Structure of diblock copolymers in supercritical carbon dioxide and critical micellization pressure

This paper reports a small angle neutron scattering investigation of micelle formation by fluorocarbon-hydrocarbon block copolymers in supercritical CO2(sc-CO2) at 65 degrees C. A sharp unimer-micelle transition is obtained due to the tuning of the solvating ability of sc-CO2 by profiling pressure, so that the block copolymer, in a semidilute solution, finds sc-CO2 a good solvent at high pressure and a poor solvent at low pressure. At high pressure the copolymer is in a monomeric state with a random coil structure. However, on lowering the pressure, aggregates are formed with a structure similar to aqueous micelles with the hydrocarbon segments forming the core and the fluorocarbon segments forming the corona of the micelle. This unimer-aggregate transition is driven by the gradual elimination of CO2 molecules solvating the hydrocarbon segments of the polymer. Comparison of these results with related data on the same polymer at different temperatures indicates that the transition is critically related to the density of the solvent. This suggests the definition of a critical micellization density, to our knowledge a new concept in colloid chemistry.

Functional neuromuscular stimulation in spinal cord injury

With recent advances in clinical medicine and biomedical engineering, functional neuromuscular stimulation (FNS) can now be added to the psychiatric armamentarium to decrease the debilitating effects of traumatic spinal cord injury. In this article, the components of FNS systems and their evolution in design are presented. The clinical implications of FNS are discussed with respect to upper and lower extremities and bladder applications, and perspectives on future developments and directions are reviewed.

Multiple myeloma: reduced plasma cell contamination in peripheral blood progenitor cell collections performed after repeated high-dose chemotherapy courses

The possibility of reducing tumour cell contamination by cytotoxic drug courses prior to peripheral blood progenitor cell (PBPC) collection was evaluated in two consecutives groups of multiple myeloma (MM) patient candidates for autograft. All patients were at disease onset and received two VAD (vincristine, doxorubicin and dexamethasone) courses as initial debulking. In the first group (44 patients), mobilization and harvest were performed 'upfront', after a single cyclophosphamide (CY) administration of 4 g/m2; in the second group (17 patients), PBPC were collected at the end of a high-dose sequential chemotherapy programme, including: CY 5 g/m2, etoposide (VP16) 2 g/m2, a chemotherapy-free interval with three courses of high-dose dexamethasone, a final mobilizing CY at 7 g/m2. G-CSF was given following each high-dose cytotoxic drug. Cytofluorimetric analysis was performed to quantify progenitors (CD34+ cells) and plasma cells, identified by the high CD38 expression and/or CD38 and CD138 coexpression. Large amounts of PBPC were collected in either group (median harvested CD34+/kg: 15.8 x 10(6) and 13.4 x 10(6), respectively; P=0.9). Circulating plasma cells were significantly higher in patients mobilized 'upfront' compared to those who received the high-dose sequence (median peak values of CD38bright/microl: 39 and 10, respectively; P=0.02); a similar difference was observed in the amount of contaminating plasma cells in the harvest products (median CD38bright/kg: 7.4 x 10(6) and 1.3 x 10(6), respectively; P=0.02). The results demonstrate that an in vivo purging approach is feasible in myeloma patients through repeated high-dose chemotherapy courses; this may provide less-contaminated material suitable for further in vitro purging procedures.

The Morphology of Block Copolymer Micelles in Supercritical Carbon Dioxide by Small-Angle Neutron and X-ray Scattering

Above its critical point, carbon dioxide forms a super-critical fluid, which promises to be an environmentally responsible replacement for the organic solvents traditionally used in polymerizations. Many lipophilic polymers such as polystyrene (PS) are insoluble in CO2, though polymerizations may be accomplished via the use of PS-fluoropolymer stabilizers, which act as emulsifying agents. Small-angle neutron and X-ray scattering have been used to show that these molecules form micelles with a CO2-phobic PS core and a CO2-philic fluoropolymer corona. When the PS block was fixed in length and the fluorinated corona block was varied, the number of block copolymer molecules per micelle (six to seven) remained constant. Thus, the coronal block molecular weight exerts negligible influence on the aggregation number, in accordance with the theoretical predictions of Halperin, Tirrell & Lodge [Adv. Polym. Sci. (1992), 100, 31–46]. These observations are relevant to understanding the mechanisms of micellization and solubilization in supercritical fluids.

Design of Nonionic Surfactants for Supercritical Carbon Dioxide

Interfacially active block copolymer amphiphiles have been synthesized and their self-assembly into micelles in supercritical carbon dioxide (CO2) has been demonstrated with small-angle neutron scattering (SANS). These materials establish the design criteria for molecularly engineered surfactants that can stabilize and disperse otherwise insoluble matter into a CO2 continuous phase. Polystyrene-b-poly(1,1-dihydroperfluorooctyl acrylate) copolymers self-assembled into polydisperse core-shell-type micelles as a result of the disparate solubility characteristics of the different block segments in CO2. These nonionic surfactants for CO2 were shown by SANS to be capable of emulsifying up to 20 percent by weight of a CO2-insoluble hydrocarbon into CO2. This result demonstrates the efficacy of surfactant-modified CO2 in reducing the large volumes of organic and halogenated solvent waste streams released into our environment by solvent-intensive manufacturing and process industries.

Challenges to clinical deployment of upper limb neuroprostheses

The technology for functional neuromuscular stimulation (FNS) as a means of providing upper limb function to people with tetraplegia has been under development by three clinical research groups for almost two decades. This paper presents the current status of the clinical trials of three FNS systems: a noninvasive system built into a cosmetic forearm splint, a 30-channel percutaneous system, and an 8-channel implantable system. The complexity of FNS systems and the unique characteristics of the individuals to whom they are applied combine to create many clinical and technical challenges that must be addressed before the devices can be deployed. The emerging challenges to widespread clinical introduction of FNS systems for hand and arm function are identified and analyzed. In addition to the demands of designed and conducting the clinical trials to satisfy regulatory requirements, the lack of knowledge, skepticism, and the complacency on the part of potential FNS recipients, as well as of rehabilitation professionals, must be overcome through education and careful consideration of economic and societal factors in the design of clinical systems.

Effects of functional electrical stimulation on the joints of adolescents with spinal cord injury

Nineteen adolescent subjects with complete spinal cord injuries resulting in paraplegia or tetraplegia participated in a functional electrical stimulation (FES) program consisting of computerized, controlled exercise and/or weight bearing. The effects of stimulated exercise and standing/walking on the lower extremity joints were prospectively studied. Plain radiographs and MRIs were obtained prior to and following completion of the exercise and standing and walking stages. In addition, the joints of five subjects were studied with synovial biopsies, arthroscopy, and the analysis of serum and synovial fluid for a 550 000 dalton cartilage matrix glycoprotein (CMGP). Pre-exercise joint abnormalities secondary to the spinal cord injury improved following the stimulation program. None of the subjects developed Charcot joint changes. Upon standing with FES, one subject with poor hip coverage prior to participation developed hip subluxation which required surgical repair. No other detrimental clinical effects occurred in the lower extremity joints of subjects participating in an FES program over a 1-year period.