STUDY OF RELAXATION TRANSITIONS IN SOME AROMATIC POLYESTERS

Методом спинового зонда проведено систематическое изучение основных релаксационных переходов жесткоцепных стеклообразных полимеров в широком интервале температур с применением спиновых зондов разного размера на примере полисульфона. В главной области релаксации ароматических полиэфиров с помощью метода спинового зонда обнаружены два перегиба. Два перегиба, обнаруженные на температурной зависимости времени корреляции вращения, являются следствием размораживания сегментальной подвижности в областях с различной упаковкой сегментов. Показано, что высокотемпературный перегиб соответствует размораживанию сегментальной подвижности кооперативного типа (а -переходу), а перегиб при более низкой температуре р -размораживанию сегментальной подвижности локального типа (а'-процессу). Для объяснения природы данного перехода была использована теоретическая модель полимера, где предполагается, что в аморфных полимерах возможны разные уровни надмолекулярной организации, т.е. существование более упорядоченных и более плотно упакованных областей, которые чередуются с более «рыхлыми» и менее упорядоченными областями. Исследовано влияние различных факторов на положение а’-перехода на температурной шкале. Выбор объема зонда на основе строго обоснованной модели его движения позволил выявить взаимосвязь между вращательным движением зонда и движением отдельных сегментов аморфного полимера ниже температуры стеклования. The spin probe method was used to systematically study the main relaxation transitions of rigid-chain glassy polymers in a wide temperature range using spin probes of different sizes using polysulfone as an example. In the main relaxation region of aromatic polyesters, two inflections were found using the spin probe method. The two inflections found in the temperature dependence of the rotation correlation time are the result of unfreezing of segmental mobility in regions with different packing of segments. It was shown that the high-temperature inflection corresponds to the defrosting of the cooperative-type segmental mobility (a -transition), and the inflection at a lower temperature corresponds to the / -defrosting of the segmental mobility of the local type (the a' -process). To explain the nature of this transition, a theoretical model of the polymer was used, where it is assumed that different levels of supramolecular organization are possible in amorphous polymers, i.e. the existence of more ordered and more densely packed regions, which alternate with looser and less ordered regions. The influence of various factors on the position of the a' -transition on the temperature scale is investigated. The choice of the probe volume on the basis of a strictly substantiated model of its motion made it possible to reveal the relationship between the rotational motion of the probe and the motion of individual segments of the amorphous polymer below the glass transition temperature.

Robot for Ligament Tensioning and Assessment of Spinal Stability

Study Design An in vitro human cadaveric biomechanics study. Objective A proof-of-concept study to quantify whether or not differences in segmental mobility associated with spinal instability could be detected by a robotic distraction system. Methods Testing was performed in fresh human cadaveric tissue. A prototype Robotic Middle Column Distractor was attached unilaterally to the pedicles of L3-4. Distraction forces up to 150 N were applied first in the intact state, and following discectomy of L3-4. Motions were recorded by time-indexed visual and fluoroscopic images, and analyzed to measure actual motions achieved. Functions of the robot unit were monitored during the procedure and evaluated qualitatively. Results A difference of 2.5 mm in z-axis motion was detected at 150 N load between the intact and post-discectomy states. The robot coupled with the image analysis method was able to clearly detect the difference between the intact (“stable”) and post-discectomy (“unstable”) spine. Data analysis of fluoroscopic images taken during the procedure showed greater motion than perceived by the investigators from qualitative review of visual data. All monitored robot functions performed within design parameters without error. Conclusion The study demonstrates the feasibility and utility of utilizing an intraoperative robotic distractor to measure the amount of spinal mobility present at a level. This could lead to an important clinical tool for both diagnostic functions as well as operative assist functions.

Molecular mobility in bulk and in near-surface nano-layers of ultra-high-molecular-weight polyethylene

A comparative study of molecular dynamics in near-surface nanolayers and in a bulk of polyethylene is presented. Molecular mobility in near-surface nanolayers of polyethylene reactor powders and melt-crystallized films of various molecular weights prepared in different crystallization conditions were studied with the help of thermoluminescence technique using high frequency glow dicharge Ar plasma for surface activation. Molecular mobility in a bulk of the same samples was investigated by the method of radio thermoluminescence, in which a deeply penetrating γ-quanta from 60Co radiation was used for activation of the bulk. A marked difference in a temperature position of the peaks on the glow curves of plasma-induced thermoluminescence and those of radiothermoluminescence correspoding to γ- and ß-transitions was found to depend on crystallisation conditions and molecular weight. Quasi-independent segmental mobility (ß-relaxation) in the near-surface nano-layers of UHMWPE reactor powder particles synthesized at low temperatures appeared to be unexpectedly unfreezed at the temperature higher than that in the bulk. It was supposed that this happend because of crystallization under the confinement conditions during low-temperature polymerization leads to formation of a specific surface structure.

Influence of the Degree of Hydration on the Relaxation Microheterogeneity of Segmental Mobility in PVA

The study of local dissipative processes by the method of free-damped torsional oscillations excited in polyvinyl alcohol (PVA) showed the presence of three loss peaks in the internal friction spectrum in different temperature ranges of this spectrum [1].

Inter-examinerreliability study of physical examination procedures to assess the cervical spine

Objective The objective of this study was to establish the level of inter-examiner reliability for six common cervical manual and physical examination procedures used to assess the cervical spine. Materials: Reliability study that used a convenience sample of 51 patients between the ages of 16–70 years presenting with a chief complaint of neck pain. Two physical therapists independently performed the same series of cervical physical examination procedures on each of the participant. The clinicians were blinded to each other’s findings and the clinical status of the patient. Kappa coefficients (κ) were calculated for levels of agreement between the clinicians for each procedure. Results When assessing for asymmetrical motion, excellent levels of reliability (κ range: 0.88–0.96) were observed for the Bilateral Modified Lateral Shear (asymmetry criterion), Bilateral C2 Spinous Kick (asymmetry criterion) and Flexion-Rotation Tests. When pain provocation was used as the indicator of a positive test during palpation of the cervical facet joints, moderate to substantial levels of reliability (κ range: 0.53–0.76) were observed. When patients were instructed not to provide feedback to the clinicians about pain provocation during facet joint palpation and clinicians relied solely on their qualitative assessment of segmental mobility, the level of reliability was lower (κ range: 0.45–0.53). Due to 100 % prevalence of negative findings, Kappa values could not be calculated for the Sharp-Purser test or the Unilateral C2 Spinous Kick Test. Conclusions Most physical examination procedures examined in this study demonstrated moderate to excellent levels of inter-examiner reliability. Palpation for segmental mobility without pain provocation demonstrated a lower level of reliability compared to palpation for pain provocation. Correlation with clinical findings is necessary to establish validity and the applicability of these procedures in clinical practice.

Long-term Radiologic and Clinical Outcomes after Three-level Contiguous Anterior Cervical Diskectomy and Fusion without Plating: A Multicentric Retrospective Study

Background Anterior cervical diskectomy and fusion (ACDF) has been providing good surgical, clinical, and radiologic outcomes in patients suffering from cervical degenerative disk disease (DDD). However, the role of anterior plating is still debated, especially in three-level procedures. This study aimed to investigate long-term clinical and radiologic outcomes and complications after three-level contiguous ACDF without plating for cervical DDD. Methods Two institutional databases were retrieved (January 2009–December 2014) for patients treated with three-level contiguous ACDF without plating. Minimum follow-up (FU) was 5 years. Demographical data, smoking status, implant types, Neck Disability Index (NDI), visual analog scale (VAS) for neck pain, complications, fusion rate, adjacent segment degeneration (ASD), cervical lordosis (CL), and residual segmental mobility were evaluated. Results We enrolled 21 patients. Tantalum and carbon fiber cages were implanted, respectively, in 13 and 8 patients. The mean FU length was 5.76 ± 0.87 years. Mean NDI score was 78.29 ± 9.98% preoperatively and 8.29 ± 1.67% at last FU (p < 0.01), whereas mean VAS score decreased from 7.43 ± 1.14 preoperatively to 0.95 ± 0.95 at last FU (p < 0.01). Complications were one postoperative hematoma, one superficial wound infection, and five cases of postoperative dysphagia (recovered within 3 days). The fusion rate was 90% and ASD was reported in three (14%) cases. The mean CL was 6.33 ± 2.70 degrees preoperatively, 8.19 ± 1.97 degrees 3 months after surgery (p = 0.02), and 7.62 ± 1.96 degrees at latest FU. There was no residual mobility on every operated segment at last FU. The smoking status was an independent risk factor for nonfusion in this case series (p = 0.02). Conclusions Three-level contiguous ACDF without plating seems to be an effective treatment for cervical DDD. Properly designed comparative clinical trials are needed to further investigate this topic.

Mechanical and Water Uptake Properties of Epoxy Nanocomposites with Surfactant-Modified Functionalized Multiwalled Carbon Nanotubes

The superior mechanical properties of multi-walled carbon nanotubes (MWCNTs) play a significant role in the improvement of the mechanical and thermal stability of an epoxy matrix. However, the agglomeration of carbon nanotubes (CNTs) in the epoxy is a common challenge and should be resolved to achieve the desired enhancement effect. The present paper investigated the thermal, mechanical, and water uptake properties of epoxy nanocomposites with surfactant-modified MWCNTs. The nanocomposites were prepared through the incorporation of different weight concentrations of MWCNTs into the epoxy matrix. Comparative analysis of neat epoxy and epoxy/CNT nanocomposites were conducted through thermal, mechanical, microscopic, and water uptake tests to reveal the improvement mechanism. The homogenous distribution of the CNTs in the epoxy was achieved by wrapping the surfactant onto the CNTs. The addition of surfactant-modified CNTs into the epoxy caused an obvious increase in the mechanical and thermal properties. This improvement mechanism could be attributed to the uniform dispersion of the CNTs in the epoxy matrix reducing the free volume between the polymer chains and restricting the chain segmental mobility, leading to strong interfacial bonding and an efficient load transfer capability between the CNTs and the epoxy matrix. However, the mechanical and thermal properties of the epoxy/CNT nanocomposite decreased owing to the agglomeration effect when the concentration of the CNTs exceeded the optimal percentage of 1.5%. Additionally, the CNTs could impart a reduction in the wettability of the surface of the epoxy/CNT nanocomposite, leading to the increase in the contact angle and a reduction in the water uptake, which was significant to improve the durability of the epoxy. Moreover, the higher weight concentration (2%) of the CNTs showed a greater water uptake owing to agglomeration, which may cause the formation of plenty of microcracks and microvoids in the nanocomposite.