Stimuli-responsive Matrix Research Articles

Functional Stimuli-Responsive Gels: Hydrogels and Microgels.

One strategy that has gained much attention in the last decades is the understanding and further mimicking of structures and behaviours found in nature, as inspiration to develop materials with additional functionalities. This review presents recent advances in stimuli-responsive gels with emphasis on functional hydrogels and microgels. The first part of the review highlights the high impact of stimuli-responsive hydrogels in materials science. From macro to micro scale, the review also collects the most recent studies on the preparation of hybrid polymeric microgels composed of a nanoparticle (able to respond to external stimuli), encapsulated or grown into a stimuli-responsive matrix (microgel). This combination gave rise to interesting multi-responsive functional microgels and paved a new path for the preparation of multi-stimuli “smart” systems. Finally, special attention is focused on a new generation of functional stimuli-responsive polymer hydrogels able to self-shape (shape-memory) and/or self-repair. This last functionality could be considered as the closing loop for smart polymeric gels.

Silicon chip with capacitors and transistors for interfacing organotypic brain slice of rat hippocampus.

Probing projections between brain areas and their modulation by synaptic potentiation requires dense arrays of contacts for noninvasive electrical stimulation and recording. Semiconductor technology is able to provide planar arrays with high spatial resolution to be used with planar neuronal structures such as organotypic brain slices. To address basic methodical issues we developed a silicon chip with simple arrays of insulated capacitors and field-effect transistors for stimulation of neuronal activity and recording of evoked field potentials. Brain slices from rat hippocampus were cultured on that substrate. We achieved local stimulation of the CA3 region by applying defined voltage pulses to the chip capacitors. Recording of resulting local field potentials in the CA1 region was accomplished with transistors. The relationship between stimulation and recording was rationalized by a sheet conductor model. By combining a row of capacitors with a row of transistors we determined a simple stimulus-response matrix from CA3 to CA1. Possible contributions of inhomogeneities of synaptic projection, of tissue structure and of neuroelectronic interfacing were considered. The study provides the basis for a development of semiconductor chips with high spatial resolution that are required for long-term studies of topographic mapping.

Mathematical Studies of the Information in the Stimulus–Response Matrix

This paper considers the information transmitted in absolute judgments as encoded in a stimulus–response matrix (e.g., see Garner and Hake, 1951). When transmitted information is plotted against the number of stimulus categories in the matrix, one obtains a curve that increases monotonically toward a plateau, which is the maximum information transmittable per stimulus for the particular range of stimuli employed. We demonstrate that although the maximum information transmitted is an attribute of the stimulus continuum itself, the shape of the curve is an empirical property of the stimulus–response matrix, which is determined, in part, by maintaining a constant stimulus category width. Therefore, in principle, each curve of information transmitted vs number of stimulus categories can be determined by a single point: the rightmost point on the graph.

Facilitating Syntax Acquisition

Despite current emphasis on semantic and pragmatic content of children's language, structure or syntax remains concern to language interventionists in reaching languagedeficient children to express that content (2). Instructional methods are required that facilitate the rule-induction process so that these children will generalize from trained to untrained exemplars of structural rules. Use of miniature linguistic sysrems offers that potential (1, 3). They are defined as a stimulus-response matrix in which responses controlled by one class of stimuli are taught to occur in sequential order with responses controlled by another class of stimuli with the end result being that the subject responds correctly to untrained combinations of stimuli from these two classes (3, p. 319). Miniature linguistic systems have been used primarily to develop generalized verbobject sequences and need to be extended to more complex language structures (3). Results of using miniature linguistic systems approach to teaching two 6-yr.-old Down's Syndrome children to express the subject-verbobject structure are reported here. This is the underlying srructure of English and provides base for further structural expansion. A 20-cell matrix was constructed using five subjects (boy, girl, dog, cat, horse) and four verb-object sequences (wear glarses, sit floor, ear food, run grass). A stimulus picture represented each cell in the matrix, e.g., girl sit floor. The children were trained, using reinforcement and imitative prompts, to express boy with each of the four verb-object sequences and wear glasres with each of the five subjects. Both children produced the subject-verb-object structure correctly for the remaining untrained cells of the matrix presented in random order on generalization test. These results suggest the potential of miniature linguistic systems for systematically developing more complex language in children following the structural hierarchy.