Ion and Molecular Sieving With Ultrathin Polydopamine Nanomembranes.

In contrast to biological cell membranes, it is still a major challenge for synthetic membranes to efficiently separate ions and small molecules due to their similar sizes in the sub-nanometer range. Inspired by biological ion channels with their unique channel wall chemistry that facilitates ion sieving by ion-channel interactions, the first free-standing, ultrathin (10-17 nm) nanomembranes composed entirely of polydopamine (PDA) are reported here as ion and molecular sieves. These nanomembranes are obtained via an easily scalable electropolymerization strategy and provide nanochannels with various amine and phenolic hydroxyl groups that offer a favorable chemical environment for ion-channel electrostatic and hydrogen bond interactions. They exhibit remarkable selectivity for monovalent ions over multivalent ions and larger species with K+/Mg2+ of ≈4.2, K+/[Fe(CN)6]3- of ≈10.3, and K+/Rhodamine B of ≈273.0 in a pressure-driven process, as well as cyclic reversible pH-responsive gating properties. Infrared spectra reveal hydrogen bond formation between hydrated multivalent ions and PDA, which prevents the transport of multivalent ions and facilitates high selectivity. Chemically rich, free-standing, and pH-responsive PDA nanomembranes with specific interaction sites are proposed as customizable high-performance sieves for a wide range of challenging separation requirements.

Preparation of Ultrathin and Degradable Polymeric Films by Electropolymerization of 3-Amino-l-tyrosine.

Bioderived polymers are one of many current research areas that promise a sustainable future. Due to their unique properties, the bioderived polymer polydopamine has been in the spotlight over the last decades. Its ability to adhere to virtually any surface and its stability over a wide pH range as well as in several organic solvents make it a suitable candidate for various applications like coatings and biosensors. However, strong light absorption over a broad range of wavelengths and high quenching efficiency limit its uses. Therefore, new bioderived polymers with similar features to polydopamine but without fluorescence quenching properties are highly desirable. Herein, the electropolymerization of a bioderived analog of dopamine, 3-amino-l-tyrosine, is demonstrated. The resulting polymer, poly(amino-l-tyrosine), exhibits several characteristics complementary to or even exceeding those of polydopamine and its analog, polynorepinephrine, rendering poly(amino-l-tyrosine) attractive for the development of sensors and photoactive devices. Cyclic voltammetry, spectro-electrochemistry, and electrochemical quartz crystal microbalance measurements are applied to study the electrodeposition of this material, and the resulting films are compared to polydopamine and polynorepinephrine. Impedance spectroscopy reveals increased ion permeability of poly(amino-l-tyrosine) compared to polydopamine and polynorepinephrine. Moreover, the reduced fluorescence quenching of poly(amino-l-tyrosine) supports its use as coating for biosensors and organic semiconductors.

Fast Light-Driven Motion of Polydopamine Nanomembranes.

The actuation of micro- and nanostructures controlled by external stimuli remains one of the exciting challenges in nanotechnology due to the wealth of fundamental questions and potential applications in energy harvesting, robotics, sensing, biomedicine, and tunable metamaterials. Photoactuation utilizes the conversion of light into motion through reversible chemical and physical processes and enables remote and spatiotemporal control of the actuation. Here, we report a fast light-to-motion conversion in few-nanometer thick bare polydopamine (PDA) membranes stimulated by visible light. Light-induced heating of PDA leads to desorption of water molecules and contraction of membranes in less than 140 µs. Switching off the light leads to a spontaneous expansion in less than 20 ms due to heat dissipation and water adsorption. Our findings demonstrate that pristine PDA membranes are multiresponsive materials that can be harnessed as robust building blocks for soft, micro-, and nanoscale actuators stimulated by light, temperature, and moisture level.

Rhodium-Complex-Functionalized and Polydopamine-Coated CdSe@CdS Nanorods for Photocatalytic NAD+ Reduction.

We report on a photocatalytic system consisting of CdSe@CdS nanorods coated with a polydopamine (PDA) shell functionalized with molecular rhodium catalysts. The PDA shell was implemented to enhance the photostability of the photosensitizer, to act as a charge-transfer mediator between the nanorods and the catalyst, and to offer multiple options for stable covalent functionalization. This allows for spatial proximity and efficient shuttling of charges between the sensitizer and the reaction center. The activity of the photocatalytic system was demonstrated by light-driven reduction of nicotinamide adenine dinucleotide (NAD+) to its reduced form NADH. This work shows that PDA-coated nanostructures present an attractive platform for covalent attachment of reduction and oxidation reaction centers for photocatalytic applications.

Nanofibrillated Cellulose Templated Membranes with High Permeance.

One of the most challenging aspects of using nanofibrillated cellulose (NFC) for membranes production is their limited permeance. When NFC membranes are produced from aqueous suspensions, depending on their grammage, the permeances are in the range of a few decades of L/(hm2MPa) not matching satisfactory filtration times. We present a fast and sustainable solution to increase the permeances of such membranes through a combination of solvent exchange of the NFC suspension with ethanol and the use of a removable template, a mixture of calcium compounds (CC). The effect of the CC/NFC ratio was screened for various concentrations. The permeance of water could be increased by as much as 2-3 times as compared to nontemplated membranes. Further, the membranes showed the ability for penetration of water-soluble macromolecules, contaminant rejection of suspended solid particles, and thus fluids (such as orange juice) could be concentrated, with a view to applications in food industry.

Adhesive-free colloidal probes for nanoscale force measurements: production and characterization.

We describe novel approaches for the production and characterization of epoxy- and adhesive-free colloidal probes for atomic force microscopy (AFM). Borosilicate glass microspheres are strongly attached to commercial AFM cantilevers exploiting the capillary adhesion force due to the formation of a water meniscus, and then a thermal annealing of the sphere-cantilever system at a temperature slightly below the softening point of borosilicate glass. Controlling the wettability of the surfaces involved turned out to be a crucial element for the control of surface adhesion and for the implementation of a completely adhesive-free production method of colloidal probes. Moreover, we present a statistical characterization protocol of the probe dimensions and roughness based on the AFM inverse imaging of colloidal probes on spiked gratings. We have assessed the influence of defects of the grating on the characterization of the probe, and discussed the accuracy of our characterization technique in comparison to the methods based on scanning electron or optical microscopy, or on the manual analysis of AFM inverse images.

Spinal fusions: bone and bone substitutes.

Vertebral arthrodesis is one of the most commonly performed, yet incompletely understood, procedures in spinal surgery. Despite major progress in internal fixation techniques, the high rate of nonunions indicates that physiologic, biologic and molecular events that are crucial to this process are not well known. This article will analyze the general biology of bone regeneration, and particularly discuss the properties and use of various bone graft materials and graft substitutes.

The efficacy of interconnected porous hydroxyapatite in achieving posterolateral lumbar fusion in sheep.

STUDY DESIGN: An animal study was performed to evaluate lumbar spinal fusion radiologically and mechanically. OBJECTIVES: To assess the efficacy of interconnected porous hydroxyapatite in achieving posterolateral lumbar arthrodesis in sheep. SUMMARY OF BACKGROUND DATA: Posterolateral spinal arthrodesis with autologous bone graft is the gold standard procedure for lumbar fusion. The procedure for harvesting bone from the iliac crest increases morbidity. Interconnected porous hydroxyapatite has been used effectively as an alternative to cancellous bone graft material in metaphyseal bone defects. Little is known about the efficacy of interconnected porous hydroxyapatite in achieving lumbar spinal fusion. METHODS: Four groups of seven sheep underwent bisegmental posterolateral lumbar fusion with instrumentation using different intertransverse graft material. In group 1, no graft material was used. In group 2, autologous bone was used. Group 3 had interconnected porous hydroxyapatite. Group 4 had an equip of interconnected porous hydroxyapatite and autologous bone. The animals were killed at 20 weeks after surgery. Radiographs and computed tomography images were obtained. The fusion masses were graded for bone resorption and trabecular connectivity on the computed tomography images. Mechanical testing of the specimens was performed, and the three-dimensional segmental motion was measured in flexion/extension, axial rotation, and lateral bending. RESULTS: The radiographic images were difficult to interpret because of the radiodense interconnected porous hydroxyapatite granules. According to mechanical stability criteria, the fusion rate for the different groups was as follows: 100% (14/14) for the autologous bone group, 72% (10/14) for the bone/interconnected porous hydroxyapatite group, 50% (7/14) for the pure interconnected porous hydroxyapatite group, and 15% (2/14) for the sham group. CONCLUSIONS: Spinal arthrodesis using interconnected porous hydroxyapatite alone or mixed with bone as graft material reduced segmental motion. It was not, however, as effective as autologous bone graft material in achieving spinal arthrodesis. The sheep model using autologous bone achieved a 100% fusion rate. Because the nonunion rate for a single level in humans may be as high as 40%, the fusion rate with bone/interconnected porous hydroxyapatite in humans may be lower than the 72% found in the sheep model. The little resorption of the radiodense interconnected porous hydroxyapatite granules made the radiologic evaluation of the fusion masses difficult.

Decompensation following scoliosis surgery: treatment by decreasing the correction of the main thoracic curve or "letting the spine go".

Coronal decompensation following correction of adolescent idiopathic scoliosis (AIS) has been reported to be due to the Cotrel-Dubousset rod derotation maneuver, or to a hypercorrection of the main thoracic curve. The treatment of such decompensation consists classically in observation, bracing, or extension of the instrumentation in the lumbar spine for a King 2 curve, or in the upper thoracic spine for a King 5 curve. As the postoperative decompensation is related to a hypercorrection of the main thoracic curve (relative to the compensatory curve), we hypothesized that if we were to "let the spine go" to some of its initial deformity, the balance of the patient would be improved. The purpose of the study was therefore to report on two cases where a postoperative imbalance following scoliosis surgery was successfully treated by decreasing the correction of the main thoracic curve. Two patients with AIS were found to have significant imbalance after scoliosis surgery. Both patients had been treated for a right thoracic curve (82 degrees and 85 degrees respectively) with an anterior release and posterior instrumentation. The revision surgery consisted for both patients in removing all the hooks between the end vertebrae of the main thoracic curve. This was done before the 3rd postoperative month for both patients. After revision surgery, the balance of both patients improved dramatically within a few weeks. The shoulders became almost level, and the trunk shift improved concomitantly. The Cobb angle increased by 8 degrees and 10 degrees, and the apical vertebra shifted to the right by 15 and 10 mm for the respective patients. These results were stable at 1-year follow-up. In the event of a persisting imbalance, we recommend, in selected cases, letting the spine go by removing all the implants located between the end vertebrae of the main thoracic curve. This adjustment or fine-tuning of the instrumentation should be done before the fusion takes place, and is best achieved with an instrumentation in which the hooks can be easily removed from the rod.

Posterolateral and anterior interbody spinal fusion models in the sheep.

Posterolateral and anterior interbody spinal arthrodesis is a frequent procedure, but high nonunion rates are reported and harvesting autologous bone graft from the iliac crest significantly increases morbidity. Bone graft substitutes are an alternative, but to date clinical results are not conclusive. Bone substitutes can be organic or inorganic, biologic or synthetic. They can have osteoconductive properties, inductive properties or both. Animal experiments are essential to investigating bone substitutes using biomechanical and histologic methods not available in clinical studies. Few authors reported on instrumented anterior fusion models, but none used the sheep model. In the current study posterolateral and anterior interbody fusion models in sheep are described. Both models used instrumented fusions, applying porous mineral scaffolds, alone or mixed with bone. The surgical techniques are described step-by-step and potential difficulties are highlighted. Preliminary results are reported for the posterolateral fusion model using coralline graft substitutes. The coral granules mixed with locally harvested bone had fusion outcomes similar to pure autologous bone. The graft substitute showed marked resorption between 12 and 20 weeks. All fusions had bone cortex and good trabecular connectivity. Histologic evaluation suggests after 20 weeks nearly the entire surface of the substitute is covered with new bone. Porous mineral bone substitutes mixed with locally harvested autologous bone are thought to be a valid alternative for posterolateral fusions.

Adolescent idiopathic thoracic scoliosis: apical correction with specialized pedicle hooks.

Forty-one patients with thoracic adolescent idiopathic scoliosis (AIS) treated with only a posterior spine fusion using specialized pedicle hooks (SPH) (hooks augmented with 3.2-mm screws) at the apex of the curve were reviewed in order to assess the effectiveness of this correction method. Inclusion in the study group required a minimum of 2 years' follow-up and the same strategy of correction where the apical vertebrae (3 or 4 vertebrae on the concave side) were instrumented with SPH. The mean preoperative Cobb angle was corrected from 55 degrees (42 degrees -80 degrees) to 18 degrees (67%) postoperatively and to 23 degrees (58%) at the last follow-up (28-50 months) for a flexibility index of 46%. Apical vertebral translation was corrected to 70% at the last follow-up. Thoracic kyphosis remained unchanged, from 23 degrees to 26 degrees, and the lumbar lordosis went from -53 degrees to -59 degrees. The lumbar curve was corrected from 38 degrees to 18 degrees. Coronal balance improved from 10 to 1 mm; shoulder balance was improved from 15 to 5 mm. The rib hump was improved from an average of 30 mm preoperatively to 15 mm postoperatively, but only to 25 mm at the last follow-up (17% of correction). One case of a spastic bladder was observed postoperatively, which resolved completely after 8 months. Three patients had to have their instrumentation removed because of pain. There was no complication related to the use of the SPH. The authors conclude that apical correction with SPH allows effective scoliosis correction without spinal distraction and does not require supra- or infralaminar hook in the spinal canal.

Halo femoral traction and sliding rods in the treatment of a neurologically compromised congenital scoliosis: technique.

In severe congenital scoliosis, traction (whether with a halo or instrumental) is known to expose patients to neurologic complications. However, patients with restrictive lung disease may benefit from halo traction during the course of the surgical treatment. The goal of treatment of such deformities is, therefore, twofold: improvement of the respiratory function and avoidance of any neurologic complications. We report our technique to treat a 17-year-old girl with a multi-operated congenital scoliosis of 145 degrees and cor pulmonale. Pre-operative halo gravity traction improved her vital capacity from 560 c.c. to 700 c.c., but led to mild neurologic symptoms (clonus in the legs). To avoid further neurologic compromise, her first surgery consisted of posterior osteotomies and the implantation of two sliding rods connected to loose dominoes without any attempt at correction. Correction was then achieved over a 3-week period with a halofemoral traction. This allowed the two rods to slide while the neurologic status of the patient was monitored. Her definitive surgery consisted of locking the dominoes and the application of a contralateral rod. Satisfactory outcome was achieved for both correction of the deformity (without neurologic sequels) and improvement of her pulmonary function (1200 c.c. at 2 years). This technique using sliding rods in combination with halofemoral traction can be useful in high-risk, very severe congenital scoliosis.

The 'MW' sacropelvic construct: an enhanced fixation of the lumbosacral junction in neuromuscular pelvic obliquity.

Fixation to the lumbosacral spine to correct pelvic obliquity in neuromuscular scoliosis has always remained a surgical challenge. The strongest fixation of the lumbosacral junction has been achieved with either a Galveston technique with rods or screws or with iliosacral screws. We have devised a new fixation system, in which iliosacral screws are combined with iliac screws. This is made possible by using the AO Universal Spine System with side opening hooks above and below the iliosacral screws and iliac screws below it. The whole sacropelvis is thus encompassed by a maximum width (MW) fixation, which gives an 'M' appearance on the pelvic radiographs and a 'W' appearance in the axial plane. We report on our surgical technique and the early results where such a technique was used. We feel that this new means of fixation (by combining the strongest fixation systems) is extremely solid and should be included in the wide armamentarium of sacropelvic fixation.

Unusual presentation of spinal cord compression related to misplaced pedicle screws in thoracic scoliosis.

Utilization of thoracic pedicle screws is controversial, especially in the treatment of scoliosis. We present a case of a 15-year-old girl seen 6 months after her initial surgery for scoliosis done elsewhere. She complained of persistent epigastric pain, tremor of the right foot at rest, and abnormal feelings in her legs. Clinical examination revealed mild weakness in the right lower extremity, a loss of thermoalgic discrimination, and a forward imbalance. A CT scan revealed at T8 and T10 that the right pedicle screws were misplaced by 4 mm in the spinal canal. At the time of the revision surgery the somatosensory evoked potentials (SSEP) returned to normal after screw removal. The clinical symptoms resolved 1 month after the revision. The authors conclude that after pedicle instrumentation at the thoracic level a spinal cord compression should be looked for in case of subtle neurologic findings such as persistent abdominal pain, mild lower extremity weakness, tremor at rest, thermoalgic discrimination loss, or unexplained imbalance.

Correction of adolescent idiopathic thoracic scoliosis with a new type of offset apical instrumentation: preliminary results.

Twenty patients were operated on with the same method using the AO Universal Spine System. The entire apex of the curvature was instrumented on the concave side with a newly designed pedicle hook augmented by 3.2-mm endplate screw. An offset configuration of apical and end vertebrae implants was done to maximize translation. The concave rod was derotated to 120 degrees without any distraction. The convex side was instrumented in the usual fashion. Prospective analysis showed a mean Cobb angle correction of 63% for a mean preoperative angle of 54 degrees. The apical vertebral translation was corrected to 72%. There was no major complication at the last follow-up (18-30 months). This technique compares favorably with the ones using CD principles, but needs no distraction and no instrumentation in the canal (supra or infralaminar hook).

[Treatment of scoliosis in the adolescent by anterior release and vertebral arthrodesis under thoracoscopy. Preliminary results]. / Traitement de la scoliose de l'adolescent par libération antérieure et arthrodèse vertébrale sous thoracoscopie. Résultats préliminaires.

PURPOSE OF THIS STUDY: The purpose was to evaluate short term results of thoracoscopic anterior release and fusion in adolescent scoliosis. MATERIAL AND METHODS: An independent observer reviewed retrospectively hospital files and X-rays of 8 consecutive patients. The average follow-up was 14 months. The mean age at the time of surgery was 12 years old, all patients were skeletally immature. The surgical technique consisted in a thoracoscopic release and fusion of the discs space followed in the same time by a posterior instrumentation and fusion. Six cases were done in the prone position, two in the lateral decubitus. RESULTS: The release could be done in 7 cases. In one case a severe bronchospasm prevented from doing discectomy. Four levels in average could be released and fused. The thoracoscopic time was 240 mn in average and the total surgical time 430 mn. The bleeding of the thoracoscopic procedure was minimal (less than 200 cc) in all but one case (2000 cc). The duration of the chest tube was 4.4 days. At last follow up the cosmetic advantage was obvious. The angular correction of the Cobb angle was 63 per cent (similar to our isolated posterior instrumentation). The radiologic aspect of the anterior fusion seemed to be less satisfactory than the ones of classic thoracotomies (although we did not observe any non union). DISCUSSION: Our experience and these results moderate the initial enthusiasm of these new techniques reported in literature. Our current indications are therefore patients at risk of crankshaft, and complementary anterior fusion of dysplasic spines. As to the major curves we still recommend the anterior release through a formal thoracotomy which allows a more complete disc excision on more levels and a more abundant graft, with a shorter surgical time, with an associated morbidity which does not seem superior.

Management of odontoid fractures.

During the past two decades, various reports on the management of odontoid and axis body fractures have been published and new methods of treatment have been developed. So far, there is no consensus, and management remains controversial. This article reviews the literature and formulates recommendations based on clinical experience.