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Special Issue "3D and 4D Printing of (Bio)Materials"

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Biomacromolecules, Biobased and Biodegradable Polymers".

Deadline for manuscript submissions: closed (31 July 2020).

Special Issue Editor

Dr. Mo Maniruzzaman
E-Mail Website
Guest Editor
Division of Molecular Pharmaceutics and Drug Delivery, College of Pharmacy, University of Texas at Austin, Austin, TX 78712, USA
Interests: 3D bioprinting; 3D printing; continuous manufacturing; drug formulation and delivery; implantable medical devices; smart biomaterials
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

3D printing has emerged as one of the most versatile fabrication technologies, referred to as the additive manufacturing technique, which involves additives such as polymers and metals deposited in sequential layers to produce a 3D object (i.e., pills or medical devices). The convergence of additive manufacturing and printing materials is of significant aptitude for the advancement of person-specific products in the pharmaceutical and medical sphere. Geometric shapes as well as the visual effects of materials currently used in additive manufacturing play essential roles towards smooth fabrication with the highest shape fidelity possible. In most of the cases, especially in biomedical applications, functions of devices and structures are surprisingly limited by the complexity of the manageable shapes. Further, traditional processing techniques such as ink jet 2D printing or molding suffer from the failure of meeting the growing needs due to both the difficulty and production-associated cost. These inimitable needs have positioned 3D printing as an attractive option because of its supreme flexibility and versatility in producing complex structures. However, the application and practical potential of the current state of 3D printing is to some extent limited due to its speed for scale-up and meeting the growing demands for increased numbers of populations.

Therefore, it is projected that moving from the stepwise layer-by-layer process which is typical in 3D printing to a continuous process may significantly accelerate the practical potential of printing technology. Being based on the traditional 3D printing, 4D printing can encompass a wide range of disciplines, such as materials science, bioengineering, and chemistry/chemical engineering, and has the true potential to emerge as the next-generation additive manufacturing technique. Using stimuli-responsive (also known as shape memory) materials, 4D printing creates structures that are capable of transforming from one shape to another, right off the print bed under various stimuli, such as heat, pH, water, etc.

The 3D printing process optimization, engineering, formulation compositions, advanced drug delivery, materials properties, and characterizations, and the state of the art and limitations that exist in the current printing modalities will be explored in this proposed Special Issue of Polymers.

Dr. Mo Maniruzzaman
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2200 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • 3D and 4D printing
  • biomaterials
  • implants
  • smart implants
  • drug delivery
  • additive manufacturing

Published Papers (17 papers)

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Research

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Article
Effect of Stereolithography 3D Printing on the Properties of PEGDMA Hydrogels
Polymers 2020, 12(9), 2015; https://doi.org/10.3390/polym12092015 - 03 Sep 2020
Cited by 2 | Viewed by 922
Abstract
Stereolithography (SLA)-based 3D printing has proven to have several advantages over traditional fabrication techniques as it allows for the control of hydrogel synthesis at a very high resolution, making possible the creation of tissue-engineered devices with microarchitecture similar to the tissues they are [...] Read more.
Stereolithography (SLA)-based 3D printing has proven to have several advantages over traditional fabrication techniques as it allows for the control of hydrogel synthesis at a very high resolution, making possible the creation of tissue-engineered devices with microarchitecture similar to the tissues they are replacing. Much of the previous work in hydrogels for tissue engineering applications have utilised the ultraviolet (UV) chamber bulk photopolymerisation method for preparing test specimens. Therefore, it is essential to directly compare SLA 3D printing to this more traditional approach to elucidate the differences in hydrogels prepared by each fabrication method. Polyethyleneglycol dimethacrylate (PEGDMA) is an ideally suited material for a comparative study of the impact that SLA fabrication has on performance, as the properties of traditional UV chamber-cured hydrogels have been extensively characterised. The present study was conducted to compare the material properties of PEGDMA hydrogels prepared using UV chamber photopolymerisation and SLA 3D printing. From the subsequent testing, SLA-fabricated hydrogels were shown to maintain similar thermal and chemical performance to UV chamber-cured hydrogels but had a higher compressive strength and tensile stiffness, as well as increased hydrophilicity. These differences are attributed to the increased exposure to UV light SLA samples received compared to traditionally UV chamber-cured samples. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Article
Novel On-Demand 3-Dimensional (3-D) Printed Tablets Using Fill Density as an Effective Release-Controlling Tool
Polymers 2020, 12(9), 1872; https://doi.org/10.3390/polym12091872 - 20 Aug 2020
Cited by 17 | Viewed by 1614
Abstract
This research demonstrates the use of fill density as an effective tool for controlling the drug release without changing the formulation composition. The merger of hot-melt extrusion (HME) with fused deposition modeling (FDM)-based 3-dimensional (3-D) printing processes over the last decade has directed [...] Read more.
This research demonstrates the use of fill density as an effective tool for controlling the drug release without changing the formulation composition. The merger of hot-melt extrusion (HME) with fused deposition modeling (FDM)-based 3-dimensional (3-D) printing processes over the last decade has directed pharmaceutical research towards the possibility of printing personalized medication. One key aspect of printing patient-specific dosage forms is controlling the release dynamics based on the patient’s needs. The purpose of this research was to understand the impact of fill density and interrelate it with the release of a poorly water-soluble, weakly acidic, active pharmaceutical ingredient (API) from a hydroxypropyl methylcellulose acetate succinate (HPMC-AS) matrix, both mathematically and experimentally. Amorphous solid dispersions (ASDs) of ibuprofen with three grades of AquaSolveTM HPMC-AS (HG, MG, and LG) were developed using an HME process and evaluated using solid-state characterization techniques. Differential scanning calorimetry (DSC), powder X-ray diffraction (pXRD), and polarized light microscopy (PLM) confirmed the amorphous state of the drug in both polymeric filaments and 3D printed tablets. The suitability of the manufactured filaments for FDM processes was investigated using texture analysis (TA) which showed robust mechanical properties of the developed filament compositions. Using FDM, tablets with different fill densities (20–80%) and identical dimensions were printed for each polymer. In vitro pH shift dissolution studies revealed that the fill density has a significant impact (F(11, 24) = 15,271.147, p < 0.0001) and a strong negative correlation (r > −0.99; p < 0.0001) with the release performance, where 20% infill demonstrated the fastest and most complete release, whereas 80% infill depicted a more controlled release. The results obtained from this research can be used to develop a robust formulation strategy to control the drug release from 3D printed dosage forms as a function of fill density. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Article
Surface Etching of 3D Printed Poly(lactic acid) with NaOH: A Systematic Approach
Polymers 2020, 12(8), 1711; https://doi.org/10.3390/polym12081711 - 30 Jul 2020
Cited by 3 | Viewed by 1054
Abstract
The article describes a systematic investigation of the effects of an aqueous NaOH treatment of 3D printed poly(lactic acid) (PLA) scaffolds for surface activation. The PLA surface undergoes several morphology changes and after an initial surface roughening, the surface becomes smoother again before [...] Read more.
The article describes a systematic investigation of the effects of an aqueous NaOH treatment of 3D printed poly(lactic acid) (PLA) scaffolds for surface activation. The PLA surface undergoes several morphology changes and after an initial surface roughening, the surface becomes smoother again before the material dissolves. Erosion rates and surface morphologies can be controlled by the treatment. At the same time, the bulk mechanical properties of the treated materials remain unaltered. This indicates that NaOH treatment of 3D printed PLA scaffolds is a simple, yet viable strategy for surface activation without compromising the mechanical stability of PLA scaffolds. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Article
Development of a 3D Printed Coating Shell to Control the Drug Release of Encapsulated Immediate-Release Tablets
Polymers 2020, 12(6), 1395; https://doi.org/10.3390/polym12061395 - 22 Jun 2020
Cited by 8 | Viewed by 1438
Abstract
The use of 3D printing techniques to control drug release has flourished in the past decade, although there is no generic solution that can be applied to the full range of drugs or solid dosage forms. The present study provides a new concept, [...] Read more.
The use of 3D printing techniques to control drug release has flourished in the past decade, although there is no generic solution that can be applied to the full range of drugs or solid dosage forms. The present study provides a new concept, using the 3D printing technique to print a coating system in the form of shells with various designs to control/modify drug release in immediate-release tablets. A coating system of cellulose acetate in the form of an encapsulating shell was printed through extrusion-based 3D printing technology, where an immediate-release propranolol HCl tablet was placed inside to achieve a sustained drug release profile. The current work investigated the influence of shell composition by using different excipients and also by exploring the impact of shell size on the drug release from the encapsulated tablet. Three-dimensional printed shells with different ratios of rate-controlling polymer (cellulose acetate) and pore-forming agent (D-mannitol) showed the ability to control the amount and the rate of propranolol HCl release from the encapsulated tablet model. The shell-print approach also showed that space/gap available for drug dissolution between the shell wall and the enclosed tablet significantly influenced the release of propranolol HCl. The modified release profile of propranolol HCl achieved through enclosing the tablet in a 3D printed controlled-release shell followed Korsmeyer–Peppas kinetics with non-Fickian diffusion. This approach could be utilized to tailor the release profile of a Biopharmaceutics Classification System (BCS) class I drug tablet (characterized by high solubility and high permeability) to improve patient compliance and promote personalized medicine. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Article
Quantifying Oxygen Levels in 3D Bioprinted Cell-Laden Thick Constructs with Perfusable Microchannel Networks
Polymers 2020, 12(6), 1260; https://doi.org/10.3390/polym12061260 - 30 May 2020
Viewed by 1002
Abstract
The survival and function of thick tissue engineered implanted constructs depends on pre-existing, embedded, functional, vascular-like structures that are able to integrate with the host vasculature. Bioprinting was employed to build perfusable vascular-like networks within thick constructs. However, the improvement of oxygen transportation [...] Read more.
The survival and function of thick tissue engineered implanted constructs depends on pre-existing, embedded, functional, vascular-like structures that are able to integrate with the host vasculature. Bioprinting was employed to build perfusable vascular-like networks within thick constructs. However, the improvement of oxygen transportation facilitated by these vascular-like networks was directly quantified. Using an optical fiber oxygen sensor, we measured the oxygen content at different positions within 3D bioprinted constructs with and without perfusable microchannel networks. Perfusion was found to play an essential role in maintaining relatively high oxygen content in cell-laden constructs and, consequently, high cell viability. The concentration of oxygen changes following switching on and off the perfusion. Oxygen concentration depletes quickly after pausing perfusion but recovers rapidly after resuming the perfusion. The quantification of oxygen levels within cell-laden hydrogel constructs could provide insight into channel network design and cellular responses. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Article
On the Tensile Behaviour of Bio-Sourced 3D-Printed Structures from a Microstructural Perspective
Polymers 2020, 12(5), 1060; https://doi.org/10.3390/polym12051060 - 06 May 2020
Cited by 3 | Viewed by 987
Abstract
The influence of the microstructural arrangement of 3D-printed polylactic acid (PLA) on its mechanical properties is studied using both numerical and experimental approaches. Thermal cycling during the laying down of PLA filament is investigated through infra-red measurements for different printing conditions. The microstructure [...] Read more.
The influence of the microstructural arrangement of 3D-printed polylactic acid (PLA) on its mechanical properties is studied using both numerical and experimental approaches. Thermal cycling during the laying down of PLA filament is investigated through infra-red measurements for different printing conditions. The microstructure induced by 3D printing is determined using X-ray micro-tomography. The mechanical properties are measured under tensile testing conditions. Finite element computation is considered to predict the mechanical performance of 3D-printed PLA by converting the acquired 3D images into structural meshes. The results confirm the leading role of the printing temperature on thermal cycling during the laying down process. In addition, the weak influence of the printing temperature on the stiffness of 3D-printed PLA is explained by the relatively small change in porosity content. However, the influence of the printing temperature on the ultimate properties is found to be substantial. This major influence is explained from finite element predictions as an effect of pore connectivity which is found to be the control factor for tensile strength. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Article
Stress Relaxation and Creep of a Polymer-Aluminum Composite Produced through Selective Laser Sintering
Polymers 2020, 12(4), 830; https://doi.org/10.3390/polym12040830 - 05 Apr 2020
Cited by 3 | Viewed by 859
Abstract
This article discusses the rheological properties (stress relaxation and creep) of polymer-aluminum composite specimens fabricated through the selective laser sintering (SLS) from a commercially available powder called Alumide. The rheological data predicted using the Maxwell–Wiechert and the Kelvin–Voigt models for stress relaxation and [...] Read more.
This article discusses the rheological properties (stress relaxation and creep) of polymer-aluminum composite specimens fabricated through the selective laser sintering (SLS) from a commercially available powder called Alumide. The rheological data predicted using the Maxwell–Wiechert and the Kelvin–Voigt models for stress relaxation and creep, respectively, were in agreement with the experimental results. The elastic moduli and dynamic viscosities were determined with high accuracy for both models. The findings of this study can be useful to designers and users of SLS prints made from the material tested. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Article
Phosphonic Acid Coupling Agent Modification of HAP Nanoparticles: Interfacial Effects in PLLA/HAP Bone Scaffold
Polymers 2020, 12(1), 199; https://doi.org/10.3390/polym12010199 - 13 Jan 2020
Cited by 35 | Viewed by 1557
Abstract
In order to improve the interfacial bonding between hydroxyapatite (HAP) and poly-l-lactic acid (PLLA), 2-Carboxyethylphosphonic acid (CEPA), a phosphonic acid coupling agent, was introduced to modify HAP nanoparticles. After this. the PLLA scaffold containing CEPA-modified HAP (C-HAP) was fabricated by selective laser sintering [...] Read more.
In order to improve the interfacial bonding between hydroxyapatite (HAP) and poly-l-lactic acid (PLLA), 2-Carboxyethylphosphonic acid (CEPA), a phosphonic acid coupling agent, was introduced to modify HAP nanoparticles. After this. the PLLA scaffold containing CEPA-modified HAP (C-HAP) was fabricated by selective laser sintering (frittage). The specific mechanism of interfacial bonding was that the PO32− of CEPA formed an electrovalent bond with the Ca2+ of HAP on one hand, and on the other hand, the –COOH of CEPA formed an ester bond with the –OH of PLLA via an esterification reaction. The results showed that C-HAP was homogeneously dispersed in the PLLA matrix and that it exhibited interconnected morphology pulled out from the PLLA matrix due to the enhanced interfacial bonding. As a result, the tensile strength and modulus of the scaffold with 20% C-HAP increased by 1.40 and 2.79 times compared to that of the scaffold with HAP, respectively. In addition, the scaffold could attract Ca2+ in simulated body fluid (SBF) solution by the phosphonic acid group to induce apatite layer formation and also release Ca2+ and PO43− by degradation to facilitate cell attachment, growth and proliferation. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Article
Development and Optimisation of Novel Polymeric Compositions for Sustained Release Theophylline Caplets (PrintCap) via FDM 3D Printing
Polymers 2020, 12(1), 27; https://doi.org/10.3390/polym12010027 - 21 Dec 2019
Cited by 18 | Viewed by 1851
Abstract
This study reports a thorough investigation combining hot-melt extrusion technology (HME) and a low-cost fused deposition modelling (FDM) 3D printer as a continuous fabrication process for a sustained release drug delivery system. The successful implementation of such an approach presented herein allows local [...] Read more.
This study reports a thorough investigation combining hot-melt extrusion technology (HME) and a low-cost fused deposition modelling (FDM) 3D printer as a continuous fabrication process for a sustained release drug delivery system. The successful implementation of such an approach presented herein allows local hospitals to manufacture their own medical and pharmaceutical products on-site according to their patients’ needs. This will help save time from waiting for suitable products to be manufactured off-site or using traditional manufacturing processes. The filaments were produced by optimising various compositions of pharmaceutical-grade polymers, such as hydroxypropyl cellulose (HPC), Eudragit® (RL PO), and polyethylene glycol (PEG), whereas theophylline was used as a model thermally stable drug. For the purpose of the study, twin-screw hot-melt extrusion (HME) was implemented from the view that it would result in the formation of solid dispersion of drug in the polymeric carrier matrices by means of high shear mixing inside the heated barrel. Four filament compositions consisting of different ratios of polymers were produced and their properties were assessed. The mechanical characterisation of the filaments revealed quite robust properties of the filaments suitable for FDM 3D printing of caplets (PrintCap), whereas the solid-state analyses conducted via DSC and XRD showed amorphous nature of the crystalline drug dispersed in the polymeric matrices. Moreover, the surface analysis conducted via SEM showed a smooth surface of the produced filaments as well as caplets where no drug crystals were visible. The in vitro drug release study showed a sustained release profile over 10 h where about 80% of the drug was released from the printed dosage forms. This indicates that our optimised 3D printed caplets could be suitable for the development of sustained release on-demand drug delivery systems. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Communication
Electrospinning on 3D Printed Polymers for Mechanically Stabilized Filter Composites
Polymers 2019, 11(12), 2034; https://doi.org/10.3390/polym11122034 - 08 Dec 2019
Cited by 19 | Viewed by 1828
Abstract
Electrospinning is a frequently used method to prepare air and water filters. Electrospun nanofiber mats can have very small pores, allowing for filtering of even the smallest particles or molecules. In addition, their high surface-to-volume ratio allows for the integration of materials which [...] Read more.
Electrospinning is a frequently used method to prepare air and water filters. Electrospun nanofiber mats can have very small pores, allowing for filtering of even the smallest particles or molecules. In addition, their high surface-to-volume ratio allows for the integration of materials which may additionally treat the filtered material through photo-degradation, possess antimicrobial properties, etc., thus enhancing their applicability. However, the fine nanofiber mats are prone to mechanical damage. Possible solutions include reinforcement by embedding them in composites or gluing them onto layers that are more mechanically stable. In a previous study, we showed that it is generally possible to stabilize electrospun nanofiber mats by 3D printing rigid polymer layers onto them. Since this procedure is not technically easy and needs some experience to avoid delamination as well as damaging the nanofiber mat by the hot nozzle, here we report on the reversed technique (i.e., first 3D printing a rigid scaffold and subsequently electrospinning the nanofiber mat on top of it). We show that, although the adhesion between both materials is insufficient in the case of a common rigid printing polymer, nanofiber mats show strong adhesion to 3D printed scaffolds from thermoplastic polyurethane (TPU). This paves the way to a second approach of combining 3D printing and electrospinning in order to prepare mechanically stable filters with a nanofibrous surface. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Article
3D Bioprinting of Novel Biocompatible Scaffolds for Endothelial Cell Repair
Polymers 2019, 11(12), 1924; https://doi.org/10.3390/polym11121924 - 22 Nov 2019
Cited by 7 | Viewed by 1752
Abstract
The aim of this study was to develop and evaluate an optimized 3D bioprinting technology in order to fabricate novel scaffolds for the application of endothelial cell repair. Various biocompatible and biodegradable macroporous scaffolds (D = 10 mm) with interconnected pores (D = [...] Read more.
The aim of this study was to develop and evaluate an optimized 3D bioprinting technology in order to fabricate novel scaffolds for the application of endothelial cell repair. Various biocompatible and biodegradable macroporous scaffolds (D = 10 mm) with interconnected pores (D = ~500 µm) were fabricated using a commercially available 3D bioprinter (r3bEL mini, SE3D, USA). The resolution of the printing layers was set at ~100 µm for all scaffolds. Various compositions of polylactic acid (PLA), polyethylene glycol (PEG) and pluronic F127 (F127) formulations were prepared and optimized to develop semi-solid viscous bioinks. Either dimethyloxalylglycine (DMOG) or erythroprotein (EPO) was used as a model drug and loaded in the viscous biocompatible ink formulations with a final concentration of 30% (w/w). The surface analysis of the bioinks via a spectroscopic analysis revealed a homogenous distribution of the forming materials throughout the surface, whereas SEM imaging of the scaffolds showed a smooth surface with homogenous macro-porous texture and precise pore size. The rheological and mechanical analyses showed optimum rheological and mechanical properties of each scaffold. As the drug, DMOG, is a HIF-1 inducer, its release from the scaffolds into PBS solution was measured indirectly using a bioassay for HIF-1α. This showed that the release of DMOG was sustained over 48 h. The release of DMOG was enough to cause a significant increase in HIF-1α levels in the bioassay, and when incubated with rat aortic endothelial cells (RAECs) for 2 h resulted in transcriptional activation of a HIF-1α target gene (VEGF). The optimum time for the increased expression of VEGF gene was approximately 30 min and was a 3-4-fold increase above baseline. This study provides a proof of concept, that a novel bioprinting platform can be exploited to develop biodegradable composite scaffolds for potential clinical applications in endothelial cell repair in cardiovascular disease (CVD), or in other conditions in which endothelial damage occurs. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Article
Microstructure and Mechanical Performance of 3D Printed Wood-PLA/PHA Using Fused Deposition Modelling: Effect of Printing Temperature
Polymers 2019, 11(11), 1778; https://doi.org/10.3390/polym11111778 - 29 Oct 2019
Cited by 22 | Viewed by 2206
Abstract
The microstructure and mechanical performance of wood-based filament is investigated in the case of Fused Deposition Modelling (FDM) technique using experimental and numerical approaches. The printing process of wood-PLA/PHA is conducted by varying the printing temperature, typically from 210 °C to 250 °C. [...] Read more.
The microstructure and mechanical performance of wood-based filament is investigated in the case of Fused Deposition Modelling (FDM) technique using experimental and numerical approaches. The printing process of wood-PLA/PHA is conducted by varying the printing temperature, typically from 210 °C to 250 °C. The filament temperature during the laying down is measured using infra-red camera to study the thermal cycling. In addition, X-ray micro-tomography is used to evaluate the material arrangement of printed wood-PLA/PHA at different length scales. Tensile experiments are performed to rank the loss in mechanical performance with respect to the filament properties. Finally, finite element computation is considered to predict the tensile behaviour based on the implementation of the real 3D microstructure issued from X-ray micro-tomography. The results show that the wood-based filament is printable over a wide range of temperatures and exhibits a marked heat accumulation tendency at high printing temperatures. However, the limited gain in tensile performance at these temperatures makes 220 °C an optimal choice for printing wood-based filament. The elongation at break of 3D-printed wood-PLA/PHA is remarkably similar to the results observed for the filament. Finite element computation reveals that despite this apparent similarity, the associated deformation mechanisms are different. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Communication
Stabilization of Electrospun Nanofiber Mats Used for Filters by 3D Printing
Polymers 2019, 11(10), 1618; https://doi.org/10.3390/polym11101618 - 06 Oct 2019
Cited by 22 | Viewed by 2215
Abstract
Electrospinning is a well-known technology used to create nanofiber mats from diverse polymers and other materials. Due to their large surface-to-volume ratio, such nanofiber mats are often applied as air or water filters. Especially the latter, however, have to be mechanically highly stable, [...] Read more.
Electrospinning is a well-known technology used to create nanofiber mats from diverse polymers and other materials. Due to their large surface-to-volume ratio, such nanofiber mats are often applied as air or water filters. Especially the latter, however, have to be mechanically highly stable, which is challenging for common nanofiber mats. One of the approaches to overcome this problem is gluing them on top of more rigid objects, integrating them in composites, or reinforcing them using other technologies to avoid damage due to the water pressure. Here, we suggest another solution. While direct 3D printing with the fused deposition modeling (FDM) technique on macroscopic textile fabrics has been under examination by several research groups for years, here we report on direct FDM printing on nanofiber mats for the first time. We show that by choosing the proper height of the printing nozzle above the nanofiber mat, printing is possible for raw polyacrylonitrile (PAN) nanofiber mats, as well as for stabilized and even more brittle carbonized material. Under these conditions, the adhesion between both parts of the composite is high enough to prevent the nanofiber mat from being peeled off the 3D printed polymer. Abrasion tests emphasize the significantly increased mechanical properties, while contact angle examinations reveal a hydrophilicity between the original values of the electrospun and the 3D printed materials. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Article
3D Bio-Printing of CS/Gel/HA/Gr Hybrid Osteochondral Scaffolds
Polymers 2019, 11(10), 1601; https://doi.org/10.3390/polym11101601 - 30 Sep 2019
Cited by 14 | Viewed by 1749
Abstract
Cartilage is an important tissue contributing to the structure and function of support and protection in the human body. There are many challenges for tissue cartilage repair. However, 3D bio-printing of osteochondral scaffolds provides a promising solution. This study involved preparing bio-inks with [...] Read more.
Cartilage is an important tissue contributing to the structure and function of support and protection in the human body. There are many challenges for tissue cartilage repair. However, 3D bio-printing of osteochondral scaffolds provides a promising solution. This study involved preparing bio-inks with different proportions of chitosan (Cs), Gelatin (Gel), and Hyaluronic acid (HA). The rheological properties of each bio-ink was used to identify the optimal bio-ink for printing. To improve the mechanical properties of the bio-scaffold, Graphene (GR) with a mass ratio of 0.024, 0.06, and 0.1% was doped in the bio-ink. Bio-scaffolds were prepared using 3D printing technology. The mechanical strength, water absorption rate, porosity, and degradation rate of the bio-scaffolds were compared to select the most suitable scaffold to support the proliferation and differentiation of cells. P3 Bone mesenchymal stem cells (BMSCs) were inoculated onto the bio-scaffolds to study the biocompatibility of the scaffolds. The results of SEM showed that the Cs/Gel/HA scaffolds with a GR content of 0, 0.024, 0.06, and 0.1% had a good three-dimensional porous structure and interpenetrating pores, and a porosity of more than 80%. GR was evenly distributed on the scaffold as observed by energy spectrum analyzer and polarizing microscope. With increasing GR content, the mechanical strength of the scaffold was enhanced, and pore walls became thicker and smoother. BMSCs were inoculated on the different scaffolds. The cells distributed and extended well on Cs/Gel/HA/GR scaffolds. Compared to traditional methods in tissue-engineering, this technique displays important advantages in simulating natural cartilage with the ability to finely control the mechanical and chemical properties of the scaffold to support cell distribution and proliferation for tissue repair. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Article
Improving Mechanical Properties for Extrusion-Based Additive Manufacturing of Poly(Lactic Acid) by Annealing and Blending with Poly(3-Hydroxybutyrate)
Polymers 2019, 11(9), 1529; https://doi.org/10.3390/polym11091529 - 19 Sep 2019
Cited by 16 | Viewed by 2149
Abstract
Based on differential scanning calorimetry (DSC), X-ray diffraction (XRD) analysis, polarizing microscope (POM), and scanning electron microscopy (SEM) analysis, strategies to close the gap on applying conventional processing optimizations for the field of 3D printing and to specifically increase the mechanical performance of [...] Read more.
Based on differential scanning calorimetry (DSC), X-ray diffraction (XRD) analysis, polarizing microscope (POM), and scanning electron microscopy (SEM) analysis, strategies to close the gap on applying conventional processing optimizations for the field of 3D printing and to specifically increase the mechanical performance of extrusion-based additive manufacturing of poly(lactic acid) (PLA) filaments by annealing and/or blending with poly(3-hydroxybutyrate) (PHB) were reported. For filament printing at 210 °C, the PLA crystallinity increased significantly upon annealing. Specifically, for 2 h of annealing at 100 °C, the fracture surface became sufficiently coarse such that the PLA notched impact strength increased significantly (15 kJ m−2). The Vicat softening temperature (VST) increased to 160 °C, starting from an annealing time of 0.5 h. Similar increases in VST were obtained by blending with PHB (20 wt.%) at a lower printing temperature of 190 °C due to crystallization control. For the blend, the strain at break increased due to the presence of a second phase, with annealing only relevant for enhancing the modulus. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Review

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Review
Natural 3D-Printed Bioinks for Skin Regeneration and Wound Healing: A Systematic Review
Polymers 2020, 12(8), 1782; https://doi.org/10.3390/polym12081782 - 10 Aug 2020
Cited by 12 | Viewed by 2454
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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Review
Review of Polymeric Materials in 4D Printing Biomedical Applications
Polymers 2019, 11(11), 1864; https://doi.org/10.3390/polym11111864 - 12 Nov 2019
Cited by 36 | Viewed by 3328
Abstract
The purpose of 4D printing is to embed a product design into a deformable smart material using a traditional 3D printer. The 3D printed object can be assembled or transformed into intended designs by applying certain conditions or forms of stimulation such as [...] Read more.
The purpose of 4D printing is to embed a product design into a deformable smart material using a traditional 3D printer. The 3D printed object can be assembled or transformed into intended designs by applying certain conditions or forms of stimulation such as temperature, pressure, humidity, pH, wind, or light. Simply put, 4D printing is a continuum of 3D printing technology that is now able to print objects which change over time. In previous studies, many smart materials were shown to have 4D printing characteristics. In this paper, we specifically review the current application, respective activation methods, characteristics, and future prospects of various polymeric materials in 4D printing, which are expected to contribute to the development of 4D printing polymeric materials and technology. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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