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Biomedical subjects

D S Jones

Publications and source records attributed to D S Jones.

At least 55 records · Page 3Linked to original sources
PubMed1997

Sequential polyurethane-poly(methylmethacrylate) interpenetrating polymer networks as ureteral biomaterials: mechanical properties and comparative resistance to urinary encrustation.

The mechanical properties and resistance to urinary encrustation of sequential-interpenetrating polymer networks (IPNs) composed of polyurethane (PU) and polymethylmethacrylate (PMMA), have been described. Mechanical properties were determined using tensile testing and dynamic mechanical analysis, whereas resistance to encrustation was examined using an in vitro model for encrustation simulating in vivo encrustation. Maximum and minimum tensile strength at break, Young's modulus, storage and loss moduli were associated with PMMA and PU, respectively. IPNs demonstrated intermediate mechanical properties which were dependent on the concentrations of the component polymers. Conversely, maximum elongation at break was observed for PU and this parameter decreased as the concentration of PMMA increased in the IPN. The dynamic mechanical damping parameter, tan delta, was similar for all IPNs at 37 degrees C. Increased advancing and decreased receding contact angles were observed for IPNs in comparison with the native PU. The rate and extent of encrustation, measured as the percentage surface coverage, was similar for PU, IPNs and PMMA. In contrast, encrustation on polyhydroxyethylmethacrylate, a model hydrogel, was greater than observed for the IPNs or component polymers. No apparent correlation was observed between the rate and/or extent of encrustation and polymer contact angle. It is concluded that these IPNs may be of clinical benefit in patients providing stent resistance to extrinsic compression of the ureter in comparison with native PU. The comparable resistance to encrustation between the IPNs and PU indicates that the use of IPNs should not be restricted in this regard.

Journal Article↗
PubMed1997

Association of enzyme inhibition with methods of museum skin preparation.

Enzyme inhibition is commonly encountered when using molecular biological techniques on museum-prepared animal skin samples, and this problem is exacerbated by a lack of information on how particular skins have been prepared for preservation. This report: (i) demonstrates that while some methods of museum preparation inhibit both proteinase K digestion and the PCR, others do not; (ii) describes a change in buffer conditions that reduces proteinase K enzyme inhibition during tissue digestion: and (iii) uses electron-dispersive X-ray microanalysis (EDXA) to show that the preparation methods for museum-preserved skin are often more complex than the treatment description provided with samples and also suggests that some of these descriptions are incorrect.

Animals↗
PubMed1996

Comparative assessment of ureteral stent biomaterial encrustation.

Long-term use of ureteral stents is hindered by the inherent problem of biomaterial encrustation which may lead to stone formation and attendant problems. The wide variety of polymeric biomaterials currently used for stent fabrication suggests that no single material is significantly superior to the others at resisting encrustation. A model representing upper urinary tract conditions was employed to compare the long-term struvite and hydroxyapatite encrustation of five materials currently used in the fabrication of ureteral stents. Silicone was least prone to struvite encrustation, followed by polyurethane, silitek, percuflex and hydrogel-coated polyurethane, in rank order. Similarly, silicone was least prone to hydroxyapatite encrustation, followed by silitek, polyurethane, percuflex and hydrogel-coated polyurethane. This study has shown that the problem of encrustation may limit the long-term use of ureteral stent biomaterials and suggests directions for improvement of biomaterials in this regard.

Analysis of Variance↗
PubMed1996

Development and mechanical characterization of bioadhesive semi-solid, polymeric systems containing tetracycline for the treatment of periodontal diseases.

PURPOSE: This study examined the mechanical characteristics and release of tetracycline from bioadhesive, semi-solid systems which were designed for the treatment of periodontal diseases. METHODS: Tetracycline release into phosphate buffered saline (pH 6.8, 0.03 M) was examined using a Caleva 7ST dissolution apparatus at 37 degrees C. The mechanical properties of each formulation (hardness, compressibility, adhesiveness, elasticity and cohesiveness) were determined using texture profile analysis. Syringeability was measured using the texture analyser in compression mode as the work of syringeability i.e. the force required to express the product from a periodontal syringe over a defined distance. RESULTS: Tetracycline release from all formulations was zero-order for 24-54 h and ranged from 1.59 +/- 0.20 to 15.80 +/- 0.50 mg h-1. Increased concentrations of hydroxyethylcellulose (HEC) decreased the rate of release of tetracycline, due to the concomitant increase in product viscosity and the subsequent decreased rate of penetration of dissolution fluid into the formulation. Conversely, an increased polyvinylpyrrolidone (PVP) concentration increased tetracycline release rates, due to an increased formulation porosity following dissolution of this polymer. Increased concentrations of HEC and PVP increased the hardness, compressibility and work of syringeability of the semi-solid formulations, due to increased product viscosity. An increase in formulation adhesiveness, a parameter related to bioadhesion, was observed as the concentrations of HEC and PVP were increased, illustrating the adhesive nature of these polymers. Increased concentrations of HEC and PVP enhanced the semi-solid nature of the product, resulting in decreased product elasticity and cohesiveness. Several statistically significant interactions between polymeric formulation components were observed within the factorial design, with respect to rate of release and all mechanical properties. These interactions arose because of variations in the physical states (dissolved or dispersed) of polymeric formulation components. CONCLUSIONS: The optimal choice of bioadhesive formulation for use in periodontal disease will involve a compromise between achieving the necessary release rate of tetracycline and the mechanical characteristics of the formulation, as these factors will affect clinical efficacy and the ease of product application into the periodontal pocket.

Acrylic Resins↗
PubMed1996

Pericytosis and edema generation: a unique clinicopathological variant of meningioma.

OBJECTIVE: We report a group of eight patients with a distinctive histological variant of meningioma that is associated with severe peritumoral edema. The clinical presentation, radiographic findings, and histology of this type of tumor may lead to misdiagnosis as an aggressive or malignant process. METHODS: We reviewed the histology from patients who had removal of meningiomas performed in our institution between 1978 and 1992. Tumors having abnormal proliferation of cells in the intramural vascular spaces were selected for study; case histories and radiographs were reviewed. Tumor material was subjected to special stains, immunocytochemical examination, and election microscopy. RESULTS: Several lesions were misread radiographically as being malignant. Patients underwent craniotomy with complete excision of the tumor. All lesions were small (< or = 3 cm), and no brain invasion, unusual tumor vascularity, or dural sinus involvement was noted in any case. Histologically, the meningioma pattern in each case was meningothelial and benign in appearance. The immunocytochemical and electron microscopic features of the unusual cells in the blood vessel walls are most consistent with their being of pericytic origin. All patients have remained asymptomatic and without evidence of tumor recurrence with follow-up from 3 to 12 years. CONCLUSION: These tumors showed proliferation of pericytes in blood vessel walls and represent a new subtype of meningothelial meningioma. The apparently benign nature of these lesions necessitates their recognition. Characteristic findings of pericytic proliferation associated with edema generation have led us to descriptively term this the PEG variant of meningioma.

Aged↗
PubMed1996

Frequency distribution of Candida albicans blastospores adhered to mucosal epithelial cells in-vitro.

Although several methods are available for examination of microbial adherence to epithelial cells, these do not distinguish between adherence of viable and non-viable micro-organisms. This study reports the use of acridine orange-stained blastospores of Candida albicans in conjunction with direct epifluorescence microscopy to determine viable (orange-fluorescing) and non-viable (green-fluorescing) blastospore adherence to buccal epithelial cells. The method was also employed to examine the effects of chlorhexidine treatment at subminimum inhibitory concentrations on the adherence of viable and non-viable blastospores. There was good correlation in the assessment of blastospore viability between the direct epifluorescence microscopy technique and the standard serial dilution and plating method for viable counting, confirming the reliability of direct epifluorescence microscopy. Chlorhexidine treatment before acridine orange staining did not alter this assessment of viability. Blastospore adherence to buccal epithelial cells resulted in a similarly skewed distribution whether examined using a crystal violet stain in conjunction with light microscopy or using direct epifluorescence microscopy, therefore validating the direct epifluorescence microscopy technique for the enumeration of blastospore adherence. Chlorhexidine treatment (0.0005% v/v, 30 min) of either blastospores or buccal epithelial cells altered the distribution of adherent blastospores per epithelial cell by increasing the number of epithelial cells having no adherent blastospores. No differences in adherence were, however, observed between blastospore or epithelial cells after treatment with this agent. Examination of the adherence of viable and non-viable blastospores to buccal epithelial cells using direct epifluorescence microscopy revealed a greater adherence capacity of non-viable than viable blastospores for buccal epithelial cells. Treatment of blastospores with chlorhexidine altered the frequency distributions of viable and non-viable blastospores with lower numbers of blastospores adherent per epithelial cell. The larger reduction in adherent viable blastospores in comparison with their non-viable counterparts is, however, an important observation which might have clinical relevance. Microbial cells adhere to epithelial cells resulting in a skewed distribution; study of this distribution gives useful information about the adherence process. Viable and non-viable components of a microbial population have different adherence capabilities and treatment of such populations with an antimicrobial agent exerting anti-adherent activity at sub-minimum inhibitory concentrations reduces the amount of adherence of these viable/non-viable components to different extents.

Adhesiveness↗
PubMed1995

Immunospecific reduction of antioligonucleotide antibody-forming cells with a tetrakis-oligonucleotide conjugate (LJP 394), a therapeutic candidate for the treatment of lupus nephritis.

A discrete tetravalent conjugate, 7a (LJP 394), consisting of four oligonucleotides attached to a common carrier or platform was prepared. Single-stranded oligonucleotide 20-mers consisting of alternating deoxycytidine-deoxyadenosine nucleotides, (CA)10, were attached to a tetrabromoacetylated platform by displacement with sulfhydryl-terminated linkers. The tetrabromoacetylated platform 3a was synthesized in three steps using triethylene glycol bis-(chloroformate). The single-stranded conjugate was characterized by polyacrylamide gel electrophoresis, DNA sequencing, phosphate analysis, carbon and nitrogen combustion analysis, and correlation of stoichiometry to conversion in the conjugation process. HPLC and capillary electrophoretic methods were developed to evaluate purity. The tetrakis, single-stranded conjugate was annealed with a stoichiometric amount of a complementary single-stranded oligonucleotide 20-mer consisting of alternating thymidine-deoxyguanosine nucleotides, (TG)10. The double-stranded conjugate LJP 394 was characterized by melt temperature and hyperchromicity, phosphate analysis, and carbon and nitrogen combustion analysis. LJP 394 inhibits binding of DNA to anti-double-stranded oligonucleotide antibodies and reduces anti-oligonucleotide-specific plaque (antibody)-forming cells in an immunized mouse model by a proposed mechanism involving cross-linking B cell surface immunoglobins.

Animals↗
PubMed1995

Patient appointment failures in pediatric resident continuity clinics.

OBJECTIVES: To determine appointment failure rates in pediatric resident continuity clinics nationally, and to identify characteristics of clinics with respect to factors that may affect appointment failure rates. DESIGN: A one-page questionnaire administered via facsimile machine to pediatric residencies' continuity clinic directors. RESULTS: Of 200 continuity clinic directors, 160 (80%) returned the survey. The mean no-show percentage was 30.9%, with a range of 3% to 80%. Among the factors studied, only mode of payment emerged as an independent predictor. CONCLUSIONS: Appointment failure is a substantial problem in pediatric resident continuity clinics, which needs attention if resident learning, patient care, and clinic efficiency are to be optimized.

Appointments and Schedules↗
PubMed1995

The effect of cetylpyridinium chloride (CPC) on the cell surface hydrophobicity and adherence of Candida albicans to human buccal epithelial cells in vitro.

PURPOSE: This study examined the effects of cetylpyridinium chloride (CPC) on cell surface hydrophobicity (CSH) and adherence of blastospores of Candida albicans (MEN strain) to human buccal epithelial cells (BEC) in vitro. METHODS: The effect of CPC treatment of either C. albicans blastospores or BEC on their subsequent adherence was determined using 35SO4 labelled blastospores in association with a Percoll gradient. The effects of CPC treatment of blastospores on their CSH was determined using Hydrophobic Interaction Chromatography. RESULTS: Treatment of exponential and stationary phase blastospores with CPC (50 micrograms mL-1) for 0.5-30 minutes, or with CPC (0.5-50 micrograms mL-1) for 15 minutes resulted in significant reductions in both blastospore CSH and adherence to BEC in vitro. No correlation was apparent (r < 0.8) between reduced CSH and reduced blastospore adherence following treatment with CPC (0.5-50 micrograms mL-1). Significantly reduced adherence of C. albicans (stationary or exponential growth phases) to human BEC was also observed following treatment of BEC with CPC (50 micrograms mL-1) for 0.5-30 minutes or with CPC (0.5-50 micrograms mL-1) for 15 minutes. Antiadherence effects were observed at both sub and super-minimum inhibitory concentrations of CPC. CONCLUSIONS: It is suggested that, whilst the ability of CPC to reduce the CSH of C. albicans may contribute to its reduced adherence to human BEC in vitro, reduced CSH is only one of several possible factors that contribute to the observed antiadherence effects.

Cell Adhesion↗
PubMed1995

Primary interactions of three quaternary ammonium compounds with blastospores of Candida albicans (MEN strain).

The absorption of three quaternary ammonium compounds (QAC), cetylpyridinium chloride, cetrimide and benzalkonium chloride, onto the surface of blastospores of Candida albicans (MEN strain) was examined at room temperature. Equilibrium uptake occurred in less than 30 seconds for cetylpyridinium chloride and cetrimide whereas 5 min contact time was required for benzalkonium chloride. The adsorption of all three agents may be mathematically described as Langmuirian and hence a concentration-dependent formation of drug-monolayer on the surface of the blastospore occurred. From this the number of molecules adsorbed onto the surface of a single blastospore was calculated to be 1.33 x 10(12), 3.17 x 10(12) and 2.32 x 10(12) for cetylpyridinium chloride, cetrimide and benzalkonium chloride, respectively. These dissimilarities are most likely due to differences in the orientations of both the cationic nitrogen atom and the accompanying lipophilic portions of each QAC at the blastospore surface. Relating these observations to the known antiadherence effects of cetylpyridinium chloride and cetrimide, it can be concluded that monolayer coverage of the blastospore surface with QAC does not account for the observed reduced adherence. This suggests that the anti-adherence effects are due to either direct interaction with, or steric blockade of, adhesions on the blastospore surface.

Adsorption↗
PubMed1993

Inside-out vein graft promotes improved nerve regeneration in rats.

Vein grafts have been used both experimentally and clinically to bridge gaps in peripheral nerves. This study describes a modification of the vein graft technique in which vein graft conduits are pulled inside-out before anastomosis with proximal and distal nerve stumps. This technique creates an autogenous vein conduit with the collagen-rich adventitial surface exposed to the regenerating axons. The inside-out technique is a fast and simple modification of the standard vein graft technique and produces an accelerated rate of nerve regeneration and significantly earlier myelination compared with the results obtained from the use of polyethylene nerve guides and standard vein graft conduits.

Animals↗
PubMed1993

Sleeve insertion and collagen coating improve nerve regeneration through vein conduits.

Vein grafts have been used as conduits for nerve regeneration in both research protocols and clinical situations. Results to date are encouraging. This study investigated several variations in the vein graft model in an attempt to enhance peripheral nerve regeneration. Results showed that the jugular vein, with an improved suture technique made possible by its larger diameter, is superior to the femoral vein as a conduit for regeneration of the sciatic nerve in the rat. The larger diameter of the jugular vein and its lack of valves provided less hinderance to regenerating axons. Results also showed that coating the luminal epithelium of the jugular vein with type I collagen gel greatly improved regeneration.

Animals↗
PubMed1993

Lack of detectable human immunodeficiency virus infection in antibody-negative children born to human immunodeficiency virus-infected mothers.

More than one-half of the children born to women with human immunodeficiency virus (HIV) infection are not infected with HIV. Most of these children, although born antibody-positive, lose maternal antibody and remain asymptomatic. However, it has been unclear how many antibody-negative children of HIV-infected women may truly be infected despite the loss of passively acquired maternal antibody. One hundred nine children who lost maternal antibody after birth to HIV-infected women recruited in four United States maternal HIV transmission studies were examined for HIV infection. Polymerase chain reaction (PCR) was used to determine whether children had HIV proviral DNA in peripheral blood mononuclear cells. A total of 268 samples from 109 children were tested. Clinical status and other laboratory findings were also evaluated. The median age at last follow-up was 25 months (range, 12 to 48 months). One hundred seven (98%) children were negative by PCR on all samples tested. None (95% confidence interval, 0.0 to 1.9%) of 109 children had a repeatedly positive PCR. Two children had single positive PCR results that could not be confirmed on subsequent testing. No other laboratory or clinical findings supported HIV infection in either of these children. The loss of HIV antibody in an asymptomatic child born to an HIV-infected woman strongly suggests that the child is not infected with HIV. Single positive PCR results, particularly in the absence of other clinical or laboratory evidence of HIV infection, should not be used alone to diagnose HIV infection.

AIDS Serodiagnosis↗
PubMed1992

Pediatric tuberculosis and human immunodeficiency virus infection in Palm Beach County, Florida.

OBJECTIVE: To describe the factors underlying an increasing incidence of tuberculosis in children. DESIGN: Descriptive case review. SETTING: Palm Beach County, Fla. PARTICIPANTS: Forty-four children with suspected and confirmed pediatric tuberculosis from 1985 through 1989. INTERVENTIONS: None. MEASUREMENTS/MAIN RESULTS: From 1988 through 1989, tuberculosis was confirmed in 15 children and suspected in another 16 compared with data from 1985 through 1987 in which the disease was confirmed in nine children and suspected in four. Pediatric tuberculosis occurred primarily in blacks younger than 5 years; the increase in the number of cases reported in 1988 and 1989 occurred only in blacks. One child in whom tuberculosis was confirmed during the recent period was infected with the human immunodeficiency virus (HIV); however, among children with suspected tuberculosis, four of the nine children tested were seropositive for HIV. There was no evidence of increased transmission of tuberculosis to children by HIV-seropositive adults compared with transmission by HIV-seronegative adults with TB. New adult tuberculosis cases in the county increased annually, from 92 cases in 1986 to 169 in 1989, of whom at least 36% were infected with HIV. CONCLUSIONS: The largest effect of the HIV epidemic on tuberculosis in children appeared to be indirect, through an increase in the number of adults with active tuberculosis serving as potential sources of tuberculosis infection for children. A direct effect of HIV infection in the progression of tuberculous disease in children is likely, but was not detected in this investigation. Case-finding for tuberculosis among children will need to increase, particularly in areas heavily affected by acquired immunodeficiency syndrome, but may be complicated by the difficulty of diagnosing tuberculosis in HIV-infected children.

Adolescent↗