Identification of two new HLA-DRB1 alleles: HLA-DRB1*1350 and DRB1*140502

Two new HLA-DRB1 alleles have been found by using high-resolution sequence-based typing. The two sequences have been officially named DRB1*1350 (HWS10001327-AY048687) and DRB1*140502 (HWS10001790-AY129430). DRB1*1350 differs from DRB1*110101 by two amino acids at positions 37 (Y-->N) and 58 (A-->E). This allele may arise from gene conversion between DRB1*110101 and DRB1*130201 or DRB1*030101, which are commonly found in Taiwan populations. The other allele, DRB1*140502, obtained from a patient with rheumatoid arthritis, differs from DRB1*140501 at codon 58 (GCC-->GCT). However, it causes no change in amino acid sequence and would therefore not have direct clinical implications.

Two novel HLA-DRB1 alleles identified using a sequence-based typing: HLA-DRB1*1443 and HLA-DRB1*1351*

Two novel HLA-DRB1 alleles, DRB1*1443 and DRB1*1351, were identified using a sequence-based typing protocol. DRB1*1443 differed from DRB1*140501 by one single-nucleotide substitution in exon-2 (codon 77, ACC-->GCC), which corresponded to an amino acid change of threonine to alanine. DRB1*1351 was identical to DRB1*1301 but differed by a single-nucleotide substitution at codon 50 (GTG-->TTG), resulting in an amino acid change of valine to leucine. Both new alleles present unique polymorphisms, which have not been seen among other DRB1 alleles and which have no known effect on peptide binding.

Identification of a new HLA-DRB1 allele, HLA-DRB1*0436

Anovel allele, HLA-DRB1*0436, was identified in a Taiwan indigenous individual by sequence-based typing. DRB1*0436 was identical to DRB1*0403 in exon2 but differed at codons 67-74 with five nucleotide substitutions. This corresponded to three amino acid changes within the P4 peptide-binding pocket of the DR molecule. These substitutions constitute a motif that is also seen in other DRB1*11 alleles. It is possible that the new allele resulted from a gene conversion event.

In vitro enzymatic biodegradation of amino acid based poly(ester amide)s biomaterials

A systematic in vitro biodegradation study of regular poly(ester amide)s (PEAs) composed of naturally occurring hydrophobic alpha-amino acids, fatty diols and dicarboxylic acids was carried out in the presence of hydrolases like trypsin, alpha-chymotrypsin, and lipase. An automatic potentiometric titration method was used to examine the biodegradation property of the PEAs. Spontaneous immobilization (absorption) of the enzymes onto the PEAs films surfaces was observed. The surface immobilized enzyme not only accelerated the erosion of the PEAs but also was able to catalyze the hydrolysis of both low-molecular-weight (ATEE) and high-molecular-weight (protein) external substrates. It was found that the enzyme surface absorption process is reversible by nature. A kinetic method for a quantitative determination of the enzyme desorbed from the film surface was developed. The enzymes could also be impregnated into the PEAs to make them "self-destructive" at a target rate. A comparison of the PEAs' in vitro biodegradation data with polylactide (PDLLA) showed that PEAs exhibited a far more tendency toward enzyme catalyzed biodegradation than PDLLA.

An effective method for axillary bud culture and RAPD analysis of cloned plants in tetraploid black locust

An efficient micropropagation technique by axillary bud multiplication was established for cloning tetraploid black locust tree (Robinia pseudoacacia L.). The result showed that the optimal medium for shoot multiplication and elongation was Murashige and Skoog (MS) medium supplemented with 0.5 mg/l 6-benzylaminopurine in combination with 0.5 mg/l kinetin and 0.1 mg/l 1-naphthaleneacetic acid. The best medium for rooting was half-strength MS medium with 0.25 mg/l indole-3-butyric acid. In the present report, we examined the genetic fidelity of the micropropagated plants by the randomly amplified polymorphic DNA (RAPD) method with 25 primers. The cloned plants of tetraploid black locust showed complete stability.

Conservation of predatory arthropods in cotton: role of action thresholds for Bemisia tabaci (Homoptera: Aleyrodidae)

Studies were conducted in 1994 and 1995 to examine the effects of a range of action thresholds for managing Bemisia tabaci (Gennadius) Biotype B (= B. argentifolii Bellows & Perring) with insecticides in cotton on populations of arthropod predators in Imperial Valley, CA, and Maricopa, AZ. Application of insecticides significantly reduced population densities of spiders, Geocoris punctipes (Say), G. pallens (Stål), Orius tristicolor (White), Nabis alternatus Parshley, Zelus renardii Kolenati, Hippodamia convergens Guerin-Méneville, Spanogonicus albofasciatus (Reuter), Drapetis sp., and Chrysoperla carnea Stephens in one or both years and sites compared with untreated controls. Use of higher B. tabaci thresholds conserved some species and groups relative to lower thresholds. Stepwise regression analyses indicated that reductions in predator populations were generally influenced more strongly by the timing of the first insecticide application than by the total number of sprays necessary to maintain suppression of the pest below any given action threshold. A predation index, which weights the importance of each predator species based on their known frequency of predation on B. tabaci and another key pest, Pectinophora gossypiella (Saunders), was developed and analyzed. Patterns were similar to results based on changes in abundance alone, but the index generally revealed less severe effects of insecticides on overall predator function. The current action threshold for conventional insecticidal control of B. tabaci in Arizona and southern California is five adults per leaf. Results here suggest that predator conservation may be enhanced by raising the initial threshold to delay the first application or initially using more selective materials such as insect growth regulators.

Small cell carcinoma of the endometrium with concomitant pelvic inflammatory disease

BACKGROUND

Small cell carcinoma of the endometrium is a rare disease entity characterized by bulkiness and predisposition to necrosis. Clinical presentations include postmenopausal bleeding, lower abdominal mass, chronic abdominal pain and menorrhagia. We present a case of small cell carcinoma of the endometrium with concomitant pelvic inflammatory disease. The literature is also reviewed.

CASE

A 64 year old female presented was admitted with the principal complaints of fever, lower abdominal pain and malodorous vaginal discharge. Bimanual examination revealed cervical motion tenderness with a WBC of 9400 cells/microL and increased levels of neutrophils, band cells and C-reactive protein. Sonography revealed an adnexal echocomplex compatible with tubo-ovarian abscess. Culture of the vaginal discharge revealed the presence of E. coli. Symptoms persisted despite three days of antibiotics administration so a laparotomy was performed with a friable hemorrhagic uterus revealed and an area of necrosis evident in the left adnexa. Malignancy was confirmed from frozen section. Total abdominal hysterectomy, with bilateral salpingooophorectomy and optimal debulking, was performed. The final pathology report confirmed small cell carcinoma of the endometrium.

CONCLUSION

Malignancy and pelvic inflammatory disease have overlapping clinical characteristics. Once pelvic inflammatory disease is suspected in a postmenopausal patient, malignancy should also be suspected, and a thorough examination and a tumor-marker analysis performed.

[The factors of improving rice transformation efficiency]

The factors influencing the rice transformation frequency have been investigated by using 8 indica and japonica rice cultivars during the transformation procedures, such as induction of calli, selection, and regeneration. The following is the results: The immature embryos were pretreated in 4 degrees C for 4 or 7 days before inoculation, and the regeneration frequency of calli would be increased. High osmotic treatment may increase the possibility of transformation, especially for calli of 6 months or older. The transformation frequency was improved when selection pressure was removed during differentiation period. The V-type selection may be better than the normal selection. There is a difference of differentiation ability among the calli of three periods and it is found that the calli of two or three months are the best for transformation. Proline and DMSO can decrease browning rate of calli.

The use of genotyping to predict the phenotypes of human platelet antigens 1 through 5 and of neutrophil antigens in Taiwan

BACKGROUND

The human platelet antigen (HPA) 1 through 5 and the human neutrophil antigen (HNA-1) systems are relevant to immune-related thrombocytopenia and neutropenia. The alloantigen distribution profiles in the population will aid in estimating the risk of alloimmunization.

STUDY DESIGN AND METHODS

Genotyping of the genes that control the expression of the HPA-1 through -5 and HNA-1 systems in Taiwanese (n = 326) and Taiwan's indigenous peoples (n = 608) was performed by PCR with the sequence-specific primer (PCR-SSP) method.

RESULTS

In the HPA system, HPA-1b and HPA-4b were absent among Taiwan's indigenous tribes and detected among other Taiwanese only with frequencies of <0.2 percent and <0.5 percent, respectively. The GP1BA*2 (HPA-2b) and GP1A*2 (HPA-5b) allele frequencies range from 1 percent to 7 percent and 0.4 percent to 3.5 percent among the two ethnic groups, respectively. GP2B*1 (HPA-3a) and GP2B*2 (HPA-3b) showed similar allele frequencies. In the HNA-1 system, the FCGR3B*1 (HNA-1a) allele frequency was about twice that of FCGR3B*2 (HNA-1b) in Taiwanese and also in most of the indigenous tribes. Three FCGR3B (HNA-1) null persons were found in one indigenous tribe (Ami tribe), for an FCGR3B null frequency of 19.8 percent. However, no FCGR3B*3 (HNA-1c) allele was detected in Taiwan.

CONCLUSION

The frequencies of HPA-1b, -2b, and -5b in the Taiwanese population were much lower than those among whites. In Taiwan, all of the HNA-1 null found was due to the deletion of the FCGR3B gene, and this deletion may be widely distributed in the Ami tribe.

Polymorphism and distribution of the Secretor alpha(1,2)-fucosyltransferase gene in various Taiwanese populations

BACKGROUND

The Secretor gene (Se or FUT2), which produces alpha(1,2)-fucosyltransferase, exhibits extensive polymorphism. Six Se genes, including the weak Se (Se(w) or Se385) and three nonsecretor alleles (se571, se685, and se849) have been detected in various populations of Taiwan. The distribution of various Lewis phenotypes among the Taiwanese population groups has been shown to vary considerably.

STUDY DESIGN AND METHODS

A PCR-RFLP analysis system, which was based on the nucleotide polymorphism variation of the different Se alleles and which can reveal the Se genotype of an individual easily and accurately, was developed. The distribution of the Se alleles among Taiwanese population groups, including the two major populations, Minnan and Hakka Taiwanese, and 11 indigenous groups, was analyzed by the method.

RESULTS

Frequencies of the Se alleles among the Taiwanese populations were revealed. The distribution of the nonsecretor alleles, especially se849, showed a marked variation. A good correlation was observed between a person's Se genotype and Lewis phenotype.

CONCLUSION

The Se genes have a polymorphic distribution among various Taiwanese populations, and this agrees with previous results for Lewis phenotype distributions. The Se(w) allele and the three se alleles are responsible for the Le(a+b+) and Le(a+b-) phenotypes, respectively.

Carbon disulfide vasculopathy: a small vessel disease

We present the clinical manifestations of 4 male patients with acute stroke-like symptoms and polyneuropathy after long-term exposure to carbon disulfide (CS2) in a viscose rayon plant. The ages of onset of polyneuropathy ranged from 42 to 45 years with a duration of CS2 exposure between 6 and 21 years. The ages of onset of stroke were from 42 to 48 years. The risk factors for stroke including heart disease and diabetes were denied, except for smoking in 4, hyperlipidemia in 2 and hypertension in 1. At the initial visit in 1992, only 2 patients developed sudden onset of hemiparesis suggesting a lacunar stroke before the diagnosis of CS2 intoxication. Brain computed tomography (CT) scans showed low-density lesions in the basal ganglia in 2 patients, cortical atrophy in 1 and normal in 1. Brain magnetic resonance image (MRI) study disclosed multiple lesions in the corona radiata and basal ganglia on T(2)-weighted images in 3 patients and cortical atrophy in 1. After the diagnosis, they left their jobs for a CS2-free environment, and improvement of the working conditions was noted. During 5 years follow-up period, another 2 patients also developed an acute episode of stroke with hemiparesis. Brain CT and/or MRI follow-up studies in these 2 patients revealed new lesions in the basal ganglia and corona radiata. Intriguingly, a patient with previous stroke also developed new lesions in the bilateral thalami and brainstem. Carotid Doppler scan, transcranial Doppler scan and/or cerebral angiography did not show any prominent stenosis or occlusion in the major intracranial large arteries. We conclude that encephalopathy may occur in patients after long-term CS2 exposure, probably due to impaired cerebral perfusion. The lesions tend to occur in the basal ganglia, corona radiata and even brainstem, particularly involving the small-sized vessels. In addition, the cerebral lesions may progress even after cessation of CS2 exposure. Therefore, we suggest that CS2 exposure may be a risk factor for stroke.

Diversity of HLA among Taiwan's indigenous tribes and the Ivatans in the Philippines

Taiwan's indigenous tribes, especially the east coast tribes are not only closely related to Oceania but also with the Australian aborigines. The Ivatans of the Batan Islands in the Philippines are closely related to the Yami tribe of Taiwan as cultural and anthropological studies have shown. Many DRB1 alleles (*15021, *16021, *0404, *04051, *11011, *12021, *1401, *08032) have high allele frequencies (>20%) in certain tribes, suggesting Taiwan's indigenous tribes are homogeneous populations. These high frequency DRB1 alleles and also some HLA-A-B-DR haplotypes found in Taiwan's indigenous tribes are also found in Oceania, Australian aborigines, south and north east Asians and American Indians, lending further support to our previous findings that Taiwan's indigenous tribes are more or less genetically related to both northern and southern Asians, possibly as well as Amerindians. HLA-A*2402 with a remarkably high frequency among Taiwan's indigenous tribes (52.1% approximately 86.3%), especially the central mountain tribes, possibly represents not only founder effects and population bottlenecks, but also positive selection of the allele. Although the Ami tribe has the highest ever reported frequencies of the DRB1*0404 and DRB1*0405, these alleles have not been found to be associated with rheumatoid arthritis as previously described for Caucasians. In addition, DRB1*1401 has a high frequency in most tribes but is not associated with psoriasis as previously indicated in some studies, suggesting the involvement of some additional genetic and/or environmental factors mechanism in the development of these diseases.

Duodenojejunal intussusception secondary to hamartomatous polyps of duodenum surrounding the ampulla of Vater

Duodenojejunal intussusception is a rare pediatric emergency. A case of duodenojejunal intussusception secondary to hamartomatous polyps of the second portion of duodenum in a 10-month-old boy is reported. Surgical excision of the polyps and reduction of the intussusception were performed. Pathologic examination found hamartomatous polyps. This is the third case report of children in literature, but this is the first case of a child with intussusception surrounding the ampulla of Vater and a successful excision performed without damaging the ampulla of Vater.

[Improvement of transformation frequency of rice mediated by Agrobacterium]

The factors influencing the frequency of rice transformation mediated by Agrobacterium have been investigated by using 16 commercially important indica and japonica rice cultivars or lines. The main results were as following: For most rice CC medium was the best for both callus initiation and subculture. With supplement of 2.5-5 mg/L ABA the quality of calli can be improved. The concentration of selective agent for Indica rice callus was lower than that for japonica rice callus. Agrobacterium tumefaciens strain EHA105 was more efficient than LBA4404 and AGL1 for rice transformation. The inhibitive effect of cefotaxime to Agrobacterium was better than that of carbenicillin. The partial desiccation treatment after co-cultivation was beneficial to inhibit the growth of Agrobacterium and increase transformation efficiency. A stable and efficient Agrobacterium-mediated transformation system has been established in ten different rice cultivars and fertile transgenic plants have been obtained.

Juvenile papillomatosis of the breast in a 9-year-old girl

Juvenile papillomatosis (JP) is a rare benign, proliferative breast tumor in children. We observed a 9-year-old girl with a large soft-tissue mass at the lower outer quadrant of the left breast. Ultrasonography showed an ill-defined, inhomogeneous mass with numerous small, hypoechoic areas. The tumor was completely excised. Histopathology revealed JP of the breast. The case is presented and the literature is reviewed.

Ventilator-associated pneumonia with circuit changes every 2 days versus every week

BACKGROUND

Frequent ventilator circuit changes are expensive and sometimes unnecessary. Following the worldwide trend to lengthen the intervals for ventilator circuit change from 2 days to 1 week, this study aims to assure that low rate of ventilator-associated pneumonia (VAP) can be maintained with cost containment.

METHODS

Ventilator circuits were routinely changed every 7 days in the study period for 2 years and every 2 days during the historical control period of another 2 years. Pediatric patients (age less than 15 years) were not included. Nosocomial pneumonia was diagnosed by the criteria of the Centers of Disease Control and Prevention (CDC) of the United States (US). VAP was identified by combining and comparing 2 databases from the Respiratory Therapy Department and the Infection Control Unit of our hospital.

RESULTS

In the study group, 225 episodes of pneumonias were observed in 7,068 patients and 87,338 ventilator days. The rate of VAP was 2.58 per 1,000 ventilator days. There were 174 episodes of pneumonia in 6,213 patients and 65,467 ventilator days of the control group. The rate of VAP was 2.66 per 1,000 ventilator days. The difference between both groups was not significant (p = 0.803). Yet, the cost curbed was around 80,000 US dollars per year.

CONCLUSIONS

Extending ventilator circuit change interval from 2 days to 7 days do not increase the risk for VAP, but the cost savings for labor and supply are substantial.

The origin of Minnan and Hakka, the so-called "Taiwanese", inferred by HLA study

The Minnan and Hakka people groups, the so-called "Taiwanese", are the descendants of early settlers from the southeast coast of China during the last few centuries. Genetically they showed affinities to southern Asian populations, as determined by phylogenetic trees and correspondence analysis calculated from HLA allele frequencies. This corresponds historically with the fact that they are the descendants of the southeast coastal indigenous population (Yueh) of China and should therefore not be considered as descendants of "pure" northern Han Chinese. A33-B58-DRB1*03 (A33-Cw10-B58-DRB1*03-DQB1*02), the most common HLA haplotype among "Taiwanese", with a haplotype frequency of 6.3%, has also been found to be the most common haplotype among Thai-Chinese and Singapore Chinese, two other populations also originating from the southeast coast of China. These observations suggests that this haplotype is the most well-conserved ancient haplotype of the Yueh.

Laser confocal microscopic study of pH profiles of synthetic absorbable fibers upon in vitro hydrolytic degradation

The objective of this study was to develop a new and non-destructive technique to measure the interior pH of synthetic absorbable biomaterials. Such a measurement would provide the required experimental evidence for validating the postulated theory that the accumulation of acidic hydrolytic degradation products within the interior of aliphatic polyesters is responsible for the observed accelerated degradation of this class of absorbable biomaterials. This new technique used a laser scanning confocal microscope coupled with pH sensitive fluorescent dyes like Texas Red sulfonyl chloride. The capability of optical thin sectioning of a laser confocal microscope would permit a non-destructive examination of the interior of biomaterials. Poly-p-dioxanone suture fibers (PDSII) of size 2/0 were used as the model compound for this new technique. The pH values of the unhydrolyzed and partially hydrolyzed PDSII fibers were found to decrease with increasing depth from the fiber surface and reached as low as about 3.5 at 70 microm depth. The largest depth that an interior pH could be measured within absorbable biomaterials was determined by the opacity of the biomaterials, i.e. a higher depth for a less opaque material. The observed interior pH profiles were correlated to the unique morphologic structure of PDSII fibers.

Repeated attacks of venous air embolism during craniotomy--a case report

Venous air embolism (VAE) is not uncommon during craniotomy, but repeated attacks of VAE during a single surgical procedure is rarely seen. We report a successful intraoperative management of repeated attacks of air embolism in a patient who sustained craniotomy for intracranial hemorrhage (ICH) in prone position. A 70-year-old male suffering from hemorrhage in the right cerebellar hemisphere with impending brainstem herniation was scheduled for craniotomy. He had history of hypertension but it was not well controlled with medical treatment. Emergent craniotomy for removal of blood clot resulting from ICH was performed. During the operation, sudden decrease of end-tidal CO2 (EtCO2) level, fall of blood pressure and increase of central venous pressure (CVP) were noted. Since air bubbles were retrieved from CVP catheter venous air embolism was highly suspected. With prompt diagnosis and proper management, we successfully improved the patient's hemodynamic status and he was discharged without any sequelae. Early detection together with aggressive treatment is the only way in the management of intraoperative venous air embolism.

Efficacy of CC traps and seasonal activity of adult Bemisia argentifolii (Homoptera: Aleyrodidae) in Imperial and Palo Verde Valleys, California

Adult whitefly Bemisia argentifolii Bellows & Perring trap (CC trap) catches were compared with suction type trap catches. CC trap catches were significantly correlated to the suction trap catches. Higher numbers of B. argentifolii adults were caught in CC traps oriented toward an untreated, B. argentifolii-infested, cotton field as compared with traps oriented toward Bermuda grass fields, farm roads, or fallow areas. CC trap catches at five heights above ground (from 0 to 120 cm) were significantly related to each other in choice and no-choice studies. CC trap catches were low in the Imperial and Palo Verde Valleys from late October to early June each of 1996, 1997, and 1998. Trap catches increased with increasing seasonal air temperatures and host availability. Trap catches were adversely affected by wind and rain. Abrupt trap catch increases of 40- to 50-fold for 1-2 d in late June to early July followed by abrupt decreases in adult catches suggest migrating activity of adults from other nearby crop sources.

Biodegradable dextran-polylactide hydrogel network and its controlled release of albumin

The objective of this paper was to study the release of bovine serum albumin (BSA) from a series of biodegradable hydrogels having a wide range of hydrophilicity to hydrophobicity, swelling, and biodegradation properties. BSA was incorporated into a series of biodegradable hydrogels made from a dextran derivative of allyl isocyanate (dex-AI, as the hydrophilic constituent) and poly(DL-lactic acid) diacrylate macromer (PDLLAM, as the hydrophobic constituent). The release kinetics of BSA from these dex-AI/PDLLAM hydrogels was studied. Laser confocal scanning microscopy was used to investigate the morphological change of the hydrogels, as well as BSA distribution in the hydrogels, as a function of dex-AI to PDLLAM composition ratio and incubation time. We found that the incorporation of PDLLAM into dex-AI reduced the initial burst release of BSA due to its more homogeneous distribution in the hydrogels. As the PDLLAM component increased, the rate of formation of a loose three-dimensional (3D) network structure increased; consequently, the sustained rate and extent of BSA release increased. Both release index and diffusion coefficient (from release kinetics data) increased as the PDLLAM component increased in the hydrogels. The data suggest that the release of BSA was controlled by both diffusion of BSA through swelling of the hydrophilic phase during an early stage, and degradation of the hydrophobic phase during a late stage, and also that the magnitude of diffusion versus degradation controlled release is dependent on composition ratio and immersion time.

Molecular cytogenetic analysis of intergeneric chromosomal translocations between wheat (Triticum aestivum L.) and Dasypyrum villosum arising from tissue culture

Fluorescence in situ hybridization (FISH) was applied with total genomic DNA extracted from Dasypyrum villosum (L.) Candargy as a probe to characterize chromosome translocations arising from tissue culture in hybrids of Triticum aestivum x (T. durum - D. villosum, amphiploid). Chromosome translocations between wheat and D. villosum occurred in callus cells at an average frequency of 1.9%. Translocations existed not only in callus cells but also in regenerants. Three plants with translocation chromosomes were characterized among 66 regenerants of T. aestivum 'Chinese Spring' x 'TH1W' and 'NPFP' x 'TH1'. One of them proved to be a reciprocal translocation with an exchange of about one third of a wheat chromosome arm with about one half of a chromosome arm of D. villosum. The breakpoints of the other two translocations were located at, or near centromeres. The results are similar for both callus cells and regenerants and provide further evidence that translocations take place in tissue culture. Other structural chromosomal changes, for example, fragments, telocentrics, dicentromeres, and deletions, as well as numerical alterations including aneuploidy and polyploidy were recorded both in callus cells and regenerants.

The study of fine and coarse particles, and metallic elements for the daytime and night-time in a suburban area of central Taiwan, Taichung

Daily average concentrations of fine and coarse particulates, and TSP samples have been measured simultaneously at daytime and night-time periods by using Universal and PS-1 sampler in a suburban area of central Taiwan from June to August 1998. The samples were analyzed by atomic absorption spectrometry to determine the fine and coarse particulate concentrations of metallic elements (Ca, Fe, Mn, Pb, Cu, Zn and Cr). The concentration of PM2.5 and TSP showed a decreased trend for the daytime period. The fine particle concentrations were about two times as that of coarse particulate concentrations. The averaged fine particulate concentrations at daytime are higher than at night-time. Ca and Fe were mostly in the coarse particulate mode. The correlation coefficients were 0.63 and 0.69 for elements Ca and Fe in the coarse particle mode for day and night periods. Pb showed a similar distribution ratio with Mn for the fine to coarse particle ratios at both day and night period. Pb and Mn are highly correlated for the day (R = 0.78) and night period (R = 0.61) at particle size <2.5 microm. Cu and Zn were mainly in fine particles at both day and night period. Fe and Ca consist of the major parts of all the elements. Elemental Mn is the lowest among the rest of the heavy metals.

Pore structure analysis of swollen dextran-methacrylate hydrogels by SEM and mercury intrusion porosimetry

The objectives of this study were to visually examine the surface and interior morphology of a new class of biodegradable hydrogels based on dextran-methacrylate and to quantify the porous structure of these hydrogels in swollen state. Two techniques (scanning electron microscopy and mercury intrusion porosimetry) were used to analyze pore structure of dextran-methacrylate hydrogels as a function of the degree of methacrylate substitution. SEM was used to observe 3-dimensional network structure of cryofixed and fractured swollen dextran-methacrylate hydrogels. Image analysis of the SEM data revealed different pore shapes and sizes, depending on the degree of substitution and the location within the hydrogel. A higher methacrylate-substituted dextran hydrogel showed a compact and rigid pore structure, while a lower substituted hydrogel showed a delicate and fragile pore structure. Mercury intrusion porosimetry analysis of the pore structure of dextran-methacrylate hydrogels provided useful and more reliable quantitative data of pore characteristics, such as total pore area, average pore diameter, their distribution, and bulk density. The total pore area and average pore diameter of swollen dextran-methacrylate hydrogels decreased with an increase in degree of methacrylate substitution, while bulk density increased with an increase in degree of substitution.