Advanced computer-aided design for bone tissue-engineering scaffolds

The design of scaffolds with an intricate and controlled internal structure represents a challenge for tissue engineering. Several scaffold-manufacturing techniques allow the creation of complex architectures but with little or no control over the main features of the channel network such as the size, shape, and interconnectivity of each individual channel, resulting in intricate but random structures. The combined use of computer-aided design (CAD) systems and layer-manufacturing techniques allows a high degree of control over these parameters with few limitations in terms of achievable complexity. However, the design of complex and intricate networks of channels required in CAD is extremely time-consuming since manually modelling hundreds of different geometrical elements, all with different parameters, may require several days to design individual scaffold structures. An automated design methodology is proposed by this research to overcome these limitations. This approach involves the investigation of novel software algorithms, which are able to interact with a conventional CAD program and permit the automated design of several geometrical elements, each with a different size and shape. In this work, the variability of the parameters required to define each geometry has been set as random, but any other distribution could have been adopted. This methodology has been used to design five cubic scaffolds with interconnected pore channels that range from 200 to 800 μm in diameter, each with an increased complexity of the internal geometrical arrangement. A clinical case study, consisting of an integration of one of these geometries with a craniofacial implant, is then presented

Automated design of trabecular structures

Additive manufacturing technologies are enabling newfound degrees of geometrical complexity to be realised, particularly with regards to internal structures. All of these manufacturing technologies are dependant on their prior design in an appropriate electronic form, either by reverse engineering, or, primarily, by computer-aided design. Within these emerging applications is the design of scaffolds with an intricate and controlled internal structure for bone tissue engineering. There is a consensus that ideal bone scaffold geometry is evident in biological trabecular structures. In their most basic topological form,these structures consist of the non-linear distribution of irregular interconnecting rods and plates of different size and shape. Complex and irregular architectures can be realised by several scaffold manufacturing techniques, but with little or no control over the main features of the internal geometry, such as size, shape and interconnectivity of each individual element. The combined use of computer aided design systems and additive manufacturing techniques allows a high degree of control over these parameters with few limitations in terms of achievable complexity. However, the design of irregular and intricate trabecular networks in computer aided design systems is extremely time-consuming since manually modelling an extraordinary number of different rods and plates, all with different parameters, may require several days to design an individual scaffold structure. In an attempt to address these difficulties, several other research efforts in this domain have largely focussed on techniques which result in designs which comprise of relatively regular and primitive shapes and do not represent the level of complexity seen biologically. Detailed descriptions of these methods are covered in chapter 1. An automated design methodology for trabecular structures is proposed by this research to overcome these limitations. This approach involves the investigation of novel software algorithms, which are able to interact with a conventional computer aided design program and permit the automated design of geometrical elements in the form of rods, each with a different size and shape. The methodology is described in chapter 2 and is tested in chapter 3. Applications of this methodology in anatomical designs are covered in chapter 4. Nevertheless, complex designed rod networks may still present very different properties compared to trabecular bone geometries due to a lack detailed information available which explicitly detail their geometry. The lack of detailed quantitative descriptions of trabecular bone geometries may compromise the validity of any design methodology, irrespective of automation and efficiency. Although flexibility of a design methodology is beneficial, this may be rendered inadequate when insufficient quantitative data is known of the target structure. In this work a novel analysis methodology is proposed in chapter 5, which may provide a significant contribution toward the characterisation and quantification of target geometries, with particular focus on trabecular bone structures. This analysis methodology can be used either to evaluate existing design techniques or to drive the development of new bio-mimetic design techniques. This work then progresses to a newly derived bio-mimetic automated design technique, driven by the newly produced quantitative data on trabecular bone geometries. This advanced design methodology has been developed and tested in chapter 6. This has demonstrated the validity of the technique and realised a significant stage of development in the context and scope of this work