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.

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.

Multi-responsive poly-catecholamine nanomembranes.

The contraction of nanomaterials triggered by stimuli can be harnessed for micro- and nanoscale energy harvesting, sensing, and artificial muscles toward manipulation and directional motion. The search for these materials is dictated by optimizing several factors, such as stimulus type, conversion efficiency, kinetics and dynamics, mechanical strength, compatibility with other materials, production cost and environmental impact. Here, we report the results of studies on bio-inspired nanomembranes made of poly-catecholamines such as polydopamine, polynorepinephrine, and polydextrodopa. Our findings reveal robust mechanical features and remarkable multi-responsive properties of these materials. In particular, their immediate contraction can be triggered globally by atmospheric moisture reduction and temperature rise and locally by laser or white light irradiation. For each scenario, the process is fully reversible, i.e., membranes spontaneously expand upon removing the stimulus. Our results unveil the universal multi-responsive nature of the considered polycatecholamine membranes, albeit with distinct differences in their mechanical features and response times to light stimulus. We attribute the light-triggered contraction to photothermal heating, leading to water desorption and subsequent contraction of the membranes. The combination of multi-responsiveness, mechanical robustness, remote control via light, low-cost and large-scale fabrication, biocompatibility, and low-environment impact makes polycatecholamine materials promising candidates for advancing technologies.

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.

Treatment of the hemolytic uremic syndrome with plasma.

Two patients with the hemolytic uremic syndrome were treated with plasma exchange an infusion: in both cases, the reduced platelet count reverted to normal values and the microangiopathic anemia ceased within a few days. Systemic blood pressure and requirement for antihypertensive drug therapy were also markedly reduced following treatment with plasma. Venousprostacyclin (antiplatelet aggregating) activity was undetectable in both patients before but was restored after treatment with plasma. The plasma samples collected before, but not those collected at various intervals after replacement therapy, had decreased capacity to stimulate prostacyclin activity in rat aortic rings. It is suggested that in patients with the hemolytic uremic syndrome or with other clinical conditions which can be included under this rubric (such as thrombotic thrombocytopenic purpura) a plasma factor is lacking which stimulates prostacyclin activity. Plasma would supply such a missing factor, thus representing a rational treatment for some of the life-threatening manifestations (thrombocytopenia, hemolytic anemia, hypertension) of this severe syndrome.

Bleeding in renal failure: a possible role of vascular prostacyclin (PGI2).

Specimens of venous tissues from a group of 25 patients with chronic uremia and 7 patients with acute renal failure generated significantly higher PGI2-like (platelet aggregation inhibiting) activity than venous tissues from 30 normal subjects. After repeated washings, when this activity could barely be detected in the controls, pronounced inhibitory activity was still evident in samples containing venous tissues from uremic patients. Both prolonged bleeding times and increased PGI2-like activity returned to normal in 4 acute uremic patients on restoration of their renal function. These findings may be relevant to the pathogenesis of bleeding in renal failure.

Pedicle fixation devices in the treatment of adult lumbar scoliosis.

Segmental pedicle screw instrumentation in adult lumbar scoliosis allows better curve correction and restoration of lumbar lordosis. In a retrospective study, to assess the value of this fixation, 9 patients treated with the AO Internal Fixator and 18 with Cotrel-Dubousset instrumentation were reviewed. Mean age at surgery was 60 years (range, 40-88), and curves were measured between 22 degrees and 82 degrees. At follow-up (mean of 56 months for the AO Internal Fixator and 42 months for Cotrel-Dubousset instrumentation), the average curve correction was better than 50% Overall satisfactory clinical results with pain relief and improved walking distance were noted in 86% of the patients. Using this technique no postoperative deaths or neurologic deficits occurred. Only a few complications and a 4% pseudarthrosis rate could be observed. Our study shows that the age of the patients with degenerative scoliosis is not a contraindication for major surgery. Meticulous posterior spine release before instrumentation is essential for curve correction and bone fusion. Lumbar lordosis is more easily restored with Cotrel-Dubousset instrumentation, which seems to correspond to the incidence of low back pain. Cases with evident neurologic deficits are best treated by additional nerve decompression.

Treatment of cervical spine injuries with anterior plating. Indications, techniques, and results.

This study analyzed 86 patients who sustained a cervical spine injury and who had 93 anterior surgical interventions of the cervical spine. The average age of the patients was 39 years, the mean follow-up 40 months. Twenty-two patients had predominantly vertebral body fractures (burst or tear-drop fractures) and were treated by bisegmental anterior bone grafting and plating. Sixty-four patients had predominantly posterior lesions, either discoligamentous or osteoligamentous, and were treated by unisegmental bone grafting and plating. Forty-three patients were neurologically intact. There were no relevant complications except in one patient, who needed reoperation because of a secondary redislocation due to a technically insufficient osteosynthesis. The technique of anterior bone grafting and plating is shown to be straight-forward, atraumatic, and reliable for predominantly anterior lesions as well as for posterior injuries when performed properly. This clinical experiences does not support experimental data and earlier clinical work, which advocate posterior surgery over anterior surgery and assert that anterior surgery should not be done in predominantly posterior lesions.

Application and results of the AO internal fixation system in nontraumatic indications.

The AO internal skeletal fixation system (ISFS) permits posterior spine fixation to be restricted to the vertebrae immediately adjacent to the lesion and allows manipulation of each instrumented vertebra in three planes. In a prospective study to assess the value of this fixation for adult spinal disorders, 68 patients were reviewed. The device was used in spondylolisthesis, postlaminectomy instability, post-traumatic kyphosis, degenerative scoliosis, spinal stenosis, tumors, and infections. A total of 322 transpedicular screws have been inserted without neurologic complication. Satisfactory results were achieved in 88% of the patients, and only four pseudarthroses (6%) occurred. The ISFS provides rigid stabilization to enhance bone graft consolidation and to allow rapid postoperative mobilization in a light external orthosis.

Treatment of severe spondylolisthesis by reduction and pedicular fixation. A 4-6-year follow-up study.

Ten consecutive patients with severe spondylolisthesis were treated with reduction and pedicular fixation (four Internal Fixator instrumentations, six Cotrel-Dubousset instrumentations). There were six Grade III spondylolisthesis and four spondyloptoses at the L5/S1 level. All patients had complete clinical and radiographic evaluation with an average follow-up of 56 months (range, 43-75 months). The percentage of slippage averaged 78.5% preoperatively and 39.6% postoperatively. The slip angle averaged 43 degrees preoperatively and 17 degrees postoperatively. Four patients with spondyloptosis were treated with combined posterolateral and interbody fusion and had solid fusion without loss of reduction. Five of six patients in whom reduction and stabilization was performed by a single posterolateral fusion demonstrated loss of reduction, nonunion, and implant failure. Four of these patients were reoperated. Ultimately all patients had resolution of pain, solid fusion, and no further slip progression. Reduction, pedicular fixation, and combined posterolateral and interbody fusion is a technically demanding procedure, which should be reserved for selected patients. Pedicular fixation systems may only allow permanent reduction and stabilization of high-grade spondylolisthesis in conjunction with a combined interbody and posterolateral fusion.

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.

Anterior transpedicular fixation of the lower thoracic and lumbar spine. Experimental verification using a new direction finder.

Currently, no anterior spinal implant provides a strong bone-screw interface because of the cancellous characteristics of the vertebral body. A more secure anchorage could be obtained by anterior transpedicular screw fixation. Four hundred transpedicular screws located between T7 and L5 were placed using the newly developed direction finder. Measurements were obtained directly from radiographs of the cadaveric specimens. In 10 cases (2.5%), the screws crossed the medial pedicle border, but never by more than 1.4 mm. A lateral protrusion was noted in another 41 screws (10%), with no protrusion greater than 2.2 mm. Encroachments beyond the superior or inferior border were not observed. The mean angle of the screws at each level measured between 7 and 19 in the transverse plane and between 2 and 4.5 in the sagittal plane. This technique should be reserved for vertebrae without significant arthritic changes. The rare screw with minimal infraction through the medial or lateral pedicle wall should not cause any vascular or neural compromise. The anterior transpedicular screw technique appeared relatively safe (88%) and encouraged the development of the new plate system for anterior spinal stabilization.

A new technique for measuring lumbar segmental motion in vivo. Method, accuracy, and preliminary results.

STUDY DESIGN: A direct method for three-dimensional in vivo spine kinematic studies was developed and used to measure segmental motion patterns in healthy subjects. OBJECTIVES: To validate the new method, and to study the L3-L4 segmental motion patterns for complex dynamic movements. SUMMARY OF BACKGROUND DATA: Conventional two-dimensional and three-dimensional radiographic methods have been used in the past to study spine kinematics. Few studies provided a direct approach to study segmental kinematics. No dynamic recordings of three-dimensional segmental motion patterns have been reported previously. METHODS: In 16 healthy men, Kirschner wires were inserted in the spinous processes of L3 and L4. Electromagnetic tracking sensors were attached to the pins. Motion data recorded during ranging exercises were used with biplanar radiographs to calculate L3-L4 segmental motion patterns. Errors resulting from pin deformation and the dynamic accuracy of the tracking system were investigated thoroughly. RESULTS: The average range of motion for flexion-extension was 16.9 degrees, for one side lateral bending 6.3 degrees and for one side axial rotation 1.1 degrees. Large intersubject variation was found in flexion-extension with values ranging from 7.1 to 29.9 degrees. Coupled motion patterns were found to be consistent among subjects in active lateral bending and inconsistent for active axial rotation. CONCLUSIONS: This new method offers dynamic recording capabilities and a measurement error comparable with stereo radiographic methods. Repetitive ranging experiments are highly reproducible. The range of motion for axial rotation seems overestimated in previous cadaveric studies. Coupling patterns show large variations between individuals.

Changes in vertebral rotation after Harrington and Luque instrumentation for idiopathic scoliosis.

This study was carried out to analyze the three-dimensional and in particular the rotational correction obtained after spine instrumentation for idiopathic scoliosis. Preoperative and postoperative radiographs and computed tomographic scans with single axial cuts through each vertebral level were obtained for 14 patients: 4 Harrington, 7 Luque, and 3 Harrington-Luque. Rotation of vertebrae relative to the spinal axis and rotation between vertebrae (segmental rotation) were measured from computed tomographic scans of instrumented and uninstrumented segments. The derotation and changes occurring after surgery were calculated. Before operation, rotation was maximal at the apex, and close to 0 at the end vertebra; segmental rotation was greatest at the end of the curve, and minimal at the apex. After Harrington instrumentation the apical vertebrae showed a median derotation of 16%, after Luque instrumentation it was 12% and after Harrington-Luque instrumentation it was 13%. Segmental derotation did not uniformly occur. Major derotation was obtained at the end vertebrae and 39% of the total derotation occurred outside of the instrumented levels of the spine.

Alignment of supracondylar/intercondylar fractures of the femur after internal fixation by AO/ASIF technique.

Fifty-nine supracondylar-intercondylar fractures of the femur in 57 patients were evaluated after a mean follow-up of 5 years 7 months (range 2 years to 11 years 3 months) after internal fixation using AO/ASIF technique. Axial alignment was compared with that of the uninjured side by orthoroentgenography in the upright position and by bilateral anteroposterior (AP) and lateral views of the femur. Identical values for varus/valgus were noted in 24%, for ante/recurvation in 72%, and for rotation in 61%; differences were within 5 degrees of varus/valgus in 74%, of ante/recurvation in 78%, and of rotation in 83%. Alignment differences were more frequent in complicated and intercondylar fractures according to the AO classification of fractures. We conclude that restoration of the distal femoral angle is far more difficult than restoration of the sagittal plane and rotation, but a satisfactory functional result appears to be compatible with angulation differences of less than or equal to 5 degrees in any plane and that this difference appears to be within the reasonably achievable limits. 93% of the patients were satisfied; 64% of patients were pain-free, and 27% had slight intermittent pain (not interfering with daily activity); 67% of the patients had unlimited walking distance, and 78% of the patients were able to walk without aid. Excellent and good results according to the rating systems of Neer et al., Pritchett, and Schatzker and Lambert were noted in 82, 39, and 26%, respectively. This discrepancy between alignment, pain, function, and results according to different rating systems underlines the need for future standardized, clearly defined reporting and classification of rating.

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.

[Development in conservatively treated scoliosis in patients with myelomeningocele (patients of the years 1964-1977)]. / Evolution des scolioses traitées conservativement chez les patients atteints de myéloméningocèle (patients des années 1964-1977).

The advances in urological and neurosurgical management in myelomeningocoele patients have led to an increased survival rate. The extremely complex spinal deformity presents a major treatment challenge. Clinical and radiological evolution of scoliosis treated conservatively for at least 10 years was studied. Eighty-nine myelomeningocoele patients born between 1964 and 1977 were reviewed. Thirty-one (35%) were noted to have scoliosis (10 congenital type, 21 developmental type). All congenital forms showed rapid progression despite brace treatment, often to curvatures in excess of 100 degrees. Among the developmental type, curves detected prior to 10 years (10 cases before 5 years, 6 cases between 6 and 10 years) were rapidly progressive beyond 70 degrees. Curves detected after 10 years (5 patients) never exceeded 30 degrees. Because of this natural history, conservative treatment should be limited to developmental forms less than 50 degrees. Spinal stabilization is indicated in all curvatures over 50 degrees without awaiting adulthood.

[Surgical treatment of spondylolisthesis with mild displacement by pedicular fixation and posterolateral fusion in adults]. / Traitement chirurgical des spondylolisthésis de l'adulte à déplacement modéré par fixation pédiculaire et fusion postéro-latérale.

Thirty-two consecutive adults with low-grade spondylolisthesis treated by stabilisation with the AO Internal Fixator and posterolateral fusion have been retrospectively reviewed with a mean follow-up time of 4 years (range, 24 to 71 months). There were 17 grade I and 15 grade II spondylolisthesis. Eight patients had degenerative and 24 patients had isthmic spondylolisthesis. An unisegmental fusion was performed in 4 cases, a bisegmental fusion in 25 cases and 3 patients had a multisegmental fusion. There was one deep infection and one nerve root compromise (3 per 100). Satisfactory results were achieved in 84 per 100 of the patients. There was non-union. This study suggests that transpedicular fixation and posterolateral fusion significantly enhances the rate of solid union to an extent which outweighs the risk of neurological complications due to the screw insertion. Fusion in situ in patients with low-grade spondylolisthesis is recommended as well as nerve root revision for all adults with concomitant radioculopathy. However, this review does not specifically support the use of the AO-internal fixator, but rather that of transpedicular fixation in general.