Tomasz Lekszycki

The influence of different geometries of matrix/scaffold on the remodeling process of a bone and bioresorbable material mixture with voids

Since internal architecture greatly influences crucial factors for tissue regeneration, such as nutrient diffusion, cell adhesion and matrix deposition, scaffolds have to be carefully designed, keeping in mind case-specific mechanical, mass transport and biological requirements. However, customizing scaffold architecture to better suit conflicting requirements, such as biological and mechanical ones, remains a challenging issue. Recent advances in printing technologies, together with the synthesis of novel composite biomaterials, have enabled the fabrication of various scaffolds with defined shape and controlled in vitro behavior. Thus, the influence of different geometries of the assemblage of the matrix and scaffold on the remodeling processes of living bone and artificial material should be investigated. To this end, two implant shapes are considered in this paper, namely a circular inclusion and a rectangular groove of different aspect ratios. A model of a mixture of bone tissue and bioresorbable material with voids was used to numerically analyze the physiological balance between the processes of bone growth and resorption and artificial material resorption in a plate-like sample. The adopted model was derived from a theory for the behavior of porous solids in which the matrix material is elastic and the interstices are void of material.

Fluorescence methods (VistaCam iX proof and DIAGNODent pen) for the detection of occlusal carious lesions in teeth recovered from archaeological context.

Diagnosis of occlusal enamel caries in archaeologically derived collections remains a controversial problem because the accumulation of contaminants in fissures can interfere with diagnosis. Certain novel light-induced fluorescence methods, such as the DIAGNODent pen 2190 (DD) and VistaCam iX Proof (VC), have been used to detect dental caries in clinical settings. In this study, the abilities of DD and VC to detect initial enamel caries in archaeologically derived material is determined and compared with those of other methods (visual inspection, X-ray, histology, and micro-CT). Dental material encompassing the remains of 58 individuals, including a total of 380 teeth from each of three historical periods: modern Islamic (AD 1850-1950), Islamic (AD 600-1200) and late Roman (AD 200-400), obtained from two archaeological sites (Terqa and Tell Masaikh) located in the Middle Euphrates valley (Syria), were analyzed. VC was found to have excellent sensitivity (98), while DD obtained lower sensitivity (76) in detecting dental caries in its early stages. The results obtained by VC and micro-CT, considered the most reliable imaging technique, were not statistically significant (P = 0.3068). By contrast, results obtained by DD and micro-CT results, and DD and VC results were statistically significant (P < 0.0001, P = 0.0015, respectively). However the presence of dirt, stain, calculus, and plaque in the pits and fissures of the occlusal surface compromise correct diagnosis of caries by VC and DD. Consequently, for teeth recovered from archaeological contexts where staining, calculus and plaque are present, the best solution remains micro-CT.

SHEARING TESTS APPLIED TO PANTOGRAPHIC STRUCTURES

With the advancements in 3D printing technology, rapid manufacturing of fabric materials with complex geometries became possible. By exploiting this technique, different materials with different structures have been developed in the recent past with the objective of making generalized continuum theories useful for technological applications. So-called pantographic structures are introduced: Inextensible fibers are printed in two arrays orthogonal to each other in parallel planes. These superimposed planes are inter-connected by elastic cylinders. Five differently-sized samples were subjected to shear-like loading while their deformation response was analyzed. Results show that deformation behavior is strong non-linear for all samples. Furthermore, all samples were capable to resist considerable external shear loads without leading to complete failure of the whole structure. This extraordinary behavior makes these structures attractive to serve as an extremely tough metamaterial.

Modelling of bone fracture healing: influence of gap size and angiogenesis into bioresorbable bone substitute

The complex process of bone fracture healing is driven by a set of mechanobiological and biochemical factors. In the present paper, a mathematical model of the angiogenesis effect on bioresorbable bone graft healing is proposed. The synthesis of bone tissue and resorption of bone and bone substitute material are stimulated by adjacent strain energy, and in the meantime regulated by a set of geometry and biochemical factors. The most important new elements included in formulation of this model are the effect of sufficient and insufficient nutrients supply, dependence of actor cell number on pore surface, and dependence of sensor cell number on bone mass. The proposed mathematical formulation was implemented in FEM software COMSOL. A simple example was selected to perform numerical simulations in order to check the effect of gap size and nutrients diffusion rate on healing process. Values of selected parameters introduced in the proposed model were estimated on the basis of experimental results reported in the literature. Agreement between the results of numerical simulations and experimental studies was observed.

Limited Angle Optical Diffraction Tomography With Generalized Total Variation Iterative Aonstraint Algorithm

The enhanced architecture of a limited angle optical diffraction tomograph is demonstrated.For accurate reconstruction we propose a new two-stage regularization strategy, named Generalized Total Variation Iterative Constraint. The results of measurement of mouse fibroblast cells are presented.

MODELING THE INTERACTIONS BETWEEN BONE TISSUE AND BIO-RESORBABLE GRAFTS

The problem of long-term interaction between bone tissue and bone-substitute materials is considered in this work. The application of bio-resorbable grafts became an everyday practice in orthopedic and in maxillofacial surgery. There exists nowadays a large number of materials already available in the market which have different chemical, structural and mechanical characteristics. They initially have the function of sustaining external mechanical loads, but are progressively resorbed by osteoclasts and partially or completely replaced by new bone tissue. Different materials give rise to different percentages of such replacement under the same conditions. An important question appears then what is the best solution to enable stable partial or complete replacement of the graft by a natural tissue which is usually better. Many factors affect the integration process after surgery. We focus here on mechanical stimulation effect which is known to play a fundamental role in the final step of healing. After graft implantation a complex process starts. To big extent it is similar to the process of bone fracture healing. Four distinct phases can be detected: formation of hematoma, inflammatory phase, reparative phase, remodeling phase. The first three of them are controlled by biological factors while the last one strongly depends on the coupling between biological and mechanical phenomena. During the initial three phases new and not fully functional bone tissue is created and bio-resorbable material is substantially not affected by this process. During the last phase, resorption takes place and the artificial material is gradually replaced by new tissue. We believe that this phase leads the main contribution to the final quality of the material [1], and we then focus on its rigorous modeling and analysis. Methods