Dosimetric assessment of the impact of low-cost materials used in stereolithography in high-dose-rate brachytherapy

PURPOSE

3D printing has become a popular and widely available technique of rapid prototyping. The impact of used materials on the dose distribution has been studied for high energy sources. However, brachytherapy sources emit lower energy photons, and materials used in 3D printing may differ. This study was conducted to analyze the influence of common materials (polylactic acid - PLA and acrylonitrile butadiene styrene - ABS) used in stereolithography.

MATERIAL AND METHODS

A 3D-printed phantom was designed, printed, and used to calibrate Gafchromic films. In the next step, a range of 1 mm thick plates of PLA and ABS (from zero to thirty) were inserted between source and detector to measure the impact of studied materials on delivered dose. Measurements were performed using a calibrated radiochromic film and Farmer ionization chamber in water.

RESULTS

No statistically significant correlation (p = 0.4854) between the thickness of inserted PLA and the dose delivered to the film was obtained. With ionization chamber, Spearman's rank order test showed a significant correlation (p = 0.00004); however, the correlation was found weak. In case of ABS measurement, a statistically significant (p = 0.0159), yet weak negative correlation was found between the thickness of used material and the dose delivered to the film. On the other hand, a weak statistically significant (p = 0.0212) but positive correlation was found when the dose was measured with Farmer ionization chamber. We find these correlations false, as all measured doses were within the measurement uncertainty range (film ±8.0%, Farmer ±8.8%) from 100% of the prescribed dose.

CONCLUSIONS

According to obtained results, with the accuracy of measurement under clinical conditions, the impact of highly filled PLA and ABS printed objects on the dose distribution from an 192Ir source in water can be omitted.

Rotating Bending Fatigue Analysis of Printed Specimens from Assorted Polymer Materials

Fused filament fabrication (FFF), as a form of additive manufacturing (AM), in recent years, has become a popular method to manufacture prototypes, as well as functional parts. FFF is an extrusion process, commonly known as 3D printing, where the object is built by depositing melted material layer by layer. The most common materials, i.e., the materials that are most widely used, are polylactic acid (PLA), acrylonitrile butadiene styrene (ABS) and acrylonitrile styrene acrylate (ASA). Although there are lot of research papers that cover the subject of the determination of mechanical properties and characteristics, theoretically and experimentally, as well as the fatigue characteristics of aforementioned materials, there is a lack of research and scientific papers dealing with the problematics of S–N curves based on the rotating bending fatigue analysis of those materials. Consequently, this paper covers the topic of rotating bending fatigue data for 3D printed specimens of given materials, under different loading values.

3D-printed suture guide for thoracic and cardiovascular surgery produced during the COVID19 pandemic

Emergency 3D-printing of medical devices came out as a potential solution to tackle shortages during the COVID-19 pandemic. Manufacturing medical devices in small series within hospitals is an exciting perspective in crisis management. Health professionals and additive manufacturing technology are ready for this revolution but regulative adaptations are still required. Here we present the design and production of a suture guide for cardiac surgery as a case study for a 3D-printed medical device manufactured during the COVID-19 pandemic.

3D-printed shields for slit lamps produced during the COVID-19 pandemic

Additive manufacturing has been extensively used during the COVID-19 pandemic to design and produce protection equipment. During clinical examinations using slit lamps, ophthalmologists are at risk of being contaminated by the SARS-CoV-2 virus, and the device itself is exposed to viral contamination. Several solutions have already been proposed for fixing transparent shields on the physician side. Here we propose a 3D-printed device fixed on the chin rest on the patient side, aiming at limiting viral spread both on the lamp itself and towards the physician.

Recommendations for simulating and measuring with biofabricated lung equivalent materials based on atomic composition analysis

Monte Carlo simulations of lung equivalent materials often involve the density being artificially lowered rather than a true lung tissue (or equivalent plastic) and air composition being simulated. This study used atomic composition analysis to test the suitability of this method. Atomic composition analysis was also used to test the suitability of 3D printing PLA or ABS with air to simulate lung tissue. It was found that there was minimal atomic composition difference when using an artificially lowered density, with a 0.8 % difference in Nitrogen the largest observed. Therefore, excluding infill pattern effects, lowering the density of the lung tissue (or plastic) in simulations should be sufficiently accurate to simulate an inhaled lung, without the need to explicitly include the air component. The average electron density of 3D printed PLA and air, and ABS and air were just 0.3 % and 1.3 % different to inhaled lung, confirming their adequacy for MV photon dosimetry. However large average atomic number differences (5.6 % and 20.4 % respectively) mean that they are unlikely to be suitable for kV photon dosimetry.

Amniotic band syndrome associated with limited dorsal myeloschisis: a case report of an unusual case and review of the literature

Amniotic band syndrome (ABS) has been known since ancient times. Descriptions in modern medicine have occurred since the mid-nineteenth century. The association of the amniotic band syndrome with tethered cord is rare. It was generally thought to be incompatible with life. Of late, with better imaging, there have been case reports of amniotic bands causing cord tethering in neurosurgical literature, but its association with limited dorsal myeloschisis has hitherto not been described. We report a case of amniotic band syndrome (ABS) associated with a cervical limited dorsal myeloschisis (LDM) in a child of 2 and a half years old. The management of LDM in ABS is essentially the same as in isolated cases.

Thermoplastic Polymers with Nanosilver Addition-Microstructural, Surface and Mechanical Evaluation during a 36-Month Deionized Water Incubation Period

Three types of thermoplastic polymers, acrylonitrile butadiene styrene (ABS), polymethyl methacrylate acrylic (PMMA) and high-density polyethylene (HDPE), were enriched with silver nanoparticles (AgNPs) of 0.5 wt.% and 1.0 wt.%, respectively. The polymers and the composites were manufactured via injection molding. Regarding the potential of these polymers as matrices for long-term use as biomaterials, the aim of this study was to examine their stability in the in vitro conditions during a three-year incubation period in deionized water. In this work, microstructural observations were performed, and mechanical properties were assessed. Surface parameters, such as roughness and contact angle, were comprehensively investigated. The microstructural evaluation showed that the silver additive was homogeneously dispersed in all the examined matrices. The 36-month immersion period indicated no microstructural changes and proved the composites’ stability. The mechanical tests confirmed that the composites retained comparable mechanical properties after the silver incorporation. The Young’s modulus and tensile strength increased during long-term incubation. The addition of silver nanoparticles did not alter the composites’ roughness. The contact angle increased with the rising AgNP content. It was also shown that the materials’ roughness increased with the incubation time, especially for the ABS- and HDPE-based materials. The water environment conditions improved the wettability of the tested materials. However, the silver nanoparticles’ content resulted in the contact angle decreasing during incubation. The conducted studies confirmed that the mechanical properties of all the polymers and composites did not deteriorate; thus, the materials may be considered stable and applicable for long-term working periods in aqueous environments.

Print Velocity Effects on Strain-Rate Sensitivity of Acrylonitrile-Butadiene-Styrene Using Material Extrusion Additive Manufacturing

The strain-rate sensitivity of the yield stress for Acrylonitrile-Butadiene-Styrene (ABS) tensile samples processed via material extrusion additive manufacturing (ME-AM) was investigated. Such specimens show molecular orientation and interstitial voids that affect the mechanical properties. Apparent densities were measured to compensate for the interstitial voids. Three different printing speeds were used to generate ME-AM tensile test samples with different molecular orientation. Printing velocities influenced molecular orientation and stretch, as determined from thermal shrinkage measurements. Likewise, infill velocity affected the strain-rate dependence of the yield stress. The ABS material manifests thermorheollogically simple behavior that can correctly be described by an Eyring flow rule. The changing activation volume, as a result of a varying print velocity, scales linearly with the molecular orientation, as captured in an estimated processing-induced pre-strain. Therefore, it is suggested that ME-AM processed ABS shows a deformation-dependent activation volume. This paper can be seen as initial work that can help to improve quantitative predictive numerical tools for ME-AM, taking into account the effects that the processing step has on the mechanical properties.

Detailed Thermal Characterization of Acrylonitrile Butadiene Styrene and Polylactic Acid Based Carbon Composites Used in Additive Manufacturing

Currently, 3D printing is an affordable technology for industry, healthcare, and individuals. Understanding the mechanical properties and thermoplastic behaviour of the composites is critical for the users. Our results give guidance for certain target groups including professionals in the field of additive manufacturing for biomedical components with in-depth characterisation of the examined commercially available ABS and PLA carbon-based composites. The study aimed to characterize these materials in terms of thermal behaviour and structure. The result of the heating-cooling loops is the thermal hysteresis effect of Ohmic resistance with its accommodation property in the temperature range of 20–84 °C for ESD-ABS and 20–72 °C for ESD-PLA. DSC-TGA measurements showed that the carbon content of the examined ESD samples is ~10–20% (m/m) and there is no significant difference in the thermodynamic behaviour of the basic ABS/PLA samples and their ESD compounds within the temperature range typically used for 3D printing. The results support the detailed design process of 3D-printed electrical components and prove that ABS and PLA carbon composites are suitable for prototyping and the production of biomedical sensors.

Characterization of contemporary and historical acrylonitrile butadiene styrene (ABS)-based objects: Pilot study for handheld Raman analysis in collections

Plastic materials are increasingly becoming part of private and public collections worldwide, either as design objects or artistic sculptures. The preservation of these highly degradable materials requires novel analytical approaches able to reveal their chemical composition to inform the tailoring of appropriate conservation procedures. In this work Raman spectroscopy and Surface-enhanced Raman Scattering (SERS) were proposed as methods for the characterization of ABS-based contemporary and historical LEGO® objects. Twenty-three objects of twelve different colors were analyzed by handheld and benchtop Raman instrumentation. In all cases clear identification of the constituent polymer matrices (ABS, polycarbonate, poly(methyl metacrylate)) was obtained. In addition, identification of major color components was achieved, such as copper phthalocyanines in green and blue objects. Low cost handheld instrumentation provided acceptable sensitivity towards polymers and coloring media, and was found suitable for initial screening of the objects. Benchtop Raman was used to confirm and further extend identification, as well as for building background information. Finally, SERS sensitivity was found comparable to the sensitivity achieved by benchtop Raman instrumentation. However, the associated minimally-invasive sampling method made SERS a valid alternative to direct Raman spectroscopy for the analysis of immovable and/or large-sized objects. Overall, this work represents the first systematic investigation on the potential of Raman and SERS spectroscopies as methods for minimal invasive and/or in situ analysis of historical and contemporary plastic objects.

3D printing goes greener: Study of the properties of post-consumer recycled polymers for the manufacturing of engineering components

This study concerns the evaluation of several properties/characteristics of 3D printed poly(lactic acid) (PLA) polymer and acrylonitrile-butadienestyrene (ABS) copolymer, recycled from food packages and car dashboards, respectively. The aim is to evaluate the potential of recycled polymers that are recovered from solid polymer waste (SPW) to be reused for functional components/parts for add-value applications. The study compared the performance of the recycled material with the obtained from the 3D printing of virgin polymer. The characterization was made considering the chemical, thermal and mechanical properties as well as surface roughness and wettability. Although the thermal characterization did not indicate significant variations between recycled and virgin material, the mechanical recycling process induced some chain scission in PLA. Consequently, the semi-crystalline polymer revealed losses of 33% both in tensile stress and flexural strength. On the contrary, recycled ABS did not show changes in the mechanical properties of the printed specimens. Both recycled polymers produced smoother surfaces with a decrease of the mean surface roughness between 55% and 65%. Considering the properties required by manufacturers of food containers and car dashboards, this study indicates that recycled materials can be reused for the same applications.

Taguchi S/N and TOPSIS Based Optimization of Fused Deposition Modelling and Vapor Finishing Process for Manufacturing of ABS Plastic Parts

Despite several additive manufacturing techniques are commercially available in market, Fused Deposition Modeling (FDM) is increasingly used by researchers and engineers for new product development. FDM is an established process with a plethora of advantages, but the visible surface roughness (SR), being an intrinsic limitation, is major barrier against utilization of fabricated parts for practical applications. In the present study, the chemical finishing method, using vapour of acetone mixed with heated air, is being used. The combined impact of orientation angle, finishing temperature and finishing time has been studied using Taguchi and ANOVA, whereas multi-criteria optimization is performed using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). The surface finish was highly responsive to increase in temperature while orientation angle of 0° yielded maximum strength; increase in finishing time led to weight gain of FDM parts. As the temperature increases, the percentage change in surface roughness increases as higher temperature assists the melt down process. On the other hand, anisotropic behaviour plays a major role during tensile testing. The Signal-to-noise (S/N) ratio plots, and ANOVA results indicated that surface finish is directly proportionate to finishing time because a longer exposure results in complete layer reflowing and settlement.

The American Brachytherapy Society prostate brachytherapy LDR/HDR simulation workshops: Hands-on, step-by-step training in the process of quality assurance

PURPOSE

Education and training on prostate brachytherapy for radiation oncology and medical physics residents in the United States is inadequate, resulting in fewer competent radiation oncology personnel to perform implants, and is a factor in the subsequent decline of an important, potentially curative cancer treatment modality for patients with cancer. The American Brachytherapy Society (ABS) leadership has recognized the need to establish a sustainable medical simulation low-dose-rate (LDR) and high-dose-rate (HDR) brachytherapy workshop program that includes physician-physicist teams to rapidly translate knowledge to establish high-quality brachytherapy programs.

METHODS

The ABS, in partnership with industry and academia, has held three radiation oncology team-based LDR/HDR workshops composed of physician-physicist teams in Chicago in 2017, in Houston in 2018, and in Denver in 2019. The predefined key metric of success is the number of attendees who returned to their respective institutions and were actively performing brachytherapy within 6 months of the prostate brachytherapy workshop.

RESULTS

Of the 111 physician/physicist teams participating in the Chicago, Houston, and Denver prostate brachytherapy workshops, 87 (78%) were actively performing prostate brachytherapy (51 [59%] HDR and 65 [75%] LDR).

CONCLUSIONS

The ABS prostate brachytherapy LDR/HDR simulation workshop has provided a successful education and training structure for medical simulation of the critical procedural steps in quality assurance to shorten the learning curve for delivering consistently high-quality brachytherapy implants for patients with prostate cancer. An ABS initiative, intended to bend the negative slope of the brachytherapy curve, is currently underway to train 300 new competent brachytherapy teams over the next 10 years.

Probing Protein Conformation Destabilization in Sterile Liquid Formulations through the Formation of 3,4-Dihydroxyphenylalanine

This work demonstrates the use of a fluorescent probe to screen protein conformational changes in mixtures of monoclonal antibodies and determine the region of where such changes may originate through a footprinting mass spectrometry approach. The oxidative stress of mixtures of two different immunoglobulins (IgG1, IgG2, or IgG4) performed in the presence of 2,2'-azobis(2-amidinopropane dihydrochloride) results in sequence-specific tyrosine oxidation reactions depending on the time of incubation of the IgG molecules and the nature of the excipients present in the formulation. The combination of a fluorescence assay, based on the detection of 3,4-dihydroxyphenylalanine (DOPA) and mass spectrometry analyses, permits the identification of protein conformation changes. In a mixture of IgG2 and IgG4, a destabilization of IgG4 in the presence of IgG2 is observed. The destabilized region involves the Fab region of IgG4 between Tyr63 and Tyr81 and potentially multiple regions of IgG2.

The ABS brachytherapy schools

The American Brachytherapy Society brachytherapy schools have been pivotal in teaching and evolving the art of brachytherapy over the past decades. Founded in 1995, the schools have consistently provided content for the major disease sites including gynecologic, prostate, and breast with ocular, vascular, head and neck, pediatric, intraluminal, systemic, and intraoperative approaches more selectively addressed. In addition, Physics schools, either coupled with clinical schools or as stand-alone venues, have provided an essential educational component for practicing physicists, a pivotal part of the brachytherapy team. Celebrating 25 years in existence, this historical overview of the American Brachytherapy Society brachytherapy schools is a tribute to the many teachers who have shared their expertise, to the many students who have been enthusiastic and interactive participants, and the staff who have made it all possible, with the reward of perpetuating the important and timely art of brachytherapy.

An explorative study of polymers for 3D printing of bioanalytical test systems

BACKGROUND

The 3D printing is relevant as a manufacturing technology of functional models for forensic, pharmaceutical and bioanalytical applications such as drug delivery systems, sample preparation and point-of-care tests.

OBJECTIVE

Melting behavior and autofluorescence of materials are decisive for optimal printing and applicability of the product which are influenced by varying unknown additives.

METHODS

We have produced devices for bioanalytical applications from commercially available thermoplastic polymers using a melt-layer process. We characterized them by differential scanning calorimetry, fluorescence spectroscopy and functional assays (DNA capture assay, model for cell adhesion, bacterial adhesion and biofilm formation test).

RESULTS

From 14 tested colored, transparent and black materials we found only deep black acrylonitrile-butadiene-styrene (ABS) and some black polylactic acid (PLA) useable for fluorescence-based assays, with low autofluorescence only in the short-wave range of 300-400 nm. PLA was suitable for standard bioanalytical purposes due to a glass transition temperature of approximately 60°C, resistance to common laboratory chemicals and easy print processing. For temperature-critical methods, such as hybridization reactions up to 90°C, ABS was better suited.

CONCLUSIONS

Autofluorescence was not a disadvantage per se but can also be used as a reference signal in assays. The rapid development of individual protocols for sample processing and analysis required the availability of a material with consistent quality over time. For fluorescence-based assays, the use of commercial standard materials did not seem to meet this requirement.

Anatomy-based diagnostic criteria for complex body wall anomalies (CBWA)

BACKGROUND

Precise diagnosis and classification of CBWA cases can be challenging. BSA are considered when there is a body wall anomaly, skeletal abnormalities, and the umbilical cord is anomalous, absent or rudimentary, and LBWC when there is a body wall and structural limb anomalies with or without craniofacial abnormalities.

METHODS

PubMed was searched for body stalk anomalies, limb body wall complex, body stalk anomalies and amniotic band syndrome, and limb body wall complex and amniotic band syndrome. Sixty nine articles were selected and reviewed. This article systematically classifies the variants of CBWA in 218 cases, the study is based on the embryological and anatomical criteria established by Martín-Alguacil and Avedillo to study BSA in the pig.

RESULTS

Eight different BSA presentation were defined. One hundred and eighty nine cases were classified as BSA, from which five were Type I, nine Type II, 20 Type III, 57 Type IV, 11Type V, 24 Type VI, 11 Type VII, and 52 Type VIII. Twenty six cases presented cranial phenotype, 114 abdominal phenotype, 42 cranio/abdominal overlapping phenotype, and five without defined phenotype. In addition, 52 BSA cases presented some kind of spinal dysraphism (SPDYS) and were classified as BSA/SPDYS, most of these cases did not show structural limb anomalies, except for three cases and were classified as LBWC/SPDYS.

CONCLUSION

This morphology-based classification represents a useful tool for clinical diagnosis, it helps to quantify and to evaluate CBWA in a precise, objective manner.

The Analysis of 3D Printer Dust for Forensic Applications,

3D printers are becoming increasingly efficient and economical, and thus more widespread and easily accessible to consumers and businesses. They have been used to print nefarious objects such as guns and suppressors. Previous research has documented the release of dust particles during the printing process; however, little has been written about the morphology and chemical features that define the dust emitted by these printers. This study was undertaken to recover, analyze, and identify the dust produced during the printing process in the context of forensic trace evidence analysis. Samples were collected from a variety of 3D fused deposition modeler printers, representing both consumer and commercial grade models. This work focused on printers that use thermoplastic filaments composed of acrylonitrile butadiene styrene (ABS) or polylactic acid (PLA), two of the most commonly used filament polymers. Swabs were used to collect dust within the printer chamber and then processed to isolate the dust particles. Particles produced from ABS filaments are most easily recognized via light microscopy through a combination of color, morphology, and fluorescence. The composition of these particles can be confirmed through analysis by either FTIR or Raman microspectroscopy. These methods can also be used to identify ABS fillers and pigments within the printer dust particles. In contrast, dust from PLA printers consistently contained finer, submicron-sized particles that could be observed by field emission scanning electron microscopy. Because the size of the particles precludes their identification using vibrational spectroscopy methods, pyrolysis-GC-MS was used to confirm the presence of PLA.

A review of the manufacturing process and infection rate of 3D-printed models and guides sterilized by hydrogen peroxide plasma and utilized intra-operatively

3D printing in the context of medical application can allow for visualization of patient-specific anatomy to facilitate surgical planning and execution. Intra-operative usage of models and guides allows for real time feedback but ensuring sterility is essential to prevent infection. The additive manufacturing process restricts options for sterilisation owing to temperature sensitivity of thermoplastics utilised for fabrication. Here, we review one of the largest single cohorts of 3D models and guides constructed from Acrylonitrile butadiene styrene (ABS) and utilized intra-operatively, following terminal sterilization with hydrogen peroxide plasma. We describe our work flow from initial software rendering to printing, sterilization, and on-table application with the objective of demonstrating that our process is safe and can be implemented elsewhere. Overall, 7% (8/114 patients) of patients developed a surgical site infection, which was not elevated in comparison to related studies utilizing traditional surgical methods. Prolonged operation time with an associated increase in surgical complexity was identified to be a risk factor for infection. Low temperature plasma-based sterilization depends upon sufficient permeation and contact with surfaces which are a particular challenge when our 3D-printouts contain diffusion-restricted luminal spaces as well as hollows. Application of printouts as guides for power tools may further expose these regions to sterile bodily tissues and result in generation of debris. With each printout being a bespoke medical device, it is important that the multidisciplinary team involved in production and application understand potential pitfalls to ensuring sterility as to minimize infection risk.

Influence of Manufacturing Parameters and Post Processing on the Electrical Conductivity of Extrusion-Based 3D Printed Nanocomposite Parts

The influence of manufacturing parameters of filament extrusion and extrusion-based Additive Manufacturing (AM), as well as different post processing techniques, on the electrical conductivity of 3D printed parts of graphene nanoplatelets (GNP)-reinforced acrylonitrile butadiene styrene (ABS) has been analyzed. The key role of the manufacturing parameters to obtain electrically conductive filaments and 3D printed parts has been demonstrated. Results have shown that an increase in extrusion speed, as well as lower land lengths, induces higher extrudate swelling, with the consequent reduction of the electrical conductivity. Additionally, filaments with lower diameter values, which result in a higher surface-to-cross-section ratio, have considerably lower electrical conductivities. These factors tune the values of the volume and surface electrical conductivity between 10^-4-10⁰ S/m and 10^-8-10^-3 S/sq, respectively. The volume and surface electrical conductivity considerably diminished after 3D printing. They increased when using higher printing layer thickness and width and were ranging between 10^-7-10^-4 S/m and 10^-8-10^-5 S/sq, respectively. This is attributed to the higher cross section area of the individual printed lines. The effect of different post processing (acetone vapor polishing, plasma and neosanding, which is a novel finishing process) on 3D printed parts in morphology and surface electrical conductivity was also analyzed.

Development of recycled blends based on cables and wires with plastic cabinets: An effective solution for value addition of hazardous waste plastics

The recycling of polyvinyl chloride (PVC) recovered from the plastic insulations in wires and cables is a rising concern in the current situation due to its hazardous behaviour during recycling. Similarly, high-impact polystyrene (HIPS) and acrylonitrile butadiene styrene (ABS) used in the structural components of electrical and electronic equipment are also generated in large quantities. In the current work, three agendas were fixed: (a) to determine the effect of recycled polymeric material (HIPS and ABS) recovered from different sources on the mechanical property of the polymeric blends; (b) to formulate a high-impact strength blend; and (c) to deduce a mechanism for improved impact strength. The mechanical characterizations were conducted on the entire blends formulated. Among them, the recycled blend composed of recycled PVC (r-PVC) and recycled ABS (r-ABS) (segregated from uninterrupted power supply housing) and recycled HIPS (r-HIPS; collected from television housing) was confined for further physio-mechanical and thermal analysis. Besides, the r-PVC/r-ABS systems had shown better mechanical properties than r-PVC/r-HIPS systems in similar composition. The impact strength of blend r-PVC/r-ABS (70:30) was found to be 250 J/m, which was 200% more than the blend r-PVC/r-ABS (0:100). The compatibility and non-compatibility in PVC/ABS and PVC/HIPS blends respectively were explained with thermal, mechanical and morphological characterizations. Furthermore, a plausible cross-linking mechanism is developed between ABS and PVC, which controls the release of chlorine atoms into the environment.

Alkylation of Aromatic Compounds with Pentabromobenzyl Bromide and Tetrabromoxylene Dibromide as a New Route to High Molecular Weight Brominated Flame Retardants

In the view of many national and international human health and environmental regulations, polymeric flame retardants are sustainable products. In this work, a series of high molecular weight and polymeric brominated flame retardants are synthesized by the alkylation of aromatic molecules or the alkylation of aromatic polymers with pentabromobenzyl bromide (PBBB) or tetrabromoxylylene dibromide (TBXDB). The flame retardants prepared via the alkylation of toluene or diphenylethane with PBBB were found to be not truly polymeric but had high M_w > 1400. However, the alkylation of the same aromatic molecules by a mixture of PBBB and TBXDP resulted in polymeric flame retardants with M_w > 130,000. Two other polymeric flame retardants were prepared by the alkylation of aromatic polymers (polyphenylene ether or polystyrene) with PBBB. It was found that the new flame retardants had a high bromine content of more than 68%. They showed high thermal stability with the onset of thermal decomposition above 360 °C and a maximum rate of weight loss at about 375-410 °C. The newly synthesized flame retardants were tested in different thermoplastics. Flame retardant efficiency and physical properties were comparable or better than the reference commercial flame retardants.

Reduced surface adsorption in 3D printed acrylonitrile butadiene styrene micro free-flow electrophoresis devices

We have 3D printed and fabricated micro free-flow electrophoresis (µFFE) devices in acrylonitrile butadiene styrene (ABS) that exhibit minimal surface adsorption without requiring additional surface coatings or specialized buffer additives. 2D, nano LC-micro free flow electrophoresis (2D nLC × µFFE) separations were used to assess both spatial and temporal broadening as peaks eluted through the separation channel. Minimal broadening due to wall adsorption was observed in either the spatial or temporal dimensions during separations of rhodamine 110, rhodamine 123, and fluorescein. Surface adsorption was observed in separations of Chromeo P503 labeled myoglobin and cytochrome c but was significantly reduced compared to previously reported glass devices. Peak widths of < 30 s were observed for both proteins. For comparison, Chromeo P503 labeled myoglobin and cytochrome c adsorb strongly to the surface of glass µFFE devices resulting in peak widths >20 min. A 2D nLC × µFFE separation of a Chromeo P503 labeled tryptic digest of BSA was performed to demonstrate the high peak capacity possible due to the low surface adsorption in the 3D printed ABS devices, even in the absence of surface coatings or buffer additives.

Considerations on the Applicability of Test Methods for Mechanical Characterization of Materials Manufactured by FDM

The lack of specific standards for characterization of materials manufactured by Fused Deposition Modelling (FDM) makes the assessment of the applicability of the test methods available and the analysis of their limitations necessary; depending on the definition of the most appropriate specimens on the kind of part we want to produce or the purpose of the data we want to obtain from the tests. In this work, the Spanish standard UNE 116005:2012 and international standard ASTM D638-14:2014 have been used to characterize mechanically FDM samples with solid infill considering two build orientations. Tests performed according to the specific standard for additive manufacturing UNE 116005:2012 present a much better repeatability than the ones according to the general test standard ASTM D638-14, which makes the standard UNE more appropriate for comparison of different materials. Orientation on-edge provides higher strength to the parts obtained by FDM, which is coherent with the arrangement of the filaments in each layer for each orientation. Comparison with non-solid specimens shows that the increase of strength due to the infill is not in the same proportion to the percentage of infill. The values of strain to break for the samples with solid infill presents a much higher deformation before fracture.

Interface Reinforcement of Pulp Fiber Based ABS Composite with Hydrogen Bonding Initiated Interlinked Structure via Alkaline Oxidation and tert-Butyl Grafting on Cellulose

Interface optimization in preparing natural fiber based biocomposite becomes a key factor that determines overall properties, especially mechanical performance. The solution for upgrading interfacial adhesion stemmed from polar fiber and nonpolar polymer remains unclear. Here, a kind of pulp fiber/acrylonitrile-butadiene-styrene (ABS) composite with content ratio of 1:1 was fabricated by functionalizing the cellulose fiber to coordinate interaction between fiber and ABS. With addition of 5 wt % polyacrylamide (PAM) there existed an interlinked three-element structure in composite. Three types of treatment to cellulose fiber, including alkali immersion, pivaloyl chloride grafting for 10 h and 20 h were conducted. Pulp fiber that was treated with alkali for one hour, followed by pivaloyl chloride reaction for ten hours, proved to be effective for interfacial adhesion. X-ray Photoelectron Spectroscopy (XPS) analysis reveals 21.9% of carbonyl and 12.1% of ester function in this fiber, which corresponds to oxidation and grafting. For its composite SEM picture displays that most of cellulose fiber are rooted in ABS and evident traces of tearing or fracture can be observed after tension test. DMA test indicates that this modified pulp fiber/ABS composite exhibits great compatibility, because of combined loss modulus peak ranging from 80 °C to 100 °C. Moreover, the well miscible composite has a tensile strength of 58.1 MPa and elastic modulus of 2515 MPa, increasing by nearly 50% and 60% from those of pure ABS, respectively.