Joop G C Wolke

Publications of Joop G C Wolke

• Effect of calcium carbonate on hardening, physicochemical properties, and in vitro degradation of injectable calcium phosphate cements.

  Authors: Kemal Sariibrahimoglu, Sander C G Leeuwenburgh, Joop G C Wolke, Li Yubao, John A Jansen

  Journal of biomedical materials research. Part A. 12/2011; 100(3):712-9.

  The main disadvantage of apatitic calcium phosphate cements (CPCs) is their slow degradation rate, which limits complete bone regeneration. Carbonate (CO₃²⁻) is the common constituent of bone and itThe main disadvantage of apatitic calcium phosphate cements (CPCs) is their slow degradation rate, which limits complete bone regeneration. Carbonate (CO₃²⁻) 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 (CaCO₃) incorporation into CPCs. To this end, the CaCO₃ amount (0-4-8-12 wt %) and its particle size (12.0-μm-coarse or 2.5-μm-fine) were systematically investigated. In comparison to calcite-free CPC, the setting time of the bone substitute was delayed with increasing CaCO₃ incorporation. Reduction of the CaCO₃ 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 CO₃²⁻ 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 CaCO₃ content. In vitro accelerated degradation tests demonstrated that calcium release and dissolution rate from the set cements increased with increasing the incorporation of CO₃²⁻, whereas differences in CaCO₃ particle size did not affect the in vitro degradation rate under accelerated conditions.

• Bone response to fast-degrading, injectable calcium phosphate cements containing PLGA microparticles.

  Authors: Rosa P Félix Lanao, Sander C G Leeuwenburgh, Joop G C Wolke, John A Jansen

  Biomaterials. 08/2011; 32(34):8839-47.

  Apatitic calcium phosphate cements (CPC) are frequently used to fill bone defects due to their favourable clinical handling and excellent bone response, but their lack of degradability inhibitsApatitic calcium phosphate cements (CPC) are frequently used to fill bone defects due to their favourable clinical handling and excellent bone response, but their lack of degradability inhibits complete bone regeneration. In order to render these injectable CaP cements biodegradable, hollow microspheres made of poly (D,L-lactic-co-glycolic) acid (PLGA) have been previously used as porogen since these microspheres were shown to be able to induce macroporosity upon degradation as well as to accelerate CPC degradation by release of acid degradation products. Recently, the capacity of PLGA microspheres to form porosity in situ in injectable CPCs was optimized by investigating the influence of PLGA characteristics such as microsphere morphology (dense vs. hollow) and end-group functionalization (acid terminated vs. end-capped) on acid production and corresponding porosity formation in vitro. The current study has investigated the in vivo bone response to CPCs containing two types of microspheres (hollow and dense) made of PLGA with two different end-group functionalizations (end capped and acid terminated). Microspheres were embedded in CPC and injected in the distal femoral condyle of New Zealand White Rabbits for 6 and 12 weeks. Histological results confirmed the excellent biocompatibility and osteoconductivity of all tested materials. Composites containing acid terminated PLGA microspheres displayed considerable porosity and concomitant bone ingrowth after 6 weeks, whereas end capped microspheres only revealed open porosity after 12 weeks of implantation. In addition, it was found that dense PLGA microspheres induced significantly more CPC degradation and bone tissue formation compared to hollow PLGA microspheres. In conclusion, it was shown that PLGA microspheres have a strong capacity to induce fast degradation of injectable CPC and concomitant replacement by bone tissue by controlled release of acid polymeric degradation products without compromising the excellent biocompatibility and osteoconductivity of the CPC matrix.

• Influence of the pore generator on the evolution of the mechanical properties and the porosity and interconnectivity of a calcium phosphate cement.

  Authors: Marco A Lopez-Heredia, Kemal Sariibrahimoglu, Wanxun Yang, Marc Bohner, Daiki Yamashita, Aliz Kunstar, Aart A van Apeldoorn, Ewald M Bronkhorst, Rosa P Félix Lanao, Sander C G Leeuwenburgh, Kiyoshi Itatani, Fang Yang, Phil Salmon, Joop G C Wolke, John A Jansen

  Acta biomaterialia. 08/2011; 8(1):404-14.

  Porosity and interconnectivity are important properties of calcium phosphate cements (CPCs) and bone-replacement materials. Porosity of CPCs can be achieved by adding polymeric biodegradablePorosity and interconnectivity are important properties of calcium phosphate cements (CPCs) and bone-replacement materials. Porosity of CPCs can be achieved by adding polymeric biodegradable pore-generating particles (porogens), which can add porosity to the CPC and can also be used as a drug-delivery system. Porosity affects the mechanical properties of CPCs, and hence is of relevance for clinical application of these cements. The current study focused on the effect of combinations of polymeric mesoporous porogens on the properties of a CPC, such as specific surface area, porosity and interconnectivity and the development of mechanical properties. CPC powder was mixed with different amounts of PLGA porogens of various molecular weights and porogen sizes. The major factors affecting the properties of the CPC were related to the amount of porogen loaded and the porogen size; the molecular weight did not show a significant effect per se. A minimal porogen size of 40 μm in 30 wt.% seems to produce a CPC with mechanical properties, porosity and interconnectivity suitable for clinical applications. The properties studied here, and induced by the porogen and CPC, can be used as a guide to evoke a specific host-response to maintain CPC integrity and to generate an explicit bone ingrowth.

• Injectable calcium phosphate cement with PLGA, gelatin and PTMC microspheres in a rabbit femoral defect.

  Authors: Hongbing Liao, X Frank Walboomers, Wouter J E M Habraken, Zheng Zhang, Yubao Li, Dirk W Grijpma, Antonios G Mikos, Joop G C Wolke, John A Jansen

  Acta biomaterialia. 12/2010; 7(4):1752-9.

  In this study, we investigated the in vivo degradation properties and tissue response towards injectable calcium phosphate cement (CPC) with no further addition, or calcium phosphate composite cementIn this study, we investigated the in vivo degradation properties and tissue response towards injectable calcium phosphate cement (CPC) with no further addition, or calcium phosphate composite cement containing approximately 50 vol.% of microspheres. Three types of spheres were assessed, i.e. poly(lactic-co-glycolic acid) (PLGA), gelatin (GEL) and poly(trimethylene carbonate) (PTMC). The cements were injected into 4.6 mm diameter and 6mm deep cylindrical defects in the femoral condyle of New Zealand white rabbits, hardened in situ and, after wound closure, left to heal for 4, 8 and 12 weeks (n=6 for each composition and time period). After retrieval, specimens were analyzed using histological and histomorphometrical methods. Results showed that non-modified CPCs showed excellent bone contact but only very limited erosion at the surface. The CPC/PLGA implant degraded almost completely, while tissue response significantly improved at each time period. CPC/PTMC showed slower degradation characteristics compared to CPC/PLGA. Finally, at all time periods, there was an evident inflammatory response to the CPC/GEL composite cement. In conclusion, the degradation properties of the CPC/PLGA microspheres composite and its bone response when implanted into the femoral condyles of rabbits were significantly better than those of CPC/gelatin and CPC/PTMC microspheres composites.

• Torque test measurement in segmental bone defects using porous calcium phosphate cement implants.

  Authors: Henriette C Kroese-Deutman, Joop G C Wolke, Paul H M Spauwen, John A Jansen

  Tissue engineering. Part C, Methods. 10/2010; 16(5):1051-8.

  This study was performed to assess the bone healing supporting characteristics of porous calcium phosphate (Ca-P) cement when implanted in a rabbit segmental defect model as well as to determine theThis study was performed to assess the bone healing supporting characteristics of porous calcium phosphate (Ca-P) cement when implanted in a rabbit segmental defect model as well as to determine the reliability of torque testing as a method to verify bone healing. The middiaphyseal radius was chosen as the area to create bilaterally increasing defect sizes (5, 10, and 15 mm), which were either filled with porous Ca-P cement or left open as a control. After 12 weeks of implantation, torque test measurements as well as histological and radiographic evaluation were performed. In two of the open 15 mm control defects, bone bridging was visible at the radiographic and histological evaluation. Bone was observed to be present in all porous Ca-P cement implants (5, 10, and 15 mm defects) after 12 weeks. No significant differences in torque measurements were observed between the 5 and 10 mm filled and open control defects using a t-test. In addition, the mechanical strength of all operated specimens was similar compared with nonoperated bone samples. The torsion data for the 15 mm open defect appeared to be lower compared with the filled 15 mm defect, but no significant difference could be proven. Within the limitation of the study design, porous Ca-P cement implants demonstrated osteoconductive properties and confirmed to be a suitable scaffold material in a weight-bearing situation. Further, the used torque testing method was found to be unreliable for testing the mechanical properties of the healed bone defect.

• The osteogenic effect of electrosprayed nanoscale collagen/calcium phosphate coatings on titanium.

  Authors: Lise T de Jonge, Sander C G Leeuwenburgh, Jeroen J J P van den Beucken, Joost Te Riet, Willeke F Daamen, Joop G C Wolke, Dieter Scharnweber, John A Jansen

  Biomaterials. 12/2009;

  For orthopedic and dental implants, the ultimate goal is to obtain a life-long secure anchoring of the implant in the native surrounding bone. To this end, nanoscale calcium phosphate (CaP) andFor orthopedic and dental implants, the ultimate goal is to obtain a life-long secure anchoring of the implant in the native surrounding bone. To this end, nanoscale calcium phosphate (CaP) and collagen-CaP (col-CaP) composite coatings have been successfully deposited using the electrospray deposition (ESD) technique. In order to study to what extent the thickness of these coatings can be reduced without losing coating osteogenic properties, we have characterized the mechanical and biological coating properties using tape tests (ASTM D-3359) and in vitro cell culture experiments, respectively. Co-deposition of collagen significantly improved coating adhesive and cohesive strength, resulting in a remarkably high coating retention of up to 97% for coating thicknesses below 100nm. In vitro cell culture experiments showed that electrosprayed CaP and col-CaP composite coatings enhanced osteoblast differentiation, leading to improved mineral deposition. This effect was most pronounced upon co-deposition of collagen with CaP, and these coatings displayed osteogenic effects even for a coating thickness of below 100nm.

• In vivo bone response and mechanical evaluation of electrosprayed CaP-nanoparticle coatings using the iliac crest of goats as implantation model.

  Authors: Corinne Schouten, Gert J Meijer, Jeroen J J P van den Beucken, Sander C G Leeuwenburgh, Lise T de Jonge, Joop G C Wolke, Paul H M Spauwen, John A Jansen

  Acta biomaterialia. 11/2009;

  Recent trends in clinical implantology include the use of endosseous dental implant surfaces embellished with nano-sized modifications. The current study was initiated to evaluate the mechanicalRecent trends in clinical implantology include the use of endosseous dental implant surfaces embellished with nano-sized modifications. The current study was initiated to evaluate the mechanical properties as well as the potential beneficial effect of electrosprayed CaP-nanoparticle coated (nanoCaP) implants on the in vivo osteogenic response with grit-blasted, acid-etched (GAE) implant surfaces as controls. For this purpose, nanoCaP-coatings were deposited on cylindrical Screw-type (St) implants and implanted bilaterally into the iliac crest of goats for 6 weeks. In addition to histological and histomorphometrical analysis, insertion torque and removal torque values were measured at implant placement and at retrieval, respectively. The present study showed similar insertion and removal torque values for nanoCaP-coated and GAE control implants, with for each individual group no statistically significant increase in torque value during the implant period. In view of bone-to-implant contact and peri-implant bone volume, no significant differences were found between nanoCaP-coated and GAE implants after 6 weeks of implantation. In conclusion, this study demonstrated that in situations in which implants are placed in a non-compromised situation using a standard press-fit implantation strategy, electrosprayed nanoCaP-coatings perform to a comparable extent as GAE implants, both with respect to implant fixation and bone healing response.

• Incorporation of biodegradable electrospun fibers into calcium phosphate cement for bone regeneration.

  Authors: Yi Zuo, Fang Yang, Joop G C Wolke, Yubao Li, John A Jansen

  Acta biomaterialia. 10/2009;

  The inherent brittleness and slow degradation are the major drawbacks for the use of calcium phosphate cements (CPCs). To address these issues, biodegradable ultrafine fibers were incorporated intoThe inherent brittleness and slow degradation are the major drawbacks for the use of calcium phosphate cements (CPCs). To address these issues, biodegradable ultrafine fibers were incorporated into the CPC in this study. Four types of fibers made of poly (epsilon-polycaprolactone) (PCL) (PCL12: 1.1mum, PCL15: 1.4mum, PCL18: 1.9mum) and poly (L-Lactic acid) (PLLA4: 1.4mum) were prepared by electrospinning using a special water pool technique, and then mixed with the CPC at the fiber weight fractions of 1%, 3%, 5% and 7%. After incubation of the composites in simulated body fluid (SBF) for 7 days, they were characterized by a gravimetric measurement for porosity evaluation, a three-point bending test for mechanical properties, microcomputer topography and scanning electron microscopy for morphological observation. The results indicated that the incorporation of ultrafine fibers increases the fracture resistance and porosity of CPCs. The toughness of the composites increased with the fiber fraction but was not affected by the fiber diameter. It was found that the incorporated fibers formed a channel-like porous structure in the CPCs. After degradation of the fibers, the created space and high porosity of the composite cement provides inter-connective channels for bone tissue ingrowth and facilitates cement resorption. Therefore, we concluded that this electrospun fiber-CPC composite may be beneficial to be used as bone fillers.

• Porcine gelatin microsphere/calcium phosphate cement composites: An in vitro degradation study.

  Authors: Wouter J E M Habraken, Joop G C Wolke, Antonios G Mikos, John A Jansen

  Journal of biomedical materials research. Part B, Applied biomaterials. 08/2009;

  Scaffolds for bone tissue engineering preferably should be mechanically stable, osteoconductive, biodegradable and porous. To comply with these characteristics, calcium phosphate cements (CPCs) withScaffolds for bone tissue engineering preferably should be mechanically stable, osteoconductive, biodegradable and porous. To comply with these characteristics, calcium phosphate cements (CPCs) with porcine (type A) gelatin microspheres were formulated. In this experiment, in vitro degradation of 10 wt % gelatin type A microsphere CPCs (GELA CPCs) was followed for 12 weeks in proteolytic medium. Results showed a gradual decrease in mass, compression strength and E-modulus. Morphology investigation showed that degradation of the spheres started at the surface of the composite and gradually proceeded to the inner part. Overall, porcine gelatin microspheres can be used to generate in situ macroporosity into an injectable CPC. (c) 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2009.

• In vitro responses to electrosprayed alkaline phosphatase/calcium phosphate composite coatings.

  Authors: Lise T de Jonge, Jeroen J J P van den Beucken, Sander C G Leeuwenburgh, Anouk A J Hamers, Joop G C Wolke, John A Jansen

  Acta biomaterialia. 04/2009;

  Surface modification of titanium implants to improve their fixation in bone tissue is of great interest. We present a novel approach to enhance implant performance by applying important principles ofSurface modification of titanium implants to improve their fixation in bone tissue is of great interest. We present a novel approach to enhance implant performance by applying important principles of bone mineralization to biomedical coatings. As an attempt to mimic the biphasic biomineralization process, both the enzyme alkaline phosphatase (ALP) and calcium phosphate (CaP) were immobilized onto Ti discs, thereby triggering enzymatically and physicochemically controlled biomineralization pathways. ALP, CaP and ALP-CaP composite coatings with preserved functionality of ALP were successfully deposited using electrospray deposition. In vitro soaking studies in cell culture medium revealed that crystal growth initially proceeded at a faster rate on CaP-coated Ti than on ALP-containing coatings, but mineral deposition onto ALP-coated Ti caught up with the calcification behaviour of CaP coatings upon long-term soaking. Cell culture experiments with osteoblast-like cells, however, demonstrated the opposite effect in mineral deposition on the electrosprayed CaP and ALP coatings. The ALP-CaP composite coatings showed delayed proliferation as well as accelerated mineralization in comparison to cells cultured on the CaP-coated and uncoated Ti. In conclusion, these in vitro results showed that the osteogenic potential of Ti can be stimulated by ALP-containing coatings.

• Introduction of enzymatically degradable poly(trimethylene carbonate) microspheres into an injectable calcium phosphate cement.

  Authors: Wouter J E M Habraken, Zheng Zhang, Joop G C Wolke, Dirk W Grijpma, Antonios G Mikos, Jan Feijen, John A Jansen

  Biomaterials. 07/2008; 29(16):2464-76.

  Poly(trimethylene carbonate) (PTMC) is an enzymatically degradable polyester with rubber-like properties. Introduction of this polymer into an injectable calcium phosphate bone cement can thereforePoly(trimethylene carbonate) (PTMC) is an enzymatically degradable polyester with rubber-like properties. Introduction of this polymer into an injectable calcium phosphate bone cement can therefore be used to introduce macroporosity into the cement for tissue engineering purposes as well as to improve mechanical properties. Aim of this study was to investigate calcium phosphate cements with incorporated PTMC microspheres (PTMC CPCs) on their physical/mechanical properties and in vitro degradation characteristics. Therefore, composites were tested on setting time and mechanical strength as well as subjected to phosphate buffered saline (PBS) and enzyme containing medium. PTMC CPCs (12.5 and 25 wt%) with molecular weights of 52.7 kg mol(-1) and 176.2 kg mol(-1) were prepared, which showed initial setting times similar to that of original CPC. Though compression strength decreased upon incorporation of PTMC microspheres, elastic properties were improved as strain-at-yield increased with increasing content of microspheres. Sustained degradation of the microspheres inside PTMC CPC occurred when incubated in the enzymatic environment, but not in PBS, which resulted in an interconnected macroporosity for the 25 wt% composites.

• In vivo behavior of a novel injectable calcium phosphate cement compared with two other commercially available calcium phosphate cements.

  Authors: Gerjon Hannink, Joop G C Wolke, B Willem Schreurs, Pieter Buma

  Journal of biomedical materials research. Part B, Applied biomaterials. 06/2008; 85(2):478-88.

  The aim of this study was to investigate the physicochemical and biological properties of a newly developed calcium phosphate cement (CPC). The novel cement was compared with two other commerciallyThe aim of this study was to investigate the physicochemical and biological properties of a newly developed calcium phosphate cement (CPC). The novel cement was compared with two other commercially available CPCs. After mixing the powder and liquid phase, the CPCs were injected as a paste into a rabbit distal femoral defect model. The CPCs were evaluated after 24 h, 6 weeks, 26 weeks, and 52 weeks. The novel CPC was easy to handle and was fast setting. X-ray diffraction (XRD) and Fourier Transform Infrared Spectrometry (FTIR) at the different implantation periods showed that the cement had converted to carbonated hydroxyapatite and remained stable over time. Histological evaluation showed bone apposition on the cement surface without any inflammatory response or fibrous encapsulation. At later time points, all CPCs were completely covered by a thin layer of bone. Osteoclast-like cells present at the interface resorbed parts of the cement mass. Histological and histomorphometrical analyses did not show any significant differences between the three implanted CPCs. The results indicate that the investigated CPC is biocompatible, osteoconductive, as well as osteotransductive and seems to be both biologically safe and effective as a bone void filler.

• Effect of platelet-rich plasma on the early bone formation around Ca-P-coated and non-coated oral implants in cortical bone.

  Authors: Dimitris Nikolidakis, Juliette van den Dolder, Joop G C Wolke, John A Jansen

  Clinical oral implants research. 03/2008; 19(2):207-13.

  OBJECTIVES: The purpose of the present study was to investigate the effect of local application of platelet-rich plasma (PRP) on the early healing of cortical bone around Ti implants with twoOBJECTIVES: The purpose of the present study was to investigate the effect of local application of platelet-rich plasma (PRP) on the early healing of cortical bone around Ti implants with two different surface configurations. MATERIAL AND METHODS: Six goats were used in this study. PRP fractions were obtained from a venous blood sample of the goats and administered immediately before implant insertion. PRP was applied via gel preparation and installation of the gel into the implant site, or via dipping of the implants in PRP fraction before insertion. A total of 36 implants (18 non-coated and 18 Ca-P-coated) were placed into the tibial cortical bone. The animals were sacrificed at 6 weeks after implantation and implants with surrounding tissue were prepared for histological examination. Histomorphometrical variables like the percentage of implant surface with direct bone-implant contact and the percentage of new and old bone adjacent to the implant were evaluated. RESULTS: More interfacial bone-to-implant contact was observed for all the three groups of Ca-P-coated implants and the Ti/PRP liquid group. All groups revealed similar percentages of old and new bone adjacent to the implant. CONCLUSIONS: It was concluded that the additional use of PRP did not have any effect on the early cortical bone response to the Ca-P-coated implants, while PRP in a liquid form showed a tendency to increase bone apposition to roughened titanium implants.

• Evaluation of the biocompatibility of calcium phosphate cement/PLGA microparticle composites.

  Authors: Dennis P Link, Juliette van den Dolder, Jeroen J J P van den Beucken, Vincent M Cuijpers, Joop G C Wolke, Antonios G Mikos, John A Jansen

  Journal of biomedical materials research. Part A. 01/2008;

  In this study, the biocompatibility of a calcium phosphate (CaP) cement incorporating poly (D,L-lactic-co-glycolic acid) (PLGA) microparticles was evaluated in a subcutaneous implantation model inIn this study, the biocompatibility of a calcium phosphate (CaP) cement incorporating poly (D,L-lactic-co-glycolic acid) (PLGA) microparticles was evaluated in a subcutaneous implantation model in rats. Short-term biocompatibility was assessed using pure CaP discs and CaP discs incorporating PLGA microparticles (20% w/w) with and without preincubation in water. Long-term biocompatibility was assessed using CaP discs incorporating varying amounts (5, 10, or 20% w/w) and diameter sizes (small, 0-50 mum; medium, 51-100 mum, or large, 101-200 mum) of PLGA microparticles. The short-term biocompatibility results showed a mild tissue response for all implant formulations, irrespective of disc preincubation, during the early implantation periods up to 12 days. Quantitative histological evaluation revealed that the different implant formulations induced the formation of similar fibrous tissue capsules and interfaces. The results concerning long-term biocompatibility showed that all implants were surrounded by a thin connective tissue capsule (<10 layers of fibroblasts). Additionally, no significant differences in capsule and interface scores were observed between the different implant formulations. The implants containing 20% PLGA with medium- and large-sized microparticles showed fibrous tissue ingrowth throughout the implants, indicating PLGA degradation and interconnectivity of the pores. The results demonstrate that CaP/PLGA composites evoke a minimal inflammatory response. The implants containing 20% PLGA with medium- and large-sized microparticles showed fibrous tissue ingrowth after 12- and 24-weeks indicating PLGA degradation and interconnectivity of the pores. Therefore, CaP/PLGA composites can be regarded as biocompatible biomaterials with potential for bone tissue engineering and advantageous possibilities of the microparticles regarding material porosity. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2008.

• Investigation as to the osteoinductivity of macroporous calcium phosphate cement in goats.

  Authors: Esther W H Bodde, Camille T R Cammaert, Joop G C Wolke, Paul H M Spauwen, John A Jansen

  Journal of biomedical materials research. Part B, Applied biomaterials. 11/2007; 83(1):161-8.

  For bone formation in critical-sized or poor healing defects, osteoinductive behavior of synthetic bone grafts is crucial. Although the osteoconductive behavior of calcium phosphate (CaP) cement isFor bone formation in critical-sized or poor healing defects, osteoinductive behavior of synthetic bone grafts is crucial. Although the osteoconductive behavior of calcium phosphate (CaP) cement is generally accepted, its osteoinductive potential is less reported. In this study, osteoinduction of porous CaP cement was investigated. Four goats received each six subcutaneous placed prehardened porous CaP cement implants. Implantation time was 3 and 6 months. After explantation, histological evaluation and scoring with a histological grading scale for soft-tissue implants were performed. The histological sections revealed that the implants degraded for more than 50% over time. The implants had lost their macroporous structure from 3 months on. A medium-thick fibrous capsule with a few inflammatory cells surrounded the implants after 3 months. This capsule significantly decreased in thickness after 6 months. Throughout the implant ingrowth of fibrous tissue was seen with scattered foci of inflammatory cells. Cement particles were surrounded by a layer of inflammatory cells. The massive inflammatory response in the interstice was seen after 3 months, which disappeared after 6 months implantation. No bone formation was detected in any of the specimens. The fast degradation and thereby collapsing of the porous structure of our CaP cement implant might have prevented osteoinduction.

• Bone regeneration of porous beta-tricalcium phosphate (Conduit TCP) and of biphasic calcium phosphate ceramic (Biosel) in trabecular defects in sheep.

  Authors: Esther W H Bodde, Joop G C Wolke, Rick S Z Kowalski, John A Jansen

  Journal of biomedical materials research. Part A. 10/2007; 82(3):711-22.

  In this study bone regeneration between porous beta-tricalcium phosphate (Conduit TCP) and biphasic calcium phosphate ceramic (Biosel), with a hydroxyapatite/beta-TCP ratio of 75/25, was compared.In this study bone regeneration between porous beta-tricalcium phosphate (Conduit TCP) and biphasic calcium phosphate ceramic (Biosel), with a hydroxyapatite/beta-TCP ratio of 75/25, was compared. The ceramic particles were implanted in sheep trabecular bone for 3, 12, and 26 weeks. Histomorphometrical analysis revealed that Conduit degraded significantly during time and only 36% of the material was left at 26 weeks implantation time. Biosel, in contrast, remained nearly intact. The degradation of Conduit was due to dissolution as well as cell-mediated. Biosel showed a high cellular intervention, although this material did not degrade. Both materials were osteoconductive. The amount of newly formed bone appeared greater in the Conduit group after 26 weeks (46% +/- 8% as compared to 37% +/- 8% for Biosel), but this difference was not significant. Bone distribution over the defect was homogeneous in Conduit, whereas Biosel showed significantly more bone in the periphery of the defect after 26 weeks in comparison to the center. In conclusion, both ceramics are biocompatible and osteoconductive. Degradation showed a difference in amount and in cellular events, with more degraded Conduit TCP with less cellular intervention as compared to Biosel.

• The effectiveness of different polymerization protocols for class II composite resin restorations.

  Authors: Lieke C G de Jong, Niek J M Opdam, Ewald M Bronkhorst, Joost J M Roeters, Joop G C Wolke, Bas Geitenbeek

  Journal of dentistry. 07/2007; 35(6):513-20.

  OBJECTIVES: To investigate the effect of reduced light exposure times on Vickers hardness (VH) of class II composite resin restorations. METHODS: Class II restorations were made in vitro in three 2mmOBJECTIVES: To investigate the effect of reduced light exposure times on Vickers hardness (VH) of class II composite resin restorations. METHODS: Class II restorations were made in vitro in three 2mm thick increments in a human molar. Two composite resins (Clearfil AP-X; Esthet-X) were polymerized with four light-curing units (Halogen; Astralis 10, LED; The Cure, L.E.Demetron I, Smartlite) following four curing protocols. Three protocols with exposure times of 10s, 20s or 40s (control) per layer. In the fourth protocol, 10s irradiation per layer was combined with additional lateral curing for 10s from buccal and palatal after removal of the metal matrix. VH of the axial surface was determined at top and bottom layers directly after light-curing and after 7 days storage. Linear regression analysis was performed to analyze the effect of protocol variables. RESULTS: Directly after light-curing VH of both composite resins was significantly influenced by curing protocols. After 7 days, curing protocols had no significant effect on VH of Clearfil AP-X, except for the Smartlite. VH of Esthet-X was still influenced by curing protocol, but differences were smaller than directly after light-curing. CONCLUSIONS: With high intensity light-curing units, exposure times of 10s/2mm increment can be sufficient to obtain under in vitro conditions a high degree of conversion, depending on materials and curing protocols. With additional lateral curing of a class II composite resin restoration a higher degree of cure can be obtained in less time.

• In vitro evaluation of different heat-treated radio frequency magnetron sputtered calcium phosphate coatings.

  Authors: Yan Yonggang, Joop G C Wolke, Li Yubao, John A Jansen

  Clinical oral implants research. 07/2007; 18(3):345-53.

  OBJECTIVES: Surface chemical compositions, such as calcium/phosphorus ratio and phase content, have a strong influence on the bioactivity and biocompatibility of calcium phosphate (CaP) coatings asOBJECTIVES: Surface chemical compositions, such as calcium/phosphorus ratio and phase content, have a strong influence on the bioactivity and biocompatibility of calcium phosphate (CaP) coatings as applied on orthopedic and dental implants. MATERIAL AND METHODS: Hydroxylapatite (HA) and dicalcium pyrophosphate (DCPP) coatings were prepared on titanium substrates by RF magnetron sputter deposition. The surfaces were left as-prepared (amorphous HA coating; A-HA, amorphous DCPP coating; A-DCPP) or heat treated with: infrared (IR) at 550 degrees C (I-HA) or at 650 degrees C (I-DCPP), and a water steam at 140 degrees C (S-HA and S-DCPP). The surface changes of these coatings were determined after incubation in simulated body fluid (SBF). Also, the growth of rat bone marrow cells (RBM) was studied with scanning electron microscopy (SEM). RESULTS: Both IR and water steam heat treatment changed the sputter-deposited coatings from the amorphous into the crystalline phase. As-prepared amorphous coatings dissolved partially in SBF within 4 weeks of incubation, while heat-treated coatings supported the deposition of a precipitate, i.e., carbonated apatite on both I-HA and S-HA specimens, and tricalciumphosphate on the I-DCPP and S-DCPP specimens. The Ca/P ratio of the A-HA, I-HA, S-HA, A-DCPP, I-DCPP and S-DCPP coatings changed, respectively, from 1.98 to 1.12, 2.01 to 1.76, 1.91 to 1.68, 0.76 to 1.23, 0.76 to 1.26 and 1.62 to 1.55 after 4 weeks of incubation in SBF. Finally, the RBM cells grew well on all heat-treated coatings, but showed different mineralization morphology during cell culturing. CONCLUSION: The different heat-treatment procedures for the sputtered HA and DCPP coatings influenced the surface characteristics of these coatings, whereby a combination of crystallinity and specific phase composition (Ca/P ratio) strongly affected their in vitro bioactivity.

• In vivo evaluation of the trabecular bone behavior to porous electrostatic spray deposition-derived calcium phosphate coatings.

  Authors: Marijke C Siebers, Joop G C Wolke, X Frank Walboomers, Sander C G Leeuwenburgh, John A Jansen

  Clinical oral implants research. 07/2007; 18(3):354-61.

  OBJECTIVES: Electrostatic spray deposition (ESD) is a new technique to deposit calcium phosphate (CaP) coatings. The aim of the present study was to evaluate the bone behavior of ESD CaP-coatedOBJECTIVES: Electrostatic spray deposition (ESD) is a new technique to deposit calcium phosphate (CaP) coatings. The aim of the present study was to evaluate the bone behavior of ESD CaP-coated implants with various degrees of crystallinities in the trabecular bone of the femoral condyle of goats. MATERIAL AND METHODS: Using the ESD technique, thin porous CaP coatings were deposited on tapered, conical, screw-shaped titanium implants. Three different heat-treatments were applied, resulting in amorphous CaP (400 degrees C, ESD1), crystalline carbonate apatite (500 degrees C, ESD2), and crystalline carbonated hydroxyapatite (700 degrees C, ESD3). Implants were inserted into the trabecular bone of the femoral condyles of goats for 12 weeks, and titanium (Ti) implants served as controls. RESULTS: The results showed that ESD-derived coatings are osteocompatible. Histomorphometrical analysis showed that the application of a CaP coating resulted in more bone contact along the press-fit area of the implant compared with the Ti implants. Moreover, the percentage bone contact of the ESD3-coated implants was increased, compared with the Ti control group. Regarding the other coatings, no differences were found compared with the control group. CONCLUSION: Crystalline carbonated hydroxyapatite ESD-coated implants positively influenced the biological performance compared with Ti control implants.

• The cytocompatibility and early osteogenic characteristics of an injectable calcium phosphate cement.

  Authors: Dennis P Link, Juliette van den Dolder, Joop G C Wolke, John A Jansen

  Tissue engineering. 04/2007; 13(3):493-500.

  In this study, the cytocompatibility and early osteogenic characteristics of rat bone marrow cells (RBMCs) on injectable calcium phosphate (CaP) cement (Calcibon) were investigated. In addition toIn this study, the cytocompatibility and early osteogenic characteristics of rat bone marrow cells (RBMCs) on injectable calcium phosphate (CaP) cement (Calcibon) were investigated. In addition to unmodified CaP cement discs, 2 other treatments were given to the discs: preincubation in MilliQ and sintering at different temperatures. After primary culture, RBMCs were dropwise seeded on the discs and cultured for 12 days. The samples were evaluated in terms of cell viability, morphology (live and dead assays and scanning electron microscopy (SEM)), cell proliferation (deoxyribonucleic acid (DNA) analyses), early cell differentiation (alkaline phosphatase (ALP) activity), and physicochemical analyses (x-ray diffraction (XRD)). The live and dead, DNA, and SEM results showed that Calcibon discs without any additional treatment were not supporting osteoblast-like cells in vitro. There were fewer cells, and cell layers were detached from the disc surface. Therefore, different preincubation periods and sintering temperatures were evaluated to improve the cytocompatibility of the CaP cement. Preincubating discs in MilliQ for periods of 1, 4, 8, and 12 weeks resulted in the hydrolysis of alpha-tri calcium phosphate (TCP) into an apatite-like structure with some beta-TCP, as shown with XRD, but the material was not cytocompatible. Sintering the discs between 800 degrees C and 1100 degrees C resulted in conversion of alpha-TCP to beta-TCP with some hydroxyapatite and an increase in crystallinity. Eventually, the discs sintered at 1100 degrees C achieved better cell attachment, more-abundant cell proliferation, and earlier differentiation than other sintered (600 degrees C, 800 degrees C, and 1000 degrees C), preincubated, and unmodified specimens. On basis of our results, we conclude that in vivo results with CaP-based cements do not guarantee in vitro applicability. Furthermore, unmodified Calcibon is not cytocompatible in vitro, although preincubation of the material results in a more-favorable cell response, sintering of the material at 1100 degrees C results in the best osteogenic properties. In contrast to in vivo studies, the Calcibon CaP cement is not suitable as a scaffold for cell-based tissue-engineering strategies.