PubMed Health⌕ Search

Biomedical subjects

Adrian P Sheppard

Publications and source records attributed to Adrian P Sheppard.

3 recordsLinked to original sources

Analysis of 3D bone ingrowth into polymer scaffolds via micro-computed tomography imaging.

This paper illustrates the utility of micro-computed tomography (micro-CT) to study the process of tissue engineered bone growth. A micro-CT facility for imaging and visualising biomaterials in three dimensions (3D) is described. The facility is capable of acquiring 3D images made up of 2000(3) voxels on specimens up to 60mm in extent with resolutions down to 2 microm. This allows the 3D structure of tissue engineered materials to be imaged across three orders of magnitude of detail. The capabilities of micro-CT are demonstrated by imaging the Haversian network within human femoral cortical bone (distal diaphysis) and bone ingrowth into a porous scaffold at varying resolutions. Phase identification combined with 3D visualisation enables one to observe the complex topology of the canalicular system of the cortical bone. Imaging of the tissue engineered bone at a scale of 1cm and resolutions of 10 microm allows visualisation of the complex ingrowth of bone into the polymer scaffold. Further imaging at 2 microm resolution allows observation of bone ultra-structure. These observations illustrate the benefits of tomography over traditional techniques for the characterisation of bone morphology and interconnectivity and performs a complimentary role to current histomorphometric techniques.

Bone Density↗

Trapping thresholds in invasion percolation.

We give numerical estimates for the site percolation trapping thresholds for invasion percolation on various three dimensional lattices. We find that in most cases the thresholds for invasion and ordinary percolation coincide. However, for coordination numbers less than five the thresholds diverge. Since most rock networks exhibit coordination numbers less than five the rules for simulating residual saturation in porous rocks must be chosen carefully.

Journal Article↗

Nonuniversality of invasion percolation in two-dimensional systems.

Employing highly efficient algorithms for simulating invasion percolation (IP) with trapping, we obtain precise estimates for the fractal dimensions of the sample-spanning cluster, the backbone, and the minimal path in a variety of two-dimensional lattices. The results indicate that these quantities are nonuniversal and vary with the coordination number Z of the lattices. In particular, while the fractal dimension D(f) of the sample-spanning cluster in lattices with low Z has the generally accepted value of about 1.82, it crosses over to the value of random percolation, D(f) approximately equal to 1.896, if Z is large enough. Since optimal paths in strongly disordered media and minimum spanning trees on random graphs are related to IP, the implication is that these problems do not also possess universal scaling properties.

Journal Article↗