Peng Shang

The effect of selected alloying element additions on properties of Mg-based alloy as bioimplants: A literature review

This review investigates the current application limitations of Mg and Mg alloys. The key issues hindering the application of biodegradable Mg alloys as implants are their fast degradation rate and biological consideration. We have discussed the effect of some selected alloying element additions on the properties of the Mg-based alloy, especially the nutrient elements in human (Zn, Mn, Ca, Sr). Different grain sizes, phase constituents and distributions consequently influence the mechanical properties of the Mg alloys. Solution strengthening and precipitation strengthening are enhanced by the addition of alloying elements, generally improving the mechanical properties. Besides, the hot working process can also improve the mechanical properties. Combination of different processing steps is suggested to be adopted in the fabrication of Mg-based alloys. Corrosion properties of these Mg-based alloys have been measured in vitro and in vivo. The degradation mechanism is also discussed in terms of corrosion types, rates, byproducts and response of the surrounding tissues. Moreover, the clinical response and requirements of degradable implants are presented, especially for the nutrient elements (Ca, Mn, Zn, Sr). This review provides information related to different Mg alloying elements and presents the promising candidates for an ideal implant.

Physical modification of polyetheretherketone for orthopedic implants

Polyetheretherketone (PEEK) is regarded as one of the most potential candidates for replacing current implant applications. To obtain good bone-implant interfaces, many modification methods have been developed to enable PEEK and PEEK-based composites from bio-inert to bioactive. Among them, physical methods have aroused significant attention and been widely used to modify PEEK for orthopedic implants. This review summarizes current physical modification techniques of PEEK for orthopedic applications, which include composite strategies, surface coating methods and irradiation treatments. The positive consequences of those modification methods will encourage continuing investigations and stimulate the wide range of applications of PEEK-based implants in orthopedics.

In vitro and in vivo evaluation of bone morphogenetic protein-2 (BMP-2) immobilized collagen-coated polyetheretherketone (PEEK)

Polyetheretherketone (PEEK) is regarded as one of the most potential candidates of biomaterials in spinal implant applications. However, as a bioinert material, PEEK plays a limited role in osteoconduction and osseointegration. In this study, recombinant human bone morphogenetic protein-2 (rhBMP-2) was immobilized onto the surface of collagen-coated PEEK in order to prepare a multi-functional material. After adsorbed onto the PEEK surface by hydrophobic interaction, collagen was cross-linked with N-(3-dimethylaminopropyl)-N′-ethyl carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). EDC/NHS system also contributed to the immobilization of rhBMP-2. Water contact angle tests, XPS and SEM clearly demonstrated the surface changes. ELISA tests quantified the amount of rhBMP-2 immobilized and the release over a period of 30 d. In vitro evaluation proved that the osteogenesis differentiation rate was higher when cells were cultured on modified PEEK discs than on regular ones. In vivo tests were conducted and positive changes of major parameters were presented. This report demonstrates that the rhBMP-2 immobilized method for PEEK modification increase bioactivity in vitro and in vivo, suggesting its practicability in orthopedic and spinal clinical applications.

A non-linear contact FE model to evaluate pressure ulcer on buttock-thigh under sitting

Pressure ulcer (PU) is one of the most common but serious medical complications experienced by people who rely on wheelchairs. Many previous finite element (FE) models related to buttock ignored the complexity including the anatomical geometry, non-linear property between skin and cushion and real physiological loading. In this investigation, a three-dimensional (3D) comprehensive FE model derived from MRI images under sitting was constructed to evaluate PU. Contact property between skin and cushion and physiological loading were considered in the model. The result shows that high pressure of 86-180 kPa in muscle under ischial tuberosity (IT) was predicted in our investigation, bigger than that of 50-80 kPa in skin and that of 40-50 kPa in fat. While differing from other literatures, the von-Mises stress of 80-120 kPa in skin was bigger than that of 10-30 kPa in fat and that of 30-50 kPa in muscle. The maximum frictional shear stress contributing to superficial pressure ulcer in anterior-posterior direction occurs just beneath the IT with the range of 3.9-6.5 kPa. In conclusion, the non-linear contact FE model proves valid in predicting mechanical response of superficial and internal tissues under sitting.

An ultrasound approach to digitizie bony landmarks in navigation assisted total hip arthroplasty

An imageless Computer-Assisted Navigation System (iCNS) in Total Hip Arthroplasty (THA) has been shown to help increase the accuracy of cup placement. iCNS relies on the location of the Anterior Superior Iliac Spines (ASISs) and the Pubic Symphysis (PS) to establish the pelvic coordinate system for operation. However, palpated location of these landmarks can be the inaccuracy in establishing the pelvic coordinate system due to the substantial amount of the soft tissue and may increase the possibility of misalignment of the hip prostheses, resulting in the failure of THA. The objective of this study was to initially evaluate an alternative solution in palpating the bony landmarks using an ultrasound probe. Bony landmarks on pelvis were measured using 3 methods, manual palpating probe of the iCNS, two ultrasound modes (“surface” ultrasound mode, “point” ultrasound mode). The X (Right), Y (Anterior) and Z (Superior) coordinates of IASIS, RASIS, PS, and the acetabular Abduction and Anteversion of cup orientation were calculated in the pelvic coordinate system established on the bony landmarks to assess the potential effect on calculating the cup orientation using landmarks obtained from different methods. The results show the cup orientation did not generate significantly different values from two ultrasound modes and manual palpation, which approves these two ultrasound methods can be an alternative solution to digitizie bony landmarks in navigation assisted total hip arthroplasty.

Morphological study of acetabulum on 3D model reconstructed from CT scan images for the southern Chinese population

To obtain the morphological measurements of acetabulum for southern Chinese population, 40 volunteers were evaluated by CT scan. The 3D model of pelvis was reconstructed from CT scan images. The AVA, ABA and SID were measured for both sides. The mean AVA, ABA showed no significant difference for sex and both sides. But the SID showed the opposite results. The comparison of these parameters with western data were performed, and it indicated that there was significant different between our results and the data for western population published. This study may provide important reference in designing proper gender- and region- prosthesis for southern Chinese population.

Effect of Suture Density on the Dynamic Behavior of the Bioprosthetic Heart Valve: A Numerical Simulation Study

This paper constructs the bioprosthetic valve leaflets’ parametric model using computer aided design.A series of accurate parameters of the bioproshtetic heart valve, such as radius of the sutural ring, height of the supporting stent and inclination of the supporting stent are determined. Numerical simulation is used to determine the effect of different shape designs and suture density on the mechanical performance of the bioprosthetic valve leaflet. The dynamic behavior of the valve during diastolic phase is analyzed. The finite element analysis results show that the stress distribution of the ellipsoidal leaflet valve is good. The ellipsoidal leaflet valve has the following advantages over the cylindrical leaflet valve: lower peak von Mises-stress, smaller stress concentration area and relatively uniform stress distribution. The suture density also has a significant effect on the dynamic behavior of the valve as it can act to reduce the pressure and improve the stress distribution. It was found that the influence of suture density in the stress of the leaflet differs on the basis of different geometries considered in the model. The degree of influence of the suture density in the bioprosthetic heart valve may also be dependent on the geometries of the valves. This indicates the need to account for the attachment edge, when manufacturing such bioproshetic heart valves for long term durability. Further research is required to assess the effect of suture density on the bioprosthetic heart valve models.

Numerical Evaluation of the Effectiveness of the Air Chamber of Shoes Pad for Diabetes with FE-SPH Method

The object of this study is to utilize FE-SPH method to simulate the dynamic behavior of the air chamber of shoes pad for diabetes during footing process. The shoes pad’ numerical models are discrete as FE mesh, and the air inside is modeled as SPH particles. The fluid structure interaction analysis between air and the shoes pad is carried out with contact algorithms. This explicit dynamic analysis is run on ANSYS software. Results show that: when the shoes pad is loaded, the velocity field concentrated on the central region of air chamber, and the particles in the fringe maintain a zero speed, which means the air flow out in the central region instead of the fringe. Thus, the shoes pad is effective in supplying air for the foot of diabetes.

The biomechanics analysis of anatomical morphology of skeleton

The skeleton is a structural, load-bearing system, much of what we see in an adults bone morphology is a result of the history of skeletal loading during adolescence. The mechanics environments from daily activities play an important role in (re)modeling of an adults bone morphology. This paper, taking typical bones (e.g. proximal femur, proximal humerus and mandible) as examples, compared the principle stress vectors predicted by FE analysis under daily activities with orientations of trabecular bone from corresponding cadaver bone for finding out the relationships between mechanics environments and (re)modeling of bone morphology. The result shows essentially similar between principle stress vectors and orientations of trabecular bone, which can be as part of proofs of functional adaptation of bone. And together with bone remodeling simulations and some orthopedic clinical diseases were discussed for explaining bone functional adaption.