A.F. Lemos

Porous bioactive calcium carbonate implants processed by starch consolidation

Abstract Macroporous calcium carbonate (CaCO 3 ) materials with porous structures suitable for implantation purposes were prepared in the present work. A new “direct consolidation” technique that uses starch granules as consolidator agent and as pore formers, combined with other larger organic inclusions, enabled us to tailor the porous microstructure for the intended application. Pore sizes as large as several hundreds of micrometers could be generated without matrix cracking, due to the high solid loading of the starting suspensions. The macroporous CaCO 3 bodies fabricated exhibit an accentuated bioactivity even for short soaking time periods. The crystalline calcium phosphate phases precipitate preferentially in the pores, pore boundaries, or in other strained sites at the surface of the samples.

Suitability evaluation of sol–gel derived Si-substituted hydroxyapatite for dental and maxillofacial applications through in vitro osteoblasts response

UNLABELLED Si-hydroxyapatite (Si-HAP) has been used in orthopedic, dental, and maxillofacial surgery as a bone substitute. OBJECTIVE The aim of this investigation was to study the effect of Si substitution into the hydroxyapatite matrices and evaluate the biocompatibility effects of Si-HAP material in vitro with human osteoblasts. METHODS Silicon-substituted hydroxyapatite (Si-HAP) bioceramic materials were prepared by incorporating small amounts of silicon into the structure of hydroxyapatite [Ca10(PO4)6(OH)2, HAP] through a sol-gel method. A series of silicon substitutions ranging from 0, 1, 3 and 5 mol%, which are comparable to the measured silicon contents in natural bone, were performed. RESULTS Single-phase Si-HAP was obtained upon calcining the as-prepared powders up to 800 degrees C since no secondary phases, such as tricalcium phosphate (TCP), tetracalcium phosphate (TeCP) or calcium oxide (CaO), were identified by X-ray diffraction analysis. The effects of silicon-substituted hydroxyapatite (Si-HAP) materials towards the responses of human osteoblast-like (HOB) cells were investigated and compared with pure hydroxyapatite. SIGNIFICANCE The Si-HAP indicated a significant increase in cell growth density with culture time irrespective of the amount of Si substituted in HAP. A high Si content (5 mol%) appears to promote rapid bone mineralization, since large amount of calcium phosphate minerals started to develop across the ECM by day 31 for a sample containing 5 mol% Si. On the other hand, a high Si content may result in fast dissolution of the material, owing to a decrease of HAP crystallite size, which might not be ideal for cell attachment for prolonged time periods. An optimum level of Si appears to exist at 3 mol%, which balances these effects.

Development of porous HAp and β-TCP scaffolds by starch consolidation with foaming method and drug-chitosan bilayered scaffold based drug delivery system

The inability to maintain high concentrations of antibiotic at the site of infection for an extended period of time along with dead space management is still the driving challenge in treatment of osteomyelitis. Porous bioactive ceramics such as hydroxyapatite (HAp) and beta-tri calcium phosphate (β-TCP) were some of the alternatives to be used as local drug delivery system. However, high porosity and high interconnectivity of pores in the scaffolds play a pivotal role in the drug release and bone resorption. Ceftriaxone is a cephalosporin that has lost its clinical popularity. But has recently been reported to exhibit better bactericidal activity in vitro and reduced probability of resistance development, in combination with sulbactam, a β-lactamase inhibitor. In this article, a novel approach of forming HAp and pure β-TCP based porous scaffolds by applying together starch consolidation with foaming method was used. For the purpose, pure HAp and β-TCP were prepared in the laboratory and after thorough characterization (including XRD, FTIR, particle size distribution, etc.) the powders were used for scaffold fabrication. The ability of these scaffolds to release drugs suitably for osteomyelitis was studied in vitro. The results of the study indicated that HAp exhibited better drug release profile than β-TCP when drug was used alone indicating the high influence of the carrier material. However, this restriction got relaxed when a bilayered scaffold was formed using chitosan along with the drug. SEM studies along with EDAX on the drug-chitosan bilayered scaffold showed closest apposition of this combination to the calcium phosphate surface.

Porous glass reinforced hydroxyapatite materials produced with different organic additives

Abstract In the present study three different organic additives were used to produce porous structures of a CaO–P2O5 glass reinforced hydroxyapatite potato starch, almond crust and wax spheres. The produced samples were analysed by scanning electron microscopy, X-ray diffraction with Rietveld refinement, differential thermal analysis and mercury porosimetry. The techniques used in this study enabled the production of glass reinforced hydroxyapatite samples with various pore diameters. Two different techniques were used to produce porous glass reinforced hydroxyapatite samples: a dry method using wax spheres as pore formers and a wet method in alcoholic suspension, where almond crust and potato starch were used as pore formers. The final microstructure consists of hydroxyapatite, α-tricalcium phosphate and β-tricalcium phosphate. X-ray diffraction and scanning electron microscopy analysis revealed different percentages of phases when comparing dense and porous glass reinforced hydroxyapatite specimens. These hard materials are intended to be used as bone defect fillers.

Hydroxyapatite scaffolds hydrothermally grown from aragonitic cuttlefish bones

Scaffolds of pure AB-type carbonated hydroxyapatite (HA) were successfully produced via hydrothermal transformation (HT) of aragonitic cuttlefish bones at 200 °C. Beyond low production cost, worldwide availability and natural biological origin of raw materials, the produced scaffolds preserved the initial structure of the cuttlefish bone, featuring pore size of ∼80 µm in width and ∼100 µm in height. The transformation was complete after 9 h and no intermediate products were registered. The kinetics were fast, since, HA was the dominant crystalline phase after only 1 h of HT. The HA crystallites formed had a size of nanoscale (∼20–50 nm) and were randomly oriented.

3D chitosan–gelatin–chondroitin porous scaffold improves osteogenic differentiation of mesenchymal stem cells

A porous 3D scaffold was developed to support and enhance the differentiation process of mesenchymal stem cells (MSC) into osteoblasts in vitro. The 3D scaffold was made with chitosan, gelatin and chondroitin and it was crosslinked by EDAC. The scaffold physicochemical properties were evaluated. SEM revealed the high porosity and interconnection of pores in the scaffold; rheological measurements show that the scaffold exhibits a characteristic behavior of strong gels. The elastic modulus found in compressive tests of the crosslinked scaffold was about 50 times higher than the non-crosslinked one. After 21 days, the 3D matrix submitted to hydrolytic degradation loses above 40% of its weight. MSC were collected from rat bone marrow and seeded in chitosan-gelatin-chondroitin 3D scaffolds and in 2D culture plates as well. MSC were differentiated into osteoblasts for 21 days. Cell proliferation and alkaline phosphatase activity were followed weekly during the osteogenic process. The osteogenic differentiation of MSC was improved in 3D culture as shown by MTT assay and alkaline phosphatase activity. On the 21st day, bone markers, osteopontin and osteocalcin, were detected by the PCR analysis. This study shows that the chitosan-gelatin-chondroitin 3D structure provides a good environment for the osteogenic process and enhances cellular proliferation.

Combining Foaming and Starch Consolidation Methods to Develop Macroporous Hydroxyapatite Implants

Hydroxyapatite (HA) is the calcium-phosphate material with c omposition closest to that of bone, what makes it suitable for osseous implant purposes. This mater ial was used to produce macroporous structures with pores larger than 100 μm, which are believed to be suitable for allowing bone ingrowth. The macroporous structures were generated and consoli dated by combining foaming and starch consolidation methods. The porous structures c ould be tailored according to the final application by varying the proportion of dif ferent foaming agents, foam-bath concentrate (FBC) and sodium lauril sulphate (SLS). Playing with these proportions it was also possible to improve foam stability and model the size of pores and pore interconnections in order to reproduce the pore structure of natural bone.

Rheological, microstructural, and in vitro characterization of hybrid chitosan-polylactic acid/hydroxyapatite composites

In this work, hybrid chitosan/hydroxyapatite composites material were developed and characterized. The polymer matrix was first dissolved in polylactic acid, and then hydroxyapatite (HA) was added as filler material. The effects of the added amounts of a crosslinking agent (genipin) and of the concentrations of lactic acid, and of the presence of HA powder on the evolution of rheological properties were evaluated. A significant decrease of gelation time with increasing amounts of crosslinking agent was observed, the effect being even more pronounced in the presence of HA. The chitosan matrix and the composites with a chitosan/HA weight ratio of 2/5 were characterized using microstructural analysis and in vitro tests. The formation of large pore sizes in the chitosan-based scaffolds was favored by low concentrations of lactic acid and genipin. The in vitro tests in synthetic body fluid revealed an extensive formation of an apatitic layer onto the surface of the chitosan/HA composite scaffolds crosslinked with genipin.

Production of Porous Biomaterials Based on Glass-Reinforced Hydroxyapatite Composites

In this study, porous GR-HA composites were produced using a calcium-phosphate glass with the composition, in mol%, 75P2O5-15CaO-10CaF2. The composites were obtained by wet mixing 4.0% (w/w) of the glasses with hydroxyapatite (HA) powder (batch P120) (Plasma Biotal; Tideswell, U.K.), pressing and sintering. Two different organic additives were used as pore formers: potato starch and almond crust. This processing route was effective in producing a homogeneous microstructure of equiaxed grains. The bulk density of the samples decreased with the volume fraction increase in the content of pore formers. Scanning electron microscopy and mercury porosimetry analyses showed to be complementary techniques in characterising the pore size and distribution. Introduction Porous biomaterials have been produced in a variety of ways [1-2] for numerous biomedical applications, such as drug delivery systems and as osteoconductive implants for bone ingrowth. These macroporous bioceramics require pores larger than 100μm to allow proper vascularisation of the newly formed bone tissue. Several glass systems have been used to produce glass reinforced hydroxyapatite (GR-HA) composites. A previous study has demonstrated that glass reinforced hydroxyapatite composite materials based on HA and 4wt% of the 75P2O5-15CaO-10CaF2 glass are partially resorbable in vivo using rabbit model [3]. During sintering, the CaO-P2O5 glass reacts with HA and some -TCP ( -tricalcium phosphate) is formed in the microstructure as demonstrated by X-ray diffraction analysis [3]. The amount of TCP depends upon the sintering temperature used and the content of glass added to prepare the composite. This phase is known to be more biodegradable than HA and therefore this composite material should augment bone ingrowth compared to unmodified HA. Furthermore, the degree of biodegradability of this type of composites may be controlled by the content of glass and the sintering temperature. Experimental procedure The composite material was developed by J.D. Santos and co-workers [4]. To produce the composite, the glass was melted in a platinum crucible at 1450°C during 1 hour with a heating rate of 2°Cmin -1 . The produced glass was firstly crushed in an agate mortar up to a granule size less than 75 μm. The composites were obtained by wet mixing 4.0% (w/w) of the glasses with hydroxyapatite (HA) powder (batch P120) (Plasma Biotal; Tideswell, U.K.). Composite powders were then dried, sieved and dispersed in ethanol in the presence of a suitable dispersant, followed by planetary ball milling for 1 hour, achieving a particle size distribution with 90% below of 5 μm. Two different organic additives were used as pore formers: a potato starch with an average granule size of about 55 μm and almond crust with an average granule size of about 410 μm (90% below 600 μm), and added to portions of the stock suspension together with a binder [Poly-vinylbutyralco-vinyl alcohol-co-cinyl acetate]. The fraction of starch was maintained constant, at 20% in Key Engineering Materials Online: 2002-10-25 ISSN: 1662-9795, Vols. 230-232, pp 483-486 doi:10.4028/www.scientific.net/KEM.230-232.483

Influence of Characteristics of the Starting Hydroxyapatite Powders and of Deagglomeration Procedure, on Rheological Behaviour of HA Suspensions

In order to evaluate how the characteristics of starting HA powders affect their dispersion ability, several tests were made, including particle size distribution, particle morphology (SEM) and rheological measurements of the suspensions. To enable the preparation of concentrated suspensions as high as possible, the influence of deagglomeration procedure on rheological behaviour of hydroxyapatite aqueous suspensions was evaluated. The results revealed significant differences in the dispersing ability of the powders and on the maximum achievable solids loading. In fact, the maximum solids volume fraction that was possible to incorporate in the initial suspension of HAR was only 35-vol.%, while with the HAS it has been possible to start from 45vol.% suspensions. Ball milling revealed to be more efficient than planetary milling in the preparation of HAR suspensions, and enabled to achieve a maximum solids volume fraction of 45vol.% at the end of long milling period, which included successive incremental additions of powder. The powder HAS exhibited a much better dispersing ability, enabling the preparation of 60-vol.% solids only after two hours of planetary milling. Introduction Because of its crystallographical similarity to various calcified tissues of vertebrates, e. g., enamel, dentine and bone, hydroxyapatite, Ca10(PO4)6(OH)2, has attracted much attention for bone repair over the past several years[1]. Hydroxyapatite ceramics may be used in granular, dense or porous form, as a part of a composite or as a coating of a metal prosthesis [2]. The properties of the starting powders (e. g., particle size and morphology and surface charge) as well as the processing procedure will affect the density, grain size and pore morphology, which in turn affect the physical properties of the final product. In recent years, attention was particularly placed on the fabrication of hydroxyapatite with “porous” configuration because the interconnecting porous network allows the ingrowth of surrounding bone and because of its effectiveness in local delivery of medicines, which further enhances the tissue-implant attachment [3]. Porous hydroxyapatite can be obtained by different techniques such as the polymeric sponge method or foaming processes, but a general problem is how to control the processing and the ultimate material properties [4]. There is also a new family of forming techniques, named Direct Consolidation Techniques, which allows generation of complex shapes, but require a good knowledge of the rheological behaviour of concentrated hydroxyapatite suspensions [5]. In this study, the influence of characteristics of the starting HA powders and of deagglomeration procedure, on rheological behaviour of concentrated suspensions and on the maximum achievable solids loading, was investigated. * corresponding author: jmf@cv.ua.pt Materials Science Forum Online: 2004-05-15 ISSN: 1662-9752, Vols. 455-456, pp 361-365 doi:10.4028/www.scientific.net/MSF.455-456.361