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Item does not contain fulltext Alkaline phosphatase (ALP), an enzyme involved in mineralization of bone, is incorporated into three hydrogel biomaterials to induce their mineralization with calcium phosphate (CaP). These are collagen type I, a mussel-protein-inspired adhesive consisting of PEG substituted with catechol groups, cPEG, and the PEG/fumaric acid copolymer OPF. After incubation in Ca-GP solution, FTIR, EDS, SEM, XRD, SAED, ICP-OES, and von Kossa staining confirm CaP formation. The amount of mineral formed decreases in the order cPEG > collagen > OPF. The mineral:polymer ratio decreases in the order collagen > cPEG > OPF. Mineralization increases Young's modulus, most profoundly for cPEG. Such enzymatically mineralized hydrogel/CaP composites may find application as bone regeneration materials. 01 augustus 2012

Item does not contain fulltext Membranes of the autologous blood-derived biomaterial platelet-rich fibrin (PRF) were functionalized by incorporation of alkaline phosphatase (ALP), an enzyme involved in mineralization of bone, and subsequently incubated in calcium glycerophosphate (CaGP) solution to induce PRFs mineralization with calcium phosphate (CaP) to improve PRFs suitability as a material for bone replacement. Incorporated ALP retained its bioactivity and induced formation of CaP material within PRF membranes, as confirmed by SEM, EDS, FTIR, and von Kossa staining. The mass percentage attributable to CaP was quantified by lyophilization and measurement of the remaining mass fraction as well as by TGA. Cytocompatibility tests (LDH, MTT, and WST) with SAOS-2 cells showed that mineralized PRF did not release substances detrimental to cell vitality. Live/dead staining and SEM showed that mineralized PRF was colonized by cells. The results show that hydrogel biomaterials such as PRF can be mineralized through functionalization with ALP. 01 mei 2012

Item does not contain fulltext Hydrogels used as injectables or in organ printing often lack the appropriate stimuli to direct osteogenic differentiation of embedded multipotent stromal cells (MSCs), resulting in limited bone formation in these matrices. Addition of calcium phosphate (CaP) particles to the printing mixture is hypothesized to overcome this drawback. In this study we have investigated the effect of CaP particles on the osteoinductive potential of cell-laden hydrogel-CaP composite matrices. To this end, apatitic nanoparticles have been included in Matrigel constructs where after the viability of embedded progenitor cells was assessed in vitro. In addition, the osteoinductive potential of cell-laden Matrigel containing apatitic nanoparticles was investigated in vivo and compared with composites containing osteoinductive biphasic calcium phosphate (BCP) microparticles after subcutaneous implantation in immunodeficient mice. Histological and immunohistochemical analysis of the tissue response as well as in vivo bone formation revealed that apatitic nanoparticles were osteoinductive and induced osteoclast activation, but without bone formation. The BCP particles were more effective in inducing elaborate bone formation at the ectopic location. (c) 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 100A: 2412-2420, 2012. 01 september 2012

Contains fulltext : 87430.pdf (Publisher’s version ) (Closed access) Since the early 1980s, research on the modification of bone implant surfaces by applying coatings has mainly focused on the application of inorganic calcium phosphate (CaP) coatings using physical deposition techniques. Organic components of the extracellular bone matrix, on the other hand, play an essential role in the process of bone healing, but cannot be applied using these physical techniques. Therefore, a recent trend in biomaterials research involves development of novel wet-chemical deposition techniques for both inorganic and organic coatings. This study reviews the major wet-chemical coating techniques that are used for the deposition of inorganic CaP coatings and organic biomolecules coatings.

Contains fulltext : 50596.pdf (Publisher’s version ) (Closed access) Mechanical properties of calcium phosphate coatings (CaP), deposited using the electrostatic spray deposition (ESD) technique, have been characterized using a range of analytical techniques, including tensile testing (ASTM C633), fatigue testing (ASTM E855), and scratch testing using blunt and sharp scratch styli. Moreover, a simple explantation procedure was successfully introduced using ESD-coated, threaded dental implants to characterize the mechanical performance of CaP coatings qualitatively under conditions that mimic clinical situations as close as possible. Generally, all analysis techniques revealed that ESD coatings need to be crystallized in order to ensure interfacial adhesion to the substrate and sufficient mechanical strength of the superficial reticular structure. Crystalline carbonated hydroxyapatite coatings (CHA, heat-treated at 700 degrees C) were resistant to fatigue as well as to plastic ploughing deformation by means of various scratch styli, and the fragile surface structure of ESD coatings was maintained to a large extent after unscrewing CHA-coated dental implants from femoral condyles of goat cadavers. From these experiments, it was concluded that interfacial adhesion of crystalline CHA ESD coatings to the titanium substrate was sufficient, but that mechanical strength of the superficial architecture of ESD coatings need to be optimized for applications where high shear and compressive stresses are imposed onto the rather fragile coating surface of reticular ESD morphologies.

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Item does not contain fulltext This study demonstrates, for the first time, that synthetic PEG-based hydrogels can be cross-linked reversibly by calcium upon functionalization of the polymer backbone with bisphosphonate groups (BPs) that allow for the formation of strong coordination bonds with divalent metal ions such as Mg(2+) and Ca(2+) . More specifically, it is shown that BP-functionalized hydrogels can be shaped by providing calcium ions as reversible physical cross-linkers.

Item does not contain fulltext The enzyme alkaline phosphatase (ALP) is added at different concentrations (i.e., 0, 2.5, and 10 mg ml(-1) ) to oligo(poly(ethylene glycol)fumarate) (OPF) hydrogels. The scaffolds are either incubated in 10 mM calcium glycerophosphate (Ca-GP) solution for 2 weeks or implanted in a rat subcutaneous model for 4 weeks. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and alizarin red staining show a strong ability to form minerals exclusively in ALP-containing hydrogels in vitro. Additionally, the calcium content increases with increasing ALP concentration. Similarly, only ALP-containing hydrogels induce mineralization in vivo. Specifically, small ( approximately 5-20 microm) mineral deposits are observed at the periphery of the hydrogels near the dermis/scaffold interface using Von Kossa and alizarin red staining.

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Item does not contain fulltext Exploring strategies to induce the mineralization of hydrogels is an important step toward the development of hydrogel-based materials for bone regeneration. In the current study, the effect of incorporating hydroxyapatite (HA) nanoparticles on the mineralization capacity of an inert poly(ethylene glycol) (PEG)-based hydrogel was investigated. HA nanoparticles were either directly loaded into oligo(poly(ethylene glycol) fumarate) (OPF) hydrogel or loaded into commonly used gelatin microsphere porogens that were subsequently integrated in the OPF matrix. Mineralization of composites after immersion of the samples in simulated body fluid up to 28 days was assessed. In contrast to the blank OPF hydrogel, the HA-containing constructs strongly mineralized such that the average rate of calcium uptake by the material was enhanced by orders of magnitude. The mineral formed was observed to be apatitic and needle shaped. The presented method allows modification of inert PEG-based hydrogels into bioactive biomaterials for applications in bone regeneration. 01 mei 2012

Item does not contain fulltext The main disadvantage of apatitic calcium phosphate cements (CPCs) is their slow degradation rate, which limits complete bone regeneration. Carbonate (CO(3)(2)(-)) is the common constituent of bone and it can be used to improve the degradability of the apatitic calcium phosphate ceramics. This study aimed to examine the effect of calcite (CaCO(3)) incorporation into CPCs. To this end, the CaCO(3) amount (0-4-8-12 wt %) and its particle size (12.0-mum-coarse or 2.5-mum-fine) were systematically investigated. In comparison to calcite-free CPC, the setting time of the bone substitute was delayed with increasing CaCO(3) incorporation. Reduction of the CaCO(3) particle size in the initial powder increased the injectability time of the paste. During hardening of the cements, the increase in calcium release was inversely proportional to the extent of CO(3)(2)(-) incorporation into apatites. The morphology of the carbonate-free product consisted of large needle-like crystals, whereas small plate-like crystals were observed for carbonated apatites. Compressive strength decreased with increasing CaCO(3) content. In vitro accelerated degradation tests demonstrated that calcium release and dissolution rate from the set cements increased with increasing the incorporation of CO(3)(2)(-), whereas differences in CaCO(3) particle size did not affect the in vitro degradation rate under accelerated conditions. 01 maart 2012

Contains fulltext : 53564.pdf (Publisher’s version ) (Closed access) Biodegradable polymers that can be processed into injectable hydrogel matrices are promising candidates for bone-substituting purposes. Furthermore, by incorporating degradable calcium phosphate (CaP) particles and growth factors into these hydrogel matrices, a bone construct can be designed which stimulates the formation of new bone by the surrounding tissue, thereby compensating for the loss of structural integrity of the degrading synthetic bone-substitute. Generally, a major challenge in synthesis of nanoceramic-reinforced polymers is the achievement of a fine dispersion of nanoparticles throughout the polymer, since the unique properties of nanocomposites are lost when nanoparticles aggregate. In the current study, composite hydrogels consisting of oligo(poly(ethylene glycol)fumarate) (OPF) matrices and CaP dispersions of varying crystallinity were successfully developed using physical or chemical preparation strategies. Physical mixing of dried, micrometer-sized CaP powders resulted into formation of irreproducible composites with a highly heterogeneous dispersion of large and agglomerated CaP microparticles throughout the OPF matrix. On the contrary, reproducible and homogeneous hydrogels were fabricated using a chemical mixing strategy, whereby CaP crystals were formed in the presence of dissolved OPF macromers. This co-precipitation technique resulted into a much higher degree of dispersion of the CaP crystals, which can enable higher CaP contents in organic matrices such as OPF. By using these CaP suspensions instead of dried powders, the nanosized structure of separated CaP crystals was preserved, resulting into a higher reactivity of the CaP phase, as indicated by a reduced swelling behavior of these hydrogels. This effect was most likely caused by a physicochemical interaction between Ca(2+) and unreacted COOH end-groups, thereby leading to increased physical cross-linking of the composite hydrogels.

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Contains fulltext : 51021.pdf (Publisher’s version ) (Closed access) This article describes the influence of the crystallinity of carbonate apatite (CA) coatings on osteoblast-like cell behavior. Porous CA coatings were produced with electrostatic spray deposition (ESD), and subsequently, received heat treatments of 400, 500, or 700 degrees C to induce various coating crystallinities. As a result, an amorphous calcium phosphate (ACP), a crystalline CA (CCA), and a crystalline carbonated hydroxyapatite (CHA) structure were formed, respectively. Uncoated titanium substrates served as the control group. After seeding rat osteoblast-like cells, the initial cell attachment was similar between the groups, and approached 100% after 6 h. Between the various coatings, no differences were observed for proliferation, differentiation, or mineralization. However, proliferation of the osteoblast-like cells was lower on all coated substrates after longer culture periods, compared to the uncoated substrates, while at the same time differentiation was stimulated. Furthermore, after 8 and 16 days of incubation, scanning electron microscopy showed more signs of mineralization on coated substrates, compared to the uncoated substrates. In conclusion, porous ESD-derived CA coatings have a positive effect on the in vitro differentiation of osteoblast-like cells, compared to uncoated, as-machined titanium. However, this effect is not further enhanced by the degree of crystallinity of the ESD-derived CA coatings.

Contains fulltext : 49054.pdf (Publisher’s version ) (Closed access) Calcium phosphate (CaP) coatings have been applied on titanium implants to improve the bioactivity in order to favor the initial bone healing response. Recently, a new technique has been developed to apply CaP coatings: electrostatic spray deposition (ESD). Although ESD-derived coatings have several benefits, it is not known whether they are degradable. This study was designed to examine the cell-mediated degradation of two ESD-derived coatings with different chemical compositions, that is, beta-tricalcium phosphate (beta-TCP) and carbonate apatite (CA). First, coatings were deposited and analyzed physiochemically. Subsequently, rat bone marrow-derived osteoclastlike cells were seeded on the coatings, and analyzed with osteoclast-specific markers, scanning electron microscopy, and transmission electron microscopy. Results showed that both coatings exhibited porous morphologies, with an average pore size of less than 1 microm (beta-TCP), or larger than 1 microm (CA). After heat treatment, both coatings were crystalline in structure. The Ca/P ratios were 1.4 to 1.5 for the beta-TCP coating, and 1.8 to 2.0 for the CA coating. After 8 and 12 days of culture, multinucleated osteoclastlike cells were observed on both coatings. The osteoclast phenotype was confirmed by tartrate resistant acid phosphatase (TRAP) staining, and immunostaining against the calcitonin receptor. Using scanning electron microscopy, numerous resorption lacunae were observed in both coatings. Finally, transmission electron microscopy of TRAP-positive cells confirmed the osteoclastlike aspect of the cells revealing multiple nuclei and a ruffled border. In conclusion, CaP coatings produced with the ESD process can be degraded by osteoclasts.

Contains fulltext : 106975.pdf (Publisher’s version ) (Open Access) Radboud Universiteit Nijmegen, 10 april 2013 Promotor : Jansen, J.A. Co-promotor : Leeuwenburgh, S.C.G.

Contains fulltext : 106967.pdf (Publisher’s version ) (Open Access) Calcium Phosphate Cements (CPC) are commonly used as bone replacement materials. Rosa Félix’s reseach specifically deals with strategies to enhance CPC degradation and its subsequent replacement by newly formed bone. In order to achieve this, several materials have been used in combination with CPC to create porosity that will increase fluid-flow and cell penetration throughout the implant material and therefore facilitate implant degradation. In this doctoral thesis research, the influence of several physico-chemical properties of varoius potential CPC porogens have been investigated in order to improve CPC degration and new bone formation. In addition, the influence of bio-active factors in this process of new bone formation has also been studied. Radboud Universiteit Nijmegen, 28 maart 2013 Promotor : Jansen, J.A. Co-promotores : Wolke, J.G.C., Leeuwenburgh, S.C.G.

Contains fulltext : 117442.pdf (Publisher’s version ) (Open Access) Radboud Universiteit Nijmegen, 31 mei 2013 Promotor : Jansen, J.A. Co-promotores : Beucken, J.J.J.P van den, Leeuwenburgh, S.C.G.

Contains fulltext : 88724.pdf (Publisher’s version ) (Open Access) RU Radboud Universiteit Nijmegen, 29 januari 2010 Promotores : Jansen, J.A., Schoonman, J. Co-promotores : Wolke, J.G.C., Leeuwenburgh, S.C.G. 227 p.