Mechanical properties of dense polylactic acid structures fabricated by three dimensional printing

Three-Dimensional Scaffolds for Bone Tissue Engineering

Immobilization using external or internal splints is a standard and effective procedure to treat minor skeletal fractures. In the case of major skeletal defects caused by extreme trauma, infectious diseases or tumors, the surgical implantation of a bone graft from external sources is required for a complete cure. Practical disadvantages, such as the risk of immune rejection and infection at the implant site, are high in xenografts and allografts. Currently, an autograft from the iliac crest of a patient is considered the "gold standard" method for treating large-scale skeletal defects. However, this method is not an ideal solution due to its limited availability and significant reports of morbidity in the harvest site (30%) as well as the implanted site (5-35%). Tissue-engineered bone grafts aim to create a mechanically strong, biologically viable and degradable bone graft by combining a three-dimensional porous scaffold with osteoblast or progenitor cells. The materials used for such tissue-engineered bone grafts can be broadly divided into ceramic materials (calcium phosphates) and biocompatible/bioactive synthetic polymers. This review summarizes the types of materials used to make scaffolds for cryo-preservable tissue-engineered bone grafts as well as the distinct methods adopted to create the scaffolds, including traditional scaffold fabrication methods (solvent-casting, gas-foaming, electrospinning, thermally induced phase separation) and more recent fabrication methods (fused deposition molding, stereolithography, selective laser sintering, Inkjet 3D printing, laser-assisted bioprinting and 3D bioprinting). This is followed by a short summation of the current osteochondrogenic models along with the required scaffold mechanical properties for in vivo applications. We then present a few results of the effects of freezing and thawing on the structural and mechanical integrity of PLLA scaffolds prepared by the thermally induced phase separation method and conclude this review article by summarizing the current regulatory requirements for tissue-engineered products.

Application of 3D printing technology combined with PBL teaching method in clinical teaching of cerebrovascular disease: An observational study

Traditional clinical teaching does not allow medical students to combine theoretical knowledge with practical knowledge. As such, we aimed to determine the effectiveness of three dimensional (3D) printing technology combined with problem-based learning (PBL) in the clinical teaching of cerebrovascular diseases. Medical interns were randomly divided into an experimental group (n = 136) that was taught using 3D printing technology + PBL method and a control group (n = 133) that was taught using traditional methods. We compared assessment results of theoretical and clinical practice skills and the subjective evaluation of teaching methods between the 2 groups. The assessment results of the experimental group were significantly higher than those in the control group (P < .05). The survey assessing the evaluation of teaching methods showed higher satisfaction with teaching methods, increased learning interest, and improvement in the spatial thinking ability of interns in the experimental group compared to the control group (P < .05). There was no significant difference when assessing which teaching method better improved the interns' understanding of cerebrovascular diseases (P < .05). The application of 3D printing technology combined with the PBL teaching method in neurosurgery clinical teaching can stimulate interest in learning and significantly improve academic performance and problem-analysis and solving skills.

The Effect of PCL Addition on 3D-Printable PLA/HA Composite Filaments for the Treatment of Bone Defects

The still-growing field of additive manufacturing (AM), which includes 3D printing, has enabled manufacturing of patient-specific medical devices with high geometrical accuracy in a relatively quick manner. However, the development of materials with specific properties is still ongoing, including those for enhanced bone-repair applications. Such applications seek materials with tailored mechanical properties close to bone tissue and, importantly, that can serve as temporary supports, allowing for new bone ingrowth while the material is resorbed. Thus, controlling the resorption rate of materials for bone applications can support bone healing by balancing new tissue formation and implant resorption. In this regard, this work aimed to study the combination of polylactic acid (PLA), polycaprolactone (PCL) and hydroxyapatite (HA) to develop customized biocompatible and bioresorbable polymer-based composite filaments, through extrusion, for fused filament fabrication (FFF) printing. PLA and PCL were used as supporting polymer matrices while HA was added to enhance the biological activity. The materials were characterized in terms of mechanical properties, thermal stability, chemical composition and morphology. An accelerated degradation study was executed to investigate the impact of degradation on the above-mentioned properties. The results showed that the materials' chemical compositions were not affected by the extrusion nor the printing process. All materials exhibited higher mechanical properties than human trabecular bone, even after degradation with a mass loss of around 30% for the polymer blends and 60% for the composites. It was also apparent that the mineral accelerated the polymer degradation significantly, which can be advantageous for a faster healing time, where support is required only for a shorter time period.

Multifunctional Material Extrusion 3D-Printed Antibacterial Polylactic Acid (PLA) with Binary Inclusions: The Effect of Cuprous Oxide and Cellulose Nanofibers

In this work, we present an effective process easily adapted in industrial environments for the development of multifunctional nanocomposites for material extrusion (MEX) 3D printing (3DP). The literature is still very limited in this field, although the interest in such materials is constantly increasing. Nanocomposites with binary inclusions were prepared and investigated in this study. Polylactic acid (PLA) was used as the matrix material, and cuprous oxide (Cu2O) and cellulose nanofibers (CNF) were used as nanoadditives introduced in the matrix material to enhance the mechanical properties and induce antibacterial performance. Specimens were built according to international standards with a thermomechanical process. Tensile, flexural, impact, and microhardness tests were conducted. The effect on the thermal properties of the matrix material was investigated through thermogravimetric analysis, and Raman spectroscopic analysis was conducted. The morphological characteristics were evaluated with atomic force microscopy (AFM), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDS) analyses. The antibacterial performance of the prepared nanomaterials was studied against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria, with a screening agar well diffusion method. All nanocomposites prepared exhibited biocidal properties against the bacteria tested. The tested PLA/1.0 CNF/0.5 Cu2O material had 51.1% higher tensile strength and 35.9% higher flexural strength than the pure PLA material.

Mod3D: A low-cost, flexible modular system of live-cell microscopy chambers and holders

Live-cell microscopy imaging typically involves the use of high-quality glass-bottom chambers that allow cell culture, gaseous buffer exchange and optical properties suitable for microscopy applications. However, commercial sources of these chambers can add significant annual costs to cell biology laboratories. Consumer products in three-dimensional printing technology, for both Filament Deposition Modeling (FDM) and Masked Stereo Lithography (MSLA), have resulted in more biomedical research labs adopting the use of these devices for prototyping and manufacturing of lab plastic-based items, but rarely consumables. Here we describe a modular, live-cell chamber with multiple design options that can be mixed per experiment. Single reusable carriers and the use of biodegradable plastics, in a hybrid of FDM and MSLA manufacturing methods, reduce plastic waste. The system is easy to adapt to bespoke designs, with concept-to-prototype in a single day, offers significant cost savings to the users over commercial sources, and no loss in dimensional quality or reliability.

Additive Manufacturing of α-Amino Acid Based Poly(ester amide)s for Biomedical Applications

α-Amino acid based polyester amides (PEAs) are promising candidates for additive manufacturing (AM), as they unite the flexibility and degradability of polyesters and good thermomechanical properties of polyamides in one structure. Introducing α-amino acids in the PEA structure brings additional advantages such as (i) good cytocompatibility and biodegradability, (ii) providing strong amide bonds, enhancing the hydrogen-bonding network, (iii) the introduction of pendant reactive functional groups, and (iv) providing good cell-polymer interactions. However, the application of α-amino acid based PEAs for AM via fused deposition modeling (FDM), an important manufacturing technique with unique processing characteristics and requirements, is still lacking. With the aim to exploit the combination of these advantages in the creation, design, and function of additively manufactured scaffolds using FDM, we report the structure-function relationship of a series of α-amino acid based PEAs. The PEAs with three different molecular weights were synthesized via the active solution polycondensation, and their performance for AM applications was studied in comparison with a commercial biomedical grade copolymer of l-lactide and glycolide (PLGA). The PEAs, in addition to good thermal stability, showed semicrystalline behavior with proper mechanical properties, which were different depending on their molecular weight and crystallinity. They showed more ductility due to their lower glass transition temperature (T_g; 18-20 °C) compared with PLGA (57 °C). The rheology studies revealed that the end-capping of PEAs is of high importance for preventing cross-linking and further polymerization during the melt extrusion and for the steadiness and reproducibility of FDM. Furthermore, our data regarding the steady 3D printing performance, good polymer-cell interactions, and low cytotoxicity suggest that α-amino acid based PEAs can be introduced as favorable polymers for future AM applications in tissue engineering. In addition, their ability for formation of bonelike apatite in the simulated body fluid (SBF) indicates their potential for bone tissue engineering applications.

Environmental Microplastic Particles vs. Engineered Plastic Microparticles-A Comparative Review

Microplastic particles (MPs) pose a novel threat to nature. Despite being first noticed in the 1970s, research on this topic has only surged in recent years. Researchers have mainly focused on environmental plastic particles; however, studies with defined microplastic particles as the sample input are scarce. Furthermore, comparison of those studies indicates a discrepancy between the particles found (e.g., in the environment) and those used for further research (e.g., exposure studies). Obviously, it is important to use particles that resemble those found in the environment to conduct appropriate research. In this review, different categories of microplastic particles are addressed, before covering an overview of the most common separation and analysis methods for environmental MPs is covered. After showing that the particles found in the environment are mostly irregular and polydisperse, while those used in studies with plastic microparticles as samples are often not, different particle production techniques are investigated and suggestions for preparing realistic plastic particles are given.

Polylactic acid production from biotechnological routes: A review

Polylactic acid (PLA) has been highlighted as an important polymer due to its high potential for applicability in various areas, such as in the chemical, medical, pharmaceutical or biotechnology field. Very recently, studies have reported its use as a basic component for the production of personal protective equipment (PPE) required for the prevention of Sars-Cov-2 contamination, responsible for the cause of coronavirus disease, which is currently a major worldwide sanitary and social problem. PLA is considered a non-toxic, biodegradable and compostable plastic with interesting characteristics from the industrial point of view, and it emerges as a promising product under the concept of "green plastic", since most of the polymers produced currently are petroleum-based, a non-renewable raw material. Biotechnology routes have been mentioned as potential methodologies for the production of this polymer, especially by enzymatic routes, in particular by use of lipases enzymes. The availability of pure lactic acid isomers is a fundamental aspect of the manufacture of PLA with more interesting mechanical and thermal properties. Due to the technological importance that PLA-based polymers are acquiring, as well as their characteristics and applicability in several fields, especially medical, pharmaceutical and biotechnology, this review article sought to gather very recent information regarding the development of research in this area. The main highlight of this study is that it was carried out from a biotechnological point of view, aiming at a totally green bioplastic production, since the obtaining of lactic acid, which will be used as raw material for the PLA synthesis, until the degradation of the polymer obtained by biological routes.

Three dimensional printed nanostructure biomaterials for bone tissue engineering

The suffering from organ dysfunction due to damaged or diseased tissue/bone has been globally on the rise. Current treatment strategies for non-union bone defects include: the use of autografts, allografts, synthetic grafts and free vascularized fibular grafts. Bone tissue engineering has emerged as an alternative for fracture repair to satisfy the current unmet need of bone grafts and to alleviate the problems associated with autografts and allografts. The technology offers the possibility to induce new functional bone regeneration using synergistic combination of functional biomaterials (scaffolds), cells, and growth factors. Bone scaffolds are typically made of porous biodegradable materials that provide the mechanical support during repair and regeneration of damaged or diseased bone. Significant progress has been made towards scaffold materials for structural support, desired osteogenesis and angiogenesis abilities. Thanks for innovative scaffolds fabrication technologies, bioresorbable scaffolds with controlled porosity and tailored properties are possible today. Despite the presence of different bone scaffold fabrication methods, pore size, shape and interconnectivity have not yet been fully controlled in most of the methods. Moreover, scaffolds with tailored porosity for specific defects are still difficult to manufacture. Nevertheless, such scaffolds can be designed and fabricated using three dimensional (3D) printing approaches. 3D printing technology, as an advanced tissue scaffold fabrication method, offers the opportunity to produce complex geometries with distinct advantages. The technology has been used for the production of various types of bodily constructs such as blood vessels, vascular networks, bones, cartilages, exoskeletons, eyeglasses, cell cultures, tissues, organs and novel drug delivery devices. This review focuses on 3D printed scaffolds and their application in bone repair and regeneration. In addition, different classes of biomaterials commonly employed for the fabrication of 3D nano scaffolds for bone tissue engineering application so far are briefly discussed.

Evaluation of the Infill Design on the Tensile Response of 3D Printed Polylactic Acid Polymer

The current study explores the effects of geometrical shapes of the infills on the 3D printed polylactic acid (PLA) plastic on the tensile properties. For this purpose, by utilizing an accessible supply desktop printer, specimens of diamond, rectangular, and hexagonal infill patterns were produced using the fused filament fabrication (FFF) 3D printing technique. Additionally, solid samples were printed for comparison. The printed tensile test specimens were conducted at environmental temperature, Ta of 23 °C and crosshead speed, V_C.H of 5 mm/min. Mainly, this study focuses on investigating the percentage infill with respect to the cross-sectional area of the investigated samples. The mechanical properties, i.e., modulus of toughness, ultimate tensile stress, yield stress, and percent elongation, were explored for each sample having a different geometrical infill design. The test outcomes for each pattern were systematically compared. To further validate the experimental results, a computer simulation using finite element analysis was also performed and contrasted with the experimental tensile tests. The experimental results mainly suggested a brittle behavior for solidly infilled specimen, while rectangular, diamond, and hexagonal infill patterns showed ductile-like behavior (fine size and texture of infills). This brittleness may be due to the relatively higher infill density results that led to the high bonding adhesion of the printed layers, and the size and thickness effects of the solid substrate. It made the solidly infilled specimen structure denser and brittle. Among all structures, hexagon geometrical infill showed relative improvement in the mechanical properties (highest ultimate tensile stress and modulus values 1759.4 MPa and 57.74 MPa, respectively) compared with other geometrical infills. Therefore, the geometrical infill effects play an important role in selecting the suitable mechanical property's values in industrial applications.

3D printing and spine surgery

Rapid prototyping (RP), also known as three-dimensional printing (3DP), allows the rapid conversion of anatomical images into physical components by the use of special printers. This novel technology has also become a promising innovation for spine surgery. As a result of the developments in 3DP technology, production speeds have increased, and costs have decreased. This technological development can be used extensively in different parts of spine surgery such as preoperative planning, surgical simulations, patient-clinician communication, education, intraoperative guidance, and even implantable devices. However, similar to other emerging technologies, the usage of RP in spine surgery has various drawbacks that are needed to be addressed through further studies.

The Study of Physico-Mechanical Properties of Polylactide Composites with Different Level of Infill Produced by the FDM Method

The aim of this study was to evaluate the changes in physical-mechanical properties of the samples manufactured by 3D printing technology with the addition of varying degrees of polylactide (PLA) infill (50, 70, 85 and 100%). Half of the samples were soaked in physiological saline. The material used for the study was neat PLA, which was examined in terms of hydrolytic degradation, crystallization, mechanical strength, variability of properties at elevated temperatures, and dissipation of mechanical energy depending on the performed treatment. A significant impact of the amount of infill on changeable mechanical properties, such as hydrolytic degradation and crystallization was observed. The FDM printing method allows for waste-free production of light weight unit products with constant specyfic strength.

Printing-Based Assay and Therapy of Antioxidants

Antioxidants are essential in regulating various physiological functions and oxidative deterioration. Over the past decades, many researchers have paid attention to antioxidants and studied the screening of antioxidants from natural products and their utilization for treatments in diverse pathological conditions. Nowadays, as printing technology progresses, its influence in the field of biomedicine is growing significantly. The printing technology has many advantages. Especially, the capability of designing sophisticated platforms is useful to detect antioxidants in various samples. The high flexibility of 3D printing technology is advantageous to create geometries for customized patient treatment. Recently, there has been increasing use of antioxidant materials for this purpose. This review provides a comprehensive overview of recent advances in printing technology-based assays to detect antioxidants and 3D printing-based antioxidant therapy in the field of tissue engineering. This review is divided into two sections. The first section highlights colorimetric assays using the inkjet-printing methods and electrochemical assays using screen-printing techniques for the determination of antioxidants. Alternative screen-printing techniques, such as xurography, roller-pen writing, stamp contact printing, and laser-scribing, are described. The second section summarizes the recent literature that reports antioxidant-based therapy using 3D printing in skin therapeutics, tissue mimetic 3D cultures, and bone tissue engineering.

Rapid Fabrication of Anatomically-Shaped Bone Scaffolds Using Indirect 3D Printing and Perfusion Techniques

Fused deposit modeling (FDM) 3D printing technology cannot generate scaffolds with high porosity while maintaining good integrity, anatomical-surface detail, or high surface area-to-volume ratio (S/V). Solvent casting and particulate leaching (SCPL) technique generates scaffolds with high porosity and high S/V. However, it is challenging to generate complex-shaped scaffolds; and solvent, particle and residual water removal are time consuming. Here we report techniques surmounting these problems, successfully generating a highly porous scaffold with the anatomical-shape characteristics of a human femur by polylactic acid polymer (PLA) and PLA-hydroxyapatite (HA) casting and salt leaching. The mold is water soluble and is easily removable. By perfusing with ethanol, water, and dry air sequentially, the solvent, salt, and residual water were removed 20 fold faster than utilizing conventional methods. The porosities are uniform throughout the femoral shaped scaffold generated with PLA or PLA-HA. Both scaffolds demonstrated good biocompatibility with the pre-osteoblasts (MC3T3-E1) fully attaching to the scaffold within 8 h. The cells demonstrated high viability and proliferation throughout the entire time course. The HA-incorporated scaffolds demonstrated significantly higher compressive strength, modulus and osteoinductivity as evidenced by higher levels of alkaline-phosphatase activity and calcium deposition. When 3D printing a 3D model at 95% porosity or above, our technology preserves integrity and surface detail when compared with FDM-generated scaffolds. Our technology can also generate scaffolds with a 31 fold larger S/V than FDM. We have developed a technology that is a versatile tool in creating personalized, patient-specific bone graft scaffolds efficiently with high porosity, good scaffold integrity, high anatomical-shaped surface detail and large S/V.

Fabrication and functionalization of 3D-printed soft and hard scaffolds with growth factors for enhanced bioactivity

Strategies to improve the acceptance of scaffolds by the body is crucial in tissue engineering (TE) which requires tailoring of the pore structure, mechanical properties and surface characteristics of the scaffolds. In the current study we used a 3-dimensional (3D) printing technique to tailor the pore structure and mechanical properties of (i) nanocellulose based hydrogel scaffolds for soft tissue engineering and (ii) poly lactic acid (PLA) based scaffolds for hard tissue engineering in combination with surface treatment by protein conjugation for tuning the scaffold bioactivity. Dopamine coating of the scaffolds enhanced the hydrophilicity and their capability to bind bioactive molecules such as fibroblast growth factor (FGF-18) for soft TE scaffolds and arginyl glycyl aspartic acid (RGD) peptide for hard TE scaffolds, which was confirmed using MALDI-TOFs. This functionalization approach enhanced the performance of the scaffolds and provided antimicrobial activity indicating that these scaffolds can be used for cartilage or bone regeneration applications. Blood compatibility studies revealed that both the materials were compatible with human red blood cells. Significant enhancement of cell attachment and proliferation confirmed the bioactivity of growth factor functionalized 3D printed soft and hard tissues. This approach of combining 3D printing with biological tuning of the interface is expected to significantly advance the development of biomedical materials related to soft and hard tissue engineering.

3D printed scaffolds with tailored bioactivity using protein conjugation.

Recent progress in drug delivery

Drug delivery systems (DDS) are defined as methods by which drugs are delivered to desired tissues, organs, cells and subcellular organs for drug release and absorption through a variety of drug carriers. Its usual purpose to improve the pharmacological activities of therapeutic drugs and to overcome problems such as limited solubility, drug aggregation, low bioavailability, poor biodistribution, lack of selectivity, or to reduce the side effects of therapeutic drugs. During 2015-2018, significant progress in the research on drug delivery systems has been achieved along with advances in related fields, such as pharmaceutical sciences, material sciences and biomedical sciences. This review provides a concise overview of current progress in this research area through its focus on the delivery strategies, construction techniques and specific examples. It is a valuable reference for pharmaceutical scientists who want to learn more about the design of drug delivery systems.

3D printing of silk fibroin-based hybrid scaffold treated with platelet rich plasma for bone tissue engineering

3D printing/bioprinting are promising techniques to fabricate scaffolds with well controlled and patient-specific structures and architectures for bone tissue engineering. In this study, we developed a composite bioink consisting of silk fibroin (SF), gelatin (GEL), hyaluronic acid (HA), and tricalcium phosphate (TCP) and 3D bioprinted the silk fibroin-based hybrid scaffolds. The 3D bioprinted scaffolds with dual crosslinking were further treated with human platelet-rich plasma (PRP) to generate PRP coated scaffolds. Live/Dead and MTT assays demonstrated that PRP treatment could obviously promote the cell growth and proliferation of human adipose derived mesenchymal stem cells (HADMSC). In addition, the treatment of PRP did not significantly affect alkaline phosphatase (ALP) activity and expression, but significantly upregulated the gene expression levels of late osteogenic markers. This study demonstrated that the 3D printing of silk fibroin-based hybrid scaffolds, in combination with PRP post-treatment, might be a more efficient strategy to promote osteogenic differentiation of adult stem cells and has significant potential to be used for bone tissue engineering.

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3D printing technology was used to fabricate silk fibroin-based hybrid scaffold for bone tissue engineering.

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Human platelet-rich plasma (PRP) was obtained and implemented to treat 3D printed scaffolds.

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The PRP treated composite scaffold improved cell proliferation and increased late marker of osteogenic gene expression.

Furfuryl Alcohol and Lactic Acid Blends: Homo- or Co-Polymerization?

Furfuryl alcohol (FA) and lactic acid (LA) are two of the most interesting biomolecules, easily obtainable from sugars and hence extremely attractive for green chemistry solutions. These substances undergo homopolymerization and they have been rarely considered for copolymerization. Typically, FA homopolymerizes exothermically in an acid environment producing inhomogeneous porous materials, but recent studies have shown that this reaction can be controlled and therefore we have implemented this process to trigger the copolymerization with LA. The mechanical tests have shown that the blend containing small amount of FA were rigid and the fracture showed patterns more similar to the one of neat polyfurfuryl alcohol (PFA). This LA-rich blend exhibited higher chloroform and water resistances, while thermal analyses (TG and DSC) also indicated a higher furanic character than expected. These observations suggested an intimate interconnection between precursors which was highlighted by the presence of a small band in the ester region of the solid state 13C-NMR, even if the FT-IR did not evidence any new signal. These studies show that these bioplastics are basically constituted of PLA and PFA homopolymers with some small portion of covalent bonds between the two moieties.

[3D-printing in trauma surgery : Planning, printing and processing]

Possible use of 3D-printing technology in orthopedic surgery ranges from preoperative planning to dedicated counselling with patients by the use of individual 3D models, intraoperative surgery tools or implants and various other applications. This article describes a technique for the creation of intraoperative tools with which the process from computed tomography (CT) images to 3D-printed tools in trauma surgery can safely be administered. For segmentation of CT images a range of different software options is available. The standard triangulation file created in this way (file ending: .stl) must subsequently be post-processed. By the use of the digital casts from bone and fractures in computer-aided design (CAD) programs implants and patient individual tools are created, which can range from ortheses to protheses to intraoperative saw guides.

Three-dimensional printing with biomaterials in craniofacial and dental tissue engineering

With the development of technology, tissue engineering (TE) has been widely applied in the medical field. In recent years, due to its accuracy and the demands of solid freeform fabrication in TE, three-dimensional printing, also known as additive manufacturing (AM), has been applied for biological scaffold fabrication in craniofacial and dental regeneration. In this review, we have compared several types of AM techniques and summarized their advantages and limitations. The range of printable materials used in craniofacial and dental tissue includes all the biomaterials. Thus, basic and clinical studies were discussed in this review to present the application of AM techniques in craniofacial and dental tissue and their advances during these years, which might provide information for further AM studies in craniofacial and dental TE.

Emerging Trends in Information-Driven Engineering of Complex Biological Systems

Synthetic biological systems are used for a myriad of applications, including tissue engineered constructs for in vivo use and microengineered devices for in vitro testing. Recent advances in engineering complex biological systems have been fueled by opportunities arising from the combination of bioinspired materials with biological and computational tools. Driven by the availability of large datasets in the "omics" era of biology, the design of the next generation of tissue equivalents will have to integrate information from single-cell behavior to whole organ architecture. Herein, recent trends in combining multiscale processes to enable the design of the next generation of biomaterials are discussed. Any successful microprocessing pipeline must be able to integrate hierarchical sets of information to capture key aspects of functional tissue equivalents. Micro- and biofabrication techniques that facilitate hierarchical control as well as emerging polymer candidates used in these technologies are also reviewed.

Personalized Design of Functional Gradient Bone Tissue Engineering Scaffold

The porous structure of the natural bone not only has the characteristics of lightweight and high strength, but also is conducive to the growth of cells and tissues due to interconnected pores. In this paper, a novel gradient-controlled parametric modeling technology is presented to design bone tissue engineering (BTE) scaffold. First of all, the method functionalizes the pore distribution in the bone tissue, and reconstructs the pore distribution of the bone tissue in combination with the pathological analysis of the bone defect area of the individual patient. Then, based on the reconstructed pore distribution, the Voronoi segmentation algorithm and the contour interface optimization method are used to reconstruct the whole model of the bone tissue. Finally, the mechanical properties of the scaffold are studied by the finite element analysis (FEA) of different density gradient scaffolds. The results show that the method is highly feasible. BTE scaffold can be designed by irregular design methods and adjustment of pore distribution parameters, which is similar with natural bone in structural characteristics and biomechanical properties.

Engineering Novel Lab Devices Using 3D Printing and Microcontrollers

The application of 3D printing and microcontrollers allows users to rapidly engineer novel hardware solutions useful in a laboratory environment. 3D printing is transformative as it enables the rapid fabrication of adapters, housings, jigs, and small structural elements. Microcontrollers allow for the creation of simple, inexpensive machines that receive input from one or more sensors to trigger a mechanical or electrical output. Bringing these technologies together, we have developed custom solutions that improve capabilities and reduce costs, errors, and human intervention. In this article, we describe three devices: JetLid, TipWaster, and Remote Monitoring Device (REMIND). JetLid employs a microcontroller and presence sensor to trigger a high-speed fan that reliably de-lids microtiter plates on a high-throughput screening system. TipWaster uses a presence sensor to activate an active tip waste chute when tips are ejected from a pipetting head. REMIND is a wireless, networked lab monitoring device. In its current implementation, it monitors the liquid level of waste collection vessels or bulk liquid reagent containers. The modularity of this device makes adaptation to other sensors (temperature, humidity, light/darkness, movement, etc.) relatively simple. These three devices illustrate how 3D printing and microcontrollers have enabled the process of rapidly turning ideas into useful devices.

Development of a Flow Evolution Network Model for the Stress-Strain Behavior of Poly(L-lactide)

Computational modeling is critical to medical device development and has grown in its utility for predicting device performance. Additionally, there is an increasing trend to use absorbable polymers for the manufacturing of medical devices. However, computational modeling of absorbable devices is hampered by a lack of appropriate constitutive models that capture their viscoelasticity and postyield behavior. The objective of this study was to develop a constitutive model that incorporated viscoplasticity for a common medical absorbable polymer. Microtensile bars of poly(L-lactide) (PLLA) were studied experimentally to evaluate their monotonic, cyclic, unloading, and relaxation behavior as well as rate dependencies under physiological conditions. The data were then fit to a viscoplastic flow evolution network (FEN) constitutive model. PLLA exhibited rate-dependent stress-strain behavior with significant postyield softening and stress relaxation. The FEN model was able to capture these relevant mechanical behaviors well with high accuracy. In addition, the suitability of the FEN model for predicting the stress-strain behavior of PLLA medical devices was investigated using finite element (FE) simulations of nonstandard geometries. The nonstandard geometries chosen were representative of generic PLLA cardiovascular stent subunits. These finite element simulations demonstrated that modeling PLLA using the FEN constitutive relationship accurately reproduced the specimen's force-displacement curve, and therefore, is a suitable relationship to use when simulating stress distribution in PLLA medical devices. This study demonstrates the utility of an advanced constitutive model that incorporates viscoplasticity for simulating PLLA mechanical behavior.

3D printing for drug manufacturing: A perspective on the future of pharmaceuticals

Since a three-dimensional (3D) printed drug was first approved by the Food and Drug Administration in 2015, there has been a growing interest in 3D printing for drug manufacturing. There are multiple 3D printing methods - including selective laser sintering, binder deposition, stereolithography, inkjet printing, extrusion-based printing, and fused deposition modeling - which are compatible with printing drug products, in addition to both polymer filaments and hydrogels as materials for drug carriers. We see the adaptability of 3D printing as a revolutionary force in the pharmaceutical industry. Release characteristics of drugs may be controlled by complex 3D printed geometries and architectures. Precise and unique doses can be engineered and fabricated via 3D printing according to individual prescriptions. On-demand printing of drug products can be implemented for drugs with limited shelf life or for patient-specific medications, offering an alternative to traditional compounding pharmacies. For these reasons, 3D printing for drug manufacturing is the future of pharmaceuticals, making personalized medicine possible while also transforming pharmacies.

Progress in Integrative Biomaterial Systems to Approach Three-Dimensional Cell Mechanotransduction

Mechanotransduction between cells and the extracellular matrix regulates major cellular functions in physiological and pathological situations. The effect of mechanical cues on biochemical signaling triggered by cell-matrix and cell-cell interactions on model biomimetic surfaces has been extensively investigated by a combination of fabrication, biophysical, and biological methods. To simulate the in vivo physiological microenvironment in vitro, three dimensional (3D) microstructures with tailored bio-functionality have been fabricated on substrates of various materials. However, less attention has been paid to the design of 3D biomaterial systems with geometric variances, such as the possession of precise micro-features and/or bio-sensing elements for probing the mechanical responses of cells to the external microenvironment. Such precisely engineered 3D model experimental platforms pave the way for studying the mechanotransduction of multicellular aggregates under controlled geometric and mechanical parameters. Concurrently with the progress in 3D biomaterial fabrication, cell traction force microscopy (CTFM) developed in the field of cell biophysics has emerged as a highly sensitive technique for probing the mechanical stresses exerted by cells onto the opposing deformable surface. In the current work, we first review the recent advances in the fabrication of 3D micropatterned biomaterials which enable the seamless integration with experimental cell mechanics in a controlled 3D microenvironment. Then, we discuss the role of collective cell-cell interactions in the mechanotransduction of engineered tissue equivalents determined by such integrative biomaterial systems under simulated physiological conditions.

Polymers for 3D Printing and Customized Additive Manufacturing

Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting. The range of polymers used in AM encompasses thermoplastics, thermosets, elastomers, hydrogels, functional polymers, polymer blends, composites, and biological systems. Aspects of polymer design, additives, and processing parameters as they relate to enhancing build speed and improving accuracy, functionality, surface finish, stability, mechanical properties, and porosity are addressed. Selected applications demonstrate how polymer-based AM is being exploited in lightweight engineering, architecture, food processing, optics, energy technology, dentistry, drug delivery, and personalized medicine. Unparalleled by metals and ceramics, polymer-based AM plays a key role in the emerging AM of advanced multifunctional and multimaterial systems including living biological systems as well as life-like synthetic systems.

Improving the trajectory of transpedicular transdiscal lumbar screw fixation with a computer-assisted 3D-printed custom drill guide

Transpedicular transdiscal screw fixation is an alternative technique used in lumbar spine fixation; however, it requires an accurate screw trajectory. The aim of this study is to design a novel 3D-printed custom drill guide and investigate its accuracy to guide the trajectory of transpedicular transdiscal (TPTD) lumbar screw fixation. Dicom images of thirty lumbar functional segment units (FSU, two segments) of L1-L4 were acquired from the PACS system in our hospital (patients who underwent a CT scan for other abdomen diseases and had normal spine anatomy) and imported into reverse design software for three-dimensional reconstructions. Images were used to print the 3D lumbar models and were imported into CAD software to design an optimal TPTD screw trajectory and a matched custom drill guide. After both the 3D printed FSU models and 3D-printed custom drill guide were prepared, the TPTD screws will be guided with a 3D-printed custom drill guide and introduced into the 3D printed FSU models. No significant statistical difference in screw trajectory angles was observed between the digital model and the 3D-printed model (P > 0.05). Our present study found that, with the help of CAD software, it is feasible to design a TPTD screw custom drill guide that could guide the accurate TPTD screw trajectory on 3D-printed lumbar models.

In Vitro Biocompatibility, Radiopacity, and Physical Property Tests of Nano-Fe₃O₄ Incorporated Poly-l-lactide Bone Screws

The aim of this study was to fabricate biodegradable poly-l-lactic acid (PLLA) bone screws containing iron oxide (Fe₃O₄) nanoparticles, which are radiopaque and 3D-printable. The PLLA composites were fabricated by loading 20%, 30%, and 40% Fe₃O₄ nanoparticles into the PLLA. The physical properties, including elastic modulus, thermal properties, and biocompatibility of the composites were tested. The 20% nano-Fe₃O₄/PLLA composite was used as the material for fabricating the 3D-printed bone screws. The mechanical performance of the nano-Fe₃O₄/PLLA bone screws was evaluated by anti-bending and anti-torque strength tests. The tissue response and radiopacity of the nano-Fe₃O₄/PLLA bone screws were assessed by histologic and CT imaging studies using an animal model. The addition of nano-Fe₃O₄ increased the crystallization of the PLLA composites. Furthermore, the 20% nano-Fe₃O₄/PLLA composite exhibited the highest thermal stability compared to the other Fe₃O₄ proportions. The 3D-printed bone screws using the 20% nano-Fe₃O₄/PLLA composite provided excellent local tissue response. In addition, the radiopacity of the 20% nano-Fe₃O₄/PLLA screw was significantly better compared with the neat PLLA screw.

Layer-by-layer bioassembly of cellularized polylactic acid porous membranes for bone tissue engineering

The conventional tissue engineering is based on seeding of macroporous scaffold on its surface ("top-down" approach). The main limitation is poor cell viability in the middle of the scaffold due to poor diffusion of oxygen and nutrients and insufficient vascularization. Layer-by-Layer (LBL) bioassembly is based on "bottom-up" approach, which considers assembly of small cellularized blocks. The aim of this work was to evaluate proliferation and differentiation of human bone marrow stromal cells (HBMSCs) and endothelial progenitor cells (EPCs) in two and three dimensions (2D, 3D) using a LBL assembly of polylactic acid (PLA) scaffolds fabricated by 3D printing. 2D experiments have shown maintain of cell viability on PLA, especially when a co-cuture system was used, as well as adequate morphology of seeded cells. Early osteoblastic and endothelial differentiations were observed and cell proliferation was increased after 7 days of culture. In 3D, cell migration was observed between layers of LBL constructs, as well as an osteoblastic differentiation. These results indicate that LBL assembly of PLA layers could be suitable for BTE, in order to promote homogenous cell distribution inside the scaffold and gene expression specific to the cells implanted in the case of co-culture system.