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Emerging design principles in biomaterials and scaffolds for tissue engineering
Griffith, L. G. (2002), Ann N Y Acad Sci 961: 83-95.
Abstract: Biomaterials and scaffolds play an essential role in tissue engineering by guiding new tissue growth in vivo and in vitro. While adaptation of existing surgical materials has fulfilled some needs in the field, new applications demand better control of bulk properties such as degradation and of surface properties that control cell interactions. Advances in molecular cell biology are driving the incorporation of new biological moieties into materials, and a set of design principles based on quantitative analysis of key cellular processes involved in regeneration is emerging. At the same time, new materials-processing methodologies are emerging to allow fabrication of these fragile materials into devices appropriate for delivery.

Emulsion strategies in the microencapsulation of cells: pathways to thin coherent membranes
Leung, A., Y. Ramaswamy, et al. (2005), Biotechnol Bioeng 92(1): 45-53.
Abstract: Microencapsulation of cell spheroids in an immunoselective, highly biocompatible, biomembrane offers a way to create viable implantation options in the treatment of insulin-dependent diabetes mellitus (IDDM). Traditionally the encapsulation process has been achieved through the injection/extrusion of alginate/cell mixtures into a calcium chloride solution to produce calcium alginate capsules around the cells. A novel alternative is explored here through a procedure using an emulsion process to produce thin adherent calcium alginate membranes around cell spheroids. In this study, a thorough investigation has been used to establish the emulsion process parameters that are critical to the formation of a coherent alginate coat both on a model spheroid system and subsequently on cell spheroids. Optical and fluorescence microscopy are used to assess the morphology and coherence of the calcium alginate/poly-L-ornithine/alginate (APA) capsules produced.

Encapsulating live cells with water-soluble chitosan in physiological conditions
Zhu, J. H., X. W. Wang, et al. (2005), J Biotechnol 117(4): 355-65.
Abstract: A new class of microcapsules was prepared under physiological conditions by polyelectrolyte complexation between two oppositely-charged, water-soluble polymers. The microcapsules consisted of an inner core of half N-acetylated chitosan and an outer shell of methacrylic acid (MAA) (20.4%)-hydroxyethyl methacrylate (HEMA) (27.4%)-methyl methacrylate (MMA) (52.2%) (MAA-HEMA-MMA) terpolymer. Both 400 and 150 kDa half N-acetylated chitosans maintained good water solubility and supplied enough protonated amino groups to coacervate with terpolymer at pH 7.0-7.4, in contrast to other chitosan-based microcapsules which must be prepared at pH <6.5. The viscosity of half N-acetylated chitosan solutions between 80 and 3000 cPas allowed the formation of microcapsules with spherical shape. Molar mass, pH and concentration of half N-acetylated chitosan, and reaction time, influenced the morphology, thickness and porosity of the microcapsules. Microcapsules formed with high concentration of half N-acetylated chitosan exhibited improved mechanical stability, whereas microcapsules formed with low concentration of half N-acetylated chitosan exhibited good permeability. This 3D microenvironment has been configured to cultivate sensitive anchorage-dependent cells such as hepatocytes to maintain high level of functions.

Encapsulation of islets in rough surface, hydroxymethylated polysulfone capillaries stimulates VEGF release and promotes vascularization after transplantation
Lembert, N., J. Wesche, et al. (2005), Cell Transplant 14(2-3): 97-108.
Abstract: The transplantation of encapsulated islets of Langerhans is one approach to treat type 1 diabetes without the need of lifelong immunosuppression. Capillaries have been used for macroencapsulation because they have a favorable surface-to-volume ratio and because they can be refilled. It is unclear at present whether the outer surface of such capillaries should be smooth to prevent, or rough to promote, cell adhesions. In this study we tested a new capillary made of modified polysulfone (MWCO: 50 kDa) with a rough, open-porous outer surface for islet transplantation. Compared with free-floating islets, encapsulation of freshly isolated rat islets affected neither the kinetics nor the efficiency of glucose-induced insulin release in perifusion experiments. Free-floating islets maintained insulin secretion during cell culture but encapsulated islets gradually lost their glucose responsiveness and released VEGF. This indicated hypoxia in the capillary lumen. Transplantation of encapsulated rat islets into diabetic rats significantly reduced blood glucose concentrations from the first week of implantation. This hypoglycaemic effect persisted until explantation 4 weeks later. Transplantation of encapsulated porcine islets into diabetic rats reduced blood glucose concentrations depending on the islet purity. With semipurified islets a transient reduction of blood glucose concentrations was observed (2, 8, 18, 18 days) whereas with highly purified islets a sustained normoglycaemia was achieved (more than 28 days). Explanted capillaries containing rat islets were covered with blood vessels. Vascularization was also observed on capillaries containing porcine islets that were explanted from normoglycaemic rats. In contrast, on capillaries containing porcine islets that were explanted from hyperglycemic rats a fibrous capsule and lymphocyte accumulations were observed. No vascularization on the surface of transplanted capillaries was observed in the absence of islets. In conclusion, encapsulated islets can release VEGF, which appears to be an important signal for the vascularization of the capillary material. The rough, open-porous outer surface of the polysulfone capillary provides a site well suited for vascular tissue formation and may allow a prolonged islet function after transplantation.

Encapsulation of recombinant cells with a novel magnetized alginate for magnetic resonance imaging
Shen, F., A. A. Li, et al. (2005), Hum Gene Ther 16(8): 971-84.
Abstract: Implanting recombinant cells encapsulated in alginate microcapsules to express therapeutic proteins has been proven effective in treating several mouse models of human diseases (neurological disorders, dwarfism, hemophilia, lysosomal storage disease, and cancer). In anticipation of clinical application, we have reported the synthesis and characterization of a magnetized ferrofluid alginate that potentially allows tracking of these microcapsules in vivo by magnetic resonance imaging (MRI). We now report the properties of these ferrofluid microcapsules important for applications in gene therapy. When a mouse myoblast cell line was encapsulated in these microcapsules, it showed similar viability as in regular unmodified alginate capsules, both in vitro and in vivo, in mice. The permeability of these magnetized microcapsules, a critical parameter for immunoisolation devices, was comparable to that of classic alginate in the transit of various recombinant molecules of various molecular masses (human factor IX, 65 kDa; murine IgG, 150 kDa; and beta-glucuronidase, 300 kDa). When followed by MRI in vitro and in vivo, the ferrofluid microcapsules remained intact and visible for extended periods, allowing quantitative monitoring of microcapsules. At autopsy, the ferrofluid microcapsules were mostly free within the intraperitoneal cavities, with no overt inflammatory response. Serological analyses demonstrated a high level of biocompatibility comparable to that of unmodified alginate. In conclusion, ferrofluid-enhanced alginate microcapsules are comparable to classic alginate microcapsules in permeability and biocompatibility. Their visibility and stability to MRI monitoring permitted qualitative and quantitative tracking of the implanted microcapsules without invasive surgery. These properties are important advantages for the application of immunoisolation devices in human gene therapy.

Encapsulation of vitamin C in tripolyphosphate cross-linked chitosan microspheres by spray drying
Desai, K. G. and H. J. Park (2005), J Microencapsul 22(2): 179-92.
Abstract: This paper describes vitamin C-encapsulated chitosan microspheres cross-linked with tripolyphosphate (TPP) using a new process prepared by spray drying intended for oral delivery of vitamin C. Thus, prepared microspheres were evaluated by loading efficiency, particles size analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), zeta potential and in vitro release studies. The microspheres so prepared had a good sphericity and shape but varied with the volume of cross-linking agent solution added. They were positively charged. The mean particle size ranged from 6.1-9.0 microm. The size, shape, encapsulation efficiency, zeta potential and release rate were influenced by the volume of cross-linking agent. With the increasing amount of cross-linking agent, both the particle size and release rate were increased. Encapsulation efficiency decreased from 45.05-58.30% with the increasing amount of TPP solution from 10-30 ml. FTIR spectroscopy study showed that the vitamin C was found to be stable after encapsulation. XRD studies revealed that vitamin C is dispersed at the molecular level in the TPP-chitosan matrix. Well-defined change in the surface morphology was observed with the varying volume of TPP. The sphericity of chitosan microspheres was lost at higher volume of cross-linking agent. The release of vitamin C from these microspheres was sustained and affected by the volume of cross-linking agent added. The release of vitamin C from TPP-chitosan microspheres followed Fick's law of diffusion.

Encrustation of biomaterials in the urinary tract
Shaw, G. L., S. K. Choong, et al. (2005), Urol Res 33(1): 17-22.
Abstract: This review considers the problem of the encrustation of biomaterials used for urinary prostheses. After a general discussion of the problem it deals with exciting new developments which may prove to be clinically applicable in preventing this costly and resource consuming complication. The widespread use of use of in vitro models which accurately simulate the conditions found in the human urinary tract will allow appropriate preliminary studies. Perhaps then clinical evaluation will be warranted.

Encrustation of biomaterials in the urinary tract
Sofer, M. and J. D. Denstedt (2000), Curr Opin Urol 10(6): 563-9.
Abstract: The present review focuses on technological advances and relevant research related to encrustation of biomaterials in the urinary tract. The importance of physical and chemical biomaterial type, biocompatibility, material coatings such as hydrogels, and infection related to alloplastic materials used in urological practice are discussed. Recent in-vitro and in-vivo research has focused on materials that will reduce encrustation and bacterial biofilm formation, complications that limit the long-term use of urinary materials. Coordinating scientific resources in a multidisciplinary manner for a better understanding of factors that are involved in encrustation and biofilm formation will offer the potential to modify or resolve the problem of encrustation of foreign materials in the urinary tract.

Endo180 binds to the C-terminal region of type I collagen
Thomas, E. K., M. Nakamura, et al. (2005), J Biol Chem 280(24): 22596-605.
Abstract: Type I collagen is a fibril-forming heterotrimer composed of two alpha1 and one alpha2 chains and plays a crucial role in cell-matrix adhesion and cell differentiation. Through a comprehensive differential display screening of oncogenic ras target genes, we have shown that the alpha1 chain of type I collagen (col1a1) is markedly down-regulated by the ras oncogene through the mitogen-activated protein kinase pathway. Although ras-transformed cells are no longer able to produce and secrete endogenous collagen, they can still adhere to exogenous collagen, suggesting that the cells express a collagen binding factor(s) on the cell surface. When the region of col1a1 encompassing the C-terminal glycine repeat and C-prodomain (amino acids 1000-1453) was affinity-labeled with human placental alkaline phosphatase, the secreted trimeric fusion protein could bind to the surface of Ras-transformed cells. Using biochemical purification followed by matrix-assisted laser desorption/ionization mass spectrometry analysis, we identified this collagen binding factor as Endo180 (uPARAP, CD280), a member of the mannose receptor family. Ectopic expression of Endo180 in CosE5 cells followed by in situ staining and quantitative binding assays confirmed that Endo180 indeed recognizes and binds to placental alkaline phosphatase. The interaction between Endo180 and the C-terminal region of type I collagen appears to play an important role in cell-matrix adhesion.

Endophthalmitis and biomaterials
Kodjikian, L., C. Burillon, et al. (2005), Acta Ophthalmol Scand 83(5): 633; author reply 633-4.

Endoscopic removal of metallic airway stents
Lunn, W., D. Feller-Kopman, et al. (2005), Chest 127(6): 2106-12.
Abstract: BACKGROUND: Complications of metallic airway stents include granulation tissue formation, fracture of struts, migration, and mucous plugging. When these complications result in airway injury or obstruction, it may become necessary to remove the stent. There have been few reports detailing techniques and complications associated with endoscopic removal of metallic airway stents. We report our experience with endoscopic removal of 30 such stents over a 3-year period. METHODS: We conducted a retrospective review of 25 patients who underwent endoscopic stent removal from March 2001 to April 2004. The patients ranged in age from 17 to 80 years (mean, 56.3 years). There were 10 male and 15 female patients. The stents had been placed for nonmalignant disease in 20 patients (80%) and malignant disease in 5 patients (20%). All procedures were done under general anesthesia with a rigid bronchoscope. Special attention was focused on the technique of stent removal and postoperative complications. RESULTS: Thirty metallic airway stents were successfully removed from 25 consecutive patients over a 3-year period. The basic method of removal involved the steady application of traction to the stent with alligator forceps. In all cases, an instrument such as the barrel of the rigid bronchoscope or a Jackson dilator was employed to help separate the stent from the airway wall before removal was attempted. In some instances, the airway wall was pretreated with thermal energy prior to stent removal. Complications were as follows: retained stent pieces (n = 7), mucosal tear with bleeding (n = 4), re-obstruction requiring temporary silicone stent placement (n = 14), need for postoperative mechanical ventilation (n = 6), and tension pneumothorax (n = 1). CONCLUSIONS: Although metallic stents may be safely removed endoscopically, complications are common and must be anticipated. Other investigators have described airway obstruction and death as a result of attempted stent removal. Placement and removal of metallic airway stents should only be performed at centers that are prepared to deal with the potentially life-threatening complications.

Endoscopic therapy for gastroesophageal reflux disease
Rothstein, R. I. and A. C. Dukowicz (2005), Surg Clin North Am 85(5): 949-65, vi.
Abstract: Within the last 15 years, novel endoscopic therapies have been developed as options for patients who have gastroesophageal reflux disease (GERD). These approaches can provide long-term relief of GERD, or can be used to "bridge" patients to future therapy, because undergoing treatment does not preclude one from future medical or surgical therapy. These therapies continue to bean active source of research and investigation. Although they are undergoing rapid development, there are only a few peer-reviewed articles detailing original studies with short-term follow-up. Future success in this arena will depend on sham-controlled trials, long-term outcome studies, and cost-effectiveness analyses. This article describes available endoscopic therapies, discusses their effectiveness and duration of response, and reviews their failures and complications.

Endoscopic treatment of sphincterotomy-associated distal common bile duct strictures by using sequential insertion of multiple plastic stents
Pozsar, J., P. Sahin, et al. (2005), Gastrointest Endosc 62(1): 85-91.
Abstract: BACKGROUND: A rare, late complication of endoscopic biliary sphincterotomy is the occurrence of short strictures extending from the papillary orifice to the distal parts of the extraduodenal common bile duct. METHODS: We evaluated the efficacy of the sequential insertion of multiple stents in the treatment of endoscopic biliary sphincterotomy associated common bile duct strictures. The design of the study is a prospective, single-arm observational study at a university-affiliated teaching hospital of 20 patients with distal common bile duct strictures because of choledocholithiasis-related endoscopic biliary sphincterotomy. Endoscopic treatment consisted of the sequential insertion of an increasing number of plastic stents with ever-larger diameters in 3-month follow-up intervals until stricture resolution. The primary outcome of the study was the rate of resolution of the stricture. The parameters measured were the duration of placement of stents, the maximum diameter, the total number of stents, and the total number of endoscopic sessions required for dilation of the strictures. RESULTS: After a median of 9.0 months of stent placement (range 3-22 months) and a median of 20F maximum stent diameter (range 10F-30F), 18 patients (90%) remained stent-free for a median of 14.5 months (range 6-38 months). Two patients (10%) had stricture recurrences at 10 and 24 months. Multivariate regression analysis demonstrated that the time elapsed after endoscopic biliary sphincterotomy was significantly associated with the stent-placement time (however, significance was removed by correction for multiple testing) and the number of ERCPs required for dilation. The initial common bile duct size was significantly associated with the total stent number and diameter needed for stricture resolution (however, significance was removed by correction for multiple testing). Limitations are the low case number and the single-arm, noncontrolled study design. CONCLUSIONS: Sequential insertion of an increasing number of biliary stents affords effective treatment of the distal biliary strictures that develop as a late complication of endoscopic biliary sphincterotomy.

Endothelial cell cultures as a tool in biomaterial research
Kirkpatrick, C. J., M. Otto, et al. (1999), J Mater Sci Mater Med 10(10/11): 589-94.
Abstract: Progress in biocompatibility and tissue engineering would today be inconceivable without the aid of in vitro techniques. Endothelial cell cultures represent a valuable tool not just in haemocompatibility testing, but also in the concept of designing hybrid organs. In the past endothelial cells (EC) have frequently been used in cytotoxicity testing of materials, especially polymers, used in blood-contacting implants, as well as for investigating seeding technologies for vascular prostheses. At present the exponential development both in theory and practice of cell and molecular biology of the endothelium offers great promise in the biomaterial field. Up until now this EC research field has mostly been non-biomaterial orientated. Nevertheless, the relevance for biomaterial research is apparent. Four aspects will be concisely reviewed under the headings inflammation, with special reference to cell adhesion molecules (CAMs) and cytokines, angiogenesis, focusing on the healing response, signal transduction, presenting examples from cytokine- and metal ion-induced up-regulation of genes coding for CAMs, and, finally, endothelial functionality, with emphasis on the principal characteristics of the physiological endothelial phenotype. Finally, the application of these fields to three foci of biomaterial research will be discussed, emphasizing the role of EC culture techniques in controlling the host response to biomaterials (microvascular EC), controlling EC functionality (promoting positive effects and down-regulating negative effects), and tissue engineering (integration of EC into hybrid organs/biosensors). The need for more co-culture and three-dimensional models will be stressed and data from the authors' laboratory presented to illustrate these principles.

Endothelial cell growth factor attachment to biomaterials
Greisler, H. P., J. Klosak, et al. (1986), ASAIO Trans 32(1): 346-9.

Endothelial microparticles affect angiogenesis in vitro: role of oxidative stress
Mezentsev, A., R. M. Merks, et al. (2005), Am J Physiol Heart Circ Physiol 289(3): H1106-14.
Abstract: Endothelium-derived microparticles have recently been described as a new marker of endothelial cell dysfunction. Increased levels of circulating microparticles have been documented in inflammatory disorders, diabetes mellitus, and many cardiovascular diseases. Perturbations of angiogenesis play an important role in the pathogenesis of these disorders. We demonstrated previously that isolated endothelial microparticles (EMPs) impair endothelial function in vitro, diminishing acetylcholine-induced vasorelaxation and nitric oxide production by rat aortic rings and simultaneously increasing superoxide production. Herein, using the Matrigel assay of angiogenesis in vitro and a topological analysis of the capillary-like network by human umbilical vein endothelial cells (HUVECs), we investigated the effects of EMPs on formation of the vascular network. All parameters of angiogenesis were affected by treatment for 48 h with isolated EMPs in a concentration of 10(5) but not 10(3) or 10(4) EMPs/ml. The effects included decreases in total capillary length (24%), number of meshes (45%), and branching points (36%) and an increase in mesh area (38%). The positional and topological order indicated that EMPs affect angiogenic parameters uniformly over the capillary network. Treatment with the cell-permeable SOD mimetic Mn(III)tetrakis(4-benzoic acid) porphyrin chloride (Mn-TBAP) partially or completely restored all parameters of angiogenesis affected by EMPs. EMPs reduced cell proliferation rate and increased apoptosis rate in time- and dose-dependent manners, and this phenomenon was also prevented by Mn-TBAP treatment. Our data demonstrate that EMPs have considerable impact on angiogenesis in vitro and may be an important contributor to the pathogenesis of diseases that are accompanied by impaired angiogenesis.

Endothelial progenitor cell capture by stents coated with antibody against CD34: the HEALING-FIM (Healthy Endothelial Accelerated Lining Inhibits Neointimal Growth-First In Man) Registry
Aoki, J., P. W. Serruys, et al. (2005), J Am Coll Cardiol 45(10): 1574-9.
Abstract: OBJECTIVES: This study was designed to evaluate whether rapid endothelialization of stainless steel stents with a functional endothelium prevents stent thrombosis and reduces the restenotic process. BACKGROUND: A "pro-healing" approach for prevention of post-stenting restenosis is theoretically favored over the use of cytotoxic or cytostatic local pharmacologic therapies. It is believed that the central role of the vascular endothelium is to maintain quiescence of the underlying media and adventitia. METHODS: Sixteen patients with de novo coronary artery disease were successfully treated with implantation of endothelial progenitor cell (EPC) capture stents. RESULTS: Complete procedural and angiographic success was achieved in all 16 patients. The nine-month composite major adverse cardiac and cerebrovascular events (MACCE) rate was 6.3% as a result of a symptom-driven target vessel revascularization in a single patient. There were no other MACCE despite only one month of clopidogrel treatment. At six-month follow-up, mean angiographic late luminal loss was 0.63 +/- 0.52 mm, and percent stent volume obstruction by intravascular ultrasound analysis was 27.2 +/- 20.9%. CONCLUSIONS: This first human clinical investigation of this technology demonstrates that the EPC capture coronary stent is safe and feasible for the treatment of de novo coronary artery disease. Further developments in this technology are warranted to evaluate the efficacy of this device for the treatment of coronary artery disease.

Endothelial progenitor cell sprouting in spheroid cultures is resistant to inhibition by osteoblasts: a model for bone replacement grafts
Stahl, A., X. Wu, et al. (2005), FEBS Lett 579(24): 5338-42.
Abstract: Survival of tissue transplants generated in vitro is strongly limited by the slow process of graft vascularization in vivo. A method to enhance graft vascularization is to establish a primitive vascular plexus within the graft prior to transplantation. Endothelial cells (EC) cultured as multicellular spheroids within a collagen matrix form sprouts resembling angiogenesis in vitro. However, osteoblasts integrated into the graft suppress EC sprouting. This inhibition depends on direct cell-cell-interactions and is characteristic of mature ECs isolated from preexisting vessels. In contrast, sprouting of human blood endothelial progenitor cells is not inhibited by osteoblasts, making these cells suitable for tissue engineering of pre-vascularized bone grafts.

Endothelialization of microporous YIGSR/PEG-modified polyurethaneurea
Jun, H. W. and J. L. West (2005), Tissue Eng 11(7-8): 1133-40.
Abstract: Bioactive polyurethaneurea modified with polyethylene glycol (PEG) and the endothelial cell-adhesive peptide YIGSR was synthesized and fabricated into microporous scaffolds. This material has shown appropriate mechanical properties for vascular graft applications, resists platelet adhesion, and promotes endothelialization. In the current study, microporous scaffolds were formed by a gasfoaming and salt-leaching method. The scaffolds showed highly interconnected open pores throughout the matrices, with porosity of approximately 78% and pore sizes of 20-200 microm. The peptide modified scaffolds showed superior mechanical properties over peptide-free scaffolds (tensile strength, 1.4 +/- 0.03 versus 0.19 +/- 0.01 MPa; p < 0.01). Bovine aortic endothelial cells were seeded on the scaffolds, and cell attachment, proliferation, extracellular matrix production, and migration were investigated. Histological and scanning electron microscopy analysis showed that few cells adhered on peptide-free scaffolds, whereas confluent endothelial cell monolayers formed along the pores in peptide-modified scaffolds. DNA content, hydroxyproline production, and cell migration were also significantly greater in peptide-modified scaffolds.

Endothelialization of small-diameter vascular prostheses
van der Zijpp, Y. J., A. A. Poot, et al. (2003), Arch Physiol Biochem 111(5): 415-27.
Abstract: In the field of arterial vascular reconstructions there is an increasing need for functional small-diameter artificial grafts (inner diameter < 6mm). When autologous replacement vessels are not available, for example because of the bad condition of the vascular system in the patient, the surgeon has no other alternative than to implant a synthetic polymer-based vessel. After implantation the initial major problem concerning these vessels is the almost immediate occlusion, due to blood coagulation and platelet deposition, under the relatively low flow conditions. As the search for the perfect bio-inert polymer has not revealed a material with suitable properties for this application, improved performance of small-diameter artificial blood vessels is now being sought in the biological field. The poor blood-compatibility of an artificial vascular graft is not simply because of its coagulation-stimulating or platelet-activating properties, but more due to its inability to actively participate in the prevention of blood coagulation and platelet deposition. As these functions are naturally performed by endothelial cells, the utilization of these cells seems inevitable for the construction of a functional small-diameter artificial blood vessels. This review describes the current status of the use of endothelial cells to improve the performance of artificial vascular prostheses.

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Last Modified: 8 February 2006