The Effect of Powder Re-Use on the Coalescence Behaviour and Isothermal Crystallisation Kinetics of Polyamide 12 within Powder Bed Fusion.

Polymer powder bed fusion (PBF) is becoming increasingly popular for the fabrication of lightweight, high-performance parts, particularly for medical and aerospace applications. This study investigates the effect of powder re-use and material aging on the coalescence behaviour, melt flowability, and isothermal crystallisation kinetics of polyamide-12 (PA-12) powder. With increased powder re-use, a progressive reduction in melt flowability and material coalescence is observed; at 200 °C, the particle consolidation time increases from 15 s in virgin powder to 180 s in powder recovered from build 6. The observed changes in the behaviour of PA-12 were attributed to polycondensation and cross-linking; these aging phenomena also create structural defects, which hinder the rate and extent of primary crystallisation. At an isothermal crystallisation temperature of 165 °C, the crystallisation half-time increased from 12.78 min in virgin powder to 23.95 min in powder re-used across six build cycles. As a result, the commonly used Avrami model was found to be unsuitable for modelling the crystallisation behaviour of aged PA-12 powder, with the co-efficient of determination (R2) reducing from >0.995 for virgin powder to as low as 0.795 for re-used powder. On the other hand, an alternative method, the Hay model, is able to successfully track full phase transformation within re-used powder (R2 > 0.99). These results highlight the importance of selecting the most appropriate model for analysing the crystallisation kinetics of PA-12 powder re-used across multiple build cycles. This understanding is crucial for obtaining the strong mechanical properties and dimensional precision required for the fabrication of functional, end-use parts within PBF.

PEDOT:PSS Conductivity Enhancement through Addition of the Surfactant Tween 80.

Replacement of indium tin oxide with the intrinsically conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been of significant interest in recent years as a result of lower processing and material costs. In addition, the inclusion of additives has been reported to further enhance the conductivity, rheology, and wettability of PEDOT:PSS. In this study, Tween 80 was shown to decrease the sheet resistance of PEDOT:PSS films from approximately 1000 to 76 Ω□-1 at a 2.67 wt% surfactant concentration. Through X-ray diffraction, Raman spectroscopy, and atomic force microscopy, it was shown that the surfactant caused phase separation and structural ordering of the PEDOT and PSS components, leading to this improvement in conductivity. Furthermore, Tween 80 altered the rheological properties and decreased the surface tension of PEDOT:PSS, making coating common commodity polymers, often used as flexible substrates, more viable.

Development of a Coaching Protocol to Enhance Self-efficacy Within Outpatient Physical Therapy.

Objective: To describe the development of the Specific, Measurable, Action-Oriented, Realistic, and Timed (SMART) Coaching Protocol to increase exercise self-efficacy in middle-aged and older adults participating in Live Long Walk Strong (LLWS) Rehabilitation Program. LLWS Rehabilitation Program is an innovative physical therapist (PT) delivered outpatient intervention for middle- and older-aged adults with slow gait speed. Design: Phase II randomized controlled trial (RCT) with masked outcome assessment. We applied the Knowledge to Action Framework to develop and implement the LLWS SMART Coaching Protocol within an RCT for the LLWS Rehabilitation Program. Data will be collected at baseline and post intervention at 2, 8 and 16 weeks. Setting: Outpatient; VA Boston Healthcare System. Participants: Community-dwelling veterans (N=198) (older than 50 years) with slow gait speed (<1.0 m/s). Interventions: Participants will be randomized to the LLWS Rehabilitation Program, an 8-week (10-session) PT-delivered intervention, or wait-list control group. Each study visit will introduce a new SMART Coaching module focused on goal setting, exercise adherence, and addressing internal and external barriers to meeting exercise goals. Main Outcome Measures: Primary outcome is gait speed and secondary outcome is the Self-Efficacy for Exercise Scale. Conclusions: Incorporating cognitive behavioral tools in physical therapy intervention research is critical for targeting motivational processes needed for exercise behavior change.

An Untargeted Thermogravimetric Analysis-Fourier Transform Infrared-Gas Chromatography-Mass Spectrometry Approach for Plastic Polymer Identification.

Reliable chemical identification of specific polymers in environmental samples represents a major challenge in plastic research, especially with the wide range of commercial polymers available, along with variable additive mixtures. Thermogravimetric analysis-Fourier transform infrared-gas chromatography-mass spectrometry (TGA-FTIR-GC-MS) offers a unique characterization platform that provides both physical and chemical properties of the analyzed polymers. This study presents a library of 11 polymers generated using virgin plastics and post-consumer products. TGA inflection points and mass of remaining residues following pyrolysis, in some cases, proved to be indicative of the polymer type. FTIR analysis of the evolved gas was able to differentiate between all but polypropylene (PP) and polyethylene (PE). Finally, GC-MS was able to differentiate between the unique chemical fingerprints of all but one polymer in the library. This library was then used to characterize real environmental samples of mesoplastics collected from beaches in the U.K. and South Africa. Unambiguous identification of the polymer types was achieved, with PE being the most frequently detected polymer and with South African samples indicating variations that potentially resulted from aging and weathering.

The Effect of a Secondary Process on the Analysis of Isothermal Crystallisation Kinetics by Differential Scanning Calorimetry.

This paper demonstrates the application of a modified Avrami equation in the analysis of crystallisation curves obtained using differential scanning calorimetry (DSC). The model incorporates a square root of time dependence of the secondary process into the conventional Avrami equation and, although previously validated using laser flash analysis and infrared spectroscopy, is not currently transferable to DSC. Application of the model to calorimetric data required long-duration isotherms and a series of data treatments. Once implemented, the square root of time dependence of the secondary process was once again observed. After separation of the secondary process from the primary, a mechanistic n value of 3 was obtained for the primary process. Kinetic parameters obtained from the analysis were used in the model to regenerate the fractional crystallinity curves. Comparison of the model with experimental data generated R2 values in excess of 0.995. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was used as model polymer due to the prominent secondary crystallisation behaviour that this polymer is known to display.

Crosslinker Copolymerization for Property Control in Inverse Vulcanization.

Sulfur is an underused by-product of the petrochemicals industry. Recent research into inverse vulcanization has shown how this excess sulfur can be transformed into functional polymers, by stabilization with organic crosslinkers. For these interesting new materials to realize their potential for applications, more understanding and control of their physical properties is needed. Here we report four new terpolymers prepared from sulfur and two distinct alkene monomers that can be predictively tuned in glass transition, molecular weight, solubility, mechanical properties, and color.

Development of a rapid method to isolate polyhydroxyalkanoates from bacteria for screening studies.

We describe a novel method of Polyhydroxyalkanoate (PHA) extraction using dimethyl sulphoxide (DMSO) for use in screening studies. Compared to conventional chloroform extraction, the DMSO method was shown to release comparable quantities of PHA from Cupriavidus necator cells, with comparable properties as determined using Fourier transform infrared spectroscopy and differential scanning calorimetry.

Stability of human growth hormone in supercritical carbon dioxide.

The instability of human growth hormone (hGH) to temperature and interfaces makes its formulation into injectable, sustained-release drug delivery systems challenging. A novel method of encapsulating hGH in polymeric microparticles has been developed using supercritical CO(2) (scCO(2)) technology, but there is limited understanding of the stability of hGH within this system. The aim of this study was to evaluate the stability of hGH in scCO(2) processing. The integrity of the protein was assessed following exposure to scCO(2) using a range of different analytical techniques. Mass spectrometry showed that no peptide cleavage occurred as a result of processing or exposure to scCO(2). Size-exclusion chromatography detected formation of aggregates at high temperatures, but not as a result of the encapsulation process. Reverse-phase chromatography demonstrated that the production of deamidation products occurred as a function of temperature, but only at temperatures higher than those used for the encapsulation process. Circular dichroism and infrared spectroscopy demonstrated that the use of scCO(2) was not detrimental to the secondary molecular structure of hGH. Together, these results show that the structural integrity of hGH is unaffected by scCO(2) processing and that hGH can be successfully encapsulated in polymer microparticles using this technique.

Differences in treatment advice for common poisons by poisons centres--an international comparison.

OBJECTIVE: To investigate how poisons centres advise on management of common drug poisonings and compare advice on gut decontamination with the EAPCCT/AACT Position Statements. METHODS: An interactive questionnaire was sent to 14 poisons centres asking about working practices, "top 20" enquiries in 2002, and management of 4 specific drug poisonings. RESULTS: Replies were received from centres in 11 countries. Annual telephone enquiry numbers varied from 620 (Sri Lanka) to over 50,000 (Germany for 2000). Recommendations for gut decontamination for acetaminophen poisoning were: activated charcoal (AC) alone (5 centres); gastric lavage (GL) alone (1); AC and/or GL (3); AC, GL and/or ipecac (2). Only 40% (4/10) recommended AC and 50% (3/6) GL within 1 hour. Intervention doses for gut decontamination ranged from 100-200 mg/kg (nine centres) and for "high-risk" groups 75-100 mg/kg (3). Plasma concentration for N-acetylcysteine (NAC) treatment ranged from 150 mg/L (four centres) to 200 mg/L (6) at 4 hours. Results were similarly varied for three other common drug poisons (benzodiazepines, amitriptyline, and paroxetine). CONCLUSIONS: Most poisons centres have protocols that differ in terms of gut decontamination, timing, and intervention doses. Many centres recommend charcoal or gastric lavage after the 1-hour limit proposed in the Position Statements. There is scope for rationalization of approaches to the management of common poisons.

Web based information on clinical toxicology for the United Kingdom: uptake and utilization of TOXBASE in 2000.

AIMS: To examine the use and uptake of TOXBASE, an Internet database for point of care provision of poisons information in the United Kingdom during its first calendar year of web-based access. METHODS: Interrogation of the database software to examine: use by different types of user and geographical origin; profile of ingredient and product access; time of access to the system; profile of access to other parts of the database. RESULTS: Registered users of the system increased in the first full year of operation (1224 new users) and usage of the system increased to 111 410 sessions with 190 223 product monograph accesses in 2000. Major users were hospitals, in particular accident and emergency departments. NHS Direct, a public access information service staffed by nurses, also made increasing use of the system. Usage per head of population was highest in Northern Ireland and Scotland, and least in southern England. Ingredients accessed most frequently were similar in all four countries of the UK. Times of use of the system reflect clinical activity, with hospitals making many accesses during night-time hours. The most popular parts of the database other than poisons information were those dealing with childhood poisoning, information on decontamination procedures, teratology information and slang terms for drugs of abuse. CONCLUSIONS: This Internet system has been widely used in its first full year of operation. The provision of clinically relevant, up to date, information at the point of delivery of patient care is now possible using this approach. It has wide implications for the provision of other types of therapeutic information in clinical areas. Web-based technology represents an opportunity for clinical pharmacologists to provide therapeutic information for clinical colleagues at the bedside.