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STUDY DESIGN: Systematic Review. OBJECTIVES: To systematically review the clinical outcomes, re-operation, and complication rates of lumbar TDR devices at mid-to long-term follow-up studies for the treatment of lumbar degenerative disc disease (DDD). METHODS: A systematic search was conducted on PubMed, SCOPUS, and Google Scholar to identify follow-up studies that evaluated clinical outcomes of lumbar TDR in patients with DDD. The included studies met the following criteria: prospective or retrospective studies published from 2012 to 2022; a minimum of 5 years post-operative follow-up; a study sample size >10 patients; patients >18 years of age; containing clinical outcomes with Oswestry Disability Index (ODI), Visual Analog Scale (VAS), complication or reoperation rates. RESULTS: Twenty-two studies were included with data on 2284 patients. The mean follow-up time was 8.30 years, with a mean follow-up rate of 86.91%. The study population was 54.97% female, with a mean age of 42.34 years. The mean VAS and ODI pain score improvements were 50.71 ± 6.91 and 30.39 ± 5.32 respectively. The mean clinical success and patient satisfaction rates were 74.79% ± 7.55% and 86.34% ± 5.64%, respectively. The mean complication and reoperation rates were 18.53% ± 6.33% and 13.6% ± 3.83%, respectively. There was no significant difference when comparing mid-term and long-term follow-up studies for all clinical outcomes. CONCLUSIONS: There were significant improvements in pain reduction at last follow-up in patients with TDRs. Mid-term follow-up data on clinical outcomes, complication and reoperation rates of lumbar TDRs were maintained longer term.

OBJECTIVE: To evaluate the global practice pattern of wound dressing use after lumbar fusion for degenerative conditions. METHODS: A survey issued by AO Spine Knowledge Forums Deformity and Degenerative was sent out to AO Spine members. The type of postoperative dressing employed, timing of initial dressing removal, and type of subsequent dressing applied were investigated. Differences in the type of surgery and regional distribution of surgeons' preferences were analyzed. RESULTS: Right following surgery, 60.6% utilized a dry dressing, 23.2% a plastic occlusive dressing, 5.7% glue, 6% a combination of glue and polyester mesh, 2.6% a wound vacuum, and 1.2% other dressings. The initial dressing was removed on postoperative day 1 (11.6%), 2 (39.2%), 3 (20.3%), 4 (1.7%), 5 (4.3%), 6 (0.4%), 7 or later (12.5%), or depending on drain removal (9.9%). Following initial dressing removal, 75.9% applied a dry dressing, 17.7% a plastic occlusive dressing, and 1.3% glue, while 12.1% used no dressing. The use of no additional coverage after initial dressing removal was significantly associated with a later dressing change (p < 0.001). Significant differences emerged after comparing dressing management among different AO Spine regions (p < 0.001). CONCLUSION: Most spine surgeons utilized a dry or plastic occlusive dressing initially applied after surgery. The first dressing was more frequently changed during the first 3 postoperative days and replaced with the same type of dressing. While dressing policies tended not to vary according to the type of surgery, regional differences suggest that actual practice may be based on personal experience rather than available evidence.

Understanding the structure-function relationship in the intervertebral disk (IVD) is crucial for the development of novel tissue engineering strategies to regenerate IVD and the establishment of accurate computational models for low back pain research. A large number of studies have improved our knowledge of the mechanical and structural properties of the nucleus pulposus (NP) and annulus fibrosus (AF), two of the main regions in the IVD. However, few studies have focused on the AF-NP interface (transition zone; TZ). Therefore, the current study aims to, for the first time, characterize the cyclic and failure mechanical properties of the TZ region under physiological loading (1, 3, and 5%s-1 strain rates) and investigate the structural integration mechanisms between the NP, TZ, and AF regions. The results of the current study reveal significant effects of region (NP, TZ, and AF) and strain rates (1, 3, and 5%s-1) on stiffness (p < 0.001). In addition, energy absorption is significantly higher for the AF compared to the TZ and NP (p <0.001) as well as between the TZ and NP (p <0.001). The current research finds adaptation, direct penetration, and entanglement between TZ and AF fibers as three common mechanisms for structural integration between the TZ and AF regions. STATEMENT OF SIGNIFICANCE: Despite a large number of studies that have mechanically, structurally, and biologically characterized the nucleus pulposus (NP) and annulus fibrosus (AF) regions, few studies have focused on the NP-AF interface region (known as Transition Zone; TZ) in the IVD; hence, our understanding of the TZ structure-function relationship is still incomplete. Of particular importance, the cyclic mechanical properties of the TZ, compared to the adjacent regions (NP and AF), are yet to be explored and the precise nature of the structural integration between the NP and AF via the TZ region is not yet known. The current study explores both the mechanical and structural properties of the TZ re

Multiscale micro-nano fibrous structures are a cutting-edge research area in material science and have drawn the attention of scientists in recent years. These structures are widely distributed in nature’s materials and hold fascinating and unique properties, such as mechanical behaviors, high surface area to volume ratio, and special multiscale biological functionalities. Herein, we demonstrate step-by-step biomimetics of a multiscale composite material system and the influence of the different structural mechanisms on mechanical behavior. This is done using systematic biomimetics and investigation of the mechanical effect of every constituent. We have fabricated and characterized mechanically and structurally different material systems to get a comprehensive understanding of the structure-function relationship in multiscale biomimetic constructs (MSBCs) and examine the influence of the material selection and structure. We first characterized the electrospun nanofibers made of polyamide 6 (PA6) and gelatin-polyamide 6 (GPA6) and then constructed and characterized the combined constructs. Our micro-nano fibrous structures were constructed from combined unique coral collagen microfibers and PA6 and GPA6 nanofibers. These hierarchical structures demonstrated an entangled network of nanobridges among the micro collagen fibers. However, the GPA6-collagen structures showed better connectivity with the microfibers and were significantly stiffer and stronger than the PA6-collagen structures due to the material compatibility. Furthermore, our structures demonstrated a considerable resemblance with soft tissue structures. We embedded the MSBC in alginate hydrogel to form biocomposites that displayed a hyperelastic nonlinear behavior with significantly improved toughness and a remarkable similarity to the mechanical behavior of native soft tissues. Our results present great potential to be further developed as tailor-designed multiscale next-generation specialized structures

Current in vitro intervertebral disc (IVD) models do not fully recapitulate the complex mechanobiology of native tissue, and so far there is no strategy to effectively evaluate IVD regeneration. The development of a modular microfluidic on-chip model is expected to enhance the physiological relevance of experimental data leading to successful clinical outcomes.

To fully investigate cellular responses to stimuli and perturbations within tissues, it is essential to replicate the complex molecular interactions within the local microenvironment of cellular niches. Here, the authors introduce Alginate-based tissue engineering (ALTEN), a biomimetic tissue platform that allows ex vivo analysis of explanted tissue biopsies. This method preserves the original characteristics of the source tissue's cellular milieu, allowing multiple and diverse cell types to be maintained over an extended period of time. As a result, ALTEN enables rapid and faithful characterization of perturbations across specific cell types within a tissue. Importantly, using single-cell genomics, this approach provides integrated cellular responses at the resolution of individual cells. ALTEN is a powerful tool for the analysis of cellular responses upon exposure to cytotoxic agents and immunomodulators. Additionally, ALTEN's scalability using automated microfluidic devices for tissue encapsulation and subsequent transport, to enable centralized high-throughput analysis of samples gathered by large-scale multicenter studies, is shown.

Despite extensive efforts over the past 40 years, there is still a significant gap in knowledge of the characteristics of elastic fibers in the intervertebral disc (IVD). More studies are required to clarify the potential contribution of elastic fibers to the IVD (healthy and diseased) function and recommend critical areas for future investigations. On the other hand, current IVD in-vitro models are not true reflections of the complex biological IVD tissue and the role of elastic fibers has often been ignored in developing relevant tissue-engineered scaffolds and realistic computational models. This has affected the progress of IVD studies (tissue engineering solutions, biomechanics, fundamental biology) and translation into clinical practice. Motivated by the current gap, the current review paper presents a comprehensive study (from the early 1980s to 2022) that explores the current understanding of structural (multi-scale hierarchy), biological (development and aging, elastin content, and cell-fiber interaction), and biomechanical properties of the IVD elastic fibers, and provides new insights into future investigations in this domain.

The current study describes a new technology, effective for readily preparing a fluorescent (FL) nanoprobe-based on hyperbranched polymer (HB) and aggregation-induced emission (AIE) fluorogen with high brightness to ultimately develop FL hydrogels. We prepared the AIE nanoprobe using a microfluidic platform to mix hyperbranched polymers (HB, generations 2, 3, and 4) with AIE (TPE-2BA) under shear stress and different rotation speeds (0-5 K RPM) and explored the FL properties of the AIE nanoprobe. Our results reveal that the use of HB generation 4 exhibits 30-times higher FL intensity compared to the AIE alone and is significantly brighter and more stable compared to those that are prepared using HB generations 3 and 2. In contrast to traditional methods, which are expensive and time-consuming and involve polymerization and post-functionalization to develop FL hyperbranched molecules, our proposed method offers a one-step method to prepare an AIE-HB nanoprobe with excellent FL characteristics. We employed the nanoprobe to fabricate fluorescent injectable bioadhesive gel and a hydrogel microchip based on polyvinyl alcohol (PVA). The addition of borax (50 mM) to the PVA + AIE nanoprobe results in the development of an injectable bioadhesive fluorescent gel with the ability to control AIEgen release for 300 min. When borax concentration increases two times (100 mM), the adhesion stress is more than two times bigger (7.1 mN/mm2) compared to that of gel alone (3.4 mN/mm2). Excellent dimensional stability and cell viability of the fluorescent microchip, along with its enhanced mechanical properties, proposes its potential applications in mechanobiology and understanding the impact of microstructure in cell studies.

Collagen fibers within the annulus fibrosus (AF) lamellae are unidirectionally aligned with alternating orientations between adjacent layers. AF constitutive models often combine two adjacent lamellae into a single equivalent layer containing two fiber networks with a crisscross pattern. Additionally, AF models overlook the inter‐lamellar matrix (ILM) as well as elastic fiber networks in between lamellae. We developed a nonhomogenous micromechanical model as well as two coarser homogenous hyperelastic and microplane models of the human AF, and compared their performances against measurements (tissue level uniaxial and biaxial tests as well as whole disc experiments) and seven published hyperelastic models. The micromechanical model had a realistic non-homogenous distribution of collagen fiber networks within each lamella and elastic fiber network in the ILM. For small matrix linear moduli (<0.2 MPa), the ILM showed substantial anisotropy (>10%) due to the elastic fiber network. However, at moduli >0.2 MPa, the effects of the elastic fiber network on differences in stress-strain responses at different directions disappeared (<10%). Variations in sample geometry and boundary conditions (due to uncertainty) markedly affected stress-strain responses of the tissue in uniaxial and biaxial tests (up to 16 times). In tissue level tests, therefore, simulations should represent testing conditions (e.g., boundary conditions, specimen geometry, preloads) as closely as possible. Stress/strain fields estimated from the single equivalent layer approach (conventional method) yielded different results from those predicted by the anatomically more accurate apparoach (i.e., layerwise). In addition, in a disc under a compressive force (symmetric loading), asymmetric stress-strain distributions were computed when using a layerwise simulation. Although all developed and selected published AF models predicted gross compression-displacement responses of the whole disc within the range of m

The development of fluorescent gels, if not the current focus, is at the center of recent efforts devoted to the invention of a new generation of gels. Fluorescent gels have numerous properties that are intrinsic to the gel structure, with additional light-emitting properties making them attractive for different applications. This review focuses on current studies associated with the development of fluorescent gels using aggregation-induced emission fluorophores (AIEgens) to ultimately suggest new directions for future research. Here, we discuss major drawbacks of the methodologies used frequently for the fabrication of fluorescent gels using traditional fluorophores compared to those using AIEgens. The fabrication strategies to develop AIE-based fluorescent gels, including physical mixing, soaking, self-assembly, noncovalent interactions, and permanent chemical reactions, are discussed thoroughly. New and recent findings on developing AIE-active gels are explained. Specifically, physically prepared AIE-based gels including supramolecular, ionic, and chemically prepared AIE-based gels are discussed. In addition, the intrinsic fluorescent properties of natural gels, known as clustering-triggered fluorescent gel, and new and recent relevant findings published in peer-reviewed journals are explained. This review also revealed the biomedical applications of AIE-based fluorescent hydrogels including drug delivery, biosensors, bioimaging, and tissue engineering. In conclusion, the current research situation and future directions are identified.

Damage to the annulus fibrosus (AF), the outer region of the intervertebral disc (IVD), results in an undesirable condition that may accelerate IVD degeneration causing low back pain. Despite intense research interest, attempts to regenerate the IVD have failed so far and no effective strategy has translated into a successful clinical outcome. Of particular significance, the failure of strategies to repair the AF has been a major drawback in the regeneration of IVD and nucleus replacement. It is unlikely to secure regenerative mediators (cells, genes, and biomolecules) and artificial nucleus materials after injection with an unsealed AF, as IVD is exposed to significant load and large deformation during daily activities. The AF defects strongly change the mechanical properties of the IVD and activate catabolic routes that are responsible for accelerating IVD degeneration. Therefore, there is a strong need to develop effective therapeutic strategies to prevent or reconstruct AF damage to support operational IVD regenerative strategies and nucleus replacement. By the way of this review, repair and regenerative strategies for AF reconstruction, their current status, challenges ahead, and future outlooks were discussed.

© 2020 the Partner Organisations. The most frequently used approach to preparing aggregation-induced emission fluorogen (AIEgen) particles is precipitation. Therefore, the addition of an AIEgen solution into water results in the formation of AIEgen particles in a very short time. Within such a short period of time and in the absence of proper mixing under shear, AIE particles are likely to be distributed in a wide range of sizes, thereby affecting their ultimate brightness and applications. Despite numerous attempts, the size of AIEgen particles is still within the range of 200-300 nm. For the first time, we developed a facile robust and cost-effective method for the fabrication of aggregation-induced emission nanoparticles with tuneable particle sizes <100 nm, high quantum yield, and excellent photostability. The direct diffusion of nanoparticles within the cell or in a single-celled organism, as an advantage of size reduction, opens new opportunities for biological and material studies. Such a significant reduction in AIE nanoparticle size has the potential for developing more efficient techniques for characterizing advanced nanomaterials and understanding biological processes and detection strategies.

Natural hydrogels, due to their unique biological properties, have been used extensively for various medical and clinical examinations that are performed to investigate the signs of disease. Recently, complex-crosslinking strategies improved the mechanical properties and advanced approaches have resulted in the introduction of naturally derived hydrogels that exhibit high biocompatibility, with shape memory and self-healing characteristics. Moreover, the creation of self-assembled natural hydrogels under physiological conditions has provided the opportunity to engineer fine-tuning properties. To highlight recent studies of natural-based hydrogels and their applications for medical investigation, a critical review was undertaken using published papers from the Science Direct database. This review presents different natural-based hydrogels (natural, natural-synthetic hybrid and complex-crosslinked hydrogels), their historical evolution, and recent studies of medical examination applications. The application of natural-based hydrogels in the design and fabrication of biosensors, catheters and medical electrodes, detection of cancer, targeted delivery of imaging compounds (bioimaging) and fabrication of fluorescent bioprobes is summarised here. Without doubt, in future, more useful and practical concepts will be derived to identify natural-based hydrogels for a wide range of clinical examination applications.

© 2020, Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature. Lipid bodies are dynamic organelles of photosynthetic microalgae that can be used as the third generation resources for biofuel production. Biosynthesis of lipids can be influenced by different signalling processes. Visualisation of these processes can provide useful information about the fate and associated roles of lipid molecules in different biological systems. In photosynthetic organisms, however, studies of calcium ediated lipid biosynthesis is bottlenecked due to the limitation of proper and efficient technologies, which also include visualisation techniques. Currently, most studies to visualise lipid droplets in vivo have used traditional dyes, and proper visualisation of lipid drops is hindered by dye-specific limitations. This hurdle could be overcome by using recently developed aggregation-induced emission biooprobes. This review reveals current knowledge gaps in the studies of lipid drops and calcium ions in microalgae, as calcium signaling is important secondary messenger to detect a wide variety of environmental stimuli in plant and animal cells. To obtain insight into the mechanisms of these processes, the merits and demerits of currently available visualisation techniques for lipid drops and calcium are also detailed. Finally, opportunities and possibilities are proposed to recommend further improvement of techniques for detecting the role of calcium during lipid formation in microalgae for biofuel production.

In recent decades, microfluidic techniques have been extensively used to advance hydrogel design and control the architectural features on the micro- and nanoscale. The major challenges with the microfluidic approach are clogging and limited architectural features: notably, the creation of the sphere, core-shell, and fibers. Implementation of batch production is almost impossible with the relatively lengthy time of production, which is another disadvantage. This minireview aims to introduce a new microfluidic platform, a vortex fluidic device (VFD), for one-step fabrication of hydrogels with different architectural features and properties. The application of a VFD in the fabrication of physically crosslinked hydrogels with different surface morphologies, the creation of fluorescent hydrogels with excellent photostability and fluorescence properties, and tuning of the structure-property relationship in hydrogels are discussed. We conceive, on the basis of this minireview, that future studies will provide new opportunities to develop hydrogel nanocomposites with superior properties for different biomedical and engineering applications.

© 2020 Elsevier Ltd The triboelectric nanogenerator (TENG) has been introduced as a revolutionary technology in the renewable electrical energy generation at micro/nanoscale. In the current study, experimental and theoretical models for augmented rotary TENGs are presented. The power generated by TENGs is found to be a function of the number of segments, rotational speed, and tribo-surface spacing. Mathematical modeling combined with artificial intelligence is applied to characterize the TENG output under various kinematics and geometric conditions. Sensitivity analysis reveals that the generated energy and the matched resistance depend highly on segmentation and angular velocity rate. It is shown that the optimized harvested energy reaches 0.369 mJ at each cycle. The TENG dynamic outputs for various structural parameters are found and described. This study enhances understanding of rotation-induced periodic TENGs and reveals optimized characteristics for disk-shaped TENG energy harvesters.

Interfacial behavior greatly affects the bulk mechanical performance of fiber reinforced polymer laminates. In this study, polydopamine modified glass fiber was used to fabricate short glass fiber reinforced polymer (GFRP) laminates. The interactions between glass fiber and polydopamine were studied experimentally and theoretically by X-ray photoelectron spectroscopy (XPS) and density functional calculation respectively. Theoretical study clearly demonstrated that electronic interactions existed between polydopamine and glass fiber, indicating the hydrogen bonds/chemical interactions between them that were also demonstrated by XPS results. The enhanced interfacial interaction significantly benefited GFRP laminates, as demonstrated by various mechanical characterizations such as single fiber pull-out and Mode I interlaminar fracture toughness tests. Combining the theoretical and experimental studies indicated that polydopamine modification of glass fiber could be an easy and effective way to significantly improve the interfacial interactions between glass fiber and matrix and enhance the mechanical properties of GFRP laminates.

In light of the rapid growth in microelectronic technology, triboelectric nanogenerators (TENGs) have been exploited as securely sustainable substitutes for energy scavenging purposes as well as self-powered sensory utilization. In essence, TENGs’ energy output and average power distribution depend highly on certain key parameters including contact area, the thickness of electric films and external resistance. This study attempts to predict the behavior of TENGs based on variation of those key parameters and tries to optimize the associated characteristics leading to high-output and light-weight sliding-mode TENGs. To meet this problem, an artificial intelligence approach is taken into consideration and solutions for load resistance and geometry are presented. Furthermore, an experimental setup is designed to evaluate the accuracy of the simulation results, demonstrating the precision of the applied theory. The results revealed that the predefined sliding-mode TENG can harvest 0.25 mJ at each cycle in an open-circuit condition where the weight is almost 42.91 g. Moreover, simulation proves that an appropriate value for the external resistor can increase the scavenged energy up to 3.65 mJ at each reciprocal movement. Finally, temporal responses for charge, current, voltage, power output, and harvested energy are plotted and discussed, facilitating understanding of the relationship between scavenged energy and optimized parameters.

Crystallization is a conventional technique for fabricating physically cross-linked poly(vinyl alcohol)-based hydrogels (PVA) with desired properties. The creation of crystalline regions induced by the freeze-thaw process is attributed to the molecular organization that serves as the junction points containing folded chains. The current study employs an aggregation-induced emission fluorogen (AIEgen) to produce a new approach for studying the kinetics of the formation of crystalline regions induced by the freeze-thaw process. For the first time, this research directly links the effects of freeze-thaw cycles to the final physical and mechanical properties of PVA hydrogels by using AIEgen. The results of the study reveal an increase in the fluorescent properties during the freeze-thaw process that reflects the rise in the percentage of crystallinity. This approach can be employed effectively to demonstrate the crystallization process using significant color and brightness differences in crystalline regions compared to amorphous areas. This capability allows researchers to visualize the crystalline regions clearly in situ and to study their kinetics, formation, and transition in the solid state. The results of this study have implications for the broad class of gels derived through polymer crystallization from solution.

© 2019 Elsevier Ltd Bacterial cellulose (BC) is an organic compound produced by certain types of bacteria. In natural habitats, the majority of bacteria synthesize extracellular polysaccharides, such as cellulose, which form protective envelopes around the cells. Many methods are currently being investigated to enhance cellulose growth. The various celluloses produced by different bacteria possess different morphologies, structures, properties, and applications. However, the literature lacks a comprehensive review of the different methods of BC production, which are critical to BC properties and their final applications. The aims of this review are to provide an overview of the production of BC from different culture methods, to analyze the characteristics of particular BC productions, to indicate existing problems associated with different methods, and to choose suitable culture approaches for BC applications in different fields. The main goals for future studies have also been discussed here.