Predicting adequate segmental lordosis correction in lumbar spinal stenosis patients undergoing oblique lumbar interbody fusion: a focus on the discontinuous segment.

PURPOSE: To identify the factors associated with a correction of the segmental angle (SA) with a total change greater than 10° in each level following minimally invasive oblique lumbar interbody fusion (MIS-OLIF). METHODS: Patients with lumbar spinal stenosis who underwent single- or two-level MIS-OLIF were reviewed. Segments with adequate correction of the SA >10° after MIS-OLIF in immediate postoperative radiograph were categorized as discontinuous segments (D segments), whereas those without such improvement were assigned as continuous segments (C segments). Clinical and radiological parameters were compared, and multivariate logistic regression analysis was performed to identify factors associated with SA correction >10° after MIS-OLIF. RESULTS: Of 211 segments included, 38 segments (18.0%) were classified as D segments. Compared with C segments, D segments demonstrated a significantly smaller preoperative SA (mean ± standard deviation [SD], - 1.1° ± 6.7° vs. 6.6° ± 6.3°, p < 0.001), larger change of SA (mean ± SD, 13.5° ± 3.4° vs. 3.1° ± 3.9°, p < 0.001), and a higher rate of presence of facet effusion (76.3% vs. 48.6%, p = 0.002). Logistic regression revealed preoperative SA (odds ratio (OR) [95% confidence interval (CI)]:0.733 [0.639-0.840], p < 0.001) and facet effusion (OR [95% CI]:14.054 [1.758-112.377], p = 0.027) as significant predictors for >10° SA correction after MIS-OLIF. CONCLUSION: Preoperative kyphotic SA and facet effusion can predict SA correction >10° following MIS-OLIF. For patients with lordotic SA and no preoperative facet effusion, supplemental procedures, such as anterior column release or posterior osteotomy, should be prepared for additional lumbar lordosis correction required for remnant global sagittal imbalance after MIS-OLIF.

Determining optimal bead central angle by applying machine learning to wire arc additive manufacturing (WAAM).

Wire arc additive manufacturing (WAAM) is being extensively used in various industrial fields. In WAAM, if a bead is deposited without considering the central angle, its shape may collapse with increasing number of layers. To address this problem, a new method for optimizing the bead geometry using a support vector machine (SVM) classifier was established in this study. The ranges of the optimal deposition conditions were determined using the SVM classifier and verified by experiments. Geometric data of deposited beads were extracted using a laser profiler, and an SVM binary classifier was used to predict suitable ranges of the deposition conditions. Data were extracted through 20 single-layer basic experiments, classification was performed based on 4°, and the appropriateness of SVM classification was found through 8 single-layer and 3 multi-layer verification experiments. The results showed that the SVM classifier successfully selected the ranges of the optimal deposition conditions. Verification experiments revealed that the results in all cases were appropriately classified based on the boundary of the classification line. Moreover, the SVM classifier was efficient even when a small amount of input data was available. The contribution of this study is that the developed method can help build desired bead geometries in scenarios where deposition is required in the WAAM process, such as re-manufacturing. Thus, this method can be used in real-world industrial applications through further research on the bead shape with multi-layer deposition.

The Fate of Pre-Existing L5-S1 Degeneration following Oblique Lumbar Interbody Fusion of L4-L5 and Above.

BACKGROUND: Previous studies have identified various risk factors for adjacent segment disease (ASD) at the L5-S1 level after fusion surgery, including preoperative sagittal imbalance, longer fusion, and preoperative disc degeneration. However, only a few studies have explored the risk factors for ASD at the L5-S1 level after oblique lumbar interbody fusion (OLIF) at the L4-L5 level and above. This study aimed to identify the risk factors for symptomatic ASD at the L5-S1 level in patients with pre-existing degeneration after OLIF at L4-L5 and above. METHODS: We retrospectively reviewed the data of patients who underwent OLIF at L4-L5 and above, with a minimum follow-up period of 2 years. Patients with central stenosis or Lee grade 2 or 3 foraminal stenosis at L5-S1 preoperatively were excluded. Patients were divided into ASD and non-ASD groups based on the occurrence of new-onset L5 or S1 radicular pain requiring epidural steroid injection (ESI). The clinical and radiological factors were analyzed. Logistic regression was used to identify the risk factors for ASD of L5-S1. RESULTS: A total of 191 patients with a mean age ± standard deviation of 68.6 ± 8.3 years were included. Thirty-four (21.7%) patients underwent ESI at the L5 root after OLIF. In the logistic regression analyses, severe disc degeneration (OR (95% confidence interval (CI)): 2.65 (1.16-6.09)), the presence of facet effusion (OR (95% CI): 2.55 (1.05-6.23)), and severe paraspinal muscle fatty degeneration (OR (95% CI): 4.47 (1.53-13.05)) were significant risk factors for ASD in L5-S1. CONCLUSIONS: In this study, the presence of facet effusion, severe disc degeneration, and severe paraspinal muscle fatty degeneration at the L5-S1 level were associated with the development of ASD at L5-S1 following OLIF at L4-L5 and above. For patients with these conditions, surgeons could consider including L5-S1 in the fusion when considering OLIF at the L4-L5 level and above.

Shape- and orientation-dependent diffusiophoresis of colloidal ellipsoids.

We present the diffusiophoresis of ellipsoidal particles induced by ionic solute gradients. Contrary to the common expectation that diffusiophoresis is shape independent, here we show experimentally that this assumption breaks down when the thin Debye layer approximation is relaxed. By tracking the translation and rotation of various ellipsoids, we find that the phoretic mobility of ellipsoids is sensitive to the eccentricity and the orientation of the ellipsoid relative to the imposed solute gradient, and can further lead to nonmonotonic behavior under strong confinement. We show that such a shape- and orientation-dependent diffusiophoresis of colloidal ellipsoids can be easily captured by modifying theories for spheres.

4D printing of self-folding and cell-encapsulating 3D microstructures as scaffolds for tissue-engineering applications.

Technology of tissue-engineering advanced rapidly in the last decade and motivated numerous studies in cell-engineering and biofabrication. Three-dimensional (3D) tissue-engineering scaffolds play a critical role in this field, as the scaffolds provide the biomimetic microenvironments that could stimulate desired cell behaviors for regeneration. However, despite many achievements, the fabrication of 3D scaffold remains challenging due to the difficulty of encapsulating cells in 3D scaffolds, controlling cell-cell organization in 3D, and being adapted by users unfamiliar with 3D biofabrication. In this study, we circumvent these obstacles by creating a four-dimensional (4D) inkjet-printing platform. This platform produces micropatterns that self-fold into a 3D scaffold. Seeding live cells uniformly onto the micropatterns before self-folding leads to cell-encapsulating 3D scaffolds with layer-wise cell-cell organization. Photo-crosslinkable biomaterial-inks of distinct swelling rates were synthesized from gelatin, and the biomaterial-inks were patterned by a customized high-precision inkjet-printer into bilayer micropatterns that were capable of self-folding into 3D microstructures. A mathematical model was developed to help design self-folding and to aid the understanding of the self-folding mechanism. Human umbilical vein endothelial cells (HUVECs) were embedded in self-folded microtubes to mimic microvessels. HUVECs in the microtube spread, proliferated, showed high cell viability, and engrafted on the microtube's inner wall mimicking the native endothelial cells. For physician and biologist end-users, this 4D printing method provides an easy-to-use platform that supports standard two-dimensional cell-seeding protocol while enabling the users to customize 3D cellularized scaffold as desired. This work demonstrated 4D printing as a promising tool for tissue-engineering applications.

Role of Surfactant in Evaporation and Deposition of Bisolvent Biopolymer Droplets.

Inkjet printing of biopolymer droplets is gaining popularity because of its potential applications in regenerative medicine, particularly the fabrication of tissue-regenerative scaffolds. The quality of bioprinting, which affects cellular behaviors and the subsequent tissue formation, is determined by the solvent evaporation and deposition processes of biopolymer droplets, during which instantaneous local viscosity and surface tension changes occur because of the redistribution of the biopolymer inside the drop. Such dynamics is complex and not well understood. Most biopolymer inks also contain multiple solvents of distinct evaporation rates, further complicating the system dynamics. Using high-speed interferometry, we directly observe in real time the instantaneous drop shape of inkjet-printed picoliter gelatin drops containing glycerol and water. It is observed that, for bisolvent gelatin drops with surfactants, highly viscous gelatin and glycerol accumulated near the pinned contact line at an early stage suppress the evaporation-driven outward flow and create a stagnation zone near the contact line region. Lower surface tension at the contact line, because of its high local surfactant concentration, as compared to the drop apex induces a strong Marangoni recirculation, which in conjunction with a stagnation zone in the contact line region causes the instantaneous drop shape to transition from a spherical cap to a volcano shape during evaporation and resulting in a volcano-like deposition profile. In contrast, the suppressed evaporation outward flow together with a weak Marangoni flow leads to a domelike deposition for the case without surfactant. The role of surfactant in polymer drop deposition with water-only solvent is also investigated and compared against that of bisolvent drops. For the single-solvent case, the deposition profile is found to shift from a coffee-eye shape in the presence of surfactant to a uniform deposition without surfactant. The results reveal new insight into the complex role surfactant plays during polymer drop evaporation and deposition processes.

Micropattern-controlled wicking enhancement in hierarchical micro/nanostructures.

Wicking in hierarchical micro/nanostructured surfaces has attracted significant attention due to its potential applications in thermal management, moisture capturing, drug delivery, and oil recovery. Although some studies have shown that hierarchical structures enhance wicking over micro-structured surfaces, others have found very limited wicking improvement. In this study, we demonstrate the importance of micropatterns in wicking enhancement in hierarchical surfaces using ZnO nanorods grown on silicon micropillars of varying spacings and heights. The wicking front over hierarchical surfaces is found to follow a two-stage motion, where wicking is faster around micropillars, but slower in between adjacent pillar rows and the latter stage dictates the wicking enhancement in hierarchical surfaces. The competition between the added capillary action and friction due to nanostructures in these two different wicking stages results in a strong dependence of wicking enhancement on the height and spacing of the micropillars. A scaling model for the propagation coefficient is developed for wicking in hierarchical surfaces considering nanostructures in both wicking stages and the model agrees well with the experiments. This microstructure-controlled two-stage wicking characteristic sheds light on a more effective design of hierarchical micro/nanostructured surfaces for wicking enhancement.

The effect of particle wettability on the stick-slip motion of the contact line.

Contact line dynamics is crucial in determining the deposition patterns of evaporating colloidal droplets. Using high-speed interferometry, we directly observe the stick-slip motion of the contact line in situ and are able to resolve the instantaneous shape of the inkjet-printed, evaporating pico-liter drops containing nanoparticles of varying wettability. Integrated with post-mortem optical profilometry of the deposition patterns, the instantaneous particle volume fraction and hence the particle deposition rate can be determined. The results show that the stick-slip motion of the contact line is a strong function of the particle wettability. While the stick-slip motion is observed for nanoparticles that are less hydrophilic (i.e., particle contact angle θ ≈ 74° at the water-air interface), which results in a multiring deposition, a continuous receding of the contact line is observed for more hydrophilic nanoparticles (i.e., θ ≈ 34°), which leaves a single-ring pattern. A model is developed to predict the number of particles required to pin the contact line based on the force balance of the hydrodynamic drag, interparticle interactions, and surface tension acting on the particles near the contact line with varying particle wettability. A three-fold increase in the number of particles required for pinning is predicted when the particle wettability increases from the wetting angle of θ ≈ 74° to θ ≈ 34°. This finding explains why particles with greater wettability form a single-ring pattern and those with lower wettability form a multi-ring pattern. In addition, the particle deposition rate is found to depend on the particle wettability and vary with time.

Deposition of Colloidal Drops Containing Ellipsoidal Particles: Competition between Capillary and Hydrodynamic Forces.

Ellipsoidal particles have previously been shown to suppress the coffee-ring effect in millimeter-sized colloidal droplets. Compared to their spherical counterparts, ellipsoidal particles experience stronger adsorption energy to the drop surface where the anisotropy-induced deformation of the liquid-air interface leads to much greater capillary attractions between particles. Using inkjet-printed colloidal drops of varying drop size, particle concentration, and particle aspect ratio, the present work demonstrates how the suppression of the coffee ring is not only a function of particle anisotropy but rather a competition between the propensity for particles to assemble at the drop surface via capillary interactions and the evaporation-driven particle motion to the contact line. For ellipsoidal particles on the drop surface, the capillary force (Fγ) increases with the particle concentration and aspect ratio, and the hydrodynamic force (Fµ) increases with the particle aspect ratio but decreases with drop size. When Fγ/Fµ > 1, the surface ellipsoids form a coherent network inhibiting their migration to the drop contact line, and the coffee-ring effect is suppressed, whereas when Fγ/Fµ < 1, the ellipsoids move to the contact line, resulting in coffee-ring deposition.

Colloidal Drop Deposition on Porous Substrates: Competition among Particle Motion, Evaporation, and Infiltration.

Recent interest in printable electronics and in particular paper- and textile-based electronics has fueled research in inkjet printing of colloidal drops on porous substrates. On nonporous substrates, the interplay of particle motion and solvent evaporation determines the final deposition morphology of the evaporating colloidal drop. For porous substrates, solvent infiltration into the pores adds a layer of complexity to the deposition patterns that have not been fully elucidated in the literature. In this study, the deposition of picoliter-sized aqueous colloidal droplets containing nanometer- and micrometer-sized particles onto nanoporous anodic aluminum oxide substrates is examined for different drop and particle sizes and relative humidities as well as pore diameters, porosities, and wettabilities of the porous substrates. For the cases considered, solvent infiltration is found to be much faster than both evaporation and particle motion near the contact line, and thus when the substrate fully imbibes the solvent, the well-known "coffee-ring" deposition is suppressed. However, when the solvent is only partially imbibed, a residual droplet volume exists upon completion of the infiltration. For such cases, two time scales are of importance: the time for particle motion to the contact line as a result of both diffusion and advection, t(P), and the evaporation time of the residual drop volume, t(EI). Their ratio, t(P)/t(EI), determines whether the coffee-ring deposition will be formed (t(P)/t(EI) < 1) or suppressed (t(P)/t(EI) > 1).

Quantitative evaluation of acquisition parameters in three-dimensional imaging with multidetector computed tomography using human skull phantom.

This study evaluated the quantitative measurements of three-dimensional (3D) volume images using multidetector row computed tomography (MDCT) and one skull specimen. Twenty-one linear distances were measured five times each by vernier caliper. A dry human skull was imaged with MDCT for various acquisition parameters at slice thicknesses of 1.25, 2.50, 3.75, and 5.00 mm for the different acquisition modes of axial and spiral scan. The distance of each corresponding item displayed on 3D rendered images was measured seven times by an uninvolved observer using a 3D software tool. Data analysis was performed to determine if there were any statistically significant differences in acquisition parameters. No significant image differences were found among the scan modes for each slice thickness. For a given scan mode, acquisition slice thickness was the important factor for quantitative measurement of 3D rendered CT images.

Quantitative analysis of three-dimensional rendered imaging of the human skull acquired from multi-detector row computed tomography.

The purpose of this study was to evaluate the quantitative accuracy of three-dimensional (3D) rendered images acquired with multi-detector row computed tomography (MDCT) by means of distance measurements of a dry human skull for various slice thicknesses and acquisition modes. A radiologist directly measured the distance of line items on the skull surface to establish reference "gold standards." The skull specimen was scanned with a MDCT with various scanning parameters (slice thicknesses and acquisition modes). An observer measured the corresponding distances of the same items on 3D rendered images. The quantitative accuracy of distance measurements was statistically evaluated. There were no significant statistical differences (P value <.05) in accuracy of distance measurements among the scan modes. However, the results showed that acquisition slice thickness was the influential factor in determining the accuracy of the 3D rendered MDCT images. The quantitative analysis of distance measurement may be a useful tool evaluating the accuracy and defining optimal parameters of 3D rendered images.