Processing and properties of bone-analogue biodegradable and bioinert polymeric composites

This paper summarizes the processing and properties of bone-analogue composites aimed to be used in temporary or permanent orthopaedic applications. The studied matrices were two biodegradable starch based blends (with ethylene-vinyl alcohol copolymer or with cellulose acetate) and three high density polyethylene (HDPE) grades. Composites of these materials with hydroxyapatite (HA—the main inorganic constituent of the human bone) were produced by extrusion compounding and subsequently injection moulded. A non-conventional injection moulding technique known as shear controlled orientation in injection moulding (SCORIM) was used deliberately to induce a strong anisotropic character to the processed composites. For the case of HDPE based composites, an alternative reinforcement system based on carbon fibres (C fibres) was also studied. For that, a special moulding technique that combines, in a single equipment, a compounding with an injection unit was used. Composites featuring a sandwich like structure were also produced by mono-sandwich injection moulding. These composites combine a HDPE/HA outer layer and HDPE/C fibre reinforced core. The aim is to produce composites with a mechanical behaviour matching that of human cortical bone and simultaneously a strong bioactive (bone-bonding) character. For all the cases, the mechanical performance of the produced composites was assessed and the structure developed investigated and related to the processing conditions. It was possible to produce, both biodegradable and bioinert matrix composites, with properties that might allow for their application the orthopaedic orthopaedic field.Subprograma Ciência e Tecnologia do 2.º Quadro Comunitário de Apoio, Ministério da Ciência e Tecnologia (Portugal)

Reinforcement and structure development in injection molding of bone-analogue composites

Composites of high density polyethylene (HDPE) with hydroxyapatite (HA—the main inorganic constituent of human bone) were produced by extrusion compounding and subsequent injection molding. Shear controlled orientation in injection molding (SCORIM) was used deliberately to induce a strong anisotropic character in the composite materials. Bi-composite moldings featuring a sandwich like morphology were also produced by mono-sandwich injection molding. These composites combine a HDPE/HA outer layer and HDPE/carbon fiber reinforced core. For all the cases, the mechanical performance of the produced composites was assessed and the structure developed investigated and related to the processing conditions

Structure development and control of injection-molded hydroxylapatite-reinforced starch/EVOH composites

This article reports on the development of novel composites of starch-based polymers reinforced with hydroxylapatite (HA). Two different grades of blends of starch and ethylene vinyl alcohol copolymers were reinforced with up to 30% (wt) of sintered and nonsintered HA. The initial compounding stage was carried out either in a rotating drum or by twin-screw extrusion (TSE). Compounds were injection molded using both conventional molding and a shear-controlled orientation in injection molding (Scorim) technique. It was possible to obtain composites with very good mechanical properties, approaching those of cortical bone. The best results were achieved for 30% sintered HA composites processed by TSE and Scorim, due to the in situ formation of HA fibers, and the development of molecular orientation and more compact microstructures in the moldings. This was confirmed by SEM analysis of the fracture surfaces, x-ray diffraction, and Raman spectroscopy. The biodegradability of the composites was also assessed and was found to be faster than that of the matrixPRAXIS XXI Programm

Patterning of polymer nanofiber meshes by electrospinning for biomedical applications

The end-product of the electrospinning process is typically a randomly aligned fiber mesh or membrane. This is a result of the electric field generated between the drop of polymer solution at the needle and the collector. The developed electric field causes the stretching of the fibers and their random deposition. By judicious selection of the collector architecture, it is thus possible to develop other morphologies on the nanofiber meshes. The aim of this work is to prepare fiber meshes using various patterned collectors with specific dimensions and designs and to evaluate how those patterns can affect the properties of the meshes relevant to biomedical applications. This study aims at verifying whether it is possible to control the architecture of the fiber meshes by tailoring the geometry of the collector. Three different metallic collector topographies are used to test this hypothesis. Electrospun nonwoven patterned meshes of polyethylene oxide (PEO) and poly(ε-capro-lactone) (PCL) were successfully prepared. Those fiber meshes were analyzed by scanning electron microscopy (SEM). Both mechanical properties of the meshes and cell contacting experiments were performed to test the effect of the produced patterns over the properties of the meshes relevant for biomedical applications. The present study will evaluate cell adhesion sensitivity to the patterns generated and the effect of those patterns on the tensile properties of the fiber meshes

Alternative tissue engineering scaffolds based on starch: processing methodologies, morphology, degradation and mechanical properties

http://www.sciencedirect.com/science/journal/09284931An ideal tissue engineering scaffold must be designed from a polymer with an adequate degradation rate. The processing technique must allow for the preparation of 3-D scaffolds with controlled porosity and adequate pore sizes, as well as tissue matching mechanical properties and an appropriate biological response. This communication revises recent work that has been developed in our laboratories with the aim of producing 3-D polymeric structures (from starch-based blends) with adequate properties to be used as scaffolds for bone tissue engineering applications. Several processing methodologies were originally developed and optimised. Some of these methodologies were based on conventional melt-based processing routes, such as extrusion using blowing agents (BA) and compression moulding (combined with particulate leaching). Other developed technologies included solvent casting and particle leaching and an innovative in situ polymerization method. By means of using the described methodologies, it is possible to tailor the properties of the different scaffolds, namely their degradation, morphology and mechanical properties, for several applications in tissue engineering. Furthermore, the processing methodologies (including the blowing agents used in the melt-based technologies) described above do not affect the biocompatible behaviour of starch-based polymers. Therefore, scaffolds obtained from these materials by means of using one of the described methodologies may constitute an important alternative to the materials currently used in tissue engineering

Dynamic studies of biomimetic coated polycaprolactone nanofiber meshes as bone extracellular matrix analogues

This work aimed at studying the effects of dynamic culture conditions and biomimetic coating on bone cells grown on nanofiber meshes. In our previous work, biomimetic calcium phosphate coated polycaprolactone nanofibre meshes (BCP-NM) proved to be more efficient for supporting cell attachment and proliferation under static conditions, when compared to polycaprolactone nanofibre meshe (PCL-NM). However, no studies on the influence of bioreactors on the behaviour of cells cultivated on these materials were developed so far. [...]info:eu-repo/semantics/publishedVersio

Dynamic mechanical properties of hydroxyapatite-reinforced and porous starch-based degradable biomaterials

It has been shown that blends of starch with a poly(ethylene-vinyl-alcohol) copolymer, EVOH, designated as SEVA-C, present an interesting combination of mechanical, degradation and biocompatible properties, specially when filled with hydroxyapatite (HA). Consequently, they may find a range of applications in the biomaterials field. This work evaluated the influence of HA fillers and of blowing agents (used to produce porous architectures) over the viscoelastic properties of SEVA-C polymers, as seen by dynamic mechanical analysis (DMA), in order to speculate on their performances when withstanding cyclic loading in the body. The composite materials presented a promising performance under dynamic mechanical solicitation conditions. Two relaxations were found being attributed to the starch and EVOH phases. The EVOH relaxation process may be very useful in vivo improving the implants performance under cyclic loading. DMA results also showed that it is possible to produce SEVA-C compact surface/porous core architectures with a mechanical performance similar to that of SEVA-C dense materials. This may allow for the use of these materials as bone replacements or scaffolds that must withstand loads when implanted

Cytocompatibility and response of osteoblastic-like cells to starch-based polymers : effect of several additives and processing conditions

This work reports on the biocompatibility evaluation of new biodegradable starch-based polymers that are under consideration for use in orthopaedic temporary applications and as tissue engineering scaffolds. It has been shown in previous works that by using these polymers it is both possible to produce polymer/hydroxyapatite (HA) composites (with or without the use of coupling agents) with mechanical properties matching those of the human bone, and to obtain 3D structures generated by solid blowing agents, that are suitable for tissue engineering applications. This study was focused on establishing the influence of several additives (ceramic fillers, blowing agents and coupling agents) and processing methods/conditions on the biocompatibility of the materials described above. The cytotoxicity of the materials was evaluated using cell culture methods, according to ISO/EN 109935 guidelines. A cell suspension of human osteosarcoma cells (HOS) was also seeded on a blend of corn starch with ethylene vinyl alcohol (SEVA-C) and on SEVA-C/HA composites, in order to have a preliminary indication on cell adhesion and proliferation on the materials surface. In general, the obtained results show that all the different materials based on SEVA-C, (which are being investigated for use in several biomedical applications), as well as all the additives (including the novel coupling agents) and different processing methods required to obtain the different properties/products, can be used without inducing a cytotoxic behaviour to the developed biomaterial

New prospects in skin regeneration and repair using nanophased hydroxyapatite embedded in collagen nanofibers

This study reflects an exploitation of a composite matrix produced by electrospinning of collagen and electrospraying of nanophased hydroxyapatite (nanoHA), for skin regeneration applications. The main goal was to evaluate the effect of nanoHA, as source of localized calcium delivery, on human dermal fibroblasts, keratinocytes, and human mesenchymal stem cells (hMSCs) growth, proliferation, differentiation, and extracellular matrix production. This study revealed that calcium ions provided by nanoHA significantly enhanced cellular growth and proliferation rates and prevented adhesion of pathogenic bacteria strains typically found in human skin flora. Moreover, hMSCs were able to differentiate in both osteogenic and adipogenic lineages. Rat subcutaneous implantation of the membranes also revealed that no adverse reaction occurred. Therefore, the mechanically fit composite membrane presents a great potential to be used either as cell transplantation scaffold for skin wound regeneration or as wound dressing material in plastic surgery, burns treatment or skin diseases.info:eu-repo/semantics/acceptedVersio

Dynamic culture of osteogenic cells in biomimetically coated poly(caprolactone) nanofibre mesh constructs

In our previous work, biomimetic calcium phosphate-coated poly(caprolactone) nanofibre meshes (BCP-NMs) were demonstrated to be more effective for supporting cell attachment and proliferation under static conditions, when compared with poly(caprolactone) nanofibre meshes (PCL-NMs). In many applications, in vitro cultivation of constructs using bioreactors that support efficient nutrition of cells has appeared as an important step toward the development of functional grafts. This work aimed at studying the effects of dynamic culture conditions and biomimetic coating on bone cells grown on the nanofibre meshes. BCP-NM and PCL-NM were seeded with osteoblast-like cells (MG63--human osteosarcoma-derived cell line). The cell-seeded constructs were cultured within a rotating bioreactor that simulated microgravity, at a fixed rotating speed, for different time periods, and then characterized. Cell morphology, viability, and phenotype were assessed. PCL-NM constructs presented a higher number of dead cells than BCP-NM constructs. Under dynamic conditions, the production of proteins associated with the extracellular matrix of bone was higher on BCP-NM constructs than in the PCL-NM ones, which indicates that coated samples may provide cells with a better environment for tissue growth. It is suggested that improved mass transfer in the bioreactor in combination with the appropriate substrate were decisive factors for this highly positive outcome for generating bone.This work was developed under the scope of the EU Project Network of Excellence "Expertissues'' (NMP3-CT-2004-500283) and supported by Alea jacta est Marie Curie Actions (MEST-CT-2004-008104). M. Alves da Silva would like to acknowledge the Portuguese Foundation for Science and Technology for her grant (SFRH-BD-28708-2006). Jose V. Araujo is grateful to S. Rathbone, H. Sura, I. Wimpenny, I. Dublon, G. Jones, and E. D. Pinho for useful technical discussions