type of solid free-form fabrication (SFF) technique that can produce intricate products that conventional subtractive manufacturing processes cannot. This character of the method is mainly helpful in biomedical applications, where the requirements are high precision, quick production time, and versatility of material along with customization of patient-specific parts. The damage to any human body tissues can disturb its regular functioning. Scaffolds can assist in regenerating damaged tissues and cells like epithelial or mucosal cells. The work aims to design and print an epithelial and mucosal scaffold made of bio-compatible material to help the cells regenerate quickly. The scaffold is printed using a photo polymeric resin-based 3D printer. This work has undergone multiple iterations to determine the optimal parameters, including raft type, support density, touchpoint size, presence of internal supports, layer thickness, and curing time. Through these iterations, the study aimed to achieve the best possible outcomes regarding scaffold printing. Once printed, the scaffold is post-processed to meet the required structural strength by proper crosslinking and solidification. Although the resin, once solidified, cannot be melted and reused, it is environmentally less polluting due to its lesser specific energy demand than subtractive manufacturing. Also, the requirement of frequent tool changes, coolant supply, and disposal can be avoided entirely in stereolithography. The SLA process utilizing the Biomed amber resin offers high precision and versatility. It is recognized as an eco-friendly and biocompatible approach, making it a promising solution for biomedical applications. Post-printing analysis of the time of printing, volume of resin used, layer thickness, washing, and curing duration have been outlined in work. The scaffold is analyzed for static strength, and the results are compared to the skin.

Antimicrobial and Biodegradable 3D Printed Scaffolds for Orthopedic Infections.

In bone tissue engineering, the performance of scaffolds underpins the success of the healing of bone. Microbial infection is the most challenging issue for orthopedists. The application of scaffolds for healing bone defects is prone to microbial infection. To address this challenge, scaffolds with a desirable shape and significant mechanical, physical, and biological characteristics are crucial. 3D printing of antibacterial scaffolds with suitable mechanical strength and excellent biocompatibility is an appealing strategy to surmount issues of microbial infection. The spectacular progress in developing antimicrobial scaffolds, along with beneficial mechanical and biological properties, has sparked further research for possible clinical applications. Herein, the significance of antibacterial scaffolds designed by 3D, 4D, and 5D printing technologies for bone tissue engineering is critically investigated. Materials such as antibiotics, polymers, peptides, graphene, metals/ceramics/glass, and antibacterial coatings are used to impart the antimicrobial features for the 3D scaffolds. Polymeric or metallic biodegradable and antibacterial 3D-printed scaffolds in orthopedics disclose exceptional mechanical and degradation behavior, biocompatibility, osteogenesis, and long-term antibacterial efficiency. The commercialization aspect of antibacterial 3D-printed scaffolds and technical challenges are also discussed briefly. Finally, the discussion on the unmet demands and prevailing challenges for ideal scaffold materials for fighting against bone infections is included along with a highlight of emerging strategies in this field.

Effect of stearic acid on the mechanical and rheological properties of PLA/HA biocomposites

In this study, biocomposite filaments of polylactic acid (PLA) combined with stearic acid (SA)-coated nano-hydroxyapatite (HA) filler were prepared and characterized. These filaments were then used in material extrusion (MEX) additive manufacturing via fused deposition modeling (FDM) to create scaffolds for bone tissue engineering (BTE). Initially, HA was characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and the Rietveld method. Particle size distribution was examined through dynamic light scattering (DLS), and its specific surface area was determined by the Brunauer-Emmett-Teller (BET) method. Subsequently, the HA nanoparticles were coated with stearic acid (SA) to explore its potential as a surfactant for PLA/HA nanocomposites. For composite fabrication, pure HA and SA-coated HA were mixed with PLA in a torque rheometer to obtain PLA/HA and PLA/HA-SA biocomposites. Their flow behavior was evaluated using a slit die rheometer, demonstrating that the SA coating improved rheological properties. The composites were extruded to produce 1.75 mm diameter filaments, which were analyzed by mechanical tensile testing, showing that the SA coating reduced the fragility of the PLA/HA filaments. The filaments exhibited high repeatability in terms of quality, facilitating scaffold printing. The FDM-manufactured scaffolds were analyzed through compressive testing, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and AlamarBlue Cell Viability Analysis. The results demonstrated that these scaffolds possess the required mechanical, thermal, and cytotoxicity properties for applications in bone tissue engineering.

3D printing of collagen scaffold with enhanced resolution in a citrate-modulated Gellan gum microgel bath.

3D printing in a microgel-based supporting bath enables the construction of complex structures with soft and watery biomaterials but the low print resolution is usually an obstacle to its practical application in tissue engineering. Herein, the high-resolution printing of a 3D collagen organ scaffold is realized by using an engineered Gellan gum (GG) microgel bath containing trisodium citrate (TSC). The introduction of TSC into the bath system not only mitigates the aggregation of GG microgels, leading to a more homogeneous bath morphology, but also suppresses the diffusion of the collagen ink in the bath due to the dehydration effect of TSC, both of which contribute to the improvement of print resolution. 3D collagen organ structures such as hand, ear and heart are successfully constructed with high shape fidelity in the developed bath. After printing, the GG and TSC can be easily removed by washing with water, and the obtained collagen product exhibits good cell affinity in a tissue scaffold application. This work offers an easy-to-operate strategy for developing a microgel bath for high-resolution printing of collagen, providing an alternative path to in vitro 3D organ construction. This article is protected by copyright. All rights reserved.

Fabrication and Characterization of Oxygen-Generating Polylactic Acid/Calcium Peroxide Composite Filaments for Bone Scaffolds.

The latest advancements in bone scaffold technology have introduced novel biomaterials that have the ability to generate oxygen when implanted, improving cell viability and tissue maturation. In this paper, we present a new oxygen-generating polylactic acid (PLA)/calcium peroxide (CPO) composite filament that can be used in 3D printing scaffolds. The composite material was prepared using a wet solution mixing method, followed by drying and hot melting extrusion. The concentration of calcium peroxide in the composite varied from 0% to 9%. The prepared filaments were characterized in terms of the presence of calcium peroxide, the generated oxygen release, porosity, and antibacterial activities. Data obtained from scanning electron microscopy and X-ray diffraction showed that the calcium peroxide remained stable in the composite. The maximum calcium and oxygen release was observed in filaments with a 6% calcium peroxide content. In addition, bacterial inhibition was achieved in samples with a calcium peroxide content of 6% or higher. These results indicate that an optimized PLA filament with a 6% calcium peroxide content holds great promise for improving bone generation through bone cell oxygenation and resistance to bacterial infections.

3D Printing of PolyLactic Acid (PLA) Scaffold Combined with Injectable Bone Substitute (IBS) for Tuberculosis Drug Delivery

Spinal tuberculosis is one of the infectious diseases which according to the World Health Organization (WHO), is a major cause of health problems and one of the top 10 causes of death worldwide. The aim of this study was to fabricate a 3D printing scaffold with the design of truncated hexahedron, then combined with Injectable Bone Substitute (IBS) paste as a method for drug delivery in the case of spinal tuberculosis. Injectable Bone Substitute (IBS) paste was synthesized by combining some materials including hydroxyapatite, gelatin, hydroxypropyl methylcellulose (HPMC), and streptomycin. The scaffold was characterized with IBS paste through the digital microscope and the mechanical test to determine the mechanical strength of the scaffold. The results of the 3D printing scaffold showed that the scaffold has interconnectivity between pores. After being injected with IBS, it was seen that the entire surface of the scaffold pores was covered by IBS paste evenly. Scanning Electron Microscope (SEM) tests showed that the surface of the scaffold has been covered by IBS paste, and proves that the pores are still formed. Energy Dispersive X-Ray (EDX) test results showed that the IBS paste containing a hydroxyapatite component consisting of Ca, P, and O elements. Mechanical tests showed that the scaffold for all pore sizes had a compressive strength of 1.49-3.97 MPa before IBS injection and increased to 3.45-4.77 MPa after IBS injection. Then the bending test showed that the scaffold had a bending strength of 16.76-36.09 MPa and increased to around 21.57-40.36 MPa after being injected with IBS. The drug release test showed that the 3D printing scaffold could release streptomycin by 4.944%-6.547%, which has met the percentage of drug release that is able to kill tuberculosis bacteria. It can be concluded that 3D printing scaffold combined with IBS paste can be applied as a drug carrier as well as a method of healing spinal tuberculosis.

Basic hydrogel polymer materials for 3D printing

Currently, 3D printing of hydrogel scaffolds, which are used in tissue engineering to come to the fore, is gaining prominence in order to restore the structure and function of soft tissues and organs. For successful printing of soft constructs, the FRESH method using a support bath is used, thanks to which the printed hydrogel is kept in the desired shape during solidification. The aim of the study is to create an overview of hydrogel materials and their properties affecting printing, to summarize previous printing of hydrogel scaffolds. The choice of material, the method of crosslinking for the formation of the hydrogel, is taken into account, while at the same time the non-toxicity and compatibility of the material with the biological environment. Specific emphasis is placed on adapting the technological procedure of the FRESH method, where the chemical composition of the support bath must be in accordance with the crosslinking agent and the rheological properties of the printed hydrogel.

Novel Airflow-Field-Driven Melt Spinning 3D Printing of Tubular Scaffolds Based on Polycaprolactone Blends

The fabrication of various 3D tissue engineering tubular scaffolds with fibrous structures, to assist the human body in rapidly repairing a variety of ailments, is receiving more and more attention. Due to the inefficiency of the majority of fibrous preparation techniques, the question of how to rapidly produce the requisite three-dimensional tubular microfiber scaffold structures has become an urgent problem. In this study, an efficient polymer fiber preparation method was developed, using a high-speed airflow drive. Melt blending of polycaprolactone (PCL), polylactic acid (PLA), and tributyl citrate (TBC), was used for the printing material, to achieve the efficient preparation of tubular microfiber scaffolds with different structures. The scaffold diameter was as small as 2 mm, the wall thickness was up to 100 μm, and the fiber injection efficiency reached 15.48 g/h. By utilizing simulations to optimize the printing parameters and by adjusting the printing settings, it was possible to achieve a controlled fiber diameter in the range of 3 μm to 15 μm. In addition, plasma treatment was applied to the microfibers' surface, to increase their wettability, and the efficiency of the hydrophilic modification was demonstrated. Furthermore, the mechanical property test demonstrated that the fibers have a tensile strength of 1.36 ± 0.16 MPa and a tensile strain of 30.8 ± 3.5%. The radial compressive strain of the tubular scaffold could reach 60% of the original scaffold's diameter. Finally, the in vitro degradation of the fibers at various pH values was tested. The results showed that, under alkaline conditions, the surface of the fibers would be severely crushed and the rate of deterioration would increase.

Sustained Release of BMSC-EVs from 3D Printing Gel/HA/nHAP Scaffolds for Promoting Bone Regeneration in Diabetic Rats.

Extracellular vesicles (EVs) play an important role in intercellular communication, and the function of EVs mainly depends on the state of source cells. To determine the effect of diabetic microenvironment on EVs secreted by bone marrow mesenchymal stem cells (BMSCs), this work explores the effect of normal glucose (5.5mm) cultured BMSCs derived EVs (NG-EVs) and high glucose (30mm) cultured BMSCs derived EVs (HG-EVs) in regulating the migration, proliferation and osteoblastic differentiation of BMSCs in vitro. In order to improve the bioavailability of EVs, this work constructs a sustained release system of polydopamine (PDA) functionalized 3D printing gelatin/hyaluronic acid/nano-hydroxyapatite (Gel/HA/nHAP) scaffolds (S/PDA) and verifies its function in the calvarial defect model of diabetic rats. This work confirms that both NG-EVs and HG-EVs can promote proliferation and migration, inhibit apoptosis and promote osteogenic differentiation, but the function of HG-EVs is weaker than that of NG-EVs. Therefore, EVs secreted by autologous cells of diabetic patients are not suitable for self-repair. This work hopes that the 3D printing scaffold designed for sustained-release EVs will provide a new strategy for acellular tissue engineering bone repair in diabetic patients.

3D printing of multifunctional gradient bone scaffolds with programmable component distribution and hierarchical pore structure

3D printing of multifunctional gradient bone scaffolds with programmable component distribution and hierarchical pore structure