An enzymatic continuous-flow reactor based on a pore-size matching nano- and isoporous block copolymer membrane.

Continuous-flow biocatalysis utilizing immobilized enzymes emerged as a sustainable route for chemical synthesis. However, inadequate biocatalytic efficiency from current flow reactors, caused by non-productive enzyme immobilization or enzyme-carrier mismatches in size, hampers its widespread application. Here, we demonstrate a general-applicable and robust approach for the fabrication of a high-performance enzymatic continuous-flow reactor via integrating well-designed scalable isoporous block copolymer (BCP) membranes as carriers with an oriented and productive immobilization employing material binding peptides (MBP). Densely packed uniform enzyme-matched nanochannels of well-designed BCP membranes endow the desired nanoconfined environments towards a productive immobilized phytase. Tuning nanochannel properties can further regulate the complex reaction process and fortify the catalytic performance. The synergistic design of enzyme-matched carriers and efficient enzyme immobilization empowers an excellent catalytic performance with >1 month operational stability, superior productivity, and a high space-time yield (1.05 × 105 g L-1 d-1) via a single-pass continuous-flow process. The obtained performance makes the designed nano- and isoporous block copolymer membrane reactor highly attractive for industrial applications.

Modification of Polyacrylonitrile Ultrafiltration Membranes to Enhance the Adsorption of Cations and Anions.

Ion adsorbing ultrafiltration membranes provide an interesting possibility to remove toxic ions from water. Furthermore, it is also possible to recover valuable elements. In this work, we demonstrate two easy strategies to modify polyacrylonitrile membranes with anion and cation adsorbing groups. The membranes were modified to have positively charged amine groups or negatively charged carboxyl groups. The success of the reactions was confirmed using IR spectroscopy and zeta-potential measurements. The membranes carrying negatively charged groups provided a negative zeta-potential and had an isoelectric point at pH 3.6, while the membranes carrying positively charged groups had a positive zeta-potential in the analyzed pH range. Since only the surface of the polymer was modified, the pore size and permeance of the membranes were not drastically affected. The membranes prepared by both modification strategies had a pure water permeance higher than 1000 L/(m2 h bar) and a water contact angle of 44.3 and 57.2°, respectively. Therefore, the membranes can be operated at low pressures with reasonable flux. Additionally, SEM images showed that the membranes were still open-pored. Adsorption tests using a positively and a negatively charged dye as well as a toxic cation and an anion were performed to analyze the adsorption behavior. Both membranes were able to adsorb the oppositely charged dyes as well as the copper and chromate ions. Therefore, these membranes are good candidates to purify water streams containing hazardous ions.

Spraying of Ultrathin Isoporous Block Copolymer Membranes-A Story about Challenges and Limitations.

Isoporous membranes can be prepared by a combination of self-assembly of amphiphilic block copolymers and the non-solvent induced phase separation process. As the general doctor-blade technique suffers from high consumption of expensive block copolymer, other methods to reduce its concentration in the casting solution are sought after. Decreasing the block copolymer concentration during membrane casting and applying the block copolymer solution on a support membrane to obtain ultrathin isoporous membrane layers with e.g., spraying techniques, can be an answer. In this work we focused on the question if upscaling of thin block copolymer membranes produced by spraying techniques is feasible. To upscale the spray coating process, three different approaches were pursued, namely air-brush, 1-fluid nozzles and 2-fluid nozzles as generally used in the coating industry. The different spraying systems were implemented successfully in a membrane casting machine. Thinking about future development of isoporous block copolymer membranes in application it was significant that a continuous preparation process can be realised combining spraying of thin layers and immersion of the thin block copolymer layers in water to ensure phase-separation. The system was tested using a solution of polystyrene-block-poly(4-vinylpyridine) diblock copolymer. A detailed examination of the spray pattern and its homogeneity was carried out. The limitations of this method are discussed.

Quaternization of a Polystyrene-block-poly(4-vinylpyridine) Isoporous Membrane: An Approach to Tune the Pore Size and the Charge Density.

Isoporous integral asymmetric membranes derived from the self-assembly of block copolymers combined with the non-solvent-induced phase separation (SNIPS) have gained great attention. To extend their utility, good control over pore size and surface functionality in a facile manner is highly desirable. Here, an approach is proposed to achieve this by quaternization of the poly(4-vinylpyridine) moiety of a polystyrene-block-poly(4-vinylpyridine) SNIPS membrane using alkyl iodides via a scalable gas-solid heterogeneous reaction. By changing the size of the alkyl groups of the quaternization agent and the degree of quaternization, the effective pore size of the membrane is tailored in a wide range from the ultrafiltration to the nanofiltration regime. A quaternization of approximately half of the 4VP repeating units of the membranes with methyl iodide, ethyl iodide, or 1-propyl iodide leads to a retention of methylene blue from a 10 mg L-1 aqueous solution of 96%, 87%, and 83%, respectively.

Changes in spino-pelvic alignment after surgical treatment of isthmic spondylolisthesis.

BACKGROUND AND PURPOSE: To analyze the changes in spino-pelvic parameters after surgical treatment of lumbar isthmic spondylolisthesis. MATERIALS AND METHODS: Sixty patients recruited from a group of consecutive series of 128 cases with isthmic spondylolisthesis operated on between 2002 and 2012 in the Department of Neurosurgery, Tarnow, Poland. All patients were operated on by the same surgeon (the first author). Spino-pelvic parameters: PI, SS, PT, LSA, and LL were measured manually on standing lateral view radiograms. Patients were divided according to Spinal Deformity Study Group classification which we modified for means of analysis: (A) low-grade group: subgroups with balanced pelvis and unbalanced pelvis (instead of normal and high PI subgroups), (B) high-grade group: subgroups with balanced and unbalanced pelvis. RESULTS: Twenty-nine patients had unbalanced pelvis before the operation. In 10 of them (34%), the procedure resulted in full correction of pelvis position meaning that they achieved balanced pelvis after the surgery. There were 6 patients with low-grade slip who had balanced pelvis preoperatively but showed unbalanced pelvis after the surgery but this loss of balanced pelvis did not affect the clinical outcome which overall was good among them. Patients with unbalanced pelvis presented changes towards restoration of spino-sacro-pelvic anatomy postoperatively: PT decreased while SS increased, although these changes were not statistically significant. CONCLUSION: Further studies are needed to confirm whether surgical correction of spino-pelvic parameters results in better clinical outcome in patients with isthmic spondylolisthesis.

Posterior keyhole corpectomy with percutaneous pedicle screw stabilization in the surgical management of lumbar burst fractures.

OBJECTIVE: The authors present a new method of minimally invasive surgical management of lumbar burst fractures through the posterior approach. The method includes minimally invasive corpectomy and interbody fusion, both of which are performed through a keyhole approach, and percutaneous pedicle screw fixation of the fracture. The technique of the posterior keyhole corpectomy presented in this report is a novel and original concept of the first author (AM). The percutaneous pedicle screw stabilization is performed with the use of a percutaneous instrumentation system (Sextant; Medtronic, Inc., Minneapolis, MN). The Sextant system has been dedicated and used in nontrauma degenerative cases; the novel aspect of this system is its application in spine fractures. Indications for the method include Denis classification subtype B or Magerl subtype A.3.1 burst fractures. Both subtypes represent fractures with failure and retropulsion of the upper part of the vertebral body. METHODS: The clinical experience of this study includes four cases of burst fractures with significant retropulsion and occlusion of the spinal canal. Long-term results were assessed at a minimum follow-up period of 1 year (maximum, 3.5 yr). The follow-up assessments included: 1) the quality of decompression and reconstruction of the spinal canal (computed tomographic and magnetic resonance imaging scanning); 2) the stability of the operated segment (dynamic x-rays); 3) the quality of interbody fusion (computed tomographic scanning and dynamic x-rays); and 4) correction of the fracture kyphosis and its postoperative loss (measurements of Cobb angles for the assessment of sagittal plane deformity). The minimum armamentarium requirements for this method include a typical micro lumbar discectomy retractor set; a surgical microscope; two-plane intraoperative fluoroscopy; and a system for percutaneous pedicle screw stabilization (Sextant). "Posterior keyhole corpectomy" indicates corpectomy of the posterior upper half of the vertebral body or removal of the retropulsed bone fragment via two keyhole skin incisions on both sides of the spinous process (each skin incision measures 2 to 3 cm long). Exposure of the retropulsed fragment (the posterior upper part of the vertebral body) is achieved by medial or complete facetectomy along with complete or medial resection of the pedicle. This has to be performed bilaterally. Percutaneous stabilization requires four additional stab skin incisions. RESULTS: We observed no surgery-related complications (neurological, hardware, dural tears, or deep or superficial wound infections); there was perfect decompression and clearance of the spinal canal (confirmed by computed tomographic and magnetic resonance imaging scanning); and there was solid stability at the affected segments (confirmed by dynamic x-rays). Healed fusion was noted in all patients but one. The latter patient had no clinical symptoms of spinal instability. Kyphotic deformity was corrected and reversed into lordosis in three patients. Loss of deformity correction was noted in all patients; however, all patients retained lordotic alignment of the affected segment. CONCLUSION: The advantages of this method include sparing the posterior elements (lamina, spinous process, supraspinous and interspinous ligaments, and paravertebral muscles), safety of the decompression provided by the use of a surgical microscope, and perfect illumination of the operating field. The drawbacks of the method include limitation to certain types of burst fractures, the method is surgically demanding, and the method requires development of a special retractor system to eliminate the cumbersome alternate insertion and the reinsertions of the typical microdiscectomy retractor set.

[Minimally invasive posterior corpectomy of the lumbar spine with transpedicular fixation]. / Minimalnie inwazyjna korpektomia tylna odcinka ledzwiowego kregoslupa ze stabilizacja przeznasadowa

The authors present their experience in the minimally invasive posterior keyhole lumbar corpectomy with transpedicular stabilization. This technique involves the removal of the posterior part of the affected vertebral body with the pedicle screw fixation through four 2-3 cm long skin incisions on the back. Two cephalad skin incisions provide an approach for corpectomy and instrumentation of the upper pedicles of the construct. Two caudal skin incisions provide an approach for instrumentation of the lower pedicles of the construct. The minimum armamentarium requirement includes classic micro lumbar discectomy retractor set and intraoperative fluoroscopy. According to the authors' best knowledge this is the first minimally invasive posterior keyhole lumbar corpectomy ever reported in the literature (2002). This is also the first minimally invasive transpedicular fixation ever performed in Poland (2002). This technique was presented during EANS Congress (Lisbon, September 2003). Some reports have recently appeared in the literature on percutaneous pedicle screw fixation of the lumbar spine in non traumatic cases. A special instrumentarium system (Sextant by Medtronic) has been developed and used in this type of minimally invasive stabilization. Although this system has not been dedicated for spine fractures it is feasible in trauma cases. We have one case of L2 burst fracture fixed percutaneously with Sextant.