Collagen I-coated titanium surfaces: Mesenchymal cell adhesion andin vivo evaluation in trabecular bone implants

Preliminary Evaluation of Bioactive Collagen-Polyphenol Surface Nanolayers on Titanium Implants: An X-ray Photoelectron Spectroscopy and Bone Implant Study

To endow an implant surface with enhanced properties to ensure an appropriate seal with the host tissue for inflammation/infection resistance, next-generation bone implant collagen-polyphenol nanolayers were built on conventional titanium surfaces through a multilayer approach. X-ray Photoelectron Spectroscopy (XPS) analysis was performed to investigate the chemical arrangement of molecules within the surface layer and to provide an estimate of their thickness. A short-term (2 and 4 weeks) in vivo test of bone implants in a healthy rabbit model was performed to check possible side effects of the soft surface layer on early phases of osteointegration, leading to secondary stability. Results show the building up of the different nanolayers on top of titanium, resulting in a final composite collagen-polyphenol surface and a layer thickness of about 10 nm. In vivo tests performed on machined and state-of-the-art microrough titanium implants do not show significant differences between coated and uncoated samples, as the surface microroughness remains the main driver of bone-to-implant contact. These results confirm that the surface nanolayer does not interfere with the onset and progression of implant osteointegration and prompt the green light for specific investigations of the potential merits of this bioactive coating as an enhancer of the device/tissue seal.

Improved Biocompatibility and Osseointegration of Nanostructured Calcium-Incorporated Titanium Implant Surface Treatment (XPEED®)

Surface treatment of implants facilitates osseointegration, with nanostructured surfaces exhibiting accelerated peri-implant bone regeneration. This study compared bone-to-implant contact (BIC) in implants with hydroxyapatite (HA), sand-blasted and acid-etched (SLA), and SLA with calcium (Ca)-coated (XPEED®) surfaces. Seventy-five disk-shaped grade 4 Ti specimens divided into three groups were prepared, with 16 implants per group tested in New Zealand white rabbits. Surface characterization was performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), digital microscopy, and a contact angle analyzer. Cell viability, proliferation, and adhesion were assessed using MC3T3-E1 cells. Apatite formation was evaluated using modified simulated body fluid (m-SBF) incubation. After 4 weeks of healing, the outcomes reviewed were BIC, bone area (BA), removal torque tests, and histomorphometric evaluation. A microstructure analysis revealed irregular pores across all groups, with the XPEED group exhibiting a nanostructured Ca-coated surface. Surface characterization showed a crystalline CaTiO3 layer on XPEED surfaces, with evenly distributed Ca penetrating the implants. All surfaces provided excellent environments for cell growth. The XPEED and SLA groups showed significantly higher cell density and viability with superior osseointegration than HA (p < 0.05); XPEED exhibited the highest absorbance values. Thus, XPEED surface treatment improved implant performance, biocompatibility, stability, and osseointegration.

Surface coating of orthopedic implant to enhance the osseointegration and reduction of bacterial colonization: a review

The use of orthopedic implants in surgical technology has fostered restoration of physiological functions. Along with successful treatment, orthopedic implants suffer from various complications and fail to offer functions correspondent to native physiology. The major problems include aseptic and septic loosening due to bone nonunion and implant site infection due to bacterial colonization. Crucial advances in material selection in the design and development of coating matrixes an opportunity for the prevention of implant failure. However, many coating materials are limited in in-vitro testing and few of them thrive in clinical tests. The rate of implant failure has surged with the increasing rates of revision surgery creating physical and sensitive discomfort as well as economic burdens. To overcome critical pathogenic activities several systematic coating techniques have been developed offering excellent results that combat infection and enhance bone integration. This review article includes some more common implant coating matrixes with excellent in vitro and in vivo results focusing on infection rates, causes, complications, coating materials, host immune responses and significant research gaps. This study provides a comprehensive overview of potential coating technology, with functional combination coatings which are focused on ultimate clinical practice with substantial improvement on in-vivo tests. This includes the development of rapidly growing hydrogel coating techniques with the potential to generate several accurate and precise coating procedures.

Biochemical Modification of Titanium Oral Implants: Evidence from In Vivo Studies

The discovery of osseointegration of titanium implants revolutionized the dental prosthesis field. Traditionally, implants have a surface that is processed by additive or subtractive techniques, which have positive effects on the osseointegration process by altering the topography. In the last decade, innovative implant surfaces have been developed, on which biologically active molecules have been immobilized with the aim of increasing stimulation at the implant-biological tissue interface, thus favoring the quality of osseointegration. Among these molecules, some are normally present in the human body, and the techniques for the immobilization of these molecules on the implant surface have been called Biochemical Modification of Titanium Surfaces (BMTiS). Different techniques have been described in order to immobilize those biomolecules on titanium implant surfaces. The aim of the present paper is to present evidence, available from in vivo studies, about the effects of biochemical modification of titanium oral implants on osseointegration.

A Versatile Surface Modification Method via Vapor-phase Deposited Functional Polymer Films for Biomedical Device Applications

For last two decades, the demand for precisely engineered three-dimensional structures has increased continuously for the developments of biomaterials. With the recent advances in micro- and nano-fabrication techniques, various devices with complex surface geometries have been devised and produced in the pharmaceutical and medical fields for various biomedical applications including drug delivery and biosensors. These advanced biomaterials have been designed to mimic the natural environments of tissues more closely and to enhance the performance for their corresponding biomedical applications. One of the important aspects in the rational design of biomaterials is how to configure the surface of the biomedical devices for better control of the chemical and physical properties of the bioactive surfaces without compromising their bulk characteristics. In this viewpoint, it of critical importance to secure a versatile method to modify the surface of various biomedical devices. Recently, a vapor phase method, termed initiated chemical vapor deposition (iCVD) has emerged as damage-free method highly beneficial for the conformal deposition of various functional polymer films onto many kinds of micro- and nano-structured surfaces without restrictions on the substrate material or geometry, which is not trivial to achieve by conventional solution-based surface functionalization methods. With proper structural design, the functional polymer thin film via iCVD can impart required functionality to the biomaterial surfaces while maintaining the fine structure thereon. We believe the iCVD technique can be not only a valuable approach towards fundamental cell-material studies, but also of great importance as a platform technology to extend to other prospective biomaterial designs and material interface modifications for biomedical applications.

An alternative ex vivo method to evaluate the osseointegration of Ti-6Al-4V alloy also combined with collagen

Due to the increasing number of orthopedic implantation surgery and advancements in biomaterial manufacturing, chemistry and topography, there is an increasing need of reliable and rapid methods for the preclinical investigation of osseointegration and bone ingrowth. Implant surface composition and topography increase osteogenicity, osteoinductivity, osteoconductivity and osseointegration of a prosthesis. Among the biomaterials used to manufacture an orthopedic prosthesis, titanium alloy (Ti-6Al-4V) is the most used. Type I collagen (COLL I) induces cell function, adhesion, differentiation and bone extracellular matrix component secretion and it is reported to improve osseointegration if immobilized on the alloy surface. The aim of the present study was to evaluate the feasibility of an alternative ex vivo model, developed by culturing rabbit cortical bone segments with Ti-6Al-4V alloy cylinders (Ti-POR), fabricated through the process of electron beam melting (EBM), to evaluate osseointegration. In addition, a comparison was made with Ti-POR coated with COLL I (Ti-POR-COLL) to evaluate osseointegration in terms of bone-to-implant contact (BIC) and new bone formation (nBAr/TAr) at 30, 60 and 90 d of culture. After 30 and 60 d of culture, BIC and nBAr/TAr resulted significantly higher in Ti-POR-COLL implants than in Ti-POR. No differences have been found at 90 d of culture. With the developed model it was possible to distinguish the biomaterial properties and behavior. This study defined and confirmed for the first time the validity of the alternative ex vivo method to evaluate osseointegration and that COLL I improves osseointegration and bone growth of Ti-6Al-4V fabricated through EBM.

Antibacterial Layer-by-Layer Coatings for Medical Implants

The widespread occurrence of nosocomial infections and the emergence of new bacterial strands calls for the development of antibacterial coatings with localized antibacterial action that are capable of facing the challenges posed by increasing bacterial resistance to antibiotics. The Layer-by-Layer (LbL) technique, based on the alternating assembly of oppositely charged polyelectrolytes, can be applied for the non-covalent modification of multiple substrates, including medical implants. Polyelectrolyte multilayers fabricated by the LbL technique have been extensively researched for the development of antibacterial coatings as they can be loaded with antibiotics, antibacterial peptides, nanoparticles with bactericide action, in addition to being capable of restricting adhesion of bacteria to surfaces. In this review, the different approaches that apply LbL for antibacterial coatings, emphasizing those that can be applied for implant modification are presented.

Osseointegration of additive manufacturing Ti-6Al-4V and Co-Cr-Mo alloys, with and without surface functionalization with hydroxyapatite and type I collagen

The introduction of additive manufacturing (AM) technologies has profoundly revolutionized the implant manufacturing industry, with a particularly significant impact on the field of orthopedics. Electron Beam Melting (EBM) and Direct Metal Laser Sintering (DMLS) represents AM fabrication techniques with a pivotal role in the realization of complex and innovative structure starting from virtual 3D model data. In this study, Ti-6Al-4V and Co-Cr-Mo materials, developed by EBM (Ti-POR) and DMLS (Co-POR) techniques, respectively, with hydroxyapatite (Ti-POR + HA; Co-POR + HA) and type I collagen (Ti-POR-COLL; Co-POR-COLL) coatings, were implanted into lateral femoral condyles of rabbits. Osseointegration process was investigated by histological, histomorphometrical and microhardness evaluations at 4 and 12 weeks after implantation. Both Ti-6Al-4V and Co-Cr-Mo implants, with or without HA and COLL coatings, demonstrated good biocompatibility. As expected, HA coating hastened bone-to-implant contact (BIC) process, while collagen did not significantly improved the osseointegration process in comparison to controls. Regarding newly trabecular bone formation (B.Ar/T.Ar), Co-POR presented the highest values, significantly different from those of Co-POR-COLL. Over time, an increase of BIC parameter and a decrease of B.Ar/T.Ar were detected. Higher mineral apposition rate was observed for Ti-POR and Co-POR in comparison to Ti-POR-COLL and Co-POR-COLL, respectively, at 12 weeks. The same behavior was found for bone formation rate between Co-POR and Co-POR-COLL at 12 weeks. In conclusion, the AM materials guarantee a good osseointegration and provide a suitable environment for bone regeneration with the peculiarity of allowing personalized and patient-specific needs customization to further improve the long-term clinical outcomes.

Bone healing at collagenated bicortically installed implants: an experimental study in rabbits

PURPOSE

To study the healing at collagenated bicortically installed implants.

METHODS

Twenty albino New Zealand rabbits were used for implant installation. Two implants with a double acid etched surface, coated with a collagen type I or left uncoated, were installed bicortically in the metaphysis and in the diaphysis of each tibia. Ten rabbits were euthanized after 2 weeks and ten after 6 weeks after installation. Ground sections were prepared for histological analyses that were performed both in the cortical layers and in the marrow regions.

RESULTS

After 2 weeks of healing, highest amounts of new bone were found at the collagenated implants (43.2 ± 6.0%) compared to the standard implants (33.9 ± 6.1%; p = 0.022). After 6 weeks of healing, similar percentages of new bone were observed, being 51.8 ± 7.3% and 50.9 ± 9.6% (p = 0.678) for the standard and collagenated surfaces, respectively.

CONCLUSIONS

A coated surface with collagen type I promoted bone apposition in the earliest periods of healing. However, the effect vanished over time so that similar results were obtained after 6 weeks of healing.

Coating of a Sand-Blasted and Acid-Etched Implant Surface with a pH-Buffering Agent after Vacuum-UV Photofunctionalization

Ultraviolet (UV) photofunctionalization can reset the biological aging of titanium after the preparation and storage of dental implants by transforming hydrophobic titanium surfaces into superhydrophilic surfaces. Blood clot formation around the implant can initialize and promote the healing process at the bone–implant interface. The aim of this study is to evaluate and compare the capabilities of surface wettability and blood clotting of implants with a conventional sand-blasted and acid-etched surface (SA), a sand-blasted and acid-etched surface with vacuum-UV treatment (SA + VUV), and a sand-blasted and acid-etched surface coated with a pH-buffering agent after vacuum-UV treatment (SA + VUV + BS). Static and dynamic tests for surface wettability and blood clotting were performed in vitro for SA + VUV and SA + VUV + BS (n = 5), while hemostasis resulting from blood clotting was evaluated in vivo for SA, SA +VUV, and SA + VUV + BS (n = 4). A Kruskal–Wallis test showed statistically significant differences (p < 0.05) in all tests, with the exception of in vitro test of static blood clotting. VUV treatment is therefore effective at making an SA surface superhydrophilic as an alternative to routine UV-C radiation. The addition of a pH-buffering agent to SA + VUV also improved surface wettability and blood clotting, which are crucial for successful osseointegration.

Customizable Implant-specific and Tissue-Specific Extracellular Matrix Protein Coatings Fabricated Using Atmospheric Plasma

Progression in implant science has benefited from ample amount of technological contributions from various disciplines, including surface biotechnology. In this work, we successfully used atmospheric plasma to enhance the biological functions of surgical implants by coating them with extracellular matrix proteins. The developed collagen and laminin coatings demonstrate advantageous material properties. Chemical analysis by XPS and morphological investigation by SEM both suggested a robust coating. Contact angle goniometry and dissolution study in simulated body fluid (SBF) elicited increased hydrophilicity and physiological durability. Furthermore, these coatings exhibited improved biological interactions with human mesenchymal and neural stem cells (NSCs). Cell adhesion, proliferation, and differentiation proved markedly refined as shown by enzymatic detachment, flow cytometry, and ELISA data, respectively. Most importantly, using the pathway-specific PCR array, our study discovered dozens of deregulated genes during osteogenesis and neurogenesis on our newly fabricated ECM coatings. The coating-induced change in molecular profile serves as a promising clue for designing future implant-based therapy. Collectively, we present atmospheric plasma as a versatile tool for enhancing surgical implants, through customizable implant-specific and tissue-specific coatings.

Titanium-Tissue Interface Reaction and Its Control With Surface Treatment

Titanium (Ti) and its alloys are widely used for medical and dental implant devices-artificial joints, bone fixators, spinal fixators, dental implant, etc. -because they show excellent corrosion resistance and good hard-tissue compatibility (bone formation and bone bonding ability). Osseointegration is the first requirement of the interface structure between titanium and bone tissue. This concept of osseointegration was immediately spread to dental-materials researchers worldwide to show the advantages of titanium as an implant material compared with other metals. Since the concept of osseointegration was developed, the cause of osseointegration has been actively investigated. The surface chemical state, adsorption characteristics of protein, and bone tissue formation process have also been evaluated. To accelerate osseointegration, roughened and porous surfaces are effective. HA and TiO2 coatings prepared by plasma spray and an electrochemical technique, as well as alkalinization of the surface, are also effective to improve hard-tissue compatibility. Various immobilization techniques for biofunctional molecules have been developed for bone formation and prevention of platelet and bacteria adhesion. These techniques make it possible to apply Ti to a scaffold of tissue engineering. The elucidation of the mechanism of the excellent biocompatibility of Ti can provide a shorter way to develop optimal surfaces. This review should enhance the understanding of the properties and biocompatibility of Ti and highlight the significance of surface treatment.

Covalently-Linked Hyaluronan versus Acid Etched Titanium Dental Implants: A Crossover RCT in Humans

Biochemical modification of titanium surfaces (BMTiS) entails immobilization of biomolecules to implant surfaces in order to induce specific host responses. This crossover randomized clinical trial assesses clinical success and marginal bone resorption of dental implants bearing a surface molecular layer of covalently-linked hyaluronan in comparison with control implants up to 36 months after loading. Patients requiring bilateral implant rehabilitation received hyaluronan covered implants in one side of the mouth and traditional implants in the other side. Two months after the first surgery, a second surgery was undergone to uncover the screw and to place a healing abutment. After two weeks, the operator proceeded with prosthetic procedures. Implants were evaluated by periapical radiographs and the crestal bone level was recorded at mesial and distal sites—at baseline and up to 36 months. One hundred and six implants were positioned, 52 HY-coated, and 48 controls were followed up. No differences were observed in terms of insertion and stability, wound healing, implant success, and crestal bone resorption at any time considered. All interventions had an optimal healing, and no adverse events were recorded. This trial shows, for the first time, a successful use in humans of biochemical-modified implants in routine clinical practice and in healthy patients and tissues with satisfactory outcomes.

Biomimetic Surfaces Coated with Covalently Immobilized Collagen Type I: An X-Ray Photoelectron Spectroscopy, Atomic Force Microscopy, Micro-CT and Histomorphometrical Study in Rabbits

Background: The process of osseointegration of dental implants is characterized by healing phenomena at the level of the interface between the surface and the bone. Implant surface modification has been introduced in order to increase the level of osseointegration. The purpose of this study is to evaluate the influence of biofunctional coatings for dental implants and the bone healing response in a rabbit model. The implant surface coated with collagen type I was analyzed through X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), micro-CT and histologically. Methods: The sandblasted and double acid etched surface coated with collagen type I, and uncoated sandblasted and double acid etched surface were evaluated by X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) analysis in order evaluate the different morphology. In vivo, a total of 36 implants were positioned in rabbit articular femoral knee-joint, 18 fixtures for each surface. Micro-CT scans, histological and histomorphometrical analysis were conducted at 15, 30 and 60 days. Results: A histological statistical differences were evident at 15, 30 and 60 days (p < 0.001). Both implant surfaces showed a close interaction with newly formed bone. Mature bone appeared in close contact with the surface of the fixture. The AFM outcome showed a similar roughness for both surfaces. Conclusion: However, the final results showed that a coating of collagen type I on the implant surface represents a promising procedure able to improve osseointegration, especially in regions with a low bone quality.

Enhanced Bioactivity of Collagen Fiber Functionalized with Room Temperature Atomic Layer Deposited Titania

Surface modifications of a biomaterial like collagen are crucial in improving the surface properties and thus enhancing the functionality and performance of such a material for a variety of biomedical applications. In this study, a commercially available collagen membrane's surface was functionalized by depositing an ultrathin film of titania or titanium dioxide (TiO₂) using a room temperature atomic layer deposition (ALD) process. A novel titanium precursor-oxidizer combination was used for this process in a custom-made ALD reactor. Surface characterizations revealed successful deposition of uniform, conformal TiO₂ thin film on the collagen fibrillar surface, and consequently, the fibers became thicker making the membrane pores smaller. The in vitro bioactivity of the ALD-TiO₂ thin film coated collagen was investigated for the first time using cell proliferation and a calcium phosphate mineralization assay. The TiO₂-coated collagen demonstrated improved biocompatibility promoting higher growth and proliferation of human osteoblastic and mesenchymal stem cells when compared to that of noncoated collagen. A higher level of calcium phosphate or apatite formation was observed on ALD modified collagen surface as compared to that on noncoated collagen. Therefore, this novel material can be promising in bone tissue engineering applications.

An in vivo study on the effect of coating stability on osteointegration performance of collagen/hyaluronic acid multilayer modified titanium implants

Aseptic loosening of implant is one of the main causes of Ti-based implant failure. In our previous work, a novel stable collagen/hyaluronic acid (Col/HA) multilayer modified titanium coatings (TCs) was developed by layer-by-layer (LBL) covalent immobilization technique, which showed enhanced biological properties compared with TCs that were physically absorbed with Col/HA multilayer in vitro. In this study, a rabbit model with femur condyle defect was employed to compare the osteointegration performance of them. Results indicated that Col/HA multilayer with favourable stability could better facilitate osteogenesis around implants and bone-implant contact. The Col/HA multilayer covalent-immobilized TC may reduce aseptic loosening of implant.

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Stability of Col/HA multilayer could promote the growth of trabecular bone around implants.

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New bone was induced to grow into the hole of Col/HA multilayer covalently immobilized TC implants.

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New bone contacted with Col/HA multilayer covalently immobilized TC implants closely.

clickECM: Development of a cell-derived extracellular matrix with azide functionalities

In vitro cultured cells produce a complex extracellular matrix (ECM) that remains intact after decellularization. The biological complexity derived from the variety of distinct ECM molecules makes these matrices ideal candidates for biomaterials. Biomaterials with the ability to guide cell function are a topic of high interest in biomaterial development. However, these matrices lack specific addressable functional groups, which are often required for their use as a biomaterial. Due to the biological complexity of the cell-derived ECM, it is a challenge to incorporate such functional groups without affecting the integrity of the biomolecules within the ECM. The azide-alkyne cycloaddition (click reaction, Huisgen-reaction) is an efficient and specific ligation reaction that is known to be biocompatible when strained alkynes are used to avoid the use of copper (I) as a catalyst. In our work, the ubiquitous modification of a fibroblast cell-derived ECM with azides was achieved through metabolic oligosaccharide engineering by adding the azide-modified monosaccharide Ac₄GalNAz (1,3,4,6-tetra-O-acetyl-N-azidoacetylgalactosamine) to the cell culture medium. The resulting azide-modified network remained intact after removing the cells by lysis and the molecular structure of the ECM proteins was unimpaired after a gentle homogenization process. The biological composition was characterized in order to show that the functionalization does not impair the complexity and integrity of the ECM. The azides within this "clickECM" could be accessed by small molecules (such as an alkyne-modified fluorophore) or by surface-bound cyclooctynes to achieve a covalent coating with clickECM.

STATEMENT OF SIGNIFICANCE

The clickECM was produced by the incorporation of azide-functionalized sugar analogues into the extracellular glycans of fibroblast cell cultures by metabolic oligosaccharide engineering. By introducing these azide groups into the glycan structures, we enabled this cell-derived ECM for bioorthogonal click reactions. Click chemistry provides extremely specific reactions with high efficiency, high selectivity, and high reaction yields. We could show that the azide functionalities within the clickECM are chemically accessible. Based on our here described clickECM technique it will be possible to create and investigate new clickECM materials with tunable bioactive properties and additional functionalities, which offers a promising approach for basic and applied research in the field of biomaterial science, biomedical applications, and tissue engineering.

Dental implant bioactive surface modifications and their effects on osseointegration: a review

BACKGROUND

The purpose of this article is to review and update the current developments of biologically active dental implant surfaces and their effect on osseointegration.

METHODS

PubMed was searched for entries from January 2006 to January 2016. Only in-vivo studies that evaluated the effects of biomolecular coatings on titanium dental implants inserted into the bone of animals or humans were included.

RESULTS

Thirty four non-review studies provided data and observations were included in this review. Within the criteria, four categories of biomolecular coatings were evaluated. The potential biomolecules include bone morphogenetic proteins in 8 articles, other growth factors in 8 articles, peptides in 5 articles, and extracellular matrix in 13 articles. Most articles had a healing period of 1 to 3 months and the longest time of study was 6 months. In addition, all studies comprised of implants inserted in animals except for one, which evaluated implants placed in both animals and humans. The results indicate that dental implant surface modification with biological molecules seem to improve performance as demonstrated by histomorphometric analysis (such as percentage of bone-to-implant contact and peri-implant bone density) and biomechanical testing (such as removal torque, push-out/pull-out tests, and resonance frequency analysis).

CONCLUSIONS

Bioactive surface modifications on implant surfaces do not always offer a beneficial effect on osseointegration. Nevertheless, surface modifications of titanium dental implants with biomolecular coatings seem to promote peri-implant bone formation, resulting in enhanced osseointegration during the early stages of healing. However, long-term clinical studies are needed to validate this result. In addition, clinicians must keep in mind that results from animal experiments need not necessarily reflect the human clinical reality.

Dental implant bioactive surface modifications and their effects on osseointegration: a review

Background

The purpose of this article is to review and update the current developments of biologically active dental implant surfaces and their effect on osseointegration.

Methods

PubMed was searched for entries from January 2006 to January 2016. Only in-vivo studies that evaluated the effects of biomolecular coatings on titanium dental implants inserted into the bone of animals or humans were included.

Results

Thirty four non-review studies provided data and observations were included in this review. Within the criteria, four categories of biomolecular coatings were evaluated. The potential biomolecules include bone morphogenetic proteins in 8 articles, other growth factors in 8 articles, peptides in 5 articles, and extracellular matrix in 13 articles. Most articles had a healing period of 1 to 3 months and the longest time of study was 6 months. In addition, all studies comprised of implants inserted in animals except for one, which evaluated implants placed in both animals and humans. The results indicate that dental implant surface modification with biological molecules seem to improve performance as demonstrated by histomorphometric analysis (such as percentage of bone-to-implant contact and peri-implant bone density) and biomechanical testing (such as removal torque, push-out/pull-out tests, and resonance frequency analysis).

Conclusions

Bioactive surface modifications on implant surfaces do not always offer a beneficial effect on osseointegration. Nevertheless, surface modifications of titanium dental implants with biomolecular coatings seem to promote peri-implant bone formation, resulting in enhanced osseointegration during the early stages of healing. However, long-term clinical studies are needed to validate this result. In addition, clinicians must keep in mind that results from animal experiments need not necessarily reflect the human clinical reality.

Activity of vancomycin release from bioinspired coatings of hydroxyapatite or TiO2 nanotubes

Herein we investigate the efficiency of various biomimetic coatings for localized drug delivery, using vancomycin as key therapeutic drug, which is a widely used antibiotic for the treatment of strong infections caused by positive Gram bacteria. We evaluate classical hydroxyapatite and biomimetic hydroxyapatite-collagen coatings obtained by electrochemical deposition as well as TiO₂ nanotubes arrays obtained by electrochemical anodization. Surface morphology, compositional and structural data confirm the incorporation of vancomycin into the layers and drug release profiles for vancomycin evaluate their release ability. Namely, hydroxyapatite coatings lead to a ≈92% vancomycin release after 30h and hydroxyapatite-collagen to 85%, while the TiO₂ nanotubes layers lead to 78% release. The antibacterial effect of such drug loaded coatings is evaluated against S. aureus (Gram-positive bacteria). Our study shows that the vancomycin incorporated hydroxyapatite coatings lead to a faster release, while the nanotubular coatings may lead to longer time release and additionally both types of coatings ensure a good antibacterial inhibition.

Classification and Effects of Implant Surface Modification on the Bone: Human Cell-Based In Vitro Studies

Implant surfaces are continuously being improved to achieve faster osseointegration and a stronger bone to implant interface. This review will present the various implant surfaces, the parameters for implant surface characterization, and the corresponding in vitro human cell-based studies determining the strength and quality of the bone-implant contact. These in vitro cell-based studies are the basis for animal and clinical studies and are the prelude to further reviews on how these surfaces would perform when subjected to the oral environment and functional loading.

In Vitro Cytokine Expression and In Vivo Healing and Inflammatory Response to a Collagen-Coated Synthetic Bone Filler

The goal of the present work was to investigate the relationship between in vivo healing and inflammatory response and in vitro cytokine expression by macrophages of a synthetic bone filler (25% hydroxylapatite-75% β-tricalcium phosphate) bearing a surface nanolayer of collagen. A clinically accepted, state-of-the-art xenograft material was used as a “negative control,” that is, as a material that provides the correct clinical response for the intended use. In vitro data show that both materials exert a very low stimulation of proinflammatory cytokines by macrophages, and this was confirmed by the very mild inflammatory response detected in in vivo tests of local response in a rabbit model. Also, in vitro findings suggest a different mechanism of healing for the test and the control material, with a higher regenerative activity for the synthetic, resorbable filler, as confirmed by in vivo observation and literature reports. Thus, the simple in vitro model adopted provides a reasonable forecast of in vivo results, suggesting that new product development can be guided by in vitro tuning of cell-materials interactions.

Covalently immobilised type I collagen facilitates osteoconduction and osseointegration of titanium coated implants

Background/Objective

Plasma-sprayed titanium coating (TC) with rough surfaces has been successfully applied in hip or knee prostheses. This study aimed to investigate the osteoconduction and osseointegration of Type I collagen covalently immobilised on TC (TC-AAC) compared with those of TC.

Methods

In vitro, the migration of human mesenchymal stem cells (hMSCs) on TC and TC-AAC was observed by scanning electron microscopy and visualised fluorescent live/dead assay. In vivo, a rabbit model with femur condyle defect was employed, and implants of TC and TC-AAC were embedded into the femur condyles.

Results

Collagen immobilised on TC could promote hMSCs' migration into the porous structure of the TC. Micro computed tomography images showed that bone trabeculae were significantly more abundant around TC-AAC implants than around TC implants. Fluorescence micrographs indicated more active new-bone formation around implants in the TC-AAC group than in the TC group. The measurement of bone–implant contact on histological sections indicated significantly greater osteointegration around TC-AAC implants than around TC ones.

Conclusion

Immobilised Type I collagen could improve the osteoconduction and osseointegration of TC implants.

Surface chemistry and effects on bone regeneration of a novel biomimetic synthetic bone filler

The paper presents results of physico-chemical and biological investigations of a surface-engineered synthetic bone filler. Surface analysis confirms that the ceramic phosphate granules present a collagen nanolayer to the surrounding environment. Cell cultures tests show that, in agreement with literature reports, surface-immobilized collagen molecular cues can stimulate progression along the osteogenic pathway of undifferentiated human mesenchymal cells. Finally, in vivo test in a rabbit model of critical bone defects shows statistically significant increase of bone volume and mineral apposition rate between the biomimetic bone filler and collagen-free control. All together, obtained data confirm that biomolecular surface engineering can upgrade the properties of implant device, by promoting more specific and targeted implant-host cells interactions.

Bioactive coatings for orthopaedic implants-recent trends in development of implant coatings

Joint replacement is a major orthopaedic procedure used to treat joint osteoarthritis. Aseptic loosening and infection are the two most significant causes of prosthetic implant failure. The ideal implant should be able to promote osteointegration, deter bacterial adhesion and minimize prosthetic infection. Recent developments in material science and cell biology have seen the development of new orthopaedic implant coatings to address these issues. Coatings consisting of bioceramics, extracellular matrix proteins, biological peptides or growth factors impart bioactivity and biocompatibility to the metallic surface of conventional orthopaedic prosthesis that promote bone ingrowth and differentiation of stem cells into osteoblasts leading to enhanced osteointegration of the implant. Furthermore, coatings such as silver, nitric oxide, antibiotics, antiseptics and antimicrobial peptides with anti-microbial properties have also been developed, which show promise in reducing bacterial adhesion and prosthetic infections. This review summarizes some of the recent developments in coatings for orthopaedic implants.

Evaluation of biocompatibility using in vitro methods: interpretation and limitations

The in vitro biocompatibility of novel materials has to be proven before a material can be used as component of a medical device. This must be done in cell culture tests according to internationally recognized standard protocols. Subsequently, preclinical and clinical tests must be performed to verify the safety of the new material and device. The present chapter focuses on the first step, the in vitro testing according to ISO 10993-5, and critically discusses its limited significance. Alternative strategies and a brief overview of activities to improve the current in vitro tests are presented in the concluding section.

Hydroxyapatite and collagen combination-coated dental implants display better bone formation in the peri-implant area than the same combination plus bone morphogenetic protein-2-coated implants, hydroxyapatite only coated implants, and uncoated implants

PURPOSE

The objective of this study was to compare peri-implant bone formation among uncoated (UC), hydroxyapatite (HA), collagen plus HA (CH), and collagen, HA, plus bone morphogenetic protein-2 (BMP-2) implant groups.

MATERIALS AND METHODS

Implants in the UC group had acid-etched surfaces. The surface coating was applied using the aerosol deposition method. The coated surfaces were examined by scanning electron microscopy, x-ray diffraction (XRD), and Fourier-transformed infrared absorption analysis. Subsequently, 6 implants from each group (total, 24 implants) were installed in the tibias of rabbits. The animals were sacrificed at 6 weeks after implant installation. Peri-implant bone formation and bone-to-implant contact (BIC) were measured in histologic sections. Significant differences among groups were evaluated using analysis of variance.

RESULTS

Based on the measured XRD patterns, there was a characteristic HA phase (International Centre for Diffraction Data [ICDD], 086-0740) coated on the titanium (ICDD, 089-3725). Subsequent coating processes for collagen and BMP-2 did not display additional diffraction peaks, but maintained the diffraction patterns of the HA-coated titanium. The presence of collagen was verified by infrared absorption analysis. When comparing these modifications with UC surfaces, only the CH coating displayed significantly greater peri-implant bone formation and BIC (P = .003 and P < .001, respectively). Adding BMP-2 to the implant surface did not produce any advantage compared with the CH coating.

CONCLUSIONS

In this study, the CH group displayed significantly greater new bone formation and BIC than the other groups. There was no significant difference among the other groups.

Fabrication and in vitro evaluation of stable collagen/hyaluronic acid biomimetic multilayer on titanium coatings

Layer-by-layer (LBL) self-assembly technique has been proved to be a highly effective method to immobilize the main components of the extracellular matrix such as collagen and hyaluronic acid on titanium-based implants and form a polyelectrolyte multilayer (PEM) film by electrostatic interaction. However, the formed PEM film is unstable in the physiological environment and affects the long-time effectiveness of PEM film. In this study, a modified LBL technology has been developed to fabricate a stable collagen/hyaluronic acid (Col/HA) PEM film on titanium coating (TC) by introducing covalent immobilization. Scanning electron microscopy, diffuse reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the PEM film. Results of Sirius red staining demonstrated that the chemical stability of PEM film was greatly improved by covalent cross-linking. Cell culture assays further illustrated that the functions of human mesenchymal stem cells, such as attachment, spreading, proliferation and differentiation, were obviously enhanced by the covalently immobilized Col/HA PEM on TCs compared with the absorbed Col/HA PEM. The improved stability and biological properties of the Col/HA PEM covalently immobilized TC may be beneficial to the early osseointegration of the implants.

Preparation and antibiotic drug release of mineralized collagen coatings on titanium

In this study, a mineralized collagen coating was electrolytically deposited onto titanium. The results showed that the mineralized collagen coatings with dense or porous morphology could be obtained. The mineral phase was mainly hydroxyapatite. In vitro evaluation showed the mineralized collagen coatings were stable in Kokubo's simulated body fluid, and displayed a good cytocompatibility in the cell multiplication test. The mineralized collagen coatings loaded with vancomycin hydrochloride showed an inhibitory effect on the growth of S. aureus. The present mineralized collagen coating demonstrates good suitability for surface modification of orthopedic metal implants.

The cytocompatibility and osseointegration of the Ti implants with XPEED® surfaces

OBJECTIVES

This study evaluated cytocompatibility and osseointegration of the titanium (Ti) implants with resorbable blast media (RBM) surfaces produced by grit-blasting or XPEED(®) surfaces by coating of the nanostructured calcium.

MATERIAL AND METHODS

Ti implants with XPEED(®) surfaces were hydrothermally prepared from Ti implants with RBM surfaces in a solution containing alkaline calcium. The surface characteristics were evaluated by using a scanning electron microscope (SEM) and surface roughness measuring system. Apatite formation was measured with SEM after immersion in modified-simulated body fluid and the amount of calcium released was measured by inductively coupled plasma optical emission. The cell proliferation was investigated by MTT assay and the cell attachment was evaluated by SEM in MC3T3-E1 pre-osteoblast cells. Thirty implants with RBM surfaces and 30 implants with XPEED(®) surfaces were placed in the proximal tibiae and in the femoral condyles of 10 New Zealand White rabbits. The osseointegration was evaluated by a removal torque test in the proximal tibiae and by histomorphometric analysis in the femoral condyles 4 weeks after implantation.

RESULTS

The Ti implants with XPEED(®) surfaces showed a similar surface morphology and surface roughness to those of the Ti implants with RBM surfaces. The amount of calcium ions released from the surface of the Ti implants with XPEED(®) surfaces was much more than the Ti implants with RBM surfaces (P < 0.05). The cell proliferation and cell attachment of the Ti implants showed a similar pattern to those of the Ti implants with RBM surfaces (P > 0.1). Apatite deposition significantly increased in all surfaces of the Ti implants with XPEED(®) surfaces. The removable torque value (P = 0.038) and percentage of bone-to-implant contact (BIC%) (P = 0.03) was enhanced in the Ti implants with XPEED(®) surfaces.

CONCLUSION

The Ti implants with XPEED(®) surfaces significantly enhanced apatite formation, removal torque value, and the BIC%. The Ti implants with XPEED(®) surfaces may induce strong bone integration by improving osseointegration of grit-blasted Ti implants in areas of poor quality bone.

Fibrin-targeted block copolymers for the prevention of postsurgical adhesions

Despite advances in surgical methods, postsurgical adhesions (PSA) remain a significant clinical challenge affecting millions of patients each year. These permanent fibrous connections between tissues result from the bridging of wounded internal surfaces by an extended fibrin gel matrix (FGM). Adhesion formation is a result of a systems level convergence of wound healing pathways, complicating the design of materials that could inhibit their occurrence. In this study, a systematic approach that identifies key material properties required for functional performance optimization was used to design a new fibrin-targeted PSA prevention material. A series of multifunctional polymers with varied molecular architectures was synthesized to investigate the effect of changing polymer structural parameters on the ability to disrupt the formation of an extended FGM. Initial studies in a murine adhesion model demonstrated a statistically significant reduction in the degree of PSA formation, demonstrating the potential value of this systematic approach.

Heterofunctional nanosheet controlling cell adhesion properties by collagen coating

Recently, biomaterials have been widely used in a variety of medical applications. We previously reported that a poly-l-lactic acid (PLLA) nanosheet shows anti-adhesive properties and constitutes a useful biomaterial for preventing unwanted wound adhesion in surgical operations. In this article, we examine whether the PLLA nanosheet can be specifically modified with biomacromolecules on one surface only. Such an approach would endow each side of the nanosheet with discrete functions, that is anti-adhesive and pro-healing properties. We fabricated two distinct PLLA nanosheets: (i) collagen cast on the surface of a PLLA nanosheet (Col-Cast-PLLA) and (ii) collagen spin-coated on the nanosheet (Col-Spin-PLLA). In the Col-Spin-PLLA nanosheet, the collagen layer had a thickness of 5–10 nm on the PLLA surface and displayed increased hydrophilicity compared to both PLLA and Col-Cast-PLLA nanosheets. In addition, atomic force microscopy showed disorganized collagen fibril formation on the PLLA layer when covered using the spin-coating method, while apparent bundle formations of collagen were formed in the Col-Cast-PLLA nanosheet. The Col-Spin-PLLA nanosheet provided a microenvironment for cells to adhere and spread. By contrast, the Col-Cast-PLLA nanosheet displayed reduced cell adhesion compared to the Col-Spin-PLLA nanosheet. Consistent with these findings, immunocytochemical analysis clearly showed fine networks of actin filaments in cells cultured on the Col-Spin-PLLA, but not the Col-Cast-PLLA nanosheet. Therefore, the Col-Spin-PLLA nanosheet was shown to be more suitable for acting as a scaffold. In conclusion, we have succeeded in developing a heterofunctional nanosheet comprising a collagen modified side, which has the ability to rapidly adhere cells, and an unmodified side, which acts as an adhesion barrier, by using a spin-coating technique.

Gene expression of markers of osteogenic differentiation of human mesenchymal cells on collagen I-modified microrough titanium surfaces

Microrough, doubly acid etched titanium surfaces (Ti) were further modified by amination and covalent coupling of fibrillar collagen type I (ColTi). Human Mesenchymal Cells (HMC) adhesion and growth, and relevant osteogenic differentiation in nonosteogenic (basal) medium were evaluated by fluorescence microscopy, scanning electron microscopy, and RT-PCR for a three-week period. Results show strongly enhanced HMC adhesion and cell density at short experimental time on ColTi, together with complete spreading of the cell body over the microrough surface topography. RT-PCR analysis of several genes involved in osteogenesis indicate, since the first week of culturing, significant progression of HMC on ColTi along the osteogenic pathway. These results indicate that the adopted process of surface immobilization of collagen, mandatory to impart collagenase resistance in implant sites, does not impair biospecific interactions between HMC and collagen. Thus, it is possible to upgrade properties arising from the control of Ti surfaces topography by surface-chemistry driven enhanced recruitment of precursor osteogenic cells and pro-osteogenic stimula.

Relative influence of surface topography and surface chemistry on cell response to bone implant materials. Part 2: Biological aspects

A current medical challenge is the replacement of tissue which can be thought of in terms of bone tissue engineering approaches. The key problem in bone tissue engineering lies in associating bone stem cells with material supports or scaffolds that can be implanted in a patient. Beside bone tissue engineering approaches, these types of materials are used daily in orthopaedics and dental practice as permanent or transitory implants such as ceramic bone filling materials or metallic prostheses. Consequently, it is essential to better understand how bone cells interact with materials. For several years, the current authors and others have developed in vitro studies in order to elucidate the mechanisms underlying the response of human bone cells to implant surfaces. This paper reviews the current state of knowledge and proposes future directions for research in this domain.

The effect of water pyrolysis on the removal torque of titanium implant inserted in rabbit tibias

OBJECTIVE

The aim of this study is to examine the effect of oxidation with water pyrolysis (OWP) method on titanium (Ti) implants by comparing the bonding strength between bone and Ti implants that were inserted in the proximal tibia metaphysic of a rabbit for 12 weeks. The removal torque was measured to evaluate the bonding strength for different Ti implants with and without the OWP method.

MATERIAL AND METHODS

Nine sets of threaded Ti implants (ASTM grade 2) of diameter 3.75 mm and length 5 mm were prepared for the experiment. Each set was composed of four specimens; one was machine-prepared (group D) and the other three were threaded followed by the OWP method at 300°C (group A), 600°C (group B), and 800°C (group C) for 10 min, respectively. Each set was used for each adult rabbit. To eliminate the effect of the sites or the legs, each rabbit received all four implants, two in the left and two in the right leg, inserted in the proximal tibia metaphyses of the left leg, using a fixed block randomization. After 12 weeks, removal torque tests were carried out.

RESULTS

The mean removal torque for the control group D was 16.19 N cm, while the mean removal torque values for the OWP groups A, B, and C were 26.75, 31.51, and 41.05 N cm, respectively. The removal torques obtained from the OWP groups B and C (showing the rutile oxide structure) were significantly greater than that for the control group by Bonferroni's-corrected Wilcoxon's signed-rank test (P<0.05).

CONCLUSION

The strongest bonding between bone and group C (OWP method at 800°C) was confirmed by the comparison of removal torques.

Block copolymers for the rational design of self-forming postsurgical adhesion barriers

Post-surgical adhesions, abnormal fibrous linkages between adjacent tissue surfaces, represent one of the most common and significant complications facing surgical recovery today. Physical barriers and gels have been the most successful at limiting their formation, yet are not effective in cases where the pro-adhesive site is either unknown or difficult to reach (e.g. during laparoscopic surgery). In this work, poly(methacrylic acid-co-t-butylmethacrylate)-b-poly(ethylene glycol (M(N) = 1000) methacrylate) diblock and statistical copolymers were synthesized as a platform for designing self-forming adhesion barriers, which can attach to exposed pro-adhesive sites through binding with the positively charged extracellular matrix, basement membrane proteins and deposited fibrin. An experimental model based upon a quartz crystal microbalance with dissipation was developed to test the diblock copolymers ability (i) to adsorb to an amine-terminated self-assembled monolayer, and (ii) to inhibit subsequent protein adsorption. These results were also confirmed using an in vitro cell attachment model. As the mole fraction of methacrylic acid content increased, polymer adsorption increased. All synthesized diblock copolymers investigated provided high resistance to protein adsorption, with blockade ranging from 55% to 81%. Except for the uncharged control polymers, the ability of these materials to resist cellular attachment showed similar trends, with the suppression of attachment approaching 75%. Energy dissipation analysis and variable-angle spectroscopic ellipsometry revealed two competing adsorption mechanisms depending on the molecular properties of the polymer.

The osteogenic effect of electrosprayed nanoscale collagen/calcium phosphate coatings on titanium

For orthopedic and dental implants, the ultimate goal is to obtain a life-long secure anchoring of the implant in the native surrounding bone. To this end, nanoscale calcium phosphate (CaP) and collagen-CaP (col-CaP) composite coatings have been successfully deposited using the electrospray deposition (ESD) technique. In order to study to what extent the thickness of these coatings can be reduced without losing coating osteogenic properties, we have characterized the mechanical and biological coating properties using tape tests (ASTM D-3359) and in vitro cell culture experiments, respectively. Co-deposition of collagen significantly improved coating adhesive and cohesive strength, resulting in a remarkably high coating retention of up to 97% for coating thicknesses below 100 nm. In vitro cell culture experiments showed that electrosprayed CaP and col-CaP composite coatings enhanced osteoblast differentiation, leading to improved mineral deposition. This effect was most pronounced upon co-deposition of collagen with CaP, and these coatings displayed osteogenic effects even for a coating thickness of below 100 nm.