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PublicationAdhesion of MC3T3-E1 cells to RGD peptides of different flanking residues: Detachment strength and correlation with long-term cellular function(2007-04-01) Lee, Mark H; Adams, Christopher S; Shapiro, Irving M; Boettiger, David; Composto, Russell J; DeGrado, William F; Ducheyne, PaulWe synthesized a series of RGD peptides and immobilized them to an amine-functional self-assembled monolayer using a modified maleimide-based conjugate technique that minimizes nonspecific interactions. Using a spinning disc apparatus, a trend in the detachment strength (τ50) of RGD peptides of different flanking residues was found: RGDSPK ≻ RGDSVVYGLR ≈ RGDS ≻ RGES. Using blocking monoclonal antibodies, cellular adhesion to the peptides was shown to be primarily α√-integrin-mediated. In contrast, the τ50 value of the cells on fibronectin (Fn)-coated substrates of similar surface density was 6-7 times higher and involved both α5β1 and ανβ3 integrins. Cellular spreading was enhanced on RGD peptides after 1 h when compared to RGE and unmodified substrates. However, no significant differences were observed between the different RGD peptides. Long-term function of MC3T3-E1 cells was also evaluated by measuring alkaline phosphatase (ALP) activity and mineral deposition. Among the four peptides, RGDSPK exhibited the highest level of ALP activity after 11 days and mineralization after 15 days and reached comparable levels as Fn substrates after 15 and 24 days, respectively. These findings collectively illustrate both the advantages and limitations of enhancing cellular adhesion and function by the design of RGD peptides. PublicationSelf-assembled monolayers of omega-functional silanes: A platform for understanding cellular adhesion at the molecular level(2007-01-01) Boettiger, David; Ducheyne, Paul; Lee, Mark H; Composto, Russell JSelf-assembly represents a powerful and versatile strategy to create substrates with controlled molecular-level physicochemical characteristics. As a result, self-assembled monolayers (SAMs) of silanes continue to find use in a multitude of applications in biotechnology and nanotechnology, both as model substrates to study interfacial interactions and as a strategy to chemically graft bioactive molecules. In our work, SAMs of various functional groups have been used for fundamental studies of cellular interactions with peptides and proteins. Namely, cellular adhesion was quantitatively probed to elucidate the roles of non-specific forces arising from the substrate and to study the specific interactions of cellular receptors with adsorbed extracellular matrix (ECM) proteins, such as fibronectin, and grafted arginine–glycine–aspartic acid (RGD) peptides. Measurements of the cellular detachment strength using a spinning disc apparatus demonstrated that the terminal functionality of the silane SAM used as the substrate exerted significant effects and highlighted the importance of substrate selection in biological applications. Quantitative comparison of the various cellular interactions demonstrated that non-specific interactions can be much larger in magnitude than peptide- and protein-mediated adhesion. As adhesion is the first step in a cascade of events through which cellular interaction with a material surface occurs, this finding has implications on assays of long-term cellular function as well. The insight provided by these studies should help in the development of optimized protein and peptide microarrays, or biochips, as well as better bioactive materials for biomaterial/tissue engineering applications. PublicationNanostructural Control of Implantabale Xerogels for the Controlled Release of Biomolecules(2003-10-13) Radin, Shula; Ducheyne, Paul PublicationThe inhibition of Staphylococcus epidermidis biofilm formation by vancomycinmodified titanium alloy and implications for the treatment of periprosthetic infection(2008-08-01) Antoci, Valentin; Adams, Christopher S; Parvizi, Javad; Composto, Russell J; Davidson, Helen M; Freeman, Theresa A; Ducheyne, Paul; Wickstrom, Eric; Jungkind, Donald; Shapiro, Irving M; Hickok, Noreen JPeri-prosthetic infections are notoriously difficult to treat as the biomaterial implant is ideal for bacterial adhesion and biofilm formation, resulting in decreased antibiotic sensitivity. Previously, we reported that vancomycin covalently attached to a Ti alloy surface (Vanc-Ti) could prevent bacterial colonization. Herein we examine the effect of this Vanc-Ti surface on Staphylococci epidermidis, a Gram-positive organism prevalent in orthopaedic infections. By direct colony counting and fluorescent visualization of live bacteria, S. epidermidis colonization was significantly inhibited on Vanc-Ti implants. In contrast, the gram-negative organism Escherichia coli readily colonized the Vanc-Ti rod, suggesting retention of antibiotic specificity. By histochemical and SEM analysis, Vanc-Ti prevented S. epidermidis biofilm formation, even in the presence of serum. Furthermore, when challenged multiple times with S. epidermidis, Vanc-Ti rods resisted bacterial colonization. Finally, when S. epidermidis was continuously cultured in the presence of Vanc-Ti, the bacteria maintained a Vanc sensitivity equivalent to the parent strain. These findings indicate that antibiotic derivatization of implants can result in a surface that can resist bacterial colonization. This technology holds great promise for the prevention and treatment of periprosthetic infections. PublicationDifferential alkaline phosphatase responses of rat and human bone marrow derived mesenchymal stem cells to 45S5 bioactive glass(2007-06-21) Radin, Shula; Riley, Gwendolyn C; Ducheyne, Paul; Chen, Andrew TBioactive glass is used as both a bone filler and as a coating on implants, and has been advocated as a potential osteogenic scaffold for tissue engineering. Rat-derived mesenchymal stem cells (MSCs) show elevated levels of alkaline phosphatase activity when grown on 45S5 bioactive glass as compared to standard tissue culture plastic. Similarly, exposure to the dissolution products of 45S5 elevates alkaline phosphatase activity and other osteogenic markers in these cells. We investigated whether human MSCs grown under the same laboratory conditions as rat MSCs would exhibit similar responses. In general, human MSCs produce markedly less alkaline phosphatase activity than rat MSCs, regardless of cell culture conditions, and do not respond to the growth factor BMP-2 in the same way as rat MSCs. In our experiments there was no difference in alkaline phosphatase activity between human MSCs grown on 45S5 bioactive glass or tissue culture plastic, in samples from five different orthopaedic patients, regardless of culture media composition. Neither was there any consistent effect of 45S5 dissolution products on human MSCs from three different donors. These results suggest that the positive effects of bioactive glass on bone growth in human patients are not mediated by accelerated differentiation of mesenchymal stem cells. PublicationEffect of rapidly resorbable bone substitute materials on the temporal expression of the osteoblastic phenotype in vitro(2008-03-15) Knabe, C.; Houshmand, A.; Berger, G.; Ducheyne, Paul; Gildenhaar, R.; Kranz, I.; Stiller, M.Ideally, bioactive ceramics for use in alveolar ridge augmentation should possess the ability to activate bone formation and, thus, cause the differentiation of osteoprogenitor cells into osteoblasts at their surfaces. Therefore, in order to evaluate the osteogenic potential of novel bone substitute materials, it is important to examine their effect on osteoblastic differentiation. This study examines the effect of rapidly resorbable calcium–alkali– orthophosphates on osteoblastic phenotype expression and compares this behavior to that of ß-tricalcium phosphate (TCP) and bioactive glass 45S5. Test materials were three materials (denominated GB14, GB9, GB9/25) with a crystalline phase Ca2KNa(PO4)2 and with a small amorphous portion containing either magnesium potassium phosphate (GB14) or silica phosphate (GB9 and GB9/25, which also contains Ca2P2O7); and a material with a novel crystalline phase Ca10[K/Na](PO4)7 (material denominated 352i). SaOS-2 human bone cells were grown on the substrata for 3, 7, 14, and 21 days, counted, and probed for an array of osteogenic markers. GB9 had the greatest stimulatory effect on osteoblastic proliferation and differentiation, suggesting that this material possesses the highest potency to enhance osteogenesis. GB14 and 352i supported osteoblast differentiation to the same or a higher degree than TCP, whereas, similar to bioactive glass 45S5, GB9/25 displayed a greater stimulatory effect on osteoblastic phenotype expression, indicating that GB9/25 is also an excellent material for promoting osteogenesis. PublicationMaterials in particulate form for tissue engineering. 1. Basic concepts(2007-01-01) Silva, Gabriela; Ducheyne, Paul; Reis, R. LFor biomedical applications, materials small in size are growing in importance. In an era where 'nano' is the new trend, micro- and nano-materials are in the forefront of developments. Materials in the particulate form aim to designate systems with a reduced size, such as micro- and nanoparticles. These systems can be produced starting from a diversity of materials, of which polymers are the most used. Similarly, a multitude of methods are to produce particulate systems, and both materials and methods are critically reviewed here. Among the varied applications that materials in the particulate form can have, drug delivery systems are probably the most prominent, as these have been in the forefront of interest for biomedical applications. The basic concepts pertaining to drug delivery are summarized, and the role of polymers as drug delivery systems conclude this review. PublicationMaterials in particulate form for tissue engineering. 2. Applications in bone(2007-03-01) Silva, Gabriela; Coutinho, O. P; Ducheyne, Paul; Reis, R. LMaterials in particulate form have been the subjects of intensive research in view of their use as drug delivery systems. While within this application there are still issues to be addressed, these systems are now being regarded as having a great potential for tissue engineering applications. Bone repair is a very demanding task, due to the specific characteristics of skeletal tissues, and the design of scaffolds for bone tissue engineering presents several difficulties. Materials in particulate form are now seen as a means of achieving higher control over parameters such as porosity, pore size, surface area and the mechanical properties of the scaffold. These materials also have the potential to incorporate biologically active molecules for release and to serve as carriers for cells. It is believed that the combination of these features would create a more efficient approach towards regeneration. This review focuses on the application of materials in particulate form for bone tissue engineering. A brief overview of bone biology and the healing process is also provided in order to place the application in its broader context. An original compilation of molecules with a documented role in bone tissue biology is listed, as they have the potential to be used in bone tissue engineering strategies. To sum up this review, examples of works addressing the above aspects are presented. PublicationIn vitro surface reaction layer formation and dissolution of calcium phosphate cement – bioactive glass composites(2008-09-01) Liu, Changsheng; Chen, Chien-Wen; Ducheyne, PaulComposites of hydrated calcium phosphate cement (CPC) and bioactive glass (BG) containing Si were immersed in vitro to study the effect of chemical composition on surface reaction layer formation and dissolution/precipitation behavior. The solutions used were 0.05M tris hydroxymethyl aminomethane/HCl (tris buffer), tris buffer supplemented with plasma electrolyte (TE) with pH 7.4 at 37°C, and this solution complemented with 10% newborn bovine serum (TES). The post-immersion solutions were analyzed for changes in Ca, PO4 and Si concentrations. The reacted surfaces were analyzed using Fourier transform infrared (FTIR), and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX). The sample weight variations after immersion were also determined. The results showed that the composition of the bioactive composite CPCs greatly affected their behavior in solution and the formation of apatite bioactive surface reaction layers. After immersion in TE solution, Ca ions were taken up by all samples during the entire immersion duration. Initially, the P ion concentration increased sharply, and then decreased. This reaction pattern reveals the formation of an amorphous calcium phosphate layer on the surface of these composite calcium phosphate cements. FTIR revealed that the layer was, in fact, poorly crystallized Ca-deficient carbonate apatite. The thickness of the layer was 12-14 μm and was composed of rod-like apatite with directional arrangement. For immersion in TES solution, the Ca and Si ion concentrations showed a similar behavior as that in TE, but the release rate of Si ion was higher. FTIR revealed that after TES immersion, not only did the typical, poorly crystallized, Ca-deficient carbonated apatite form, as it did in TE, but that the serum proteins co-adsorbed on the surface and thereby affected the surface reaction layer formation. A thinner apatite layer was formed and was composed of a micro-porous layer comprising rounded particles in a glue-like appearing matrix. The addition of BG to the calcium phosphate cements to create composite calcium phosphate cements obviously is at the basis of this altered behavior of the cements. All data combined are useful for the design and optimization of degradable implant materials for use in bone tissue repair and regeneration procedures. PublicationSolution mediated effect of bioactive glass in poly (lactic-co-glycolic acid)-bioactive glass composites on osteogenesis of marrow stromal cells(2005-12-15) Yao, Jun; Radin, Shula; Reilly, Gwendolen; Leboy, Phoebe S.; Ducheyne, PaulA previous study demonstrated that the incorporation of bioactive glass (BG) into poly (lactic-co-glycolic acid) (PLGA) can promote the osteoblastic differentiation of marrow stromal cells (MSC) on PLGA by promote the formation of a calcium phosphate rich layer on its surface. To further understand the mechanisms underlying the osteogenic effect of PLGA-BG composite scaffolds, we tested whether solution-mediated factors derived from composite scaffolds/hybrids can promote osteogenesis of marrow stromal cells. The dissolution product from PLGA-30%BG scaffold stimulated osteogenesis of MSC, as was confirmed by increased mRNA expression of osteoblastic markers such as osteocalcin (OCN), alkaline phosphatase (ALP), and bone sialoprotein (BSP). The three-dimensional structure of the scaffolds may contribute to the production of cell derived factors which promoted distant MSC differentiation. Thus PLGABG composites demonstrates significant potential as a bone replacement material.