Zihui Li

Effects of a hybrid micro/nanorod topography-modified titanium implant on adhesion and osteogenic differentiation in rat bone marrow mesenchymal stem cells

Background and methods Various methods have been used to modify titanium implant surfaces with the aim of achieving better osseointegration. In this study, we fabricated a clustered nanorod structure on an acid-etched, microstructured titanium plate surface using hydrogen peroxide. We also evaluated biofunctionalization of the hybrid micro/nanorod topography on rat bone marrow mesenchymal stem cells. Scanning electron microscopy and x-ray diffraction were used to investigate the surface topography and phase composition of the modified titanium plate. Rat bone marrow mesenchymal stem cells were cultured and seeded on the plate. The adhesion ability of the cells was then assayed by cell counting at one, 4, and 24 hours after cell seeding, and expression of adhesion-related protein integrin β1 was detected by immunofluorescence. In addition, a polymerase chain reaction assay, alkaline phosphatase and Alizarin Red S staining assays, and osteopontin and osteocalcin immunofluorescence analyses were used to evaluate the osteogenic differentiation behavior of the cells. Results The hybrid micro/nanoscale texture formed on the titanium surface enhanced the initial adhesion activity of the rat bone marrow mesenchymal stem cells. Importantly, the hierarchical structure promoted osteogenic differentiation of these cells. Conclusion This study suggests that a hybrid micro/nanorod topography on a titanium surface fabricated by treatment with hydrogen peroxide followed by acid etching might facilitate osseointegration of a titanium implant in vivo.

Osteocyte-derived insulin-like growth factor I is essential for determining bone mechanosensitivity

This study sought to determine whether deficient Igf1 expression in osteocytes would affect loading-induced osteogenic response. Tibias of osteocyte Igf1 conditional knockout (KO) mice (generated by cross-breeding Igf1 floxed mice with Dmp1-Cre transgenic mice) and wild-type (WT) littermates were subjected to four-point bending for 2 wk. Microcomputed tomography confirmed that the size of tibias of conditional mutants was smaller. Loading with an equivalent loading strain increased periosteal woven bone and endosteal lamellar bone formation in WT mice but not in conditional KO mice. Consistent with the lack of an osteogenic response, the loading failed to upregulate expression of early mechanoresponsive genes (Igf1, Cox-2, c-fos) or osteogenic genes (Cbfa-1, and osteocalcin) in conditional KO bones. The lack of osteogenic response was not due to reduced osteocyte density or insufficient loading strain. Deficient osteocyte Igf1 expression reduced the loading-induced upregulation of expression of canonical Wnt signaling genes (Wnt10b, Lrp5, Dkk1, sFrp2). The loading also reduced (by 40%) Sost expression in WT mice, but the loading not only did not reduce but upregulated (~1.5-fold) Sost expression in conditional KO mice. Conditional disruption of Igf1 in osteocytes also abolished the loading-induced increase in the bone β-catenin protein level. These findings suggest an impaired response in the loading-induced upregulation of the Wnt signaling in conditional KO mice. In summary, conditional disruption of Igf1 in osteocytes abolished the loading-induced activation of the Wnt signaling and the corresponding osteogenic response. In conclusion, osteocyte-derived IGF-I plays a key determining role in bone mechanosensitivity.

Biofunctionalization of a titanium surface with a nano-sawtooth structure regulates the behavior of rat bone marrow mesenchymal stem cells.

Background: The topography of an implant surface can serve as a powerful signaling cue for attached cells and can enhance the quality of osseointegration. A series of improved implant surfaces functionalized with nanoscale structures have been fabricated using various methods. Methods: In this study, using an H2O2 process, we fabricated two size-controllable sawtooth-like nanostructures with different dimensions on a titanium surface. The effects of the two nano-sawtooth structures on rat bone marrow mesenchymal stem cells (BMMSCs) were evaluated without the addition of osteoinductive chemical factors. Results: These new surface modifications did not adversely affect cell viability, and rat BMMSCs demonstrated a greater increase in proliferation ability on the surfaces of the nano-sawtooth structures than on a control plate. Furthermore, upregulated expression of osteogenic-related genes and proteins indicated that the nano-sawtooth structures promote osteoblastic differentiation of rat BMMSCs. Importantly, the large nano-sawtooth structure resulted in the greatest cell responses, including increased adhesion, proliferation, and differentiation. Conclusion: The enhanced adhesion, proliferation, and osteogenic differentiation abilities of rat BMMSCs on the nano-sawtooth structures suggest the potential to induce improvements in bone-titanium integration in vivo. Our study reveals the key role played by the nano-sawtooth structures on a titanium surface for the fate of rat BMMSCs and provides insights into the study of stem cell-nanostructure relationships and the related design of improved biomedical implant surfaces.

In vivo monitoring of bone architecture and remodeling after implant insertion: The different responses of cortical and trabecular bone

The mechanical integrity of the bone-implant system is maintained by the process of bone remodeling. Specifically, the interplay between bone resorption and bone formation is of paramount importance to fully understand the net changes in bone structure occurring in the peri-implant bone, which are eventually responsible for the mechanical stability of the bone-implant system. Using time-lapsed in vivo micro-computed tomography combined with new composite material implants, we were able to characterize the spatio-temporal changes of bone architecture and bone remodeling following implantation in living mice. After insertion, implant stability was attained by a quick and substantial thickening of the cortical shell which counteracted the observed loss of trabecular bone, probably due to the disruption of the trabecular network. Within the trabecular compartment, the rate of bone formation close to the implant was transiently higher than far from the implant mainly due to an increased mineral apposition rate which indicated a higher osteoblastic activity. Conversely, in cortical bone, the higher rate of bone formation close to the implant compared to far away was mostly related to the recruitment of new osteoblasts as indicated by a prevailing mineralizing surface. The behavior of bone resorption also showed dissimilarities between trabecular and cortical bone. In the former, the rate of bone resorption was higher in the peri-implant region and remained elevated during the entire monitoring period. In the latter, bone resorption rate had a bigger value away from the implant and decreased with time. Our approach may help to tune the development of smart implants that can attain a better long-term stability by a local and targeted manipulation of the remodeling process within the cortical and the trabecular compartments and, particularly, in bone of poor health.

Wettability control by DLC coated nanowire topography

Here we have developed a convenient method to fabricate wettability controllable surfaces that can be applied to various nanostructured surfaces with complex shapes for different industrial needs. Diamond-like carbon (DLC) films were synthesized on titanium substrate with a nanowire structured surface using plasma immersion ion implantation and deposition (PIII&D). The nanostructure of the DLC films was characterized by field emission scanning electron microscopy and found to grow in a rippling layer-by-layer manner. Raman spectroscopy was used to investigate the different bonding presented in the DLC films. To determine the wettability of the samples, water contact angles were measured and found to vary in the range of 50°-141°. The results indicated that it was critical to construct a proper surface topography for high hydrophobicity, while suitable I(D)/I(G) and sp²/sp³ ratios of the DLC films had a minor contribution. Superhydrophobicity could be achieved by further CF₄ implantation on suitably structured DLC films and was attributed to the existence of fluorine. In order to maintain the nanostructure during CF₄ implantation, it was favorable to pre-deposit an appropriate carbon content on the nanostructure, as a nanostructure with low carbon content would be deformed during CF₄ implantation due to local accumulation of surface charge and the following discharge resulting from the low conductivity.

Bone remodeling and mechanobiology around implants: Insights from small animal imaging

Anchorage of orthopedic implants depends on the interfacial bonding between the implant and the host bone as well as on the mass and microstructure of peri‐implant bone, with all these factors being continuously regulated by the biological process of bone (re)modeling. In osteoporotic bone, implant integration may be jeopardized not only by lower peri‐implant bone quality but also by reduced intrinsic regeneration ability. The first aim of this review is to provide a critical overview of the influence of osteoporosis on bone regeneration post‐implantation. Mechanical stimulation can trigger bone formation and inhibit bone resorption; thus, judicious administration of mechanical loading can be used as an effective non‐pharmacological treatment to enhance implant anchorage. Our second aim is to report recent achievements on the application of external mechanical stimulation to improve the quantity of peri‐implant bone. The review focuses on peri‐implant bone changes in osteoporotic conditions and following mechanical loading, prevalently using small animals and in vivo monitoring approaches. We intend to demonstrate the necessity to reveal new biological information on peri‐implant bone mechanobiology to better target implant anchorage and fracture fixation in osteoporotic conditions.

Impaired bone formation in ovariectomized mice reduces implant integration as indicated by longitudinal in vivo micro-computed tomography

Although osteoporotic bone, with low bone mass and deteriorated bone architecture, provides a less favorable mechanical environment than healthy bone for implant fixation, there is no general agreement on the impact of osteoporosis on peri-implant bone (re)modeling, which is ultimately responsible for the long term stability of the bone-implant system. Here, we inserted an implant in a mouse model mimicking estrogen deficiency-induced bone loss and we monitored with longitudinal in vivo micro-computed tomography the spatio-temporal changes in bone (re)modeling and architecture, considering the separate contributions of trabecular, endocortical and periosteal surfaces. Specifically, 12 week-old C57BL/6J mice underwent OVX/SHM surgery; 9 weeks after we inserted special metal-ceramics implants into the 6th caudal vertebra and we measured bone response with in vivo micro-CT weekly for the following 6 weeks. Our results indicated that ovariectomized mice showed a reduced ability to increase the thickness of the cortical shell close to the implant because of impaired peri-implant bone formation, especially at the periosteal surface. Moreover, we observed that healthy mice had a significantly higher loss of trabecular bone far from the implant than estrogen depleted animals. Such behavior suggests that, in healthy mice, the substantial increase in peri-implant bone formation which rapidly thickened the cortex to secure the implant may raise bone resorption elsewhere and, specifically, in the trabecular network of the same bone but far from the implant. Considering the already deteriorated bone structure of estrogen depleted mice, further bone loss seemed to be hindered. The obtained knowledge on the dynamic response of diseased bone following implant insertion should provide useful guidelines to develop advanced treatments for osteoporotic fracture fixation based on local and selective manipulation of bone turnover in the peri-implant region.

Time-lapsed in vivo bone response to implantation in a mouse model of disease and treatment

The long-term success of orthopaedic implant fixation depends on a good integration of the implant into the host bone. In osteoporotic bone where the risk of fracture is higher than healthy bone, bone-implant integration is believed to be jeopardized by the low bone quality. However, the influence of osteoporosis on peri-implant bone regeneration is not well understood. Mechanical loading has the ability to stimulate bone formation and to decrease bone resorption. Enhanced bone formation has also been observed at the bone-implant interfaces; therefore mechanical loading is considered a possible anabolic treatment to promote implant integration. To date, less is known on the effect of mechanical loading on periimplant bone regeneration. In order to develop effective loading protocols to improve implant integration especially in osteoporotic bone, a greater understanding of the in vivo load-induced bone regeneration around the implant must be achieved. This review aims firstly to provide an overview of the in vivo studies investigating the possible influence of osteoporosis on implant integration and, secondly, to report the recent achievements on the use of external mechanical loading to improve the quality of the peri-implant bone which is ultimately related to implant integration.