Biodegradable and bioactive porous polymer/inorganic composite scaffolds for bone tissue engineering

Mammalian skeletal muscle comprises different fiber types, whose identity is first established during embryonic development by intrinsic myogenic control mechanisms and is later modulated by neural and hormonal factors. The relative proportion of the different fiber types varies strikingly between species, and in humans shows significant variability between individuals. Myosin heavy chain isoforms, whose complete inventory and expression pattern are now available, provide a useful marker for fiber types, both for the four major forms present in trunk and limb muscles and the minor forms present in head and neck muscles. However, muscle fiber diversity involves all functional muscle cell compartments, including membrane excitation, excitation-contraction coupling, contractile machinery, cytoskeleton scaffold, and energy supply systems. Variations within each compartment are limited by the need of matching fiber type properties between different compartments. Nerve activity is a major control mechanism of the fiber type profile, and multiple signaling pathways are implicated in activity-dependent changes of muscle fibers. The characterization of these pathways is raising increasing interest in clinical medicine, given the potentially beneficial effects of muscle fiber type switching in the prevention and treatment of metabolic diseases.

Fiber types in mammalian skeletal muscles.

A model is developed of the human lower extremity to study how changes in musculoskeletal geometry and musculotendon parameters affect muscle force and its moment about the joints. The lines of action of 43 musculotendon actuators were defined based on their anatomical relationships to three-dimensional bone surface representations. A model for each actuator was formulated to compute its isometric force-length relation. The kinematics of the lower extremity were defined by modeling the hip, knee, ankle, subtalar, and metatarsophalangeal joints. Thus, the force and joint moment that each musculotendon actuator develops can be computed for any body position. The joint moments calculated with the model compare well with experimentally measured isometric joint moments. A graphical interface to the model has also been developed. It allows the user to visualize the musculoskeletal geometry and to manipulate the model parameters to study the biomechanical consequences of orthopaedic surgical procedures. For example, tendon transfer and lengthening procedures can be simulated by adjusting the model parameters according to various surgical techniques. Results of the simulated surgeries can be analyzed quickly in terms of postsurgery muscle forces and other biomechanical variables. >

An interactive graphics-based model of the lower extremity to study orthopaedic surgical procedures

Mammalian skeletal muscle shows an enormous variability in its functional features such as rate of force production, resistance to fatigue, and energy metabolism, with a wide spectrum from slow aer...

Calcium Ion in Skeletal Muscle: Its Crucial Role for Muscle Function, Plasticity, and Disease

Polymeric Materials for Bone and Cartilage Repair

A three-dimensional mathematical model of the human masticatory system predicting maximum possible bite forces

The existence of an interaction among bite force magnitude, jaw muscle size (e.g., cross-sectional area, thickness), and craniofacial morphology is widely accepted. Bite force magnitude depends on the size of the jaw muscles and the lever arm lengths of bite force and muscle forces, which in turn are dictated by craniofacial morphology. In this study, the relative contributions of craniofacial morphology and jaw muscle thickness to the bite force magnitude were studied. In 121 adult individuals, both magnitude and direction of the maximal voluntary bite force were registered. Craniofacial dimensions were measured by anthropometrics and from lateral radiographs. The thicknesses of the masseter, temporal, and digastric muscles were registered by ultrasonography. After a factor analysis was applied to the anthropometric and cephalometric dimensions, the correlation between bite force magnitude, on the one hand, and the "craniofacial factors" and jaw muscle thicknesses, on the other, was assessed by stepwise multiple regression. Fifty-eight percent of the bite force variance could be explained. From the jaw muscles, only the thickness of the masseter muscle correlated significantly with bite force magnitude. Bite force magnitude also correlated significantly positively with vertical and transverse facial dimensions and the inclination of the midface, and significantly negatively with mandibular inclination and occlusal plane inclination. The contribution of the masseter muscle to the variation in bite force magnitude was higher than that of the craniofacial factors.

Contribution of Jaw Muscle Size and Craniofacial Morphology to Human Bite Force Magnitude

A mathematical model of the patellofemoral joint

Background
The human jaw-closing and jaw-opening muscles produce forces leading to the development of three-dimensional bite and chewing forces and to three-dimensional movements of the jaw. The length of the sarcomeres is a major determinant for both force and velocity, and the maximal work, force, and shortening range each muscle is capable of producing are proportional to the architectural parameter volume, physiological cross-sectional area, and fiber length, respectively. In addition, the mechanical role the muscles play is strongly related to their three-dimensional position and orientation in the muscle–bone–joint system. The objective of this study was to compare relevant architectural characteristics for the jaw-closing and jaw-opening muscles and to provide a set of data that can be used in biomechanical modeling of the masticatory system.

Methods: In eight cadavers, sarcomere lengths, muscle masses, fiber lengths, pennation angles, and physiological cross-sectional areas were determined for the following muscles: superficial and deep masseter, anterior and posterior temporalis, anterior and posterior medial pterygoid, inferior and superior lateral pterygoid, posterior and anterior digastric, geniohyoid, posterior and anterior mylohyoid, and stylohyoid. To determine the spatial position of their action lines, the three-dimensional coordinates of the attachment sites were registered.

Results: Compared with the jaw openers, the jaw closers were characterized by shorter sarcomere lengths at the closed jaw, larger masses of contractile and tendinous tissue, larger physiological cross-sectional areas, larger pennation angles, shorter fiber lengths, shorter moment arms, and lower fiber-length-to-muscle-length ratios. In addition, architectural features differed across the muscles of the same functional group. Sarcomere length did not differ significantly among the regions of the same muscle. In contrast, in some muscles, significant intramuscular differences were found with respect to, e.g., physiological cross-sectional area, fiber length, pennation angle, and moment arm length.

Conclusions: The results suggest that the jaw-closing muscles have architectural features that suit them for force production. Conversely, the jaw-opening muscles are better designed to produce velocity and displacement. Anat. Rec., 248:464-474, 1997. © 1997 Wiley-Liss, Inc.

T.M.G.J. van Eijden

Papers

A three-dimensional mathematical model of the human masticatory system predicting maximum possible bite forces

Contribution of Jaw Muscle Size and Craniofacial Morphology to Human Bite Force Magnitude

A mathematical model of the patellofemoral joint

Architecture of the human jaw-closing and jaw-opening muscles

Three-dimensional finite element analysis of the human temporomandibular joint disc.