Evaluating the 'Labeled Magnitude Scale' for measuring sensations of taste and smell

The Labeled Magnitude Scale (LMS) is a semantic scale of perceptual intensity characterized by a quasi-logarithmic spacing of its verbal labels. The LMS had previously been shown to yield psychophysical functions equivalent to magnitude estimation (ME) when gustatory, thermal and nociceptive stimuli were presented and rated together, and the upper bound of the LMS was defined as the 'strongest imaginable oral sensation'. The present study compared the LMS to ME within the more limited contexts of taste and smell. In Experiment 1, subjects used both methods to rate either taste intensity produced by sucrose and NaC1 or odor intensity produced by acetic acid and phenyl ethyl alcohol, with the upper bound of the LMS defined as either the 'strongest imaginable taste' or the 'strongest imaginable odor'. The LMS produced psychophysical functions equivalent to those produced by ME. In, Experiment 2 a new group of subjects used both methods to rate the intensity of three different taste qualities, with the upper bound of the LMS defined as the 'strongest imaginable [sweetness, saltiness, or bitterness]'. In all three cases the LMS produced steeper functions than did ME. Experiment 3 tested the hypothesis that the LMS yields data comparable to ME only when the perceptual domain under study includes painful sensations. This hypothesis was supported when the LMS again produced steeper functions that ME after subjects had been explicitly instructed to omit painful sensations (e.g. the 'burn' of hot peppers) from the concept of 'strongest imaginable taste'. We conclude that the LMS can be used to scale sensations of taste and smell when they are broadly defined, but that it should be modified for use in scaling specific taste (and probably odor) qualities. The implications of these results for theoretical issues related to ME, category-ratio scales and the size of the perceptual range in different sensory modalities are discussed.

Guidance of glial cell migration and axonal growth on electrospun nanofibers of poly-ε-caprolactone and a collagen/poly-ε-caprolactone blend

Our long-term goal is to develop an artificial implant as a conduit for axonal regeneration after peripheral nerve injury. In this study, biodegradable, aligned poly-epsilon-caprolactone (PCL) and collagen/PCL (C/PCL) nanofibers designed as guidance structures were produced by electrospinning and tested in cell culture assays. We compared fibers of 100% PCL with fibers consisting of a 25:75% C/PCL blend. To test their biocompatibility, assays of cell adhesion, survival, migration, effects on cell morphology, axonal growth and axonal guidance were performed. Both types of eletrospun fibers supported oriented neurite outgrowth and glial migration from dorsal root ganglia (DRG) explants. Schwann cell migration, neurite orientation, and process formation of Schwann cells, fibroblasts and olfactory ensheathing cells were improved on C/PCL fibers, when compared to pure PCL fibers. While the velocity of neurite elongation from DRG explants was higher on PCL fibers, analysis of isolated sensory neurons showed significantly better axonal guidance by the C/PCL material. The data demonstrate that electrospun fibers composed of a collagen and PCL blend represent a suitable substrate for supporting cell proliferation, process outgrowth and migration and as such would be a good material for artificial nerve implants.

Evidence from Turner's syndrome of an imprinted X-linked locus affecting cognitive function

Turner's syndrome is a sporadic disorder of human females in which all or part of one X chromosome is deleted. Intelligence is usually normal but social adjustment problems are common. Here we report a study of 80 females with Turner's syndrome and a single X chromosome, in 55 of which the X was maternally derived (45,X[m]) and in 25 it was of paternal origin (45,X[p]). Members of the 45,X[p] group were significantly better adjusted, with superior verbal and higher-order executive function skills, which mediate social interactions. Our observations suggest that there is a genetic locus for social cognition, which is imprinted and is not expressed from the maternally derived X chromosome. Neuropsychological and molecular investigations of eight females with partial deletions of the short arm of the X chromosome indicate that the putative imprinted locus escapes X-inactivation, and probably lies on Xq or close to the centromere on Xp. If expressed only from the X chromosome of paternal origin, the existence of this locus could explain why 46,XY males (whose single X chromosome is maternal) are more vulnerable to developmental disorders of language and social cognition, such as autism, than are 46,XX females.

Direct writing by way of melt electrospinning

Melt electrospun fibers of poly(ϵ-caprolactone) are accurately deposited using an automated stage as the collector. Matching the translation speed of the collector to the speed of the melt electrospinning jet establishes control over the location of fiber deposition. In this sense, melt electrospinning writing can be seen to bridge the gap between solution electrospinning and direct writing additive manufacturing processes.

Degradable polyester scaffolds with controlled surface chemistry combining minimal protein adsorption with specific bioactivation

Advanced biomaterials and scaffolds for tissue engineering place high demands on materials and exceed the passive biocompatibility requirements previously considered acceptable for biomedical implants. Together with degradability, the activation of specific cell–material interactions and a three-dimensional environment that mimics the extracellular matrix are core challenges and prerequisites for the organization of living cells to functional tissue. Moreover, although bioactive signalling combined with minimization of non-specific protein adsorption is an advanced modification technique for flat surfaces, it is usually not accomplished for three-dimensional fibrous scaffolds used in tissue engineering. Here, we present a one-step preparation of fully synthetic, bioactive and degradable extracellular matrix-mimetic scaffolds by electrospinning, using poly(D,L-lactide-co-glycolide) as the matrix polymer. Addition of a functional, amphiphilic macromolecule based on star-shaped poly(ethylene oxide) transforms current biomedically used degradable polyesters into hydrophilic fibres, which causes the suppression of non-specific protein adsorption on the fibres’ surface. The subsequent covalent attachment of cell-adhesion-mediating peptides to the hydrophilic fibres promotes specific bioactivation and enables adhesion of cells through exclusive recognition of the immobilized binding motifs. This approach permits synthetic materials to directly control cell behaviour, for example, resembling the binding of cells to fibronectin immobilized on collagen fibres in the extracellular matrix of connective tissue.

Fiber templating of poly(2-hydroxyethyl methacrylate) for neural tissue engineering

We have developed a method to create longitudinally oriented channels within poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels for neural tissue engineering applications. Incorporated into an entubulation strategy, these scaffolds have the potential to enhance nerve regeneration after transection injuries of either the spinal cord or the peripheral nerve by increasing the available surface area and providing guidance to extending axons and invading cells. The fabrication process is straightforward and the resultant scaffolds are highly reproducible. Polycaprolactone (PCL) fibers were extruded and embedded in transparent, crosslinked pHEMA gels. Sonication of the pHEMA/PCL composite in acetone resulted in the complete dissolution of the PCL, leaving longitudinally oriented, fiber-free channels in the pHEMA gel. Regulating the size and quantity of the PCL fibers allowed us to control the diameter and number of channels. Small and large channel scaffolds were fabricated and thoroughly characterized. The small channel scaffolds had 142+/-7 channels, with approximately 75% of the channels in the 100-200 micro m size range. The large channel scaffolds had 37+/-1 channels, with approximately 77% of the channels in the 300-400 micro m range. The equilibrium water content (EWC), porosity and compressive modulus were measured for each of the structures. Small and large channel scaffolds had, respectively, EWCs of 55.0+/-1.2% and 56.2+/-2.9%, porosities of 35+/-1% and 40+/-1% and compressive moduli of 191+/-7 and 182+/-4kPa.

Growth factor enhancement of peripheral nerve regeneration through a novel synthetic hydrogel tube

OBJECT

The authors' long-term goal is repair of peripheral nerve injuries by using synthetic nerve guidance devices that improve both regeneration and functional outcome relative to an autograft. They report the in vitro processing and in vivo application of synthetic hydrogel tubes that are filled with collagen gel impregnated with growth factors.

METHODS

Poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PHEMA-MMA) porous 12-mm-long tubes with an inner diameter of 1.3 mm and an outer diameter of 1.8 mm were used to repair surgically created 10-mm gaps in the rat sciatic nerve. The inner lumen of the tubes was filled with collagen matrix alone or matrix supplemented with either neurotropin-3 at 1 microg/ml, brain-derived neurotrophic factor at 1 microg/ml, or acidic fibroblast growth factor (FGF-1) at 1 or 10 microg/ml. Nerve regeneration through the growth factor-enhanced tubes was assessed at 8 weeks after repair by histomorphometric analysis at the midgraft level and in the nerve distal to the tube repair. The tubes were biostable and biocompatible, and supported nerve regeneration in more than 90% of cases. Nerve regeneration was improved in tubes in which growth factors were added, compared with empty tubes and those containing collagen gel alone (negative controls). Tubes filled with 10 microg/ml of FGF-1 dispersed in collagen demonstrated regeneration comparable to autografts (positive controls) and showed significantly better regeneration than the other groups.

CONCLUSIONS

The PHEMA-MMA tubes augmented with FGF-1 in their lumens appear to be a promising alternative to autografts for repair of nerve injuries. Studies are in progress to assess the long-term biocompatibility of these implants and to enhance regeneration further.

Psychophysical and behavioral characteristics of olfactory adaptation

Sensory adaptation allows organisms to reach behavioral equilibrium with the ambient environment and respond primarily to changes in stimulation. Given its functional significance, it is not surprising that adaptation in the olfactory system exhibits many of the same characteristics as adaptation in other sensory systems, including vision. Repeated or prolonged exposure to an odorant typically leads to stimulus-specific decreases in olfactory sensitivity to that odorant, but sensitivity recovers over time in the absence of further exposure. Psychophysical analysis shows that olfactory adaptation results in elevations in odor thresholds and in reduced responsiveness to suprathreshold stimulation. Further, the magnitude of the decrease and the time course of adaptation and recovery are dependent on the concentration of the odor and on the duration of exposure. It is generally agreed that olfactory adaptation can occur at multiple levels in the olfactory system and can involve both peripheral (receptor level) and more central (post-receptor) components. Evidence for peripheral and central involvement comes from studies showing that monorhinal stimulation results in adaptation in both the ipsilateral and contralateral nostril, although the degree of adaptation in the ipsilateral nostril is more profound and recovery is slower. Additional evidence for central involvement comes from studies that have found relatively small decreases in peripheral response following repeated stimulation despite substantial reductions in perceived intensity. Most psychophysical studies of adaptation, however, have not differentiated the peripheral and central processes. Although relatively few in number, studies of the parametric features of olfactory adaptation in both vertebrate (e.g. rat) and invertebrate (e.g. Drosophila, Caenorhabditis elegans) animal models appear to replicate the findings in psychophysical studies of adult humans. Despite the broad overall similarity of olfactory adaptation to adaptation in other sensory systems, olfactory adaptation exhibits some unique features. Adaptation in olfaction has been shown to be very long-lasting in some cases and may be modulated by the contribution of pre-neural events and physico-chemical properties of the odorant molecules that govern diffusion to receptor sites and post-receptor clearance.

Manufacture of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) hydrogel tubes for use as nerve guidance channels

Hydrogel tubes of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (p(HEMA-co-MMA)) made by liquid-liquid centrifugal casting are being investigated as potential nerve guidance channels in the central nervous system. An important criterion for the nerve guidance channel is that its mechanical properties are similar to those of the spinal cord, where it will be implanted. The formulated p(HEMA-co-MMA) tubes are soft and flexible, consisting of a gel-like outer layer, and an interconnected macroporous, inner layer. The relative thickness of the gel phase to macroporous phase is controlled by the formulation chemistry, and specifically by the ratio of co-monomers, HEMA and MMA. By varying the surface chemistry of the mold within which the tubes are synthesized, tubes were prepared with either a "cracked" or a smooth outer morphology. Tubes with the cracked outer morphology had periodic channels that traversed the wall of the tube, which resulted in a lower modulus than smooth outer morphology tubes, yet likely greater diffusive permeability. For tubes (and not rods) to be formed, phase separation must precede gelation as is detailed in a formulation phase diagram for HEMA, MMA and water. The tensile elastic modulus of p(HEMA-co-MMA) tubes reflected the formulation chemistry, with greater moduli (up to 400 kPa) recorded for tubes having 10 wt% MMA. The p(HEMA-co-MMA) tubes therefore had similar mechanical properties to those of the spinal cord, which has a reported elastic modulus range between 200 and 600 kPa.

Histology of the gastroesophageal junction: an autopsy study

Current diagnostic criteria for reflux disease and Barrett's esophagus are based on the belief that the gastroesophageal junction normally contains 2 cm of cardiac mucosa composed of mucous glands devoid of parietal cells. This autopsy study disproves this belief. Even when the entire circumference of the gastroesophageal junction is examined, pure cardiac mucosa was completely absent in 56% of patients. All patients had oxyntocardiac mucosa, in which glands contained a mixture of mucous and parietal cells. Cardiac and oxyntocardiac mucosae were present only in part of the circumference of the junction in 50% of patients. The measured maximum length of cardiac plus oxyntocardiac mucosa was less than 0.5 cm in 76% of patients. There was a tendency for the presence and extent of cardiac mucosa to increase with age. Cardiac mucosa at the junction is therefore frequently absent, has considerable individual variation, is very small in extent when present, is commonly absent from some part of the circumference of the junction, and increases in prevalence and length with age. These characteristics of cardiac mucosa make it highly unlikely that it is a normal structure. We develop the hypothesis that cardiac mucosa represents an early histologic manifestation of gastroesophageal reflux.

Melt electrospinning

Melt electrospinning is relatively under-investigated compared to solution electrospinning but provides opportunities in numerous areas, in which solvent accumulation or toxicity are a concern. These applications are diverse, and provide a broad set of challenges to researchers involved in electrospinning. In this context, melt electrospinning provides an alternative approach that bypasses some challenges to solution electrospinning, while bringing new issues to the forefront, such as the thermal stability of polymers. This Focus Review describes the literature on melt electrospinning, as well as highlighting areas where both melt and solution are combined, and potentially merge together in the future.

Matrix inclusion within synthetic hydrogel guidance channels improves specific supraspinal and local axonal regeneration after complete spinal cord transection

We have previously shown that a novel synthetic hydrogel channel composed of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (pHEMA-MMA) is biocompatible and supports axonal regeneration after spinal cord injury. Our goal was to improve the number and type of regenerated axons within the spinal cord through the addition of different matrices and growth factors incorporated within the lumen of the channel. After complete spinal cord transection at T8, pHEMA-MMA channels, having an elastic modulus of 263+/-13 kPa were implanted into adult Sprague Dawley rats. The channels were then filled with one of the following matrices: collagen, fibrin, Matrigel, methylcellulose, or smaller pHEMA-MMA tubes placed within a larger pHEMA-MMA channel (called tubes within channels, TWC). We also supplemented selected matrices (collagen and fibrin) with neurotrophic factors, fibroblast growth factor-1 (FGF-1) and neurotrophin-3 (NT-3). After channel implantation, fibrin glue was applied to the cord-channel interface, and a duraplasty was performed with an expanded polytetrafluoroethylene (ePTFE) membrane. Controls included animals that had either complete spinal cord transection and implantation of unfilled pHEMA-MMA channels or complete spinal cord transection. Regeneration was assessed by retrograde axonal tracing with Fluoro-Gold, and immunohistochemistry with NF-200 (for total axon counts) and calcitonin gene related peptide (CGRP, for sensory axon counts) after 8 weeks survival. Fibrin, Matrigel, methylcellulose, collagen with FGF-1, collagen with NT-3, fibrin with FGF-1, and fibrin with NT-3 increased the total axon density within the channel (ANOVA, p<0.05) compared to unfilled channel controls. Only fibrin with FGF-1 decreased the sensory axon density compared to unfilled channel controls (ANOVA, p<0.05). Fibrin promoted the greatest axonal regeneration from reticular neurons, and methylcellulose promoted the greatest regeneration from vestibular and red nucleus neurons. With Matrigel, there was no axonal regeneration from brainstem motor neurons. The addition of FGF-1 increased the axonal regeneration of vestibular neurons, and the addition of NT-3 decreased the total number of axons regenerating from brainstem neurons. The fibrin and TWC showed a consistent improvement in locomotor function at both 7 and 8 weeks. Thus, the present study shows that the presence and type of matrix contained within synthetic hydrogel guidance channels affects the quantity and origin of axons that regenerate after complete spinal cord transection, and can improve functional recovery. Determining the optimum matrices and growth factors for insertion into these guidance channels will improve regeneration of the injured spinal cord.

Distribution and significance of epithelial types in columnar-lined esophagus

An abnormal columnar-lined esophagus (CLE) is characterized by the presence of cardiac mucosa (CM) oxynto-cardiac mucosa (OCM), and intestinal metaplastic epithelium (IM) between gastric oxyntic mucosa and esophageal squamous epithelium. Thirty-two patients with CLE measuring 2-16 cm long had 5-37 biopsies per patient that showed CM, OCM, or IM for a total of 424 biopsies. Detailed mapping of the distribution of epithelial types within the CLE showed a distinct zonation of epithelial types; CM was present throughout the CLE, whereas OCM and IM tended to occur in the distal and proximal part of the CLE, respectively. All 32 patients (64 of 68 biopsies) showed IM at the most proximal level, compared with 22 of 32 patients (40 of 102 biopsies) in the most distal level biopsies. The density of goblet cells was highest in the most proximal level. The differences in prevalence and density of goblet cells between most proximal and most distal level biopsies were highly significant. These data suggest that for a given number of biopsies within the CLE, the likelihood of finding IM is greatest when the biopsies are concentrated in the most proximal area of the CLE. We suggest that glandular transformation of squamous epithelium results in CM. which evolves into OCM and IM by development of specialized parietal cells and goblet cells, respectively. The severity and nature of reflux cause these epithelial transformations in a constant and predictable manner. Recognition of these changes permits the development of morphologic definitions of reflux disease and the characterization of the sequence of epithelial changes that represent the reflux-adenocarcinoma sequence.

Synthetic hydrogel guidance channels facilitate regeneration of adult rat brainstem motor axons after complete spinal cord transection

Synthetic guidance channels or tubes have been shown to promote axonal regeneration within the spinal cord from brainstem motor nuclei with the inclusion of agents such as matrices, cells, or growth factors to the tube. We examined the biocompatibility and regenerative capacity of synthetic hydrogel tubular devices that were composed of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PHEMA-MMA). Two PHEMA-MMA channels, having a mean elastic modulus of either 177 or 311 kPa were implanted into T8-transected spinal cords of adult Sprague Dawley rats. The cord stumps were inserted into the channels and fibrin glue was applied to the cord-channel interface. An expanded polytetrafluoroethylene (ePTFE) membrane was used for duraplasty. Controls underwent cord transection alone. Gross and microscopic examination of the spinal cords showed continuity of tissue within the synthetic guidance channels between the cord stumps at 4 and 8 weeks. There was a trend towards an increased area and width of bridging neural tissue in the 311-kPa guidance channels compared to the 177-kPa channels. Neurofilament stained axons were visualized within the bridging tissue, and serotonergic axons were found to enter the 311-kPa channel. Retrograde axonal tracing revealed regeneration of axons from reticular, vestibular, and raphe brainstem motor nuclei. For both channels, there was minimal scarring at the channel-cord interface, and less scarring at the channel-dura interface compared to that observed next to the ePTFE. The present study is the first to show that axons from brainstem motor nuclei regenerated in unfilled synthetic hydrogel guidance channels after complete spinal cord transection.

Melt Electrospinning Writing of Highly Ordered Large Volume Scaffold Architectures

The additive manufacturing of highly ordered, micrometer-scale scaffolds is at the forefront of tissue engineering and regenerative medicine research. The fabrication of scaffolds for the regeneration of larger tissue volumes, in particular, remains a major challenge. A technology at the convergence of additive manufacturing and electrospinning-melt electrospinning writing (MEW)-is also limited in thickness/volume due to the accumulation of excess charge from the deposited material repelling and hence, distorting scaffold architectures. The underlying physical principles are studied that constrain MEW of thick, large volume scaffolds. Through computational modeling, numerical values variable working distances are established respectively, which maintain the electrostatic force at a constant level during the printing process. Based on the computational simulations, three voltage profiles are applied to determine the maximum height (exceeding 7 mm) of a highly ordered large volume scaffold. These thick MEW scaffolds have fully interconnected pores and allow cells to migrate and proliferate. To the best of the authors knowledge, this is the first study to report that z-axis adjustment and increasing the voltage during the MEW process allows for the fabrication of high-volume scaffolds with uniform morphologies and fiber diameters.

Dimension-Based Design of Melt Electrowritten Scaffolds

The electrohydrodynamic stabilization of direct-written fluid jets is explored to design and manufacture tissue engineering scaffolds based on their desired fiber dimensions. It is demonstrated that melt electrowriting can fabricate a full spectrum of various fibers with discrete diameters (2-50 µm) using a single nozzle. This change in fiber diameter is digitally controlled by combining the mass flow rate to the nozzle with collector speed variations without changing the applied voltage. The greatest spectrum of fiber diameters was achieved by the simultaneous alteration of those parameters during printing. The highest placement accuracy could be achieved when maintaining the collector speed slightly above the critical translation speed. This permits the fabrication of medical-grade poly(ε-caprolactone) into complex multimodal and multiphasic scaffolds, using a single nozzle in a single print. This ability to control fiber diameter during printing opens new design opportunities for accurate scaffold fabrication for biomedical applications.

Direct in Vitro Electrospinning with Polymer Melts

The electrospinning of polymer melts can offer an advantage over solution electrospinning, in the development of layered tissue constructs for tissue engineering. Melt electrospinning does not require a solvent, of which many are cytotoxic in nature, and the use of nonwater soluble polymers allows the collection of fibers on water or onto cells. In this article, melt electrospinning of a blend of PEO-block-PCL with PCL was performed with in vitro cultured fibroblasts as the collection target. The significant parameters governing electrospinning polymer melts were determined before electrospinning directly onto fibroblasts. In general, a high electric field resulted in the most homogeneous and smallest fibers, although it is important that an optimal pump rate to the spinneret needs to be determined for different configurations. Many parameters governing melt electrospinning differ to those reported for solution electrospinning: the pump rate was a magnitude lower and the viscosity a magnitude higher than successful parameters for solution electrospinning. Cell vitality was maintained throughout the electrospinning process. Six days after electrospinning, fibroblasts adhered to the electrospun fibers and appeared to detach from the underlying flat substrate. The morphology of the fibroblasts changed from spread and flat, to long and spindle-shaped as adherence onto the fiber progressed. Therefore, an important step for producing layer-on-layer tissue constructs of cells and polymers in view of scaffold construction for tissue engineering was successfully demonstrated. The process of using cultured cells as the collection target was termed "direct in vitro electrospinning".

Design and fabrication of tubular scaffolds via direct writing in a melt electrospinning mode

Flexible tubular structures fabricated from solution electrospun fibers are finding increasing use in tissue engineering applications. However it is difficult to control the deposition of fibers due to the chaotic nature of the solution electrospinning jet. By using non-conductive polymer melts instead of polymer solutions the path and collection of the fiber becomes predictable. In this work we demonstrate the melt electrospinning of polycaprolactone in a direct writing mode onto a rotating cylinder. This allows the design and fabrication of tubes using 20 μm diameter fibers with controllable micropatterns and mechanical properties. A key design parameter is the fiber winding angle, where it allows control over scaffold pore morphology (e.g. size, shape, number and porosity). Furthermore, the establishment of a finite element model as a predictive design tool is validated against mechanical testing results of melt electrospun tubes to show that a lesser winding angle provides improved mechanical response to uniaxial tension and compression. In addition, we show that melt electrospun tubes support the growth of three different cell types in vitro and are therefore promising scaffolds for tissue engineering applications.