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Endotoxin contamination in wound dressings made of natural biomaterials
Nakagawa, Y., T. Murai, et al. (2003), J Biomed Mater Res B Appl Biomater 66(1): 347-55.
Abstract: Contamination by endotoxin of nine kinds of wound dressings made of natural biomaterials (calcium alginate, collagen, chitin, and poly-L-leucine) was examined with the use of water extracts. By applying the Limulus amoebocyte lysate (LAL) test, high concentrations of endotoxin were detected in extracts from three kinds of products made of calcium alginate. These extracts evoked fever in rabbits and induced the release of a proinflammatory (pyrogenic) cytokine, interleukin-6 (IL-6), from human monocytic cells (MM6-CA8). The effects disappeared when the extracts were treated with endotoxin-removing gel column chromatography or with an endotoxin antagonist, B464, confirming that the contaminating pyrogen was endotoxin. A noteworthy finding was that one of the endotoxin-containing extracts showed very weak IL-6-inducibility in human monocytic cells in contrast to its high pyrogenicity to rabbits. The discrepancy could be explained based on differences between humans and rabbits in sensitivity to the endotoxin, because the extract showed higher proinflammatory-cytokine (TNF-alpha)-inducibility in rabbit whole-blood cells (WBCs) than human WBCs. The results suggest that the LAL test is a useful method of detecting endotoxin contamination in wound dressings and the MM6-CA8 assay is a good supplement to the LAL test for evaluating pyrogenicity in humans accurately.

Endotoxin: the uninvited guest
Gorbet, M. B. and M. V. Sefton (2005), Biomaterials 26(34): 6811-7.
Abstract: In the laboratory environment where biomaterials are synthesized and their biocompatibility assessed, we find that endotoxin contamination is hard to avoid and must not be ignored. In those relatively few cases where endotoxin was known to be present, it has been clearly shown that endotoxin can significantly affect the biological response observed and hence confound any effect of the material. This short review explains what endotoxin is, how to test for it and remove it and what its effect on the biological response to biomaterials is. We advocate routine testing of endotoxin on biomaterials and of reagents used in experimental evaluation of biomaterials and this should be the responsibility of every scientist to ensure the validity of any biomaterial study.

Endovascular delivery of vein segments with valves versus direct anastomosis
Kucher, T., B. Brener, et al. (2005), J Endovasc Ther 12(3): 366-70.
Abstract: PURPOSE: To demonstrate an experimental model designed to allow placement of a vein segment containing a valve into a femoral vein without the need for anastomoses or surgical incision on the target limbs. METHODS: Segments of jugular veins containing valves were harvested bilaterally from 7 female dogs weighing 30 to 40 kg. One of the vein segments was then interposed into one femoral vein, using a standard surgical end-to-end anastomosis. Another segment was loaded into a self-expanding nitinol stent, everted, and secured outside of the stent. This vein-coated stent was then deployed from the jugular approach into the opposite common femoral vein. The endpoint of the study was thrombosis of one of the veins segments or patency at 120 days. The function of the valves was tested prior to completion of the study by instilling dye under incremental pressures and recording the pressure necessary to cause reflux. Light microscopy and electron microscopy were utilized to evaluate structure of the valves at study endpoint. RESULTS: Both grafts in one dog occluded during the second week after surgery. Anastomotic and vein-stented sites remained patent in the remaining 6 animals for 120 days. Retrograde phlebography demonstrated valve competency bilaterally in all cases. The reflux pressures on the stented side averaged 70 mmHg while the transplanted vein segment averaged 55 mmHg. Light microscopy and electron microscopy showed intact vein valve structure in all segments at the completion of the study. CONCLUSIONS: This experimental work demonstrates that endovascular delivery of a native canine vein containing a competent valve is feasible and effective.

Endovascular stent configuration affects intraluminal flow dynamics and in vitro endothelialization
Akagawa, E., K. Ookawa, et al. (2004), Biorheology 41(6): 665-80.
Abstract: Neointimal hyperplasia influenced by intravascular hemodynamics is considered partly responsible for restenosis after endovascular stenting. To evaluate the effect of stent configuration on fluid flow behavior, we visualized flow near stents, and measured the proliferation of cultured endothelial cells (ECs). A single-coil stent (coil pitch; CP = 2.5, 5, or 10 mm) was inserted into a glass tube and perfused at 30-90 ml/min, while the flow pattern was determined by particle imaging velocimetry. The reduction of the flow velocity near the wall was correlated with the decrease in the coil interval of the stent. In perfusion cultures with stents, the proliferation of ECs was influenced by the local flow velocity distribution. When a stent with a CP value of 10 mm was used, the doubling time of ECs was 30.7 h, while the doubling time was 38.5 h when the CP was 5 mm. The doubling time of ECs was shorter at sites upstream of the stent wire where the velocity was higher than downstream of the wire. In conclusion, a single-coil stent can be used to modify hemodynamic factors, suggesting that improved stent design may facilitate rapid endothelialization after stent implantation.

Engineered skin substitutes: practices and potentials
Supp, D. M. and S. T. Boyce (2005), Clin Dermatol 23(4): 403-12.
Abstract: Wound healing can be problematic in several clinical settings because of massive tissue injury (burns), wound healing deficiencies (chronic wounds), or congenital conditions and diseases. Engineered skin substitutes have been developed to address the medical need for wound coverage and tissue repair. Currently, no engineered skin substitute can replace all of the functions of intact human skin. A variety of biologic dressings and skin substitutes have however contributed to improved outcomes for patients suffering from acute and chronic wounds. These include acellular biomaterials and composite cultured skin analogs containing allogeneic or autologous cultured skin cells.

Engineering bone: challenges and obstacles
Logeart-Avramoglou, D., F. Anagnostou, et al. (2005), J Cell Mol Med 9(1): 72-84.
Abstract: Repair of large bone defects is still a challenge for the orthopaedic, reconstructive and maxillo-facial surgeon. Availability of pluripotent stem cells from either autologous or allogenic sources and the potential of inducing the osteogenic phenotype is motivating exploration and development of custom-tailored materials known as "bioengineered bone constructs". In such cases, the clinical scenario involves either expansion of stem cells in monolayer and loading them into a porous scaffold prior to surgery or direct cell expansion within the scaffold, and implanting this novel construct back into the donor patient. In this review, we delineate, from an engineering perspective, the progress that has been made to date and the challenges remaining in successfully translating this promising (but not yet definitively established) approach from bench to the bed site.

Engineering craniofacial scaffolds
Hollister, S. J., C. Y. Lin, et al. (2005), Orthod Craniofac Res 8(3): 162-73.
Abstract: OBJECTIVE: To develop an integrated approach for engineering craniofacial scaffolds and to demonstrate that these engineered scaffolds would have mechanical properties in the range of craniofacial tissue and support bone regeneration for craniofacial reconstruction. EXPERIMENTAL VARIABLE: Scaffold architecture designed to achieve desired elasticity and permeability. Scaffold external shape designed to match craniofacial anatomy. OUTCOME MEASURE: Final fabricated biomaterial scaffolds. Compressive mechanical modulus and strength. Bone regeneration as measured by micro-CT scanning, mechanical testing and histology. SETTING: Departments of Biomedical Engineering, Oral/Maxillofacial Surgery, and Oral Medicine, Pathology and Oncology at the University of Michigan. RESULTS: Results showed that the design/fabrication approach could create scaffolds with designed porous architecture to match craniofacial anatomy. These scaffolds could be fabricated from a wide range of biomaterials, including titanium, degradable polymers, and degradable calcium phosphate ceramics. Mechanical tests showed that fabricated scaffolds had compressive modulus ranging 50 to 2900 MPa and compressive strength ranging from 2 to over 56 MPa, within the range of human craniofacial trabecular bone. In vivo testing of designed scaffolds showed that they could support bone regeneration via delivery of BMP-7 transduced human gingival fibroblasts in a mouse model. Designed hydroxyapatite scaffolds with pore diameters ranging from 400 to 1200 microns were implanted in minipig mandibular defects for 6 and 18 weeks. Results showed substantial bone ingrowth (between 40 and 50% at 6 weeks, between 70 and 80% at 18 weeks) for all scaffolds, with no significant difference based on pore diameter. CONCLUSION: Integrated image-based design and solid free-form fabrication can create scaffolds that attain desired elasticity and permeability while fitting any 3D craniofacial defect. The scaffolds could be manufactured from degradable polymers, calcium phosphate ceramics and titanium. The designed scaffolds supported significant bone regeneration for all pore sizes ranging from 300 to 1200 microns. These results suggest that designed scaffolds are clinically applicable for complex craniofacial reconstruction.

Engineering criteria for biomaterials: some thought on in situ measurements
Katz, J. L. (1979), Biomater Med Devices Artif Organs 7(1): 81-7.
Abstract: Several non-destructive techniques now exist which show promise of providing information about implant performance in situ. Surface wave ultrasonics have been used successfully in the laboratory to measure the anisotropic properties of bone. It has also been used clinically to assess rates of fracture healing. Acoustic emission has been used experimentally to investigate bone abnormalities such as microfracture and osteoporosis in vitro. Application of these techniques to clinical studies depends upon the establishment of the appropriate parameters for bone and the various biomaterials used as implants. Surface wave ultrasound may also provide information about tissue ingrowth into porous systems. Acoustic emission can be especially significant in the early detection of implant failure.

Engineering micropatterned surfaces for the coculture of hepatocytes and Kupffer cells
Zinchenko, Y. S. and R. N. Coger (2005), J Biomed Mater Res A 75(1): 242-8.
Abstract: Bioartificial liver (BAL) devices are used for applications ranging from pharmaceutical testing to temporary liver replacement. The capabilities of these devices can be improved by optimizing the range of hepatocyte functions that the BAL is able to perform. One means of achieving this is to design the BAL such that it establishes communication between hepatocytes and nonparenchymal cells. To understand how these heterotypic interactions can be favorably utilized in BAL design, it is first necessary to establish a culture environment that permits the controlled interactions of multiple cell types. This is the goal of the current study, which focuses on micropatterned cocultures of hepatocytes with Kupffer cells. The micropatterning technique relies on a polydimethylsiloxane (PDMS) membrane to achieve various two-dimensional configurations of the ECM prior to seeding the cell populations. The easy and inexpensive method of making the PDMS membranes differs from that reported in the literature and is detailed in the current study. To demonstrate the success of the method, surface characterization of the resultant micropatterns, as well as morphological and functional results are also presented.

Engineering of biomaterials surfaces by hyaluronan
Morra, M. (2005), Biomacromolecules 6(3): 1205-23.
Abstract: This review addresses the area of study that defines the field of surface modification of biomedical materials and devices by hyaluronan (HA), as related to the exploitation of HA biological properties. To provide a comprehensive view of the subject matter, initial sections give a quick introduction to basic information on HA-protein and HA-cell interactions, together with some discussion on the bioactive role of HA in wound healing and related phenomena. This is followed by a description of current theories that correlate HA properties to its molecular structure in aqueous media, underlying how HA molecular details are crucial for its biological interaction and role. Finally, existing approaches to surface modification by HA are reviewed, stressing the need for HA-surface engineering founded on the knowledge and control of the surface-linked HA molecular conformation at the solid/aqueous interface.

Engineering the extracellular matrix: a novel approach to polymeric biomaterials. I. Control of the physical properties of artificial protein matrices designed to support adhesion of vascular endothelial cells
Welsh, E. R. and D. A. Tirrell (2000), Biomacromolecules 1(1): 23-30.
Abstract: Methods of genetic engineering were applied to the design and biosynthesis of three extracellular matrix protein analogues constructed from identical elastin- and fibronectin-derived repeating units but characterized by different molecular weights in the range of 14,000 to 59,000. Expression levels were enhanced by the serendipitous choice of an N-terminal fusion sequence such that gram-scale syntheses were achieved for each protein. Purification protocols were developed that resulted in proteins of high purity and correct sequence, as determined by amino acid analysis, NMR spectroscopy, and lower critical solution temperature (LCST). Glutaraldehyde was shown to insolubilize the otherwise soluble proteins in a concentration-dependent manner. Tensile moduli of cross-linked protein films were measured and found to be inversely related to the molecular weights of the engineered proteins, which in each case corresponds to the theoretical molecular weight between cross-links. At the highest cross-link density (lowest molecular weight) the elastic modulus was similar to that of native elastin.

Engrafting periodontal fibroblasts with new 3-dimensional polylactide foams
Poll, B., P. Buttler, et al. (2005), Int J Artif Organs 28(8): 827-33.
Abstract: In clinical periodontics, "tissue engineering" techniques have been developed to guide the regenerative process following periodontal disease. We explored a new shaped biomaterial in order to promote cellular adhesion, proliferation and migration of periodontal cells. Granules of poly-D, L-lactide were foamed in specially designed moulds by a controlled gas-loading process. Explant cultures of periodontal tissue were seeded at different densities on the 3-dimensional scaffolds following analysis of cytotoxicity, cell proliferation and differentiation. The moulding procedure led to porous structures with predetermined tubes for cellular locomotion. Cells adhered to and populated the material's surface and inner cavities while retaining fibroblastic phenotype. An optimal ratio between cellular proliferation and mortality rate was achieved at a seeding density of > 10 6 cells/cm 3 scaffold. We designed modified polylactide scaffolds capable of acting as a stent and a cell carrier matrix. The foaming process is easy, cheap and suitable for commercial production.

Enhanced attachment and growth of human endothelial cells derived from umbilical veins on ammonia plasma modified surfaces of PTFE and ePTFE synthetic vascular graft biomaterials
Sipehia, R., G. Martucci, et al. (1993), Biomater Artif Cells Immobilization Biotechnol 21(4): 455-68.
Abstract: Ammonia plasma generated by electrical discharge at low pressure was employed for the surface modification of PTFE and ePTFE. A new chemistry at the plasma treated surfaces is reported. X-ray photoelectron spectroscopy studies showed the incorporation of C-N, C-O, C = O etc functional groups on the plasma treated surfaces. Human endothelial cells derived from umbilical veins (HUEC) were used to seed the plasma treated PTFE and ePTFE surfaces to assess the attachment and growth. Enhanced attachment and growth of HUEC was observed on the plasma treated surfaces. In addition, the performance of these surfaces in this respect was found to be considerably superior to human collagen or human fibronectin or collagen-fibronectin coated PTFE. HUEC attachment and growth on these plasma treated surfaces was further enhanced by immobilizing collagen or fibronectin or collagen-fibronectin. Ammonia plasma treated and untreated ePTFE vascular graft samples were seeded with 3.6 X 10(4) cells/sample. At 24 hrs after seeding, HUEC cell attachment was studied. Although, HUEC attachment on collagen or fibronectin coated ePTFE was improved, but there was no significant difference between the number of cells attached to these surfaces when compared with those adhered to plasma treated ePTFE without collagen or fibronectin coating. Collagen or fibronectin coated plasma treated surfaces showed better performance over their respective controls.

Enhanced bone formation by controlled growth factor delivery from chitosan-based biomaterials
Lee, J. Y., S. H. Nam, et al. (2002), J Control Release 78(1-3): 187-97.
Abstract: For the purpose of obtaining high bone forming efficacy, development of chitosan was attempted as a tool useful as a scaffolding device. Porous chitosan matrices, chitosan-poly(L-lactide) (PLLA) composite matrices and chitosan coated on PLLA matrices were dealt with in this research. Porous chitosan matrix was fabricated by freeze-drying and cross-linking aqueous chitosan solution. Porous chitosan matrix combined with ceramics and constituents of extracellular matrices were prepared and examined for their bone regenerative potential. Composite porous matrix of chitosan-PLLA was prepared by mixing polylactide with chitosan and freeze-drying. All chitosan based devices demonstrated improved bone forming capacity by increasing mechanical stability and biocompatibility. Release of platelet-derived growth factor-BB (PDGF-BB) from these matrices exerted significant osteoinductive effect in addition to the high osteoconducting capacity of the porous chitosan matrices. The hydrophobic surface of PLLA matrices was modified by chitosan to enhance cell affinity and wettability. The chitosan coated PLLA matrix induced increased osteoblast attachment as compared with intact PLLA surface. Overall results in this study demonstrated the usefulness of chitosan as drug releasing scaffolds and as modification tools for currently used biomaterials to enhance tissue regeneration efficacy. These results may expand the feasibility of combinative strategy of controlled local drug delivery concept and tissue engineered bone formation in reconstructive therapy in the field of periodontics, orthopedics and plastic surgery.

Enhanced catalase synthesis by a novel combined system of photocatalytic reactor and fermentor
Yan, G., Z. Hua, et al. (2005), Biotechnol Lett 27(10): 683-7.
Abstract: A novel combined system of a photocatalytic reactor, with UV and titanium dioxide as photocatalyst, and a fermentor with Bacillus sp. F26 as catalase producer was developed. Production of catalase was enhanced by 14% to 18.5 U ml-1 without affecting cell growth.

Enhanced effects of lithocholic acid incorporation into liquid-crystalline biopolymer poly(coumaric acid) on structural ordering and cell adhesion
Matsusaki, M., T. Hang Thi, et al. (2005), Biomaterials 26(32): 6263-70.
Abstract: A novel thermotropic liquid-crystalline biocopolymer, poly{trans-4-hydroxycinnamic acid (4HCA: trans-coumaric acid)-co-lithocholic acid (LCA)}, was synthesized by a thermal polycondensation of 4HCA and LCA. When the LCA composition of P(4HCA-co-LCA) was 0, 5, 7, 23, 27, and 45 mol%, the copolymers showed a nematic liquid-crystalline phase. The melting point of the copolymers was 120-250 degrees C depending on the LCA composition, and showed a maximum at 7 mol%. Wide angle X-ray diffraction (WAXD) analyses showed a typical diffraction pattern of a hexagonal arrangement for 0, 7, 23, and 27 mol% LCA composition, which were cooled from a nematic melt. The other polymers showed no distinct diffraction. In particular, the copolymer of 7 mol% LCA composition showed four distinct diffractions corresponding to spacings with a reciprocal ratio of 1, radical3, 2, and radical7, indicating the highest structural ordering of all copolymers prepared here. The results of the cell adhesion and static contact angle tests suggest that the 7 mol% LCA composition copolymer had the highest hydrophobicity and cell adhesion ability, which was easily controlled by altering in feed. We conclude that the structural ordering may have a significant correlation with cell adhesion activity.

Enhanced granulation by natural ionic polymer additives in UASB reactor treating low-strength wastewater
Tiwari, M. K., S. Guha, et al. (2005), Water Res 39(16): 3801-10.
Abstract: Effect of natural ionic polymer additives on granulation in lab-scale UASB reactors treating low-strength synthetic wastewater (COD 750-850 mg/L) was examined. The organic loading rate was 1.477+/-0.118 kgCOD/m3/day. Under identical conditions four similar reactors were operated in parallel with the following additives: control with no additive, anionic part of Reetha (Sapindus trifoliata) extract, cationic part of Reetha extract, and Chitosan. By the end of the study period, Chitosan as an additive produced largest granules with mean size of 0.15 mm closely followed by the cationic fraction of the Reetha extract with mean size of 0.144 mm, and anionic fractions of the Reetha extract with 0.139 mm. Control reactor with no additives had the smallest size granules with mean size of 0.128 mm. The fraction of granules in the sludge bed of size >0.1 mm showed similar trend. The largest granule size observed in the reactors with additives was 4-5mm as compared to 2 mm in the control reactor. Cationic polymers were more effective additives for enhancing sludge granulation. Exo-cellular protein, lipid, sugar and total polymer increased with granulation in the reactors. A COD removal efficiency of 95-98% was achieved in all the reactors.

Enhanced osteoinduction by controlled release of bone morphogenetic protein-2 from biodegradable sponge composed of gelatin and beta-tricalcium phosphate
Takahashi, Y., M. Yamamoto, et al. (2005), Biomaterials 26(23): 4856-65.
Abstract: Biodegradable gelatin sponges at different contents of beta-tricalcium phosphate (beta-TCP) were fabricated to allow bone morphogenetic protein (BMP)-2 to incorporate into them. The in vivo osteoinduction activity of the sponges incorporating BMP-2 was investigated, while their in vivo profile of BMP-2 release was evaluated. The sponges prepared had an interconnected pore structure with an average pore size of 200 microm, irrespective of the beta-TCP content. The in vivo release test revealed that BMP-2 was released in vivo at a similar time profile, irrespective of the beta-TCP content. The in vivo time period of BMP-2 retention was longer than 28 days. When the osteoinduction activity of gelatin or gelatin-beta-TCP sponges incorporating BMP-2 was studied following the implantation into the back subcutis of rats in terms of histological and biochemical examinations, homogeneous bone formation was histologically observed throughout the sponges, although the extent of bone formation was higher in the sponges with the lower contents of beta-TCP. On the other hand, the level of alkaline phosphatase activity and osteocalcin content at the implanted sites of sponges decreased with an increase in the content of beta-TCP. The gelatin sponge exhibited significantly higher osteoinduction activity than that of any gelatin-beta-TCP sponge, although every sponge with or without beta-TCP showed a similar in vivo profile of BMP-2 release. In addition, the in vitro collagenase digestion experiments revealed that the gelatin-beta-TCP sponge collapsed easier than the gelatin sponge without beta-TCP incorporation. These results suggest that the maintenance of the intrasponge space necessary for the osteoinduction is one factor contributing to the osteoinduction extent of BMP-2-incorporating sponges.

Enhanced peripheral nerve regeneration through a poled bioresorbable poly(lactic-co-glycolic acid) guidance channel
Bryan, D. J., J. B. Tang, et al. (2004), J Neural Eng 1(2): 91-8.
Abstract: In this study we investigated the effects of materials prepared with electrical poling on neurite outgrowth in vitro and nerve regeneration in vivo. Neuro-2a cells were seeded on poled and unpoled poly(lactic-co-glycolic) (PLGA) films and observed at time periods 24, 48 and 72 h post-seeding. The percentage of cells with neurites and the neurites per cell were quantified using light microscopy. At 48 and 72 h post-seeding, both the number of cells with neurites and the neurites per cell were significantly increased on the poled films compared to those on unpoled films. An established rat sciatic nerve model was used for in vivo studies to assess the effects of PLGA guides, poled for two different periods, on peripheral nerve regeneration. Guides were inserted in rats to bridge a 1.0 cm gap created in the right sciatic nerve. After four weeks, nerves regenerated through poled guides displayed a significant increase in conduction velocity and significantly increased numbers of axons across the guides, as compared to nerves regenerating through an unpoled guidance channel. Electrical poling was shown to promote neurite growth, axon regeneration and the conduction rate of the repaired nerve. We concluded that guides prepared with electrical poling enhance peripheral nerve regeneration.

Enhanced photocatalytic degradation of VOCs using Ln3+-TiO2 catalysts for indoor air purification
Li, F. B., X. Z. Li, et al. (2005), Chemosphere 59(6): 787-800.
Abstract: Two types of lanthanide ion-doped titanium dioxide (Ln3+-TiO2) catalysts including La3+-TiO2 and Nd3+-TiO2 were prepared by a sol-gel method. The effects of the lanthanide ion doping on the crystal structure, surface area, adsorption properties, pore size distribution, and surface chemical state of the catalysts were investigated by means of XRD, BET, and XPS. As results, the crystal size decreased significantly, while the specific surface area, t-plot total surface area, micropore volume, and the total pore volume increased owing to the lanthanide ion doping. The nitrogen adsorption-desorption isotherms of the catalysts showed that the N2 adsorption ability of the Ln3+-TiO2 catalysts was better than the TiO2 catalyst. Among them, the 0.7% Ln3+-TiO2 catalysts demonstrated the highest adsorption ability. The photocatalytic activity of the catalysts was investigated in the experiments of the photocatalytic degradation of benzene, toluene, ethylbenzene and o-xylene (BTEX) in a gaseous phase. The photocatalytic efficiency of the TiO2 catalysts with the lanthanide ion doping was remarkably enhanced by BTEX removal. The 1.2% Ln3+-TiO2 catalysts achieved the highest photocatalytic activity. The enhanced photodegradation of BTEX is possibly due to the improved adsorption ability and the enhanced electron-hole pairs separation due to the presence of Ti3+ on the surface of Ln3+-TiO2 catalysts and the electron transfer between the conduction band/defect level and lanthanide crystal field state.

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Last Modified: 8 February 2006