Fully reactive 3D inkjet printing of polydimethylsiloxane and polyurethane

Additive Manufacturing (AM) encompasses several different technologies, such as inkjet printing, extrusion, and laser melting processes, to selectively transform a processable phase, such as a liquid or powder, to a solid phase, e.g. through solidification, chemical reaction or powder melting and solidification. The geometry is initially defined as a 3D CAD model, which is subsequently ‘sliced’ to create a geometrical representation suitable for the layer-wise manufacturing process. These layers are “printed” in series on a substrate and are additively stacked. Some AM processes can also include multiple materials or voids in this process to increase the design freedom and geometric complexity. With any new process there are challenges, the key one for most AM processes is the limited material selection. Different processes have different material requirements and many current AM materials are sourced from other processes, for example a number of stereolithography processes use materials originally developed as finishes or coatings. The various AM processes have different criteria that must be met for a material to be suitable for processing, such as particle size and distribution, melting temperature and laser absorption in the case of laser-powder bed systems. This PhD is concerned with materials for ink jet printing, a major advantage of this process being the capability to co-deposit different materials. As the materials in jetting are not fed from a single bed or on a platform, there is complete control over material placement. The basic technology behind material jetting is the same as that seen in desktop inkjet printers, and the major challenge in transforming this to a 3D printing method is in materials development. Currently, the process is dominated by fast curing UV based resins, which are primarily acrylate based, and solvent based inks. The solvent inks highlight their 2D printing origins as they have a low material loading resulting in thin layers. These solvent systems are typically used to transport a conductive solute e.g. silver nanoparticles or graphene oxide. The focus of this PhD was to develop new materials for AM jetting by combining reactive components during processing. This process, called Fully Reactive Inkjet Printing (FRIJP), is only possible because of the freedom of material jetting to use multiple materials. In this work two reactions were selected for the development of FRIJP inks. The first was the crosslinking of polysiloxane based polymers (PDMS), the second was the addition polymerisation of polyurethane. These two reactions schemes were chosen because they involve the combination of two different reactive species and produce no unwanted by-products. For the FRIJP of PDMS a commercial two-part chemistry was used that separated the cross-linker and catalyst. When these two components are combined they produce a transparent PDMS rubber. The PDMS was found to have a viscosity that was too high for inkjet printing so a compatible solvent was selected and the concentration modified. Once a printable ink had been created, trials were conducted which involved printing the two components onto a substrate. It was found that by control of the mixing ratio and substrate heating, high reaction rates could be achieved and complex designs could be printed. These designs were then analysed using FTIR and Raman spectroscopy and it was found that there was comparable curing to the bulk mixing. It was also determined that for the selected PDMS there were no issues with substrate mixing which would result in concentration gradients. The second reaction investigated was the addition polymerisation of polyurethane, which involves combination of the diol and diisocyanate. For this work, the inks were developed from monomers that had printable viscosities through thermal modification. However, one ink used did contain a low concentration of solvent. For the polyurethane work the printing environment was controlled to minimise the moisture which could produce unwanted polyurea and amines. The metric used to determine how suitable the inks were for inkjet printing was the molecular weight of the polymer chain. The analysis was conducted using Size Exclusion Chromatography on the printed samples. It was found that after in development, it was possible to achieve an average molecular weight over 20,000, which was identified as the point whereby the polymer printing was successful. This PhD also demonstrates that when printing these two chemistries, the small size of the droplets facilitates complete mixing of the inks. Importantly, with the immiscibility of the polyurethane monomers before reaction, it was found that the small droplet size allowed for the reaction and successive molecular diffusion to achieve the high degrees of conversion required for the production of functional polymers

Fully reactive 3D inkjet printing of polydimethylsiloxane and polyurethane

Additive Manufacturing (AM) encompasses several different technologies, such as inkjet printing, extrusion, and laser melting processes, to selectively transform a processable phase, such as a liquid or powder, to a solid phase, e.g. through solidification, chemical reaction or powder melting and solidification. The geometry is initially defined as a 3D CAD model, which is subsequently ‘sliced’ to create a geometrical representation suitable for the layer-wise manufacturing process. These layers are “printed” in series on a substrate and are additively stacked. Some AM processes can also include multiple materials or voids in this process to increase the design freedom and geometric complexity. With any new process there are challenges, the key one for most AM processes is the limited material selection. Different processes have different material requirements and many current AM materials are sourced from other processes, for example a number of stereolithography processes use materials originally developed as finishes or coatings. The various AM processes have different criteria that must be met for a material to be suitable for processing, such as particle size and distribution, melting temperature and laser absorption in the case of laser-powder bed systems. This PhD is concerned with materials for ink jet printing, a major advantage of this process being the capability to co-deposit different materials. As the materials in jetting are not fed from a single bed or on a platform, there is complete control over material placement. The basic technology behind material jetting is the same as that seen in desktop inkjet printers, and the major challenge in transforming this to a 3D printing method is in materials development. Currently, the process is dominated by fast curing UV based resins, which are primarily acrylate based, and solvent based inks. The solvent inks highlight their 2D printing origins as they have a low material loading resulting in thin layers. These solvent systems are typically used to transport a conductive solute e.g. silver nanoparticles or graphene oxide. The focus of this PhD was to develop new materials for AM jetting by combining reactive components during processing. This process, called Fully Reactive Inkjet Printing (FRIJP), is only possible because of the freedom of material jetting to use multiple materials. In this work two reactions were selected for the development of FRIJP inks. The first was the crosslinking of polysiloxane based polymers (PDMS), the second was the addition polymerisation of polyurethane. These two reactions schemes were chosen because they involve the combination of two different reactive species and produce no unwanted by-products. For the FRIJP of PDMS a commercial two-part chemistry was used that separated the cross-linker and catalyst. When these two components are combined they produce a transparent PDMS rubber. The PDMS was found to have a viscosity that was too high for inkjet printing so a compatible solvent was selected and the concentration modified. Once a printable ink had been created, trials were conducted which involved printing the two components onto a substrate. It was found that by control of the mixing ratio and substrate heating, high reaction rates could be achieved and complex designs could be printed. These designs were then analysed using FTIR and Raman spectroscopy and it was found that there was comparable curing to the bulk mixing. It was also determined that for the selected PDMS there were no issues with substrate mixing which would result in concentration gradients. The second reaction investigated was the addition polymerisation of polyurethane, which involves combination of the diol and diisocyanate. For this work, the inks were developed from monomers that had printable viscosities through thermal modification. However, one ink used did contain a low concentration of solvent. For the polyurethane work the printing environment was controlled to minimise the moisture which could produce unwanted polyurea and amines. The metric used to determine how suitable the inks were for inkjet printing was the molecular weight of the polymer chain. The analysis was conducted using Size Exclusion Chromatography on the printed samples. It was found that after in development, it was possible to achieve an average molecular weight over 20,000, which was identified as the point whereby the polymer printing was successful. This PhD also demonstrates that when printing these two chemistries, the small size of the droplets facilitates complete mixing of the inks. Importantly, with the immiscibility of the polyurethane monomers before reaction, it was found that the small droplet size allowed for the reaction and successive molecular diffusion to achieve the high degrees of conversion required for the production of functional polymers

Inkjet printing of polyimide insulators for the 3D printing of dielectric materials for microelectronic applications

In this article, we report the first continuous fabrication of inkjet-printed polyimide films, which were used as insulating layers for the production of capacitors. The polyimide ink was prepared from its precursor poly(amic) acid, and directly printed on to a hot substrate (at around 160 °C) to initialize a rapid thermal imidization. By carefully adjusting the substrate temperature, droplet spacing, droplet velocity, and other printing parameters, polyimide films with good surface morphologies were printed between two conducting layers to fabricate capacitors. In this work, the highest capacitance value, 2.82 ± 0.64 nF, was achieved by capacitors (10 mm × 10 mm) with polyimide insulating layers thinner than 1 μm, suggesting that the polyimide inkjet printing approach is an efficient way for producing dielectric components of microelectronic devices. © 2016 The Authors Journal of Applied Polymer Science Published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43361

Randomized controlled trial and economic evaluation of nurse-led group support for young mothers during pregnancy and the first year postpartum versus usual care

Background Child maltreatment is a significant public health problem. Group Family Nurse Partnership (gFNP) is a new intervention for young, expectant mothers implemented successfully in pilot studies. This study was designed to determine the effectiveness and cost effectiveness of gFNP in reducing risk factors for maltreatment with a potentially vulnerable population. Methods A multi-site randomized controlled parallel-arm trial and prospective economic evaluation was conducted, with allocation via remote randomization (minimization by site, maternal age group) to gFNP or usual care. Participants were expectant mothers aged <20 with at least one live birth, or 20–24 with no live births and with low educational qualifications. Data from maternal interviews at baseline and when infants were two, six and 12 months, and video recording at 12 months, were collected by researchers blind to allocation. Cost information came from weekly logs completed by gFNP family nurses and other service delivery data reported by participants. Primary outcomes measured at 12 months were parenting attitudes (Adult- Adolescent Parenting Index, AAPI-2) and maternal sensitivity (CARE index). The economic evaluation was conducted from a UK NHS and personal social services perspective with cost-effectiveness expressed in terms of incremental cost per quality-adjusted life year (QALY) gained. Main analyses were intention to treat with additional complier average causal effects (CACE) analyses. Results Between August 2013 and September 2014, 492 names of potential participants were received of whom 319 were eligible and 166 agreed to take part, 99 randomly assigned to receive gFNP and 67 to usual care. There were no between-arms differences in AAPI-2 total (7·5/10 in both, SE 0.1), difference adjusted for baseline, site and maternal age-group 0·06 (95% CI -0·15 to 0·28, p=0·59) or CARE Index (intervention 4·0 (SE 0·3); control 4·7(SE 0·4); difference adjusted for site and maternal age-group -0·68; 95% CI -1·62 to 0·16, p=0·25) scores. The probability that gFNP is cost-effective based on the QALY measure did not exceed 3%. Conclusions The trial did not support gFNP as a means of reducing the risk of child maltreatment in this population but slow recruitment adversely affected group size and consequently delivery of the intervention

Results of Screening of Apparently Healthy Senior and Geriatric Dogs

Background: There is a growing interest in health care of elderly dogs; however, scientific information about physical and laboratory examination findings in this age group is limited. Objectives: To describe systolic blood pressure (SBP), and results of physical examination and laboratory tests in senior and geriatric dogs that were judged by the owner to be healthy. Animals: Hundred client-owned dogs. Methods: Dogs were prospectively recruited. Owners completed a questionnaire. SBP measurement, physical, orthopedic and neurologic examination, direct fundoscopy and Schirmer tear test were performed. Complete blood count, serum biochemistry, and urinalysis were evaluated. Results: Forty-one senior and 59 geriatric dogs were included. Mean SBP was 170 38 mmHg, and 53 dogs had SBP > 160 mmHg. Thirty-nine animals were overweight. A heart murmur was detected in 22, severe calculus in 21 and 1 or more (sub)cutaneous masses in 56 dogs. Thirty-two dogs had increased serum creatinine, 29 hypophosphatemia, 27 increased ALP, 25 increased ALT, and 23 leukopenia. Crystalluria, mostly amorphous crystals, was commonly detected (62/96). Overt proteinuria and borderline proteinuria were detected in 13 and 18 of 97 dogs, respectively. Four dogs had a positive urine bacterial culture. Frequency of orthopedic problems, frequency of (sub)cutaneous masses, and platelet count were significantly higher in geriatric compared with senior dogs. Body temperature, hematocrit, serum albumin, and serum total thyroxine concentration were significantly lower in geriatric compared with senior dogs. Conclusions and Clinical Importance: Physical and laboratory abnormalities are common in apparently healthy elderly dogs. Veterinarians play a key role in implementing health screening and improving health care for elderly pets

3D printing of biocompatible supramolecular polymers and their composites

A series of polymers capable of self-assembling into infinite networks via supramolecular interactions have been designed, synthesized, and characterized for use in 3D printing applications. The biocompatible polymers and their composites with silica nanoparticles were successfully utilized to deposit both simple cubic structures, as well as a more complex twisted pyramidal feature. The polymers were found to be not toxic to a chondrogenic cell line, according to ISO 10993-5 and 10993-12 standard tests and the cells attached to the supramolecular polymers as demonstrated by confocal microscopy. Silica nanoparticles were then dispersed within the polymer matrix, yielding a composite material which was optimized for inkjet printing. The hybrid material showed promise in preliminary tests to facilitate the 3D deposition of a more complex structure

Pathology of Gastrointestinal Organs in a Porcine Model of Cystic Fibrosis

Cystic fibrosis (CF), which is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR), is characterized by multiorgan pathology that begins early in life. To better understand the initial stages of disease, we studied the gastrointestinal pathology of CFTR−/− pigs. By studying newborns, we avoided secondary changes attributable to environmental interactions, infection, or disease progression. Lesions resembling those in humans with CF were detected in intestine, pancreas, liver, gallbladder, and cystic duct. These organs had four common features. First, disease was accelerated compared with that in humans, which could provide a strategy to discover modifying factors. Second, affected organs showed variable hyperplastic, metaplastic, and connective tissue changes, indicating that remodeling was a dynamic component of fetal life. Third, cellular inflammation was often mild to moderate and not always present, which raises new questions as to the role of cellular inflammation in early disease pathogenesis. Fourth, epithelial mucus-producing cells were often increased, producing a striking accumulation of mucus with a layered appearance and resilient structure. Thus, mucus cell hyperplasia and mucus accumulation play prominent roles in early disease. Our findings also have implications for CF lung disease, and they lay the foundation for a better understanding of CF pathogenesis