In recent years, there has been a surge of interest in magnesium (Mg) and its alloys as biomaterials for orthopaedic applications, as they possess desirable mechanical properties, good biocompatibility, and biodegradability. Also shown to be osteoinductive, Mg-based materials could be particularly advantageous in functional tissue engineering to improve healing and serve as scaffolds for delivery of drugs, cells, and cytokines. In this paper, we will present two examples of Mg-based orthopaedic devices: an interference screw to accelerate ACL graft healing and a ring to aid in the healing of an injured ACL. In vitro tests using a robotic/UFS testing system showed that both devices could restore function of the goat stifle joint. Under a 67-N anterior tibial load, both the ACL graft fixed with the Mg-based interference screw and the Mg-based ring-repaired ACL could restore anterior tibial translation (ATT) to within 2 mm and 5 mm, respectively, of the intact joint at 301, 601, and 901 of flexion. In-situ forces in the replacement graft and Mg-based ring-repaired ACL were also similar to those of the intact ACL. Further, early in vivo data using the Mg-based interference screw showed that after 12 weeks, it was non-toxic and the joint stability and graft function reached similar levels as published data. Following these positive results, we will move forward in incorporating bioactive molecules and ECM bioscaffolds to these Mg-based biomaterials to test their potential for functional tissue engineering of musculoskeletal and other tissues.

No abstract

A common complication associated with aging is the stiffening of skeletal muscles. The purpose of this study was to determine the ability of magnetic resonance elastography (MRE) to study this phenomenon in vivo. Twenty female subjects were included in the study with an age range of 50 to 70 years. Shear modulus was calculated for the tibialis anterior of each subject. There was not a significant relationship between age and shear modulus. However, three subjects had abnormally high values and were among the oldest subjects tested. There was a significant relationship between age and tissue stiffness homogeneity. More research is needed to determine whether the changes seen here are reflective of increased tissue cross-linking or related to reduced muscle quality. However, MRE shows promise as a tool to study aging-related muscle stiffness changes or to evaluate treatments to counteract these changes. Keywordsadvanced glycation end products; biomechanics; aging; MRE A common complication associated with aging is the stiffening of skeletal muscles. This has been confirmed by several experimental studies (e.g., Gajdosik et al., 2005). There are two primary sources for passive tension in a muscle: the intracellular titin and the extra-cellular collagen matrix (Prado et al. 2005). An increase in muscle stiffness as a result of aging would therefore likely be a result of stiffening of one of these sources of passive tension.One potential mechanism that may cause increased muscle stiffness is the accumulation of advanced glycation end products (AGEs). It is known that during aging AGEs result in cross-linking of collagen fibers in tissues throughout the body (Avery & Bailey, 2005). These cross-links result in increased tissue stiffness. Negative effects of this stiffening have been seen in numerous tissues, including cardiac muscle (Asif et al., 2000), bone (Vashishth et al., 2001), and articular cartilage (Verzijl et al., 2000). Cross-links have also been shown to accumulate in the skeletal muscle of aged rats (Gosselin et al., 1998).Stiffening of the collagen matrix of a muscle could explain aging-related increases in muscle stiffness, and an accumulation of AGEs may also explain reduced muscle quality that some authors have seen in aged muscle (e.g., Lynch et al., 1999). It is known that the formation of cross-links makes collagen more resistant to enzyme activity (Schnider & Kohn, 1982). Normally, matrix metalloproteinases act to break down damaged extracellular matrix (Birkedal-Hansen, 1995) as part of the muscle-remodeling process. This process would be impaired as a result of cross-link formation. Advanced glycation end products are also known to up-regulate insulin-like growth) factor-binding protein-related protein-2, which is known to stimulate the production of extracellular matrix (Twigg et al., 2001). Collectively, these consequences will result in the increase in the amount of connective tissue within a muscle and may explain the reduction in muscle quality known to accompany aging. NIH Public Ac...

Introduction-Idiopathic inflammatory myopathies (IIM or myositis), is a group of autoimmune diseases that result in decreased muscle strength and/or endurance. Non-invasive tools to assess muscle may improve our understanding of the clinical and functional consequences of myopathies and their response to treatment. This study examined Magnetic Resonance Elastography (MRE), a non-invasive technique that assesses the shear modulus (stiffness) of muscle, in IIM subjects.

Advances in imaging technologies such as magnetic resonance elastography (MRE) have allowed researchers to gain insights into muscle function in vivo. MRE has been used to examine healthy and diseased muscle by calculating shear modulus. However, additional information can be measured from visualizing a mechanical wave as it passes through a tissue. One such measurable quantity is wave attenuation. The purpose of this study was to determine if a simple measure of wave attenuation could be used to distinguish between healthy and diseased muscle. Twenty seven subjects (14 healthy controls, 7 hyperthyroid myopathy patients, 6 myositis patients) participated in this study. Wave amplitude was determined along a linear profile through the center of the muscle, and an exponential decay curve was fit to the data. This measure was able to find significant differences in attenuation between healthy and diseased muscle. Furthermore, four hyperthyroid myopathy subjects who were tested following treatment all showed improvement by this measure. A likely reason for patients with hyperthyroid myopathy and myositis behaving similarly is that this measurement may reflect similar changes in the muscle extracellular matrix. In addition to modulus, attenuation seems to be an important parameter to measure in skeletal muscle. Further research is needed to investigate other potential measures of attenuation as well as examining other potential measures that can be found from visualizing wave propagation. Future studies should also include muscle biopsies to confirm that the changes seen are as a result of changes in extracellular matrix structure.