Active learning for prediction of tensile properties for material extrusion additive manufacturing.

Machine learning techniques were used to predict tensile properties of material extrusion-based additively manufactured parts made with Technomelt PA 6910, a hot melt adhesive. An adaptive data generation technique, specifically an active learning process based on the Gaussian process regression algorithm, was employed to enable prediction with limited training data. After three rounds of data collection, machine learning models based on linear regression, ridge regression, Gaussian process regression, and K-nearest neighbors were tasked with predicting properties for the test dataset, which consisted of parts fabricated with five processing parameters chosen using a random number generator. Overall, linear regression and ridge regression successfully predicted output parameters, with < 10% error for 56% of predictions. K-nearest neighbors performed worse than linear regression and ridge regression, with < 10% error for 32% of predictions and 10-20% error for 60% of predictions. While Gaussian process regression performed with the lowest accuracy (< 10% error for 32% of prediction cases and 10-20% error for 40% of predictions), it benefited most from the adaptive data generation technique. This work demonstrates that machine learning models using adaptive data generation techniques can efficiently predict properties of additively manufactured structures with limited training data.

Predicting mechanical properties of material extrusion additive manufacturing-fabricated structures with limited information.

Mechanical properties of additively manufactured structures fabricated using material extrusion additive manufacturing are predicted through combining thermal modeling with entanglement theory and molecular dynamics approaches. A one-dimensional model of heat transfer in a single road width wall is created and validated against both thermography and mechanical testing results. Various model modifications are investigated to determine which heat transfer considerations are important to predicting properties. This approach was able to predict tear energies on reasonable scales with minimal information about the polymer. Such an approach is likely to be applicable to a wide range of amorphous and low crystallinity thermoplastics.

Half-life modeling of basic fibroblast growth factor released from growth factor-eluting polyelectrolyte multilayers.

Growth factor-eluting polymer systems have been widely reported to improve cell and tissue outcomes; however, measurements of actual growth factor concentration in cell culture conditions are limited. The problem is compounded by a lack of knowledge of growth factor half-lives, which impedes efforts to determine real-time growth factor concentrations. In this work, the half-life of basic fibroblast growth factor (FGF2) was determined using enzyme linked immunosorbent assay (ELISA). FGF2 release from polyelectrolyte multilayers (PEMs) was measured and the data was fit to a simple degradation model, allowing for the determination of FGF2 concentrations between 2 and 4 days of culture time. After the first hour, the FGF2 concentration for PEMs assembled at pH = 4 ranged from 2.67 ng/mL to 5.76 ng/mL, while for PEMs assembled at pH = 5, the concentration ranged from 0.62 ng/mL to 2.12 ng/mL. CRL-2352 fibroblasts were cultured on PEMs assembled at pH = 4 and pH = 5. After 2 days, the FGF2-eluting PEM conditions showed improved cell count and spreading. After 4 days, only the pH = 4 assembly condition had higher cells counts, while the PEM assembled at pH = 5 and PEM with no FGF2 showed increased spreading. Overall, the half-life model and cell culture study provide optimal concentration ranges for fibroblast proliferation and a framework for understanding how temporal FGF2 concentration may affect other cell types.

Effect of surface wettability on the interfacial adhesion of a thermosetting elastomer on glass.

Interfacial adhesion dictates properties and performance of both composites and adhesively bonded structures. Weak adhesion at the interfaces of polymer composites leads to void formation and debonding, which adversely affect composite structural integrity and mechanical performance. This work investigated the relationship between surface wettability and interfacial fracture energy with the goal of tailoring interfacial adhesion within polymer composites. A series of model functionalized surfaces was created using silane coupling agents with different organo-functionalities to alter surface wettability. Based on the analysis of interfacial fracture energy between a thermosetting elastomeric polymer network and model surfaces, interfacial adhesion was found to be positively correlated to resin wettability. The results provide a fast and simple approach to screen different material combinations for the development of novel polymeric composites and adhesively bonded structures with tailorable adhesion.

Impact of molecular weight on polyelectrolyte multilayer assembly and surface properties.

Polyelectrolyte multilayers (PEMs) are a versatile category of materials due to their ability to modify surface properties for applications ranging from protective coatings to improved cell adhesion. Polyelectrolyte choice, including its structure and molecular weight (MW), is known to greatly influence PEM assembly and surface properties. In this work, poly(acrylic acid)/poly-l-lysine PEMs using three pairs of MWs (1.8k/15-30k, 100k/120k, and 250k/275k) were studied to determine the effects of their MWs on PEM assembly, topography and surface energy. PEMs assembly was monitored in a quartz crystal microbalance with dissipation, resulting in masses of 3.90 ± 0.87 µg/cm2, 10.80 ± 4.189 µg/cm2, and 30.04 ± 13.68 µg/cm2 for 10 bilayers of low, medium, and high MW pairs, respectively. The low MW PEM was more rigid. Low and high MW PEMs exhibited higher roughness than medium MW, caused by polyelectrolyte stripping. Surface energy remained constant with bilayer count in the low and high MW PEMs, but steadily increased in the medium MW PEM. Differences between medium MW PEMs from low and high MW systems indicate that, while PEM properties change with MW, they are not monotonically correlated and are instead related to changes in internal charge distributions and the resultant stripping that may occur.

Early hMSC morphology and proliferation on model polyelectrolyte multilayers.

Polyelectrolyte multilayers (PEMs) are a category of materials commonly used as coatings on surfaces that interact with cells. The properties of PEMs have been established to be controlled by not only polyelectrolyte choice, but by the identity of the initially applied (bottom) layer. In this work, 5-bilayer PEMs consisting of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) were coated on gold-sputtered quartz substrates with different first layer materials. A final poly-l-lysine (PLL) layer was added to all PEMs to provide identical top layers conducive to cell growth. As in previous work, initial layer selection affected PEM roughness. All coated surfaces, including the PLL-only control, showed increased dispersive surface energy but decreased polar surface energy, as compared to uncoated surfaces. When human mesenchymal stem cells (hMSCs) were cultured on these surfaces, analysis through lateral cell imaging for the first 90 min and fluorescent staining after 1 day showed improved attachment on surfaces with a PDADMAC bottom layer. However, after 4 days, a higher cell density was observed on the PLL-only and uncoated control surfaces, indicating that the PEMs negatively affected hMSC proliferation. Both the long and short time period results did not correlate to any of the roughness and surface energy trends, indicating more complex interactions between the cells and the surface relating to charge distribution and functional group density.

Growth-Factor-Releasing Polyelectrolyte Multilayer Films to Control the Cell Culture Environment.

Polyelectrolyte multilayers (PEMs) are of great interest as cell culture surfaces because of their ability to modify topography and surface energy and release biologically relevant molecules such as growth factors. In this work, fibroblast growth factor 2 (FGF2) was adsorbed directly onto polystyrene, plasma-treated polystyrene, and glass surfaces with a poly(methacrylic acid) and poly-l-histidine PEM assembled above it. Up to 14 ng/cm2 of FGF2 could be released from plasma-treated polystyrene surfaces over the course of 7 days with an FGF2 solution concentration of 100 µg/mL applied during the adsorption process. This release rate could be modulated by adjusting the adsorption concentration, decreasing to as low as 2 ng/cm2 total release over 7 days using a 12.5 µg/mL FGF2 solution. The surface energy and roughness could also be regulated using the adsorbed PEM. These properties were found to be substrate- and first-layer-dependent, supporting current theories of PEM assembly. When released, FGF2 from the PEMs was found to significantly enhance fibroblast proliferation as compared to culture conditions without FGF2. The results showed that growth factor release profiles and surface properties are easily controllable through modification of the PEM assembly steps and that these strategies can be effectively applied to common cell culture surfaces to control the cell fate.

The Princess and the Pea Effect: Influence of the first layer on polyelectrolyte multilayer assembly and properties.

In many applications of polyelectrolyte multilayers (PEMs), a base polycation layer is adsorbed to promote adhesion of the PEM to the substrate. In this report, the effect of the first polyelectrolyte adsorbed in a PEM was investigated by assembling PEMs with first layer polycations of different chemistries and molecular weights. In this study, quartz crystal microbalance with dissipation monitoring (QCM-D) was used to monitor the PEM assembly process. First layer choice affects the total mass accumulation of the PEM as well as the stoichiometry of the PEM, although linear growth was observed in all cases. PEM thickness was also affected by first layer choice, although not consistent with changes in mass. Combined with the stoichiometry results, these findings indicate that the structure of a PEM is fundamentally different depending on first layer chemistry and molecular weight. PEM topography is also affected by first layer choice. Selection of appropriate first layer material is therefore an important consideration in the design of a PEM, and changing first layer material may be a facile way to tailor the structure and properties of PEMs.

Effect of Assembly pH on Polyelectrolyte Multilayer Surface Properties and BMP-2 Release.

The effect of solution pH during layer-by-layer assembly of polyelectrolyte multilayer (PEM) coatings on properties relevant to orthopedic implant success was investigated. Bone morphogenetic protein 2 (BMP-2), a potent osteoconductive growth factor, was adsorbed onto the surface of anodized titanium, and PEM coatings prepared from solutions of poly-l-histidine and poly(methacrylic acid) were built on top of the BMP-2. High levels of BMP-2 released over several months were achieved. Approximately 2 µg/cm(2) of BMP-2 were initially adsorbed on the anodized titanium and a pH-dependent release behavior was observed, with more stable coatings assembled at pH = 6-7. Three different diffusion regimes could be determined from the release profiles: an initial burst release, a sustained release regime, and a depletion regime. BMP-2 was shown to maintain bioactivity after release from a PEM and the presence of a PEM was shown to preserve BMP-2 structure. No visible change was observed in surface roughness as the assembly pH was varied, whereas the surface energy decreased for samples prepared at more basic pH. These results indicate that the initial BMP-2 layer affects PEM surface structure, but not the functional groups exposed on the surface.

Satisfaction with support versus size of network: differential effects of social support on psychological distress in parents of pediatric cancer patients.

OBJECTIVE: This study examined the direct and buffering effects of social support on longer-term global psychological distress among parents coping with pediatric cancer. In both sets of analyses, we examined whether these effects depended on the dimension of social support provided (i.e., satisfaction with support versus size of support network). METHOD: Participants were 102 parents of pediatric cancer patients. At study entry, parents reported their trait anxiety, depression, and two dimensions of their social support network (satisfaction with support and size of support network). Parents subsequently reported their psychological distress in 3- and 9-month follow-up assessments. RESULTS: Parents' satisfaction with support had a direct effect on longer-term psychological distress; satisfaction was negatively associated with distress at both follow-ups. In contrast, size of support network buffered (moderated) the impact of trait anxiety and depression on later distress. Parents with smaller support networks and higher levels of trait anxiety and depression at baseline had higher levels of psychological distress at both follow-ups; for parents with larger support networks, there was no relationship. CONCLUSION: Social support can attenuate psychological distress in parents coping with pediatric cancer; however, the nature of the effect depends on the dimension of support. Whereas interventions that focus on increasing satisfaction with social support may benefit all parents, at-risk parents will likely benefit from interventions that ensure they have an adequate number of support resources.

Parent caregiver self-efficacy and child reactions to pediatric cancer treatment procedures.

This study examined how parents' sense of self-efficacy specific to caregiving for their child during cancer treatment procedures affected children's distress and cooperation during procedures. Potential correlates of caregiver self-efficacy (ie, demographics, child clinical characteristics, parent dispositional attributes, and social support) were also examined. Participants were 119 children undergoing cancer treatment procedures and their parents. Parents' self-efficacy about 6 procedure-specific caregiver tasks was measured. Parents, children, nurses, and observers rated child distress and parents, nurses and observers rated child cooperation during procedures. Higher parent self-efficacy about keeping children calm during procedures predicted lower child distress and higher child cooperation during procedures. Parent dispositional attributes (eg, enduring positive mood, empathy) and social support predicted self-efficacy. Parent caregiver self-efficacy influences child distress and cooperation during procedures and is associated with certain parent attributes. Findings suggest the utility of identifying parents who would benefit from targeted interventions to increase self-efficacy about caregiving during treatment procedures.

Growth factor release from polyelectrolyte-coated titanium for implant applications.

Polyelectrolyte multilayer coatings based on poly(methacrylic acid) and poly-l-histidine were formed on anodized titanium surfaces with adsorbed bone morphogenetic protein 2 (BMP-2) or basic fibroblast growth factor (FGFb). These coatings are proposed for use on titanium implanted devices. Coatings were capable of sustained release of growth factor over 25 days, with BMP-2 and FGFb exhibiting approximately identical release profiles. Cell culture on growth factor-eluting surfaces was more effective for preosteoblasts on BMP-2-eluting surfaces than for fibroblasts on FGFb-eluting surfaces. Cell counts at all time points on BMP-2-eluting surfaces were significantly higher than for those on anodized titanium or polyelectrolyte surfaces that did not contain BMP-2. Alkaline phosphatase levels were significantly higher after 21 days on BMP-2-eluting surfaces, indicating increased bone growth.

Posttraumatic Stress Symptoms in Parents of Pediatric Cancer Patients: A Mediational Analysis.

OBJECTIVE: Prior research finds that anxiety and depression among parents of pediatric cancer patients are associated with posttraumatic stress symptoms in response to children's cancer. This study examined whether this relationship is mediated by parents' negative affective reactions in response to their children's cancer-related treatment procedures. METHODS: Participants were parents of 101 patients within six months of diagnosis who had completed at least two treatment-related procedures. Parents completed measures of trait anxiety and depression at baseline and posttraumatic stress symptoms at 3-month follow-up assessment. On the day of each treatment procedure, parents completed measures of state anxiety immediately before and negative mood and distress immediately after the procedure. RESULTS: Trait anxiety was positively associated with state anxiety immediately before procedures and negative mood after procedures. Depression was positively associated with state anxiety immediately before procedures and negative mood and distress after procedures. Both trait anxiety and depression were positively associated with posttraumatic stress symptoms at 3-months follow-up. Parent state anxiety, negative mood, and distress partially mediated the effects of trait anxiety and/or depression on posttraumatic stress symptoms. Controlling for child age and social desirability did not affect these relationships. CONCLUSIONS: Parents' trait anxiety and depression may influence cancer-related posttraumatic stress partially through their effect on parents' negative affective reactions at the time of their child's treatment procedures. These findings provide a more nuanced understanding of how parents' affect in response to procedures contributes to parent posttraumatic stress and suggest that interventions targeting treatment-related affective reactions of parents with high trait anxiety and/or depression may reduce the risk for longer-term distress and posttraumatic stress symptoms.

Room temperature self-healing thermoset based on the Diels-Alder reaction.

A self-healing epoxy-amine thermoset based on the compatible functionalization of the thermoset and encapsulated healing agent has been successfully developed. Healing of the thermoset resulted from the reaction of furans in the thermoset and multimaleimides (MMIs) in the healing agent solution. The healing agent, MMI dissolved in phenyl acetate, was encapsulated using a urea-formaldehyde encapsulation method. Autonomic healing of the thermoset was achieved by incorporating microcapsules filled with the healing agent solution within a furan-functionalized epoxy-amine thermoset. The resulting self-healing thermoset recovered 71% of its initial load after fracture.

Kinetic considerations for strength recovery at the fiber-matrix interface based on the Diels-Alder reaction.

The Diels-Alder reaction was used to yield thermal reversibility of the bonding between a partially furan-functionalized epoxy thermosetting matrix and a maleimide-treated glass fiber. Under ambient temperature conditions, the covalent bond forming product reaction dominates, but this reaction reverses at elevated temperatures to allow for interfacial healing. Single-fiber microdroplet pull-out testing was used to characterize the coupled effects of healing temperature and the glass transition temperature (T(g)) of the epoxy on interfacial strength recovery. In particular, the roles of mobility and reaction kinetics were independently varied to understand the individual effects of both.

Longitudinal study of parent caregiving self-efficacy and parent stress reactions with pediatric cancer treatment procedures.

BACKGROUND: Pain/distress during pediatric cancer treatments has substantial psychosocial consequences for children and families. We examined relationships between parents' caregiving self-efficacy, parents' affect in response to their children's cancer-related treatment procedures, and parents' symptoms of post-traumatic stress at follow-up. METHODS: Participants were 75 pediatric cancer patients and parents. On the day of each of three procedures (i.e., port-start, lumbar puncture, or bone marrow aspiration), parents rated their self-efficacy for six caregiving goals. Parents also self-reported their negative affect (i.e., state anxiety, negative mood, and distress) in response to each procedure. Three months after the last procedure, parents reported their level of post-traumatic stress symptoms (PTSS). RESULTS: Higher parent self-efficacy about keeping children calm before treatment and/or keeping children calm during the procedure was associated with lower state anxiety. Self-efficacy for keeping the child calm during procedures was significantly correlated with distress in parents at the time of procedures, and self-efficacy for keeping the child calm before procedures was significantly correlated with PTSS. All three negative affect measures significantly mediated the effects of parents' caregiving self-efficacy for both goals on parents' PTSS 3 months later. CONCLUSIONS: Parents' caregiving self-efficacy influences their immediate and longer-term distress reactions to their children's treatment procedures. These findings provide a more nuanced understanding of how parents' cognitions contribute to their ability to cope with their children's treatment and suggest the benefit of an intervention that targets parents' procedure-specific caregiver self-efficacy.

pH-controlled release of proteins from polyelectrolyte-modified anodized titanium surfaces for implant applications.

Titanium is a popular choice of implant material given its strength, durability, and biocompatibility; however, strong interfaces with the surrounding tissue are not achieved, resulting in stress shielding and implant loosening. One option for improving adhesion is modification of the surface chemistry and topography through anodization, while another option is coating the titanium surface with a protein-eluting polyelectrolyte complex. Morphogenetic proteins such as BMP-2 have been shown to cause cell migration, expression of different genes, and development of different tissues. Anodization was used to form a porous oxide structure across the surface. A polyelectrolyte coating of poly-l-histidine and poly(methacrylic acid) was prepared and was shown to be effective for sustained release of negatively charged species under physiological conditions. This complex demonstrated pH-dependent release, with maximum release at pH = 5-6, but low levels of sustained release at pH = 7-8. Smaller initial burst release and higher amounts of sustained release were observed when lower molecular weight poly(methacrylic acid) was used. Different methods of loading the polyelectrolyte with the model species were compared. Immersion of the coating for loading provided greater release, albeit a larger initial burst release.

Room-temperature healing of a thermosetting polymer using the Diels-Alder reaction.

Self-healing materials are particularly desirable for load-bearing applications because they offer the potential for increased safety and material lifetimes. A furan-functionalized polymer network was designed that can heal via covalent bonding across the crack surface with the use of a healing agent consisting of a bismaleimide in solution. Average healing efficiencies of approximately 70% were observed. The healing ability of fiber-reinforced composite specimens was investigated with flexural, short beam shear, and double cantilever beam specimens. It was found that solvent amount and maleimide concentration play key roles in determining healing efficiency.

Reversibly cross-linked polymer gels as healing agents for epoxy-amine thermosets.

The Diels-Alder reaction was used to develop a reversibly cross-linking gel as a healing agent for traditional epoxy-amine thermosets. Direct application of the reversibly cross-linking network to a crack surface in an epoxy-amine thermoset resulted in the recovery of 37% of the initial epoxy-amine network's strength. Composites in which the reversibly cross-linking gel was incorporated as a secondary particulate phase recovered 21% of the initial composite strength after the first healing cycle, with healing possible up to five times.

Influence of clinical communication on patients' decision making on participation in clinical trials.

PURPOSE: To investigate how communication among physicians, patients, and family/companions influences patients' decision making about participation in clinical trials. PATIENTS AND METHODS: We video recorded 235 outpatient interactions occurring among oncologists, patients, and family/companions (if present) at two comprehensive cancer centers. We combined interaction analysis of the real-time video-recorded observations (collected at Time 1) with patient self-reports (Time 2) to determine how communication about trial offers influenced accrual decisions. RESULTS: Clinical trials were explicitly offered in 20% of the interactions. When offers were made and patients perceived they were offered a trial, 75% of patients assented. Observed messages (at Time 1) directly related to patients' self-reports regarding their decisions (2 weeks later), and how they felt about their decisions and their physicians. Specifically, messages that help build a sense of an alliance (among all parties, including the family/companions), provide support (tangible assistance and reassurance about managing adverse effects), and provide medical content in language that patients and family/companions understand are associated with the patient's decision and decision-making process. CONCLUSION: In two urban, National Cancer Institute-designated comprehensive cancer centers, a large percentage of patients are not offered trials. When offered a trial, most patients enroll. The quality and quantity of communication occurring among the oncologist, patient, and family/companion when trials are discussed matter in the patient's decision-making process. These findings can help increase physician awareness of the ways that messages and communication behaviors can be observed and evaluated to improve clinical practice and research.