Multi-functional variational porosity in bone tissue scaffolds

Commonly used homogeneous scaffolds do not capture the intricate spatial material concentration presented in bone internal architecture. On the other hand gradient in porosity along the internal scaffold architecture might contribute for performing diverse mechanical, biological and chemical functions of scaffold. Thus the need for reproducible and fabricatable scaffold design with interconnected and continuous pore and controllable gradient in porosity for tissue regeneration is obvious but is thwarted by design and fabrication limitations. In this work, a novel heterogeneous scaffold modeling approach has been proposed targeting the bio-mimetic porosity design. First, an optimum filament deposition angle has been determined in slices based on the contour geometry of targeted region. And the internal region has been discritized considering the homogeneity factor along the deposition angle. Finally, an area weight based approach has been used to generate the spatial porosity function that determines the filament deposition location for desired bio-mimetic porosity. The proposed methodology has been implemented an illustrative examples using computer simulation. A comparison result of effective porosity has been presented between proposed design model and conventional fixed filament distance scaffolds respectively. The result shows a significant error reduction towards the achieving bio-mimetic scaffold design concept and provides more control over the desired porosity level. Moreover, the resultant model can easily be fabricated with simple SFF processes

Functionally gradient tissue scaffold design and deposition path planning for bio-additive processes

A layer-based tissue scaffold is designed with heterogeneous internal architecture. The proposed layer-based design uses a bi-layer pattern of radial and spiral layer consecutively to generate functionally gradient porosity following the geometry of the scaffold. Medial region is constructed from medial axis and used as an internal geometric feature for each layer. The radial layers are generated with sub-region channels by connecting the boundaries of the medial region and the layer’s outer contour. Proper connections with allowable geometric properties are ensured by applying optimization algorithms. Iso-porosity regions are determined by dividing the sub-regions into pore cells. The combination of consecutive layers generates the pore cells with desired pore sizes. To ensure the fabrication of the designed scaffolds, both contours have been optimized for a continuous, interconnected, and smooth deposition path-planning. The proposed methodologies can generate the structure with gradient (linear or non-linear), variational or constant porosity that can provide localized control of variational porosity along the scaffold architecture. The designed porous structures can be fabricated using bio-additive fabrication processes

Conformal tissue scaffold with multi-functional porosity for wound healing

In tissue engineering and wound healing, porous scaffolds can stimulate the wound healing process by regenerating the damaged or diseased tissue. But when applied in wound area various forces like bandage, contraction and self weight act upon these visco-elastic scaffold/membrane and cause deformation. As a result, the geometry and the designed porosity change which eventually alters the desired choreographed functionality such as material concentration, design parameters, cytokines distribution over the wound device geometry. In this work, a novel scaffold modelling approach has been proposed that will minimize the change in effective porosity with the designed porosity due to its deformation. First the targeted wound surface model has been extracted and sliced along its depth. Then the height based contours are projected and descritized into functional regions Surface profile for each region have been extracted with contour area weight based slope method. Finally, the filament deposition locations have been generated considering the region profile. Thus the proposed method will give a better functionality of tissue membrane providing predictable material concentration along the wound surface and optimum environment under deformed conditions. The methodology has been implemented using a bi-layer porous membrane via computer simulation. A comparison of the results of effective porosity between the proposed design and conventional design has also been provided. The result shows a significant improvement and control over desired porosity with the proposed method

Designing heterogeneous porous tissue scaffolds for additive manufacturing processes

A novel tissue scaffold design technique has been proposed with controllable heterogeneous architecture design suitable for additive manufacturing processes. The proposed layer-based design uses a bi-layer pattern of radial and spiral layers consecutively to generate functionally gradient porosity, which follows the geometry of the scaffold. The proposed approach constructs the medial region from the medial axis of each corresponding layer, which represents the geometric internal feature or the spine. The radial layers of the scaffold are then generated by connecting the boundaries of the medial region and the layer's outer contour. To avoid the twisting of the internal channels, reorientation and relaxation techniques are introduced to establish the point matching of ruling lines. An optimization algorithm is developed to construct sub-regions from these ruling lines. Gradient porosity is changed between the medial region and the layer's outer contour. Iso-porosity regions are determined by dividing the subregions peripherally into pore cells and consecutive iso-porosity curves are generated using the isopoints from those pore cells. The combination of consecutive layers generates the pore cells with desired pore sizes. To ensure the fabrication of the designed scaffolds, the generated contours are optimized for a continuous, interconnected, and smooth deposition path-planning. A continuous zig-zag pattern deposition path crossing through the medial region is used for the initial layer and a biarc fitted isoporosity curve is generated for the consecutive layer with C-1 continuity. The proposed methodologies can generate the structure with gradient (linear or non-linear), variational or constant porosity that can provide localized control of variational porosity along the scaffold architecture. The designed porous structures can be fabricated using additive manufacturing processes

Modeling of variational gradient porous architecture with multi-directional filament deposition in 3D scaffolds

Porous scaffolds with interconnected and continuous pores have recently been developed to stimulate tissue regeneration. Even though few researches have focused on the internal architecture of porous scaffolds but concluded that properly interconnected and continuous pores with spatial distribution might perform diverse mechanical, biological and chemical functions of a scaffold. Thus the need for reproducible and fabricatable scaffold design with controllable gradient porosity is obvious but is hardly achieved because of design and fabrication limitations. In this paper, a novel functionally gradient variational porosity architecture has been proposed with continuous material deposition planning scheme. The medial axis transformation for the scaffold has been calculated to generate an internal feature of the geometric domain. The medial axis is then used as a base to develop the medial boundary to define the medial regions. Then the complex internal architecture of scaffolds is divided into sub-regions using the ruling lines that are generated between the slice’s contour and the medial boundary. The desired controlled variational porosity along the scaffold architecture has been achieved with the combination of two geometrically oriented consecutive layers while meeting the tissue scaffold design constraints. This ensures truly porous structures in every direction as well as controllable porosity with interconnected pores along the scaffold architecture. The proposed methodology has been implemented and illustrative examples are also provided. A sample designed structure has been fabricated with a NC motion controlled micro-nozzle deposition system

Spatially multi-functional porous tissue scaffold

A novel tissue scaffold design technique has been proposed with controllable heterogeneous architecture design suitable for additive manufacturing processes. The proposed layer-based design uses a bi-layer pattern of radial and spiral layer consecutively to generate functionally gradient porosity, which follows the geometric shape of the scaffold. The proposed approach constructs the medial region from the medial axis of each corresponding layer. The radial layers of the scaffold are then generated by connecting the boundaries of the medial region and the layer's outer contour. Gradient porosity is changed between the medial region and the layer's outer contour. Iso-porosity regions are determined by dividing the sub-regions peripherally into pore cells and consecutive iso-porosity curves are generated using the iso-points from those pore cells. The combination of consecutive layers generates the pore cells with desired pore sizes. To ensure the fabrication of the designed scaffolds, the generated contours are optimized for a continuous, interconnected, and smooth deposition path-planning. The proposed methodologies can generate the structure with gradient (linear or non-linear), variational or constant porosity that can provide localized control of variational porosity along the scaffold architecture. The designed porous structures can be fabricated using additive Manufacturing processes