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PubMed2005

Effect of hirudin versus heparin on hemocompatibility of blood contacting biomaterials: an in vitro study.

Hirudin serves as an alternative anticoagulant for extracorporeal blood circulation. Comparing anticoagulation with hirudin (2.5 or 5.0 microg/mL) and heparin (2.0 or 4.0 IU/mL) human blood was circulated in a modified 'Chandler System' using PVC-tubes for 2 hours at 37 degrees C. Activation of coagulation (thrombin-antithrombin III-complex, prothrombin fragment 1+2 and D-Dimer), platelet (platelet factor 4 - PF4) and complement systems was analyzed. Both heparin concentrations and 5.0 microg/dL hirudin led to as significantly less activated plasmatic coagulation as 2.5 microg/dL hirudin. Decreased levels of PF4 and anaphylatoxin C5a (p<0.05) as well as terminal complement complex demonstrated improved hemocompatibility after anticoagulation with heparin in contrast to hirudin. Because initial coagulation cascade, platelet activation and complement activation is less influenced by hirudin than by heparin, hemocompatibility is more dependent on the characteristics of the biomaterials used. This predestines hirudin as anticoagulant for in vitro studies analyzing hemocompatibility of biomaterials or surface modifications.

Analysis of Variance↗

PubMed2006

Attachment and growth of fibroblasts on poly(L-lactide/epsilon-caprolactone) scaffolds prepared in supercritical CO2 and modified by polyethylene imine grafting with ethylene diamine-plasma in a glow-discharge apparatus.

In this study, a copolymer of L-lactide and epsilon-caprolactone (Mn: 73,523, Mw: 127,990 and PI: 1.74) was synthesized by ring-opening polymerization by using stannous octoate as the catalyst. FTIR, 1H-NMR and DSC confirmed the copolymer formation. The copolymer films were prepared and a novel method was developed to produce highly porous sponges for potential use in tissue engineering. Films were subjected to supercritical CO2 at 3300 psi and 70 degrees C to create porous structures for production of possible tissue engineering scaffolds. The pore sizes were in the range of 40-80 microm. The copolymer films were pre-wetted with polyethylene imine (PEI) and then treated with ethylene diamine (EDA)-plasma in glow-discharge apparatus. Gas plasma surface modification of three-dimensional scaffolds fabricated by supercritical carbon dioxide technique was demonstrated to enhance cell adhesion, proliferation, and differentiation over 6 days in culture using L929 fibroblast cell line. Alkaline phosphatase (ALP) activity and glucose uptake in cell culture medium were followed in the cell culture experiments. Fibroblastic cell attachment and growth on the EDA-plasma treated scaffolds were rather low. However, both cell attachment and growth were significantly increased by PEI pre-treatment before EDA-plasma. The changes in ALP activity and glucose uptake also supported the cell growth behavior on these PEI and EDA-plasma treated scaffolds.

Carbon Dioxide↗

PubMed2000

Effects of double cross-linking technique on the enzymatic degradation and calcification of bovine pericardia.

The strength, resorption rates, and biocompatibility of collagenous biomaterials are profoundly influenced by the method of cross-linking. The in vitro and in vivo calcification and enzymatic degradation of bovine pericardia (BP) after a series of surface modifications were studied as a function of exposure time. Collagenase degradations of modified BP were monitored by scanning electron microscopy and tensile strength measurements. Bovine pericardium was modified by a combination of different tissue fixatives such as glutaraldehyde (GA), carbodiimide (EDC), diisocyanate (HMDIC), and polyethylene glycol (PEG). GA-PEG-EDC-PEG and GA-PEG-HMDIC-PEG combination treated BP retained maximum stability in collagenase digestion compared to GATBP. In vitro calcification studies and in vivo rat subcutaneous implantations of modified pericardium have shown substantial reduction in the calcification of double cross-linked BP with PEG modification. Further, the biocompatibility aspects of pericardial tissues were established by platelet adhesion and octane contact angle. It seems that cross-links involving amino and carboxyl residues may provide new ways of controlling biodegradation and calcification.

Animals↗

PubMed1999

Biomedical applications of polyurethanes: a review of past promises, present realities, and a vibrant future.

Polyurethanes, having extensive structure/property diversity, are one of the most bio- and blood-compatible materials known today. These materials played a major role in the development of many medical devices ranging from catheters to total artificial heart. Properties such as durability, elasticity, elastomer-like character, fatigue resistance, compliance, and acceptance or tolerance in the body during the healing, became often associated with polyurethanes. Furthermore, propensity for bulk and surface modification via hydrophilic/hydrophobic balance or by attachments of biologically active species such as anticoagulants or biorecognizable groups are possible via chemical groups typical for polyurethane structure. These modifications are designed to mediate and enhance the acceptance and healing of the device or implant. Many innovative processing technologies are used to fabricate functional devices, feeling and often behaving like natural tissue. The hydrolytically unstable polyester polyurethanes were replaced by more resistant but oxidation-sensitive polyether polyols based polyurethanes and their clones containing silicone and other modifying polymeric intermediates. Chronic in vivo instability, however, observed on prolonged implantation, became a major roadblock for many applications. Presently, utilization of more oxidation resistant polycarbonate polyols as soft segments, in combination with antioxidants such as Vitamin E, offer materials which can endure in the body for several years. The applications cover cardiovascular devices, artificial organs, tissue replacement and augmentation, performance enhancing coatings and many others. In situ polymerized, cross-linked systems could extend this biodurability even further. The future will expand this field by revisiting chemically-controlled biodegradation, in combination with a mini-version of RIM technology and minimally invasive surgical procedures, to form, in vivo, a scaffold, by delivery of reacting materials to the specific site in the body and polymerizing the mass in situ. This scaffold will provide anchor for tissue regeneration via cell attachment, proliferation, control of inflammation, and healing.

Animals↗

PubMed2005

Characterization by electron spin resonance spectroscopy of reactive oxygen species generated by titanium dioxide and hydrogen peroxide.

The influence of reactive oxygen species (ROS) on the surface modification of titanium implants and osseointegration is unclear. The aim of this study was to evaluate the ability of titanium dioxide (TiO2) to generate ROS in the presence of H2O2 and to determine whether any ROS thus generated play a role in osseointegration, as measured by electron spin resonance (ESR) spin-trapping with 5,5-dimethyl-1-pyrolline-N-oxide (DMPO). We demonstrate that TiO2 together with H2O2 generated hydroxyl radicals (HO*), as shown by a time-dependent increase in the spin concentration of the ESR signal for the DMPO-OH spin adduct, indicating HO* generation. Interestingly, irradiated TiO2 with H2O2 generated the superoxide (O2*-), as shown by an increase in the spin concentration of the signal for the DMPO-OOH spin adduct, indicating O2*- generation during the period of irradiation (0-5 min). These results suggest that ROS generated from the TiO2 layer may be involved in creating appropriate conditions for the osseointegration of dental implants into alveolar bone tissues.

Biocompatible Materials↗

PubMed1979

The role of sialated glycoproteins in endocytosis, permeability and transmural passage in the myeloid endothelium.

Changes in the anionic charge distribution at the luminal face of the endothelium of the sinusoids of the bone marrow have been studied at sites of endocytosis by large bristle coated vesicles and at the sites of molecular permeability through diaphragmed fenestrae. The anionic charge distribution has also been studied at the abluminal aspect of these vessels at sites of transmural blood cell passage. Cationic surface markers such as colloidal iron, native ferritin and polycationic ferritin used at low pH, 1.8, and the use of neuraminidase show that the nonmodified endothelial cell surface has exposed sialic acid groups, which are absent at the sites of these functional specializations. Polycationic ferritin binding over a range of pH levels indicates the prsence of another species of anionic materials present at both the nonmodified cell surface and at the sites of the cell surface modifications. This second group of anionic compounds is neuraminidase resistant and has a pKa higher than that of sialic acid (pKa:2.6).

Binding Sites↗

PubMed2006

Nomarski imaging interferometry to measure the displacement field of micro-electro-mechanical systems.

We propose to use a Nomarski imaging interferometer to measure the out- of-plane displacement field of micro-electro-mechanical systems. It is shown that the measured optical phase arises from both height and slope gradients. By using four integrating buckets, a more efficient approach to unwrap the measured phase is presented, thus making the method well suited for highly curved objects. Slope and height effects are then decoupled by expanding the displacement field on a functions basis, and the inverse transformation is applied to get a displacement field from a measured optical phase map change with a mechanical loading. A measurement reproducibility of approximately 10 pm is achieved, and typical results are shown on a microcantilever under thermal actuation, thereby proving the ability of such a setup to provide a reliable full-field kinematic measurement without surface modification.

Journal Article↗

PubMed2006

Giant enhancement of band edge emission in ZnO and SnO nanocomposites.

ZnO/SnO nanocomposites have been designed to enhance the band edge emission and suppress the defect emission of ZnO nanorods simultaneously. It is found that the intensity ratio between the band edge and defect emission can be improved by up to 4 orders of magnitude. The underlying mechanism is interpreted in terms of surface modification as well as carrier transfer from SnO nanoparticles to ZnO nanorods. Our approach is very useful for creating highly efficient optoelectronic devices.

Journal Article↗

PubMed2003

Biomedical applications of electrostatic layer-by-layer nano-assembly of polymers, enzymes, and nanoparticles.

The introduction of electrostatic layer-by-layer (LbL) self-assembly has shown broad biomedical applications in thin film coating, micropatterning, nanobioreactors, artificial cells, and drug delivery systems. Multiple assembly polyelectrolytes and proteins are based on electrostatic interaction between oppositely charged layers. The film architecture is precisely designed and can be controlled to 1-nm precision with a range from 5 to 1000 nm. Thin films can be deposited on any surface including many widely used biomaterials. Microencapsulation of micro/nanotemplates with multilayers enabled cell surface modification, controlled drug release, hollow shell formation, and nanobioreactors. Both in vitro and in vivo studies indicate potential applications in biology, pharmaceutics, medicine, and other biomedical areas.

Biomimetic Materials↗

PubMed2007

Polymeric nanogel formulations of nucleoside analogs.

Nanogels are colloidal microgel carriers that have been recently introduced as a prospective drug delivery system for nucleotide therapeutics. The crosslinked protonated polymer network of nanogels binds oppositely charged drug molecules, encapsulating them into submicron particles with a core-shell structure. The nanogel network also provides a suitable template for chemical engineering, surface modification and vectorisation. This review reveals recent attempts to develop novel drug formulations of nanogels with antiviral and antiproliferative nucleoside analogs in the active form of 5'-triphosphates, discusses structural approaches to the optimisation of nanogel properties, and discusses the development of targeted nanogel drug formulations for systemic administration. Notably, nanogels can improve the CNS penetration of nucleoside analogs that are otherwise restricted from passing across the blood-brain barrier. The latest findings reviewed here demonstrate an efficient intracellular release of nucleoside analogs, encouraging further applications of nanogel carriers for targeted drug delivery.

Animals↗

PubMed2006

Soft contact lens biomaterials from bioinspired phospholipid polymers.

Soft contact lens (SCL) biomaterials originated from the discovery of a poly(2-hydroxyethyl methacrylate) (poly[HEMA])-based hydrogel in 1960. Incorporation of hydrophilic polymers into poly(HEMA) hydrogels was performed in the 1970-1980s, which brought an increase in the equilibrium water content, leading to an enhancement of the oxygen permeability. Nowadays, the poly(HEMA)-based hydrogels have been applied in disposable SCL. At the same time, high oxygen-permeable silicone hydrogels were produced, which made it possible to continually wear SCL. Recently, numerous trials for improving the water wettability of silicone hydrogels have been performed. However, little attention has been paid to improving their anti-biofouling properties and biocompatibility. Since biomimetic phospholipid polymers possess excellent anti-biofouling properties and biocompatibility they have the potential to play a valuable role in the surface modification of the silicone hydrogel. The representative phospholipid polymers containing a 2-methacryloyloxyethyl phosphorylcholine (MPC) unit suppressed nonspecific protein adsorption, increased cell compatibility and contributed to blood compatible biomaterials. The MPC polymer coating on the silicone hydrogel improved its water wettability and biocompatibility, while maintaining high oxygen permeability compared with the original silicone hydrogel. Furthermore, the newly prepared phospholipid-type intermolecular crosslinker made it possible to synthesize a 100% phospholipid polymer hydrogel that can enhance the anti-biofouling properties and biocompatibility. In this review, the authors discuss how polymer hydrogels should be designed in order to obtain a biocompatible SCL and future perspectives.

Biocompatible Materials↗

PubMed2000

Surface remodeling associated with vasopressin-induced membrane traffic in L6 myogenic cells.

The plasma membrane is dynamically remodeled as a function of the cell cycle, motility and membrane traffic. We have previously shown that arg8-vasopressin (AVP) stimulation of L6 myoblasts induces the activation of phosholipase D during the first minutes of stimulation, and the differentiation of 1,6 myoblasts as a long term effect. We now report that AVP also induces two types of morphological responses in L6 cells within a few minutes of stimulation: exocytosis, apparent as uncoated pits, and the generation of membrane projections and reffles. Thus, such an experimental model is suitable for the study of hormone-induced morphological surface modifications and their regulatory mechanisms. In L6 cells, AVP-induced projection generation depends on the integrity of microfilaments, intermediate filaments, and microtubules. Moreover, projection generation and exocytosis appear to be independently regulated phenomena: in fact, inhibition of the de novo synthesis of phosphatidylcholine inhibits membrane traffic but fails to block projection appearance. Conversely, the latter phenomenon, unlike exocytosis, is mediated by PI3-kinase signaling. Thus, AVP induces two early, independently regulated morphological modifications in L6 cells: exocytosis, involved in plasma membrane phospholipid turnover, and membrane projections, likely involved in cell migration.

Acridine Orange↗

PubMed2005

Specific targets in tumor tissue for the delivery of therapeutic genes.

Gene therapy is part of a growing field in molecular medicine, which will gain importance in the treatment of human diseases. Until now, almost two thirds of all clinical trials performed in gene therapy are directed against Cancer As solid tumors exceeding a certain size rely on blood supply, the administration of particulate gene delivery vectors via the bloodstream is a promising concept. Tumor cells and the tumor vasculature both offer specific molecular targets, which can be utilized for the site directed delivery of therapeutic genes. Passive targeting of macromolecular drugs including gene delivery vectors to tumors can be achieved by the so called enhanced permeability and retention (EPR) effect. The specificity can be markedly enhanced when tumor targeting ligands are used. Viral vectors, which usually do not have a natural tropism for tumor tissue, were generated to carry tumor targeting molecules on their surface. Synthetic gene delivery vectors, based on cationic lipids or cationic polymers were biochemically modified to incorporate ligands specific for tumor cells or tumor vasculature. For systemic application, these delivery systems have to fulfill certain conditions. The delivery vector should not induce any immunogenic and inflammatory responses. Several studies were conducted to reduce the immunogenicity of viral vectors; surface modification of non-viral gene delivery systems reduced their non-specific interaction with blood components. On the genetic level, tumor specific promoters add additional layers of specificity restricting the transgene expression to the tumor tissue. This review will cover the systemic application of particulate gene transfer vectors targeted to tumors and will give an overview of therapeutic concepts for cancer gene therapy.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed2005

[Needs and current research directions of biological regenerative medicine in prosthodontic practice--to attain reliable and sophisticated dental implant therapy].

Appropriate dental implants are known to improve the quality of life in totally and partially edentulous patients, as well as to prevent future tooth loss, and so prosthetic treatment modalities have drastically changed recently with reconstruction therapy. However, dental implant therapy did not win the confidence of the dental community in the early developmental stage, until osseointegration between titanium and surrounding bone tissue was discovered and the modality utilizing osseointegration became reliable and produced durable treatment outcomes for long-term function. On the other hand, the biological mechanism of osseointegration has not been clarified yet and the time required for osseointegration is still long, e.g. three to four months. As well, when the implant is applied in the upper posterior region, the acquisition of osseointegration and the long-term survival of the implant are still not clinically adequate. Therefore, to reduce the time required for osseointegration and to regenerate enough alveolar bone mass in the target implantation site, the oral implant modality must be made more useful and potent as one of the treatment options for partial and total edentulism. With this background, we have studied biological strategies for reducing the time required for osseointegration and for regenerating enough alveolar bone mass, e.g., investigation of the specific genes for osseointegration between titanium and bone, nano-level surface modification of the titanium, biodegradable apatite foam for alveolar bone regeneration, application of bone formation-related growth factors with biological scaffold, and autologous cell transplantation of bone marrow derived mesenchymal stem cells. In this article, we review the current status of regenerative medicine being applied in prosthodontics and discuss our future research direction.

Alveolar Process↗

PubMed2004

Comparison of microfocus- and synchrotron X-ray tomography for the analysis of osteointegration around Ti6Al4V implants.

Micro-computed tomography (microCT) provides quantitative three-dimensional information of bone around titanium implants similar to classical histology. The study, based on an animal model, containing cuboid-shaped biofunctionalised Ti6Al4V implants with surrounding bone after 4 weeks, is performed using 3 microCT-systems with X-ray tubes, one synchrotron-radiation-based microCT-system (SRmicroCT), and classical histology. Although the spatial resolution of the microCT-systems is comparable, only the results of SRmicroCT agree with results of classical histology. The X-ray tube sources give rise to huge artefacts in the tomograms (interface scattering, beam hardening), which impaired the quantitative analysis of bone up to about 200microm from the implant surface. Due to the non-destructive character of microCT the specimens can be subsequently examined by classical histology without restriction. The quantitative comparison of bone formation uncovers the strong dependence of the newly formed bone from the selected slice. This implies the necessity of 3D analysis. SRmicroCT and classical histology prove that surface modifications of the titanium implant significantly influence the bone formation. Using SRmicroCT, the preparation artefacts due to cutting and polishing are excluded.

Animals↗

PubMedDate not supplied

For insulin infusion: a miniature precision peristaltic pump and silicone rubber reservoir.

This paper describes a miniature precision peristaltic pump and a silicone rubber reservoir developed for the infusion of insulin in diabetic subjects. The ability of the 100-ml reservoir to maintain sterility of its contents over 26 refilling cycles (48 days) is demonstrated. Accelerated bench tests on 10 pumps over 30 days indicate an accuracy of +/- 1% on flow rate whether measured over 10 min or 24 h and with or without 1 atm of outlet back pressure. Comparison of calibrations made before and after 58 animal and clinical tests of 6--71 days' duration showed a percentage difference in calibration that varied with a mean +/- SD of 0.05 +/- 3.09%. Microscopic examination of pump tube samples after 21 days of clinical use indicated redistribution of surface material without evidence of particle spallation. Samples subjected to accelerated wear equivalent to 620 days of clinical use showed extensive luminal surface modification and particulate deposits on downstream filters. These were identified by X-ray spectroscopy as silicon compounds.

Animals↗

PubMedDate not supplied

Tantalum loaded silicone microspheres as particulate emboli.

Chloroform solutions of medical grade silicone resin were cured in an aqueous dispersion medium containing poly(vinyl alcohol) (PVA) as the drop stabilizer at 40-60 degrees C to generate smooth, spherical, elastic microspheres. The microspheres were encapsulated with tantalum powder to render them radiopaque. Tantalum loaded microspheres having diameter more than 1.00 mm could be prepared by this technique. Incorporation of radiopaques such as barium sulphate and methyl iothalamate resulted in the instability of the suspension giving rise to an agglomerated product. Microspheres were grafted with hydrophilic monomers such as 2-hydroxyethyl methacrylate (HEMA) and N-vinyl pyrrolidone (NVP) using ionizing radiation from a 60Co source in an effort to make their surfaces hydrophilic. While the graft yield was very little when HEMA alone was used for grafting, a combination of HEMA/NVP in a 1:1 ratio produced better graft yields resulting in improved surface hydrophilicity. The tantalum loaded microspheres were found to be very resistant to surface modification. Microspheres could be dispersed in water with the aid of small quantities of surfactants such as Tween 20. These microspheres may find use in particulate embolization.

Chemical Phenomena↗

PubMed1982

The mesothelium and its reactions: a review.

The origins, nature, and reactions of the mesothelium have intrigued investigators for over 100 years. Recently, the use of sophisticated techniques has clarified earlier impressions of its development, structure, and function. The structure of mesothelium reflects its functional properties, its long slender microvilli entrapping a layer of glycosoaminoglycans, providing a frictionless free surface between the parietal and visceral serosa. Transport requirements are met by various surface modifications and both inter- and intra-cellular mechanisms occur. The presence of stomatal openings in the mesothelial membrane has been established, and they may have a major role to play in the movement of cells to and from the serosal cavities. In addition, mesothelial cells can respond to situations of increased functional demand and during the course of inflammation, the mesothelium's fibrinolytic properties are of major importance in preventing the formation of adhesions and the enhancement of healing. Of all the unanswered questions the most significant is the nature, localization, and potentialities of mesothelial precursors. A mesodermal origin is readily acknowledged, but the healing process of damaged mesothelium is less clear. It seems probable that "mature" mesothelium is one source of cell renewal, but mesenchymal cells located in the submesothelial serosa are also strong contenders. Neoplastic mesothelium can adopt a spectrum of histological appearances, reflecting its mesodermal origins. In fact, overacceptance of this concept has erroneously led to the classification of other neoplasms arising in the serosal area as mesotheliomas. Although the ocogenic sequence is still obscure, asbestos is recognized as the major etiologic agent in malignant mesotheliomas. In 1955, Hartwell described differing impressions of the peritoneum as seen through the eyes of an anatomist, an histologist, and a surgeon. In this review on the mesothelium we have attempted to unravel some of its complexities as viewed by embryologists, electronmicroscopists, cell biologists, pathologists, and oncologists.

Biological Transport↗