Manufacture of Multilayered Artificial Cell Membranes through Sequential Bilayer Deposition on Emulsion Templates

Efforts to manufacture artificial cells that replicate the architectures, processes and behaviours of biological cells are rapidly increasing. Perhaps the most commonly reconstructed cellular structure is the membrane, through the use of unilamellar vesicles as models. However, many cellular membranes, including bacterial double membranes, nuclear envelopes, and organelle membranes, are multilamellar. Due to a lack of technologies available for their controlled construction, multilayered membranes are not part of the repertoire of cell-mimetic motifs used in bottom-up synthetic biology. To address this, we developed emulsion-based technologies that allow cell-sized multilayered vesicles to be produced layer-by-layer, with compositional control over each layer, thus enabling studies that would otherwise remain inaccessible. We discovered that bending rigidities scale with the number of layers and demonstrate inter-bilayer registration between coexisting liquid–liquid domains. These technologies will contribute to the exploitation of multilayered membrane structures, paving the way for incorporating protein complexes that span multiple bilayers.     

Structural performance of a climbing cactus: making the most of softness

Climbing plants must reach supports and navigate gaps to colonize trees. This requires a structural organization ensuring the rigidity of so-called ‘searcher’ stems. Cacti have succulent stems adapted for water storage in dry habitats. We investigate how a climbing cactus Selenicereus setaceus develops its stem structure and succulent tissues for climbing. We applied a ‘wide scale’ approach combining field-based bending, tensile and swellability tests with fine-scale rheological, compression and anatomical analyses in laboratory conditions. Gap-spanning ‘searcher’ stems rely significantly on the soft cortex and outer skin of the stem for rigidity in bending (60–94%). A woody core contributes significantly to axial and radial compressive strength (80%). Rheological tests indicated that storage moduli were consistently higher than loss moduli indicating that the mucilaginous cortical tissue behaved like a viscoelastic solid with properties similar to physical or chemical hydrogels. Rheological and compression properties of the soft tissue changed from young to old stages. The hydrogel–skin composite is a multi-functional structure contributing to rigidity in searcher stems but also imparting compliance and benign failure in environmental situations when stems must fail. Soft tissue composites changing in function via changes in development and turgescence have a great potential for exploring candidate materials for technical applications.     

The dorsolateral pre‑frontal cortex bi‑polar error‑related potential in a locked‑in patient implanted with a daily use brain–computer interface

While brain computer interfaces (BCIs) offer the potential of allowing those suffering from loss of muscle control to once again fully engage with their environment by bypassing the affected motor system and decoding user intentions directly from brain activity, they are prone to errors. One possible avenue for BCI performance improvement is to detect when the BCI user perceives the BCI to have made an unintended action and thus take corrective actions. Error-related potentials (ErrPs) are neural correlates of error awareness and as such can provide an indication of when a BCI system is not performing according to the user’s intentions. Here, we investigate the brain signals of an implanted BCI user suffering from locked-in syndrome (LIS) due to late-stage ALS that prevents her from being able to speak or move but not from using her BCI at home on a daily basis to communicate, for the presence of error-related signals. We first establish the presence of an ErrP originating from the dorsolateral pre-frontal cortex (dLPFC) in response to errors made during a discrete feedback task that mimics the click-based spelling software she uses to communicate. Then, we show that this ErrP can also be elicited by cursor movement errors in a continuous BCI cursor control task. This work represents a first step toward detecting ErrPs during the daily home use of a communications BCI.     

Review

THE EXPERIENCE OF NATURE: A PSYCHOLOGICAL PERSPECTIVE by Rachel Kaplan & Stephen Kaplan, Cambridge University Press, 1989, 337pp, £10.95 (p/b), 0-521-34939-7.

THE ECOLOGY OF URBAN HABITATS by 0. L. Gilbert, Chapman & Hall, London, 1989, 369pp, 0-412-28270-4, £35.00.

DIRECTORY FOR THE ENVIRONMENT: ORGANISATIONS IN BRITAIN AND IRELAND 1986-7, Michael J. C. Barker, ed., London: Routledge & Kegan Paul, 1986. Second edition, pp. xviii + 278, £18.99, PB, ISBN 0-7102-0961-4.

THE URBAN ENVIRONMENT: A SOURCEBOOK FOR THE 1990s, Gerald Dawe, ed., Birmingham: Centre for Urban Ecology, 1990, pp. 636, £55.00, PB, ISBN 0-907272-07-X.

PLANTS IN THE LANDSCAPE (2nd Edn.), by Philip L. Carpenter and Theodore D. Walker, W. H. Freeman, New York and Oxford, 1990, 401 pp., ISBN 0-7167-1808-1, £29.95 HB.

SPORTS GEOGRAPHY by John Bale, E. & F. N. Spon, 1989, 0-419-14390-4, £16.95 PB.

THE POLITICS OF PARK DESIGN: A HISTORY OF URBAN PARKS IN AMERICA by Galen Cranz, ISBN 0 262 53084 8, 347pp, London: M.I.T. Press, 1989, £11.25, P.B.     

Book reviews

Nationality and Planning in Scotland and Wales. R. Macdonald & H. Thomas (Eds). Cardiff, University of Wales Press, 1997, 312 pp., hb £35.00, ISBN 0–7083–1398–1.

Urban Land and Property Markets in Sweden. Thomas Kalbro & Hans Mattsson. London, UCL Press, 1995, 208 pp., £48.00 hb, ISBN 1–85728–052–0.

Contested Countryside Cultures: Otherness, Marginalisation and Rurality. P. Cloke & J. Little (Eds). London, Routledge, 1997, 304 pp., £15.99 hb, ISBN 0–415–14075–7.     

Disinfection by-product formation after biologically assisted GAC treatment of water supplies with different bromide and DOC content

Chlorination of drinking water in the presence of bromide and dissolved organic carbon (DOC) leads to the formation of brominated and chlorinated disinfection by-products (DBP). The concentration of bromide ions in the raw water is a significant factor in the speciation of DBP formed, and causes shifts in trihalomethane (THM) formation from chlorinated to brominated species. Drinking water treatment techniques that remove organic contaminants without affecting bromide ion concentrations cause increases in the brominated THM. For the present study, three water supplies containing different DOC and ambient bromide concentrations were filtered through biologically assisted granular activated carbon (BGAC). Similar to adsorption and coagulation treatment, this treatment does not remove bromide from drinking water; also, THMFP (trihalomethane formation potential) analysis indicated that the chlorinated effluent contained higher concentrations of brominated THM in comparison to the influent. Although BGAC may increase the brominated THM, which may be more toxic than the chlorinated THM, the overall reduction of THMFP by DOC removal far exceeds this negative change, thereby producing a much less toxic finished drinking water. This work is part of a study to make high DOC surface waters on the Canadian prairie safe and palatable for small volume users (individuals or small communities).     

Book reviews

Managing Cities. The New Urban Context. P. Healey, S. Cameron, S. Davoudi, S. Graham & A. Madani‐Pour (Eds) Chichester, John Wiley and Sons, 1995, £14.95 pb, ISBN 0–471–95533–7

Industrial Property: Policy and Economic Development. Rick Ball & Andy Pratt (Eds). London, Routledge, 1994, £45.00 hb, ISBN 0–415–09152–7

Grassroots Environmental Action: People's Participation in Sustainable Development. Dharam P. Ghai & Jessica M. Vivian (Eds). London and New York, Routledge, 1995 (pb), 347 pp., ISBN 0–415–12703–3

Services and Space: Key Aspects of Urban and Regional Development. N. Marshall & P. Wood. Essex, Longman Scientific and Technical, 1995, 294 pp., £17.99 pb, ISBN 0–582–25162–1

Servicing The Middle Classes: Class, Gender and Waged Domestic Labour in Contemporary Britain. Nicky Gregson & Michelle Lowe. Routledge, 1994, vii + 327 pp., £13.99 pb, ISBN 0–419–08531–4

Urban Development Planning: Lessons for the Economic Reconstruction of South Africa's Cities. Richard Tomlinson. Johannesburg, Witwatersrand University Press, 1994, 277 pp., £14.95 pb, ISBN 1–868–14258–2     

Reactive Liners Prepared Using Powders of Aluminum and Aluminum‐Magnesium Alloys

Cylindrical reactive liners filled with powders of aluminum, aluminum‐magnesium alloys, and aluminum‐magnesium powder blends were prepared and initiated by a centrally located explosive charge. The experiments were performed in a cubic chamber. Several transient pressure measurements were taken in addition to the quasistatic pressure caused by the explosion. Results were compared against a reference case with an inert liner filled with aluminum oxide powder. For all reactive liners, an increase in both quasistatic pressure and blast wave strength were observed compared to the case of an inert liner. In experiments with mechanically alloyed Al ⋅ Mg powders, the quasistatic pressure is effectively the same as in experiments with pure aluminum. An improvement in the achieved quasistatic pressure is observed for the liners with a cast alloyed Al ⋅ Mg powder. Most interestingly, a substantial contribution to the air blast indicative of very early reaction occurring in sub‐millisecond time scale is observed for all experiments with reactive liners. The most substantial improvement in the blast characteristics is observed in experiments with mechanically alloyed Al ⋅ Mg powders. While the mechanisms of prompt reactions of metals and alloys remain largely unexplored, the present results highlight the importance of such reactions for reactive liners and other components of energetic systems.     

Transverse depth-dependent changes in corneal collagen lamellar orientation and distribution

It is thought that corneal surface topography may be stabilized by the angular orientation of out-of plane lamellae that insert into the anterior limiting membrane. In this study, micro-focus X-ray scattering data were used to obtain quantitative information about lamellar inclination (with respect to the corneal surface) and the X-ray scatter intensity throughout the depth of the cornea from the centre to the temporal limbus. The average collagen inclination remained predominantly parallel to the tissue surface at all depths. However, in the central cornea, the spread of inclination angles was greatest in the anterior-most stroma (reflecting the increased lamellar interweaving in this region), and decreased with tissue depth; in the peripheral cornea inclination angles showed less variation throughout the tissue thickness. Inclination angles in the deeper stroma were generally higher in the peripheral cornea, suggesting the presence of more interweaving in the posterior stroma away from the central cornea. An increase in collagen X-ray scatter was identified in a region extending from the sclera anteriorly until about 2 mm from the corneal centre. This could arise from the presence of larger diameter fibrils, probably of scleral origin, which are known to exist in this region. Incorporation of this quantitative information into finite-element models will further improve the accuracy with which they can predict the biomechanical response of the cornea to pathology and refractive procedures.