Papers by Jan Van Humbeeck
Journal of Manufacturing Science and Engineering, 2014
Cracks and delamination, resulting from residual stresses, are a barrier in the world of additive... more Cracks and delamination, resulting from residual stresses, are a barrier in the world of additive manufacturing and selective laser melting (SLM) that prohibits the use of many metals in this field. By preheating the baseplate, thermal gradients are lowered and stresses can be reduced. In this work, some initial tests were performed with M2 high speed steel (HSS). The influence of preheating on density and mechanical and physical properties is investigated. The paper shows many promising results for the production of SLM parts in materials that are very sensitive to crack formation and delamination. When using a preheating of 200 C, crack-free M2 HSS parts were produced with a relative density of 99.8%.
Materials science & engineering. C, Materials for biological applications, 2015
While the current research focus in the search for biocompatible low-modulus alloys is set on β-t... more While the current research focus in the search for biocompatible low-modulus alloys is set on β-type Ti-based materials, the potential of fully martensitic Ti-based alloys remains largely unexplored. In this work, the influence of composition and pre-straining on the elastic properties of martensitic binary Ti-Nb alloys was studied. Additionally, the phase formation was compared in the as-cast versus the quenched state. The elastic moduli and hardness of the studied martensitic alloys are at a minimum of 16wt.% Nb and peak between 23.5 and 28.5wt.% Nb. The uniaxial deformation behavior of the alloys used is characterized by the absence of distinct yield points. Monotonic and cyclic (hysteretic) loading-unloading experiments were used to study the influence of Nb-content and pre-straining on the elastic moduli. Such experiments were also utilized to assess the recoverable elastic and anelastic deformations as well as hysteretic energy losses. Particular attention has been paid to the...
Materials Science and Engineering: C, 2015
Additive manufacturing techniques are getting more and more established as reliable methods for p... more Additive manufacturing techniques are getting more and more established as reliable methods for producing porous metal implants thanks to the almost full geometrical and mechanical control of the designed porous biomaterial. Today, Ti6Al4V ELI is still the most widely used material for porous implants, and none or little interest goes to pure titanium for use in orthopedic or load-bearing implants. Given the special mechanical behavior of cellular structures and the material properties inherent to the additive manufacturing of metals, the aim of this study is to investigate the properties of selective laser melted pure unalloyed titanium porous structures. Therefore, the static and dynamic compressive properties of pure titanium structures are determined and compared to previously reported results for identical structures made from Ti6Al4V ELI and tantalum. The results show that porous Ti6Al4V ELI still remains the strongest material for statically loaded applications, whereas pure titanium has a mechanical behavior similar to tantalum and is the material of choice for cyclically loaded porous implants. These findings are considered to be important for future implant developments since it announces a potential revival of the use of pure titanium for additively manufactured porous implants.
Molecular Pharmaceutics, 2015
The reproducibility and consistency of physicochemical properties and pharmaceutical performance ... more The reproducibility and consistency of physicochemical properties and pharmaceutical performance are major concerns during preparation of solid dispersions. The crystallization kinetics of drug/polyethylene glycol solid dispersions, an important factor that is governed by the properties of both drug and polymer has not been adequately explored, especially in systems containing high drug loadings. In this paper, by using standard and modulated differential scanning calorimetry and X-ray powder diffraction, we describe the influence of drug loading on crystallization behavior of dispersions made up of indomethacin and polyethylene glycol 6000. Higher drug loading increases the amorphicity of the polymer and inhibits the crystallization of PEG. At 52% drug loading, polyethylene glycol was completely transformed to the amorphous state. To the best of our knowledge, this is the first detailed investigation of the solubilization effect of a low molecular weight drug on a semicrystalline polymer in their dispersions. In mixtures containing up to 55% indomethacin, the dispersions exhibited distinct glass transition events resulting from amorphous-amorphous phase separation which generates polymer-rich and drug-rich domains upon the solidification of supercooled polyethylene glycol, whereas samples containing at least 60% drug showed a single amorphous phase during the period in which crystallization normally occurs. The current study demonstrates a wide range in physicochemical properties of drug/polyethylene glycol solid dispersions as a result of the complex nature in crystallization of this system, which should be taken into account during preparation and storage.
Materials science & engineering. C, Materials for biological applications, 2015
While the current research focus in the search for biocompatible low-modulus alloys is set on β-t... more While the current research focus in the search for biocompatible low-modulus alloys is set on β-type Ti-based materials, the potential of fully martensitic Ti-based alloys remains largely unexplored. In this work, the influence of composition and pre-straining on the elastic properties of martensitic binary Ti-Nb alloys was studied. Additionally, the phase formation was compared in the as-cast versus the quenched state. The elastic moduli and hardness of the studied martensitic alloys are at a minimum of 16wt.% Nb and peak between 23.5 and 28.5wt.% Nb. The uniaxial deformation behavior of the alloys used is characterized by the absence of distinct yield points. Monotonic and cyclic (hysteretic) loading-unloading experiments were used to study the influence of Nb-content and pre-straining on the elastic moduli. Such experiments were also utilized to assess the recoverable elastic and anelastic deformations as well as hysteretic energy losses. Particular attention has been paid to the...
Acta Biomaterialia, 2015
The medical device industry's interest in open porous, metallic biomaterials has increased in res... more The medical device industry's interest in open porous, metallic biomaterials has increased in response to additive manufacturing techniques enabling the production of complex shapes that cannot be produced with conventional techniques. Tantalum is an important metal for medical devices because of its good biocompatibility. In this study selective laser melting technology was used for the first time to manufacture highly porous pure tantalum implants with fully interconnected open pores. The architecture of the porous structure in combination with the material properties of tantalum result in mechanical properties close to those of human bone and allow for bone ingrowth. The bone regeneration performance of the porous tantalum was evaluated in vivo using an orthotopic load-bearing bone defect model in the rat femur. After 12 weeks, substantial bone ingrowth, good quality of the regenerated bone and a strong, functional implant-bone interface connection were observed. Compared to identical porous Ti-6Al-4V structures, laser-melted tantalum shows excellent osteoconductive properties, has a higher normalized fatigue strength and allows for more plastic deformation due to its high ductility. It is therefore concluded that this is a first step towards a new generation of open porous tantalum implants manufactured using selective laser melting.
a b s t r a c t SBA-15 ordered mesoporous material is an excellent carrier material for the poorl... more a b s t r a c t SBA-15 ordered mesoporous material is an excellent carrier material for the poorly soluble drug molecule itraconazole. Immediate itraconazole release is obtained upon contacting the formulation with simulated biological fluid. The stability of the formulation upon storage was investigated. Samples were stored for 3, 6 and 12 months at 4 and 25°C and relative humidity of 0%, 52% and 97%. The original release behavior was maintained upon storage in dry conditions. Surprisingly, long-term storage at a relative humidity of 52% or 97% had a beneficial effect on the release. The surface chemical modification of the formulation upon storage in humid atmosphere was investigated using nitrogen adsorption, 29 Si MAS NMR, TGA-MS, XPS and DSC. Itraconazole phase analysis using DSC and analysis of the presence of itraconazole concentration gradients using XPS revealed that storage did not cause migration, aggregation nor crystallization of itraconazole. The surface of the pores of SBA-15 was found to undergo hydroxylation at high relative humidity. The enhanced hydrophilicity was responsible for the observed improvement of itraconazole release upon contact with water. These findings contribute to the understanding of drug delivery systems based on mesoporous silica carrier materials.
Journal of Pharmaceutical Sciences, 2009
In order to establish a knowledge base for nanosuspension production, a screening was performed o... more In order to establish a knowledge base for nanosuspension production, a screening was performed on 13 different stabilizers at 3 concentrations for 9 structurally different drug compounds. Concerning the stabilizers tested, the group of semi-synthetic polymers was the least performant (stable nanosuspensions were obtained in only 1 out of 10 cases). For the linear synthetic polymers, better results were obtained with povidones, however poly(vinyl alcohol) did not result in adequate stabilization. The synthetic copolymers showed even higher success rates, resulting in nanosuspensions in two out of three cases when applied at a 100 wt% concentration (relative to the drug weight). Finally, the surfactants gave the best results, with TPGS being successful at concentrations of 25 or 100 wt% of the drug weight for all compounds tested. From the point of view of drug compound, large differences could be observed upon evaluation of the relative number of formulations of that compound resulting in nanosuspensions. It was found that the hydrophobicity of the surfaces, as estimated by the adsorbed amount of TPGS per unit of surface area of nanosuspensions stabilized with 25 wt% TPGS, was decisive for the agglomeration tendency of the particles and hence the ease of nanosuspensions stabilization. ß
Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2011
Abstract Complexation in solution between danazol and two different cyclodextrins [2-hydroxypropy... more Abstract Complexation in solution between danazol and two different cyclodextrins [2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and 2-hydroxypropyl-γ-cyclodextrin (HP-γ-CD)] was studied using phase solubility analysis, and one-and two-dimensional 1 H-NMR. The increase of danazol solubility in the aqueous cyclodextrin solutions showed a linear relationship (AL profile). The apparent stability constant, K 1: 1, of each complex was calculated and found to be 51.7× 10 3 and 7.3× 10 3 M− 1 for danazol–HP-β-CD and ...
status: published, 2008
Associatie KULeuven. ...
status: published, Sep 9, 2008
Associatie KULeuven. ...
status: published, 2009
Evaluation of various mesoporous silica-based formulation concepts for their potential to improve... more Evaluation of various mesoporous silica-based formulation concepts for their potential to improve the absorption of the poorly soluble weak base itraconazole M. Van Speybroeck 1, R. Mellaerts 2, T. Do Thi 1, JA Martens 2, J. Van Humbeeck 3, J. Vermant 4, P. Annaert 1, G. Van den Mooter 1, P. Augustijns 1 1 KU Leuven, Laboratory for Pharmacotechnology and Biopharmacy, 2 KU Leuven, Centre for Surface Chemistry and Catalysis, 3 KU Leuven, Department of Metallurgy and Materials Engineering, 4 KU Leuven, Department of Chemical Engineering Purpose. ...
status: published, 2009
Associatie KULeuven. ...
Cracks and delamination, resulting from residual stresses are a barrier in the world of Additive ... more Cracks and delamination, resulting from residual stresses are a barrier in the world of Additive Manufacturing and Selective Laser Melting (SLM) that prohibits the use of many metals in this field. By pre-heating the baseplate, thermal gradients are lowered and stresses can be reduced. In this work, some initial tests were performed with M2 Tool Steel. Results show that pre-heating enables the production of dense M2 parts. The influence of pre-heating on density and mechanical and physical properties is investigated. The paper shows many promising results for the production of SLM parts in materials that are very sensitive to crack formation and delamination. When using a pre-heating of 200°C, crack-free parts were produced with a relative density of 99.8%.
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Papers by Jan Van Humbeeck