Hollow Fiber Devices Research Articles

Hydrodynamics and mass transfer in straight fiber bundles with non-uniform porosity

The present study investigates the effects of non-uniformity in a bundle’s porosity by considering a model channel made up of “dense” (low porosity) and “loose” (high porosity) regions. In a first, simplified, approach these regions are treated as non-interacting porous media and previously obtained computational results are used for the Darcy permeability and the Sherwood number. In a second, and more complete, approach 3-D CFD simulations are conducted for a checkerboard arrangement of alternately “dense” and “loose” regions with square-arrayed fibers, accounting for entry effects and for interactions between regions. Non-uniformity causes a significant increase of the permeability and a strong reduction of the Sherwood number. These effects are larger, approaching those obtained for non-interacting regions, if the regions’ length scale is large. The attainment of fully developed conditions is greatly shifted forward in non-uniform bundles and the mass transfer development length may largely exceed the physical length of most hollow-fiber devices.

Vitrification of mouse two-cell and blastocyst stage embryos in simplified closed system using either a hemi-straw or a hollow fiber device.

Two-cell stage and blastocyst stage mouse embryos were equilibrated in a medium containing 7.5% ethylene glycol (EG) and 7.5% dimethyl sulfoxide (DMSO) for 8-15 min. Vitrification was performed in a medium containing 0.5M sucrose and either 15% EG + 15% DMSO, 17.5% EG + 17.5% DMSO, or 20% EG + 20% DMSO for 30 s. They were then placed either on a hemi-straw (HS) or a hollow fiber vitrification (HFV) device and vitrified by cooled air inside a 0.5-ml straw. In two-cell embryos, a 100% survival rate was obtained from all groups except the 20% HS group (P > .05). All vitrified two-cell groups showed similar rates of blastocyst development to that of fresh control group (P > .05), except 17.5% and 20% HFV groups, which were significantly lower than the other groups (P < .05). In the blastocyst embryos, the HFV groups were divided into two subgroups (non-collapsed; HFV-NC and collapsed; HFV-C blastocyst). Re-expansion rate in 15% HFV-NC, 17.5% HFV-NC, and 15% HFV-C groups was reduced (P < .05), whereas the rest were similar to control. In conclusion, we established a simplified, reliable, and closed system for HFV vitrification applying hemi-straw, which does not require skilled practitioners.

A High Cell-Bearing Capacity Multibore Hollow Fiber Device for Macroencapsulation of Islets of Langerhans.

Macroencapsulation of islets of Langerhans is a promising strategy for transplantation of insulin-producing cells in the absence of immunosuppression to treat type 1 diabetes. Hollow fiber membranes are of interest there because they offer a large surface-to-volume ratio and can potentially be retrieved or refilled. However, current available fibers have limitations in exchange of nutrients, oxygen, and delivery of insulin potentially impacting graft survival. Here, multibore hollow fibers for islets encapsulation are designed and tested. They consist of seven bores and are prepared using nondegradable polymers with high mechanical stability and low cell adhesion properties. Human islets encapsulated there have a glucose induced insulin response (GIIS) similar to nonencapsulated islets. During 7 d of cell culture in vitro, the GIIS increases with graded doses of islets demonstrating the suitability of the microenvironment for islet survival. Moreover, first implantation studies in mice demonstrate device material biocompatibility with minimal tissue responses. Besides, formation of new blood vessels close to the implanted device is observed, an important requirement for maintaining islet viability and fast exchange of glucose and insulin. The results indicate that the developed fibers have high islet bearing capacity and can potentially be applied for a clinically applicable bioartificial pancreas.

Post-combustion CO2 capture and recovery by pure activated methyldiethanolamine in crossflow membrane contactors having coated hollow fibers

Gas absorption and stripping using membrane contactors is one of a number of carbon capture and storage technologies being investigated for separating CO2 from flue gas. Energy consumption in CO2 absorption-stripping employing amine-containing aqueous absorbent solutions is strongly influenced by demanding stripping conditions involving higher temperatures. The utility of using pure methyldiethanolamine (MDEA) activated by piperazine as a reactive absorbent was studied using a compact hollow fiber device for the absorber as well as the stripper. Water needed for reactive absorption of CO2 in tertiary amine MDEA was obtained from simulated humidified flue gas stream which is saturated with moisture in actual practice. This study investigated also the absorption and stripping performances of aqueous absorbent solutions containing 80% and 90% activated MDEA (aMDEA). Considerable CO2 stripping from CO2-loaded pure aMDEA absorbent was achieved at 92 °C while absorption was carried out at 25–46 °C. Further, the CO2 stripping rate was far higher for pure MDEA compared to the other two aMDEA solutions with water. Results are reported for the performance of the absorption-stripping process as a function of humidified simulated flue gas flow rate and the absorbent flow rate. High values of the overall mass transfer coefficients (MTCs) have also been reported for absorption. The highest volumetric gas phase based overall MTC obtained was 0.504 sec−1. This system has a much lower absorbent circulation load, eliminates the energy needed to heat and evaporate water present in aqueous absorbent solutions and benefits from the absence of excess water during stripping.

Preconcentration and Determination Of Fluoxetine and Norfluoxetine in Biological and Water Samples with β-cyclodextrin Multi-walled Carbon Nanotubes as a Suitable Hollow Fiber Solid phase Microextraction Sorbent and High Performance Liquid Chromatography

‒A simple, selective and sensitive hollow fiber solid phase microextraction (SPME) combined with HPLC for the determination of fluoxetine (FLX) and norfluoxetine (NFLX) in human urine and real water samples has been developed and fully validated. Two solid phase microextraction sorbents, β-cyclodextrin functionalized multi-walled carbon nanotubes (βCD-MWCNTs) and acyl chloride functionalized MWCNTs, were synthesized and placed in the surface and pores of polypropylene hollow fiber by sol‒gel technique. In order to compare the analytical performance of βCD-MWCNTs as a new SPME sorbent with acyl chloride functionalized MWCNTs and MWCNTs, the hollow fiber device was directly immersed into the sample solution under a magnetic stirring. The βCD-MWCNTs are quite effective for extraction of fluoxetine and norfluoxetine. The extraction parameters such as pH of donor phase, donor phase volume, stirring rate, extraction time, type and volume of desorption solvent, and desorption time were thoroughly optimized. Under optimal conditions, the proposed method shows good linearity in the range of 1‒340 and 0.9‒360 ng/mL with a correlation coefficients of 0.9952 and 0.9967, low limits of detection of 0.4 and 0.3 ng/mL, and the high pre-concentration factors of 144 and 151 for determination of FLX and NFLX, respectively. Usage of proposed method for determination of FLX and NFLX in human urine and real water samples demonstrated a promising, simple, selective and sensitive sample preparation and determination method that can be applied in routine analysis.

Cooling Crystallization of Sodium Chloride via Hollow Fiber Devices to Convert Waste Concentrated Brines to Useful Products

Cooling crystallization via hollow fiber devices emerges as a new technology suitable for salt production from concentrated seawater brine. To generate high-quality NaCl crystals, a solid hollow fiber cooling crystallization (SHFCC) system was developed in this study using lab-made PVDF hollow fibers as the heat-exchanger and magnetic stirring as the downstream mixing device. Experiments were conducted to investigate the influences of downstream agitation methods and operation parameters on crystal properties. Narrowly distributed NaCl crystals with a small size of around 35 μm were successfully produced by the SHFCC system combined with ultrasonication or magnetic stirring. Specifically, the magnetic stirring-based agitation was the most effective in facilitating crystal generation with the highest rates of nucleation and crystal salt production due to the enhanced mass transfer in the diffusion-controlled crystallization process. The influences of feed solution and stirring speed on NaCl crystal product...

A Receptor‐Based Bioadsorbent to Target Advanced Glycation End Products in Chronic Kidney Disease

The accumulation of advanced glycation end products (AGEs) has been reported to be a major contributor to chronic systemic inflammation. AGEs are not efficiently removed by hemodialysis or the kidney of a chronic kidney disease (CKD) patient. The goal of this study was to develop a receptor for AGEs (RAGE)-based bioadsorbent device that was capable of removing endogenous AGEs from human blood. The extracellular domain of RAGE was immobilized onto agarose beads to generate the bioadsorbent. The efficacy of AGE removal from saline, serum, and whole blood; biological effects of AGE reduction; and hemocompatibility and stability of the bioadsorbent were investigated. The bioadsorbent bound AGE-modified bovine serum albumin (AGE-BSA) with a binding capacity of 0.73 ± 0.07 mg AGE-BSA/mL bioadsorbent. The bioadsorbent significantly reduced the concentration of total AGEs in serum isolated from end-stage kidney disease patients by 57%. AGE removal resulted in a significant reduction of vascular cell adhesion molecule-1 expression in human endothelial cells and abolishment of osteoclast formation in osteoclast progenitor cells. A hollow fiber device loaded with bioadsorbent-reduced endogenous AGEs from recirculated blood to 36% of baseline levels with no significant changes in total protein or albumin concentration. The bioadsorbent maintained AGE-specific binding capacity after freeze-drying and storage for 1 year. This approach provides the foundation for further development of soluble RAGE-based extracorporeal therapies to selectively deplete serum AGEs from human blood and decrease inflammation in patients with diabetes and/or CKD.

Experimental evaluation and theoretical modeling of oxygen transfer rate for the newly developed hollow fiber bioreactor with three compartments

Bioartificial liver support provides a bridge to transplantation which is at present the only proven specific treatment for acute liver failure. In this paper, a novel multi-coaxial hollow fiber bioreactor so-called "Fibre-in-Fibre FIF Bioartificial liver device" with three compartments is experimentally and mathematically studied. The mathematical model in this paper is an extension of Krogh cylinder model for hollow fibre devices by including one more zone for oxygen transfer, i.e. oxygenation compartment. Three simultaneous linear differential equations were derived for pressure in plasma and cell compartments and flow rate in cell compartment. To validate the model, Oxygen Transfer Rate and hydrostatic pressure experimental measurements for different flow rates, 17-400 ml/min, and different number of hollow fibres pairs are used. Several important parameters of the Michaelis-Menten was investigated, namely, constant Vmax (the maximum oxygen consumption per unit volume of the cell mass), the oxygen partial pressure, the flow rate of the perfusate at device inlet. The results showed that the oxygenation compartment should easily secure Oxygen to the cells in compartment B.

Hollow fibre liquid-phase microextraction of functionalised carboxylic acids from atmospheric particles combined with capillary electrophoresis/mass spectrometric analysis

A method was developed to enrich various mono- and dicarboxylic acids from aqueous extracts of atmospheric particles by three-phase hollow fibre liquid-phase microextraction. Analysis was performed by capillary electrophoresis/electrospray ionisation mass spectrometry applying a previously reported separation method. Several extraction parameters (pH of donor and acceptor phase, composition of supported liquid membrane, shaking speed, and extraction time) were tested for their influence on analyte recovery. A strong dependence of the recovery on the acceptor phase pH was observed. The final method consisted of 10% (w/v) trioctylphosphine oxide in dihexylether as supported liquid membrane, 1.8ml aqueous particle extract, acidified by sulfuric acid to a pH of 2 as donor phase, and 15μl of 50mM aqueous ammonia solution as acceptor phase. The extraction devices were shaken at 2200rpm for 2h. With this method, the recoveries from aqueous standards were between 10 and 80% with a repeatability of 4–14% for most compounds. Generally, more polar compounds were extracted less efficient than less polar ones. A few of the most polar compounds showed recoveries <10% with a repeatability of 20–55%. The enrichment factor was typically 10–100. The analyte recovery from real samples was found to strongly depend on the sample matrix due to co-extraction of mineral acids and organic acidic material present in atmospheric particles. Quantification was achieved by the method of standard addition. The easy handling of the hollow fibre devices, the low costs per extraction and the possibility to do many extractions in parallel allowed for an application of the developed method to a large set of real samples.

Hollow Fiber Vitrification: A Novel Method for Vitrifying Multiple Embryos in a Single Device

Current embryo vitrification methods with proven efficacy are based on the minimum volume cooling (MVC) concept by which embryos are vitrified and rewarmed ultrarapidly in a very small amount of cryopreserving solution to ensure the high viability of the embryos. However, these methods are not suitable for simultaneously vitrifying a large number of embryos. Here, we describe a novel vitrification method based on use of a hollow fiber device, which can easily hold as many as 40 mouse or 20 porcine embryos in less than 0.1 μl of solution. Survival rates of up to 100% were obtained for mouse embryos vitrified in the presence of 15% DMSO, 15% ethylene glycol and 0.5 M sucrose using the hollow fiber vitrification (HFV) method, regardless of the developmental stage of the embryos (1-cell, 2-cell, morula or blastocyst; n = 50/group). The HFV method was also proven to be effective for vitrifying porcine in vitro- and in vivo-derived embryos that are known to be highly cryosensitive. For porcine embryos, the blastocyst formation rate of in vitro maturation (IVM)-derived parthenogenetic morulae after vitrification (48/65, 73.8%) did not decrease significantly compared with non-vitrified embryos (59/65, 90.8%). Transfer of 72 in vivo-derived embryos vitrified at the morula/early blastocyst stages to 3 recipients gave rise to 29 (40.3%) piglets. These data demonstrate that the HFV method enables simultaneous vitrification of multiple embryos while still adhering to the MVC concept, and this new method is very effective for cryopreserving embryos of mice and pigs.

Bio-inspired onboard membrane separation of water from engine oil

In colder environment, atmospheric moisture as well as water produced by gasoline engine combustion condense in the engine oil and introduce a significant amount of water. This water affects the engine oil performance. Hollow fiber membrane-based artificial kidney successfully removes waste metabolites from human blood. A similar hollow fiber membrane based device has been studied here for the removal of emulsified water in engine oil. The oil containing emulsified water flows on one side of the hollow fiber membrane; air flowing on the other side strips the moisture from the oil through a hydrogel membrane present in the hollow fiber membrane wall. Of the four types of hemodialysis membranes studied, regenerated cellulose-based hollow fiber membranes were found to be most suitable over the temperature range studied, −10 °C to 80 °C. All studies were conducted with SAE 5W30 motor oil containing emulsified water at the level of 1–4%. Batch recirculation studies demonstrated 90%+ removal of emulsified water in parallel flow modules containing 300 regenerated cellulose (RC) capillaries having a surface area of 150 cm 2. Studies were successfully carried out over a range of temperatures, oil flow rates, water content and oil temperature ramping with the oil flowing through the bore of hollow fiber membranes and air flowing outside. The water-removal capabilities of such modules decreased slowly on repeated dewatering tests over 7–8 days due to membrane fouling by the emulsion; the membrane fouling was also prevalent at the hollow fiber tube sheet. A cross flow hollow fiber device built with the engine oil flowing outside the fibers in cross flow demonstrated no such membrane fouling on repeated use. A mathematical model was developed to extract water mass transfer coefficient from the experimental data. The water mass transfer resistance in the oil film was found to be important. The cross flow device decreased this resistance substantially suggesting that a small membrane module should be able to remove moisture effectively in an automobile.

Impact of alginate type and bead diameter on mass transfers and the metabolic activities of encapsulated C3A cells in bioartificial liver applications

Liver-assist devices have been developed in the last few decades to support patients with liver failure on the road to recovery or transplantation. Fluidised bed bio-artificial livers--where liver cells are encapsulated within alginate beads--appear to be a valuable alternative to hollow fibre devices for improving mass transfers and enhancing treatment efficacy. This approach nevertheless deserves optimization in terms of bead production. The aim of this study was to investigate the impact of alginate type and of two bead diameters (1000 µm and 600 µm) on mass transfers within beads and on the biological functions of encapsulated C3A cells. After assessing the effect of the encapsulation process on bead quality, we investigated cell viability and metabolic activities (ammonia, albumin, alpha-fetoprotein synthesis and glucose consumption). They were successfully maintained over 48 h within fluidised bed bioreactors, independently of alginate type and bead diameter. Mass transfers were not significantly influenced by the latter parameters. Finally, suggestions are made for improving the entrapment process as a means of enhancing the treatment efficiency of the fluidised bed bioartificial liver.

Optimization, evaluation, and characterization of a hollow fiber supported liquid membrane for sampling and speciation of lead(II) from aqueous solutions

Hollow fiber supported liquid membrane sampling and speciation of lead(II) from aqueous solution using a selective carrier (Kelex 100) is studied. An optimization of different variables affecting permeation performance (chemical conditions of the sampling module – pH, concentration and nature of the acceptor phase, extractant concentration; membrane impregnation form; sampling time; and hollow fiber length) and an evaluation of those that influence the performance of the device under sampling conditions (sample pH; interfering cations – Cu(II), Cr (VI), Co(II), Cd(II), Ni(II), and Zn(II); anions – NO 2 −, SO 4 2−, Cl −, NO 3 −, CO 3 2−, CN − –, and organic matter – humic acids; lead concentration; and sample temperature) are reported. Kelex 100 concentration within the range 12–47 mmol dm −3, acceptor solution pH 2.2, hollow fiber length within the range 15–100 cm, and impregnation using mode III were found as optimal conditions for operation of the device. A linear equation described well the dependency of enrichment factor on sample pH in the 5.7–7.0 interval, the presence of 1 × 10 −6 mol dm −3 of Cu(II), Cr(VI), Co(II), Cd(II), Ni(II), or Zn(II) did not interfere in Pb(II) enrichment factor, 50 mg dm −3 of anions capable of forming labile complexes (NO 2 −, SO 4 2−, Cl −, NO 3 −, CO 3 2−) and 5 mg dm −3 of CN − produced a catalyzing effect in the permeation rate, which increased as lead concentration diminished. The presence of strong humic acid inert complexes in the donor phase caused a reduction in the enrichment factor, which additionally increases linearly as temperature increases. The possibilities for using the hollow fiber device for lead speciation in terms of permeation of free and labile species and rejection of inert complexes are discussed on the basis of such analyses. Composition–performance relationships for sampling module characterization and evaluation are analyzed as well.

Precipitation of barium sulphate in a hollow fiber membrane contactor: Part II The influence of process parameters

In this second of two papers, we investigated the influence of process parameters on BaSO 4 particle precipitation in a hollow fiber membrane device. The solution of barium chloride was passed tangentially over the membrane surface and reacted with a solution of K 2SO 4 introduced through the membrane pores. The resulting supersaturation induced nucleation and particle growth on the lumen side of the hollow fibers. A specific technique was developed to measure crystal size directly at the outlet of the hollow fiber device by using EDTA as a neutralizing agent of crystal nucleation and growth. Concentrations of barium chloride and potassium sulphate were shown to influence mainly the CSD, the effect of inlet flow rates on the lumen and shell sides being less pronounced. The chemical conversions measured were between 3.7% and 20.5%. We propose improvements in the design of hollow fiber devices in order to give higher chemical conversions.

Characterization of mixing in a hollow fiber membrane contactor by the iodide–iodate method: Numerical simulations and experiments

Abstract This paper presents numerical simulations and experimental data on the iodide–iodate reaction in a hollow fiber membrane device. The principle of reactive mixing in a membrane device is the following. Component A flows through the inlet of the lumen side and component B comes from the membrane pores (shell side). Components A and B then mix and react inside the lumen side. Experimental measurements of the segregation index were carried out under various experimental conditions and for two different hollow fiber devices. The numerical and experimental segregation indexes, X S , were found in the range 10 −2 –10 −3 , indicating effective mixing. The numerical simulations showed that I 3 − ions were produced mainly in the first part of the lumen side of the hollow fiber. This confirmed our previous results on precipitation which showed that high supersaturation data and experimental fouling were obtained in this part of the hollow fibers.

A clinical evaluation of the Dideco Kids D100 neonatal oxygenatora

In August 2006, Duke University Perfusion Services had the opportunity to be the first institution in the United States to clinically evaluate the Dideco D100 Neonatal Oxygenator. The device was used on six pediatric patients to facilitate correction or palliation of their cardiac defects, which included two arterial switch operations, two truncus arteriosus repairs, one stage 1 Norwood and one repair of total anomalous pulmonary venous return. The average patient weight was 3.1 kg. The average cardiopulmonary bypass (CPB) time was 135 minutes and the average cross-clamp time was 61 minutes. Arterial and venous blood gasses were drawn and used to calculate oxygen transfer. The average oxygen transfer was 14.8 +/- 10.3 ml/O2/min. The Dideco D100 Oxygenator is the first oxygenation device designed specifically for neonates. The Dideco D100 is a microporous hollow-fiber device. It has a static priming volume of 31 ml and a maximum rated flow of 700 ml/min. The integral hard-shell venous reservoir has a minimum operating level of 10 ml and a reservoir capacity of 500 ml. For this evaluation, the Dideco Kids D100 Neonatal Oxygenator performed adequately on patients weighing up to 5 kg. This device provides an excellent first step towards offering very small children appropriate circuitry without having to sacrifice safety or performance.

Cooling Crystallization of Paracetamol in Hollow Fiber Devices

We examine here cooling crystallization of aqueous paracetamol solutions in hollow fiber devices. It is shown that a solid hollow fiber crystallizer (SHFC)−static mixer assembly can be operated successfully up to 30−40°C below the metastable zone limit. Such a capability is not existent in industrial cooling crystallizers; it allows the decoupling of nucleation and growth, an opportunity offered currently only by impinging jet mixers for antisolvent crystallization. In addition, it leads to the achievement of very high nucleation rates and hence small crystal sizes. The former were 2−4 orders of magnitude higher than values previously obtained in solid hollow fiber crystallizers for potassium nitrate and salicylic acid and reached values encountered only in impinging jet crystallization. A qualitative comparison with existing literature data showed that the SHFC−static mixer combination confined the crystal size distribution (CSD) to smaller sizes and a narrower range. Finally, a linear relationship betwe...

Characterizing short-term release and neovascularization potential of multi-protein growth supplement delivered via alginate hollow fiber devices

Multi-protein (10-250 kDa) endothelial cell growth supplement (ECGS) contains growth factors of varying sizes resulting in advanced release rates from diffusion-based drug delivery devices. As a result, the biochemical stimulus provided by ECGS for neovascularization in the critical initial stages of cell transplantation in artificial organs may differ from that for single growth factor delivery. In this study, both in vitro and in vivo studies were conducted with ECGS to correlate in vitro release of multiple angiogenic growth factors to vascularization potential in vivo. The short-term release of ECGS from calcium alginate gels supported in the lumen of polypropylene (PP) hollow fibers was investigated in vitro for up to 142 h. The overall time constant increased from 2, 2.2 and 6.3 h as the alginate concentration was increased from 1.5%, 2% and 3%, respectively. However, time constants for individual species ranged from 1.5 to 77 h. The in vivo bioactivity of released ECGS was assessed for up to 21 days using a Lewis rat model implanted with 1.5% calcium alginate gels supported in PP and polysulfone hollow fibers. For the ECGS-releasing PP hollow fiber system, a two-fold increase in neovascularization with respect to the control was observed for the period between 7 and 17 days post-implantation at the device-tissue interface (p<0.05).

Optimization of copper sorbing?desorbing cycles with confined cultures of the exopolysaccharide-producing cyanobacterium Cyanospira capsulata

The aim of this study was to compare the copper removal capability of the exopolysaccharide-producing cyanobacterium Cyanospira capsulata confined into various filtering devices and to assess its reuse for several metal sorbing-desorbing cycles. C. capsulata cultures were confined into three dialysis devices and two hollow fibre systems with different surface to volume ratios. The maximum amount of Cu was removed by the biomass confined into dialysis cassettes, followed by the dialysis tubing systems and by the two hollow fibre devices. The experiments on the sorbing-desorbing cycles showed that, with the most effective desorbing agents, the same biomass can be utilized for eight consecutive sorbing-desorbing cycles. The efficiency of the metal removal process is directly related to a high surface to volume ratio of the confining system and the biomass can be utilized for multiple sorbing-desorbing cycles without significant loss in the metal removal efficiency. The feasibility of a metal removal process using EPS-producing cyanobacteria confined into filtering devices has been shown, pointing out the potential of this technique for industrial applications in the removal of metals from waste waters or in the recovery of valuable metals from water solutions.

Antisolvent crystallization in porous hollow fiber devices

This paper examines antisolvent crystallization under a new perspective and in the unique environment offered by porous hollow fiber membrane devices. The latter are compact, extremely efficient on a volumetric basis, easy to scale up and control. Their inherent characteristics promote the creation of homogeneous concentration conditions on a scale considerably smaller than existing industrial crystallizers without the necessity of a large energy input, properties that are desirable but rarely achieved in industrial crystallizers. Mixing studies were performed to examine the maximum achievable supersaturation in porous hollow fiber devices. It was shown that they are able to offer the supersaturation levels necessary to perform antisolvent crystallization. Moreover, supersaturation is created uniformly due to the large number of feed introduction points, the membrane pores. In addition, radial mixing is substantial in contrast with traditional tubular devices and the characteristic time involved in this process is comparable to the device residence time. Porous hollow fiber antisolvent crystallization of aqueous L-asparagine monohydrate systems proved successful. Mean crystal sizes up to two times smaller compared to batch stirred crystallizers were obtained in standalone membrane hollow fiber crystallizers (MHFC) and their combinations with completely stirred tanks. The CSD was confined below 165 μ m for the former and 75 μ m for the latter, levels that are sufficient for most pharmaceutical crystalline products, for which bioavailability and formulation concerns dictate the desired CSD. In addition, porous hollow fiber devices achieved comparable or slightly higher nucleation rates with respect to batch stirred crystallizers and similar values compared to tubular precipitators. Considerable improvements can be obtained by carefully designing membrane hollow fiber crystallizers.