Podoplanin immunopositive lymphatic vessels at the implant interface in a rat model of osteoporotic fractures

Insertion of bone substitution materials accelerates healing of osteoporotic fractures. Biodegradable materials are preferred for application in osteoporotic patients to avoid a second surgery for implant replacement. Degraded implant fragments are often absorbed by macrophages that are removed from the fracture side via passage through veins or lymphatic vessels. We investigated if lymphatic vessels occur in osteoporotic bone defects and whether they are regulated by the use of different materials. To address this issue osteoporosis was induced in rats using the classical method of bilateral ovariectomy and additional calcium and vitamin deficient diet. In addition, wedge-shaped defects of 3, 4, or 5 mm were generated in the distal metaphyseal area of femur via osteotomy. The 4 mm defects were subsequently used for implantation studies where bone substitution materials of calcium phosphate cement, composites of collagen and silica, and iron foams with interconnecting pores were inserted. Different materials were partly additionally functionalized by strontium or bisphosphonate whose positive effects in osteoporosis treatment are well known. The lymphatic vessels were identified by immunohistochemistry using an antibody against podoplanin. Podoplanin immunopositive lymphatic vessels were detected in the granulation tissue filling the fracture gap, surrounding the implant and growing into the iron foam through its interconnected pores. Significant more lymphatic capillaries were counted at the implant interface of composite, strontium and bisphosphonate functionalized iron foam. A significant increase was also observed in the number of lymphatics situated in the pores of strontium coated iron foam. In conclusion, our results indicate the occurrence of lymphatic vessels in osteoporotic bone. Our results show that lymphatic vessels are localized at the implant interface and in the fracture gap where they might be involved in the removal of lymphocytes, macrophages, debris and the implants degradation products. Therefore the lymphatic vessels are involved in implant integration and fracture healing

Biomechanical comparison of different surface modifications for dental implants

Purpose: A satisfactory clinical outcome in dental implant treatment relies on primary stability for immediate load bearing. While the geometric design of an implant contributes to mechanical stability, the nature of the implant surface itself is also critically important. Biomechanical and microcomputerized tomographic evaluation of implant osseointegration was performed to compare alternative structural, chemical and biochemical, and/or pharmaceutical surface treatments applied to an identical established implant design. Materials and Methods: Dental implants with the same geometry but with 6 different surface treatments were tested in vivo in a sheep model (pelvis). Peri-implant bone density and removal torque were compared at 2, 4, and 8 weeks after implantation. Implant surfaces tested were: sandblasted and acid-etched titanium (Ti), sandblasted and etched zirconia, Ti coated with calcium phosphate (CaP), Ti modified via anodic plasma-chemical treatment (APC), bisphosphonate-coated Ti (Ti + Bisphos), and Ti coated with collagen containing chondroitin sulfate (CS). Results: All dental implants were well integrated at the time of sacrifice. There were no significant differences observed in peri-implant bone density between implant groups. After 8 weeks of healing, removal torque values for Ti, Ti + CaP, Ti + Bisphos, and Ti + collagen + CS were significantly higher than those for zirconia and Ti + APC. Conclusions: Whereas the sandblasted/acid-etched Ti implant can still be considered the reference standard surface for dental implants, functional surface modifications such as bisphosphonate or collagen coating seem to enhance early peri-implant bone formation and should be studied further

Podoplanin staining at the plain iron foam (Fe).

<p>The interface of the wedge-shaped implant (m) was covered with granulation tissue (gt) that infiltrated the interconnected pores (p) near the interface (A-B). Podoplanin immunopositive lymphatic vessels (arrow) were found in the granulation tissue often close to the yellow cells with the resorbed iron (C). Granula of resorbed iron (star) were found in lymphatic capillaries (D). Lymphatics were also situated next to iron fragments (arrowhead, E). Islets with podoplanin stained osteocytes were detected in the granulation tissue (F). Nuclei were counterstained with hematoxylin. Bar represents 1 mm in A, 200 µm in B, 20 µm in C-D.</p

CPC based implants.

<p>Podoplanin immunopositive lymphatic vessels (arrow) were localized in the granulation tissue (gt) at the interface of the CPC implant (A-E) as well as at the strontium functionalized CPC (CPC-S in E-F) where an improved fragmentation was found (F). Lympatics were often associated with blood vessels that were identified by Microfil^® perfusion (star in C). Podoplanin also stained osteocytes (arrowhead in B-F) and mature osteoblasts (O). Nuclei were counterstained with hematoxylin. m = bone substitution material. Bars: 1 mm in A, F, 200 µm in B, G, and 20 µm in C-E.</p

Number of lymphatic vessels localized in the interconnected pores of iron-foams.

<p>A significant increase was calculated for the correlation of the counted number of lymphatic vessels localized in the Fe-S implant in comparison to the Fe (p = 0.004) as well as the Fe-BP implants (p = 0.001). Data are presented as box plots with the median indicated by solid line within the box. Small circles illustrate data beyond 3 x standard deviation (SD). ** = p ≤ 0.01, *** = p ≤ 0.001.</p

Expression of podoplanin in empty defects.

<p>No regulation of the podoplanin expression was detected for the empty defects by means of real-time RT-PCR. The results are presented as box plot with the median, the 0^th, 25^th, 75^th, and 100^th percentile. Small circles illustrate data beyond 3 x standard deviation (SD).</p

Podoplanin immunohistochemistry at the implant of iron foam with a strontium coating (Fe-S).

<p>Podoplanin labeled lymphatic vessels (arrow) were found in the granulation tissue (gt) at the implant (m) interface and in the interconnected pores (A-B). Higher magnification showed the adjacency of the bone substitution material and the lymphatics (C). A high amount of cells with yellow granular cytoplasm were localized in the granulations tissue (D). These cells are supposed to resorb the degraded implant. They are often found close to the lymphatic vessels that sometimes seem to contain lymphocytes (D). Nuclei were counterstained with hematoxylin. Bar represents 1 mm in A, 200 µm in B, 20 µm in C-D.</p

Number of lymphatic vessels in empty defects.

<p>The 4 mm sized empty defect contained a significant lower number of lymphatic vessels in comparison to the 3 mm and 5 mm defects. The results are present as box plot where the median is indicated by a solid line within the box, the 25^th and 75^th percentile as bottom and top of the box, the 0^th and 100^th percentile as lower and upper whiskers, respectively. Small circles illustrate data beyond 3 x standard deviation (SD). ** = p ≤ 0.01.</p