Modeling of multifunctional deformable porous scaffolds for soft tissue engineering

Porous membranes/scaffolds such as guided tissue regeneration (GTR) membranes, cell sheets, tissue matrices or polymeric meshes are being widely used in soft tissue engineering to regenerate damaged, diseased tissue or wound. These membranes are mostly regular porous structures with repeating internal architecture. When they are applied onto wound area, various forces caused by bandage, contraction and self weight might cause deformation. As a result, the geometry and the designed porosity changes which eventually alters the desired choreographed functionality. To avoid the negative effect cause by such deformation and its associated consequences, a novel design methodology has been proposed to determine and include the resultant deformation. The proposed design will minimize the variation in effective porosity while ensuring its surface conformity. Thus the proposed design will provide a better functionality by providing both structural integrity and proper biological properties. The proposed methodology has been implemented and results will be shown with illustrative examples. Also a comparison study showing effective porosity for both the proposed method and conventional regular porosity will be presented for a free-form surface mimicking a wound

Designing bio-mimetic variational porosity for tissue scaffolds

Reconstructing or repairing the damaged or diseased tissues with porous scaffolds to restore the mechanical, biological and chemical functions is one of the major tissue engineering strategies. Development of Solid Free Form (SFF) techniques and improvement in biomaterial properties by synergy have provided the leverage to fabricate controlled and interconnected porous scaffold structures. But homogeneous scaffolds with regular porosity do not provide all the biological and mechanical requirements of an ideal tissue scaffold. Thus achieving controllable, continuous, interconnected gradient porosity with reproducible and fabricatable design is critical for successful regeneration of the replaced tissue. In this research, a novel scaffold modeling approach has been proposed to achieve bio-mimetic tissue scaffolds. Firstly, the optimum filament deposition angle has been determined based on the internal heterogeneous regions and their locations. Then an area-weight based approach has been applied to generate the spatial porosity function to determine the filament deposition location for the desired bio-mimetic porosity. The proposed methodology has been implemented using computer simulation. A micro-nozzle biomaterial deposition system driven by NC motion control has been used to fabricate a sample designed structure

Functionally heterogeneous porous scaffold design for tissue engineering

Most of the current tissue scaffolds are mainly designed with homogeneous porosity which does not represent the spatial heterogeneity found in actual tissues. Therefore engineering a realistic tissue scaffolds with properly graded properties to facilitate the mimicry of the complex elegance of native tissues are critical for the successful tissue regeneration. In this work, novel bio-mimetic heterogeneous porous scaffolds have been modeled. First, the geometry of the scaffold is extracted along with its internal regional heterogeneity. Then the model has been discretized with planner slices suitable for layer based fabrication. An optimum filament deposition angle has been determined for each slice based on the contour geometry and the internal heterogeneity. The internal region has been discritized considering the homogeneity factor along the deposition direction. Finally, an area weight based approach has been used to generate the spatial porosity function that determines the filament deposition location for desired biomimetic porosity. The proposed methodology has been implemented and illustrative examples are provided. The effective porosity has been compared between the proposed design and the conventional homogeneous scaffolds. The result shows a significant error reduction towards achieving the biomimetic porosity in the scaffold design and provides better control over the desired porosity level. Moreover, sample designed structures have also been fabricated with a NC motion controlled micro-nozzle biomaterial deposition system

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

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

Modeling of multifunctional porous tissue scaffolds with continuous deposition path plan

A novel modeling technique for porous tissue scaffolds with targeting the functionally gradient variational porosity with continuous material deposition planning has been proposed. To vary the porosity of the designed scaffold functionally, medial axis transformation is used. The medial axis of each layers of the scaffold is calculated and used as an internal feature. The medial axis is then used connected to the outer contour using an optimum matching. The desired pore size and hence the porosity have been achieved by discretizing the sub-regions along its peripheral direction based on the pore size while meeting the tissue scaffold design constraints. This would ensure the truly porous nature of the structure in every direction as well as controllable porosity with interconnected pores. Thus the desired controlled variational porosity along the scaffold architecture has been achieved with the combination of two geometrically oriented consecutive layers. A continuous, interconnected and optimized tool-path has been generated for successive layers for additive-manufacturing or solid free form fabrication process. The proposed methodology has been computationally implemented with illustrative examples. Furthermore, the designed example scaffolds with the desired pore size and porosity has been fabricated with an extrusion based bio-fabrication process

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