Biomedical subjects

Guigen Zhang

Publications and source records attributed to Guigen Zhang.

6 recordsLinked to original sources

PubMed2006

Biomechanical Analysis of Unilateral External Skeletal Fixators Combined with IM-Pin and Without IM-Pin Using Finite-Element Method.

OBJECTIVES: To determine if a unilateral external skeletal fixator (ESF) with a carbon fiber connecting rod (IMEX SK) without an intramedullary (IM)-pin is mechanically comparable with a unilateral ESF with a stainless-steel connecting rod (IMEX KE) with an IM-pin. STUDY DESIGN: Finite-element method (FEM)-computer simulation. METHODS: FEM models were validated by comparison against data from mechanical testing. Three-dimensional FEM models of a femur with a mid-diaphyseal fracture with a 20 mm gap were developed with 4 unilateral external skeletal fixator devices (6-pin KE, 6-pin KE IM-pin, 6-pin SK, and 6-pin SK IM-pin). A 300 N load was applied to the femur at the proximal end in a direction of theta = 10 degrees distally and phi = 10 degrees laterally cranially. Relative displacements in x-, y- and z-directions at the gap were obtained and the overall stiffness was calculated as 300 N/total displacement. Load transfer at the pin-bone interface (PBI) was assessed by determining the von Mises stress maxima at the PBI-related nodes. RESULTS: The 6-pin SK had superior mechanical performance compared with the 6-pin KE by exhibiting smaller displacements in all directions and higher stiffness. Compared with the 6-pin KE IM-pin, the 6-pin SK (without IM-pin) was superior in craniocaudal and lateromedial displacements, but inferior in axial displacements, overall stiffness and von Mises stress maxima. The 6-pin SK IM-pin was superior to the 6-pin KE IM-pin based on smaller displacements and higher stiffness. CONCLUSIONS: Although the SK device had superior mechanical performance compared with a KE device in a unilateral configuration, the addition of an IM-pin continues to be a powerful method of enhancing mechanical performance of either IMEX SK or IMEX KE unilateral constructs in clinical cases. CLINICAL RELEVANCE: Based on the results of this FEM study we recommend the use of the "tied-in" IM-pin with the ESF clinically when striving for high rigidity. In less challenging situations, a unilateral SK ESF without IM-pin might provide sufficient rigidity for a successful fracture repair.

Animals↗

PubMed2005

Fast fourier transform analysis of pore pattern in anodized alumina formed at various conditions.

A quantitative investigation of the effect of process parameters such as electrolyte concentration, temperature, anodization duration and anodization potential on the pore pattern (including pore diameter and distribution) in anodic alumina was performed based on aluminum anodization experiments. Using fast Fourier transform (FFT) analysis, we developed a method to quantify the orderedness of pore distribution. We found that at a lower temperature the anodization protocol of a 1 hr first step followed by a 4 hr second step did not cause any change in pore orderedness as opposed to the anodization protocol of a 12 hr first step followed by a 1 hr second step, but at a higher temperature the former improved the pore orderedness. Increasing the electrolyte concentration, improved the pore orderedness. Varying the electrolyte concentration, temperature, and anodization duration did not have any effect on the pore diameter. Increasing the anodization potential, however, not only improved the pore orderedness but also increased the pore diameter. Linear relationships exist between the pore diameter and anodization potential and between the center to center pore spacing and applied anodization potential.

Aluminum Oxide↗

PubMed2004

Geometric and material nonlinearity in tensioned wires of an external fixator.

OBJECTIVE: To investigate the fundamental characteristics of a tensioned wire in an external fixator. DESIGN: Many factors that may influence the wire performance including the change in wire geometry, material hardening and yielding, loading and unloading, and levels of pre-tension are considered in order to obtain a whole spectrum of the wire characteristics. BACKGROUND: External fixation is widely used in the treatment of unstable fractures, limb lengthening, and congenital and pathological orthopedic deformities. With the use of tensioned wires, external fixation provides attractive features such as minimal invasiveness, maximum tailorability, and versatility. These seemingly simple wires actually fulfill a very complex duty. To be able to maximize the benefit of these wires, it is necessary to know their fundamental characteristics. METHODS: A single wire was isolated from an external Ilizarov ring-frame, and nonlinear elastic and plastic analyses of the wire were performed using the method of finite element analysis. RESULTS: The nonlinear behavior of the wire originates not only from the material hardening and yielding but also from the change in its geometry. Pre-tension reduces wire deflection, delays the onset of full-plastic deformation, and elevates the limiting plastic moment, but at the same time leads to early material hardening and yielding. CONCLUSIONS: An entire load-deflection curve is necessary when comes to describe the wire performance. To enhance the wire performance, further efforts should be directed to exploiting the benefit of geometric nonlinearity of the wire. RELEVANCE: The findings will lead to refinement of external fixation design and provide engineering information to surgeons regarding the application of pre-tension during surgery.

Bone Wires↗

PubMed2004

Avoiding the material nonlinearity in an external fixation device.

BACKGROUND: External fixation devices are widely used for treating unstable bone fractures because of their attractive features including minimal invasiveness, maximum tailorability, and extreme versatility. In one type of these devices (i.e., the fine-wire fixators), these unique features are made possible by the use of tensioned wires to support bone fragments. The major problem with these wires is their yielding. Once the wires yield, the fracture healing process will be adversely affected. A recent study showed that the nonlinear behavior observed in these tensioned wires can be geometric and material, and the geometric nonlinearity will stiffen the wires while the material nonlinearity will cause the wires to yield. This study is to investigate if it is possible to avoid the material nonlinearity in order to retain the elastic and repeatable performance for the wires. METHODS: Nonlinear and large deformation finite element analyses were conducted. Models of a bone segment transfixed by pairs of cross-aligned wires subjected to various levels of pre-tension were developed. The bone segment was subjected to a vertical load, and the load-displacement curves, wire tensions and wire tensile stresses were obtained under a full cycle of loading and unloading regime. FINDINGS: Pre-tensioning the wires is beneficial for stiffening a fixation device, but is disadvantageous to maintaining the wire elasticity. By limiting the level of the pre-tension, we can avoid the material nonlinearity. Doing so we will be able to stiffen the fixation device and retain elastic and predictable mechanical performance at the same time. INTERPRETATION: The findings will lead to a new paradigm toward enhancing the performance of external fixation devices.

Bone Wires↗

PubMed2004

Brief synopsis of cranial sutures: optimization by adaptation.

This article reviews the form and function of cranial sutures across the temporal and spatial scales. The temporal scale spans 530 million years, from ostracoderms to contemporary humans. The spatial scale spans eight orders of magnitude, from the macroarchitectural level (the entire cranium), through the mesoarchitectural (the local/regional bone-suture-bone complex) and microarchitectural levels (tissues and cells), to the nanoarchitectural level (molecules within and outside the cells). A mechanomorphologic loop, or cycle, exists. The mechanical strain experienced by the sutures eventually alters the morphology of the sutures. In turn, these morphological changes affect the strain distribution within and around the sutures. At the microarchitectural level, the responses of bone and sutural cells to environmental perturbations depend on the content (what that perturbation is), the context (the other coexisting extrinsic and intrinsic factors), and the history of the perturbation (how often and for how long).

Animals↗

PubMedDate not supplied

Neurite development in PC12 cells on flexible micro-textured substrates under cyclic stretch.

We investigated the combined effect of micro-texture and mechanical strain on neuronal cell development such as neurite length and neurite density in a rat pheochromocytoma cell line (PC12 cells). Cells were seeded on flexible silicone substrates with micro-texture or no texture (smooth) and cultured under static and dynamic conditions. In the static condition substrates were not stretched and in the dynamic conditions substrates were subjected to cyclic uniaxial stretching at three different strain levels of 4%, 8%, and 16% with each at three different strain rates at 0.1, 0.5, and 1.0 Hz. Results showed that of all cell cultures there was no significant difference in neurite development between cells on smooth and textured substrates, except in the static and 4% at 0.1 Hz conditions, where micro-texture induced significantly longer neurites. With both types of substrates, a lower mechanical condition (4% at 1.0 Hz or 16% at 0.1 Hz) resulted in more and longer neurites and lower cell density, and a higher mechanical condition (16% at 1.0 Hz) resulted in fewer and shorter neurites and lower cell density as compared to the static condition. These findings suggest that the effect of the micro-texture on neurite development is more prominent in low mechanical conditions than in high mechanical conditions and that the strain level and strain rate have an interrelated effect on neurite development: a higher strain level at a lower strain rate has a similar effect as a lower strain level at a higher strain rate in terms of promoting neurite development.

Animals↗