Cells typically respond to a variety of geometrical cues in their environment, ranging from nanoscale surface topography to mesoscale surface curvature. The ability to control cellular organisation and fate by engineering the shape of the extracellular milieu offers exciting opportunities within tissue engineering. Despite great progress, however, many questions regarding geometry-driven tissue growth remain unanswered.

Here, we combine mathematical surface design, high-resolution microfabrication, in vitro cell culture, and image-based characterization to study spatiotemporal cell patterning and bone tissue formation in geometrically complex environments. Using concepts from differential geometry, we rationally designed a library of complex mesostructured substrates (10¹-10³ µm). These substrates were accurately fabricated using a combination of two-photon polymerisation and replica moulding, followed by surface functionalisation. Subsequently, different cell types (preosteoblasts, fibroblasts, mesenchymal stromal cells) were cultured on the substrates for varying times and under varying osteogenic conditions. Using imaging-based methods, such as fluorescent confocal microscopy and second harmonic generation imaging, as well as quantitative image processing, we were able to study early-stage spatiotemporal cell patterning and late-stage extracellular matrix organisation. Our results demonstrate clear geometry-dependent cell patterning, with cells generally avoiding convex regions in favour of concave domains. Moreover, the formation of multicellular bridges and collective curvature-dependent cell orientation could be observed. At longer time points, we found clear and robust geometry-driven orientation of the collagenous extracellular matrix, which became apparent with second harmonic generation imaging after ∼2 weeks of culture.

Our results highlight a key role for geometry as a cue to guide spatiotemporal cell and tissue organisation, which is relevant for scaffold design in tissue engineering applications. Our ongoing work aims at understanding the underlying principles of geometry-driven tissue growth, with a focus on the interactions between substrate geometry and mechanical forces.

Introduction

Suture anchor have been used in surgical procedure of tendon or ligament repair. Recently, there has been developed an all suture anchor (soft anchor) which can be used even when the insertion area is narrow. But, the stability of soft anchors due to narrow zone has not been elucidated. This purpose of this study was to investigate stability of soft anchors with respect to their fixation intervals.

We have reviewed 70 patients with bilateral simultaneous total hip arthroplasties to determine the rate of failure and to compare polyethylene wear and osteolysis between an implant with a cobalt-chrome head and Hylamer liner with that of a zirconia head and Hylamer liner. The mean thickness of the polyethylene liner was 11.0 mm (8.8 to 12.2) in the hip with a zirconia head and 10.7 mm (8.8 to 12.2) in that with a cobalt-chrome head.

At follow-up at 6.4 years no acetabular or femoral component had been revised for aseptic loosening and no acetabular or femoral component was loose according to radiological criteria in both the cemented and cementless groups. The mean rate of linear wear and annual wear rate were highest in the 22 mm zirconia femoral head (1.25 mm (SD 1.05) and 0.21 mm (SD 0.18), respectively) and lowest in the 22 mm cobalt-chrome femoral head (0.70 mm (SD 0.39) and 0.12 mm (SD 0.07), respectively). The mean volumetric wear was highest in the 28 mm zirconia femoral head (730.79 mm³) and lowest in the 22 mm cobalt-chrome femoral head (264.67 mm³), but if the results were compared by size of the femoral head and type of material there was no statistical difference (p > 0.05). Sequential measurements of annual wear showed that the zirconia femoral head had a relatively higher rate of penetration than the cobalt-chrome head over the first three years; thereafter the rate of wear was reduced and compared favourably with that of cobalt-chrome heads.

There was a statistically significant relationship between the wear of the polyethylene liner and the age of the patient, male gender and the degree of abduction angle of the cup, but not diagnosis, weight, hip score, range of movement, or amount of anteversion. Osteolysis was identified on both sides of the acetabulum in six patients (9%). Of 12 hips with acetabular osteolysis, six had a 28 mm cobalt-chrome femoral head and the remaining six a 28 mm zirconia head. Osteolysis was observed in zones 1A and 7A of the femur in two hips (3%) with a 28 mm zirconia head (cemented hip) and in four (6%) with a 28 mm cobalt-chrome femoral head (cementless hip).

Our findings suggest that although the performance of a zirconia femoral head with a Hylamer liner was not statistically different from that of a cobalt-chrome femoral head and Hylamer liner, there was a trend for the zirconia head to be worse than the cobalt-chrome femoral head.

Six pairs of human cadaver femora were divided equally into two groups one of which received a non-cemented reference implant and the other a very short non-dependent experimental implant. Thirteen strain-gauge rosettes were attached to the external surface of each specimen and, during application of combined axial and torsional loads to the femoral head, the strains in both groups were measured.

After the insertion of a non-cemented femoral component, the normal pattern of a progressive proximal-to-distal increase in strains was similar to that in the intact femur and the strain was maximum near the tip of the prosthesis. On the medial and lateral aspects of the proximal femur, the strains were greatly reduced after implantation of both types of implant. The pattern and magnitude of the strains, however, were closer to those in the intact femur after insertion of the experimental stem than in the reference stem. On the anterior and posterior aspects of the femur, implantation of both types of stem led to increased principal strains E1, E2 and E3. This was most pronounced for the experimental stem.

Our findings suggest that the experimental stem, which has a more anatomical proximal fit without having a distal stem and cortex contact, can provide immediate postoperative stability. Pure proximal loading by the experimental stem in the metaphysis, reduction of excessive bending stiffness of the stem by tapering and the absence of contact between the stem and the distal cortex may reduce stress shielding, bone resorption and thigh pain.