Marsupialization of percutaneous implants in presence of deep connective tissue

The primary substratum for epithelial migration during marsupialization of percutaneous implants is adjacent connective tissue. The purpose of this investigation was to test the hypothesis that if the latter is composed of deep connective tissue or other deep tissue, it will inhibit this process. One-hundred-forty-two smooth-surfaced polyethylene implants of a simple geometric design were implanted in dorsal skin of 6-8-week-old male C57/BL/6 mice such that the stems passed through and deep to the panniculus carnosus (PC), which is a deep tissue. Animals were sacrificed in groups between 1 and 11 weeks, and the implants and surrounding tissue were harvested, embedded in historesin, and 3-microns thick step serial sections prepared. No implants were lost by extrusion and 133 were suitable for examination. Epithelial investment of the devices proceeded deep to PC around only five of the implants over the time course. In the remainder, the mean distance of the advancing epithelial edge from the upper border of the PC was 0.25 mm by 1 week and this did not change significantly thereafter (p = 0.647). Significant extrusion of all devices occurred (p = 0.0001). It was concluded that these results are consistent with the hypothesis that deep connective tissue, such as the fascia surrounding the PC or muscle tissue such as the PC itself, can act as a functional barrier to marsupialization, and that exfoliation of such devices is not an epithelial function.

In-vitro corrosion and wear of titanium alloys in the biological environment

Cyclic anodic polarization studies were undertaken for several titanium alloys of varying composition and phase structures. All materials were exposed to an accelerated corrosion test using a potentiostat and their electrochemical behaviour was analysed within a potential range of 0 to 5000 mV. The electrolyte used was a phosphate buffered saline (PBS) solution at pH = 5, 7.4 and 9. The polarization curves obtained represented both the passive and active regions of the materials and these curves were used to compare the resistance to pitting corrosion of each material. The sliding-wear of these materials was studied in both non-corrosive and corrosive environments. A simple pin-on-disc type wear apparatus was designed and built to simulate the co-joint action of corrosion and sliding-wear. Using this apparatus, it was also possible to evaluate the effect of wear-accelerated corrosion, which was also evaluated by wearing the surface of the specimens prior to corrosion. It was evident that the mixed phase alpha-beta alloys (Ti-6AI-4V and Ti-6AI-7Nb) possessed the best combination of both corrosion and wear resistance, although commercially pure titanium and the near-beta (Ti-13Nb-13Zr) and beta (Ti-15Mo) alloys displayed the best corrosion resistant properties.

Influence of wall shear rate on parameters of blood compatibility of intravascular catheters

Three polymeric materials (silicone, PVC and nylon) were compared in an in vitro perfusion model, whereby 5 ml whole blood were perfused along 1 m lengths of polymeric tubing of 1 mm internal diameter at wall shear rates of up to 1000 s-1. Perfusion took place at 37 degrees C for 30 min. The polymers were investigated for platelet activation, granulocyte secretion, complement activation and contact phase activation. These parameters were also analysed in static contact for comparison. All the parameters measured displayed a dependence on wall shear rate. In all the materials studied, platelet adhesion and platelet activation increased with increasing flow rate. Granulocyte elastase release increased slightly with increasing flow rate up to 300 s-1. Complement activation was greatest for PVC at 1000 s-1, greatest for nylon at 100 s-1, but there was no measurable difference at either rate for silicone. All samples caused an increase in clotting time with increasing wall shear rate. PVC was the most platelet compatible material, nylon the worst. Silicone caused least contact phase activation, PVC and nylon the most.

Large-scale selection of CD34+ peripheral blood progenitors and expansion of neutrophil precursors for clinical applications

Hematopoietic recovery after high-dose chemotherapy is characterized by an obligate period of neutropenia of approximately 8-10 days. It is postulated that if a pool of neutrophil precursors and progenitors were expanded in vitro and reinfused, the duration of neutropenia may be substantially shortened by these cells capable of providing mature neutrophils within days of reinfusion. In this study, peripheral blood progenitor cell products were obtained from six normal donors mobilized with rhG-CSF and two patients mobilized with cyclophosphamide and rhG-CSF. CD34+ cells were isolated using the Isolex immunomagnetic bead method. A mean of 8.26 x 10(7) CD34+ cells with a mean purity of 74.5% were seeded at a concentration of 1 x 10(5)/ml into a 12 day stroma-free liquid culture using gas-permeable bags. A serum-free growth medium supplemented with PIXY321 was used. On day 7, there was a mean cellular expansion of fourfold, at which time the cells were resuspended at the initial concentration, yielding a mean culture volume of 3L (1-6 L). On day 12, there was an additional mean fold cellular expansion of 10 x, achieving an overall mean fold expansion of 41 +/- 16. Cellular characterization of the expanded cells revealed predominantly neutrophil precursors by morphology (mean 70.1%) and flow cytometric analysis. A mean of 52.3% of the expanded cells expressed CD15. Immunohistochemical staining revealed a mean of 7.1% CD41a+ megakaryocytic progenitors in the final cultured cell product. Detectable CD34+ cells were maintained only in those cultures initiated with greater than 90% CD34+ cells. Colony-forming units-granulocyte-macrophage (CFU-GM) were maintained in the 12 day culture at a level similar to the preculture number, whereas CFU mixed were depleted in all samples. On day 0, there were few CFU clusters (colonies containing fewer than 50 cells) identified, but by day 12, a mean total of 8.3 x 10(6) CFU clusters were identified. On day 12, the expanded cells were harvested and pooled using the Fenwal CS3000 Plus blood cell separator and resuspended in Plasma-Lyte-A with 1% human serum albumin. The mean harvest recovery of expanded progenitors was 91%, with a mean viability of 86%.

Quantitative assessment of the tissue response to films of hyaluronan derivatives

The aim of this study was to evaluate the in vivo response following implantation into a rat model of three innovative hyaluronan derivatives for clinical use: HYAFF 7, HYAFF 11 and HYAFF 11p75 (respectively, the 100% ethyl ester, 100% and 75% benzyl esters). The tissue reaction evoked by films of these new biomaterials implanted into the dorsolumbar musculature of rats was assessed quantitatively using a well established technique based upon an image analysis system. The number of inflammatory cells present and the patterns of cell distribution around the implant up to a distance of 642 microns were examined at different time periods after implantation. Since a well-delineated tissue-material interface was needed for this type of investigation, it was not possible to apply image analysis to sections once dissolution of the implanted materials had begun. Films of both the total esters, HYAFF 7 and HYAFF 11, were found to undergo a slow dissolution process and, after a month, films of these materials were still present at the site of implantation. Differences in response to the two materials were observed only during the first two weeks, particularly with respect to neutrophil distribution and total cellularity. HYAFF 7 was found to be more reactive, with higher numbers of neutrophils near the surface of the implant than HYAFF 11. Thereafter, the differences between the two materials were minimal and owing mainly to a faster dissolution of HYAFF 7 films. After 3 and 5 months, considerable degradation of films of both total esters had occurred. Significant quantities of material appeared inside numerous macrophages with an ED1-positive phenotype. Only a very thin layer of fibrous connective tissue, indicative of low reactivity, was found to surround the site of implantation, separating the dissolved material and the phagocytic cells from healthy muscular tissue. ED2-positive macrophages were primarily confined within the lining connective tissue. The partial benzyl ester, HYAFF 11p75, showed a different behaviour. In fact, evidence of film dissolution was already present a week after the implantation. After two weeks, the implanted films were completely dissolved and numerous ED1-positive macrophages phagocytosing the material were observed at the site of implantation. Therefore, in agreement with previous in vitro studies, which showed a greater susceptibility to degradation of hyaluronan derivatives with lower percentage of esterification, HYAFF 11p75 underwent resorption faster than the corresponding total ester.

Effect of biomaterial surface charge on the inflammatory response: evaluation of cellular infiltration and TNF alpha production

A rat model was used to investigate the effect of net surface charge on polymer biocompatibility and its potential to modify and stimulate the inflammatory response. Poly(ether)urethane was taken as the base material and the net charge altered by introducing sulphonate ionic groups to the polymer backbone. Three differently charged poly(ether)urethanes were made with 10, 20, and 30% sulphonate substitution, giving a range of negative charge, with unmodified poly(ether)urethane used as a control. The polymers were implanted intramuscularly into rats for 2 days, and for 1, 2, and 12 weeks. After explantation, the cellular infiltration in the tissue surrounding the implants was evaluated using immunohistochemistry to stain for specific cell types: macrophages, neutrophils, lymphocytes, and the cytokine TNF alpha. In situ hybridization was used to detect expression of mRNA encoding TNF alpha. Stained sections were analyzed and the cellular response quantified using image analysis. Initially macrophages and neutrophils were observed around all the materials, but neutrophils were absent in all samples at 12 weeks. The 2-day time point had significantly more macrophages than the later time points. By 2 weeks the 20%-charged polymer elicited significantly less neutrophil infiltration than the other three polymers. In all samples where macrophages were observed, cells staining positive fore TNF alpha protein and message also were observed. No T or B lymphocytes were observed in the infiltrates around the materials at any time point. The results indicate that surface charge can influence the early phase acute inflammatory response to an implanted material.

Ambient noise interferes with auscultatory blood pressure measurement during exercise

This study was designed to investigate whether the acoustical characteristics of the Korotkoff sounds (K-sounds) were altered during exercise and/or masked by the ambient noise. After signing informed consent, 11 subjects (8 females, 3 males; 27 +/- 2 yr; 166.2 +/- 3.2 cm; 62 +/- 5 kg; means +/- SD) underwent a cycle ergometer exercise test that increased in workload by 30 W every 3 min until volitional fatigue. Heart rate, auscultatory systolic (SBP) and diastolic blood pressure (DBP), and oxygen consumption were monitored 1 and 2 min into each work stage. The auscultatory K-sounds were recorded with a microphone mounted in a stethoscope tube for later frequency (Hz) and sound pressure level (dB SPL) analysis. Frequency and SPL of ambient noise (99 +/- 13 Hz and 64 +/- 1 db at maximum, respectively) increased during the exercise test to magnitudes similar to the SBP and DBP K-sounds (166 Hz, 66 db; and 128 Hz, 69 db, respectively). Additionally, the ambient noise was responsible for a significant damping of the frequency and SPL of the measured blood pressure K-sounds and a rise in the measured frequency of the SBP K-sounds. Furthermore, we observed "inaudible" K-sounds at lower frequencies than adjoining audible K-sounds (100 Hz vs 126 Hz), supporting the known underestimation of SBP by auscultation. The increase in ambient noise during exercise testing dampens and may mask the auscultatory K-sounds, thus making detection of the proper K-sounds during exercise difficult at best. Furthermore, the presence of inaudible K-sounds may further explain the published discrepancies between auscultatory and intraarterial blood pressure measurements during exercise.

Effects of speech and language disorders on raters' perceptions

Using semantic differential scales with nine trait pairs, 465 students at two universities rated five descriptions, one portraying an individual without a disorder and four depicting communicative disorders. Statistical analyses indicated that the descriptions with no disorder and with a language disorder were rated significantly lower in ambition than those depicting stuttering, voice, or articulation disorders. Other differences emerged when the raters were divided by geographical location and age. Location was a significant factor in the responses for the traits of social adjustment, employability, and ambition. Age of respondent correlated significantly with ratings of tension and employability.

Reversible loss of light perception after vitreoretinal surgery

PURPOSE

We studied reversible loss of light perception after vitreoretinal surgery to show that functional vision can return in some patients.

METHODS

We reviewed the medical records of seven patients who had postoperative reversible loss of light perception in the eye that underwent vitreoretinal surgery. Differences in the postoperative courses and interventions were studied.

RESULTS

Five of the seven patients had diabetes mellitus but none had hypertension. The indications for vitreoretinal surgery were severe proliferative diabetic retinopathy in five patients and retinal detachment with advanced proliferative vitreoretinopathy in two patients. Seven patients had reversible loss of light perception within the first three postoperative days. Six of the seven patients had an intraocular pressure greater than 26 mm Hg at the time the eye had no light perception. Decreasing the intraocular pressure was associated with return of light perception in five of seven patients. Return of useful vision was gradual. Four of seven patients had a visual acuity of 20/400 or better one month after surgery, and all seven had a visual acuity of 20/400 or better three months after surgery. Visual acuity in four eyes improved further to 20/70 or better at six months or more after surgery.

CONCLUSION

Reversible loss of light perception after vitreoretinal surgery does occur in some patients. Monitoring vision and intraocular pressure is important because prompt treatment may assist in the recovery of functional vision.

Pharaoh ant (Hymenoptera: Formicidae) colony development after consumption of pyriproxyfen baits

Pharaoh ant, Monomorium pharaonis (L.), colonies were effectively controlled following ingestion of pyriproxyfen formulated in peanut butter oil. Pyriproxyfen, a juvenile hormone analog, reduced egg production in the queens, decreased the amount of brood due to delayed death in the eggs and larvae, caused death of pupae about 3 wk after treatment, and decreased the number of workers due to attrition and toxic effects. Queens, which continued to produce a small amount of eggs, eventually died. Queen death may have been caused by lack of workers required to tend them, old age or toxic effects. At concentrations of 0.25, 0.5 and 1%, pyriproxyfen was more effective than the once commercially available bait, Pharorid (methoprene) for the control of the Pharaoh ant.

Echographic pseudoextension of uveal melanomas

BACKGROUND

Standardized echography is routinely utilized to assess uveal melanomas. Echographic pseudoextension is defined as normal structures mimicking intrascleral or extrascleral extension of tumor on echography.

METHODS

The records of 151 consecutive uveal melanoma patients evaluated with standardized echography over a 6-year period (1986-1991) were reviewed to identify those in which pseudoextension or true extension was diagnosed.

RESULTS

Fourteen (9%) cases of pseudoextension were noted, with causes including juxtapapillary tumor location (seven cases), extraocular muscle insertion (five cases), vortex ampullae (one case), and post-brachytherapy changes (one case). Clinical, echographic, and/or histopathologic follow-up confirmed absence of true extension. Six (4%) cases of true extrascleral extension were identified and confirmed histopathologically.

CONCLUSION

Differentiating extraocular tumor extension from pseudoextension is critical, and use of standardized A-scan and contact B-scan echography is integral in this assessment.

Multiple fire ant stings indoors

The progressive spread and increasing colony density of imported fire ants throughout the southeastern United States will result in increasing numbers of individuals with untoward reactions to the stings of these insects. In order to alert physicians that imported fire ant colonies may exist within homes and other inhabited dwellings and result in multiple stings to the occupants and to provide information about the management of this problem, we report two cases where individuals were stung indoors by imported fire ants. One of these cases involved the attack of a bed-bound patient by a colony of ants. The other report documents the establishment of an intact fire ant colony within an inhabited dwelling. Physicians should become familiar with the biology of these insects to assist patients in dealing with this problem.

Quantifying the soft tissue response to implanted materials

As the diversity of biomaterials increases, new developments are aimed at these materials becoming interactive rather than passive with respect to the environment they are placed in. The need accurately and reproducibly to assess the response of the body to these materials increases. Historically, quantification of tissue responses has taken many forms but with the continuing development of powerful computers, our ability to quantify the tissue response to implanted materials has become a reality. Computer systems can now analyse sections automatically and then go on to sort the huge quantities of data created, into in depth patterns and cross comparisons so that subtle changes in tissue responses can be detected and understood.

Vitrectomy for vitreomacular traction syndrome with macular detachment

PURPOSE

To describe the clinical characteristics of the vitreomacular traction syndrome with macular detachment and to report our surgical experience with this condition.

METHODS

A retrospective chart and photographic review was performed on nine patients (nine eyes) who had a symptomatic decrease in visual acuity from a macular traction retinal detachment caused by vitreomacular traction syndrome. Vitrectomy was performed in each eye to reattach the retina.

RESULTS

Intraoperative observation confirmed partial posterior vitreous separation with adherence of the posterior hyaloid to the detached retina and separation of the posterior hyaloid from the attached retina. After surgery the macula was reattached in seven eyes (78%). Visual acuity was improved in four eyes, stable in four eyes, and worse in one eye.

CONCLUSION

Macular detachment may occur secondary to vitreomacular traction syndrome. Although the retina may be reattached surgically in these cases, visual improvement may be limited by chronic detachment, premacular fibrosis, cystoid macular edema, or macular schisis.

Surgical management of submacular hemorrhage. A series of 47 consecutive cases

BACKGROUND

The development of a thick submacular hemorrhage usually carries a poor visual prognosis. The surgical removal of submacular blood may improve the otherwise poor outlook in these cases.

SUBJECTS AND METHODS

Forty-seven consecutive patients underwent vitrectomy with surgical removal of submacular hemorrhage. The patient population consisted of two consecutive groups. Group 1 (1989 to 1991) included 23 patients (20 with age-related macular degeneration [ARMD], one with idiopathic submacular hemorrhage, one with presumed ocular histoplasmosis syndrome [POHS], and one with angioid streaks) who underwent mechanical clot extraction. Group 2 (1991 to 1993) included 24 patients (19 with ARMD, two with POHS, two with arterial macroaneurysm, and one with angioid streaks) who underwent tissue plasminogen activator-assisted drainage of thick submacular hemorrhage. The dose of tissue plasminogen activator ranged from 10 to 40 micrograms. All patients had surgery within 72 hours of diagnosis.

RESULTS

In group 1, the mean size of the submacular hemorrhage was 11 disc areas (range, 1 to 16 disc areas). Mean follow-up was 40 weeks. Mean postoperative visual acuity for eyes with ARMD was 20/200. (Visual acuity improved in six eyes, was stable in seven eyes, and deteriorated in seven eyes.) All three of the eyes without ARMD had visual improvement with a mean postoperative visual acuity of 20/70. Overall, visual acuity stabilized or improved in 13 (57%) of 23 patients and decreased in 10 (43%) patients. In group 2, the mean size of the submacular hemorrhage was 11 disc areas (range, 3 to 16 disc areas). Mean follow-up was 24 weeks. Mean postoperative visual acuity for eyes with ARMD was 20/480 (visual acuity was stable in 15 eyes, improved in two eyes, and deteriorated in two eyes). Four of five eyes without ARMD had visual improvement and one was stable, with a mean postoperative visual acuity of 20/60. Visual acuity stabilized or improved in 22 (92%) of 24 patients and decreased in two (8%). The degree of clot lysis was variable.

CONCLUSIONS

Submacular hemorrhage secondary to ARMD has a poor visual prognosis, with or without surgical drainage. The addition of tissue plasminogen activator-assisted clot lysis does not appear to significantly improve the visual outcome following surgery. The determination of whether surgical intervention is appropriate in these cases requires a prospective, randomized clinical trial.

Molecular biointeractions of biomedical polymers with extracellular exudate and inflammatory cells and their effects on the biocompatibility, in vivo

The stability of biomedical polymers in physiological environments is crucial for the normal operation of devices, as well as determining their effect on the tissue response. Degradation is an important factor in polymer biocompatibility, since the environment of the human body can be aggressive to polymers. Most implanted polymers suffer degradation to some extent, and the kinetics and mechanisms of the processes can be affected significantly by various biologically active species, especially enzymes, lipids, peroxides, free radicals and phagocytic cells. The degradation of poly(caprolactone) and poly(DL-lactic acid) under controlled in vivo conditions was studied using a poly(methyl methacrylate) chamber designed to control the exposure of polymers to physiological environments. In particular they may be designed to allow access of extracellular exudate only or access to cells as well as the fluid. The chambers, sealed with filters of pore size either 0.45 micron (impervious to cells) or 3.0 microns (allowing cells to enter the chamber), were implanted subcutaneously into experimental animals for 10, 20 and 30 wk periods. Degradation and molecular interactions of the polymers were characterized by gel permeation chromatography and scanning electron microscopy. The extracellular exudate formed within the implanted chamber is active in promoting the degradation of some biomedical polymers. Inflammatory cells are involved in the biodegradation of implanted polymers by releasing biologically active species such as free radicals into the area surrounding the implant. The data have demonstrated that the hydroxyl radical is likely to be one of the main causes of polymer degradation.

Modelling the pattern of cell distribution around implanted materials

The analysis of the cellular soft tissue response has traditionally focused on using highly skilled human assessment to determine the severity or presence of a particular type of response. This has taken the form of many different assessment criteria, some even attempting some form of 'quantitative' grading index. With the complexity of this response and the availability of high performance computer systems it is not sufficient and no longer necessary to describe a tissue response subjectively. The soft tissue response to a number of implanted materials has been analysed using a combination of immunohistochemistry and image analysis to reproducibly stain and count the cells involved in a soft tissue response to implanted materials, as well as measure their position relative to the implanted material. The combination of cell count and pattern of cell distribution revealed that although the magnitude of the cellular responses changes with respect to time the position of cells with respect to an implanted material does not change significantly over time. The position of cells is controlled more by the type of implant material and the change in subject the material is implanted in.

Biodegradation of hyaluronic acid derivatives by hyaluronidase

Hyaluronic acid (salt) (HA) has been chemically modified as a biomaterial for medical applications such as controlled drug release matrices, nerve guides and wound dressings. A series of HA derivatives, which include different ester types and different degrees of esterification, have been used to investigate the stability of these materials in testicular hyaluronidase. Gel permeation chromatography and capillary viscometer have been employed to determine the size of the molecules, the former used for the water insoluble derivatives that dissolve in dimethyl sulphoxide, the latter for the water soluble samples. The preliminary experimental results indicated that the molecular weight of fully esterified hyaluronic acid (both ethyl and benzyl esters) did not decrease after treatment in the enzyme for 7 and 14 days while the water soluble partially esterified HA were degraded by the enzyme producing a sharp reduction of viscosity within minutes. These observations tend to suggest that the carboxylic groups in the beta-glucoronic acid unit are the activation centre of this enzyme and the total blockage of these groups can restrict the cleavage of beta (1-->4) glycoside bonds by this enzyme.

Granule secretion markers on fluid-phase platelets in whole blood perfused through capillary tubing

The effect of material composition and shear rate on fluid-phase platelet activation was investigated using a capillary perfusion model. Citrated whole blood was perfused along the lumens of tubes constructed from silicone, PVC, Pellethane, W124 (an experimental polyetherurethane), and glass. Platelet activation was determined by measuring the increase in alpha-granule membrane protein P-selectin (GMP-140, CD62) and the lysosomal granule membrane protein GP-53 (CD63) on fluid-phase platelets by flow cytometry. All tubes caused an increase over the negative control in the number of P-selectin and GP-53 molecules detectable on the surface of these platelets. The activation response of platelets to changes in shear rate was also investigated. It was found that lysosomal release paralleled alpha-granule release in glass, but not in Pellethane, over a range of wall shear rates (100-1,000 s-1).

Pars plana vitrectomy for treatment of stage 2 macular holes

OBJECTIVE

To assess the anatomic outcome and visual acuities at follow-up after pars plana vitrectomy in the management of stage 2 macular holes.

DESIGN

Retrospective.

SETTING

Retina Consultants, Ltd, St Louis, Mo.

PATIENTS

Thirty-three patients, aged 43 to 75 years, with stage 2 macular holes.

INTERVENTION

Total pars plana vitrectomy with separation of the posterior hyaloid membrane and injection of intraocular gas followed by postoperative face-down positioning.

MAIN OUTCOME MEASURES

Visual acuity and anatomic appearance of the macular hole.

RESULTS

Postoperatively, 20 (61%) of 33 eyes attained a visual acuity of 20/50 or greater. Twenty (61%) of 33 eyes showed an improvement in visual acuity, while nine (27%) of 33 were stable. Four (12%) of 33 eyes showed a decline in postoperative visual acuity with progression to a stage 3 macular hole. Twenty-five (76%) of 33 eyes showed stabilization or improvement in the appearance of the macular hole.

CONCLUSIONS

Pars plana vitrectomy in conjunction with postoperative intraocular gas tamponade may result in visual and anatomic stabilization or improvement in eyes with stage 2 macular holes. However, because of limited natural history data, it is unknown whether these results are any better than those that might occur without surgery.

Plasma recalcification as a measure of contact phase activation and heparinization efficacy after contact with biomaterials

The rate of plasma clotting was measured in order to investigate two different processes. In both cases normal, pooled platelet-poor plasma was used as a substrate for measurement of clotting. The intrinsic coagulation pathway was studied by bringing a variety of biomaterials into contact with a plasma aliquot and observing the rate of clotting diminish by virtue of factor XII activation. The efficacy of heparinization was investigated by measuring the increase in clotting time of a plasma aliquot during biomaterial contact. In both cases, clotting time was measured turbidometrically. Marked differences in intrinsic pathway activation were observed between a variety of materials. There were clear differences between the materials and the negative and positive controls. The assay showed that heparinized materials could be distinguished from non-heparinized materials and a non-activated plasma control.

Human neutrophil chemokinesis and polarization induced by hyaluronic acid derivatives

Neutrophils and macrophages are known to undergo significant modifications in their morphology and basal metabolism in response to chemical factors, in particular changes in the shape, movement, phagocytic activity and degranulation. These phenomena often involve an increase in chemokinesis and cellular secretory activity, usually expressed in antimicrobial activity. Once activated, the cells can move quickly towards the source of the stimulus, where they produce and release great amounts of enzymes (e.g. proteases, hydrolases, lysozyme) and reactive oxygen metabolites (e.g. O2-., H2O2, OH.). This study has examined the ability of surfaces of selected biomaterials to influence neutrophil morphology and locomotion. The surface of two films derived from hyaluronic acid derivatives were compared with that of glass. The two hyaluronic acid derivatives, despite having a similar chemical structure, were shown to interact with human neutrophils in different ways. A hyaluronic acid ethyl ester stimulated the whole population of neutrophils to take up a non-spherical morphology (polarize) and to move with a velocity similar to that of N-formyl-methionine-leucine-phenylalanine-stimulated cells on a glass surface. In contrast, only 44% of the examined cells on the surface of hyaluronic acid benzyl ester were polarized and their mean speed was only slightly higher with respect to that found with non-stimulated cells on glass. Moreover, while on the benzyl ester and on glass a correlation between neutrophil circularity (i.e. the shape of the cell) and cell speed was found, the ethyl ester did not show any correlation.

The economics of advanced biomaterials

A patient who has previously lost an eye through trauma develops a cataract in his remaining eye. Two types of intraocular lens are available for his treatment, one of modest cost, which is effective in all but a few high-risk patients, the other much more expensive, which gives marginally better results on average, but better performance in those with diabetes or glaucoma. Should the higher-cost lens be used even if there is no direct evidence that it will do better in this patient who does not have these conditions, or is it ethically justified to use the lower-cost lens even though failure would result in the total loss of sight? This case is used as the basis of a discussion on the use of high-cost materials and medical devices.

Mechanisms of polymer degradation in implantable devices. 2. Poly(DL-lactic acid)

The hydrolytic degradation of poly(DL-lactic acid) in an aqueous environment in which hydroxyl radicals have been generated has been investigated. Different methods (gel permeation chromatography, differential scanning calorimetry, and scanning electron microscopy) were employed to study the mechanisms of degradation of this amorphous physiologically absorbable polymer. The data indicated that the hydroxyl radical is likely to be a significant factor in the degradation of this polymer.

Biocompatibility of glass ionomer cements

Glass ionomer cements (GICs) are widely used in the dental field and are increasingly being considered as materials with potentially good osteogenic properties. This paper details a comprehensive biocompatibility evaluation of a number of GICs. These include conventional, commercially available materials, novel formulations and a new light cured material. The experimental programme entailed in vitro cell culture studies using direct contact and extraction tests and an in vitro rat model in which the GICs were in intimate contact with bone for periods up to 8 wk. The results demonstrate clear differences between the materials and in particular highlight the poor cellular response to the light cured material. Methylthiazolyldiphenyl tetrazolium assay demonstrates stimulation of cell growth by some GIC formulations and indicates that cytotoxic leachable agents can be removed from others. The results obtained following implantation into bone are comprehensively presented using photomicrographs. New bone formation with time is demonstrated with a number of formulations.

Mechanisms of polymer degradation in implantable devices. I. Poly(caprolactone)

Poly(caprolactone) is a biodegradable aliphatic (poly(alpha-hydroxy acid), with important applications in the field of human therapy, due to its biocompatibility and bioresorbability. The degradation of poly(alpha-hydroxy acids) depends on chemical hydrolysis, but there is much interest in the precise mechanisms, including the role of free radicals, especially oxygen free radicals and their role in human disease. The hydrolytic degradation of poly(caprolactone) in aqueous environments was used as the control in a study of the effects of hydroxyl radicals in aqueous solutions. Different methods (GPC, DSC, SEM) were employed to investigate the mechanism of degradation of this semicrystalline physiologically absorbable polymer. The data indicate that hydroxyl radical is likely to be a major factor in the degradation of this polymer.

Quantitative in vivo assessment of the tissue response to dermal sheep collagen in abdominal wall defects

We quantified the tissue response, tissue organization and patency of biodegradable patches for the repair of abdominal wall defects. We used dermal sheep collagen, cross-linked with hexamethylenediisocyanate in a model. The collagen patches were implanted either untreated or plasma polymerized with tetrafluoroethylene (TFE), to improve the properties of the patch for bowel adhesion and rate of degradation. The implants with surrounding tissue were retrieved after 3 d, 1, 2, 4, 6 and 8 wk, then sectioned and stained specifically for macrophages, neutrophils, T-lymphocytes and endothelium. Only macrophages and neutrophils were observed in the implant and surrounding tissue, with different antigen expression in the macrophages. This was found to be dependent on whether the macrophages were found within the implant or in the surrounding tissue. The neutrophils and macrophages were assessed using image analysis techniques to quantify the tissue responses to treated and untreated collagen, enabling comparison of the respective tissue responses. No significant differences were found between the two forms of this collagen. Infection played a key role in the severity of the tissue response around both types of implants, resulting in large variations in cell counts at each time period. Treating the collagen with TFE did not significantly improve its performance in this application.

Does the fibrin coat around a central venous catheter influence catheter-related sepsis?

The purpose of this study was to determine whether the fibrin sheath that develops around an intravenous silicone catheter influences catheter-related sepsis. A rat model with a central intravenous silicone catheter was used. Staphylococcus aureus, dose 1 x 10(7) colony forming units (cfu), were injected via the tail vein, either immediately after catheter insertion (group 1, n = 23) or after the catheter had been in situ for at least 7 days (group 2, n = 22). Blood cultures were done on at 24 hours and 7 days. Animals were killed on day 7 and the catheter was removed for culture (Maki and broth) and scanning electronmicroscopy (SEM). The was no significant difference (P > .05) between the number of positive blood cultures in groups 1 and 2 at 24 hours (16 v 9) and 7 days (12 v 6). In group 1 there were significantly more positive catheter cultures by both methods (23 v 16 in group 2; P < .05) and more cfu/per centimeter catheter (group 1 mean, 520, range, 197 to 600; group 2 mean 195, range 9 to 600; P < .001). In group 1, 12 animals had catheter sepsis compared with 5 in group 2 (P = NS). On SEM a fibrinous sheath was identified on all catheters removed on day 7 but not on 5 catheters inserted and removed after 10 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Schistosoma mansoni: membranes from adult worms reversibly perturb shape, volume, and membrane organization of intact human red blood cells

Adult forms of Schistosoma mansoni ingest host (human) red blood cells (RBCs). To elucidate potential mechanisms by which contact with adult parasites perturbs RBC membranes, we studied the effects of the membrane fraction of isolated schistosomes on RBC shape, volume, potassium ion content, and phospholipid and transmembrane protein lateral mobility. S. mansoni-treated RBCs exhibited rapid but spontaneously reversible shape change from discocytes to spheroechinocytes, reversible decrease in cell volume, and rapid loss of intracellular potassium ions. Treated RBCs also showed rapid but spontaneously reversible immobilization of membrane phospholipids and of band 3, the major transmembrane protein. These data suggest that components of adult S. mansoni membranes can perturb host RBC volume and membrane organization. In the absence of RBC lysis, RBC metabolic and repair mechanisms can reverse these effects.

Image analysis in the evaluation of biomaterials

An examination regime, based on a computer-aided image analysis system, has been developed for the quantitative evaluation of the local tissue response to biomaterials. This procedure involves the immunoenzymic staining of tissue sections using monoclonal antibodies specific for certain inflammatory cell types. An avidin-biotin-horseradish peroxidase staining method is used to identify antibody binding sites and the sections are assayed using a computer-aided image analysis system. This regime facilitates the rapid and accurate measurement of 30 cell related parameters in sections stained for macrophages, polymorphonuclear leucocytes, and other cells.

Fleas (Siphonaptera) infesting giant kangaroo rats (Dipodomys ingens) on the Elkhorn and Carrizo Plains, San Luis Obispo County, California

The giant kangaroo rat, Dipodomys ingens (Merriam), has a limited distribution in the San Joaquin Valley, CA. Because of reductions in its geographic range, largely resulting from humans, the species was listed as an endangered species in 1980 by the California Fish and Game Commission. As part of a study of the community ecology of southern California endangered species, including D. ingens, we were able to make flea collections from the rats when they were trapped and marked for population studies. All but one of the fleas collected from the D. ingens in this study were Hoplopsyllus anomalus, a flea normally associated with ground squirrels (Sciuridae). It has been suggested that giant kangaroo rats fill the ground squirrel niche within their range. Our data indicate that this role includes a normal association with Hoplopsyllus anomalus.

The characteristics and performance of dentine bonding agents

Several attempts have been made to synthesise dentine bonding systems, but low bonding strength, increased variance, toxicity and poor hydrolytic stability were some of the disadvantages excluding them from being widely approved. However, many dentine bonding systems are considered to be biocompatible and have become commercially available. These adhesives are thought to have one or two bifunctional agents where one part of the molecule is intended to bond to the inorganic part of the dentine (calcium ions of the apatite), or to the organic part of the dentine (amino and hydroxy groups of the collagen), and the methacrylate part of the molecule is intended to copolymerise with the restorative resin. This review demonstrates that further work is needed to achieve the synthesis of novel dentine bonding agents which bond chemically to dentine by strong covalent bonds, and which are hydrolytically durable and non-toxic to the oral environment.

Non-invasive magnetic resonance imaging of the soft tissue response to a biomaterial

Magnetic resonance imaging (MRI) has been employed to visualize the tissue response to hydrogel implants in rats. High contrast MR images of the implant site were obtained. Distinct tissue variations in the MR images have been observed. These can be attributed to either the surgical procedure or the application of a tissue irritant to produce inflammation and have been verified histologically. This study demonstrates that MRI is potentially a useful tool for the non-invasive in-vivo evaluation of biomaterials.

Synolite as a base resin for dental composites and related biomaterials

Synolite resin was analysed using FTIR, NMR and HPLC to determine its components and purity. The resin was found to be predominantly BIS-GMA containing traces of its two isomers. The analysis indicated that there was no unreacted methacrylic acid or other impurities.

Outcome and cost analysis of scheduled versus emergency scleral buckling surgery

BACKGROUND

Retinal detachments are usually considered to be a surgical emergency. However, there are additional risks and costs for unnecessary emergency surgeries. The purpose of this study is to evaluate whether the conventional wisdom for treating all retinal detachments as emergencies needs to be re-examined.

METHODS

Forty-eight patients who had an emergency scleral buckle and 89 patients who had a scheduled procedure were randomly selected from 884 consecutive patients who had a primary scleral buckling procedure during a 4 1/2-year period. The medical records of each patient were used to obtain detailed information related to prognosis. The visual acuity measurements of each patient, taken 6 months after the procedure, were obtained from the records of the ophthalmologist following the patient. Linear regression analysis was used to compare the final visual outcome for patients who had emergency surgery with patients who had scheduled surgery after taking into account patient factors related to prognosis.

RESULTS

Patients selected for emergency surgery had better visual prognoses than scheduled patients but had the same risk of systemic complications and the same extent of detachment if the macula was not involved. None of the 18 patients with an attached macula experienced macular involvement while awaiting scheduled surgery. There were no differences between emergency and scheduled patients in ocular or systemic complications, rate of reattachment, rate of decreased visual acuity after surgery, visual outcome adjusted for prognosis, or, since 1985, length of hospital stay. A greater cost was incurred for the patients having emergency surgery due to difference in pay scales for support personnel.

CONCLUSIONS

Because the study is not large and the patients were not randomized to treatment, the results are not definitive. However, they suggest that emergency surgery is unnecessary for many patients with a detached retina.

Recombinant basic fibroblast growth factor in red blood cell ghosts accelerates incisional wound healing

The pharmacological manipulation of wound healing with locally applied growth factors is now a practical possibility. The effect of topical applications of recombinant basic fibroblast growth factor (bFGF) on the strength and cellularity of healing incisional rat skin wounds was investigated. Applications of bFGF in a simple vector (either a collagen suspension or saline) were not associated with any positive effects on wound breaking load at 7 days after injury in comparison with vector-treated control wounds; at the highest dose of 50 micrograms per wound, breaking loads were significantly decreased from a mean(s.e.m.) of 287(22) g/cm2 in controls to 201(23) g/cm2 (P < 0.005). Increasing doses of applied peptide were paralleled by increasing wound cellularity. Delay of bFGF release at the site of application was achieved by encapsulation into red blood cell ghosts. Wounds treated with bFGF in such ghosts were 50 per cent stronger than paired control wounds (388(27) versus 256(28) g/cm2, P < 0.002) 7 days after injury. Treated wounds were significantly more cellular at 4 days than paired control wounds. Topical applications of bFGF applied at the time of injury exert a positive effect on incisional wound strength only when a vector that delays release is used.

Surgical management of subfoveal choroidal neovascularization

BACKGROUND

Subfoveal choroidal neovascularization (CNV) usually is associated with a poor visual prognosis. Laser photocoagulation of certain subfoveal membranes secondary to age-related macular degeneration (ARMD) appears preferable to observation based on recent Macular Photocoagulation Study (MPS) findings but is associated with decreased vision. The authors explored the use of vitreoretinal surgical techniques as an alternative method of eradicating subfoveal CNV.

METHODS

After vitrectomy, a small retinotomy technique was used to extract or disconnect from the choroidal circulation subfoveal CNV in 58 eyes. There were 33 eyes with ARMD, 20 eyes with presumed ocular histoplasmosis, and 5 eyes with miscellaneous etiologies. Five eyes also received subfoveal RPE patches.

RESULTS

With limited follow-up, significant improvement in vision (defined as 2 Snellen lines) was achieved in 7 of 22 eyes with ARMD CNV removal (1 eye 20/20), 0 of 4 eyes with ARMD CNV removal and RPE patches, and 1 of 7 eyes with ARMD CNV disconnection. Significant improvement was achieved in 6 of 16 eyes with presumed ocular histoplasmosis removal and 0 of 4 eyes with presumed ocular histoplasmosis CNV disconnection. In 5 eyes with miscellaneous CNV, 2 improved (20/20 and 20/40). CNV recurred in 29%.

CONCLUSIONS

Some patients with subfoveal CNV appear to benefit from surgical removal. Only rarely do eyes with ARMD improve. Longer-term follow-up and refined case selection are required before this approach can be widely recommended.

Stimulation of neutrophil movement by metal ions

The interaction between corrosion products of metallic implants and the surrounding tissue is important in determining the biocompatibility of the implant, in particular the interaction of corrosion products with inflammatory cells such as neutrophils and macrophages. Such cells are capable of releasing enzymes and high-energy oxygen radicals which can damage the tissue. Clearly, any factors that influence cell movement to the implant site could influence the biocompatibility of the implant. The present study examined the influence that copper and nickel ions had on neutrophil locomotion. Both copper and nickel ions stimulated a proportion of the neutrophil population to take up a nonspherical morphology and to locomote. These metal ion stimulated cells have higher circularity values and move slower than neutrophils incubated with FMLP. For both FMLP and nickel ion stimulated cells, there is a correlation between the speed of neutrophil locomotion and neutrophil circularity; as the neutrophil circularity value decreases, the speed of locomotion increases.