Reduction of leakage from insertion site during continuous femoral nerve block with catheter-through-needle versus catheter-over-needle technique for postoperative analgesia after total knee arthroplasty: a randomized controlled trial

BACKGROUND

Continuous femoral nerve block (CFNB) is a common procedure used for postoperative analgesia in total knee arthroplasty. Continuous nerve block using a conventional needle (catheter-through-needle/CTN) is complicated by leakage of the anesthetic from the catheter insertion site. A different type of needle (catheter-over-needle/ CON) is now available, which is believed to reduce leakage as the diameter of the catheter is larger than that of the needle. The purpose of this study was to compare the incidence of leakage from the catheter insertion site during CFNB while using CTN and CON for postoperative analgesia after total knee arthroplasty (TKA).

METHODS

This prospective, randomized, single-blinded controlled study included 60 patients who were scheduled for TKA at our facility between May 2016 and November 2017. Patients were randomly allocated to the CTN or CON groups. All patients in both groups received CFNB and sciatic nerve block for postoperative analgesia. The administration of 0.16% levobupivacaine mixed with 6 mg of indigo carmine (a dye added to easily identify leakage) was started at 6 ml/h at the end of surgery. The primary outcome was the incidence of leakage from the catheter insertion site. We further investigated the degree of leakage, the incidence of catheter migration, pain scores using the numerical rating scale at 48 h postoperatively, and the number of days until the operated knee could be flexed 120 degrees postoperatively in both groups.

RESULTS

The CON group had a significantly lower incidence and degree of leakage from the catheter insertion site. There were no significant differences in other measurement outcomes.

CONCLUSIONS

Use of CON reduces the incidence of leakage from the catheter insertion site during CFNB in the use of postoperative analgesia for total knee arthroplasty. Future research is needed to determine additional benefits of using CON related to decreased leakage.

TRIAL REGISTRATION

The study was registered in the University Hospital Medical Information Network (UMIN) Clinical Trials Registry ( UMIN000021537 ), prospectively registered on 18 March 2016.

Recognition and differentiation of dural puncture click sensation: A subjective and objective prospective study of dural puncture forces using fine-gauge spinal needles

BACKGROUND

We hypothesized that the click perceived when puncturing the dura-arachnoid with fine-gauge spinal needles can be subjectively identified, and investigated whether it may be distinguishable among different needle types.

METHODS

Subjective and objective evaluations were performed. First, physicians punctured the polyamide film or porcine dura mater (n = 70 and n = 20, respectively) with seven types of spinal needles and numerically evaluated the perceived click sensations. Using an 11-point numerical rating scale (from "0" for "no click sensation" to "10" for "the strongest click perceived") data, subjective differentiation among needle types was assessed. Second, in the objective part of the study, total forces elicited by polyamide film or porcine dura mater punctures with each needle were measured using a biomechanical testing device, and load-displacement curves evaluated. Third, the results of subjective and objective evaluations were compared.

RESULTS

All participants recognized the click and could discriminate among needles of different tip shape. The load-displacement curves for polyamide film and porcine dura mater were similar and needle-specific. The subjective numerical rating scale values corresponded well with the objectively measured changes in total forces (R2 = 0.862 and R2 = 0.881 for polyamide film and porcine dura mater, respectively), indicating that an increase in the largest drop in total force value of 0.30 N or 0.21 N would produce an increase of numerical rating scale value of 1 for polyamide film and porcine dura mater, respectively.

CONCLUSIONS

We provide an objective proof of the click sensation felt upon dural puncture using different fine-gauge spinal needles. Click recognition could be used as an additional indicator of successful spinal puncture.

Performance of titanium dioxide microcapsules as a photo-oxidation catalyst for decolourization of methylene blue

The performance of anatase type titanium dioxide (TiO(2)) encapsulated with styrenic copolymers via the solvent evaporation or suspension polymerization process was investigated as a photocatalyst for the decolourization of methylene blue (MB, 3,4-bis(dimethylamino)-phenothiazine-5-thionium chloride) in the aqueous phase. The TiO(2) microcapsules, loaded with 4-8 wt% TiO(2), were dispersed in a MB aqueous solution containing an adequate amount of hydroperoxide as an oxygen source, and the mixture was exposed to 365 nm UV light. The decolourization of MB proceeded according to the first order of the MB concentration. The apparent rate constant, defined based on the unit weight of loaded TiO(2), depended on the initial concentration of MB. The capsule walls, composed of cross-linked and/or uncross-linked poly(styrene-co-2-ethylhexyl acrylate), favoured the adsorption of MB on the capsule surface and promoted the decomposition. The observations of the cross-section of microcapsules by transmission electron microscopy (TEM) showed similar morphology of microcapsules regardless of preparation method; a thin layer of hydrophilic TiO(2) particles being localized near the particle surface. The sustainability of the microcapsules was also proved by doing experiments successively for 7 days. Smaller size microcapsules were favoured for the decomposition of MB, and the rate constant increased with the surface area of microcapsules in unit volume of the reaction mixture. Although large size microcapsules with uncross-linked polymer wall had a disadvantage of breaking under high shear agitation, those prepared with cross-linked polymer wall by suspension polymerization still remained effective after the sustainability test for 7 days.

Preparation of uniform titanium dioxide (TiO2) polystyrene-based composite particles using the glass membrane emulsification process with a subsequent suspension polymerization

Uniform titanium dioxide (TiO(2))-polystyrene-based composite particles were prepared using the glass membrane emulsification process followed by a subsequent suspension polymerization. The oil phase, consisting of anatase TiO(2) fine powder, monomers, methyl laurate as the hydrophobic additive, Disperbyk-180 and the poly(styrene-co-2-ethyl hexylacrylate) were emulsified through the membrane pores into the aqueous phase containing stabilizers to form a (solid-in-oil)-in-water (S/O/W) emulsion of monomer droplets. The suspension polymerization was carried out at 343 K for 24 h under a nitrogen atmosphere. An SPG membrane with a pore size of 5.25 microm was employed and 20-25 microm TiO(2)-polystyrene based composite particles were obtained depending on the composition of polymerizing oil phase. The effects of the co-monomer, 2-ethylhexyl acrylate and the cross-linking agent, divinyl benzene on the dispersion stability of TiO(2) in the oil phase, the surface feature of the particle and the encapsulation loading were investigated in this study. The membrane emulsification process was capable of preparing the composite particles with approximately 5 wt% of TiO(2) encapsulated, which accounts for with at least 85 wt% of TiO(2) in the oil phase.

Uniform titanium dioxide (TiO(2)) microcapsules prepared by glass membrane emulsification with subsequent solvent evaporation

Anatase-type titanium dioxide (TiO(2)) was encapsulated using an Shirasu porous glass (SPG) membrane emulsification technique and followed by solvent evaporation. The oil phase, consisting of fine#10; powder of anatase TiO(2), Disperbyk-180, the hydrophobic oil phase additive, and polymer wall solution, was pushed through the membrane pores into the aqueous phase of poly(vinyl alcohol) and sodium dodecyl sulfate to form the solid-in-oil-in water, (S/O)/W, emulsion droplets. Three types of styrene-based copolymer poly(styrene-co-acrylic acid) (PS-AA), poly(styrene-co-2-ethyl hexyl acrylate) (PS-2EHA) and poly(styrene-co-dimethyl aminoethylmethacrylate) (PS-DMAEMA) were used as an encapsulating shell. Uniform droplets were successfully obtained by modifying the oil phase using methyl laurate or hexadecanol as the oil phase additive, together with carefully monitoring the emulsification flow rate during the emulsification. The (S/O)/W emulsion was gently stirred in a sealed reactor, and evacuation of solvent started under moderate heating with increasing a vacuum intensity. Those uniform-sized TiO(2) microcapsules revealed fine porous morphologies on their surfaces as a result of a mild phase separation induced from the addition of the oil phase additive. The encapsulation efficiency was influenced by the stability of TiO(2) in the oil phase, the polymer wall employed, and the operational control of the glass membrane emulsification process. The membrane emulsification process could prepare the TiO(2) microcapsules with about approximately 6-8.5 wt% of encapsulation loadings. PS-AA and PS-2EHA copolymers provided better encapsulation efficiency compared to PS-DMAEMA. SPG membranes with 1.42, 2.8, 5.25, 7.0, or 9.5 microm were employed and 2-20 microm microcapsules were subsequently obtained.

Magnetite (Fe3O4) microcapsules prepared using a glass membrane and solvent removal

Fine magnetite powders dispersed in polymer solution were encapsulated from an oil-in-water emulsion prepared by an emulsification process employing a porous glass membrane and subsequent evaporation of the solvent. Styrene-based copolymers were dissolved in a magnetic fluid, and then continuously pushed through the pores of glass membrane into the aqueous phase, which had dissolved polyvinyl alcohol (PVA) and sodium dodecyl sulphate (SDS) as a mixed stabilizer. P(styrene-co-acrylic acid) (PS-AA), P(stryrene-co-butyl acrylate) (PS-BA) and styrene-butadiene rubber (SBR) were dissolved in the specially ordered magnetite fluid (25 wt% magnetite dispersed in toluene) separately or as a mixture, and uniform droplets suspending the magnetic particles were obtained. After the evaporation of toluene, PS-AA capsules retained a spherical shape and uniformity, whereas PS-AA/PS-BA capsules revealed a creased surface and broader size distribution. The microcapsules entrapped 30-40 wt% of magnetite, and the encapsulation yield of magnetite was 20-40%. Glass membranes with 9.5, 5.25 and 1.42 microm pore size were employed and 5-40 microm microcapsules were obtained depending on the pore size. When magnetite suspended in chloroform was used, magnetite capsules with broader size distributions were obtained because of the sticking of the droplets to the membrane wall. The advantage of the membrane emulsification which provides uniform sized droplets was lost.

[The spread and time to two-segment regression of spinal anesthesia with 0.25% hyperbaric bupivacaine]

The spread and time to two-segment regression of spinal anesthesia with 0.25% hyperbaric bupivacaine 2.0 ml (5 mg) were studied clinically in 20 patients for elective lower extremity, urological or gynecological surgery. Lumbar puncture was performed at the L 3-4 interspace with the patient in horizontal lateral decubitus positions using a 25-G Quincke needle. After injection of the local anesthetic solution at the rate of 0.2 ml.sec-1, the patient was placed immediately in supine position. Sensory block was assessed by using pinprick and motor block was assessed by using a four-point Bromage scale in every 5 min until 30 min, then every 10 min thereafter until two-segment regression of sensory block had recovered. Results were expressed as mean values +/- SD. Maximum sensory block level was Th 10.6 +/- 2.3, and time to two-segment regression was 51.5 +/- 14.6 min. Complete motor block was observed in three out of twenty patients (15%). These results indicate that spinal anesthesia with 0.25% hyperbaric bupivacaine is useful for a short case, which dose not require motor block or is performed as day-care surgery.

Effect of Lauryl Alcohol on Morphology of Uniform Polystyrene-Poly(methyl methacrylate) Composite Microspheres Prepared by Porous Glass Membrane Emulsification Technique

Fairly uniform poly(styrene)-poly(methyl methacrylate) (PST-PMMA) composite microspheres were prepared by employing an SPG (Shirasu Porous Glass) membrane emulsification technique. A mixture of PST, PMMA, and cosurfactant [lauryl alcohol (LOH)] dissolved in dichloromethane (DCM) was used as the dispersed phase, and an aqueous phase containing poly(vinyl alcohol) and sodium lauryl sulfate was used as the continuous phase. It is necessary to add LOH to obtain uniform particles with the SPG emulsification technique. The effects of the volume of LOH on the morphology of the final particles were investigated by varying the volume of LOH from 0 to 2 ml (per 1.2 g polymer). A three-component model was developed for different PMMA/PST ratios and LOH/polymer ratios, based on Sundberg's theory; and the calculation on morphology was carried out by using the three-component model. Agreement was obtained between experimental and calculated results. When 2 ml of LOH was added, it was found that LOH can engulf the polymer particles completely; a hemicore (HCP1P2P3) morphology, where PST and PMMA formed a hemisphere core inside a LOH shell, was observed when the PMMA/PST ratio was high, while core-shell-shell (CSP1P2P3) morphology, where PMMA formed a core and PST and LOH formed an inner shell and an outer shell, respectively, was observed when the PMMA/PST ratio was low. When the volume of LOH was below 1 ml (per 1.2 g polymer), however, LOH could not always engulf the inner polymer particles completely; cored hemisphere (CHSP3P2P1), core-shell-shell (CSP2P1P3), and hemicore (HCP1P2P3) morphologies were observed, depending on the PMMA/PST ratio and volume of LOH. Copyright 1999 Academic Press.

Nurse practitioners in developing countries: some ethical considerations

One of the principles of health care ethics is the principle of justice. An important expression of justice is equity. The provision of basic primary health care services to all people is the key to eliminating the gross inequities in health status existing in many countries. For many years nurses in developing countries have 'led the way' in bringing these essential services to poor rural communities, including the diagnosis and treatment of illnesses, and the prescribing and dispensing of medications. Nurses are the most appropriate health workers for this role, but most have not been prepared adequately for it. This is unsafe for patients and puts nurses at legal risk. Justice requires that patients should obtain access to safe health care and that nurses should receive appropriate education. Nurse practitioner programmes are being established to prepare nurses for this advanced practice role, but here again ethical considerations apply. Justice will be served only if nurse practitioner programmes are accessible to the nurses who are most likely to work in medically underserved communities where the need is greatest.

Study on Preparation and Morphology of Uniform Artificial Polystyrene-Poly(methyl methacrylate) Composite Microspheres by Employing the SPG (Shirasu Porous Glass) Membrane Emulsification Technique

Fairly uniform polystyrene-poly(methyl methacrylate) (PST-PMMA) composite microspheres were prepared by employing the SPG (Shirasu Porous Glass) membrane emulsification technique. PST, PMMA, and cosurfactant (lauryl alcohol, LOH) dissolved in dichloromethane (DCM) were used as a dispersed phase, and an aqueous phase containing poly(vinyl alcohol) and sodium lauryl sulfate was the continuous phase. The effects of LOH amount on the critical pressure of emulsification (Pcr), size distribution of droplets, and morphologies of final particles were investigated. It was found that Pcr decreased with increasing LOH amount because of preferential partition of LOH on the surface of the droplets in the initial stage of emulsification. When polymer concentration or PMMA/PST ratio was low, the size distribution of droplets decreased with increasing LOH amount, whereas an inverse trend was observed when both polymer concentration and PMMA/PST ratio were high. When polymer concentration was low, PST-PMMA core-shell particles always were obtained in the absence of LOH, irrespective of the PMMA/PST ratio. In the presence of LOH, however, microdomain, hemisphere, and inverted core-shell morphologies were formed as the PMMA/PST ratio decreased from 5/5 to 1/9 (g/g). When polymer concentration was high, different morphologies such as multiplet and inverted core-core-shell were observed. Theoretical calculations of morphologies were carried out, and agreement was obtained between experimental and calculated results. Copyright 1999 Academic Press.

Strengthening routine immunization services in the Western Pacific through the eradication of poliomyelitis

Infant immunization coverage in the Western Pacific Region of the World Health Organization was reviewed to evaluate the impact of polio eradication activities on routine immunization services. The trend in bacille Calmette-Guérin (one dose; BCG), diphtheria-tetanus toxoids-pertussis (three doses; DTP3), and measles (one dose) vaccination rates was analyzed from the beginning of eradication activities in 1990 to 1994 in the five polio-endemic countries that conducted supplementary oral polio vaccine immunization. In China and the Philippines, coverage for each antigen remained at or above 90% and 85%, respectively, while in Vietnam, coverage for all three antigens rose from 85% to 95%. BCG, DTP3, and measles vaccine coverage more than doubled in the People's Democratic Republic of Lao and increased by >30% in the Kingdom of Cambodia during the same period.

Development and coordination of the Polio Laboratory Network in the Western Pacific Region of the World Health Organization

A multitiered network of polio laboratories, consisting of specialized reference laboratories, regional reference laboratories, national laboratories and, in the case of China, provincial laboratories, was established in the Western Pacific Region of the World Health Organization (WHO) in 1992. The network currently consists of 43 laboratories within the Region and is coordinated through the WHO Regional Office in Manila. As the levels and extent of supplementary immunization and acute flaccid paralysis surveillance activities have increased, so has the work load of network laboratories. The total number of stool specimens collected and processed in Polio Laboratory Network laboratories in this WHO region in 1995 exceeded 15,000. With the Region now establishing the criteria necessary for certification of polio-free status, it is essential for the Polio Laboratory Network to establish international confidence in its ability to carry out its role in the eradication of polio.

Poliomyelitis eradication in the Western Pacific Region

Polio eradication activities in the Western Pacific Region (WPR) have reduced the transmission of wild poliovirus to one remaining focus of endemic transmission in the Mekong Delta area of South Vietnam and Cambodia. There has been a high level of government commitment for national immunization days in all WPR countries in which poliomyelitis was previously endemic and for continuous improvement in acute flaccid paralysis (AFP) surveillance quality. The total number of reported confirmed poliomyelitis cases in 1995 (as of June 1996) was 432, only 7% of the total of 5825 cases reported in 1990. In 1995, wild poliovirus was isolated from only 19 of 4800 AFP patients from whom specimens were collected and analyzed. There has been one importation of wild poliovirus type 1 into China from a neighboring country. An international Regional Commission for the Certification of Poliomyelitis Eradication in the WPR has been formed and met for the first time in April 1996.

The experience of countries in the Western Pacific Region in conducting national immunization days for poliomyelitis eradication

Experience with national immunization days (NIDs) in six countries of the Western Pacific Region has shown that political support at all levels, detailed logistics plans, strategies appropriate to the local situation, and simple social mobilization messages have been key factors in the success of NIDs. Conventional strategies that may apply to conducting routine Expanded Programme on Immunization vaccinations do not necessarily apply to NIDs, in which the maximum number of children must be immunized in 1 or 2 days. Setting up temporary immunization posts at sites convenient to the local situation, moving the posts once or twice during the course of a day, and using volunteers to staff them are among many of the adaptations used successfully. Coverage figures published immediately after an NID can be misleading because of uncertainty about the true denominator. The true measure of the success of NIDs is in surveillance for wild poliovirus after the event.

[Spinal anesthesia with 2% plain lidocaine for ultrasonically guided vaginal oocyte retrieval]

Spinal anesthesia with 3 ml of 2% plain lidocaine was administered to 10 women for ultrasonically guided vaginal oocyte retrieval. Spread of anesthesia was assessed by skin vasodilatation, change of skin texture, loss of goose flesh reflex, and loss of cold as well as pin-prick sensation, and we studied time to complete motor block, time to two-segment regression, time to full motor and sensory recovery, ambulation time, haemodynamic parameters, and postoperative complications. The highest sensory block assessed by pin-prick was up to Th 8.3 +/- 3.4 10 min following spinal anesthesia. All patients had complete motor block and this was achieved at 9.0 +/- 1.7 min. Times to two-segment regression, full motor and sensory recovery, and ambulation were 84.5 +/- 31.0, 147.5 +/- 24.7, 176.5 +/- 23.2, and 203.3 +/- 50.0 min, respectively. No serious side effects were observed during the operation and postoperatively. We concluded that 3 ml of 2% plain lidocaine provided adequate spinal anesthesia for ultrasonically guided vaginal oocyte retrieval.

[The spread of thoracic epidural anesthesia]

The spread of a test dose in epidural anesthesia provides many important informations. The current study was performed to evaluate the possibility that early and quick detection method of block level by the test dose of 2% lidocaine 2 ml. Forty patients undergoing elective surgery were studied regarding the spread of continuous epidural anesthesia performed in T9-10 interspace. The block levels were assessed by skin vasodilatation, loss of goose flesh reflex, and loss of cold as well as pin-prick sensation. Extent of loss of goose flesh reflex was found for 7.7 +/- 2.2 dermatomes by 2% lidocaine 2 ml and, for 14.1 +/- 4.3 dermatomes by 2% lidocaine 5 ml after the test dose. Incomplete but extensive sympathetic block was obtained by the test dose in this study. For the purpose of early detection of the spread of sympathetic block, loss of goose flesh reflex and skin vasodilatation were the most reliable objective clinical signs. However, this sympathetic block by the test dose was not enough to produce circulatory changes.

Microencapsulation of pheromone-analogue and measurement of the sustained release

A model study was conducted to establish 2 feasible production and application systems for the long-term, sustained release of pheromone into the atmosphere of targeted areas. The desired goal of effective release was set at least half a year. 2-Ethylhexyl acetate (EHA) was selected as a pheromone analogue due to its similar structure and easier access for quantitative analysis. At first EHA was impregnated in wax particles, which were then encapsulated employing the complex coacervation of a gelatin-gum arabic system. The release period of EHA through the gelatin wall, however, turned out to be too short--only a week at most. As a second attempt, a modification of the two-phase emulsion technique was employed to encapsulate multiple numbers of wax particles in hydrated networks of gelatin. Though the initial release rate of EHA was still too high, 60 per cent of encapsulated EHA underwent sustained release over six months after absorbed moisture had completely evaporated. A two-step mechanism of mass transfer was proposed and the related parameters in terms of the capacity coefficient and effective diffusion coefficient were estimated.

Defects in the precore region of hepatitis B virus DNA in a plasma pool from carriers seropositive for antibody against e antigen and with infectivity in chimpanzees

A plasma pool from 12 asymptomatic carriers seropositive for antibody against hepatitis B e antigen (anti-HBe) contained hepatitis B virus (HBV) with chimpanzee infectious doses of 1-100/mL, and another pool from 12 carriers positive for hepatitis B e antigen (HBeAg) contained 10(8)/mL doses or more. The HBeAg-positive pool contained 10(6)-fold more HBV DNA than the anti-HBe-positive pool, reflecting the difference in infectivity in chimpanzees. The precore region sequences of HBV DNA in the two plasma pools were amplified by polymerase chain reaction, and separate HBV DNA clones were propagated for determining the nucleotide sequence. Of 114 clones from the anti-HBe-positive pool, 113 displayed a point mutation from guanine to adenine at nucleotide 83 in the precore region, which converted codon 28 for tryptophan (TGG) to a stop codon (TAG), and the remaining clone had a point mutation from adenine to cytosine at the first letter of codon 1 (CTG) to inhibit the translation initiation of the precore region. Precore region defects, in contrast, were observed in only 10 (8%) of 119 clones from the HBeAg-positive pool. These results indicate the infectious capacity of HBV mutants, defective in the precore region and incapable of directing the synthesis and secretion of HBeAg, which prevail in the circulation of hosts after they seroconvert from HBeAg to anti-HBe.

Trans-complementation of the C gene of human and the P gene of woodchuck hepadnaviruses

A 5 bp insertion was introduced into the BstEII site at nucleotide 2815 in DNA of hepatitis B virus (HBV) and a mutant HBV genome was produced, which coded for envelope and core proteins, but not for DNA polymerase, due to a frameshift. Cultured hepatoma cells (HepG2) were simultaneously transfected with a plasmid harbouring a tandem dimer of the mutant HBV DNA and another plasmid harbouring a tandem dimer of DNA of woodchuck hepatitis virus or duck hepatitis B virus. The replication of mutant HBV DNA, incapable of encoding DNA polymerase, was accomplished by cotransfecting woodchuck hepatitis virus DNA, but not by duck hepatitis B virus DNA. These results indicated a trans-complementation of the C and P genes in mammalian hepadnaviruses beyond a species barrier.

Application of encapsulated enzyme dispersed in a continuous stirred tank reactor

An application of encapsulated lipase to the hydrolysis of triacetin (triglyceride of acetic acid) was carried out with a continuous stirred tank reactor, in which the encapsulated enzyme was dispersed. An automatic control device to control pH of the reaction mixture at a desired level was designed and installed in the reactor system. Conversion of triacetin at the steady state operation with pH controlled became significantly higher than that without pH control. A particular kinetic model proposed by the authors, which regarded the mass-transfer through the wall of microcapsules as a dominant resistance to the overall reaction rate, was also applicable to simulate the behaviour of CSTR system as in the case of packed-bed reactor.

Application of encapsulated enzyme as a continuous packed-bed reactor

In the previous report, microencapsulation of lipase employing a (w/o)/w multiple phase emulsion technique, with 2:1 polystyrene (PS)-SBR mixture being used as a wall material, was proposed. Catalysis of the encapsulated enzyme was investigated, and the hydrolysis of triacetin (triglyceride of acetic acid) was successfully simulated by the reaction model based upon the Michaelis-Menten mechanism. Other factors affecting the mechanism such as the mass-transfer resistance of the substrate molecules through the wall and the decrease in pH due to the formation of acetic acid were also taken into consideration. In this report, the particular microcapsules were applied to the continuous tubular reactor system, essentially a packed column reactor, and longevity and mechanical strength of the microcapsules were fully demonstrated. The reaction model derived for a well-stirred batch reactor was also applicable to simulate the behaviour in the packed-column reactor as it was proved that there is no mass transfer resistance between the reactant stream and the surface of microcapsules. The observed data agreed quite well with the calculated values. Similarity of the behaviours of catalysis observed between two reactor systems was thoroughly confirmed. No leakage of the enzyme was detected after repeated usage over the duration of a few months, the temperature being maintained in the range between 293 and 323 K, and pH reset after each operation. Commercial feasibility of the microcapsules for the enzyme catalysis with substrates, small enough to permeate through the wall, was established by these fundamental investigations.

Immobilization of enzyme by microencapsulation and application of the encapsulated enzyme in the catalysis

Microencapsulation of lipase (Pseudomonas fluorescens) was carried out using (W/O)/W two-phase emulsion technique. Polystyrene (PS) and Styrene-Butadiene Rubber (SBR) were utilized as wall materials either separately or in mixture. A particular composition of 2:1 PS-SBR yielded homogeneous and tough wall structure, resilient to the impact and tight confinement of enzyme macromolecules. Performance of the encapsulated enzyme was evaluated employing the hydrolysis of triacetin (triglyceride of acetic acid) as a model substrate of the enzyme catalysis. A mathematical model was developed to simulate the behaviour of hydrolysis, which was derived under the assumption that the diffusion of small molecules (substrate and products) through the wall of microcapsules plays a dominant role to the reaction rate. Inhibition of the reaction by the decreasing pH due to the release of acetic acid was also taken into account. The calculated values agreed quite well with the observed data.

The loss of subtypic determinants in alleles, d/y or w/r, on hepatitis B surface antigen

Hepatitis B surface antigen possesses the group-specific determinant called a and one or another member from each of two pairs of allelic determinants, d and y as well as w and r, thereby creating the four major subtypes, adw, adr, ayw and ayr. In the sequence of major surface antigen polypeptides made of 226 amino acid residues, lysine or arginine at amino acid position 122 specifies d or y determinant, and lysine or arginine at position 160 specifies w or r determinant, respectively. By means of site-directed mutagenesis and expression of mutant genes in cultured cells, the mechanism for the loss of subtypic determinants on surface antigens was investigated at the molecular level. A rare sample of surface antigen of subtype ad, devoid of w or r determinant, had asparagine at position 160. When it was converted to lysine, the surface antigen of subtype adw was obtained. Two samples of surface antigen were subtyped as ar. They lacked d determinant, despite having lysine at position 122 which usually specified it. They differed from all reported sequences of surface antigen in amino acid 144 or 145. They displayed d determinant when amino acid 144 was converted from glutamic acid to aspartic acid, or when amino acid 145 was changed from alanine to glycine. These results indicate that the key amino acid residue at position 122 or 160 is indispensable for the expression of subtypic determinants and that some distant residues are also crucially involved in conforming them.

A fundamental study of the microencapsulation procedure utilizing coacervation in a polystyrene-cyclohexane solution

Coacervation in polystyrene (PS)-cyclohexane solution induced by the lowering of temperature was utilized to investigate the fundamental problems involved in the microencapsulation procedure. Polydispersity of PS played a vital role in determining variables at the critical state of phase separation, such as the composition of coacervate (dense) and lean phases. This also depended on temperature. Observations revealed that microcapsules of glass beads consist of a wall with a thin film of PS covered with a thick shell of talc. Poor utilization of PS may limit practical applications of this system unless effective measures are taken for the recovery of unutilized PS. Controlled release behaviour from microcapsules was successfully investigated by using encapsulated anhydrous sodium sulphate (ASS) particles, and applying the Higuchi model to the estimation of the effective diffusion coefficient of ASS through the composite wall. The values of diffusion coefficient decreased from an order of 10(-7) to 10(-8) cm/s by lowering the encapsulation temperature.