António Veloso

Ion beam deposition of Mn-Ir spin valves

Half-biased spin valves have been prepared by ion beam deposition. The magnetoresistance (MR) signal reaches 7.7% and the exchange field is 350 Oe with a coupling field of 15 Oe and a coercivity of the free layer equal to 4 Oe. The [111] texture induced by a very thin Ta buffer layer (thickness <10 /spl Aring/) has a strong effect in increasing the MR signal and coupling field, while decreasing the exchange field and coercivity. The blocking temperature of the MnIr-biased spin valves is 250/spl deg/C and a thermal stability study shows that the exchange field is constant up to 300/spl deg/C, under consecutive 5-h anneals at each temperature. After these anneals, the MR signal is still equal to 5%. These films show better thermal stability than equivalent samples prepared by sputtering.

Use of hybrid chitosan membranes and N1E-115 cells for promoting nerve regeneration in an axonotmesis rat model

Many studies have been dedicated to the development of scaffolds for improving post-traumatic nerve regeneration. The goal of this study was to develop and test hybrid chitosan membranes to use in peripheral nerve reconstruction, either alone or enriched with N1E-115 neural cells. Hybrid chitosan membranes were tested in vitro, to assess their ability in supporting N1E-115 cell survival and differentiation, and in vivo to assess biocompatibility as well as to evaluate their effects on nerve fiber regeneration and functional recovery after a standardized rat sciatic nerve crush injury. Functional recovery was evaluated using the sciatic functional index (SFI), the static sciatic index (SSI), the extensor postural thrust (EPT), the withdrawal reflex latency (WRL) and ankle kinematics. Nerve fiber regeneration was assessed by quantitative stereological analysis and electron microscopy. All chitosan membranes showed good biocompatibility and proved to be a suitable substrate for plating the N1E-115 cellular system. By contrast, in vivo nerve regeneration assessment after crush injury showed that the freeze-dried chitosan type III, without N1E-115 cell addition, was the only type of membrane that significantly improved posttraumatic axonal regrowth and functional recovery. It can be thus suggested that local enwrapping with this type of chitosan membrane may represent an effective approach for the improvement of the clinical outcome in patients receiving peripheral nerve surgery.

Effects of collagen membranes enriched with in vitro-differentiated N1E-115 cells on rat sciatic nerve regeneration after end-to-end repair

Peripheral nerves possess the capacity of self-regeneration after traumatic injury but the extent of regeneration is often poor and may benefit from exogenous factors that enhance growth. The use of cellular systems is a rational approach for delivering neurotrophic factors at the nerve lesion site, and in the present study we investigated the effects of enwrapping the site of end-to-end rat sciatic nerve repair with an equine type III collagen membrane enriched or not with N1E-115 pre-differentiated neural cells. After neurotmesis, the sciatic nerve was repaired by end-to-end suture (End-to-End group), end-to-end suture enwrapped with an equine collagen type III membrane (End-to-EndMemb group); and end-to-end suture enwrapped with an equine collagen type III membrane previously covered with neural cells pre-differentiated in vitro from N1E-115 cells (End-to-EndMembCell group). Along the postoperative, motor and sensory functional recovery was evaluated using extensor postural thrust (EPT), withdrawal reflex latency (WRL) and ankle kinematics. After 20 weeks animals were sacrificed and the repaired sciatic nerves were processed for histological and stereological analysis. Results showed that enwrapment of the rapair site with a collagen membrane, with or without neural cell enrichment, did not lead to any significant improvement in most of functional and stereological predictors of nerve regeneration that we have assessed, with the exception of EPT which recovered significantly better after neural cell enriched membrane employment. It can thus be concluded that this particular type of nerve tissue engineering approach has very limited effects on nerve regeneration after sciatic end-to-end nerve reconstruction in the rat.

Use of PLGA 90:10 Scaffolds Enriched with In Vitro–Differentiated Neural Cells for Repairing Rat Sciatic Nerve Defects

Poly(lactic-co-glycolic acid) (PLGA) nerve tube guides, made of a novel proportion (90:10) of the two polymers, poly(L-lactide): poly(glycolide) and covered with a neural cell line differentiated in vitro, were tested in vivo for promoting nerve regeneration across a 10-mm gap of the rat sciatic nerve. Before in vivo testing, the PLGA 90:10 tubes were tested in vitro for water uptake and mass loss and compared with collagen sheets. The water uptake of the PLGA tubes was lower, and the mass loss was more rapid and higher than those of the collagen sheets when immersed in phosphate-buffered saline (PBS) solution. The pH values of immersing PBS did not change after soaking the collagen sheets and showed to be around 7.4. On the other hand, the pH values of PBS after soaking PLGA tubes decreased gradually during 10 days reaching values around 3.5. For the in vivo testing, 22 Sasco Sprague adult rats were divided into four groups--group 1: gap not reconstructed; group 2: gap reconstructed using an autologous nerve graft; group 3: gap reconstructed with PLGA 90:10 tube guides; group 4: gap reconstructed with PLGA 90:10 tube guides covered with neural cells differentiated in vitro. Motor and sensory functional recovery was evaluated throughout a healing period of 20 weeks using sciatic functional index, static sciatic index, extensor postural thrust, withdrawal reflex latency, and ankle kinematics. Stereological analysis was carried out on regenerated nerve fibers. Both motor and sensory functions improved significantly in the three experimental nerve repair groups, although the rate and extent of recovery was significantly higher in the group where the gap was reconstructed using the autologous graft. The presence of neural cells covering the inside of the PLGA tube guides did not make any difference in the functional recovery. By contrast, morphometric analysis showed that the introduction of N1E-115 cells inside PLGA 90:10 tube guides led to a significant lower number and size of regenerated nerve fibers, suggesting thus that this approach is not adequate for promoting peripheral nerve repair. Further studies are warranted to assess the role of other cellular systems as a foreseeable therapeutic strategy in peripheral nerve regeneration.

A Biomechanical Model of the Scapulothoracic Joint to Accurately Capture Scapular Kinematics during Shoulder Movements

The complexity of shoulder mechanics combined with the movement of skin relative to the scapula makes it difficult to measure shoulder kinematics with sufficient accuracy to distinguish between symptomatic and asymptomatic individuals. Multibody skeletal models can improve motion capture accuracy by reducing the space of possible joint movements, and models are used widely to improve measurement of lower limb kinematics. In this study, we developed a rigid-body model of a scapulothoracic joint to describe the kinematics of the scapula relative to the thorax. This model describes scapular kinematics with four degrees of freedom: 1) elevation and 2) abduction of the scapula on an ellipsoidal thoracic surface, 3) upward rotation of the scapula normal to the thoracic surface, and 4) internal rotation of the scapula to lift the medial border of the scapula off the surface of the thorax. The surface dimensions and joint axes can be customized to match an individual’s anthropometry. We compared the model to “gold standard” bone-pin kinematics collected during three shoulder tasks and found modeled scapular kinematics to be accurate to within 2mm root-mean-squared error for individual bone-pin markers across all markers and movement tasks. As an additional test, we added random and systematic noise to the bone-pin marker data and found that the model reduced kinematic variability due to noise by 65% compared to Euler angles computed without the model. Our scapulothoracic joint model can be used for inverse and forward dynamics analyses and to compute joint reaction loads. The computational performance of the scapulothoracic joint model is well suited for real-time applications; it is freely available for use with OpenSim 3.2, and is customizable and usable with other OpenSim models.

Kinematic Analysis of Gait in the Second and Third Trimesters of Pregnancy

The kinematic analysis of gait during pregnancy provides more information about the anatomical changes and contributes to exercise and rehabilitation prescription. The purposes were to quantify the lower limb kinematics of gait and to compare it between the second and third trimesters of pregnancy and with a control group. A three-dimensional analysis was performed in twenty-two pregnant women and twelve nonpregnant. Repeated Measures and Manova tests were performed for comparisons between trimesters and between pregnant and controls. The walking speed, stride width, right-/left-step time, cycle time and time of support, and flight phases remain unchanged between trimesters and between pregnant and controls. Stride and right-/left-step lengths decreased between trimesters. Double limb support time increased between trimesters, and it increased when compared with controls. Joint kinematics showed a significant decrease of right-hip extension and adduction during stance phase between trimesters and when compared with controls. Also, an increase in left-knee flexion and a decrease in right-ankle plantarflexion were found between trimesters. The results suggested that pregnant women need to maintain greater stability of body and to become more efficient in locomotion. Further data from the beginning of pregnancy anthropometric data may contribute to the analysis.

Use of chitosan scaff olds for repairing rat sciatic nerve defects

Neurotmesis must be surgically treated by direct end-to-end suture of the two nerve stumps or by a nerve graft harvested from elsewhere in the body in case of tissue loss. To avoid secondary damage due to harvesting of the nerve graft, a tube-guide can be used to bridge the nerve gap. Previously, our group developed and tested hybrid chitosan membranes for peripheral nerve tubulization and showed that freeze-dried chitosan type III membranes were particularly effective for improving peripheral nerve functional recovery after axonotmesis. Chitosan type III membranes have about 110 microm pores and about 90% of porosity, due to the employment of freeze-drying technique. The present study aimed to verify if chitosan type III membranes can be successfully used also for improving peripheral nerve functional recovery after neurotmesis of the rat sciatic nerve. Sasco Sprague-Dawley adult rats were divided into 6 groups: Group 1: end-to-end neurorrhaphy enwrapped by chitosan membrane type III (End-to-EndChitll); Group 2: 10mm-nerve gap bridged by an autologous nerve graft enwrapped by chitosan membrane type III (Graf180degreeChitIII); Group 3: 10 mm-nerve gap bridged by chitosan type III tube-guides (GapChitIII); These 3 experimental groups were compared with 3 control groups, respectively: Group 4: 10 mm-nerve gap bridged by an autologous nerve graft (Graft180degree); Group 5: 10 mm-nerve gap bridged by PLGA 90:10 tube-guides (PLGA); Group 6: end-to-end neurorrhaphy alone (End-to-End). Motor and sensory functional recovery were evaluated throughout a healing period of 20 weeks using extensor postural thrust (EPT), withdrawal reflex latency (WRL) and ankle kinematics. Regenerated nerves withdrawn at the end of the experiment were analysed histologically. Results showed that nerve regeneration was successful in all experimental and control groups and that chitosan type III tubulization induced a significantly better nerve regeneration and functional recovery in comparison to PLGA tubulization control. Further investigation is needed to explore the mechanisms at the basis of the positive effects of chitosan type III on axonal regeneration.

Osteogenic index of step exercise depending on choreographic movements, session duration, and stepping rate

Background: Step exercise has been promoted as a low impact physical activity recommended for the improvement of cardiorespiratory and muscular fitness. This recreational activity might also be recommended to improve bone health since mechanical load plays an important role in the normal development of the skeleton. Methods: Our main purpose was to characterised 100 step sessions and to calculated osteogenic index (OI) according to Turner and Robling: OI (one session) = peak ground reaction force(BW)*ln(number of loading cycles+1). Results: Main results (mean±SD) were as follows: OI was 12.0±0.8; peak ground reaction force (GRF) was 1.40±0.10 times body weight (BW); session duration was 38.6±8.3 min; stepping rate was 134.6±4.7 beats per minute (bpm); the movements performed most often were marching, knee hop, side leg, L step, and over the top; and the number of loading cycles was 4194.1±1055.2. OI and GRF increased significantly when stepping rate was higher than 135 bpm. This stepping rate might be used as a reference for higher intensity classes. A frequency of two to three sessions per week of step exercise is recommended. Conclusions: Despite the benefits that have been stated when step classes are structured correctly and adapted to the participants, further research is needed concerning biomechanical load, exercise prescription, and injury prevention.

The sensitivity of two-dimensional hindlimb joint kinematics analysis in assessing functional recovery in rats after sciatic nerve crush.

Walking analysis in the rat is increasingly used to assess functional recovery after peripheral nerve injury. Here we assess the sensitivity and specificity of hindlimb joint kinematics measures during the rat gait early after sciatic nerve crush injury (DEN), after twelve weeks of recovery (REINN) and in sham-operated controls (Sham) using discriminant analysis. The analysis addressed gait spatiotemporal variables and hip, knee and ankle angle and angular velocity measures during the entire walking cycle. In DEN animals, changes affected all studied joints plus spatiotemporal parameters of gait. Both the spatiotemporal and ankle kinematics parameters recovered to normality within twelve weeks. At this time point, some hip and knee kinematics values were still abnormal when compared to sham controls. Discriminant models based on hip, knee and ankle kinematics displayed maximal sensitivity to identify DEN animals. However, the discriminant models based on spatiotemporal and ankle kinematics data showed a poor performance when assigning animals to the REINN and Sham groups. Models using hip and knee kinematics during walking showed the best sensitivity to recognize the reinnervated animals. The model construed on the basis of hip joint kinematics was the one combining highest sensitivity with robustness and high specificity. It is concluded that ankle joint kinematics fails in detecting minor functional deficits after long term recovery from sciatic nerve crush and extending the kinematic analysis during walking to the hip and knee joints improves the sensitivity of this functional test.

Neural cell transplantation effects on sciatic nerve regeneration after a standardized crush injury in the rat.

The goal of the present study was to assess whether in vitro‐differentiated N1E‐115 cells supported by a collagen membrane would enhance rat sciatic nerve regeneration after a crush injury. To set up an appropriate experimental model for investigating the effects of neural cell transplantation, we have recently described the sequence of functional and morphologic changes occurring after a standardized sciatic nerve crush injury with a nonserrated clamp. Functional recovery was evaluated using the sciatic functional index, the static sciatic index, the extensor postural thrust, the withdrawal reflex latency, and ankle kinematics. In addition, histomorphometric analysis was carried out on regenerated nerve fibers by means of the 2D‐disector method. Based on the results of the EPT and of some of the ankle locomotor kinematic parameters analyzed, the hypothesis that N1E‐115 cells may enhance nerve regeneration is partially supported although histomorphometry disclosed no significant difference in nerve fiber regeneration between the different experimental groups. Therefore, results suggest that enrichment of equine type III collagen membrane with the N1E‐115 cellular system in the rat sciatic nerve crush model may support recovery, at least in terms of motor function. The discrepancy between functional and morphological results also suggests that the combined use of functional and morphological analysis should be recommended for an overall assessment of recovery in nerve regeneration studies.