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Record 4241 to 4260

Three-dimensional polarization sensitizes hepatocytes to Fas/CD95 apoptotic signalling
Haouzi, D., S. Baghdiguian, et al. (2005), J Cell Sci 118(Pt 12): 2763-73.
Abstract: Maintenance of epithelial cell shape and polarity determines many vital cell functions, including the appropriate response to external stimuli. Murine hepatocytes cultured in a three-dimensional Matrigel matrix formed highly polarized organoids characterized by specific localization of an ERM (ezrin/radixin/moesin) protein, radixin, at microvillus-lined membrane domains. These apical domains surrounded a lumen and were bordered by tight junctions. The hepatocyte organoids were functional as judged by the high level of albumin secretion and accumulation of bilirubin. Stimulation of the Fas/CD95 death receptor, which is highly hepatotoxic in vivo, was a strong inducer of apoptosis in the polarized organoids. This was in sharp contrast to the monolayer hepatocyte cultures, which were protected from death by exacerbated NF-kappaB signalling following engagement of the death receptors. Thus, hepatocytes in polarized, functional organoids modulate an intracellular signal transduction pathway, allowing the recapitulation of their physiological response to an apoptotic stimulus.

Three-dimensional reconstruction of confocal laser microscopy images to study the behaviour of osteoblastic cells grown on biomaterials
Ramires, P. A., A. Giuffrida, et al. (2002), Biomaterials 23(2): 397-406.
Abstract: The adhesion, spreading and cytoskeletal organization of osteoblastic cells seeded onto titanium and titania/hydroxyapatite composite coating (TiO2/HA) were studied using images acquired by confocal laser scanning microscopy. The fluorescence staining technique was employed to visualize actin cytoskeletal organization of cells, 2-D images were exhaustive when the cells were seeded at low density (in the first 24 h of incubation), but they were less clear when the cells proliferated and appeared stacked. Since the shareware software were not satisfactory, a new 3-D image reconstruction was developed using ordinary software and a model was obtained directly from the optical section set, in order to achieve a more realistic and faithful vision of morphological structures and to evaluate the behaviour of bone cells grown on materials. The results showed that the cells grown on titanium conform to the irregular substrate surfaces maximizing the contact between the cell membrane and the substrate and proliferate disposing close to each other. On the contrary, the osteoblasts seeded onto TiO2/HA coating develop clusters where the cells aggregated extending processes in order to establish intercellular connections. Cell aggregation is an early and critical event leading to cell differentiation and mineralization process and could be a first signal of the tendency of TiO2/HA coating to stimulate cell differentiation.

Thrombogenic influence of biomaterials in patients with the Omni series heart valve: pyrolytic carbon versus titanium
Phillips, S. J. (2001), Asaio J 47(5): 429-31.
Abstract: An opportunity to assess the thromboembolic rates caused by the construction materials on valve replacements is possible with the Omni series of mechanical heart valves. The Omnicarbon and Omniscience valves are identical in form but differ in that the Omnicarbon valve is constructed entirely of pyrolytic carbon, whereas the Omniscience valve uses titanium for its housing, the rest of its structure being pyrolytic carbon. The literature was reviewed and a comparison in similar groups of patients was made between these two model valves for their thromboembolic rates in the mitral and aortic positions. A total of 569 aortic Omnicarbon valves (4,146 patient years [pt yrs.1) had a thromboembolic events (T/E rate) of 0.5% compared with 1.7% for 468 aortic Omniscience (1,552 pt yrs); p < 0.0001. A total of 298 mitral Omnicarbon valves (3,333 pt yrs) had a T/E rate of 1.6% compared with 2.6% for 716 mitral Omniscience valves (2,134 pt yrs), p < 0.001. There was no difference in the anticoagulation management between the two model valves although the Omniscience valve required higher prothrombin or International Normalized Rate maintenance levels, which resulted in higher bleeding rates among patients with Omniscience valves.

Thrombospondin 1 as possible key factor in the hemocompatibility of endocoronary prostheses
Hoffmann, J., P. Simon, et al. (2005), Biomaterials 26(25): 5240-50.
Abstract: Intracoronary stenting has markedly improved the patency of native coronary arteries after percutaneous transluminal coronary angioplasty (PTCA). Advances in stent technology and design, including drug releasing stents, have contributed to reduce the long-term restenosis rate. However, stenosis caused by neointimal hyperplasia, vascular remodeling and thrombosis is still a major problem after endocoronary stent procedures. This study focuses on differential gene expression of circulating peripheral blood cells after 90 min exposure to stents to search for initially activated cellular pathways, which may foster restenosis. Fresh human whole blood (1 IU heparin/ml), taken from non-medicated healthy volunteers, was incubated under flow conditions in an in vitro closed-loop stent-testing model (modified Chandler-Loop). Differential gene expression compared to resting conditions and to the experimental controls was investigated by a DNA-microarray technique encoding for over 17,000 genes simultaneously. As expected, a large variety of genes showed differential gene expression. Interestingly, Thrombospondin 1 (TSP-1), which plays a key role in initial immune defense, was found to be the most markedly up-regulated gene. We propose TSP-1 expression as an early indicator for the activation of immune responses following intracoronary stenting. After clarifying the participation of TSP-1 in vivo, future studies will therefore focus on TSP-1 as a potential prognostic factor, which may also help to develop and control new surface materials with an improved biocompatibility.

Time-of-flight secondary ion mass spectrometry: techniques and applications for the characterization of biomaterial surfaces
Belu, A. M., D. J. Graham, et al. (2003), Biomaterials 24(21): 3635-53.
Abstract: The surface of a biomaterial plays a critical role in the success of an implant. Much effort is currently being focused on controlling the chemistry at biomaterial surfaces to ensure favorable results in vivo. The successful tailoring of the surface chemistry will require a detailed surface characterization to verify that the desired changes have been made. This will include the ability to determine the composition, structure, orientation, and spatial distribution, of the molecules and chemical structures on the surface. TOF-SIMS is a powerful surface characterization technique that is able to address these requirements through both spectral analysis and direct chemical state imaging. The flexibility of the TOF-SIMS technique, and the wealth of data produced have generated much interest in its use for biomaterial characterization. This review discusses the strengths, weaknesses, and challenges of static TOF-SIMS for biomaterial surface characterization. First the basic principles of TOF-SIMS are introduced, giving an overview of the technique. Next, sample type, and other sample considerations are discussed. Then data interpretation is overviewed using examples from both spectral and imaging data. Finally, quantitative SIMS analysis is discussed and an outlook for TOF-SIMS analysis of biomaterials will be given.

Time-related contact angle measurements with human plasma on biomaterial surfaces
Rakhorst, G., H. C. Van der Mei, et al. (1999), Int J Artif Organs 22(1): 35-9.
Abstract: Axisymmetric drop shape analysis by profile (ADSA-P) was used to assess in time contact angle changes of human plasma drops placed on four different biomaterials. Results were related with conventional blood compatibility measurements: albumin adsorption, fibrinogen adsorption and platelet adhesion. While contact angle measurements with water are material-related but constant in time, contact angle measurements with plasma changed over time owing to protein adsorption on the solid-liquid interface. The contact medium plasma did not influence the initial contact angle. Contact angles on PDMS decreased most in time (41 degrees) and demonstrated highest levels of conventionally measured albumin and fibrinogen adsorption and platelet adhesion. PTFE, with the lowest contact angle decrease over a 500 minutes period (19 degrees), showed low fibrinogen and albumin adsorption as well as low platelet adhesion. PU and HDPE demonstrated almost similar initial contact angles with plasma and contact angle decreases (26 and 27 degrees), intermediate protein adsorption, and platelet adhesion. We conclude that biocompatibility properties of the tested materials may be more related to the behaviour of their contact angles in time, than to the initial hydrophobic or hydrophilic state.

TiO(2) type influences fibronectin adsorption
Sousa, S. R., P. Moradas-Ferreira, et al. (2005), J Mater Sci Mater Med 16(12): 1173-8.
Abstract: Human fibronectin (FN) plays a key role in the biointegration of implants as the success depends on adsorption of proteins like FN [1]. Indeed FN can be an intermediary between the biomaterial surface and cells.The adsorption of human fibronectin (FN) on commercially pure titanium with a titanium oxide layer formed in a H(2)O(2) solution (TiO(2) cp) and TiO(2) sputtered on Si (TiO(2) sp) was studied. Adsorption isotherms and the work of adhesion were assessed by wettability studies, X-ray photoelectron spectroscopy (XPS), and by radiolabelling of FN with (125)I, (125)I-FN. Exchangeability of bound FN by free FN, was also evaluated by the radiolabelling technique.Contact angle determinations have shown that FN displays higher affinity for the TiO(2) cp surface than for the TiO(2) sp. As expected from the surface free energy values, the work of adhesion of FN is higher for the TiO(2) cp substrate, the more hydrophilic one, and lower for the TiO(2) sp substrate, the more hydrophobic one.The adsorption isotherms were evaluated by two different techniques: radiolabelling of FN ((125)I-FN) and XPS. TiO(2) cp adsorbs more FN than the TiO(2) sp surfaces as shown by the radiolabelling data. FN molecules are also more strongly attached to the former surface as indicated by the work of adhesion and by the exchangeability studies. Results using (125)I-FN also suggests that FN adsorbs as a multilayer for FN concentrations in solution higher than 100 mug/mL.

TiO2 phytate films as hosts and conduits for cytochrome c electrochemistry
McKenzie, K. J., F. Marken, et al. (2005), Bioelectrochemistry 66(1-2): 41-7.
Abstract: Cytochrome c is accumulated into a film of TiO(2) nanoparticles and phytate by adsorption from an aqueous solution into the mesoporous structure. Stable voltammetric responses and high concentrations of redox protein within the TiO(2) phytate layer can be achieved. Two types of electrode systems are reported with (i) the modified TiO(2) phytate film between electrode and aqueous solution phase and (ii) the modified TiO(2) phytate film buried under a porous gold electrode ('porotrode'). The electrical conductivity of TiO(2) phytate films is measured and compared in the dry and in the wet state. Although in the dry state essentially insulating, the TiO(2) phytate film turns into an electrical conductor (with approximately 4 Omega cm specific resistivity assuming ohmic behaviour) when immersed in aqueous 0.1 M phosphate buffer solution at pH 7. The redox protein cytochrome c is therefore directly connected to the electrode via diffusion and migration of electrons in the three dimensional mesoporous TiO(2) phytate host structure. Electron transfer from cytochrome c to TiO(2) is proposed to be the rate-determining step for this conduction mechanism.

TiO2-photocatalyzed As(II) oxidation in aqueous suspensions: reaction kinetics and effects of adsorption
Ferguson, M. A., M. R. Hoffmann, et al. (2005), Environ Sci Technol 39(6): 1880-6.
Abstract: Oxidation of arsenite, As(III), to arsenate, As(V), is required for the efficient removal of arsenic by many water treatment technologies. The photocatalyzed oxidation of As(III) on titanium dioxide, TiO2, offers an environmentally benign method for this unit operation. In this study, we explore the efficacy and mechanism of TiO2-photocatalyzed As(III) oxidation at circumneutral pH and over a range of As(III) concentrations approaching those typically encountered in water treatment systems. We focus on the effect of As adsorption on observed rates of photooxidation. Adsorption (in the dark) of both As(III) and As(V) on Degussa P25 TiO2 was examined at pH 6.3 over a range in dissolved arsenic concentrations, [As]diss, of 0.10-89 microM and 0.2 or 0.05 g L(-1) TiO2 for As(III) and As(V), respectively. Adsorption isotherms generally followed the Langmuir-Hinshelwood model with As(III) exhibiting an adsorption maxima of 32 micromol g(-1). As(V) adsorption did not reach a plateau under the experimental conditions examined; the maximum adsorbed concentration observed was 130 micromol g(-1). The extent of As(III) and As(V) adsorption observed at the beginning and end of the kinetic studies was consistent with that observed in the adsorption isotherms. Kinetic studies were performed in batch systems at pH 6.3 with 0.8-42 microM As(III) and 0.05 g L(-1) TiO2; complete oxidation of As(III) was observed within 10-60 min of irradiation at 365 nm. The observed effect of As(III) concentration on reaction kinetics was consistent with surface saturation at higher concentrations. Addition of phosphate at 0.5-10 microM had little effect on either As(III) sorption or its photooxidation rate but did inhibit adsorption of the product As(V). The selective use of hydroxyl radical quenchers and superoxide dismutase demonstrated that superoxide, O2-, plays a major role in the oxidation of As(III) to As(V).

TIPS with expanded polytetrafluoroethylene-covered stent: results of an Italian multicenter study
Vignali, C., I. Bargellini, et al. (2005), AJR Am J Roentgenol 185(2): 472-80.
Abstract: OBJECTIVE: Our objective is to describe the results of a multicenter prospective trial on the safety and efficacy of transjugular intrahepatic portosystemic shunts (TIPS) using the Viatorr stent-graft. SUBJECTS AND METHODS: From 2001 to 2003, 114 patients (75 men and 39 women; mean age, 59.3 years) with portal hypertension underwent TIPS with the Viatorr stent-graft. Indications for treatment were variceal bleeding (n = 49, 43.0%), refractory ascites (n = 52, 45.6%), hypertensive gastropathy (n = 10, 8.8%), Budd-Chiari syndrome (n = 1, 0.9%), and hepatorenal syndrome (n = 2, 1.7%). Eight patients (7.0%) had Child-Pugh class A cirrhosis; 60 (52.6%), Child-Pugh class B; and 46 (40.4%), Child-Pugh class C. Patients were monitored by color Doppler sonography and phlebography. RESULTS: The procedure was successful in 113 (99.1%) of 114 patients; in one patient, creation of the track was not feasible. The mean portosystemic pressure gradient decreased from 21.8 to 8.7 mm Hg. Three minor immediate complications (2.6%) occurred (two cases of self-limiting hemoperitoneum and one extrahepatic portal puncture requiring covered stenting). At a mean follow-up of 11.9 months, the overall mortality rate was 31.0% (35/113), with a 30-day mortality rate of 8.8% (10/113). Mortality was significantly higher in patients in Child-Pugh class C with refractory ascites and with post-procedural encephalopathy. Cumulative primary patency rates were 91.9%, 79.9%, and 75.9% at 6, 12, and 24 months' follow-up, respectively. Restenosis occurred in 15 patients (13.3%) within the stent (n = 8, 53.3%) or at the ends of the portal (n = 1, 6.7%) or hepatic (n = 6, 40%) veins and was solved by percutaneous transluminal angioplasty (n = 11), stenting (n = 3), or parallel TIPS (n = 1). The secondary patency rate was 98.2%. Post-procedural encephalopathy occurred in 27 patients (23.9%). CONCLUSION: The Viatorr stent-graft is safe and effective in TIPS creation, with high primary patency rates. Covering the entire track up to the inferior vena cava can increase patency.

Tissue colonization from implantable biomaterials with low numbers of bacteria
Merritt, K., V. M. Hitchins, et al. (1999), J Biomed Mater Res 44(3): 261-5.
Abstract: This study was undertaken to evaluate the risk of infection (defined as the recovery of the relevant organism from the implant site) in a mouse model when low numbers of bacteria were present on an implanted biomaterial. Segments of different types of suture with adherent bacteria were implanted subcutaneously into mice. The infection risk with Staphylococcus aureus was greater than with Staphylococcus epidermidis RP62A or Candida albicans. The infection risk with the implantation of multifilament sutures was significantly greater than with monofilament sutures. When <10 colony forming units (cfu) of S. aureus were present on monofilament suture material, the infection rate was 3%. When <10 cfu of S. aureus were present on multifilament suture material, the infection rate was 7%. An infection rate of 15% occurred with <10 cfu of S. aureus on multifilament nylon sutures. When >10 but <20 cfu of S. aureus were present, the infection rates were 4 and 51%, respectively. These data confirm that the infection rate with multifilament sutures (or porous materials) is greater than with monofilament sutures (or solid materials) when the organisms are encountered at implantation (acute model) and indicate that a significant risk of infection may occur when only a few organisms are on a device at implantation.

Tissue engineering and autologous transplant formation: practical approaches with resorbable biomaterials and new cell culture techniques
Sittinger, M., J. Bujia, et al. (1996), Biomaterials 17(3): 237-42.
Abstract: The engineering of living tissues in vivo requires new concepts in cell culture technology. In contrast to conventional cell cultures, the development of tissues depends on a three-dimensional arrangement of cells and the formation or synthesis of an appropriate extracellular matrix. Special emphasis is given to the major role of the extracellular matrix and cell differentiation in an artificial tissue. New technical approaches of in vitro tissue engineering are compared to the natural development of tissues in vivo. Current methods using resorbable biomaterials, tissue encapsulation and perfusion culture are discussed. Major consideration is given to scaffold structures of biomaterials that define a three-dimensional shape of a tissue or guide matrix formation. The different goals of tissue engineering such as in vitro models and transplant production are taken into account in the described techniques. Practical concepts comprising cell multiplication and differentiation in subsequent steps for future clinical applications are outlined.

Tissue engineering of biomaterials for composite reconstruction: an experimental model
Walton, R. L. and R. E. Brown (1993), Ann Plast Surg 30(2): 105-10.
Abstract: The fibrovascular integration of a biomaterial scaffold was examined in a rabbit model. Eight disks of expanded polytetrafluoroethylene measuring 2 x 2 x 0.2 cm were placed adjacent to dissected vascular pedicles in the ears of four rabbits and sealed between leaves of silicone sheeting. Fibrovascular outgrowth from the vascular pedicles completely integrated the biomaterial scaffolds by 6 weeks and was sufficient to sustain split-thickness skin grafts. Division of the distal vascular pedicle allowed isolation of the blood flow circuit to the construct. Successful microsurgical transfer was achieved in one construct. This model has proved useful in the study of tissue engineering of biomaterials for reconstruction and may well have use in the study of neovascularization as an isolated event.

Tissue engineering of bone: search for a better scaffold
Mastrogiacomo, M., A. Muraglia, et al. (2005), Orthod Craniofac Res 8(4): 277-84.
Abstract: BACKGROUND: Large bone defects still represent a major problem in orthopedics. Traditional bone-repair treatments can be divided into two groups: the bone transport (Ilizarov technology) and the graft transplant (autologous or allogeneic bone grafts). Thus far, none of these strategies have proven to be always resolving. As an alternative, a tissue engineering approach has been proposed where osteogenic cells, bioceramic scaffolds, growth factors and physical forces concur to the bone defect repair. Different sources of osteoprogenitor cells have been suggested, bone marrow stromal cells (BMSC) being in most cases the first choice. METHODS AND RESULTS: In association with mineral tridimensional scaffolds, BMSC form a primary bone tissue which is highly vascularized and colonized by host hemopoietic marrow. The chemical composition of the scaffold is crucial for the osteoconductive properties and the resorbability of the material. In addition, scaffolds should have an internal structure permissive for vascular invasion. Porous bioceramics [hydroxyapatite (HA) and tricalcium phosphate] are osteoconductive and are particularly advantageous for bone tissue engineering application as they induce neither an immune nor an inflammatory response in the implanted host. Earlier, we first reported a cell-based tissue engineering procedure to treat three patients with long bone segmental defects. Cells were loaded on a 100% HA porous ceramic. These scaffolds proved to have good osteoconductive properties resulting in a good functional recovery, but they have not been resorbed after more than 5 years from the implant. In addition, due to the high density of the mineral and the relatively low porosity (50-60%), it was very difficult to monitor the patient recovery during the post-surgery time using X-rays. CONCLUSIONS: We report here some pre-clinical testing of new scaffolds. To compare these second generation ceramic scaffolds more suitable for a tissue engineering approach we had to first establish animal models and analysis procedures including the use of X-ray-computed microtomography associated with X-rays synchroton radiation.

Tissue engineering of bovine articular cartilage within porous poly(ether ester) copolymer scaffolds with different structures
Mahmood, T. A., V. P. Shastri, et al. (2005), Tissue Eng 11(7-8): 1244-53.
Abstract: The potential of porous poly(ether ester) scaffolds made from poly(ethylene glycol) terephthalate: poly(butylene terephthalate) (PEGT:PBT) block copolymers produced by various methods to enable cartilaginous tissue formation in vitro was studied. Scaffolds were fabricated by two different processes: paraffin templating (PT) and compression molding (CM). To determine whether PEGT:PBT scaffolds are able to support chondrogenesis, primary bovine chondrocytes were seeded within cylindrical scaffolds under dynamic seeding conditions. On day 3, constructs were transferred to six-well plates and evaluated for glycosaminoglycan (GAG) distribution (3, 10, and 24 days), type II collagen distribution, cellularity, and total collagen and GAG content (10 and 24 days). It was observed that better cell distribution during infiltration within PT scaffolds allowed greater chondrogenesis, and at later time points, than in CM scaffolds. The amount of GAG remained constant for all groups from 10 to 24 days, whereas collagen content increased significantly. These data suggest that PEGT:PBT scaffolds are suitable for cartilage tissue engineering, with the PT process enabling greater chondrogenesis than CM.

Tissue engineering of cartilage using an injectable and adhesive chitosan-based cell-delivery vehicle
Hoemann, C. D., J. Sun, et al. (2005), Osteoarthritis Cartilage 13(4): 318-29.
Abstract: OBJECTIVE: Adult articular cartilage shows a limited intrinsic repair response to traumatic injury. To regenerate damaged cartilage, cell-assisted repair is thus viewed as a promising therapy, despite being limited by the lack of a suitable technique to deliver and retain chondrogenic cells at the defect site. DESIGN: We have developed a cytocompatible chitosan solution that is space-filling, gels within minutes, and adheres to cartilage and bone in situ. This unique combination of properties suggested significant potential for its use as an arthroscopically injectable vehicle for cell-assisted cartilage repair. The primary goal of this study was to assess the ability of this polymer system, when loaded with primary articular chondrocytes, to support cartilage formation in vitro and in vivo. The chitosan gel was cultured in vitro, with and without chondrocytes, as well as injected subcutaneously in nude mice to form subcutaneous dorsal implants. In vitro and in vivo constructs were collectively analyzed histologically, for chondrocyte mRNA and protein expression, for biochemical levels of glycosaminoglycan, collagen, and DNA, and for mechanical properties. RESULTS: Resulting tissue constructs revealed histochemical, biochemical and mechanical properties comparable to those observed in vitro for primary chondrocytes cultured in 2% agarose. Moreover, the gel was retained after injection into a surgically prepared, rabbit full-thickness chondral defect after 1 day in vivo, and in rabbit osteochondral defects, up to 1 week. CONCLUSIONS: The in situ-gelling chitosan solution described here can support in vitro and in vivo accumulation of cartilage matrix by primary chondrocytes, while persisting in osteochondral defects at least 1 week in vivo.

Tissue engineering osteochondral implants for temporomandibular joint repair
Schek, R. M., J. M. Taboas, et al. (2005), Orthod Craniofac Res 8(4): 313-9.
Abstract: Tissue engineering has provided an alternative to traditional strategies to repair and regenerate temporomandibular joints (TMJ). A successful strategy to engineer osteochondral tissue, such as that found in the TMJ, will produce tissue that is both biologically and mechanically functional. Image-based design (IBD) and solid free-form (SFF) fabrication can be used to generate scaffolds that are load bearing and match patient and defect site geometry. The objective of this study was to demonstrate how scaffold design, materials, and biological factors can be used in an integrated approach to regenerate a multi-tissue interface. IBD and SFF were first used to create biomimetic scaffolds with appropriate bulk geometry and microarchitecture. Biphasic composite scaffolds were then manufactured with the same techniques and used to simultaneously generate bone and cartilage in discrete regions and provide for the development of a stable interface between cartilage and subchondral bone. Poly-l-lactic acid/hydroxyapatite composite scaffolds were differentially seeded with fibroblasts transduced with an adenovirus expressing bone morphogenetic protein-7 in the ceramic phase and fully differentiated chondrocytes in the polymeric phase, and were subcutaneously implanted into mice. Following implantation in the ectopic site, the biphasic scaffolds promoted the simultaneous growth of bone, cartilage, and a mineralized interface tissue. Within the ceramic phase, the pockets of tissue generated included blood vessels, marrow stroma, and adipose tissue. This combination of IBD and SFF-fabricated biphasic scaffolds with gene and cell therapy is a promising approach to regenerate osteochondral defects and, ultimately, the TMJ.

Tissue engineering strategies for bone regeneration
Mistry, A. S. and A. G. Mikos (2005), Adv Biochem Eng Biotechnol 94: 1-22.
Abstract: Bone loss due to trauma or disease is an increasingly serious health problem. Current clinical treatments for critical-sized defects are problematic and often yield poor healing due to the complicated anatomy and physiology of bone tissue, as well as the limitations of medical technology. Bone tissue engineering offers a promising alternative strategy of healing severe bone injuries by utilizing the body's natural biological response to tissue damage in conjunction with engineering principles. Osteogenic cells, growth factors, and biomaterial scaffolds form the foundation of the many bone tissue engineering strategies employed to achieve repair and restoration of damaged tissue. An ideal biomaterial scaffold will provide mechanical support to an injured site and also deliver growth factors and cells into a defect to encourage tissue growth. Additionally, this biomaterial should degrade in a controlled manner without causing a significant inflammatory response. The following chapter highlights multiple strategies and the most recent advances in various areas of research for bone tissue regeneration.

Tissue factor expression by rat osteosarcoma cells adherent to tissue culture polystyrene and selected orthopedic biomaterials
Bledsoe, J. G. and S. M. Slack (1998), J Biomater Sci Polym Ed 9(12): 1305-12.
Abstract: Tissue factor (TF), a transmembrane glycoprotein expressed by numerous cell types, plays a critical role in the initiation of blood coagulation at sites of vascular injury. Activated products of the coagulation cascade may then enhance the inflammatory responses associated with wound healing. In the present investigation the ability of rat osteosarcoma (ROS) cells to express TF activity was examined following their growth on tissue-culture polystyrene (TCPS) and selected orthopedic biomaterials (titanium and zirconium alloys, and stainless steel). ROS cells exhibited significant TF activity as evidenced by the conversion of Factor X to Factor Xa in the presence of TF, Factor VIIa, and Ca2+. Factor Xa concentrations ranged from 1.0 fM per cell at 10 min to 6.0 fM per cell after 60 min. Additionally, ROS cells stimulated with calcium ionophore (A23187) exhibited approximately twice the activity of non-stimulated cells when grown on TCPS but not on the metallic substrates. ROS cells (stimulated or unstimulated) adherent to the zirconium alloy generated lower amounts of Factor Xa compared to those bound to the other alloys and unstimulated cells grown on TCPS. These results indicate that ROS cells cultured on these synthetic surfaces differentially express procoagulant activity and that cells grown on TCPS, but not the metallic alloys, exhibit increased TF activity in response to stimulation by calcium ionophore. This procoagulant activity may potentiate subsequent inflammatory responses associated with the use of orthopedic biomaterials and thereby influence the tissue compatibility of the implant.

Tissue factor, its inhibitor, and the thrombogenicity of two new synthetic membranes
Zemanova, P., K. Opatrny, et al. (2005), Artif Organs 29(8): 651-7.
Abstract: BACKGROUND: The aim of the study was to compare the effect of new high-flux hemodialysis membranes made from polyacrylonitrile (AN69ST) and polysulfone (Helixone) on the plasma levels of tissue factor (TF) and tissue factor pathway inhibitor (TFPI) playing a key role in hemostasis. Established thrombogenicity markers were also determined. METHODS: In a clinical prospective randomized study, 10 patients were examined using either membrane at the start and at minutes 15, 60, and 240 of hemodialysis. RESULTS: Increases in the plasma TF levels reached significance at the end of hemodialysis with both membranes, with the Helixone also after 15 min. TFPI levels tended to rise significantly from minute 15 onward while not differing from baseline at the end of the procedure. Judging by the increase in thrombin-antithrombin III complexes, both membranes significantly activated coagulation at the end of hemodialysis. Platelet factor 4 levels, released during thrombocyte and endothelial stimulation, were elevated from the start of procedures. There were no significant differences between the AN69ST and the Helixone in any of the assessed markers. CONCLUSIONS: The AN69ST and Helixone membranes do not differ in their effects on TF and TFPI or even in established thrombogenicity markers.

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