Poly(vinyl alcohol) hydrogel as a biocompatible viscoelastic mimetic for articular cartilage.

The prevalence of suboptimal outcome for surgical interventions in the treatment of full-thickness articular cartilage damage suggests that there is scope for a materials-based strategy to deliver a more durable repair. Given that the superficial layer of articular cartilage creates and sustains the tribological function of synovial joints, it is logical that candidate materials should have surface viscoelastic properties that mimic native articular cartilage. The present paper describes force spectroscopy analysis by nano-indentation to measure the elastic modulus of the surface of a novel poly(vinyl alcohol) hydrogel with therapeutic potential as a joint implant. More than 1 order of magnitude decrease in the elastic modulus was detected after adsorption of a hyaluronic acid layer onto the hydrogel, bringing it very close to previously reported values for articular cartilage. Covalent derivatization of the hydrogel surface with fibronectin facilitated the adhesion and growth of cultured rat tibial condyle chondrocytes as evidenced morphologically and by the observance of metachromatic staining with toluidine blue dye. The present results indicate that hydrogel materials with potential therapeutic benefit for injured and diseased joints can be engineered with surfaces with biomechanical properties similar to those of native tissue and are accepted as such by their constituent cell type.

Falls in older people: effects of age and blurring vision on the dynamics of stepping.

PURPOSE: The risk of falling increases dramatically with age, and visual impairment is known to be an important risk factor. Therefore, it is highly pertinent to assess the effects of age and vision on the performance of everyday tasks linked to falling, such as stepping from one level to another. METHODS: Nine young (age, 26 +/- 4 years) and ten elderly (age, 72 +/- 5 years) subjects performed a stepping-up task of three different heights. Their stepping strategies with blurred and optimally corrected vision were compared. Center of mass (CM), center of pressure (CP) dynamics (in the mediolateral and anteroposterior directions), and foot clearance parameters were determined, and statistical regression modeling was applied. RESULTS: Elderly subjects spent 20% more time (P = 0.03) than young subjects during double support and they had reduced anteroposterior CM-CP divergence (P < 0.001) during double support and slower anteroposterior (P < 0.001) and mediolateral (P = 0.002) CM velocities during initiation of movement and single limb support. Blur caused similar adaptations, such as increased toe clearance, across both age groups, though mediolateral (ML) CM-CP divergence in elderly subjects was significantly more reduced than in young subjects (P < 0.001). CONCLUSIONS: Findings indicate, in general, that older subjects used a more cautious and controlled stepping strategy. However, the lack of significant age differences in toe clearance suggests this strategy was mainly aimed at reducing ML instability rather than increasing margins of safety regarding toe clearance.

The effects of blurred vision on the mechanics of landing during stepping down by the elderly.

Visual impairment is an important risk factor for falls. However, relatively little is known about how visual impairment affects stair or step negotiation. The aim of the present study was to determine the effects of blurred vision on the mechanics of landing during stepping down by the elderly. Twelve elderly subjects (72.3 +/- 4.7 year) stepped down from three levels (7.2 cm, 14.4 cm and 21.6 cm). Step execution time, ankle and knee joint angular displacements at the instance of ground contact, and vertical landing stiffness and the amount of bodyweight supported by the contralateral (support) limb during the initial contact period were recorded. Measurements were repeated with vision blurred by light scattering lenses. With blurred vision, step execution time increased (P < 0.05), knee flexion and ankle plantar-flexion increased (P < 0.05), vertical stiffness decreased (P < 0.01), and the amount of bodyweight being supported by the contralateral leg increased (P < 0.05). These findings suggest that under conditions of blurred vision, subjects were more cautious and attempted to 'feel' their way to the floor rather than 'drop' on to it. This may have been an adaptation to increase the kinaesthetic information from the lower limb to make up for the unreliable or incomplete visual information. Correcting common visual problems such as uncorrected refractive errors and cataract may be an important intervention strategy in improving how the elderly negotiate stairs.

Stepping up to a new level: effects of blurring vision in the elderly.

PURPOSE: . To determine the effects of blurring vision on whole-body center-of-mass (CM) dynamics and foot-clearance parameters in elderly individuals performing a single step up to a new level. METHODS: . Twelve healthy subjects (mean age, 72.3 +/-4.17 years) performed a single step up to a new level (heights of 73 and 146 mm). Trials were undertaken with vision optimally corrected and with vision diffusively blurred by light-scattering lenses (cataract simulation). CM and foot-clearance parameter data were assessed by analyzing data collected by a five-camera, three-dimensional (3-D) motion analysis system. RESULTS: . When vision was blurred, subjects took 11% longer to execute the stepping task (P < 0.05), mediolateral displacement of the point of application of the ground reaction force vector (i.e., weighted average of all pressures over the area in contact with the ground; the so called center of pressure, CP) decreased from 37.6% of stance width to 28.3% (P < 0.01), maximum distance between the mediolateral position of the CM and CP decreased by 9.8 mm (P < 0.01), and toe clearance (distance between tip of shoe and edge of step) increased in both the horizontal (28%) and vertical (19%) direction (P < 0.05). CONCLUSIONS: . These findings suggest that when vision was blurred, subjects used a twofold safety-driven adaptation: First, to increase dynamic stability they ensured that the horizontal position of their CM was kept close to the center of the base of support and second, they increased horizontal and vertical toe clearance while swinging their lead limb forward to reduce the risk of tripping.