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In vivo biological performance of composites combining micro-macroporous biphasic calcium phosphate granules and fibrin sealant
Jegoux, F., E. Goyenvalle, et al. (2005), Arch Orthop Trauma Surg 125(3): 153-9.
Abstract: INTRODUCTION: Fibrin glues are currently used by surgeons and can facilitate the handling of biomaterials. Combining fibrin glue with calcium phosphate bioceramics gives a mouldable composite that cements the granules into the implantation site. In addition to the mechanical aspect of the composite, it has been suggested that the mixture also promotes wound healing. These human blood derivatives contain natural (aprotinin) or synthetic (tranexamic acid) antifibrinolytic substances. We compared the bioactivity of two composites combining calcium phosphate granules with two different types of fibrin glue, one with aprotinin and the other with tranexamic acid. MATERIALS AND METHODS: The composite was composed of fibrin glue (Tissucol) and 1 to 2 mm granules of biphasic calcium phosphate granules (MBCP) with a volume ratio of 1 for 2. Bone cavities were drilled in 12 New Zealand rabbits and filled with a composite with aprotinin-fibrin glue on the right condyle and one with tranexamic acid-fibrin glue on the left condyle. The rabbits were randomized into two groups: 3 and 6 weeks of delay. Light microscopy, scanning electron microscopy and image analysis were performed. RESULTS: No adverse reactions were observed in either sample. Bony ingrowth associated with bioceramic resorption by osteoclastic TRAP-positive cells was noted. No significant difference was observed between the two composites. The bony ingrowth and ceramic resorption were qualitatively and quantitatively similar with both composites. CONCLUSION: This study demonstrated that the choice of a natural (aprotinin) or synthetic (tranexamic acid) antifibrinolytic agent in the fibrin sealant associated with calcium phosphate granules and used as a bone substitute had no effect on the bioactivity of the composite. It remained efficient in bone reconstruction, no adverse effects were observed, and the bony ingrowth was qualitatively and quantitatively equivalent with the two types of fibrin sealant.

In vivo biostability of polyether polyurethanes with polyethylene oxide surface-modifying end groups; resistance to biologic oxidation and stress cracking
Ebert, M., B. Ward, et al. (2005), J Biomed Mater Res A 75(1): 175-84.
Abstract: Polyethylene oxide (PEO) on polymer surfaces has been reported to reduce cellular adhesion, a very desirable property for cardiac pacing leads. A Shore 80A polyether polyurethane with up to 6% PEO surface-modifying end groups (SME) was evaluated for its chronic in vivo biostability. In a short-term (12 week) screening test, strained samples appeared to develop the same surface oxidation as unmodified polymer, but did not produce visible cracking > or =500x, prompting a longer-term study. By the time the longer-term study was initiated, most of the PEO SME had disappeared from the starting material's surface. After 1 year in vivo, surface oxidation, shallow surface cracking, and environmental stress cracking (ESC) developed on highly strained samples to the point of failure, so that there was no significant difference between the SME polymer and its control (the same polymer without SME). No further change was seen for up to 2 years of implantation. Unstrained PEO SME polymer developed shallow surface cracking, but no ESC up to 2 years of implantation. Thus, PEO SME slightly delayed, but did not stop biodegradation, and under unstrained conditions, has no adverse effect on biostability.

In vivo bone formation by human marrow stromal cells in biodegradable scaffolds that release dexamethasone and ascorbate-2-phosphate
Kim, H., H. Suh, et al. (2005), Biochem Biophys Res Commun 332(4): 1053-60.
Abstract: An unsolved problem with stem cell-based engineering of bone tissue is how to provide a microenvironment that promotes the osteogenic differentiation of multipotent stem cells. Previously, we fabricated porous poly(D,L-lactide-co-glycolide) (PLGA) scaffolds that released biologically active dexamethasone (Dex) and ascorbate-2-phosphate (AsP), and that acted as osteogenic scaffolds. To determine whether these osteogenic scaffolds can be used for bone formation in vivo, we seeded multipotent human marrow stromal cells (hMSCs) onto the scaffolds and implanted them subcutaneously into athymic mice. Higher alkaline phosphatase expression was observed in hMSCs in the osteogenic scaffolds compared with that of hMSCs in control scaffolds. Furthermore, there was more calcium deposition and stronger von Kossa staining in the osteogenic scaffolds, which suggested that there was enhanced mineralized bone formation. We failed to detect cartilage in the osteogenic scaffolds (negative Safranin O staining), which implied that there was intramembranous ossification. This is the first study to demonstrate the successful formation of mineralized bone tissue in vivo by hMSCs in PLGA scaffolds that release Dex and AsP.

In vivo bone regeneration with injectable calcium phosphate biomaterial: a three-dimensional micro-computed tomographic, biomechanical and SEM study
Gauthier, O., R. Muller, et al. (2005), Biomaterials 26(27): 5444-53.
Abstract: This in vivo study investigated the efficiency of an injectable calcium phosphate bone substitute (IBS) for bone regenerative procedures through non-destructive three-dimensional (3D) micro-tomographic (microCT) imaging, biomechanical testing with a non-destructive micro-indentation technique and 2D scanning electron microscopy (SEM) analysis. The injectable biomaterial was obtained by mixing a biphasic calcium phosphate (BCP) ceramic mineral phase and a cellulosic polymer. The BCP particles were 200-500 microm or 80-200 microm in diameter. The injectable material was implanted for 6 weeks into critical-sized bone defects at the distal end of rabbit femurs. Extensive new bone apposition was noted with both 2D and 3D techniques. Micro-CT showed that newly formed bone was in perfect continuity with the trabecular host bone structure and demonstrated the high interconnectivity of the restored bone network. For both IBS formulations, SEM and microCT gave very close measurements. The only detected significant difference concerned the amount of newly formed bone obtained with IBS 80-200 that appeared significantly higher with microCT analysis than with SEM (p=0.00007). Student t-tests did not show any significant difference in the amount of newly formed bone and remaining ceramic obtained from microCT analysis or SEM. Regression analysis showed satisfactory correlation between both the amount of newly formed bone and remaining ceramic obtained from microCT or SEM. For IBS 200-500, the newly formed bone rate inside the defect was 28.0+/-5.2% with SEM and yield strength of the samples was 18.8+/-5.4 MPa. For IBS 80-200, the newly formed bone rate inside the defect was 31.7+/-5.1% with SEM and yield strength of the samples was 26.8+/-4.5 MPa. Yield strength appeared well correlated with the amount of newly formed bone, specially observed with microCT. This study showed the ability of non-destructive techniques to investigate biological and mechanical aspects of bone replacement with injectable biomaterials.

In vivo characterization of titanium implants coated with synthetic hydroxyapatite by electrophoresis
Costa Cde, A., L. A. Sena, et al. (2005), Braz Dent J 16(1): 75-81.
Abstract: This study compared in vivo the performances of commercially pure titanium (cp Ti) screw dental implants either uncoated or coated with synthetic hydroxyapatite (HA) by electrophoresis. The HA coating was characterized by scanning electron microscopy, energy dispersive spectroscopy (EDS) and Fourier-transform infrared (FT-IR) spectroscopy. Well-adhered carbonated-hydroxyapatite layers (4- to-8-microm-thick) were obtained. In vivo tests were carried out by insertion of both uncoated and HA-coated implants into rabbit tibiae for 8 or 12 weeks. Histomorphometric analysis was performed by scanning electron microscopy with the aid of image-processing software. Results showed significantly greater bone-implant contact for HA-coated implants (p<0.05) than cp Ti implants. Comparison of bone content inside the screw implants showed no significant differences (p>0.05) between both types of implants, although cp Ti had numerically higher percentage of bone content than HA-coated implants. In conclusion, the HA-coated implants had better performance regarding the bone-implant contact area than the uncoated implants; coating by electrophoresis proved to be a valuable process to coat metallic implants with an osteoconductive material such as hydroxyapatite.

In vivo comparison of the inflammatory response induced by different vascular biomaterials
Busuttil, S. J., C. Drumm, et al. (2005), Vascular 13(4): 230-5.
Abstract: Biomaterial implants induce a local inflammatory response. A comparison of the inflammatory cell response was made between several biomaterials commonly used as vascular prostheses. Disks of polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), aluminum, titanium, copper, and stainless steel were surgically placed into the peritoneum of mice. Recruited macrophage and neutrophil populations were measured after recovery from the disk surface and peritoneal lavage. Following peritoneal biomaterial implants, there was no difference in total neutrophil or macrophage recruitment between mice implanted with PET, PTFE, aluminum, or titanium disks. However, there was significant attenuation of total neutrophil and macrophage recruitment to stainless steel compared with the other implants. Similarly, there was no significant difference in the percentage of leukocytes adherent to the PET, aluminum, or titanium disks. Macrophage adherence to the stainless steel disks was attenuated by 19.1%, and the number of neutrophils was attenuated by 69.1% when compared with PET implant mice. Mice implanted with copper disks universally expired. Leukocyte recruitment did not differ between PET, PTFE, aluminum, or titanium disks, suggesting that these materials stimulate similar inflammatory responses. Stainless steel disks recruited both fewer neutrophils and fewer macrophages and support lower adherence of these cells than the other biomaterials. Copper incited an overwhelming and fatal response.

In vivo degradation of polyethylene liners after gamma sterilization in air
Kurtz, S. M., C. M. Rimnac, et al. (2005), J Bone Joint Surg Am 87(4): 815-23.
Abstract: BACKGROUND: Ultra-high molecular weight polyethylene degrades during storage in air following gamma sterilization, but the extent of in vivo degradation remains unclear. The purpose of this study was to quantify the extent to which the mechanical properties and oxidation of conventional polyethylene acetabular liners treated with gamma sterilization in air change in vivo. METHODS: Fourteen modular cementless acetabular liners were revised at an average of 10.3 years (range, 5.9 to 13.5 years) after implantation. All liners, which had been machined from GUR 415 resin, had been gamma-sterilized in air; the average shelf life was 0.3 year (range, 0.0 to 0.8 year). After removal, the components were expeditiously frozen to minimize ex vivo changes to the polyethylene prior to characterization. The average duration between freezing and testing was 0.6 year. Mechanical properties and oxidation were measured with use of the small-punch test and Fourier transform infrared spectroscopy, respectively, in the loaded and unloaded regions of the liners. RESULTS: There was substantial regional variation in the mechanical properties and oxidation of the retrieved liners. The ultimate load was observed to vary by >90% near the surface. On the average, the rim and the unloaded bearing showed evidence of severe oxidation near the surface after long-term in vivo aging, but these trends were not typically observed on the loaded bearing surface or near the backside of the liners. CONCLUSIONS: The mechanical properties of polyethylene that has been gamma-sterilized in air may decrease substantially in vivo, depending on the location in the liner. The most severe oxidation was observed at the rim, suggesting that the femoral head inhibits access of oxygen-containing body fluids to the bearing surface. This is perhaps why in vivo oxidation has not been associated with clinical performance to date.

In vivo dielectric analysis of free water content of biomaterials by time domain reflectometry
Naito, S., M. Hoshi, et al. (1997), Anal Biochem 251(2): 163-72.
Abstract: A method of in vivo analysis of the free water content in living organisms by dielectric analysis in the time domain is described. Human skin is chosen as an example of living tissue. The cells suitable for the measurement of various layers of human skin and calculation procedures for the waveform reflected from the probe end are described. The approach was confirmed to be effective for the determination of the water content through measurement of the standard samples, keratin-water mixtures. This method was also applied to human skin in vivo. Water content data measured with a probe specially designed for surface layer analysis were sensitive to humidity around the subject. The formula expressing the relation between the electrical field character of the probe, the permittivity depth profile, and the measured permittivity was used to analyze the water content profile as a function of the depth from the skin surface. The use of several kinds of probes, differing in their electric field characteristics, permitted evaluation of the water content depth profile of human skin. This procedure is easy and applicable to any sample due to its simplicity. The measurement needs only a touch of the probe on a sample spot. It is therefore a promising method of physicochemical research on living organisms and biomaterials.

In vivo effect of fluoride-substituted apatite on rat bone
Inoue, M., H. Nagatsuka, et al. (2005), Dent Mater J 24(3): 398-402.
Abstract: Different types of calcium phosphate compounds are commercially available for medical and dental applications as bone substitute materials. Biological apatites contain several kinds of minor elements such as carbonate (CO3), magnesium (Mg), and fluoride (F) in enamel, dentin, and bone. It has been shown that F ion and F-substituted apatite promoted osteoblast proliferation and inhibited osteoclast cell activity. The purpose of this study was to investigate the in vivo rat tibia activity on F-substituted apatite (FAp). Apatites of unsintered calcium deficient apatite (CDA), and FAps, with low, medium, and high F concentrations, were implanted in rat tibia for 1 and 2 weeks. Implanted tissues were embedded in paraffin blocks, stained with hematoxylin-eosin and histomorphometrically observed. Results showed that low F concentration induced better and faster new bone formation in vivo compared to CDA. Therefore the results suggested that F as a minor element in bone rendered a suitable effect on bone formation in vivo.

In vivo effects of RGD-coated titanium implants inserted in two bone-gap models
Elmengaard, B., J. E. Bechtold, et al. (2005), J Biomed Mater Res A 75(2): 249-55.
Abstract: RGD (Arg-Gly-Asp) coating has been suggested to enhance implant fixation by facilitating the adhesion of osteogenic cells to implant surfaces. Orthopedic implants are unavoidably surrounded partly by gaps, and these regions represent a challenging environment for osseointegration. We examined the effects of cyclic RGD-coated implants on tissue integration and implant fixation in two cancellous bone-gap models. In canines, we inserted loaded RGD-coated implants with 0.75-mm gap (n = 8) and unloaded RGD-coated implants with 1.5-mm gap (n = 8) into the distal femur and proximal tibia, respectively. Control gap implants without RGD were inserted contralaterally. The titanium alloy (Ti-6Al-4V) implants were plasma sprayed and cylindrical. The observation period was 4 weeks and the fixation was evaluated by push-out test and histomorphometry. Mechanical implant fixation was improved for RGD-coated implants. Unloaded RGD-coated implants showed a significant increase in bone whereas both loaded and unloaded implants showed a significant reduction in fibrous tissue anchorage. The results are encouraging, because RGD had an overall positive effect on the fixation of titanium implants in regions where gaps exist with the surrounding bone. RGD peptide coatings can potentially be used to enhance tissue integration in these challenging environments.

In vivo engineering of organs: the bone bioreactor
Stevens, M. M., R. P. Marini, et al. (2005), Proc Natl Acad Sci U S A 102(32): 11450-5.
Abstract: Treatment of large defects requires the harvest of fresh living bone from the iliac crest. Harvest of this limited supply of bone is accompanied by extreme pain and morbidity. This has prompted the exploration of other alternatives to generate new bone using traditional principles of tissue engineering, wherein harvested cells are combined with porous scaffolds and stimulated with exogenous mitogens and morphogens in vitro and/or in vivo. We now show that large volumes of bone can be engineered in a predictable manner, without the need for cell transplantation and growth factor administration. The crux of the approach lies in the deliberate creation and manipulation of an artificial space (bioreactor) between the tibia and the periosteum, a mesenchymal layer rich in pluripotent cells, in such a way that the body's healing mechanism is leveraged in the engineering of neotissue. Using the "in vivo bioreactor" in New Zealand White rabbits, we have engineered bone that is biomechanically identical to native bone. The neobone formation followed predominantly an intramembraneous path, with woven bone matrix subsequently maturing into fully mineralized compact bone exhibiting all of the histological markers and mechanical properties of native bone. We harvested the bone after 6 weeks and transplanted it into contralateral tibial defects, resulting in complete integration after 6 weeks with no apparent morbidity at the donor site. Furthermore, in a proof-of-principle study, we have shown that by inhibiting angiogenesis and promoting a more hypoxic environment within the "in vivo bioreactor space," cartilage formation can be exclusively promoted.

In vivo evaluation and comparison of collagen, acetylated collagen and collagen/glycosaminoglycan composite films and sponges as candidate biomaterials
Srivastava, S., S. D. Gorham, et al. (1990), Biomaterials 11(3): 155-61.
Abstract: Native collagen, acetylated collagen, collagen/10% chondroitin sulphate, collagen/2.5% hyaluronic acid and collagen/20% hyaluronic acid were implanted both as film and as sponge into rat lumbar muscle for 7 and 14 d. After 7 d implantation, all materials elicited an acute inflammatory cell response characterized by numerous polymorphs and histocytes. The cell population after 14 d was principally mononuclear, i.e. leucocytes, neutrophils, macrophages, lymphocytes and fibroblasts. Both films and sponges followed a similar pattern. Native collagen elicited a subacute inflammatory response after 7 d. However, 14 d after implantation, a marked infiltration by neutrophils was apparent with subsequent degradation of existing collagen material. Acetylated collagen film evoked a much greater inflammatory cell response than native collagen. Both collagen/hyaluronic acid composites elicited a similar response. The collagen/10% chondroitin sulphate composite elicited the least inflammatory cell response at 7 d, whereas infiltration by host fibroblasts after 14 d implantation was clearly seen.

In vivo evaluation of hydroxyapatite coatings of different crystallinities
Oh, S., E. Tobin, et al. (2005), Int J Oral Maxillofac Implants 20(5): 726-31.
Abstract: PURPOSE: The influence of calcium phosphate (CaP) and hydroxyapatite (HA) crystallinity on bone-implant osseointegration is not well established. In this study, the effect of HA crystallinity and coating method on bone-implant osseointegration was investigated using a rat tibia model. MATERIALS AND METHODS: HA coatings 1 to 5 microm thick were produced using a supersonic particle acceleration (SPA) technology. The HA crystallinities used for this study were weight ratios of 30%, 50%, 70%, and 90%. A total of 128 HA-coated implants were placed into the tibiae of 64 male Sprague-Dawley rats. Bone-implant interfaces were evaluated using histology and push-out strength testing at 3 and 9 weeks after implantation. RESULTS: The 70% crystalline coatings exhibited significantly greater interfacial strength (5 implants/time point/treatment) than the 30%, 50%, and 90% crystalline coatings at 3 and 9 weeks following implantation. The implants with coatings of 70% crystallinity also had the greatest bone contact length. In addition, the HA coatings produced with SPA demonstrated greater interfacial strength and bone contact length than plasma-sprayed HA coatings (except for the HA coating with 30% crystallinity). DISCUSSION: HA coatings of different crystallinities exhibited different dissolution and re-precipitation properties which may enhance early bone formation and bone bonding. CONCLUSIONS: This study suggested that coating crystallinity and coating methods can influence the bone-implant interface.

In vivo evaluation of the biocompatibility of implanted biomaterials: morphology of the implant-tissue interactions
Steflik, D. E., R. S. Corpe, et al. (1998), Implant Dent 7(4): 338-50.
Abstract: Electron microscopic observations were made from tissues apposing titanium and ceramic root form and blade implants. The tissue was serially sectioned from the most coronal epithelium, through the gingival connective tissue, to the osseous support tissues, and directly to the most apical tissue support. Of the thousands of sections analyzed for each implant, 500 micrographs were routinely viewed for each of the implants analyzed by this study. Of the 120 total implants placed in 30 adult dogs, 60 were used for electron microscopy. Osseointegrated implants were often apposed by a mineralized matrix of collagenous fibers. The dense mineralized collagen matrix was often separated from the implant by only a ruthenium positive electron dense deposit 20 to 50 nanometers thick. Areas of the same implant were also apposed by an unmineralized collagen fiber stroma, which ranged in thickness, that contained osteoblasts. Interaction of the osteoblasts and the unmineralized collagen fibers resulted in the mineralization events of osteogenesis. Also apposing other areas of the same integrated implants were lacunar areas containing osteoclasts and vessels. These zones were similar to Howship's Lacunae. These results demonstrated that a normal homeostasis of catabolic osteoclastic activity and metabolic osteoblastic activity resulted in a dynamic implant-tissue interface. This biocompatible and dynamic support complex provides a construct for the long-term clinical serviceability of osseointegrated implants.

In vivo leukocyte cytokine mRNA responses to biomaterials are dependent on surface chemistry
Brodbeck, W. G., G. Voskerician, et al. (2003), J Biomed Mater Res A 64(2): 320-9.
Abstract: An in vivo mouse cage implant system was used to determine whether leukocyte cytokine mRNA responses to implanted biomaterials were dependent on surface chemistry. Surfaces displaying various chemistries (hydrophobic, hydrophilic, anionic, and cationic) were placed into stainless steel cages and implanted subcutaneously. Semiquantitative RT-PCR analyses revealed that hydrophilic surfaces showed a decreased expression of proinflammatory cytokines, IL-6 and IL-8, and pro-wound healing cytokines, IL-10 and TGF-beta by adherent cells, and mRNA levels of the proinflammatory cytokine, IL-1beta, and the pro-wound healing cytokine IL-13 were decreased in surrounding, exudate cells. Cytokine responses by adherent and exudate cells to hydrophobic, anionic and cationic surfaces were similar and indicative of a strong inflammatory response at the earliest time point followed by a wound healing response at later time points. However, no differences in the types or levels of exudate cells for any of the surfaces or the empty cage at each of the respective time points were observed, indicating their respective biocompatibility. These studies identify hydrophilic surface chemistries as having significant effects on leukocyte cytokine responses in vivo by decreasing the expression of inflammatory and wound healing cytokines by inflammatory cells adherent to the biomaterial as well as present in the surrounding exudate.

In vivo rabbit acute model tests of polyurethane catheters coated with a novel antithrombin-heparin covalent complex
Du, Y. J., P. Klement, et al. (2005), Thromb Haemost 94(2): 366-72.
Abstract: Catheter use has been associated with an increased risk of thrombotic complications. The objective was to make catheters less thrombogenic with the use of antithrombin-heparin covalent complex (ATH). The antithrombotic activity of ATH-coated catheters was compared to uncoated (control) and heparincoated catheters in an acute rabbit model of accelerated occluding clot formation. Anaesthetized rabbits were pre-injected with rabbit (125)I-fibrinogen, followed by insertion of test catheters into the jugular vein. Blood was drawn and held in a syringe, reinjected, then flushed with saline. The experiment was terminated when blood could no longer be withdrawn (occluding clot). Efficacy was defined as the ability of catheters to remain unoccluded. Clot formation, determined by measuring deposition of radiolabeled fibrin, was a secondary endpoint. ATH-coated catheters were resistant to clotting for the full 240-minute duration, while uncoated and heparin-coated catheters had an average clotting time of 78 and 56 minutes, respectively. The patency of ATH coating was dependant on intact heparin pentasaccharide sequences, rather than the chemistries of the basecoat, the PEO spacer arm, or the antithrombin (AT) protein. The ATH coating was stable to ethylene oxide sterilization, modest abrasion, protease attack, and the coating did not appear to leach off the catheter. Surface tension measurements showed that the ATH modified surface was more hydrophilic than uncoated control catheters or heparin-coated catheters. Thus, ATH-coated catheters are better at preventing clots than uncoated or heparin-coated catheters and show promise as an alternative to the currently available catheters in reducing thrombotic complications associated with its use.

In vivo regeneration of small-diameter (2 mm) arteries using a polymer scaffold
Lepidi, S., G. Abatangelo, et al. (2005), Faseb J
Abstract: The difficulty of obtaining significant long-term patency and good wall mechanical strength in vivo has been a significant obstacle in achieving small-diameter vascular prostheses. The aim of the present study was to develop a prosthetic graft that could perform as a small-diameter vascular conduit. Tubular structures of hyaluronan (HYAFF-11 tubules, 2 mm diameter, 1 cm length) were grafted in the abdominal aorta of 30 rats as temporary absorbable guides to promote regeneration of vascular structures. Performance was assessed by histology, immunohistochemistry, and ultra-structural analysis. These experiments resulted in three novel findings: 1) complete endothelialization of the tube's luminal surface occurred; 2) sequential regeneration of vascular components led to complete vascular wall regeneration 15 days after surgery; and 3) the biomaterial used created the ideal environment for the delicate regeneration process during the critical initial phases, yet its biodegradability allowed for complete degradation of the construct four months after implantation, at which time, a new artery remained to connect the artery stumps. This study assesses the feasibility to create a completely biodegradable vascular regeneration guide in vivo, able to sequentially orchestrate vascular regeneration events needed for very small artery reconstruction.

In vivo tissue compatibility of two radio-opaque polymeric biomaterials
Kruft, M. A., F. H. van der Veen, et al. (1997), Biomaterials 18(1): 31-6.
Abstract: Polymeric biomaterials featuring intrinsic radio-opacity continue to attract considerable scientific attention. This work focusses on two polymers that contain covalently bound iodine, rendering the materials radio-opaque. The first material is hard, transparent and glass-like, and consists of methyl methacrylate, 2-(2'-iodobenzoyl)-ethyl methacrylate (1) and 2-hydroxyethyl methacrylate (HEMA), in the molar ratio 65:20:15, respectively. The second material is a cross-linked hydrophilic network, consisting of HEMA and 1, in the molar ratio 80:20, respectively. Both materials were characterized by means of different physico-chemical techniques, including magic-angle-spinning solid state NMR spectroscopy, infrared spectroscopy and differential scanning calorimetry. Moreover, both materials were implanted subcutaneously in rats for 24 days. Upon explanation and histological examination, it appeared that both materials were well tolerated. No tissue necrosis, abscess formation or inflammation were observed. The samples were found to be surrounded by a vascularized capsule consisting of connective tissue cells. The results reveal excellent tissue compatibility for both materials. This is an important observation, since tissue compatibility is absolutely necessary for the applications which are foreseen for this type of radio-opaque biomaterials.

Inactivation of Streptococcus gordonii SspAB alters expression of multiple adhesin genes
Zhang, Y., Y. Lei, et al. (2005), Infect Immun 73(6): 3351-7.
Abstract: SspA and SspB (antigen I/II family proteins) can bind Streptococcus gordonii to other oral bacteria and also to salivary agglutinin glycoprotein, a constituent of the salivary film or pellicle that coats the tooth. To learn if SspA and SspB are essential for adhesion and initial biofilm formation on teeth, S. gordonii DL1 was incubated with saliva-coated hydroxyapatite (sHA) for 2 h in Todd-Hewitt broth with 20% saliva to develop initial biofilms. Sessile cells attached to sHA, surrounding planktonic cells, and free-growing cells were recovered separately. Free-growing cells expressed more sspA-specific mRNA and sspB-specific mRNA than sessile cells. Free-growing cells expressed the same levels of sspA and sspB as planktonic cells. Surprisingly, an SspA(-) SspB(-) mutant strain showed 2.2-fold greater biofilm formation on sHA than wild-type S. gordonii DL1. To explain this observation, we tested the hypothesis that inactivation of sspA and sspB genes altered the expression of other adhesin genes during initial biofilm formation in vitro. When compared to wild-type cells, expression of scaA and abpB was significantly up-regulated in the SspA(-) SspB(-) strain in sessile, planktonic, and free-growing cells. Consistent with this finding, ScaA antigen was also overexpressed in planktonic and free-growing SspA(-) SspB(-) cells compared to the wild type. SspA/B adhesins, therefore, were strongly suggested to be involved in the regulation of multiple adhesin genes.

Inactivation of thrombin by antithrombin III on a heparinized biomaterial
Goosen, M. F., M. V. Sefton, et al. (1980), Thromb Res 20(5-6): 543-54.

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