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Biomedical subjects

H Alexander

Publications and source records attributed to H Alexander.

At least 91 records · Page 5Linked to original sources
PubMed1994

Effect of surface plasma treatment on the chemical, physical, morphological, and mechanical properties of totally absorbable bone internal fixation devices.

The purpose of this work was threefold: to enhance the adhesion between the reinforced absorbable calcium phosphate (CaP) fibers and the absorbable polyglycolide acid (PGA) matrix, to improve the hydrolytic degradation of the CaP fibers, and preliminarily to evaluate the cytotoxicity of the plasma treated surface of CaP fibers. A CH4 plasma treatment was used to achieve these goals. The microbond method was used to evaluate the effects of the plasma treatment on the interfacial shear strength between the PGA matrix and CaP fibers. The treatment increased the mean interfacial shear strength of the CaP/PGA composite system by 30%. AFM data showed that CH4-treated CaP fibers had considerable microscopic surface roughness, which facilitated mechanical interlocking between the reinforced CaP fibers and PGA matrix. The untreated and plasma-treated fibers were also subjected to in vitro hydrolytic degradation in a phosphate buffer solution of pH 7.44 at 37 degrees C for up to 15 h. CH4 plasma treatment resulted in a considerable lower polar term of the surface energy and a significantly higher disperse term in water media. This change in the proportion of surface energy terms may reduce the capillary wicking phenomena of water through the CaP fiber/PGA matrix interface. The CaP fiber dissolution studies revealed that both CH4 and Parylene plasma polymer coatings appeared to reduce the solubility of CaP fibers, and that the magnitude of reduction was higher in an acidic than a physiologic pH environment. A preliminary cytotoxicity test revealed that both CH4 and Parylene plasma-treated CaP fibers were noncytotoxic. Additional research should be done to determine the optimum plasma conditions and the possible use of other plasma gases to improve the interfacial shear stress of the composite and the dissolution properties of CaP fibers.

1-Propanol↗
PubMed1994

Formation of a calcium phosphate-rich layer on absorbable calcium carbonate bone graft substitutes.

The use of natural coral as a bone graft substitute is common in Europe. However, the bone-coral bonding mechanism remains elusive. A rat subcutaneous model was used to demonstrate changes at the surface of resorbable calcium carbonate in the form of natural coral. Histological results indicated in vivo formation of a calcium phosphate (CaP)-rich layer on the surface of the coral confirmed by backscattered electron imaging and X-ray microanalysis. There appears to be a combination solution-mediated dissolution/cell-mediated degradation of the natural coral with subsequent surface conversion or precipitation. The end result is a CaP-rich layer on the coral. Though this layer has been observed previously, it was originally thought to be a histological artifact. This result is similar, however, to what is seen with Bioglass and glass ceramics and may also explain the good bonding of bone to hydroxyapatite. The fact that this layer is also present on natural coral after implantation in soft tissue sites may explain the intimate bone apposition observed when natural coral is placed in bony sites.

Absorption↗
PubMed1994

In vivo evaluation of collagen-coated Dacron fiber in bone.

To evaluate the influence of type I collagen and hydroxyapatite coatings on the ability of Dacron fiber to achieve biologic fixation to bone, tows with the following coatings were evaluated in vivo: avian collagen (A); an avian collagen/hydroxyapatite composite (AH); bovine tendon collagen (B); a bovine tendon collagen/hydroxyapatite composite (BH); and plain (uncoated) Dacron tow (C). The Dacron tows were placed unstressed in the cancellous bone of both lateral femoral condyles of rabbits. Tissue reaction to each kind of Dacron tow was evaluated histopathologically, histomorphometrically and biomechanically. Inflammatory reaction was apparent around the AH and BH Dacron fibers at 2 weeks. There was no such reaction in the A, B, and C specimens, thus implicating the hydroxyapatite particles as the cause. At later time periods specimens A, B, and C all induced new bone formation. Direct contact between the Dacron fibers and trabecular bone was apparent in A and B. The pull-out strength of the B fibers was higher than the controls at a statistically significant level, but there was no significant difference between any of the other specimens and C (controls). There was no significant difference between any coating and controls at 8 or 16 weeks. Dacron fibers coated with bovine tendon collagen exhibited the best biocompatibility to bone and improved the anchoring to bone in the early time intervals by maintaining direct contact between Dacron fibers and trabecular bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Accuracy of reported family history of heart disease: the impact of 'don't know' responses.

BACKGROUND: Usual 'Yes/No' definitions of a family history of heart disease do not allow for 'Don't know' responses. In some families, misclassification of family history may result if these are not considered. AIMS: To study the accuracy of family history reporting and the impact of 'Don't know' responses. METHODS: We compared reported family history of coronary heart disease (CHD) and cancer among 360 deceased relatives of 59 probands with 'gold standard' diagnoses recorded on official death certificates. RESULTS: For first degree relatives, sensitivity of reporting was 81% for CHD, 86% for any heart disease and 60% for cancer, while for second degree relatives, sensitivity was 73%, 69% and 90%, respectively. When 'Don't know' responses were classified as 'No', sensitivity in first degree relatives was not affected, but in second degree relatives, it fell to 49%, 41% and 60%, respectively. Specificities were unchanged. These data show that in families where information beyond first degree relatives is considered, failing to account for 'Don't know' responses is likely to lead to misclassification of family history of CHD.

Adult↗
PubMed1994

[Directional coronary atherectomy: effect of vessel size on primary results and long-term results].

Of 325 consecutive patients undergoing DCA, 263 patients with 277 stenoses were successfully treated with DCA alone and had angiographic follow-up 3-6 months later. Depending upon the initial reference diameter (RD) patients were divided into two subgroups: group I (n = 159) with a RD > 3 mm and group II (n = 104) showing a RD < or = 3 mm. In contrast to other series DCA was predominantly performed with 7F atherectomy devices using balloon inflation pressures of approximately 5 atm. Angiographic data including the minimal luminal diameter (MLD), percentage of stenosis (%D) and reference diameter (RD) were assessed by quantitative computer-assisted analysis before (pre), after (post) DCA and at a 3-6 months angiographic follow-up (FU). The percentage of diameter stenosis pre/post/FU in group I was 59.9 +/- 12.6%/18.4 +/- 12.8%/29.8 +/- 17.6%, and in group II 55.6 +/- 10.8%/17.8 +/- 12.3%/33.7 +/- 16.1% with a net gain at FU of 1.0 +/- 0.89 mm for group I and 0.86 +/- 0.66 mm for group II. Based on an angiographic restenosis criterion of at least 50% diameter obstruction at FU and or recurrence of symptoms warranting interventional re-treatment of the target lesion, the incidence of restenosis in group I was 20.6% and in group II 28.0% (p: n.s.). There was no significant difference between the two groups concerning complications. Our data show that DCA leads to a satisfying long-term result.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Human monoclonal antibodies recognize early and late viral proteins of human cytomegalovirus.

Human monoclonal antibodies directed against human cytomegalovirus were generated by fusion of in vitro stimulated human spleen lymphocytes from an HCMV-seropositive 53-year-old organ donor with the mouse myeloma cell line Ag8.653. Fourteen human/mouse hybridomas producing anti-cytomegalovirus IgG were screened by an ELISA technique and four selected clones have been established since March 1988, generating about 5-40 micrograms/24 h IgG per ml culture supernatant. Reference and local cytomegalovirus strains were stained by the antibodies without showing cross-reactivity to other herpes viruses. Three monoclonal antibodies, A4B4 (IgG11), A6B3 (IgG1k) and A6A2 (IgG1k), immunoprecipitated a 68 kDa early viral protein which appears during the infectious cycle, first in the nucleus (18-24 h) and then also in the cytoplasm (24-96 h) of infected cells. Inhibition of DNA replication restricted the detection of the 68 kDa viral protein to the nucleus of infected cells. Staining of unfixed infected cells showed that two of the antibodies bound at the surface of a few cells. The fourth monoclonal antibody A3C5 (IgG11) immunoprecipitated a 34/38 kDa late viral protein which appears in the nucleus (48-72 h) of infected cells. These antibodies enable us to study the human host response to human cytomegalovirus and to elucidate the functions of human antibodies especially in their interaction with the T-cell response.

Animals↗
PubMed1993

Diffusion of fibroblast growth factor from a plaster of Paris carrier.

Fibroblast growth factor (FGF) is a polypeptide that has been shown to have a stimulatory effect on osseous tissues in vitro. This study characterized the release of FGF from plaster of Paris (PLP) and measured the dissolution of PLP in various solutions with the aim of developing a reliable carrier system for the release of FGF in vivo. The study consisted of five experiments: (I) FGF diffusion from PLP pellets, (II) FGF diffusion from PLP discs, (III) PLP dissolution in saline, (IV) PLP dissolution in serum, and (V) FGF adsorption by commercially pure titanium. FGF was observed to be released at a rate directly proportional to the rate of dissolution of the PLP carrier, suggesting that either the FGF binds to the PLP; or, alternatively, the FGF may be entrapped by the PLP. Dissolution rate, and thus release rate, could be varied by varying the mass of the carrier. Greater diffusion of FGF was observed in larger, more slowly dissolving PLP carriers. Dissolution of PLP was observed to be slower in serum than in saline, apparently due to stabilization by factors in the serum but not due to a concentration gradient effect. Titanium coupons did not adsorb significant amounts of FGF. These results indicate that PLP, which has been shown in the past neither to aggravate inflammatory response nor to interfere with bone ingrowth, may serve as delivery vehicle for FGF to osseous tissues in vivo.

Adsorption↗
PubMed1993

Wound botulism in a patient with a tooth abscess: case report and review.

We describe a case of wound botulism associated with a tooth abscess in a 5-year-old boy. We reviewed the literature and reports to the Centers for Disease Control and Prevention (Atlanta) of laboratory-confirmed cases of wound botulism. From 1943 through 1990, 47 cases were reported. Type A botulinus toxin was identified in 32 cases, type B in 13, types A and B in 1, and an unknown type in 1. Botulism was associated with wounds from trauma, use of injectable drugs, and surgery. Sinusitis after use of intranasal cocaine has also been associated with botulism. Treatment for wound botulism includes prompt debridement of the wound for eliminating anaerobic conditions, intensive care, and treatment with antitoxin.

Botulinum Toxins↗
PubMed1993

Delay in cooling negates the beneficial effect of mild resuscitative cerebral hypothermia after cardiac arrest in dogs: a prospective, randomized study.

OBJECTIVE: Previously, we documented that mild hypothermia (34 degrees C) induced immediately with reperfusion after ventricular fibrillation cardiac arrest in dogs improves functional and morphologic cerebral outcome. This study was designed to test the hypothesis that a 15-min delay in the initiation of cooling after reperfusion would offset this beneficial effect. DESIGN: Prospective, randomized, controlled study. SETTING: Animal intensive care unit. SUBJECTS: A total of 22 custom-bred coonhounds. INTERVENTIONS: Eighteen dogs underwent normothermic ventricular fibrillation arrest (no blood flow) of 12.5 mins, reperfusion with brief cardiopulmonary bypass, defibrillation within 5 mins, intermittent positive-pressure ventilation to 20 hrs, and intensive care to 96 hrs. Three groups of six dogs each were studied: group 1, normothermic controls; group 2, core temperature 34 degrees C from reperfusion to 1 hr; and group 3, delayed initiation of cooling until 15 mins after normothermic reperfusion, and 34 degrees C from 15 mins to 1 hr 15 mins after cardiac arrest. MEASUREMENTS AND MAIN RESULTS: Tympanic membrane temperature (which represented brain temperature) in group 2 reached 34 degrees C at 6 +/- 3 (SD) mins after reperfusion; and in group 3 at 29 +/- 1 mins after reperfusion. Best overall performance categories achieved (1, normal; 5, brain death) compared with group 1, were better in group 2 (p < 0.5) but not in group 3 (NS). Similar results were found with best neurologic deficit scores (0%, normal; 100%, brain death), i.e., 44 +/- 4% in group 1, 19 +/- 15% in group 2 (p < .01), and 38 +/- 9% in group 3 (NS). Total brain histologic damage scores (< 30 minimal damage; > 100 severe damage), however, were 150 +/- 32 in group 1, 81 +/- 13 in group 2 (p < .001 vs. group 1), and 107 +/- 17 in group 3 (p < .05 vs. group 1). CONCLUSIONS: Mild, resuscitative cerebral hypothermia induced immediately with reperfusion after cardiac arrest improves cerebral functional and morphologic outcome, whereas a delay of 15 mins in initiation of cooling after reperfusion may not improve functional outcome, although it may slightly decrease tissue damage.

Animals↗
PubMed1993

The effect of resuscitative moderate hypothermia following epidural brain compression on cerebral damage in a canine outcome model.

A canine model of temporary epidural cerebral compression and standardized intensive care was developed to evaluate the effect of resuscitative (postinsult) moderate systemic hypothermia. A balloon was inflated over the temporal region to maintain contralateral intraventricular pressure (IVP) at 62 mm Hg for 90 minutes. For a 66-hour period after initiation of brain compression, the intubated dogs received controlled ventilation and standard intensive care. From 66 to 90 hours postinjury, the extubated dogs were evaluated as to functional outcome. Morphological brain damage was evaluated at 90 hours or earlier if brain death occurred. Eight dogs in a control group were maintained at a body of temperature of 38 degrees C. Eight treated dogs had core body temperature reduced by surface cooling starting 15 minutes after balloon inflation, first to 31 degrees C for 5 hours and then to 35 degrees C from 5 to 62 hours after insult. Intraventricular pressure increased to 20 mm Hg or greater in the control group at a mean of 2.9 hours (range 2 to 4 hours) following the insult, and in the hypothermic group at a mean of 14.8 hours (range 5 to 30 hours)--that is, during the time period when the body temperature was 35 degrees C, not 31 degrees C (p = 0.01). There was no difference in peak pressures between the two groups. Brain death occurred in four of the eight dogs in the normothermic group at 18, 24, 24, and 48 hours (mean +/- standard deviation 28 +/- 13 hours) and in three of the eight in the hypothermic group at 27, 42, and 45 hours (mean 38 +/- 10 hours) (not significant). The animals surviving 90 hours (four in the normothermic and five in the hypothermic group) were neurologically near normal. The total mean macroscopically damaged brain volume was 2584 +/- 1890 cu mm in the normothermic versus 765 +/- 611 cu mm in the hypothermic group (p = 0.03). The mean necrotic volume was 741 +/- 599 cu mm in the normothermic versus 263 +/- 346 cu mm in the hypothermic group (p = 0.07). Microscopically, the damaged regions consisted of ischemic neurons, reactive glia, edema, vascular endothelial hypertrophy, and erythrocyte extravasation. It is concluded that, in this model, immediate postinsult hypothermia of 31 degrees C (not 35 degrees C) for 5 hours prevents a rise in IVP and significantly decreases cerebral tissue damage, but does not prevent brain herniation during rewarming.

Animals↗
PubMed1992

Altering the antigenicity of proteins.

To better understand the binding interaction between antigen and antibody we need to distinguish protein residues critical to the binding energy and mechanism from residues merely localized in the interface. By analyzing the binding of monoclonal antibodies to recombinant wild-type and mutant myohemerythrin (MHr) proteins, we were able to test the role of individual critical residues at the highly antigenic site MHr-(79-84), within the context of the folded protein. The results directly show the existence of antigenically critical residues, whose mutations significantly reduce antibody binding to the folded protein, thus verifying peptide-based assignments of these critical residues and demonstrating the ability of buried side chains to influence antigenicity. Taken together, these results (i) distinguish the antigenic surface from the solvent-exposed protein surface before binding, (ii) support a two-stage interaction mechanism allowing inducible changes in protein antigens by antibody binding, and (iii) show that protein antigenicity can be significantly reduced by alteration of single critical residues without destroying biological activity.

Amino Acid Sequence↗
PubMed1992

Evaluation of a low-temperature calcium phosphate particulate implant material: physical-chemical properties and in vivo bone response.

A study was conducted to evaluate the osteoconductive ability of a particulate, low-temperature hydroxylapatite (HA(LT)) material (OsteoGen; Impladent, Holliswood, NY). An implantable chamber model was used to determine the ability of this material to encourage bone ingrowth into channels lined with either rough-surfaced titanium or rough-surfaced plasma-sprayed hydroxylapatite. The HA(LT) material increased bone ingrowth into the titanium-lined channels comparable with that in plasma-sprayed hydroxylapatite-coated channels. It was incorporated into ingrowing bone without intervening soft tissue, with the bone bonding directly to the material surface in much the same fashion as it bonds at the plasma-sprayed hydroxylapatite surface. Mechanical testing of the ingrown bone showed no weakness because particles were incorporated. At 12 weeks, the particles began to show signs of dissolution. It was concluded that the HA(LT) material is a biocompatible, osteoconductive material that conducts bone ingrowth in much the same way as high-temperature particulate hydroxylapatite ceramics. This material has the additional desirable property of being slowly resorbable, a beneficial characteristic for many bone-filling applications.

Animals↗
PubMed1992

[Secretion of hCG by mononuclear cells--a specific and essential reaction in pregnancy?].

Mononuclear cells in peripheral blood secrete immunoreactive hCG (ir-hCG) when they are stimulated in in-vitro culture with the proteinkinase C - activator phorbol-myristat-acetate (TPA). We examined the ir-hCG secretion in 61 fertile and 191 pregnant women and 38 men. Mononuclear cells of pregnant women secrete after TPA stimulation significantly more ir-hCG than mononuclear cells on non-pregnant but fertile women. This effect can be detected as early as 23rd days of a menstrual cycle which is accompanied by conception and persisted over the entire duration of a pregnancy. Maximal effects were observed in the 7th to 19th and 30th to 34th weeks of pregnancy. An artefact caused by adhesive serum-hCG could be excluded. The elevated potential of the mononuclear cells to be stimulated remained intact for about 14 days after termination of a normal pregnancy in the first trimester. An ir-hCG secretion similar to that seen in nonpregnant women was found in patients with early abortion. The possible physiological importance of the in-vivo secretion of beta-HCG during pregnancy is discussed.

Abortion, Incomplete↗
PubMed1991

Synthesis and characterization of a recombinant myohemerythrin protein encoded by a synthetic gene.

The antigenic epitopes of the myohemerythrin (MHr) molecule have been studied extensively. The critical amino acid residues responsible for its immune recognition have been identified by using synthetic peptides and the technique of epitope scanning. To assess the true relevance of these techniques for determining the molecular mechanism of antigenic recognition and immunogenicity, the results obtained with isolated peptides should be tested in the context of the folded protein. To this end, we have designed and constructed a synthetic MHr gene, in modular form, which will allow subsequent alterations of nucleotide sequence encoding epitopes of interest. We have produced the recombinant protein at high level, and have shown by several criteria that it possesses the chemical, physical and immunological properties of the native worm protein. Thus, we have developed a valuable system for detailed immunological studies of the structure and chemistry required for antibody binding to protein.

Amino Acid Sequence↗
PubMed1991

In vitro tendon cell growth rates on a synthetic fiber scaffold material and on standard culture plates.

Growth rates of rat tendon fibroblasts cultured in a three-dimensional carbon fiber matrix were compared with those of cells cultured on standard flat culture plates. The carbon fiber has been used as a tissue scaffold for tendon and ligament repair in animal and clinical studies. While cell growth on the culture plates appears to follow a growth curve containing a lag phase, a log phase, and plateau phase of growth, cell growth in the fiber matrix was characterized by a suppressed log phase of growth. SEM and cytotoxicity studies indicated that this effect was not caused by growth-inhibiting or cytotoxic substances from the carbon fiber. While we cannot rule out the possibility that cell growth was influenced by the surface chemistry of the carbon substrate, evidence from this and other studies suggests that the observed effect was caused by a lack of readily available surface area for cell attachment and growth on the small fibers. Because cell colonies growing on individual fibers are limited (at least in theory) to growing in two directions only, they enjoy limited opportunities for cell migration and growth--in contrast with cell colonies on flat culture plates. These results suggest fundamental differences in the mechanisms controlling cell growth on planar vs. three-dimensional fiber substrates.

Animals↗