Modulated bone matrix‐related gene expression is associated with differences in interfacial strength of different implant surface roughness

Harder and Stiffer Bone Osseointegrated to Roughened Titanium

Mechanisms underlying the beneficial anchorage of roughened titanium implants have not been identified. We hypothesized that the implant surface roughness alters intrinsic biomechanical properties of bone integrated to titanium. Nano-indentation performed on two- and four-week post-implantation bone specimens of rats revealed that bone integrated to acid-etched titanium was approximately 3 times harder than that integrated to the machined titanium, both at the osseointegration interface and at the inner area of the peri-implant bone. The hardness of the acid-etched surface-associated bone was equivalent to that of untreated cortical bone at week 4, while the bone hardness around the machined surface was equivalent to that of the untreated trabecular bone. The elastic modulus of the integrated bone was 1.5 to 2.5 times greater around the acid-etched surface than around the machined surface. Analysis of the data suggests that the implant surface roughness affects the biomechanical quality of osseo-integrated bone, and that the bone integrated to the acid-etched surface is harder and stiffer than the bone integrated to the machined surface.

Genes Differentially Expressed in Titanium Implant Healing

Bone generation occurs around titanium implants; however, its underlying mechanisms are unknown. We hypothesized that molecular determinants distinct from those undertaking normal bone healing regulate osseointegration. Using differential display-polymerase chain-reaction in the male rat model, we isolated 3 genes that are differentially expressed in bone healing with implants, but not in osteotomy healing. A homology search indicated that these 3 genes are apolipoprotein E, prolyl 4-hydroxylase α-subunit, and an unknown transcript. Differential expression of these genes was remarkable during early healing stages up to week 2, and accelerated with rough acid-etched surfaces compared with machined surfaces. The differential expression was confirmed in the female rats, with enhanced expression for the acid-etched surfaces. The osseointegration-unfavorable condition created by gonadal estrogen deficiency reduced the level of differential expression. This study provides evidence that selected gene transcripts are induced by titanium implants under regulatory control strongly associated with the nature of osseointegration.

Enhanced osteoblast differentiation and osseointegration of a bio-inspired HA nanorod patterned pore-sealed MgO bilayer coating on magnesium

The osteogenetic capability of Mg was significantly enhanced by a bio-inspired hydroxyapatite (HA) nanorod patterned pore-sealed MgO bilayer coating.

Nanometer-scale features on micrometer-scale surface texturing: a bone histological, gene expression, and nanomechanical study

Micro- and nanoscale surface modifications have been the focus of multiple studies in the pursuit of accelerating bone apposition or osseointegration at the implant surface. Here, we evaluated histological and nanomechanical properties, and gene expression, for a microblasted surface presenting nanometer-scale texture within a micrometer-scale texture (MB) (Ossean Surface, Intra-Lock International, Boca Raton, FL) versus a dual-acid etched surface presenting texture at the micrometer-scale only (AA), in a rodent femur model for 1, 2, 4, and 8weeks in vivo. Following animal sacrifice, samples were evaluated in terms of histomorphometry, biomechanical properties through nanoindentation, and gene expression by real-time quantitative reverse transcription polymerase chain reaction analysis. Although the histomorphometric, and gene expression analysis results were not significantly different between MB and AA at 4 and 8 weeks, significant differences were seen at 1 and 2 weeks. The expression of the genes encoding collagen type I (COL-1), and osteopontin (OPN) was significantly higher for MB than for AA at 1 week, indicating up-regulated osteoprogenitor and osteoblast differentiation. At 2 weeks, significantly up-regulated expression of the genes for COL-1, runt-related transcription factor 2 (RUNX-2), osterix, and osteocalcin (OCN) indicated progressive mineralization in newly formed bone. The nanomechanical properties tested by the nanoindentation presented significantly higher-rank hardness and elastic modulus for the MB compared to AA at all time points tested. In conclusion, the nanotopographical featured surfaces presented an overall higher host-to-implant response compared to the microtextured only surfaces. The statistical differences observed in some of the osteogenic gene expression between the two groups may shed some insight into the role of surface texture and its extent in the observed bone healing mechanisms.

Photofunctionalization increases the bioactivity and osteoconductivity of the titanium alloy Ti6Al4V

This study examined the effect of photofunctionalization on bioactivity and osteoconductivity of titanium alloy Ti6Al4V. We also tested a hypothesis that the effect of photofunctionalization is as substantial as the one of surface roughening. Two different surface morphology, a roughened surface (sandblasted and acid-etched surface) and relatively smooth surface (machined surface), was tested. Ti6Al4V samples were photofunctionalized with UV light for 15 min using a photo device. Photofunctionalization converted Ti6Al4V surfaces from hydrophobic to superhydrophilic. The attachment, spread, proliferation, and the expression of functional phenotype of bone marrow-derived osteoblasts were promoted on photofunctionalized Ti6Al4V surfaces. The strength of bone-implant integration examined using a biomechanical push-in test in a rat femur model was at least 100% greater for photofunctionalized implants than for untreated implants. These effects were seen on both surface types. The strength of bone-implant integration for photofunctionalized machined implants was greater than that for untreated roughened implants, indicating that the impact of photofunctionalization may be greater than that of surface roughening. Newly prepared Ti alloy was hydrophilic, whereas the hydrophilic status degraded with time and was converted to hydrophobic in 4 weeks. This finding uncovered biological aging of Ti alloy and allowed us to consider photofunctionalization as a countermeasure for aging. These results suggest that photofunctionalization accelerates and enhances bone-implant integration of Ti6Al4V regardless of smooth and roughened surface features, supporting photofunctionalization as an effective and viable measure for improving efficacy of a wide range of Ti6Al4V-based materials used in dental and orthopedic medicine.

Effect of photofunctionalization on fluoride-treated nanofeatured titanium

The objective of this study was to evaluate the effect of ultraviolet light treatment, known as photofunctionalization, on the biological and osseointegration capability of nanofeatured titanium created by a combination of sandblasting and hydrofluoric acid treatment. Titanium samples in disk and cylinder forms were photofunctionalized by treatment with ultraviolet light for 15 min. The nanofeatured surface was converted from hydrophobic to superhydrophilic after photofunctionalization. The strength of osseointegration measured by a biomechanical push-in test in a rat model was stronger for photofunctionalized implants than for untreated implants by 2.2 and 2.3 times, respectively, at the early (week 2) and late (week 4) stages of healing, implying that photofunctionalization did not only accelerate but also increased the degree of osseointegration. Culture studies using bone marrow-derived osteoblasts showed that the attachment, spread, and functional phenotypes of osteogenic cells, such as alkaline phosphatase activity and mineralization, were remarkably increased on photofunctionalized titanium. In conclusion, photofunctionalization substantially increased biological and osseointegration capability of a nanofeatured titanium surface. In light with proven effectiveness on microfeatured surfaces in the literature, photofunctionalization may provide a novel and practical avenue to further improve osseointegration capability of implants in a wide range of surface morphology with micro-to-nano features.

Bone integration capability of alkali- and heat-treated nanobimorphic Ti-15Mo-5Zr-3Al

The role of nanofeatured titanium surfaces in a number of aspects of in vivo bone-implant integration, and, in particular, their potential advantages over microfeatured titanium surfaces, as well as their specific contribution to osteoconductivity, is largely unknown. This study reports the creation of a unique nanobimorphic titanium surface comprised of nanotrabecular and nanotuft-like structures and determines how the addition of this nanofeature to a microroughened surface affects bone-implant integration. Machined surfaces without microroughness, sandblasted microroughened surfaces, and micro-nano hybrid surfaces created by sandblasting and alkali and heat treatment of Ti-15Mo-5Zr-3Al alloy were subjected to biomechanical, interfacial and histological analyses in a rat model. The presence of microroughness enabled accelerated establishment of biomechanical implant fixation in the early stages of healing compared to the non-microroughened surfaces; however, it did not increase the implant fixation at the late stages of healing. The addition of nanobimorphic features to the microroughened surfaces further increased the implant fixation by as much as 60-100% over the healing time. Bone area within 50 μm of the implant surface, but not beyond this distance, was significantly increased by the presence of nanobimorphic features. Although the percentage of bone-implant contact was also significantly increased by the addition of nanobimorphic features, the greatest improvement was found in the soft tissue intervention between the bone and the implant, which was reduced from >30% to <5%. Mineralized tissue densely deposited with calcium-binding globular proteins was observed in an extensive area of nanobimorphic surfaces after biomechanical testing. This study clearly demonstrates the nanofeature-enhanced osteoconductivity of titanium by an alkali- and heat-treated nanobimorphic surface compared to that by microfeatured surfaces, which results not only in an acceleration but also an improvement of bone-implant integration. The identified biological parameters that successfully detect the advantages of nanofeatures over microfeatures will be useful in evaluating new implant surfaces in future studies.

Harmful lifestyles on orthopedic implantation surgery: a descriptive review on alcohol and tobacco use

Alcohol abuse and smoking habits have adverse effects on bone health and are a risk factor for osteoporosis, fractures and impaired fracture repair. Osteointegration processes around implanted biomaterials involve a coordinated cascade of complex events that are very similar to those occurring during fracture repair and require a suitable microenvironment and the coordinated action of cells and signal molecules. Therefore, diseases and harmful lifestyles that impair the normal bone healing process can reduce the success of implant surgery and may negatively influence the osteointegration of prostheses and implant devices for fracture fixation such as screws, nails and plates. Understanding the effects of harmful lifestyles on bone implant osteointegration is important for successful implant therapy, orthopedic reconstructive surgery and tissue-engineered-based therapies. However, the mechanisms by which smoking and alcoholism affect bone metabolism, bone mass and the balance of bone resorption and formation, also in the presence of an orthopedic implant, are not completely understood and remain inadequately elucidated. This review aims to analyze in vitro and in vivo studies regarding orthopedic implant integration in the presence of tobacco smoking and alcohol consumption with a focus on pathophysiology and local or systemic mechanisms of action on bone.

Effects of pico-to-nanometer-thin TiO2 coating on the biological properties of microroughened titanium

The independent, genuine role of surface chemistry in the biological properties of titanium is unknown. Although microtopography has been established as a standard surface feature in osseous titanium implants, unfavorable behavior and reactions of osteogenic cells are still observed on the surfaces. To further enhance the biological properties of microfeatured titanium surfaces, this study tested the hypotheses that (1) the surface chemistry of microroughened titanium surfaces can be controllably varied by coating with a very thin layer of TiO(2), without altering the existing topographical and roughness features; and (2) the change in the surface chemistry affects the biological properties of the titanium substrates. Using a slow-rate sputter deposition of molten TiO(2) nanoparticles, acid-etched microroughened titanium surfaces were coated with a TiO(2) layer of 300-pm to 6.3-nm thickness that increased the surface oxygen levels without altering the existing microtopography. The attachment, spreading behavior, and proliferation of osteoblasts, which are considered to be significantly impaired on microroughened surfaces compared with relatively smooth surfaces, were considerably increased on TiO(2)-coated microroughened surfaces. The rate of osteoblastic differentiation was represented by the increased levels of alkaline phosphatase activity and mineral deposition as well as by the upregulated expression of bone-related genes. These biological effects were exponentially correlated with the thickness of TiO(2) and surface oxygen percentage, implying that even a picometer-thin TiO(2) coating is effective in rapidly increasing the biological property of titanium followed by an additional mild increase or plateau induced by a nanometer-thick coating. These data suggest that a super-thin TiO(2) coating of pico-to-nanometer thickness enhances the biological properties of the proven microroughened titanium surfaces by controllably and exclusively modulating their surface chemistry while preserving the existing surface morphology. The improvements in proliferation and differentiation of osteoblasts attained by this chemical modification is of great significance, providing a new insight into how to develop new implant surfaces for better osseointegration, based on the established microtopographic surfaces.

Effects of nicotine on gene expression and osseointegration in rats

BACKGROUND

While many studies have focused on the hazardous effects of smoking, there is little direct evidence regarding the specific detrimental effects of the nicotine on the osseointegration of implants.

OBJECTIVE

To understand the effects of nicotine on gene expression and osseointegration of titanium implants in rats.

MATERIAL AND METHODS

Forty-four rats were administered with nicotine or saline for a period of 8 weeks. The femurs were then harvested and analyzed using a three-point bending test. Osseointegration level was determined using bone/implant contact ratio at 2 or 4 weeks after implants were placed. Expression levels of bone matrix-related genes were measured by quantitative real-time polymerase chain reaction.

RESULTS

The results of the three-point bending showed that there was no significant difference detected in stiffness between control and nicotine groups at 8 weeks post-saline/nicotine delivery (P=0.705). The bone/implant contact ratio in nicotine-delivered group was significantly decreased compared with those in the control group at 4 weeks (P<0.05). Also, expression levels of osteopontin, type II collagen, bone morphogenic protein-2, bone sialoprotein, and core-binding factor α-1 were significantly down-regulated in the nicotine-delivered group compared with the control.

CONCLUSIONS

Although systemic exposure to nicotine did not affect rat bone development, bone wound healing around the implant after placement was affected. These findings suggest that nicotine might inhibit the bone matrix-related gene expressions required for wound healing and thereby diminish implant osseointegration at late stage.

Selective cell affinity of biomimetic micro-nano-hybrid structured TiO2 overcomes the biological dilemma of osteoblasts

OBJECTIVE

There is a great demand for dental implant surfaces to accelerate the process of peri-implant bone generation to reduce its healing time and enable early loading. To this end, an inverse correlation between the proliferation and functional maturation (differentiation) in osteoblasts presents a challenge for the rapid generation of greater amounts of bone. For instance, osteoblasts exhibit faster differentiation but slower proliferation on micro-roughened titanium surfaces. Using a unique micro-nano-hierarchical topography of TiO(2) that mimics biomineralized matrices, this study demonstrates that this challenge can be overcome without the use of biological agents.

METHODS

Titanium disks of grade 2 commercially pure titanium were prepared by machining (smooth surface). To create a microtexture with peaks and valleys (micropit surface), titanium disks were acid-etched. To create 200-nm TiO(2) nanonodules within the micropits (nanonodule-in-micropit surface), TiO(2) was sputter-deposited onto the acid-etched surface. Rat bone marrow-derived osteoblasts and NIH3T3 fibroblasts were cultured on machined smooth, micropit, and nanonodule-in-micropit surfaces.

RESULTS

Despite the substantially increased surface roughness, the addition of 200-nm nanonodules to micropits increased osteoblast proliferation while enhancing their functional differentiation. In contrast, this nanonodule-in-micropit surface decreased proliferation and function in fibroblasts.

SIGNIFICANCE

The data suggest the establishment of cell-selectively functionalized nano-in-micro smart titanium surfaces that involve a regulatory effect on osteoblast proliferation, abrogating the inhibitory mechanism on the micropitted surface, while enhancing their functional differentiation. Biomimetic and controllable nature of this nanonodules-in-micropits surface may offer a novel micro-to-nanoscale hierarchical platform to biologically optimize nanofeatures of biomaterials. Particularly, this micro-nano-hybrid surface may be an effective approach to improve current dental implant surfaces for accelerated bone integration.

Enhancement of bone-titanium integration profile with UV-photofunctionalized titanium in a gap healing model

In this study, we tested the potential of UV-photofunctionalized titanium surfaces to overcome compromised bone-titanium integration in a gap healing model. Titanium in rod and disk forms was acid etched and then stored for 4 weeks under dark ambient conditions. Titanium rods with and without UV pretreatment were placed into a rat femur with (contact healing) or without (gap healing) contact with the innate cortical bone. The titanium implants were subjected to a biomechanical push-in test, micro-CT bone morphometry, and surface elemental analysis after 2 weeks of healing. The strength of bone-titanium integration in the gap healing model was one-third of that in the contact healing model. However, UV-treated implants in the gap healing condition produced a strength of bone-titanium integration equivalent to that of untreated implants in the contact healing condition. Bone volume around UV-treated implants was 2- to 3-fold greater than that around the untreated implants in the gap healing model. A bone generation profile drawn along the long axis of the implant exhibited greater contrast between the untreated and UV-treated surfaces in the cortical area than in the bone marrow area. The bone tissue formed on UV-treated implants showed a higher Ca/P ratio than that formed on untreated titanium. The rate of cell proliferation, alkaline phosphatase activity, and calcium deposition in femoral periosteal cells and in bone marrow-derived osteoblasts were greater in cultures on UV-treated titanium disks than in cultures on untreated disks. The UV-enhanced function in periosteal cells was more pronounced when they were co-cultured with bone marrow-derived osteoblasts, indicating a synergistic effect of UV-treated titanium with biological signals from bone marrow-derived osteoblasts. Within the limitation of the model used in this study, UV-photofunctionalized titanium surfaces may overcome the challenging condition of bone-titanium integration without cortical bone support. UV treatment of implants induced marked improvements in the behavior of bone formation and quantity and quality of bone tissue around the implants. These effects may be related to the promoted function of both periosteum- and bone marrow-derived osteogenic cells at the local level around UV-treated titanium surfaces.

Implant surface treatments affect gene expression of Runx2, osteogenic key marker

STATEMENT OF PROBLEM

The aim of this study was to study the effects of various surface treatments to a titanium surface on the expression of Runx2 in vitro.

MATERIAL AND METHODS

Human Osteosarcoma TE-85 cells were cultured on machined, sandblasted, or anodic oxidized cpTi discs. At various times of incubation, the cells were collected and then processed for the analysis of mRNA expression of Runx2 using reverse transcription-PCR.

RESULTS

The expression pattern of Runx2 mRNA was differed according to the types of surface treatment. When the cells were cultured on the untreated control culture plates, the gene expression of Runx2 was not increased during the experiments. In the case of that the cells were cultured on the machined cpTI discs, the expression level was intermediate at the first day, but increased constitutively to day 5. In cells on sandblasted cpTi discs, the expression level was highest in the first day sample and the level was maintained to 5 days. In cells on anodized cpTi discs, the expression level increased rapidly to 3 days, but decreased slightly in the 5-th day sample.

CONCLUSION

Different surface treatments may contribute to the regulation of osteoblast function by influencing the level of gene expression of key osteogenic factors.

The effect of ultraviolet functionalization of titanium on integration with bone

Titanium implants are used as a reconstructive anchor in orthopedic and dental diseases and problems. Recently, ultraviolet (UV) light-induced photocatalytic activity of titanium has earned considerable and broad interest in environmental and clean-energy sciences. This study determines whether UV treatment of titanium enhances its osteoconductive capacity. Machined and acid-etched titanium samples were treated with UV for various time periods up to 48h. For both surfaces, UV treatment increased the rates of attachment, spread, proliferation and differentiation of rat bone marrow-derived osteoblasts, as well as the capacity of protein adsorption, by up to threefold. In vivo histomorphometry in the rat model revealed that new bone formation occurred extensively on UV-treated implants with virtually no intervention by soft tissue, maximizing bone-implant contact up to nearly 100% at week 4 of healing. An implant biomechanical test revealed that UV treatment accelerated the establishment of implant fixation 4 times. The rates of protein adsorption and cell attachment strongly correlated with the UV dose-responsive atomic percentage of carbon on TiO2, but not with the hydrophilic status. The data indicated that UV light pretreatment of titanium substantially enhances its osteoconductive capacity, in association with UV-catalytic progressive removal of hydrocarbons from the TiO2 surface, suggesting a photofunctionalization of titanium enabling more rapid and complete establishment of bone-titanium integration.

High-throughput gene expression analysis in bone healing around titanium implants by DNA microarray

OBJECTIVE

Bone generation occurs around titanium implants; however, its underlying mechanisms are relatively unknown. We attempt to identify gene transcripts specifically upregulated in in vivo bone healing with titanium implants using DNA microarray.

MATERIAL AND METHODS

Titanium implants were placed into rat femurs, and total RNA was extracted from the implant-associated tissue at weeks 1, 2 and 4 of healing. As a control, RNA was extracted from the tissue undergoing osteotomy healing. The RNA samples were hybridized onto oligo DNA microarray.

RESULTS

Most of the 20,000 genes tested were expressed similarly in both the implant- and osteotomy-healing groups. Eighty-six genes were upregulated (>2-fold) in the implant-healing group compared with the osteotomy-healing group in at least one time point of healing. Twelve genes were upregulated in the implant healing at week 2 and earlier, while 31 genes were upregulated at week 2 and later. Only one gene was upregulated specifically at week 1, while three genes were consistently upregulated from weeks 1 to 4. The upregulated genes included collagenous and non-collagenous extracellular matrix (ECM)-related genes, proteoglycans and bone resorption-related genes. Pathway analysis revealed the involvement of ECM and receptor interaction in implant healing.

CONCLUSIONS

This study provides evidence that a set of gene transcripts is upregulated in the implant healing over the osteotomy healing, which seems to represent the coordinated biological events of long-lasting osteogenesis and bone remodeling required for osseointegration. Further studies are needed to identify the significance and biological roles of the transcripts in osseointegration. Proven reliability and usefulness of microarray technology should encourage future approaches to develop a high-throughput molecular assessment for osseointegration capacity of new implant surfaces.

The effect of superficial chemistry of titanium on osteoblastic function

The surface topography and chemistry of titanium are postulated to be two major factors that affect the osseointegration capacity of titanium implants. However, it is extremely difficult to control one factor without changing the other, which prevents the isolation of the genuine effect of one factor. This study aimed to determine whether surface chemistry of titanium alone affects osteoblastic function. Two different titanium surfaces were prepared by sputter depositioning of titanium (Ti; 99.99% purity) or titanium dioxide (TiO2; 99.99% purity) (50-nm thick for each) onto machined commercially pure titanium disks. Rat bone marrow-derived osteoblastic cells were cultured on each of the two surfaces. TiO2 surface showed 4.4 times higher elemental oxygen concentration and higher water wettability than Ti surface. Scanning electron microscopic and atomic force microscopic examination revealed no differences in surface topography and roughness values between the two surfaces. The cell proliferated more on TiO2 than on Ti by up to 60%. Although the expression of collagen I gene increased more rapidly on TiO2 at early culture stage of day 3, the late stage marker genes for osteoblastic differentiation, including osteopontin and osteocalcin, were not modulated between the two cultures. The alkaline phosphatase positive area and mineralized nodule area were approximately two times larger on TiO2 than on Ti. In conclusion, titanium materials having different superficial chemistry, that is, titanium or titanium dioxide, may exert different biological capacity of osteoblasts; titanium dioxide may induce superior osteoconduction, primarily because of the increased osteoblastic proliferation.

Biological responses in osteoblast-like cell line according to thin layer hydroxyapatite coatings on anodized titanium

Several features of the implant surface, such as roughness, topography and composition play a relevant role in implant integration with bone. This study was conducted in order to determine the effects of various thin layer hydroxyapatite (HA) coatings on anodized Ti surfaces on the biological responses of a human osteoblast-like cell line (MG63). MG63 cells were cultured on 100 nm HA (100 nm HA coating on anodized surface), 500-700 nm HA (500-700 nm HA coating on anodized surface), 1 mum HA (1 mum HA coating on anodized surface) and anodize (non-HA coating on anodized surface) Ti. The morphology of these cells was assessed by scanning electron microscopy (SEM). The cDNAs prepared from the total RNAs of the MG63 were hybridized into a human cDNA microarray (1152 elements). The appearances of the surfaces observed by SEM were different on each of the four dental substrate types. MG63 cells cultured on 100 nm HA, 1 mum HA and anodize exhibited cell-matrix interactions. It was 500-700 nm HA surface showing cell-cell interaction. In the expression of genes involved in osseointegration, several genes, including bone morphogenetic protein 2, latent transforming growth factor beta binding protein 1, catenin (cadherin-associated protein), integrin, PDGFRB and GDF-1 growth differentiation factor 1 were up-regulated on the different surfaces. Several genes, including fibroblast growth factor receptor 3, fibroblast growth factor 12 and CD4 were down-regulated on the different surfaces. The attachment and expression of key osteogenic regulatory genes were enhanced by the surface morphology of the dental materials used.

Ultrastructure of the Interface Between Titanium and Surrounding Tissue in Rat Tibiae ? A Comparison Study on Titanium-Coated and -Uncoated Plastic Implants

PURPOSES

The purposes of this study were to prepare experimental titanium-coated plastic implants suitable for electron microscopy examination of the titanium-bone interface and the response of tissue surrounding titanium, and to histologically compare surrounding tissue responses in coated and uncoated implants.

MATERIALS AND METHODS

Experimental plastic implants were prepared from a plastic rod coated with a thin film of titanium. Plastic implants without coatings were used as controls. The implants were placed into tibiae of 10-week-old male rats. The specimens with implants were harvested 4 weeks after placement and observed under a light microscope, a transmission electron microscope, and a scanning electron microscope.

RESULTS

In the transmission electron microscopy, the titanium layer of the experimental implant was a uniform layer that was approximately 150- to 250-nm wide. The new bone formation was observed around both titanium-coated implants and plastic implants. However, there was no direct bone contact with the plastic implant.

DISCUSSION

The responses of tissue surrounding the experimental implants varied. Under an electron microscope, the following areas were observed: (1) an area with a direct contact between the titanium and bone, (2) an area at the interface where an amorphous layer was observed, (3) an area with progressing calcification in the surrounding tissue where the cells were adjacent to the titanium surface, and (4) an area in which bone resorption and apposition were observed and remodeling was thought to be occurring.

CONCLUSION

The experimental titanium was homogenous and was considered to be highly useful in observing the responses of the surrounding tissue to the titanium surface.

Effect of various implant coatings on biological responses in MG63 using cDNA microarray

During the process of bone formation, titanium (Ti) surface is an important factor in the modulation of osteoblastic function. This study was conducted in order to determine the effects of different Ti surfaces on the biological responses of a human osteoblast-like cell line (MG63). MG63 cells were cultured on smooth (S), sandblasted large-grit and acid etching (SLA), hydroxyapatite (HA), hydroxyfluoride (HF), titanium nitrate (TIN), and diamond-like carbon (DLC) Ti. The morphology of these cells were assessed by SEM. The cDNAs prepared from the total RNAs of the MG63 were hybridized into a human cDNA microarray (1152 elements). The appearances of the surfaces observed by SEM were different on each of the six dental substrate types. The SLA and HA surfaces were determined to be rougher than the others. MG63 cells cultured on SLA and HA exhibited cell-matrix interactions. In the expression of genes involved in osseointegration, several genes, including bone morphogenetic protein, cadherin, integrin, and insulin-like growth factors, were upregulated on the different surfaces. Several genes, including fibroblast growth factor receptor 4, Bcl 2-related protein, and collagen, were downregulated on the different surfaces. The attachment and expression of key osteogenic regulatory genes were enhanced by the surface roughness of the dental materials used.

Biological factors involved in the osseointegration of oral titanium implants with different surfaces: a pilot study in minipigs

BACKGROUND

The stability of titanium implants is determined by the rigid load-bearing connections that are formed by the bone, a process that involves a complex network of cells, pro- and anti-inflammatory mediators, and growth factors. The osseointegration processes at the interfaces of machined and porous implants were studied using molecular and histological techniques.

METHODS

Two machined and two porous titanium implants were inserted into the tibiae of four minipigs. The animals were sacrificed at 15, 30, 60, and 90 days post-implantation. The levels of bone morphogenetic protein (BMP)-4, transforming growth factor (TGF)-beta1, and tumor necrosis factor (TNF)-alpha were quantified in the peri-implant osseous samples. The levels of interleukin (IL)-1beta, IL-6, IL-10, and TNF-alpha in the serum were also assessed.

RESULTS

Histomorphological analysis showed evidence of bone ossification around the porous implant at 60 days. Surrounding the machined implants, highly sclerotic fibrous pads started the healing response at 90 days, and the levels of TGF-beta1 and BMP-4 began to increase at 60 days, at which time bone ossification around the porous implants was already evident. TNF-alpha was not present in the bone next to the implants. The serum levels of cytokines IL-1beta, IL-6, and IL-10 were not increased. The serum level of TNF-alpha increased during the healing process.

CONCLUSIONS

We observed that the levels of BMP-4 and TGF-beta1, which play essential roles in the osteogenesis process, increased earlier around the porous implants than around the machined implants. Similarly, the ossification process was initiated earlier at the surfaces of the porous implants than at the surfaces of the machined implants.

Glycosaminoglycan degradation reduces mineralized tissue–titanium interfacial strength

Although the localization of the proteoglycan/glycosaminoglycan (GAG) complex at the bone-titanium implant interface has been implied, the role of proteoglycans on the establishment of bone-titanium integration is unknown. The hypothesis to be tested was that proteoglycans play an important role in establishing bone-titanium interfacial adhesion. The objective of this study is to investigate the effect of proteoglycan knockdown by GAG enzymatic degradation on the interfacial strength between mineralized tissue and titanium having different surface topographies. Rat bone marrow-derived osteoblastic cells were cultured on either a machined titanium disk or an acid-etched titanium disk. At day 21 of culture, one of the three following GAG degradation enzymes was added into the culture; chondroitinase AC, chondroitinase B, or keratanase. After 3 days of incubation (at day 24 of culture), the laser spallation technique was applied to the samples in order to assess the tissue-titanium interfacial strength. In this technique, a laser-generated stress wave is used to separate the tissue-titanium interface, and the interfacial strength is determined interferometrically by recording the transient free surface velocity of the tissue. Mineralized tissue cultured on the acid-etched titanium showed 20-30% higher tissue interfacial strength than that cultured on the machined titanium (p < 0.0001). For both the machined and acid-etched surface cultures, administration of the enzyme reduced the interfacial strength by 25-30% compared with the untreated control cultures (p < 0.0001). There were no differences in the effect among the three different enzymes tested. A nanoindentation study revealed that the enzyme treatment did not affect the elastic modulus of the mineralized tissue. Scanning electron microscopic and energy dispersive spectroscopic analyses revealed less post-spallation tissue remnant on the titanium substrates when treated with the enzymes. The tissue remnant was greater in amount on the acid-etched surface than on the machined surface. The results suggest that there exists not only mechanical interlocking but also biological interfacial adhesion between the mineralized tissue and titanium, in which the proteoglycan/GAG complex is involved.

Osteoblasts generate harder, stiffer, and more delamination-resistant mineralized tissue on titanium than on polystyrene, associated with distinct tissue micro- and ultrastructure

This study revealed that osteoblasts generate harder, stiffer, and more delamination-resistant mineralized tissue on titanium than on the tissue culture polystyrene, associated with modulated gene expression, uniform mineralization, well-crystallized interfacial calcium-phosphate layer, and intensive collagen deposition. Knowledge of this titanium-induced alteration of osteogenic potential leading to enhanced intrinsic biomechanical properties of mineralized tissue provides novel opportunities and implications for understanding and improving bone-titanium integration and engineering physiomechanically tolerant bone.

INTRODUCTION

Bone-titanium integration is a biological phenomenon characterized by continuous generation and preservation of peri-implant bone and serves as endosseous anchors against endogenous and exogenous loading, of which mechanisms are poorly understood. This study determines the intrinsic biomechanical properties and interfacial strength of cultured mineralized tissue on titanium and characterizes the tissue structure as possible contributing factors in biomechanical modulation.

MATERIALS AND METHODS

Rat bone marrow-derived osteoblastic cells were cultured either on a tissue culture-grade polystyrene dish or titanium-coated polystyrene dish having comparable surface topography. Nano-indentation and nano-scratch tests were undertaken on mineralized tissues cultured for 28 days to evaluate its hardness, elastic modulus, and critical load (force required to delaminate tissue). Gene expression was analyzed using RT-PCR. The tissue structural properties were examined by scanning electron microscopy (SEM), collagen colorimetry and localization with Sirius red stain, mineral quantification, and localization with von Kossa stain and transmission electron microscopy (TEM).

RESULTS

Hardness and elastic modulus of mineralized tissue on titanium were three and two times greater, respectively, than those on the polystyrene. Three times greater force was required to delaminate the tissue on titanium than that on the polystyrene. SEM of the polystyrene culture displayed a porous structure consisting of fibrous and globular components, whereas the titanium tissue culture appeared to be uniformly solid. Cell proliferation was remarkably reduced on titanium. Microscopic observations revealed that the mineralized tissue on titanium was composed of uniform collagen-supported mineralization from the titanium interface to the outer surface, with intensive collagen deposition at tissue-titanium interface. In contrast, tissue on the polystyrene was characterized by collagen-deficient mineralization at the polystyrene interface and calcium-free collagenous matrix formation in the outer tissue area. Such characteristic microstructure of titanium-associated tissue was corresponded with upregulated gene expression of collagen I and III, osteopontin, and osteocalcin mRNA. Cross-sectional TEM revealed the apposition of a high-contrast and well-crystallized calcium phosphate layer at the titanium interface but not at the polystyrene interface.

CONCLUSIONS

Culturing osteoblasts on titanium, compared with polystyrene, enhances the hardness, elastic modulus, and interfacial strength of mineralized tissue to a higher degree. Titanium per se possesses an ability to alter cellular phenotypes and tissue micro- and ultrastructure that result in enhanced intrinsic biomechanical properties of mineralized tissue.

Enhanced intrinsic biomechanical properties of osteoblastic mineralized tissue on roughened titanium surface

The biological mechanisms underlying bone-titanium integration and biomechanical properties of the integrated bone are poorly understood. This study assesses intrinsic biomechanical properties of mineralized tissue cultured on titanium having different surface topographies. The osteoblastic phenotypes associated with mineral deposition and collagen synthesis underlying the biomechanical modulation are also reported. Rat bone marrow-derived osteoblastic cells were cultured either on the machined titanium disc or acid-etched titanium disc. Nano-indentation study of day 28 culture revealed that the mineralized tissue on the acid-etched surface shows 3-3.5 times greater hardness than that on the machined surface (p < 0.01). Elastic modulus of the mineralized tissue was also 2.5-3 times greater on the acid-etched surface than on the machined surface (p < 0.01). After 28 days of culture, mineralized nodule area was significantly lower on the acid-etched surface than on the machined surface (p = 0.0105), while total calcium deposition did not differ between the two surfaces, indicating denser mineral deposition on the acid-etched surface. Osteopontin and osteocalcin gene expressions assayed by the reverse transcriptase-polymerase chain reaction were upregulated in the acid-etched titanium culture. Collagen synthesis measured by Sirius red stain-based colorimetry was 1.5-10 times higher on the acid-etched surface than on the machined surface in the initial culture period of day 1 to day 14 (p < 0.0001). The amount of collagen synthesis corresponded with the enhanced gene expression of prolyl 4-hydroxylase, a key enzyme for post-translational modification of collagen chains. Scanning electron microscopic images revealed that tissue cultured on the acid-etched titanium exhibited plate-like, compact surface morphology, while the tissue on the machined titanium appeared porous and was covered by fibrous and punctate structures. We conclude that culturing osteoblasts on rougher titanium surfaces enhances hardness and elastic modulus of the mineralized tissue, associated with condensed mineralization, accelerated collagen synthesis, and upregulated expression of selected bone-related genes.

Enhanced mineralized tissue adhesion to titanium over polystyrene assessed by the nano-scratch test

The critical load determined by the scratch test is regarded to be a representative measure of coating adhesion in the field of engineering. This study aimed to evaluate the method for its usefulness for assessing the mineralized tissue-titanium interface strength. Osteoblastic cells derived from rat bone marrow were cultured on polystyrene, titanium-coated polystyrene, and titanium disks with either a machined or dual-acid etched surface. Nano-scratch testing was performed on mineralized tissue specimens at culture day 28. The scratch path was monitored by light microscopy until complete delamination of mineralized tissue from the substrate occurred, and the required force was recorded as the critical load. Energy-dispersive spectroscopic analysis was used to verify the delamination. The mean critical load values (+/- standard deviations) were as follows: polystyrene 31 mN (+/-1), titanium-coated polystyrene 67 mN (+/-4), machined titanium 76 mN (+/-4), DAE titanium 107 mN (+/-3), with statistical differences (P < 0.05; ANOVA). No elemental calcium and phosphorous were observed in the delaminated areas. The nano-scratch test applied to cultured mineralized tissue differentiated the critical load from various culture conditions: polystyrene vs. titanium; titanium with different surface topographies. Culturing mineralized tissue on titanium, especially on roughened surfaces, increased the tissue critical load. The nano-scratch test may be useful to evaluate mineralized tissue adhesion properties in titanium cultures.