Bone Tissue Implants Research Articles

The physicochemical/biological properties of porous tantalum and the potential surface modification techniques to improve its clinical application in dental implantology.

More rapid restoration and more rigid functionality have been pursued for decades in the field of dental implantology. Under such motivation, porous tantalum has been recently introduced to design a novel type of dental implant. Porous tantalum bears interconnected porous structure with pore size ranging from 300 to 600μm and a porosity of 75-85%. Its elastic modulus (1.3-10GPa) more closely approximates that of natural cortical (12-18GPa) and cancellous bone (0.1-0.5GPa) in comparison with the most commonly used dental materials, such as titanium and titanium alloy (106-115GPa). Porous tantalum is highly corrosion-resistant and biocompatible. It can significantly enhance the proliferation and differentiation of primary osteoblasts derived from elderly people than titanium. Porous tantalum can allow bone ingrowth and establish not only osseointegration but also osseoincorporation, which will significantly enhance the secondary stability of implants in bone tissue. In this review, we summarize the physicochemical, mechanical and biological properties of porous tantalum. We further discuss the performance of current tantalum dental implants and present the methodologies of surface modifications in order to improve their biological performance.

Degradability and cytocompatibility of tricalcium phosphate/poly(amino acid) composite as bone tissue implants in orthopaedic surgery

In this study, a tricalcium phosphate (TCP) and poly (amino acid) copolymer (PAA) biocomposite were fabricated for bone repair and characterized. The results show that the compressive strength of the TCP/PAA composites increased with an increase in the TCP content at TCP contents less than 40 w%. The weight loss of the composite after soaking in phosphate buffered saline for 12 weeks significantly increased with an increase in the TCP content, revealing its good degradability. In addition, the composite maintained adequate mechanical strength during the degradation period because it underwent a surface erosion process. In vitro MG63 cell culture experiments showed that the composite is non-cytotoxic and thus allows cells to adhere, proliferate and differentiate. Osteoid formation was evidenced on the composite surfaces 12 weeks after its implantation into the femoral bone of dogs. Furthermore, the composite combined directly with the host bone tissue without fibrous capsule tissue, and no inflammatory responses were found, showing the good biocompatibility of the composite. It is expected that the composite may be used for the development of bone implants for orthopaedic surgery.

Bifunctional Designed Peptides Induce Mineralization and Binding to TiO2

A limitation of titanium implants is the rather poor bonding between the metal and the surrounding tissue. In this research, we aimed at developing functional peptides in the form of monomolecular coatings intended to improve adhesion between the native oxide of the metal (TiO2) and the calcium-phosphate mineralization layer with which it is in contact. Accordingly, a bifunctional peptide with a β-strand motif assumed to strongly bind to the oxide through two phosphorylated serine residues, both situated on the same face of the strand, was designed. The β-strand motif was extended by a mineralization "tail" composed of consecutive acidic amino acids capable of adsorbing calcium ions. This peptide was studied together with two additional control peptides, one serving to elucidate the role of the β-strand in stabilizing bonding with the oxide and the other demonstrating the ability of the tail to induce mineralization. The strong adsorption of the three peptides to the oxide surface was revealed by HPLC. That peptide presenting the mineralization tail showed the highest levels of adsorbed calcium and phosphate ions, as well as the largest area of cellular adherence, demonstrating its potential advantages for use with titanium implants in bone tissue.

Hydrothermal fabrication of hydroxyapatite/chitosan/carbon porous scaffolds for bone tissue engineering

Porous carbon fiber felts (PCFFs) have great applications in orthopedic surgery because of the strong mechanical strength, low density, high stability, and porous structure, but they are biologically inert. To improve their biological properties, we developed, for the first time, the hydroxyapatite (HA)/chitosan/carbon porous scaffolds (HCCPs). HA/chitosan nanohybrid coatings have been fabricated on PCFFs according to the following stages: (i) deposition of chitosan/calcium phosphate precursors on PCFFs; and (ii) hydrothermal transformation of the calcium phosphate precursors in chitosan matrix into HA nanocrystals. The scanning electron microscopy images indicate that PCFFs are uniformly covered with elongated HA nanoplates and chitosan, and the macropores in PCFFs still remain. Interestingly, the calcium-deficient HA crystals exist as plate-like shapes with thickness of 10-18 nm, width of 30-40 nm, and length of 80-120 nm, which are similar to the biological apatite. The HA in HCCPs is similar to the mineral of natural bone in chemical composition, crystallinity, and morphology. As compared with PCFFs, HCCPs exhibit higher in vitro bioactivity and biocompatibility because of the presence of the HA/chitosan nanohybrid coatings. HCCPs not only promote the formation of bone-like apatite in simulated body fluid, but also improve the adhesion, spreading, and proliferation of human bone marrow stromal cells. Hence, HCCPs have great potentials as scaffold materials for bone tissue engineering and implantation.

Gelation and biocompatibility of injectable alginate–calcium phosphate gels for bone regeneration

An emerging approach toward development of injectable, self-setting, and fully biodegradable bone substitutes involves the combination of injectable hydrogel matrices with a dispersed phase consisting of nanosized calcium phosphate particles. Here, novel injectable composites for bone regeneration have been developed based on the combination of ultrapure alginate as the matrix phase, crystalline CaP [monetite and poorly crystalline hydroxyapatite (HA)] powders as both a dispersed mineral phase and a source of calcium for cross-linking alginate, glucono-delta-lactone (GDL) as acidifier and glycerol as both plasticizer and temporary sequestrant. The composites were maximized with respect to CaP content to obtain the highest amount of osteoconductive filler. The viscoelastic and physicochemical properties of the precursor compounds and composites were analyzed using rheometry, elemental analysis (for calcium release and uptake), acidity [by measuring pH in simulated body fluid (SBF)], general biocompatibility (subcutaneous implantation in rabbits), and osteocompatibility (implantation in femoral condyle bone defect of rabbits). The gelation of the resulting composites could be controlled from seconds to tens of minutes by varying the solubility of the CaP phase (HA vs. monetite) or amount of GDL. All composites mineralized extensively in SBF for up to 11 days. In vivo, the composites also disintegrated upon implantation in subcutaneous or bone tissue, leaving behind less degradable but osteoconductive CaP particles. Although the composites need to be optimized with respect to the available amount of calcium for cross-linking of alginate, the beneficial bone response as observed in the in vivo studies render these gels promising for minimally invasive applications as bone-filling material.

Mechanical forces regulate stem cell response to surface topography

The interactions between bone tissue and orthopedic implants are strongly affected by mechanical forces at the bone-implant interface, but the interplay between surface topographies, mechanical stimuli, and cell behavior is complex and not well understood yet. This study reports on the influence of mechanical stretch on human mesenchymal stem cells (hMSCs) attached to metallic substrates with different roughness. Controlled forces were applied to plasma membrane of hMSCs cultured on smooth and rough stainless steel surfaces using magnetic collagen-coated particles and an electromagnet system. Degree of phosphorylation of focal adhesion kinase (p-FAK) on the active form (Tyr-397), prostaglandin E2 (PGE2) and vascular endothelial growth factor (VEGF) levels increased on rough samples under static conditions. Cell viability and fibronectin production decreased on rough substrates, while hMSCs maturated to the osteoblastic lineage to a similar extent on both surfaces. PGE2 production and osteoprotegerin/receptor activator of nuclear factor kappa-B ligand ratio increased after force application on both surfaces, although to a greater extent on smooth substrates. p-FAK on Tyr-397 was induced fairly rapidly by mechanical stimulation on rough surfaces while cells cultured on smooth samples failed to activate this kinase in response to tensile forces. Mechanical forces enhanced VEGF secretion and reduced cell viability, fibronetin levels and osteoblastic maturation on smooth surfaces but not on rough samples. The magnetite beads model used in this study is well suited to characterize the response of hMSCs cultured on metallic surfaces to tensile forces and collected data suggest a mechanism whereby mechanotransduction driven by FAK is essential for stem cell growth and functioning on metallic substrates.

Preparing Technology of Porous Hydroxyapatite/Chitosan Bioceramics

Hydroxyapatite/Chitosan bioceramics were fabricated by combining in-situ chemical synthesis and freeze drying method, using (NH4)2HPO4, Ca(NO3)2·4H2O, and chitosan(CS) as raw materials. The effect of solid loading and freeze-drying time on microstructures of hydroxyapatite/Chitosan bioceramics was studied. The microstructures of the fabricated porous bioceramics were investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the hydroxyapatite/Chitosan bioceramics have interconnected porous structures from several microns to 200um, more suitable to bone tissue implantation. In addition, the porous structures are affected solid loading of slurry and freeze-drying time.

Bone Regeneration Associated with Nontherapeutic and Therapeutic Surface Coatings for Dental Implants in Osteoporosis

Oral implantology is considered as the treatment of choice for replacing missing teeth in elderly people. However, implant complications may occur in patients with osteoporosis. The pathogenesis underlying osteoporosis is due to an alteration in bone cell response to hormonal, nutritional, and aging factors. For such challenging situations, improved bone regeneration has been shown around dental implants for certain surface modifications. These modifications include coatings of titanium implants with calcium phosphate (CaP) ceramics. Surface coating developments also allow for the addition of organic biomolecules, like growth factors, into the inorganic coatings that increase the bone formation process at the bone-implant interface. The application of therapeutic-based coatings is becoming a rapidly growing research field of interest. CaP-coated implants have the ability to incorporate anti-osteoporotic drugs, which then can be locally released over time from an implant surface in a controlled manner. Thus, it can be anticipated that nontherapeutic and/or therapeutic coated implants can significantly increase low bone density as well as improve impaired bone regeneration in osteoporosis. This review aims to provide a thorough understanding of the underlying mechanisms for impaired bone regeneration around dental implants in osteoporosis. Secondly, the review will focus on biological interactions and beneficial role of the surface-coated (i.e., nontherapeutics and therapeutics) bone implants in osteoporotic bone tissue.

Aggravation of inflammatory response by costimulation with titanium particles and mechanical perturbations in osteoblast- and macrophage-like cells

The interface between bone tissue and metal implants undergoes various types of mechanical loading, such as strain, compression, fluid pressure, and shear stress, from daily activities. Such mechanical perturbations create suboptimal environments at the host bone-implant junction, causing an accumulation of wear particles and debilitating osseous integration, potentially leading to implant failure. While many studies have focused on the effect of particles on macrophages or osteoprogenitor cells, differential and combined effects of mechanical perturbations and particles on such cell types have not been extensively studied. In this study, macrophages and osteoprogenitor cells were subjected to physiological and superphysiological mechanical stimuli in the presence and absence of Ti particles with the aim of simulating various microenvironments of the host bone-implant junction. Macrophages and osteoprogenitor cells were capable of engulfing Ti particles through actin remodeling and also exhibited changes in mRNA levels of proinflammatory cytokines under certain conditions. In osteoprogenitor cells, superphysiological strain increased proinflammatory gene expression; in macrophages, such mechanical perturbations did not affect gene expression. We confirmed that this phenomenon in osteoprogenitor cells occurred via activation of the ERK1/2 signaling pathway as a result of damage to the cytoplasmic membrane. Furthermore, AZD6244, a clinically relevant inhibitor of the ERK1/2 pathway, mitigated particle-induced inflammatory gene expression in osteoprogenitor cells and macrophages. This study provides evidence of more inflammatory responses under mechanical strains in osteoprogenitor cells than macrophages. Phagocytosis of particles and mechanical perturbation costimulate the ERK1/2 pathway, leading to expression of proinflammatory genes.

Adipose stem cell combined with plasma-based implant bone tissue differentiation in vitro and in a horse with a phalanx digitalis distalis fracture: a case report

A horse suffering from an undetected hoof bone fracture was diagnosed three weeks after injury. The formation of callus tissue was detected at the fracture site. Standard orthopaedic screw application was augmented by a novel method, a combination of stem cells and plasma components. For experimental therapy, fat tissue and blood samples were collected from the patient to isolate stem cells and plasma proteins. The obtained and characterised mesenchymal stem cell population was applied to the wound area, together with an implant prepared from plasma, wrapped over the orthopaedic screw. Additionally, cells with implant were differentiated in vitro into bone tissue, to evaluate if cells could successfully produce extracellular matrix in such material. Three weeks after application, the hoof was significantly regenerated, and after three months – the bone was completely rebuilt. The in vitro experiment also gave positive results, with completely differentiated cells after three weeks. Our data show that enriching the standard orthopaedic material with mesenchymal stem cells adds therapeutic value to the treatment of refractory bone fractures.

Study of Porous Hydroxyapatite/Chitosan Bioceramics for Bone Implantation

hydroxyapatite/Chitosan bioceramics were fabricated by combining in-situ chemical synthesis and freeze drying method, using (NH4)2HPO4, Ca(NO3)2·4H2O, and chitosan(CS) as raw materials. The effect of freezing temperatures, solid loading and freeze-drying time on microstructures of hydroxyapatite/Chitosan bioceramics was studied. The microstructures of the fabricated porous bioceramics were investigated by means of Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The results showed that the hydroxyapatite/Chitosan bioceramics have interconnected porous structures from several microns to 200um, more suitable to bone tissue implantation. In addition, the porous structures are affected by freezing temperature.

Simultaneous Reduction and Surface Functionalization of Graphene Oxide for Hydroxyapatite Mineralization

In this study, we present the synthesis of reduced graphene oxide/hydroxyapatite (RGO/HA) hybrid materials by an environmental-friendly route. Graphene oxide (GO) was first simultaneously reduced and surface functionalized by one-step oxidative polymerization of dopamine (PDA). The bioinspired surface was further used for biomimetic mineralization of hydroxyapatite. When incubated in a simulated body fluid (SBF), the PDA layer enabled efficient interaction between the RGO surface and the mineral ions to improve the bioactivity, promoted the formation of the HA nanoparticles. A detailed structural and morphological characterization of the mineralized composite was performed. The HA-based hybrid materials exhibited no cytotoxic effect on L929 fibroblast cells, showing potential capacity of being a scaffold material for bone tissue regeneration and implantation. This facile strategy also can be a useful platform for other RGO-based nanocomposites.

A Novel Approach for the Utilization of Biocellulose Nanofibres in Polyurethane Nanocomposites for Potential Applications in Bone Tissue Implants

With the increasing number of surgical bone grafts per year, the application of biomaterials in tissue engineering has become a popular issue. In the present work, the potential of biocellulose-nanofibre-reinforced polyurethane nanocomposites to act as bone scaffold implants is established. Investigating properties of polyurethane shows that this widely applied biomaterial group cannot fulfil all properties required for bone implants in a stand-alone fashion. Bone implants require a high Young's modulus and tensile strength but low strain which makes it difficult to find a suitable polyurethane since higher hard segment content will reduce tensile strength and lower hard segment content will reduce the Young's modulus. Other factors such as biodegradation also become important. A literature review on carbon nanotube and nanofibre composites with polyurethanes shows that nanofibrous reinforcement leads to favourable implant properties. Young's modulus and tensile strength increase dramatically. Other properties such as thermal conductivity and viscosity are also affected. These types of nanofibrous materials, however, are the subject of an ongoing debate about toxicity and their use in bone implants is questionable. Biocellulose nanofibres formed from bacteria (also called bacterial cellulose (BC)) possess favourable mechanical properties and are highly biocompatible. A survey on works done on BC nanofibres and their composites show that nanostructured biocomposites that contains the nanofibres reinforced in polymer composites result in changes that are comparable to those of carbon nanotubes in regards to bone scaffold applications. Showing improvement on biocompatibility and mechanical properties, biocellulose nanofibre reinforcement on polyurethanes possesses strong potential for bone implants and other tissue-engineering applications.

Osseointegration of dental implants in irradiated bone tissue: experimental study

Osseointegration of dental implants in irradiated bone tissue: experimental study

An electrically driven jetting technique for diverse high-resolution surface structures of nanometre hydroxyapatite crystals

Nanometre hydroxyapatite (nHA) coated metallic materials have been successfully used for bone tissue implantation for several decades now due to its sound biological and mechanical properties. The microstructure and surface topography of the implant material are well-known to play a crucial role in influencing cellular responses to implants and bone tissue regeneration ultimately. Recently, a novel jet-based patterning technique, template-assisted electrohydrodynamic atomisation (TAEA) spraying, has been devised to prepare depositions with defined surface topography for guiding the cellular response. In this study, an improvement investigation of this patterning process was carried out to precisely control the nHA surface structure in terms of geographies and dimensions via an angular needle jetting during the patterning process. More importantly, the mechanism of such improvement of the TAEA patterning technique was also discussed and uncovered. A range of diverse nHA surface structures with high-resolution was therefore achieved, which paves the way for the research of the new generation implant materials with defined cellular response.

Mussel-inspired functionalization of carbon nanotubes for hydroxyapatite mineralization

Hydroxyapatite (HAp)/carbon nanotubes (CNTs) hybrid composite materials are successfully synthesized via a biomineralization process that employs poly(dopamine) (PDA), a synthetic mimic of mussel adhesive proteins. Creating bio-inorganic composites for regenerative medicine requires appropriate fillers to enhance their mechanical robustness; for example, natural bones are composed mainly of HAp supported by collagen fibers. In this regard, many efforts have been made to harness HAp as a bone substitute through its integration with reinforcing fibrous materials such as CNTs. We found that the formation of a PDA ad-layer on the surface of CNTs changed the hydrophobic CNTs to become bioactive. This enabled efficient interaction between the CNTs and mineral ions (e.g., Ca2+), which facilitated the mineralization of HAp. CNTs functionalized with PDA (CNT-PDA) highly accelerated the formation of HAp when incubated in a simulated body fluid and exhibited a minimal cytotoxic effect on bone osteoblast cells compared to pristine or carboxylated CNTs. Our results show the potential of CNT-PDA as a scaffold material for bone tissue regeneration and implantation.

Silicon in living organisms and new-generation biocomposite materials (review)

The effect of silicon compounds on the formation and growth of natural bone tissue is examined, and the concentrations of silicon compounds in different organ tissues are presented. The inductive action of different implantation substrates containing silica on the vital activity of cultures of osteogenic cells is described. It is suggested that the process resulting in bonding between bone tissue and silicate implantation material is affected by the presence of a substantial number of silanol groups on the surface of the material, which determine its high hydrophilicity. It is shown that the solubility of silicate glasses depends on the presence in them of a phase which corresponds to the composition of liquid glass, and its role in the biodegradation of the materials in physiological media is described.

Fabrication of bioceramic/biopolymer bone implants using selective laser sintering

This paper presents an overview of the research work carried out for the rapid manufacture of hydroxyapatite (HA) based components by means of Selective Laser Sintering (SLS) technique, to be used for bone tissue implantation aiming to replace and/or repair bone defects due to traumatised, damaged or lost bone. SLS is a Rapid Prototyping Technology (RPT) that selectively sinters powders of engineering materials by means of a CO 2 laser. HA is a bioceramic used since several years for medical applications although being mainly processed by conventional methods (cast, machined or manually produced). For this purpose CAD/CAM, RPT and medical imaging techniques were integrated and this enabled the customised production of anatomical models. This approach provides a direct method of producing HA-based prostheses.

Biological Response to Wollastonite Doped α-Tricalcium Phosphate Implants in Hard and Soft Tissues in Rats

The biological response following subcutaneous and bone implantation of β-wollastonite(β-W)-doped α-tricalcium phosphate bioceramics in rats was evaluated. Tested materials were: tricalcium phosphate (TCP), consisting of a mixture of α- and β-polymorphs; TCP doped with 5 wt. % of β-W (TCP5W), composed of α-TCP as only crystalline phase; and TCP doped with 15 wt. % of β-W (TCP15), containing crystalline α-TCP and β-W. Cylinders of 2x1 mm were implanted in tibiae and backs of adult male Rattus norvegicus, Holtzman rats. After 7, 30 and 120 days, animals were sacrificed and the tissue blocks containing the implants were excised, fixed and processed for histological examination. TCP, TCP5W and TCP15W implants were biocompatible but neither bioactive nor biodegradable in rat subcutaneous tissue. They were not osteoinductive in connective tissue either. However, in rat bone tissue β-W-doped α-TCP implants (TCP5W and TCP15W) were bioactive, biodegradable and osteoconductive. The rates of biodegradation and new bone formation observed for TCP5W and TCP15W implants in rat bone tissue were greater than for non-doped TCP.

Establishment of CXCR4-small interfering RNA retrovirus vector driven by human prostate-specific antigen promoter and its biological effects on prostate cancer in vitro and in vivo

CXC chemokine receptor-4 (CXCR4) is closely involved in bone metastasis of prostate cancer, and CXCR4 levels are frequently increased in prostate cancer cells and tissues. In the present study, its biological effects on prostate cancer in vitro and in vivo and feasibility to be a therapy target were investigated using a RNA interfering retrovirus vector targeting CXCR4 gene driven by human prostate-specific antigen promoter (pPSA). We established a pPSA-siCXCR4 retrovirus vector and transfected prostate cancer cell PC-3m, LNCaP and breast cancer cell MCF-7, respectively. The expression of CXCR4 mRNA and protein was detected by RT-PCR and western blot, and the ability of adhesion, migration, invasion of prostate cancer cells was assessed using Transwell chamber. A metastasizing model using BALB/cA mice with human bone tissue implantation was established too, and transfected prostate cancer cells were via caudal vein. Survival time of mice suffering bone metastatic tumor as well as the weight and volume of these tumors were recorded and analyzed. The expression of CXCR4 mRNA and protein in androgen-responsive LNCaP cells was blocked by the pPSA-siCXCR4 vector, but it could not work in non androgen-responsive PC-3m cell and breast cancer cell MCF-7. The results of experiments in vitro also showed that the adhesion, transendothelial migration and invasive ability of transfected LNCaP cells were impaired, while there was no change in PC-3m and MCF-7 cells after transfection. pPSA-siCXCR4 represented a similar inhibitory effect in fluorescent bone metastasis model of LNCaP cells compared with PC-3m cells. These results suggest that the downstream siRNA controlled by PSA promoter in retrovirus system can express selectively in androgen-responsive prostate cancer in vitro and in vivo, and CXCR4 plays an important role in prostate cancer metastasis. We believe that the pPSA-siCXCR4 retrovirus vector is a potential choice in gene therapy for androgen-responsive prostate cancer.