Biomimetic modification of the gliding surface of extrasynovial tendon
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Tendons may be classified as intrasynovial or extrasynovial based upon their anatomic location. We studied the physical properties of extrasynovial and intrasynovial tendons. Extrasynovial tendon has a rougher surface and higher friction than intrasynovial tendon. A number of carbodiimide derivatized biomaterials were developed to modify the irregular surface of an extrasynovial tendon to mimic the smooth surface of an intrasynovial tendon. We found that carbodiimide derivatized hyaluronic acid-gelatin (cd-HA-gelatin) chemically bonded to the extrasynovial tendon surface and optimally reduced gliding resistance in vitro. This biosynthetic, biomimetic modification of the extrasynovial tendon surface may prove to be a useful clinical product.
I. INTRODUCTION
Tendons attach muscle to bone and transfer the power of the muscle to bone over a distance. Tendons can be characterized based on their anatomic location as either intrasynovial or extrasynovial.1–3 The intrasynovial tendons, such as the flexor digitorum profundus (FDP), have parietal and visceral synovial sheaths that form a closed compartment that contains synovial fluid for lubrication and nutrition. In extrasynovial tendons, such as the peroneus longus (PL), there is a peritendinous sheet of loose fibrillar tissue, the paratenon, which functions as an elastic sleeve, permitting limited movement of the tendon against the surrounding tissue. The structure of tendon is directly related to its physical and physiological function. Tensile force is the major mechanical stimulus to this fibrous tissue. However, tendons also experience other mechanical stimuli, including shear and compression. As tendons move, they experience shearing forces due to friction with the surrounding tissues. Functional adaptations of the tendon surface in regions whose mechanical environment varies are well described.4 Extrasynovial tendons have rougher surfaces than intrasynovial tendons.5–7 Extrasynovial tendons also create higher friction against a pulley compared to intrasynovial tendons.7,8 Extrasynovial tendons are often used to replace damaged intrasynovial tendons clinically, but the results are often poor.6,9,10
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0253 J. Mater. Res., Vol. 21, No. 8, Aug 2006
We hypothesized that altering the surface of extrasynovial tendon to mimic intrasynovial tendon would result in reduced friction. To this end, carbodiimide derivatized (cd) hyaluronan (HA) and gelatin biomaterials have been developed to reduce the friction of extrasynovial tendon, and the resulting biopolymer-tendon composite has been studied in vitro to optimize the formulation. II. METHODS
Dogs were chosen as experimental animals due to the similarity to humans in flexor tendon anatomy.6 The PL tendon was used as the extrasynovial donor tendon to be modified. The FDP tendon was chosen as the intrasynovial tendon to mimic. All studies were approved by our Institutional Animal Care and Use Committee. The gliding resistance betwee
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