Final Activity Report Summary - NOVELSCAFF (Novel fabrication techniques to produce scaffolds for tissue engineering applications)
This programme addressed a series of challenges related to producing biomaterials specifically designed to aid regeneration of bone or blood vessels. The projects involved the application of a selection of promising manufacturing technologies to the production of scaffolds. These have tightly defined microscale characteristics which are conducive to the cellular processes involved in tissue regeneration. All of the technologies involve the use of powdered biomaterials; Hydroxyapatite (HA, a ceramic) and polycaprolactone (PCL, a polymer) in the case of bone scaffolds, and polyvinyl alcohol (PVA) and natural biomacromolecules (such as gelatin) for blood vessel scaffolds.
For bone scaffolds, a study on the effect of material composition was performed for porous composites of HA and PCL that were prepared by a number of methods (salt leaching, phase separation, gas forming, freeze drying). Based on extensive characterisation experiments, including compatibility with bone cells, the optimum composites were found to contain 4 % HA: 96 %PCL, and were formed at a thickness of 1.2 mm for solvent evaporation, and a thickness of 10 mm for phase separation.
The performance of scaffolds for bone tissue regeneration is also partly related to how cells, attached to the scaffolds, deform in response to both biomechanical loading and biological fluid flow. Three-dimensional (3D) images of the honeycomb-like structure of human bone were obtained using micro-CT scanning, and 3D printing technology was used to prepare artificial bone samples from powdered materials. A custom built image analysis system was constructed to study how strain is distributed in the trabeculae of the porous scaffolds under compressive loading. A series of permeability tests determined the fluid transport properties of the scaffolds. The 3D scaffold printing technology was further investigated using calcium phosphate cement (Dicalcium Phosphate Anhydrous / sodium phosphate) for improved biocompatibility.
Selective laser sintering is a prototyping technology that produces solid objects with complex three dimensional shapes. It involves the localised melting of powdered materials by a laser whose focal point can trace a 3D path to define the shape of an object. The energy density delivered by the laser is usually considered to have the dominant effect on the quality of the structure, but this study showed that the process is also sensitive to other parameters such as scan count and part position. Statistical models were developed which can better predict the mechanical and dimensional properties of scaffolds manufactured from HA and PCL powder blends.
A further set of studies was carried out using a low energy plasma spray process to deposit free standing samples of HA alone, and in combination with either PCL or titanium dioxide (TiO2). Statistically designed experiments were used to identify the effect of three process parameters on sample properties. With porosity being a restricting characteristic, results point to limited likelihood that these processes can be used to form bone scaffolds.
The studies on tissue engineered blood vessels resulted in a method which combines electrospinning (which produces ultrafine fibres), photopolymerisation (with an ultraviolet lamp) and a freeze-thaw process to create blood vessel scaffolds which mimic the structural characteristics of arteries. The mechanical compliance of these vessels was similar to arteries under pulsatile flow conditions. A process for encapsulating smooth muscle cells in PVA / gelatin gels was developed ensuring cells are distributed within the scaffold as a precursor to the tissue generation process. A method for rapidly seeding the surface of the gels with endothelial cells (found on the inside surface of blood vessels) by applying a dynamic shear stress was also developed. The ability to culture both sets of cells simultaneously on the scaffold was also demonstrated.
For bone scaffolds, a study on the effect of material composition was performed for porous composites of HA and PCL that were prepared by a number of methods (salt leaching, phase separation, gas forming, freeze drying). Based on extensive characterisation experiments, including compatibility with bone cells, the optimum composites were found to contain 4 % HA: 96 %PCL, and were formed at a thickness of 1.2 mm for solvent evaporation, and a thickness of 10 mm for phase separation.
The performance of scaffolds for bone tissue regeneration is also partly related to how cells, attached to the scaffolds, deform in response to both biomechanical loading and biological fluid flow. Three-dimensional (3D) images of the honeycomb-like structure of human bone were obtained using micro-CT scanning, and 3D printing technology was used to prepare artificial bone samples from powdered materials. A custom built image analysis system was constructed to study how strain is distributed in the trabeculae of the porous scaffolds under compressive loading. A series of permeability tests determined the fluid transport properties of the scaffolds. The 3D scaffold printing technology was further investigated using calcium phosphate cement (Dicalcium Phosphate Anhydrous / sodium phosphate) for improved biocompatibility.
Selective laser sintering is a prototyping technology that produces solid objects with complex three dimensional shapes. It involves the localised melting of powdered materials by a laser whose focal point can trace a 3D path to define the shape of an object. The energy density delivered by the laser is usually considered to have the dominant effect on the quality of the structure, but this study showed that the process is also sensitive to other parameters such as scan count and part position. Statistical models were developed which can better predict the mechanical and dimensional properties of scaffolds manufactured from HA and PCL powder blends.
A further set of studies was carried out using a low energy plasma spray process to deposit free standing samples of HA alone, and in combination with either PCL or titanium dioxide (TiO2). Statistically designed experiments were used to identify the effect of three process parameters on sample properties. With porosity being a restricting characteristic, results point to limited likelihood that these processes can be used to form bone scaffolds.
The studies on tissue engineered blood vessels resulted in a method which combines electrospinning (which produces ultrafine fibres), photopolymerisation (with an ultraviolet lamp) and a freeze-thaw process to create blood vessel scaffolds which mimic the structural characteristics of arteries. The mechanical compliance of these vessels was similar to arteries under pulsatile flow conditions. A process for encapsulating smooth muscle cells in PVA / gelatin gels was developed ensuring cells are distributed within the scaffold as a precursor to the tissue generation process. A method for rapidly seeding the surface of the gels with endothelial cells (found on the inside surface of blood vessels) by applying a dynamic shear stress was also developed. The ability to culture both sets of cells simultaneously on the scaffold was also demonstrated.