Hydroxyapatite Matrix Research Articles

Synthesis, structural and 3-D architecture of lanthanum oxide added hydroxyapatite composites for bone implant applications: Enhanced microstructural and mechanical properties

Abstract In the present study, pure hydroxyapatite (HAp) nano powder was prepared successfully via microwave irradiation method. To enhance the mechanical properties of pure HAp, La 2 O 3 was taken as an additive. HAp composites were synthesized with addition of different concentrations of La 2 O 3 (0.1, 0.2, 0.3 and 0.5 wt%) by conventional solid state route. The HAp-La 2 O 3 powders were sintered at 1200 °C for 3 h. On the basis of XRD results, formation of HAp-La 2 O 3 was confirmed. The surface morphology of the composite samples was studied by scanning electron microscopy (SEM). Transmission electron microscopy (TEM) confirmed the presence of tiny particles of La 2 O 3 in the HAp matrix with adequate porosity. The mechanical properties of the pure HAp and its composites were determined by universal testing machine (UTM). The 0.5 wt% of HAp-La 2 O 3 sample exhibited the highest density, 2.85 g/cm 3 and mechanical strength ~ 108.89 MPa. The calculated values of Young's modulus, fracture toughness and load bearing capability are 90.75 GPa, 130.06 MJ/m 3 and ~ 3.85 kN respectively. It was observed that the addition of La 2 O 3 significantly improved the mechanical properties of HAp. To see the cytotoxicity effect on HAp-La 2 O 3 composites (0.1 and 0.5 wt%), MTT assay were performed using osteoblast cells.

Synthesis and Characterization of Carbon Nanotubes Doped Hydroxyapatite Nanoceramic for Orthopedic Applications

Nano-sized bioceramic hydroxyapatite (HAp) reinforced with carbon nanotubes (CNT) is synthesized using the sol–gel technique with phosphoric acid and calcium nitrate tetrahydrate as a phosphorous and calcium precursor, respectively. The ‘as synthesized’ nanocomposite powder is characterized for phase and structural analysis using X-ray diffractometry, FTIR and Raman spectroscopy. The morphological analysis of HAp/CNT nanocomposite is done using field emission scanning electron microscopy. The tribological properties including wear rate and coefficient of friction are done by coating HAp and HAp/CNT nanocomposite on implant material (SS 316L) using spin coating technique. The wear is reduced by 24.57% for HAp-coated SS316L and 29.6% for HAp-5% CNT-coated SS316 substrate. The addition of CNT in HAp matrix leads to lowering of the coefficient of friction.

Determination of pre-cecal phosphorus digestibility of inorganic phosphates and bone meal products in broilers

A broiler study was performed to determine the pre-cecal phosphorus (P) digestibility of 5 P sources, 3 from animal (Delfos, Calfos, and porcine bone meal) and 2 of inorganic (monocalcium phosphate [MCP] and dicalcium phosphate [DCP]) origin. Delfos is processed from bones resulting in a dicalcium phosphate product, and Calfos is processed from bones in which part of the gelatin is removed but in which the hydroxy-apatite matrix is preserved. During the first 14 d, birds were housed in floor pens bedded with wood shavings and received a commercial starter diet. At d 14, broilers were randomly assigned to pens (0.9 m2, 10 birds/pen) with a slatted floor. From d 14 onwards, one of the 6 experimental diets (a basal diet, and 5 diets containing the P sources) was provided. Test diets were replicated 6 times, and the basal diet 8 times. Electron microscopy images of test products were made in order to verify whether the spatial structure of the test products could be related to the pre-cecal P digestibility of the same products. Diets met or exceeded CVB (2011) requirements for all nutrients except for P and were formulated to contain a calcium to total P ratio of between 1.4 and 1.6 and a minimal amount of phytate P. Diets contained 5 g/kg titanium oxide as a marker to determine digestibility of P. At d 24 all birds were euthanized, after which the content of the terminal part of the ileum was sampled. The P digestibility was calculated by linear regression according to World's Poultry Science Association (WPSA) protocol for determination of pre-cecal P digestibility. Pre-cecal P digestibility of MCP, DCP, Delfos, Calfos, and porcine bone meal was 88.5, 82.4, 94.5, 86.9, and 78.2%, respectively. Based on visual inspection of electron microscopy images of test products, the spatial structure of the test products might be related to P digestibility. It is concluded that processing of bone meal increases the pre-cecal P digestibility in broilers.

Cobalt adsorption on the nano-hydroxyapatite matrix: isotherm and kinetic studies

Abstract Cobalt radionuclide is one of the prime contaminants generated during operation of pressurized heavy water. The paper reports the study of cobalt adsorption on hydroxyapatite (HAp) nanoceramic. A modified wet chemical precipitation method is used for HAp synthesis. The HAp nano-material is characterized by XRD, FTIR, TG/DTA, AFM, SEM, and EDAX. Experiments are performed in batches to observe the effect of cobalt adsorption on HAp matrix. The adsorption of cobalt on HAp is examined at room temperature. The isotherm and kinetic studies showed that the Freundlich isotherm and pseudo-second order model are the best choices to describe the nature of adsorption.

Examination of Sol-Gel Derived Hydroxyapatite Enhanced with Silver Nanoparticles using OCT and Raman Spectroscopy

Abstract Hydroxyapatite (HAp) has been attracting widespread interest in medical applications. In a form of coating, it enables to create a durable bond between an implant and surrounding bone tissues. With addition of silver nanoparticles HAp should also provide antibacterial activity. The aim of this research was to evaluate the composition of hydroxyapatite with silver nanoparticles in a non-destructive and non-contact way. For control measurements of HAp molecular composition and solvent evaporation efficiency the Raman spectroscopy has been chosen. In order to evaluate dispersion and concentration of the silver nanoparticles inside the hydroxyapatite matrix, the optical coherence tomography (OCT) has been used. Five samples were developed and examined ‒ a reference sample of pure HAp sol and four samples of HAp colloids with different silver nanoparticle solution volume ratios. The Raman spectra for each solution have been obtained and analyzed. Furthermore, a transverse-sectional visualization of every sample has been created and examined by means of OCT.

Sintering And Characterization Of A Hydroxya-patite Matrix And Hydroxyapatite Matrix Nano-composites

Microporous calcium phosphate biomaterials are known for their physical and biological applications. Among the best known are the stoichiometric hydroxyapatite (HA) and tricalcium phosphate (TCP). This is because these biomaterials exhibit chemical and crystallographic compositions which are similar to that found in bones and teeth. The use of nanotechnology enables obtaining calcium phosphate nanostructured powders and calcium phosphate nanocomposite matrix formed by a second nano phase of type SiO2, TiO2, Al2O3-a, ZrO2, Mg. Different methods and techniques for the synthesis and preparation of nanostructured powders and biomaterials are noted in the literature, but it is known that not all lead to the same results. Calcium phosphates nanostructured biomaterials are a new class of biomaterials which provide new physical, morphological, nanostructural and microstructural features with interconnected microporosity which are promising to wettability, capillary action, cell adhesion and proliferation on the surface of grains and micropores. Based on research of these biomaterials, it has been found that they show potential applications in traumatology, orthopedic and dental applications in reconstruction, defects and bone tissue repairing, implants attachment and dental remineralization treatment. This study was aimed at the sintering and characterization of an HA matrix and three nanocomposite biomaterials with 5% by volume of the respective second phases: SiO2, ZrO2 and Al2O3-a in the HA matrix. The HA powder and nanocomposite HA/SiO2 were sintered at 1100 °C/2h. HA/ZrO2 nanocomposite powder followed two sintering conditions: a temperature of 1100 °C/2h and the other, at 1300 ºC/2h. HA/Al2O3-a nanocomposite powder was only sintered at 1300 ºC/2h. The biomaterials were characterized by scanning electron microscopy, X-ray diffraction and open porosity and hydrostatic density were also determined by applying the Arthur method. The results are encouraging and show for HA, HA/SiO2, HA/ZrO2 biomaterials (obtained by sintering at 1100 °C) interconnected microporous microstructures, formed by fine grains which are favorable for the expected wettability and capillarity characteristics.

Synthesizing and characterization of nano-Graphene Oxide-reinforced Hydroxyapatite Coatings on laser treated Ti6Al4V surfaces.

Laser-treated Ti6Al4V surfaces were coated by the single-layer hydroxyapatite (HA) and double-layer hydroxyapatite reinforced by the reduced nano-graphene oxide (rGO) using the sol-gel method. The effects of rGO reinforcement at different ratios and sintering temperatures on surface morphology and adhesion strength of the single and double layer coatings (rGO/HA) were analysed. As the initial treatment process, a laser texturing was patterned on the alloy and then, prepared samples were coated. The coated laser-modified HA and HA/rGO-coated Ti6Al4V surfaces were characterized by Raman spectroscopy, X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) and the adhesion strength between the coat and substrates were determined by the standard adhesion tests. The conducted analyses indicated that the substitution of rGO into HA matrix revealed a homogeneous morphology and relatively crack-free coatings on the laser-treated Ti substrate surfaces. Adhesion tests showed that, the HA + rGO (1.0 wt. %) biocomposites exhibited a significant increase in adhesion strength compared to untreated surfaces and to the single HA-coated Ti6Al4V substrates.

Study of Mechanical and Tribological Properties of Nanomica Dispersed Hydroxyapatite Based Composites for Biomedical Applications

Present research aims to assess the influence of nanocrystalline mica (NM) dispersion (10, 15, 20, and 25 vol.%) in hydroxyapatite (HA) matrix on its mechanical and tribological properties and bioactivity. Nanosized mica (NM) was prepared by mechanical milling of commercial mica powder. The composite was prepared by mechanically mixing the milled mica with HA and consolidated by microwave sintering at 1200°C for 10 min. Phase characterization by X-ray diffraction (XRD) shows dissociation of HA into β-TCP (tetra calcium phosphate) in sintered compact. Estimated densification is the highest (~98%) with 20% NM addition. HA-20%NM also shows an optimum combination of mechanical (hardness 2.80 GPa and indentation fracture toughness 1.51 MPa m1/2) and tribological properties (wear rate ~1.6 × 10−6 mm3/Nm). Scanning electron microscopy (SEM) of worn out surface elicits that wear mechanism is governed mainly by delamination and abrasive mode. Biocompatibility assessment in simulated body fluid (SBF) indicates that no elemental change occurs (confirmed by energy dispersive spectroscopy (EDS)) even after 60 days of emersion. It reveals that the optimized composition is satisfying fundamental requirements of an implant material.

Synthesis and Characterization of a Nanostructured Matrix of Hydrated Calcium Phosphate

Bone reconstruction biomaterials are topics of interest in dentistry, orthopedics, scientific, commercial. The most popular bone repairing and reconstruction biomaterials are calcium phosphates. The demand for biomaterials is associated with the chemical and crystallographic characteristics of the human bone apatite. The wet synthesis method is common in the production of nanostructured powders of hydrated calcium phosphates, providing nanoparticles with sizes less than 50nm. This study aimed to synthesize and characterize hydrated calcium phosphate powders in the molar ratio of Ca/P = 1.67. After calcination at temperature 900°C/2h, these powders provide nanostructured hydroxyapatite matrix. The characterization studies were performed with Scanning Electron Microscopy, X-rays diffraction and Infrared Spectroscopy by Fourier Transform. The results show that the synthesis method provides hydrated calcium phosphate powders formed by aggregated and agglomerated nanoparticles. The thermal treatment of hydrated calcium phosphate powder led to formation of hydroxyapatite matrix.

The incorporation of fluoride and strontium in hydroxyapatite affects the composition, structure, and mechanical properties of human cortical bone.

Strontium ranelate and fluoride salts are therapeutic options to reduce fracture risk in osteoporosis. Incorporation of these elements in the physiological hydroxyapatite matrix of bone is accompanied by changes in bone remodeling, composition, and structure. However, a direct comparison of the effectiveness of strontium and fluoride treatment in human cortical bone with a focus on the resulting mechanical properties remains to be established. Study groups are composed of undecalcified specimens from healthy controls, treatment-naïve osteoporosis cases, and strontium ranelate or fluoride-treated osteoporosis cases. Concentrations of both elements were determined using instrumental neutron activation analysis (INAA). Backscattered electron imaging was carried out to investigate the calcium content and the cortical microstructure. In comparison to osteoporotic patients, fluoride and strontium-treated patients have a lower cortical porosity indicating an improvement in bone microstructure. Mechanical properties were assessed via reference point indentation as a measure of bone's resistance to deformation. The strontium-incorporation led to significantly lower total indentation distance values compared to osteoporotic cases; controls have the highest resistance to indentation. In conclusion, osteoporosis treatment with strontium and fluoride showed positive effects on the microstructure and the mechanical characteristics of bone in comparison to treatment-naïve osteoporotic bone. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 433-442, 2017.

A method for whole protein isolation from human cranial bone

The presence of the dense hydroxyapatite matrix within human bone limits the applicability of conventional protocols for protein extraction. This has hindered the complete and accurate characterization of the human bone proteome thus far, leaving many bone-related disorders poorly understood. We sought to refine an existing method of protein extraction from mouse bone to extract whole proteins of varying molecular weights from human cranial bone. Whole protein was extracted from human cranial suture by mechanically processing samples using a method that limits protein degradation by minimizing heat introduction to proteins. The presence of whole protein was confirmed by western blotting. Mass spectrometry was used to sequence peptides and identify isolated proteins. The data have been deposited to the ProteomeXchange with identifier PXD003215. Extracted proteins were characterized as both intra- and extracellular and had molecular weights ranging from 9.4 to 629 kDa. High correlation scores among suture protein spectral counts support the reproducibility of the method. Ontology analytics revealed proteins of myriad functions including mediators of metabolic processes and cell organelles. These results demonstrate a reproducible method for isolation of whole protein from human cranial bone, representing a large range of molecular weights, origins and functions.

A simple sol-gel route to the construction of hydroxyapatite inverted colloidal crystals for bone tissue engineering

Hydroxyapatite (HAp) scaffolds with uniform pore size and interconnected pore network were constructed based on the inverted colloidal crystal (ICC) geometry and a simple sol-gel formulation. Monodisperse polystyrene microspheres were self-assembled and annealed into a hexagonal close packed structure. HAp sol-gel was infiltrated in this template followed by thermal treatment for simultaneous HAp matrix sintering and polymeric colloidal crystal calcination. The resultant ICC scaffolds exhibit an ordered architecture that was able to offer a favorable environment for human osteoblasts adhesion and proliferation, an essential feature for bone ingrowth in tissue engineering applications.

Research on the preparation, biocompatibility and bioactivity of magnesium matrix hydroxyapatite composite material

In this paper, magnesium matrix hydroxyapatite composite material was prepared by electrophoretic deposition method. The optimal process parameters of electrophoretic deposition were HA suspension concentration of 0.02 kg/L, aging time of 10 days and voltage of 60V. Animal experiment and SBF immersion experiment were used to test the biocompatibility and bioactivity of this material respectively. The SD rats were divided into control group and implant group. The implant surrounding tissue was taken to do tissue biopsy, HE dyed and organizational analysis after a certain amount of time in the SD rat body. The biological composite material was soaked in SBF solution under homeothermic condition. After 40 days, the bioactivity of the biological composite material was evaluated by testing the growth ability of apatite on composite material. The experiment results showed that magnesium matrix hydroxyapatite biological composite material was successfully prepared by electrophoretic deposition method. Tissue hyperplasia, connective tissue and new blood vessels appeared in the implant surrounding soft tissue. No infiltration of inflammatory cells of lymphocytes and megakaryocytes around the implant was found. After soaked in SBF solution, a layer bone-like apatite was found on the surface of magnesium matrix hydroxyapatite biological composite material. The magnesium matrix hydroxyapatite biological composite material could promot calcium deposition and induce bone-like apatite formation with no cytotoxicity and good biocompatibility and bioactivity.

Multi-loaded ceramic beads/matrix scaffolds obtained by combining ionotropic and freeze gelation for sustained and tuneable vancomycin release

For a targeted release against bacteria-associated bone diseases (osteomyelitis) ceramic beads with a high drug loading capacity, loaded with vancomycin as model antibiotic, are synthesized as drug carrier and successfully incorporated in an open porous hydroxyapatite matrix scaffold via freeze gelation to prevent bead migration at the implantation site and to extend drug release. We demonstrate that the quantity of loaded drug by the hydroxyapatite and β-tricalcium phosphate beads, produced by ionotropic gelation, as well as drug release can be tuned and controlled by the selected calcium phosphate powder, sintering temperature, and high initial vancomycin concentrations (100mg/ml) used for loading. Bead pore volume up to 68mm3/g, with sufficiently large open pores (pore size of up to 650nm with open porosity of 72%) and high surface area (91m2/g) account likewise for a maximum drug loading of 236mg/g beads or 26mg/sample. Multi-drug loading of the beads/matrix composite can further increase the maximum loadable amount of vancomycin to 37mg/sample and prolong release and antibacterial activity on Bacillus subtilis up to 5days. The results confirmed that our approach to incorporate ceramic beads as drug carrier for highly increased drug load in freeze-gelated matrix scaffolds is feasible and may lead to a sustained drug release and antibacterial activity.

Structure design and fabrication of porous hydroxyapatite microspheres for cell delivery

Porous microspheres fabricated from bioceramics have great potential for cell delivery in injectable tissue engineering application. The size and structure of pores in the microspheres are important for the effective protection and transportation of cells. In this study, porous hydroxyapatite microspheres are fabricated through the water-in-oil emulsion method followed by a calcination treatment at the high temperature. Both self-made resorcinol-formaldehyde (RF) composite spheres and camphene are used as pore-forming agents to produce big pores corresponding to the size of RF spheres and connected channel among big pores in hydroxyapatite matrix. The properties of the microspheres are characterized using X-ray diffraction, thermogravimetry analysis, universal material machine, field emission scanning electron microscopy. Cell assays are carried out to evaluate the cellular compatibility of the microspheres. The results showed that the hydroxyapatite microspheres with controllable pore structure and high porosity could be fabricated by this method, which have better strength to resist the compressive force. The microspheres are conducive to support adhesion, proliferation and differentiation of MC3T3-E1 cells. The results indicate that the obtained porous hydroxyapatite microspheres can be a permeable microenvironment for cell delivery in injectable tissue engineering.

Inhibited grain growth in hydroxyapatite–graphene nanocomposites during high temperature treatment and their enhanced mechanical properties

Nanostructured hydroxyapatite (HA)–graphene nanosheet (GN) composites have been fabricated by spark plasma sintering consolidation. Nanostructual evolution of the bioceramic-based composites during further high temperature heat treatment is characterized and enhanced mechanical strength is assessed. GN keeps intact after the treatment and its presence at HA grain boundaries effectively inhibits HA grain growth by impeding interconnection of individual HA grains. Microstructural characterization discloses strong coherent interfaces between GN and the (300) plane of HA crystals. This particular matching state in the composites agrees well with the competitive theoretical pull-out energy for single graphene sheet being departed from HA matrix. The toughening regimes that operate in HA–GN composites at high temperatures give clear insight into potential applications of GN for ceramic matrix composites.

Facilitated receptor-recognition and enhanced bioactivity of bone morphogenetic protein-2 on magnesium-substituted hydroxyapatite surface.

Biomaterial surface functionalized with bone morphogenetic protein-2 (BMP-2) is a promising approach to fabricating successful orthopedic implants/scaffolds. However, the bioactivity of BMP-2 on material surfaces is still far from satisfactory and the mechanism of related protein-surface interaction remains elusive. Based on the most widely used bone-implants/scaffolds material, hydroxyapatite (HAP), we developed a matrix of magnesium-substituted HAP (Mg-HAP, 2.2 at% substitution) to address these issues. Further, we investigated the adsorption dynamics, BMPRs-recruitment, and bioactivity of recombinant human BMP-2 (rhBMP-2) on the HAP and Mg-HAP surfaces. To elucidate the mechanism, molecular dynamic simulations were performed to calculate the preferred orientations, conformation changes, and cysteine-knot stabilities of adsorbed BMP-2 molecules. The results showed that rhBMP-2 on the Mg-HAP surface exhibited greater bioactivity, evidenced by more facilitated BMPRs-recognition and higher ALP activity than on the HAP surface. Moreover, molecular simulations indicated that BMP-2 favoured distinct side-on orientations on the HAP and Mg-HAP surfaces. Intriguingly, BMP-2 on the Mg-HAP surface largely preserved the active protein structure evidenced by more stable cysteine-knots than on the HAP surface. These findings explicitly clarify the mechanism of BMP-2-HAP/Mg-HAP interactions and highlight the promising application of Mg-HAP/BMP-2 matrixes in bone regeneration implants/scaffolds.

Fabrication and properties of carbon nanotube-reinforced hydroxyapatite composites by a double in situ synthesis process

Carbon nanotube (CNT)-reinforced hydroxyapatite (HA) composites were successfully fabricated by a double in situ synthesis process, which combined the in situ synthesis of CNTs in HA powders by chemical vapor deposition (CVD) with the further encapsulation of CNTs using HA by a sol–gel method. This double in situ synthesis approach not only improves the homogeneous dispersion of CNTs within the HA matrix, but also enhances the interfacial bonding between the CNTs and HA, thus leading to enhanced mechanical properties. Flexural tests indicated that the flexural strength of the composite is 1.6 times higher than that of pure HA, and significantly higher than that of the commercial and in situ synthesized CNT/HA composites. Furthermore, the in vitro cell culture experiments indicated that the CNT/HA composites fabricated by this double in situ process significantly accelerate the proliferation of fibroblast cells (L-929), compared with those fabricated by traditional methods, confirming their biocompatibility. With this biocompatibility and excellent mechanical properties, the obtained CNT/HA composites have a high potential as biomaterials, particularly in bone tissue engineering applications.

Development of a dual setting hydroxyapatite cement system with pseudoplastic mechanical behavior

Event Abstract Back to Event Development of a dual setting hydroxyapatite cement system with pseudoplastic mechanical behavior Theresa Brückner1, Katrin Hurle2, Jürgen Neubauer2, Friedlinde Götz-Neunhoeffer2, Jürgen Groll1 and Uwe Gbureck1 1 University of Würzburg, Department for Functional Materials in Medicine and Dentistry, Germany 2 Friedrich-Alexander-University of Erlangen-Nuremberg, GeoZentrum Nordbayern – Mineralogy, Germany Introduction: Self-setting and osteoconductive calcium phosphate cements (CPC) are widely used in clinics, but their application is limited to non-load bearing defects [1] as they are brittle with low fracture toughness and bending strength. For an improvement of their mechanical properties, hydrogel forming water soluble monomers were added in this study into the liquid phase of the cement paste. Upon mixing the CPC powder with the monomer solution, cement setting and hydrogel formation simultaneously occur so that a dual setting, interpenetrating network of organic and inorganic components is formed. Here, we analysed the influence of 2-hydroxyethylmethacrylate (HEMA) on a ceramic matrix of calcium deficient hydroxyapatite (HA) [2], with a special focus on both mechanical properties as well as detailed time-dependent studies about precipitation and hydration of HA in the poly-HEMA gel. Materials and Methods: α-Ca3(PO4)2 was either mixed with a 2.5 wt% Na2HPO4 solution or with modified liquid phase containing 50 % HEMA. Both variations were prepared in a powder-to-liquid-ratio of 3.0 g/mL. Hydrogel formation was initiated via an ammoniumpersulfate/ tetramethylethylendiamine system. The cement paste was transferred into silicon molds (3x4x45 mm), demolded after 1 h and stored underwater at 37 °C. Relevant mechanical properties were determined in a time dependent manner up to 7 d and corresponding crystal sizes and conversion to HA was analyzed via quantitative in situ XRD calculations according to literature [3]. Results: Cements without HEMA showed an increase in bending strength from 0.7±0.3 MPa after 2 h to 6.4±2.1 MPa after 7 d. The dual setting system showed similar tendencies but the initial bending strength even reached 2.8±0.7 to 9.9±2.7 MPa after 7 d. An increase in flexural modulus from 0.2±0.1 to 2.7±0.4 GPa was visible for reference probes whereas its development was less brittle for HEMA-cements and showed up to 1.0±0.2 GPa. Work of fracture was marginal for reference probes (up to 0.3±0.2 Nmm), but at least one order of magnitude higher for the dual setting system (Figure 1). The improved mechanical performance came along with a delayed setting reaction and minor HA crystal sizes. Figure 1: Time-dependent work of fracture of reference and 50 % HEMA containing samples. Discussion: The mechanical performance of HA forming CPC could be improved by the introduction of an interpenetrating organic network, at which the setting reaction of both components did not occur simultaneously. Initially, the formation of a poly-HEMA hydrogel with a certain mechanical performance was observed, followed by its successive mineralization with HA. So, HEMA containing probes reached certain strength earlier with simultaneously being less brittle but rather pseudoplastic. Conclusion: Time-dependent experiments revealed the setting kinetics of HA/poly-HEMA composite and therefore its suitability for clinical application in load bearing defect sites, as peseudoplastic behavior and strongly increased work of fracture were obtained. We gratefully acknowledge financial support by: DFG State Major Instrumentation Programme, funding the crossbeam scanning electron microscope Zeiss CB 340 (INST 105022/58-1 FUGG)

Development of a new osteoconductive bone wax

Event Abstract Back to Event Development of a new osteoconductive bone wax Theresa Brückner1, Martha Schamel1, Alexander Kübler2, Jürgen Groll1 and Uwe Gbureck1 1 University of Würzburg, Department for Functional Materials in Medicine and Dentistry, Germany 2 University of Würzburg, Department of Cranio-Maxillo-Facial Surgery, Germany Introduction: Bone wax based on mixtures of beeswax and vaseline is commonly used as physical barrier to treat bleeding of cancellous bone during surgery. Although it is easy to handle and cost-effective, disadvantages such as foreign body reactions, infections, tissue damage and a hindered osteogenesis in vivo are observed[1]. Previous approaches to overcome these problems are waxes consisting of biodegradable polymers (poly(ethylene glycol), PEG) and hemostatic agents (pregelatinized starch) to create an intrinsically hemostatic bone sealant[2]. Here, we additionally incorporated osteoconductive hydroxyapatite (HA) forming calcium phosphate cement (CPC) precursors to create a malleable system, which initially can seal bone wounds and hardens after contact with physiological fluids due to diffusion exchange of PEG and water molecules. Materials and Methods: 4 g tetracalcium phosphate (TTCP)/monetite were mixed with 1 g NaH2PO4 and up to 10 wt.% corn starch and dispersed in 3 g of a molten PEG 1,500/400 mixture. After hardening, the bone wax was softened and kneaded until a homogeneous texture was reached. Cuboidal samples (6x6x12 mm) were deposited in phosphate buffered saline for up to 24 d at 37°C. Compressive strength, porosity, mass loss, phase composition, PEG release, water sealing duration, antibiotic release and antibacterial properties via vancomycin hydrochloride addition were tested. Results: The compressive strength of the tested bone waxes varied between 2.0-2.9 (no starch) and 2.4-2.6 MPa (10 % starch) with corresponding porosities of 66 and 63 %. The 10 % probes lost about 3 % of their initial weight while an overall mass loss of 9 % occurred for the starch-less samples. After 24 d, a matrix of nanocrystalline HA was formed with small residues of unreacted TTCP. After 6 d of deposition, possible PEG residues were beyond the detection limit of FTIR analysis. Under blood pressure conditions, all bone waxes had a liquid sealing duration of 47 h at most. Concerning the cumulative vancomycin release, an initial burst was observed with a quantitative release being reached after 6 d. Testing against Staphylococcus aureus proved antibacterial activity. Discussion: We could show that PEG-CPC bone wax almost completely converted to HA without organic residues. HA is known to be biocompatible, osteoconductive and similar to biological apatite[3] and the obtained strengths were comparable to those of cancellous bone[4]. Furthermore, a sealing ability of almost 2 d confirms its suitability as mechanically effective hemostatic agent. Furthermore, such novel bone waxes can be modified with antibiotics without affecting the activity of the released drug. Conclusion: To the best of our knowledge, a PEG-CPC bone wax system is a novel and sophisticated approach to create a bone wax with ameliorated properties being osteoconductive, self-setting, partially degradable, hemostatic and antibacterial if necessary. We gratefully acknowledge financial support by: DFG State Major Instrumentation Programme, funding the crossbeam scanning electron microscope Zeiss CB 340 (INST 105022/58-1 FUGG)