Cylindrical Constructs Research Articles

Load transfer mechanisms in cylindrical interbody cage constructs.

A finite-element model was created to study parametrically the load transfer characteristics of a lower lumbar motion segment implanted with dual anteroposterior cylindrical interbody cages. To describe the frontal plane bone-implant interface stresses acting on a generic cylindrical interbody cage, to evaluate the effect of implant material properties on these stresses, and to determine the associated load transfer mechanisms. From a biomechanical perspective, the long-term success of an interbody cage fusion depends on effective load transfer. The cage must stress the graft sufficiently to promote fusion, while keeping bone-implant interface stresses in a range that will prevent implant subsidence or loosening. At this writing, no published study has described interface stresses or load transfer mechanisms for these devices. A planar finite-element model was used to simulate uniform compression loading of the implanted segment. Material properties of the interbody cage were varied to simulate cortical bone, titanium, and stainless steel implants. Normal and shear interface stresses were output along the length of the interface. Magnitudes of both the normal and shear interface stresses were substantially higher at the medial and lateral sides of the interface than in the center. Interface stresses were largely independent of implant material. Cylindrical interbody implants have inherent limitations, including stress concentrations at the bone-implant interface and possible stress shielding of the graft. The results from the current study suggest that implants made of cortical bone have substantially the same load transfer characteristics as metal devices of similar geometry.

Liquid acrylate-endcapped biodegradable poly(epsilon-caprolactone-co-trimethylene carbonate). I. Preparation and visible light-induced photocuring characteristics.

Photocurable liquid biodegradable copolymers were prepared by ring-opening copolymerization of epsilon-caprolactone (CL) and trimethylene carbonate (TMC) in the presence of a multifunctional hydroxyl group-bearing substance (di-, tri-, and tetra-functional alcohol and poly(ethylene glycol) (PEG) and its four-branched derivative) as an initiator and subsequent endcapping with acryloyl chloride at their hydroxyl terminals. These multifunctional, viscous liquid copolymers (molecular weights; approximately 2 x 10(3) to 7 x 10(3) g/mol) were converted to crosslinked solids by visible-light irradiation in the presence of camphorquinone as an initiator. The photocuring rate of these copolymers was enhanced by both higher functionality and lower molecule weight of the copolymers used. The photocuring rate depended on the amount of reducing agent (methacrylic acid 2-dimethylaminoethyl ester). Upon immersion in a phosphate buffer solution (pH 7.4), hydrolysis occurred preferentially on the surface except for photocured PEG-based copolymers that were degraded faster via both surface erosion and bulk degradation than low molecular weight alcohols-based copolymers. Cylindrical photocured constructs prepared by photoirradiation to the whole body in a mold filled with the liquid copolymer was demonstrated as an example of shape fabrication of biodegradable biomedical devices.

Kinematics of stochastic motion in hilbert space

We formulate and prove results for development of Nelson's kinematic theory of stochastic motion in Hilbert space, extend stochastic integral of Metivier and Pellaumail with respect to cylindrical martingales and construct a diffusion from kinematical assumptions using the extended integration