|Articles about Biomaterials|
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| Growth of miniature pig parotid cells on biomaterials in vitro
Sun, T., J. Zhu, et al. (2005), Arch Oral Biol
Abstract: Both Sjogren's syndrome and therapeutic irradiation for head and neck cancer lead to irreversible damage of the parenchyma of the salivary glands. This report describes an attempt to grow miniature pig (minipig) parotid gland cells on artificial films and tubular scaffolds with the ultimate intention of developing bio-engineered replacement tissue. Minipig parotid cells were isolated and cultured. The growth and structural and physiological features of the cells which were cultured on films and porous tubular scaffolds made from poly(ethylene glycol)-terephthalate (PEGT)/poly(butylene terephthalate) (PBT) were examined. By 9 days, the parotid cells on the films and the tubular scaffolds formed continuous monolayers. The secretory granules and nuclei of the cultured acinar cells remained polarised. Desmosomes, gap junctions and tight-like junctions were still present between the apical regions of adjacent cells. Amylase activity decreased during the culture period but was still evident in the medium after 10 days of culture. In conclusion, minipig parotid cells are well-maintained in vitro on both a flat surface and a three-dimensional (3D) scaffold. The addition of a Matrigel coating to the surface of synthetic materials aids cell growth and maintenance of a morphology that more closely resembles normal epithelium.
| Growth of nano-scale hydroxyapatite using chemically treated titanium oxide nanotubes
Oh, S. H., R. R. Finones, et al. (2005), Biomaterials 26(24): 4938-43.
Abstract: A vertically aligned nanotube array of titanium oxide was fabricated on the surface of titanium substrate by anodization. The nanotubes were then treated with NaOH solution to make them bioactive, and to induce growth of hydroxyapatite (bone-like calcium phosphate) in a simulated body fluid. It is shown that the presence of TiO2 nanotubes induces the growth of a "nano-inspired nanostructure", i.e., extremely fine-scale (approximately 8 nm feature) nanofibers of bioactive sodium titanate structure on the top edge of the approximately 15 nm thick nanotube wall. During the subsequent in-vitro immersion in a simulated body fluid, the nano-scale sodium titanate, in turn, induced the nucleation and growth nano-dimensioned hydroxyapatite (HAp) phase. The kinetics of HAp formation is significantly accelerated by the presence of the nanostructures. Such TiO2 nanotube arrays and associated nanostructures can be useful as a well-adhered bioactive surface layer on Ti implant metals for orthopaedic and dental implants, as well as for photocatalysts and other sensor applications.
| Growth of uniformly aligned ZnO nanowire heterojunction arrays on GaN, AlN, and Al0.5Ga0.5N substrates
Wang, X., J. Song, et al. (2005), J Am Chem Soc 127(21): 7920-3.
Abstract: Vertically aligned single-crystal ZnO nanorods have been successfully fabricated on semiconducting GaN, Al0.5Ga0.5N, and AlN substrates through a vapor-liquid-solid process. Near-perfect alignment was observed for all substrates without lateral growth. Room-temperature photoluminescence measurements revealed a strong luminescence peak at approximately 378 nm. This work demonstrates the possibility of growing heterojunction arrays of ZnO nanorods on AlxGa1-xN, which has a tunable band gap from 3.44 to 6.20 eV by changing the Al composition from 0 to 1, and opens a new channel for building vertically aligned heterojunction device arrays with tunable optical properties and the realization of a new class of nanoheterojunction devices.
| Guided periodontal regeneration using bilayered collagen membranes and bovine bone mineral in fenestration defects in the canine
Tal, H., Z. Artzi, et al. (2005), Int J Periodontics Restorative Dent 25(5): 509-18.
Abstract: This study was performed to evaluate the effect of deproteinized bovine porous bone mineral (BBM) and BBM-collagen (BBMC) used alone or in combination with a bilayer collagen membrane in guided periodontal regeneration. In 12 dogs, contralateral surgical circular fenestration defects 5 mm in diameter were produced at the midbuccal aspect of the alveolar bone in 24 maxillary canines. Bone, periodontal ligament, and cementum were completely removed. Experimental sites were filled with BBM or BBMC. Bilayered collagen membranes covered half the experimental sites (BBM+M and BBMC+M), and the other half were left uncovered. Control sites remained empty; half were covered with collagen membranes (cont+M) and the underlying space spontaneously filled with blood, and half were left uncovered (cont). Three months postsurgery, undecalcified sections were prepared. Measurements were made using a caliper on a projection microscope, and the surface area of new bone and BBM particles within the healed surgical defect was evaluated using the point-counting method. In the experimental defects, new cementum covered 31% to 67% of the exposed dentin, with a significant difference between defects covered with membranes and defects that were not covered (P <.05). New cementum in the control (unfilled) defects also differed significantly between covered and uncovered defects. New bone growth presented a pattern similar to the cementum. There was no statistical difference between defects treated with BBM and BBMC, within both covered and uncovered groups. There was less connective tissue in the covered defects than in the uncovered defects (P <.05). The defects were filled with new bone, new connective tissue/bone marrow, and bovine bone particles. New bone area fraction was 23.4% to 25.2% in defects filled with BBMC and BBM, respectively (P = NS). Bone fraction area in membrane-covered defects ranged from 34.4% to 36.8% in experimental defects (P = NS). All membrane-treated defects showed higher values for bone area fraction in comparison to the uncovered control defects. Particle area fraction ranged between 17.4% and 26.2%, with only BBMC and BBM+M defects showing a statistically significant difference (P <.05). Defects filled with submembranous blood clot exhibited significantly more new cementum and bone regeneration than experimental defects filled with BBM or BBMC. Treatment of defects with BBM or BBMC showed similar influences on bone and cementum regeneration in fenestration periodontal defects. The presence or absence of bilayered collagen membranes was the predominant factor influencing bone and cementum regeneration.
| Guidelines for the hematologic evaluation of contrast media. For the Subcommittee on Rheology, Biomaterials, and Contact Activation of the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis
Grabowski, E. F. (1994), Thromb Haemost 72(2): 322-4.
| Guidelines for the performance of fusion procedures for degenerative disease of the lumbar spine. Part 16: bone graft extenders and substitutes
Resnick, D. K., T. F. Choudhri, et al. (2005), J Neurosurg Spine 2(6): 733-6.
Abstract: Despite the large volume of animal data regarding the use of synthetic bone graft substitutes or extenders, there are very few data regarding the use of these substances for fusion in lumbar degenerative disease. The best available data indicate that rhBMP-2 is a viable alternative to autograft bone for interbody fusion procedures. This same substance may also be a viable alternative to autograft for PLF; however, definitive medical evidence is not yet available. There is little, if any, medical evidence to support the use of other biological agents at the present time. As promising new compounds are brought to market, well-designed cohort studies and randomized trials will be required to determine the actual usefulness of these compounds in clinical practice. It is important not to generalize the results obtained with one preparation or application to different preparations or applications. The use of synthetic calcium phosphate ceramics as graft extenders appears to be reasonable in certain situations. The medical evidence available regarding their use is limited and of poor quality. Further study will be required to establish their utility for use in spinal fusion.
| HA/TCP compounding of a porous CaP biomaterial improves bone formation and scaffold degradation--a long-term histological study
Schopper, C., F. Ziya-Ghazvini, et al. (2005), J Biomed Mater Res B Appl Biomater 74(1): 458-67.
Abstract: In the present study, two biphasic calcium phosphate biomaterials (BCP) with HA/TCP ratios of 50/50 and 30/70 were obtained from a pure HA biomaterial. The biomaterials which showed the same three-dimensional geometry were implanted into corticocancellous costal defects of sheep. In the specimens of all three biomaterials, abundant bone formation, mineral dissolution from the biomaterial scaffolds, and active cellular resorption of the scaffolds was present after 6 and 12 months. Backscattered electron microscopy showed bone invasion into the pores of the scaffolds and micromechanical interlocking at the bone/biomaterial interface without intervening soft tissue. The pattern of bone formation and scaffold resorption was different for cortical and cancellous bone. No time-based effect, however, was observed. Overall, the BCP biomaterials had formed significantly more bone than the HA biomaterial. Also, scaffold resorption, which was followed by a replacement with newly formed bone, was significantly higher in the BCP biomaterials. Although no significant differences were observed between both BCP biomaterials, the present study had confirmed the assumption that HA/TCP compounding was suitable to improve bone formation and scaffold resorption in the investigated biomaterials and at the same time maintain the osteoconductive properties of the scaffolds.
| Haemocompatibility of polymer-coated stainless steel stents as compared to uncoated stents
Mrowietz, C., R. P. Franke, et al. (2005), Clin Hemorheol Microcirc 32(2): 89-103.
Abstract: Acute and subacute stent thrombosis still represent an unsolved problem in connection with endovascular stents. For this reason coatings are tested now with the intention to reduce thrombogenicity of stainless steel surfaces. This comparative study examined whether a polymeric stent coating affected the haemocompatibility of a stainless steel stent. For compatibility testing, coated and non-coated stents were implanted in a low-grade thrombogenic closed-loop system perfused with platelet rich plasma at shear rates far below the threshold value at which shear-rate-induced activation of thrombocytes occurs. After 21 circulations of the filling volume (exposure time: 6.2 min), the number of single circulating platelets in the perfusion system with uncoated stainless steel stents decreased almost twice as much as was the case with polymer-coated stents. This is thought to indicate that more thrombocytes had adhered to the uncoated stainless steel stent, or that the thrombocytes were clustered in circulating aggregates. Parallel to the platelet aggregation/adherence, a release reaction took place, as was evident from the TAT complexes indicating the generation of thrombin. In the case of the implantation of uncoated stainless steel stents, both the number of activated circulating thrombocytes and the level of platelet reactivity (number of thrombocytes circulating in the plasma as aggregates) were notably higher than in the system with polymer-coated stents. At the same time it should be noted that the activation or aggregation is almost wholly attributable to the exogenic surface of the implanted stent, since activation due to the tube system or to shear rate can be excluded (as shown by measurements of the system without a stent). In addition to activation of the thrombocytes, a notable increase in the number of receptors per platelet (significant only in the system with the uncoated stent) took place. This supports both the adherence of the thrombocytes and their readiness to aggregate, since more receptors (docking places for ligands) are available. The better haemocompatibility of the polymer-coated stents, as verified in the laboratory, was also evident under microscopic examination of the explanted stents following the perfusion tests.
| Handling characteristics of precoated and operator-coated brackets
Hirani, S. (2005), J Clin Orthod 39(7): 429-31.
| Hard tissue remodeling using biofabricated coralline biomaterials
Vago, R., D. Plotquin, et al. (2002), J Biochem Biophys Methods 50(2-3): 253-9.
Abstract: Biotechnical and biomedical approaches were combined in an attempt to identify potential uses of biofabricated marine carbonate materials in biomedical applications, particularly as biomatrices for remodeling bone and cartilage tissue. After grafting, it is desirable for bone ingrowth to proceed as quickly as possible because the strength of the implanted region depends on a good mechanical bond forming between the implant and surrounding regions in the body. Ingrowth can take place as a result of growth of tissue and cells into the implanted porous material, or it may be promoted by transplanting cells seeded onto such a material. The rate at which ingrowth occurs is dependent on many factors, including pore size and the interconnectivity of the implanted structure. In vivo graftings into osteochondral defects demonstrated that our biofabricated porous material is highly biocompatible with cartilage and bone tissue. The biofabricated matrix was well incorporated into the biphasic osteochondral area. Resorption was followed by bone and cartilage formation, and after 4 months, the biomaterial had been replaced by new tissue. Ossification was induced and enhanced without introduction of additional factors. We believe that this is the first time that such biofabricated materials have been used for biomedical purposes. In face of the obvious environmental disadvantages of harvesting from limited natural resources, we propose the use of bioengineered coralline and other materials such as those cultured by our group under field and laboratory conditions as a possible biomatrix for hard tissue remodeling.
| Harmonic and impulse rheological tests of biomaterials
Geiger, D., D. Trevisan, et al. (1984), Biorheology Suppl 1: 193-200.
Abstract: Up to now, not so much attention has been paid concerning the dynamic rheological behaviour of soft tissues although non linear viscoelastic effects have often been reported when mechanical properties of biomaterials are concerned. In order to characterize such properties different rheological tests have been proposed, the two principal being the study of the sample stresses responses to applied strains which are either harmonic with time or of step function type. Two different apparatus have been designed in our laboratory which allow specific rheological tests on biological materials under controlled environmental conditions. With one of them, harmonic uniaxial extension tests are performed in a large domain of frequencies (001 Hz to 100 Hz) and forces (up to 20 daN); with the other, the samples are submitted to relaxation tests in uniaxial elongation up to 5 cm deformation within time duration of the order of 20 ms. The principal characteristics, limitations and performances of such apparatus are presented and few examples of data thus obtained are given. On the basis of quasi linear viscoelasticity models, it can be shown that both two types of tests with their proper limitations are leading to the same rheological parameters.
| Hastings lecture. Breaking the blood-biomaterial barrier
Edmunds, L. H., Jr. (1995), Asaio J 41(4): 824-30.
| Healing of a critical-sized defect in the rat femur with use of a vascularized periosteal flap, a biodegradable matrix, and bone morphogenetic protein
Vogelin, E., N. F. Jones, et al. (2005), J Bone Joint Surg Am 87(6): 1323-31.
Abstract: BACKGROUND: The purpose of this study was to evaluate the osseous healing of a critical-sized femoral defect in a rat model with use of recombinant human bone morphogenetic protein-2 (rhBMP-2), a matrix fabricated of D,D-L,L-polylactic and hyaluronan acid (OPLA-HY), and a vascularized periosteal flap. METHODS: The carrier matrix OPLA-HY with or without rhBMP-2 was implanted in a 1-cm-long femoral defect and secured with a plate and screws. In some groups, a vascularized periosteal flap was harvested from the medial surface of the tibia. In group 1, the femoral defects in the animals were filled with the OPLA-HY matrix alone; in group 2, the OPLA-HY matrix was covered by the vascularized periosteal flap; in group 3, 20 mug of rhBMP-2 was added to the OPLA-HY matrix; and in group 4, the femoral defect containing the OPLA-HY matrix and 20 mug of rhBMP-2 was wrapped circumferentially by the vascularized periosteal flap. The presence and density of new bone formation in the femoral defect were evaluated radiographically, histologically, and with histomorphometry at four and eight weeks postoperatively. RESULTS: Groups 1 and 2, which were not treated with rhBMP-2, showed no radiographic or histologic evidence of mature bone formation at four or eight weeks. Both groups 3 and 4, which were treated with rhBMP-2, demonstrated excellent bone formation. However, with the periosteal flap, group 4 demonstrated more bone formation on histomorphometric analysis at eight weeks (43.1%) than did group 3 (28.3%) (p < 0.01). Additionally, heterotopic bone formed outside the boundaries of the defect in eight of the fifteen animals in group 3, which had no periosteal flap. CONCLUSIONS: Bone-tissue engineering with use of the OPLA-HY matrix and rhBMP-2 produced good bone formation in the rat femoral defect model. However, the addition of a vascularized periosteal flap significantly increased bone formation within the boundaries of the defect and prevented heterotopic ossification.
| Healing of dehiscence-type defects in implants placed together with different barrier membranes: a comparative clinical study
Moses, O., S. Pitaru, et al. (2005), Clin Oral Implants Res 16(2): 210-9.
Abstract: OBJECTIVE: Premature exposure of membranes used in guided bone regeneration (GBR) results in decreased bone formation. The effect of an expanded polytetrafluoroethylene (e-PTFE) and two collagen membrane on bone healing of buccal dehiscence defects around implants in cases with and without premature membrane exposure was clinically evaluated. METHODS: Three groups were established: Group OS (Ossix, n=73 implants, 41 patients), Group BG (Bio-Gide, n=53 implants, 28 patients) and Group GT (e-PTFE, Gore-Tex, n=34 implants, 17 patients). Defect height and width were measured at the time of implant placement and at second stage surgery. Surface area was calculated as half ellipses. When several implants were placed simultaneously, a mean of their defect width and height was calculated. RESULTS: Mean percentage reduction of defect area (92.2+/-13.78% Group OS, 94.6+/-6.69% Group BG, and 97.3+/-4.91% Group GT) and height (81.6+/-23.19%, 85.4+/-12.26%, and 93.4+/-9.39% respectively) did not show statistically significant differences between groups. Differences between groups were not statistically significant for all parameters when cases without spontaneous membrane exposure were compared. However, differences were significant when spontaneous membrane exposure occurred. Mean percentage reduction of defect area among cases where membrane exposure occurred was 91.5+/-10.86% Group OS, 71.5+/-8.61% Group BG, and 73.7+/-13.97% Group GT. Mean percentage reduction of defect height among cases with membrane exposure was 76.4+/-18.28%, 53.4+/-9.86%, and 49.4+/-11.05%, respectively. CONCLUSIONS: Premature exposure of membranes and subsequent and consequent exposure of implants results in impaired bone healing. Certain barrier membranes, as used in group OS, are apparently capable of supporting gingival healing even when prematurely exposed that could be advantageous in GBR procedures.
| Healing of extraction sockets and surgically produced - augmented and non-augmented - defects in the alveolar ridge. An experimental study in the dog
Cardaropoli, G., M. Araujo, et al. (2005), J Clin Periodontol 32(5): 435-40.
Abstract: OBJECTIVES: The current experiments had three aims (i) to determine whether the absence of the periodontal ligament (PDL) may alter features of the healing of an extraction socket, (ii) to examine if there were differences in the proportion of different tissues in resolved extraction sockets and surgically produced defects after 3 months of healing, (iii) to study the influence of different biomaterials on the healing of surgically produced bone defects. MATERIAL AND METHODS: Extraction sites: In five dogs, the 4th mandibular pre-molars were hemi-sected and the distal roots were removed. The extraction socket of one of the pre-molars was instrumented to eliminate all remnants of the PDL tissue. The socket of the contra-lateral pre-molar was left without instrumentation. The dogs were sacrificed after 3 months of healing. Defect sites: In five dogs, the pre-molars and 1st molars on both sides of the mandible were first removed and 3 months of healing allowed. After this interval three standardized cylindrical defects were prepared in each side of the mandible. The defects were 3.5 mm in diameter and 8 mm deep. In each quadrant one defect was grafted with Bio-Oss Collagen, one with Collagen Sponge and one defect was left non-grafted. The dogs were sacrificed 3 months after the grafting procedure. RESULTS: Extraction sites: The two categories of extraction sockets did not differ with respect to gross morphological features. The tissue of the extraction sites, apical of a newly formed bone bridge, was dominated by bone marrow. Few trabeculae of lamellar bone were also present. Defect sites: The non-augmented defect was sealed by a hard-tissue bridge. In the central and apical portions of the defect bone marrow made up about 61%, and mineralized bone 39% of the tissues. The invagination of the surface of this crestal bone was 0.8+/-0.3 mm. The defect augmented with Collagen Sponge was covered by a hard-tissue bridge 38% of the tissue within the defect was made up of bone marrow while the remaining 62% was occupied by mineralized bone. The invagination of the hard-tissue bridge was on the average 0.6+/-0.1 mm. In defects augmented with Bio-Oss Collagen the biomaterial occupied a substantial portion of the tissue volume. Eighty-five percent of the periphery of the Bio-Oss particles were found to be in direct contact with newly formed mineralized bone. Woven bone and bone marrow made up 47% and 26% of the newly formed tissue. The invagination of the most coronal part of the bone defect was 0.1+/-0.1 mm. CONCLUSION: Sockets that following tooth removal had their PDL tissue removed exhibited similar features of healing after 3 months as sockets which had the PDL retained. The tissues present in an extraction site appeared to be more mature than those present in a surgically produced defect of similar dimension. The Bio-Oss Collagen augmented defect exhibited less wound shrinkage than the non-augmented defect.
| Healing of intra-bony defects following treatment with a composite bovine-derived xenograft (Bio-Oss Collagen) in combination with a collagen membrane (Bio-Gide PERIO)
Sculean, A., G. C. Chiantella, et al. (2005), J Clin Periodontol 32(7): 720-4.
Abstract: AIM: The purpose of the present study was to compare clinically the treatment of deep intra-bony defects with a combination of a composite bovine-derived xenograft (BDX Coll) and a bioresorbable collagen membrane [guided tissue regeneration (GTR)] to access flap surgery only. METHODS: Thirty-two patients, each of whom displayed one intra-bony defect, were treated either with BDX Coll+GTR (test) or with access flap surgery (control). The results were evaluated at 1 year following therapy. RESULTS: No differences in any of the investigated parameters were observed at baseline between the two groups. Healing was uneventful in all patients. At 1 year after therapy, the test group showed a reduction in the mean probing depth (PD) from 8.3+/-1.5 to 2.9+/-1.3 mm (p<0.001) and a change in the mean clinical attachment level (CAL) from 9.4+/-1.3 to 5.3+/-1.5 mm (p<0.0001). In the control group, the mean PD was reduced from 8.0+/-1.2 to 4.4+/-1.7 mm (p<0.001) and the mean CAL changed from 9.6+/-1.3 to 7.9+/-1.6 mm (p<0.01). The test treatment resulted in statistically higher PD reductions (p< or =0.05) and CAL gains (p<0.001) than the control one. In the test group, all sites (100%) gained at least 3 mm of CAL. In this group, a CAL gain of 3 or 4 mm was measured at 10 sites (62%), whereas at six sites (38%), the CAL gain was 5 or 6 mm. In the control group, no CAL gain occurred at three sites (19%), whereas at 10 sites (62%), the CAL gain was only 1 or 2 mm. A CAL gain of 3 mm was measured in three defects (19%). CONCLUSIONS: Within the limits of the present study, it can be concluded that the combination of BDX Coll+GTR resulted in significantly higher CAL gains than treatment with access flap surgery alone, and thus appears to be a suitable alternative for treating intra-bony periodontal defects.
| Heart valve regeneration
Rabkin-Aikawa, E., J. E. Mayer, Jr., et al. (2005), Adv Biochem Eng Biotechnol 94: 141-79.
Abstract: The valves of the heart cannot regenerate spontaneously. Therefore, heart valve disease generally necessitates surgical repair or replacement of the diseased tissue by mechanical or bioprosthetic valve substitutes in order to avoid potentially fatal cardiac or systemic consequences. Although survival and quality of life is enhanced for many patients treated surgically, currently available valve substitutes remain imperfect. This is especially the case in pediatric applications, where physiologically corrective procedures can be successfully performed, but reoperations are frequently required to replace failed valve substitutes or accommodate growth of the patient. While much work is currently underway to incrementally improve existing valve substitutes, a major impact will require radically new technologies, including tissue engineering or regeneration. The use of engineered tissue offers the potential to create a non-obstructive, non-thrombogenic tissue valve substitute containing living cells capable of providing ongoing remodeling and repair of cumulative injury to the extracellular matrix. Ideally, this would allow growth in maturing recipients. The innovative fabrication of materials and the development of sophisticated methods to repair or regenerate damaged or diseased heart valves requires integration of a diverse array of basic scientific principles and enabling technologies. Thus, heart valve tissue engineering requires an understanding of relationships of structure to function in normal and pathological valves (including mechanisms of embryological development, tissue repair and functional biomechanics), and the ability to control cell and tissue responses to injury, physical stimuli and biomaterial surfaces, through chemical, pharmacological, mechanical and potentially genetic manipulations. These approaches created by advances in cell biology raise exciting possibilities for in situ regeneration and repair of heart valves.
| Heat-stabilized phospholipid films: film characterization and the production of protein-resistant surfaces
Stine, R., M. V. Pishko, et al. (2005), Langmuir 21(24): 11352-6.
Abstract: Phospholipid films have been shown in a number of studies to exhibit potential as nonfouling surfaces for biomaterial applications. However, the practical application of such films has been hindered by instability in aqueous solutions and significant detachment under mild shear stresses. Methods for stabilizing lipid films have been investigated, but to date require the presence of specific functional groups or chemical modification of the lipid molecule. In contrast to these methods, we present a process for heat-stabilization of lipid films. These heat-stabilized films have been shown to be able to withstand repeated rinsing without significant detachment. Phosphatidylcholine monolayers were formed on hydrophobic self-assembled monolayers using the liposome fusion method and stabilized at 80 degrees C. The films were characterized using Fourier transform infrared spectroscopy, ellipsometry, and atomic force microscopy and were shown to be defect free after repeated rinsing. Further experiments using a quartz crystal microbalance showed that the heat-stabilized lipid films were highly resistant to nonspecific protein adhesion and compared very favorably with poly(ethylene glycol)-coated surfaces under identical exposure conditions.
| Helical rosette nanotubes: a biomimetic coating for orthopedics?
Chun, A. L., J. G. Moralez, et al. (2005), Biomaterials 26(35): 7304-9.
Abstract: Helical rosette nanotubes (HRN) are obtained through an entropically driven self-assembly process of low-molecular-weight synthetic modules under physiological conditions. Counter-intuitively, these materials undergo extensive self-assembly under the effect of temperature, resulting in networks of very long nanotubes. We have previously shown, using an in vitro model, that titanium (Ti) coated with HRN containing a lysine side chain (HRN-K1) displayed enhanced osteoblast (OB) adhesion when compared to uncoated Ti (p < 0.01). Because it has been widely known that proteins play a critical role in OB adhesion on nanophase materials, here we examine OB adhesion on heated (+T) and unheated (-T) HRN-K1-coated Ti under serum (+S, presence of proteins) and serum-free (-S, absence of proteins) conditions. The results demonstrated that (a) while proteins enhanced OB adhesion on +T HRN-K1-coated Ti, they had no effect on -T HRN-K1-coated Ti, suggesting an active role played by the rosette nanotubes in promoting OB adhesion, and (b) under -S conditions, +T HRN-K1 induced the same level of OB adhesion as uncoated Ti under +S conditions, suggesting that +T HRN-K1 acts as a protein substitute. Finally, transmission electron microscopy and atomic force microscopy studies of +T and -T HRN-K1-coated Ti revealed a significant change in surface coverage, density and hierarchical organization of the nanotubes upon heating, which was correlated with their ability to promote cell adhesion.
| Hemocompatibility of poly(acrylonitrile-co-N-vinyl-2-pyrrolidone)s: swelling behavior and water states
Wan, L. S., Z. K. Xu, et al. (2005), Macromol Biosci 5(3): 229-36.
Abstract: Hemocompatibility is an essential aspect of blood contacting polymers. Knowledge of the relationship between polymer structure and hemocompatibility is important in designing such polymers. In this work, the effect of swelling behavior and states of water on the hemocompatibility of poly(acrylonitrile-co-N-vinyl-2-pyrrolidone) (PANCNVP) films was studied. Platelet adhesion and plasma recalcification time tests were used to evaluate the hemocompatibility of the films. Considering the importance of surface properties on the hemocompatibility of polymers, static water contact angles were measured by both sessile drop and captive bubble methods. It was found that, on the film surface of PANCNVP with a higher NVP content, adhered platelets were remarkably suppressed and the recalcification time was longer. The total water content adsorbed on the PANCNVP film was determined through swelling experiments performed at temperatures of interest. Differential scanning calorimetry and thermogravimetric analysis were used to probe the states of water in the films. Based on the results from these experiments, it was hypothesized that the better hemocompatibility of PANCNVP films with higher NVP contents was due to their higher free water content, because water molecule exchange at the polymer/liquid interface, facilitated by a high free water content, is unfavorable for the formation of surface bound water, which causes poor hemocompatibility. [diagram in text].
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