Study on the removal efficiency of UF membranes using bacteriophages in bench-scale and semi-technical scale.

To determine the removal efficiency of ultrafiltration (UF) membranes for nano-particles in the size range of viruses the state of the art uses challenge tests with virus-spiked water. This work focuses on bench-scale and semi-technical scale experiments. Different experimental parameters influencing the removal efficiency of the tested UF membrane modules were analyzed and evaluated for bench- and semi-technical scale experiments. Organic matter in the water matrix highly influenced the removal of the tested bacteriophages MS2 and phiX174. Less membrane fouling (low ΔTMP) led to a reduced phage reduction. Increased flux positively affected phage removal in natural waters. The tested bacteriophages MS2 and phiX174 revealed different removal properties. MS2, which is widely used as a model organism to determine virus removal efficiencies of membranes, mostly showed a better removal than phiX174 for the natural water qualities tested. It seems that MS2 is possibly a less conservative surrogate for human enteric virus removal than phiX174. In bench-scale experiments log removal values (LRV) for MS2 of 2.5-6.0 and of 2.5-4.5 for phiX174 were obtained for the examined range of parameters. Phage removal obtained with differently fabricated semi-technical modules was quite variable for comparable parameter settings, indicating that module fabrication can lead to differing results. Potting temperature and module size were identified as influencing factors. In conclusion, careful attention has to be paid to the choice of experimental settings and module potting when using bench-scale or semi-technical scale experiments for UF membrane challenge tests.

Continuous rhamnolipid production with integrated product removal by foam fractionation and magnetic separation of immobilized Pseudomonas aeruginosa.

Increasing interest in biological surfactants has led to intensified research directed at more cost-efficient production of biosurfactants, relative to traditional surface-active components based on petrochemical feedstocks. This publication will focus on a new integrated process for continuous rhamnolipid (RL) production. RL was synthesized by Pseudomonas aeruginosa DSM 2874 and was continuously removed in situ by foam fractionation. To prevent loss of the biocatalyst through foaming, bacteria were entrapped in magnetic alginate beads. Immobilizates were retained from the foam by high-gradient magnetic separation and back-flushed in the bioreactor at constant intervals. It was demonstrated that continuous RL production in a 10-L bioreactor over several cycles with intermediate growth periods is feasible. Complete separation of RLs from the production medium with an average enrichment ratio of 15 in the collapsed foam was demonstrated, yielding a final RL amount of 70 g after four production cycles.

Influence of different magnetites on properties of magnetic Pseudomonas aeruginosa immobilizates used for biosurfactant production.

During the last decades, whole-cell immobilization has been used successfully in many bioprocesses. In particular, it is aimed at implementing continuous production processes, reaching higher production rates, and reusing the biocatalyst. In some cases, effective retention of immobilizates in the bioprocess is not feasible by membranes or sieves due to pore plugging or undesired losses of immobilizates. In the present publication, it is reported about the investigation of magnetic immobilizates of Pseudomonas aeruginosa for application in continuous biosurfactant production of rhamnolipids by foam fractionation and retention of entrained immobilizates by high-gradient magnetic separation from foam. Different materials and methods were tested with respect to important parameters, such as stability, diffusion properties or magnetic separation. Good magnetic separation of immobilizates was achieved at 5% (w/w) magnetite loading. Best results in terms of homogeneous embedding, good diffusion properties, and stability enhancement vis-à-vis pure alginate beads was achieved with alginate beads with embedded Bayoxide magnetite or MagPrep silica particles. Although polyurethane immobilizates showed higher stabilities compared with alginate beads, rhamnolipid diffusion in immobilizates was superior in magnetic alginate beads. Regarding bead production, smaller immobilizates were achieved with suspension polymerization compared to droplet extrusion by the JetCutting technology. In total, magnetic immobilizates are a promising tool for an easier handling of biocatalysts in a continuous biological production process, but they have to be adapted to the current production task.

Development and trends of biosurfactant analysis and purification using rhamnolipids as an example.

During the last few decades, increasing interest in biological surfactants led to an intensification of research for the cost-efficient production of biosurfactants compared with traditional petrochemical surface-active components. The quest for alternative production strains also is associated with new demands on biosurfactant analysis. The present paper gives an overview of existing analytical methods, based on the example of rhamnolipids. The methods reviewed range from simple colorimetric testing to sophisticated chromatographic separation coupled with detection systems like mass spectrometry, by means of which detailed structural information is obtained. High-performance liquid chromatography (HPLC) coupled with mass spectrometry currently presents the most precise method for rhamnolipid identification and quantification. Suitable approaches to accelerate rhamnolipid quantification for better control of biosurfactant production are HPLC analysis directly from culture broth by adding an internal standard or Fourier transform infrared attenuated total reflectance spectroscopy measurements of culture broth as a possible quasi-online quantification method in the future. The search for alternative rhamnolipid-producing strains makes a structure analysis and constant adaptation of the existing quantification methods necessary. Therefore, simple colorimetric tests based on whole rhamnolipid content can be useful for strain and medium screening. Furthermore, rhamnolipid purification from a fermentation broth will be considered depending on the following application.

Evaluation of magnetic polymer micro-beads as carriers of immobilised biocatalysts for selective and stereoselective transformations.

The kinetic, selective and stereoselective properties of enzyme immobilised on magnetic polymer beads with diameters in the range 1 microm was studied with penicillin amidase from E. coli. The enzyme was immobilised on epoxy and glutaraldehyde-activated poly(vinyl alcohol), poly(methylmetacrylate) and poly(vinyl acetate-divinylbenzene) magnetic beads. The amount of covalently bound active protein was dependent on the chemical modification of the matrix and increased at higher ionic strength of the immobilisation buffer. The small size of the magnetic beads, that reduces mass transfer limitations, and the decreased charge density in the electric double layer resulted in lower apparent Km values and higher efficiency for benzylpenicillin hydrolysis, higher stereoselectivity in condensation of R-phenylglycine amide with S- and R-Phe and in hydrolysis of racemic phenylacetyl-Phe and higher selectivity in kinetically controlled synthesis of cephalexin compared to the enzyme immobilised on larger and porous carriers.

Cerclage fibreux in the treatment of hallux valgus.

Resection arthroplasty was performed in 62 feet, with follow-up at an average of 36 months (range, 17-68 months). All cases were performed using a combined cerclage fibreux. The mean age at operation was 61 years (range, 49-77 years). The mean score according to the hallux metatarsophalangeal-interphalangeal scale of the American Orthopaedic Foot and Ankle Society was 81 points (range, 25-100 points). Correction of the hallux valgus angle at follow-up averaged 23 degrees (range, 0-45 degrees). The first intermetatarsal angle had been corrected an average of 3 degrees (range, 0-14 degrees). Transfer metatarsalgia was encountered in eight patients. No hallux varus or cock-up deformity was detected.

Predisposing factors for infection in spine surgery: a survey of 850 spinal procedures.

A retrospective survey of 850 spinal procedures was conducted to determine risk factors for postoperative spinal infection. Some 574 posterior and 276 anterior procedures were evaluated. Infections were classed as early (within 19 weeks postoperatively) and late (> or = 20 weeks postoperatively), as well as deep and superficial infections. Previously postulated risk factors (i.e., diabetes, corticosteroid therapy, previous spinal surgery, obesity, chronic infection, and smoking) were investigated. Furthermore, it was hypothesized that three additional factors: extended preoperative hospitalization, prolonged operation duration, and high blood loss were risk factors not previously considered. A postoperative infection was evident in 22 of 850 procedures (19 early/three late infections, four superficial/18 deep infections). Most infections (n = 21) occurred with posterior instrumentation. Previously described factors were proven as risk factors. Extended preoperative hospitalization (p < 0.04), high blood loss (p < 0.01), and prolonged operation time (p < 0.001) were additionally determined as risk factors. The results suggest that routine prophylactic antibiotics might be unnecessary in anterior surgery, whereas extended prophylactics should be considered in posterior instrumentation, especially when risk factors are apparent.

Computed tomography in the determination of leg geometry.

In 286 adults with misalignment of the lower limb the length and torsional angles of the femur and tibia were determined using a method based on computed tomography. Depending on the location of the axial scan values for femoral antetorsion changed substantially. Normal values obtained in non injured extremities by this technique were an internal torsion of 23.5 +/- 8.6 degrees (mean +/- SD) in the femur and an external torsion of 34.9 +/- 8.6 degrees in the tibia. Mean intraindividual side differences in the femur and tibia were 4 degrees, the 95% confidence interval was 11.0 degrees in the femur and 12.3 degrees in the tibia. CT-methods can only be used for the determination of torsional angles in the femur and tibia if reproducible and standardized locations for the acquisition of axial scans are defined.

[Computerized tomography measurement of torsion angle of the lower extremities]. / Computertomographische Torsionswinkelbestimmung der unteren Extremitäten.

The precise evaluation of post-traumatic deformities is indispensable when planning a corrective osteotomy. Torsional angles of the lower extremities of 186 patients were measured using CT. The mean age of the studied population was 34 years (18-80). It consisted of 131 men and 55 women. All patients had sustained a fracture of at least one of the leg's bony segments. The normal femoral (n = 293) inward torsion measured 23.47 degrees +/- 17.16 degrees (mean +/- 2 SD). Normal tibia (n = 263) outward torsion was 34.03 degrees +/- 17.22 degrees. The intraindividual torsional differences were not normally distributed. Normal femoral (n = 103) intraindividual torsional difference measured 11 degrees (95% percentile) and 15 degrees (99% percentile), with a median of 4 degrees. The tibiae (n = 76) showed a normal intraindividual torsional difference of 12 degrees (95% percentile) and 15 degrees (99% percentile). Right tibiae showed a statistically significant greater outward rotation when compared to their left counterpart (P < 0.001). No correlation to sex could be established. Preoperative planning of a corrective osteotomy should include the geometric evaluation of all four bony segments of the leg. Intraindividual torsional differences must be considered. A corrective osteotomy appears to be unnecessary with a torsional difference smaller than 15 degrees in the femora and smaller than 15 degrees in the tibiae.

Longitudinal growth pattern of the radius after forearm fractures conservatively treated in children.

In a 3-year prospective study, the growth pattern of the radius following fracture was analyzed in 64 children < 15 years old with forearm fractures treated by conservative methods. Comparative radiographic studies of the fractured and the uninjured radius were carried out in all patients at 3, 6, 12, and 18 months after fracture. Only 40 patients, 28 boys and 12 girls, with an average age of 9 years, completed the follow-up period. The series included 19 buckle fractures of the radius, 11 green-stick, and 10 complete fractures. Fracture of the ulna was associated in 11 cases. Maximal average radial growth rate was observed from age 9 through 12 years. Overall, the length discrepancy between the fracture and the healthy radius at the end of the follow-up period averaged 0.03 cm (range -0.50 to +1). In nine cases (21%), the fractured radius showed an average overgrowth of +0.44 cm. In 10 other patients (25%), a radial shortening could be detected (average discrepancy -0.29). Five of the nine cases with radial overgrowth had an associated fracture of the ulna. This association was not found in any of the 10 patients with radial shortening. These observations allow us to reconsider the classic etiopathogenic theories concerning overgrowth in the long bones of children following fracture. Factors other than the increased vascularity of the growth plate--as is postulated for the femur and tibia--must be investigated further to explain the frequent absence of radial overgrowth following fracture.

[Intraoperative recording of intramedullary pressures with a microprobe]. / Intraoperative Messung von intramedullären Drucken mit einer Mikro-Sonde.

The implantation of femoral prostheses and intramedullary nailing for fracture stabilisation are well-established techniques in traumatology. Nevertheless, the obvious biomechanical advantages of intramedullary splinting are partly offset by occasional disturbances of pulmonary circulation and function. These disorders of pulmonary function are apparently correlated with an operation-induced increase in intramedullary pressure. A simple, low-invasive and reliable system for the measurement of intramedullary pressure is presented. The heart of the system is a microtip probe that converts changes in pressure into electrical impulses, which are then filtered and amplified in the pressure measuring system (PMS).

Treatment of adolescent tibia vara by asymmetrical physeal distraction.

We have treated 12 adolescent patients with idiopathic tibia vara by asymmetrical physeal distraction using a modified Wagner external fixator. There were no major complications and a mean correction of 13 degrees was achieved. The main advantages of the technique are that no osteotomy, internal fixation or bone graft is needed, and that the operation can be performed on both tibiae simultaneously. No shortening is produced and lengthening can be added to angular correction if required.

The microtip intramedullary probe for intraoperative pressure measurement.

The implantation of femoral stem prostheses and intramedullary fracture stabilisation are well-established techniques in traumatology. Although the biomechanical advantages of intramedullary splinting are obvious, impairments of pulmonary circulation and respiratory function are typical and feared complications. These pulmonary disturbances are strikingly correlated with operation-induced intramedullary hypertension. A simple, low-invasive and reliable system for the measurement of intramedullary pressure is presented. At the heart of the system is a microtip probe, transforming changes of pressure into electric impulses, filtered and amplified in a pressure measuring system (PMS).