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Biomedical subjects

L G Harris

Publications and source records attributed to L G Harris.

13 recordsLinked to original sources
PubMed2007

Mimicking a Stenocara beetle's back for microcondensation using plasmachemical patterned superhydrophobic-superhydrophilic surfaces.

A simple two-step plasmachemical methodology is outlined for the fabrication of microcondensor surfaces. This comprises the creation of a superhydrophobic background followed by pulsed plasma deposition of a hydrophilic polymer array. Microcondensation efficiency has been explored in terms of the chemical nature of the hydrophilic pixels and their dimensions. These results are compared to the hydrophilic-hydrophobic pattern present on the Stenocara beetle's back, which is used by the insect to collect water in the desert. Potential applications include fog harvesting, microfluidics, and biomolecule immobilization.

Animals↗
PubMed2006

Bacteria and cell cytocompatibility studies on coated medical grade titanium surfaces.

Acute and chronic osteomyelitis caused by staphylococci can be difficult to treat by conventional means and often has marked consequences for the patient. Current methods of treatment involve the use of systemic antibiotics, the local implantation of nondegradable drug carriers, and surgical debridement. A possible solution that could prevent initial bacterial adhesion could be to modify the implant surface with an antimicrobial coating while maintaining biocompatibility to host cells. This study describes the cytocompatibility evaluation of different coatings (poly(D,L-lactide) (PDLLA), politerefate (PTF), calcium phosphate/anodic plasma-chemical treatment (CaP/APC), polyurethane (PU), and polyvinylpyrollidone (PVP) on titanium surfaces with and without chlorhexidine diacetate (CHA) to Staphylococcus aureus, Staphylococcus epidermidis, and hTERT human fibroblasts. Surface characterization of the coatings showed no significant variation in the roughness or hydrophobicity of the coated surfaces, except the CaP/APC surface that was porous yet the smoothest, and PVP, PVP+CHA, and CaP/APC+CHA that were more hydrophilic in nature than the others. On the surfaces without CHA, both staphylococcal strains and spread fibroblasts were observed, but on the CHA impregnated surfaces few bacteria and no intact fibroblasts were seen. Flow cytometry found fewer bacteria in the media and on the surfaces containing CHA in comparison to the surfaces without CHA. The release kinetics varied from slow (over 200 h) to burst release: PDLLA>PTF>PU>CaP/APC=PVP. This study showed that PDLLA and PTF have the best potential as coatings on implants for drug delivery, as they were cytocompatible to hTERT fibroblasts, eluted CHA effectively, and passed mechanical testing. The actual release kinetics of PDLLA and PTF are important, as the amount of CHA present should remain above the minimal inhibitory concentration value for a limited time before disappearing completely.

Cell Line, Transformed↗
PubMed2006

Biodegradable polyurethane cytocompatibility to fibroblasts and staphylococci.

Biodegradable polyurethanes have potential for use as implantable devices (orthopedic, maxillofacial, cardiovascular, wound dressing and plastic surgery) because of their controllable elasticity, and the possibility of changing their chemistry and structure. Studying bacterial and cell adhesion to polyurethanes helps to determine surface cytocompatibility and suitability for in vivo trials. Staphylococcus aureus, Staphylococcus epidermidis and hTERT human fibroblast cells were used to determine the cytocompatibility of experimental biodegradable polyurethanes (PUs) with different hydrophobic-to-hydrophilic (pho:phi) content ratios (100% pho, 70% pho, and 30% pho). Poly(L/DL-lactide) 70/30% (PLDL) and Thermanox were used as control surfaces. Surface characterization using noncontact profilometry, contact angles, and scanning electron microscopy (SEM) showed that the three PU surfaces, PLDL, and Thermanox have different properties. On the 100% PU and 30% PU surfaces, hTERT cells spread less in comparison to the 70% PU, PLDL, and Thermanox surfaces. The adsorption of fibronectin to the surfaces had no effect on the adhesion and spreading of hTERT cells when compared to the uncoated surfaces. The trend for S. aureus was the most adhered on the 70% PU and 30% PU, then Thermanox, followed by 100% PU and PLDL, respectively. The amount of S. epidermidis adhesion followed the trend of the most on 70% PU, then 100% PU, then 30% PU and PLDL, and the least on Thermanox. These results suggest that the 70% PU surface is cytocompatible to hTERT fibroblasts, while the 100% PU and 30% PU were not. All surfaces encouraged S. aureus and S. epidermidis colonization, particularly the 70% PU.

Bacterial Adhesion↗
PubMed2006

Biofilm formation in medical device-related infection.

Medical device-associated infections, most frequently caused by coagulase-negative staphylococci, especially Staphylococcus epidermidis, are of increasing importance in modern medicine. Regularly, antimicrobial therapy fails without removal of the implanted device. The most important factor in the pathogenesis of medical device-associated staphylococcal infections is the formation of adherent, multilayered bacterial biofilms. There is urgent need for an increased understanding of the functional factors involved in biofilm formation, the regulation of their expression, and the interaction of those potential virulence factors in device related infection with the host. Significant progress has been made in recent years which may ultimately lead to new rational approaches for better preventive, therapeutic, and diagnostic measures.

Adhesins, Bacterial↗
PubMed2004

Staphylococcus aureus adhesion to titanium oxide surfaces coated with non-functionalized and peptide-functionalized poly(L-lysine)-grafted-poly(ethylene glycol) copolymers.

Implanted biomaterials are coated immediately with host plasma constituents, including extracellular matrix (ECM); this reaction may be undesirable in some cases. Poly(L-lysine)-grafted-poly(ethylene glycol) (PLL-g-PEG) has been shown to spontaneously adsorb from aqueous solution onto metal oxide surfaces, effectively reducing the degree of non-specific adsorption of blood and ECM proteins, and decreasing the adhesion of fibroblastic and osteoblastic cells to the coated surfaces. Cell adhesion through specific peptide-integrin receptors could be restored on surfaces coated with PLL-g-PEG functionalized with peptides of the RGD (Arg-Asp-Gly) type. To date, no study has examined the effect of surface modifications by PLL-g-PEG-based polymers on bacterial adhesion. The ability of Staphylococcus aureus to adhere to the ECM and plasma proteins deposited on biomaterials is a significant factor in the pathogenesis of medical-device-related infections. This study describes methods for visualizing and quantifying the adhesion of S. aureus to smooth and rough (chemically etched) titanium surfaces without and with monomolecular coatings of PLL-g-PEG, PLL-g-PEG/PEG-RGD and PLL-g-PEG/PEG-RDG. The different surfaces were exposed to S. aureus cultures for 1-24h and bacteria surface density was evaluated using scanning electron microscopy and fluorescence microscopy. Coating titanium surfaces with any of the three types of copolymers significantly decreased the adhesion of S. aureus to the surfaces by 89-93% for PLL-g-PEG, and 69% for PLL-g-PEG/PEG-RGD. Therefore, surfaces coated with PLL-g-PEG/PEG-RGD have the ability to attach cells such as fibroblasts and osteoblasts while showing reduced S. aureus adhesion, resulting in a selective biointeraction pattern that may be useful for applications in the area of osteosynthesis, orthopaedic and dental implantology.

Bacterial Adhesion↗
PubMed2004

Staphylococcus aureus adhesion to different treated titanium surfaces.

Staphylococcus aureus is a major pathogen, associated with medical-device related infections. Converting biomaterial surfaces into non-interactive surfaces requires a specific surface/interface design. One approach is to polish the surface, and a second is to coat the surface with an antimicrobial or protein resistant coating. This study showed that polishing a titanium surface or coating titanium with various treatments that decreased the surface's coefficient of friction, had no significant effect on minimising S. aureus adhesion to these surfaces under static conditions in comparison to standard medical grade titanium. The cell promoting coating, TAST, was found to increase the S. aureus density on its surface as expected. The only coating that significantly decreased the density of adhering S. aureus was the titanium surface coated with sodium hyaluronate. Thus such a coating could have potential use as a coating for ostoesynthesis, orthopaedic or dental implants.

Anti-Bacterial Agents↗
PubMed2002

An introduction to Staphylococcus aureus, and techniques for identifying and quantifying S. aureus adhesins in relation to adhesion to biomaterials: review.

The ability of Staphylococcus aureus to adhere to the extracellular matrix and plasma proteins deposited on biomaterials is a significant factor in the pathogenesis of orthopaedic-device related infections. S. aureus possesses many adhesion proteins on its surface, but it is not known how they interact with each other to form stable interactions with the substrate. A novel method was developed for extracting adhesins from the S. aureus cell wall, which could then be further analysed. The protocol involves using a FastPrep instrument to mechanically disrupt the cell walls resulting in native cell walls. Ionically and covalently bound proteins were then solubilised using sodium dodecyl sulphate (SDS) and lysostaphin, respectively. Western blot analysis of covalently bound proteins using anti-protein A and anti-clumping factor A sera showed that S. aureus produces most surface proteins in early growth, and less in post-exponential and stationary growth. Immuno-gold labelling of protein A, and clumping factor A was observed all over the bacteria and showed no distinct surface distribution pattern. However, this labelling showed expression of surface associated proteins varied in a growth-phase dependent and cell-density dependent manner.

Journal Article↗
PubMed2001

Measurement of fibroblast and bacterial detachment from biomaterials using jet impingement.

Fibroblast and Staphylococcus aureus detachment strength from orthopaedic alloys and a tissue culture plastic (Thermanox) have been investigated with jet impingement. For S. aureus, unlike fibroblasts, detachment is caused more by pressure than shear. For these biomaterials, detachment strength is much higher for S. aureus than fibroblasts. Comparing materials under equivalent flow conditions, S. aureus attach to stainless steel and titanium with equal strength and more strongly than to Thermanox. For fibroblasts, detachment strength from all materials was similar. Fibroblast detachment strength from these biomaterials substantially decreases with time at equal flow rates and increases with flow rate at equal exposure times. Detachment strength is very similar for 3T3 and L929 fibroblasts on Thermanox for equivalent flow rate/time combinations, though enhanced adhesion of 3T3 cells was often noted for metals. Time effects are less evident for S. aureus. S. aureus adhesion to metals is more affected by flow rate than fibroblast adhesion.

Alloys↗
PubMed2000

Influence of parathyroid hormone, calcitonin, 1,25(OH)2 cholecalciferol, calcium, and the calcium ionophore A23187 on erythrocyte morphology and blood viscosity.

Parathyroid hormone and calcitonin, both endocrine modulators of calcium homeostasis, may influence blood rheology. Parathyroid hormone is known to reduce erythrocyte survival, leading to anemia. Calcitonin has been found to have some vascular effects. We have analyzed the Influence of parathyroid hormone (10(-7) to 10(-10) mol/L), calcitonin (10(-6) to 10(-12) mol/L), 1,25(OH)2 cholecalciferol (10(-7) to 10(-10) mol/L), additional calcium in plasma (+1 and 2 mmol/L), and the calcium lonophore A23187 (50 micromol/L) on erythrocyte morphology and blood viscosity at high shear rate (94 s(-1)) and low shear rate (0.1 s(-1)) in vitro. The loading of erythrocytes with calcium by the ionophore A23187 produced a marked echinocytic shape transformation, an increased blood viscosity at high shear rate caused by decreased deformability of these cells, and a decreased viscosity at low shear rate caused by decreased aggregation of echinocytes. In contrast, increasing plasma calcium concentrations, parathyroid hormone, calcitonin, and 1,25(OH)2 vitamin D3 had no effect on erythrocyte morphology and blood viscosity. We conclude that an increase in intraerythrocytic calcium leads to severe echinocytosis and altered blood viscosity. The endocrine modulators of calcium homeostasis--namely, parathyroid hormone, calcitonin, and 1,25(OH)2 vitamin D3--apparently do not influence intraerythrocytic calcium to a significant degree and have, therefore, no influence on cell morphology and blood viscosity.

Blood Viscosity↗
PubMed1999

Influence of nitrovasodilators and endothelin-1 on rheology of human blood in vitro.

1. The shear stress of flowing blood profoundly influences the release of endothelium-dependent vasodilative and constrictive factors. Conversely, the influence of these mediators such as nitric oxide (NO) or endothelin-1 (ET-1) on blood rheology remains elusive. In the present study the influence of nitrovasodilators and ET-1 on red blood cell (RBC) shape and whole blood viscosity were investigated. 2. Incubation of whole blood with sodium-nitroprusside (SNP, 10-5 - 10-2 M), glyceryl trinitrate (GTN, 0.0001 - 0.1 mg mL-1), S-nitroso-N-acetylpenicillamine (SNAP, 10-6 - 10-3 M), and the active metabolite of molsidomine (SIN-1, 10-6 - 10-3 M), but not molsidomine (10-6 - 10-3 M), resulted in significantly increased amounts of methaemoglobin, indicating a relevant interaction with RBCs. Treatment with SNP at 10-2 M induced a marked echinocytosis (morphological index: 2.23+/-0.98 vs -0.17+/-0.10; P<0.001) and increased blood viscosity (haematocrit 45%) at a high shear rate of 94.5 s-1 (6.46+/-0.60 vs 5.07+/-0.35 mPa.s; P<0.01) and a low shear rate of 0.1 s-1 (88.6+/-36.8 vs 42.1+/-11.7 mPa.s; P<0.01). Echinocytosis was probably due to cyanide accumulation. SIN-1 at 10-3 M slightly decreased high shear viscosity (4.88+/-0.28 vs 4. 95+/-0.30 mPa.s; P<0.05). SNAP at 10-3 M slightly increased both high (5.14+/-0.23 vs 5.05+/-0.24 mPa.s; P<0.01) and low shear (53.9+/-7.2 vs 51.2+/-5.9 mPa.s; P<0.05) viscosity. Molsidomine and GTN failed to influence whole blood viscosity. ET-1 (10-9 - 10-6 M) had no effect on RBC shape and viscosity. 3. We conclude that the most important modulators of vascular tone, NO and ET-1, do not affect RBC shape and blood viscosity, which is important from both a physiological and a pharmacological point of view.

Adult↗
PubMed1998

Spinal and combined spinal epidural techniques for labor analgesia: clinical application in a small hospital.

Providing safe and effective analgesia to laboring parturients presents a challenge to anesthesia providers in small hospitals. The necessary time commitment and additional staff needed to provide coverage for the obstetrical area can strain resources. Offering the spinal opioid block as the first choice for labor analgesia and the combined spinal epidural block in selected cases permits a labor anesthesia service to address the needs of the community hospital. Sufentanil injected into cerebral spinal fluid provides effective analgesia for 124 minutes. Adding 2.5 mg of bupivacaine further increases effective analgesia time to 170 minutes. The combined spinal epidural block offers the advantages of spinal opioid analgesia but with the flexibility of having an epidural catheter in place. The epidural catheter can be dosed intermittently for parturients in whom labor is prolonged, who require surgical manipulation for vaginal delivery, or who require cesarean section for delivery. By offering both blocks to laboring parturients, the appropriate block can be applied in each situation.

Analgesia, Epidural↗
PubMed1981

An infraciliary network in statocyst hair cells.

Ultrastructural analysis of the statocyst, a primitive vestibular organ, of the nudibranch mollusc Hermissenda crassicornis, indicates that in addition to the basal foot, there is an infraciliary rootlet system between basal bodies of adjacent sensory cilia. These rootlets project perpendicularly from the basal bodies and parallel to the cell surface in an astral array. A polarity within the network also appears to exist; the array is longest and most extensive on the side of the basal body directed away from the cell centre, but the overall arrangement of the basal bodies indicates a multidirectional sensitivity for each of the 13 sensory cells. This rootlet system, in conjunction with the attachment system of the basal bodies to the cell membrane (button anchors), may serve an integrative function for the mechanical stimuli experienced by sensory cells and/or be involved with their transductive processes by maximizing the stress to, and membrane distortion of, the transductive site caused by weighting of the cilia. Evidence was also obtained for the intracellular synthesis of statoconia by the nonsensory supporting cells.

Animals↗