Enhanced repair of segmental bone defects in rabbit radius by porous tantalum scaffolds modified with the RGD peptide

Progress of research on the surface functionalization of tantalum and porous tantalum in bone tissue engineering

Tantalum and porous tantalum are ideal materials for making orthopedic implants due to their stable chemical properties and excellent biocompatibility. However, their utilization is still affected by loosening, infection, and peripheral inflammatory reactions, which sometimes ultimately lead to implant removal. An ideal bone implant should have exceptional biological activity, which can improve the surrounding biological microenvironment to enhance bone repair. Recent advances in surface functionalization have produced various strategies for developing compatibility between either of the two materials and their respective microenvironments. This review provides a systematic overview of state-of-the-art strategies for conferring biological functions to tantalum and porous tantalum implants. Furthermore, the review describes methods for preparing active surfaces and different bioactive substances that are used, summarizing their functions. Finally, this review discusses current challenges in the development of optimal bone implant materials.

Preparation, biological activity and antibacterial properties of tantalum surface-doped Ca2+/Zn2+nanorods

In this research, we utilize porous tantalum, known for its outstanding elastic modulus and biological properties, as a base material in biomedical applications. The human skeletal system is rich in elements like Ca and Zn. The role of Zn is crucial for achieving a spectrum of sterilizing effects, while Ca is known to effectively enhance cell differentiation and boost cellular activity. The focus of this study is the modification of porous tantalum using a hydrothermal method to synthesize Ca2+/Zn2+-doped Ta2O5nanorods. These nanorods are subjected to extensive characterization techniques to confirm their structure and composition. Additionally, their biological performance is evaluated through a range of tests, including antibacterial assessments, MTT assays, and bacteria/cell scanning electron microscopy (SEM) analyses. The objective is to determine the most effective method of surface modification for porous tantalum, thereby laying a foundational theoretical framework for its surface enhancement.

Surface hardening of Ti-Al-V superalloy spinal implant by using the boronization method

BACKGROUND

We compared the raw Ti-Al-V super alloy transpedicular implant screws with boronized and surface-hardened transpedicular implant screws.

OBJECTIVE

To improve patients' postoperative prognosis with the production of harder and less fragile screws.

METHODS

Surface hardening was achieved by applying green-body encapsulation of the specimen with elemental boron paste which is sintered at elevated temperatures to ensure the boron-metal diffusion. Boron transported into the Ti-Al-V super alloy matrix gradually while suppressing aluminum and a homogeneously boronized surface with a thickness of ∼15 microns was obtained. The uniform external shell was enriched with TiB2, which is one of the hardest ceramics. The Ti-Al-V core material, where boron penetration diminishes, shows cohesive transition and ensures intact core-surface structure.

RESULTS

Scanning electron microscope images confirmed a complete homogeneous, uniform and non-laminating surface formation. Energy-dispersive X-ray monitored the elemental structural mapping and proved the replacement of the aluminum sites on the surface with boron ending up the TiB2. The procedure was 8.6 fold improved the hardness and the mechanical resistance of the tools.

CONCLUSIONS

Surface-hardened, boronized pedicular screws can positively affect the prognosis. In vivo studies are needed to prove the safety of use.

Bioactivity and antibacterial properties of zinc-doped Ta2O5nanorods on porous tantalum surface

This paper focuses on the preparation of Zn2+-doped Ta2O5nanorods on porous tantalum using the hydrothermal method. Porous tantalum is widely used in biomedical materials due to its excellent elastic modulus and biological activity. Porous tantalum has an elastic modulus close to that of human bone, and its large specific surface area is conducive to promoting cell adhesion. Zinc is an important component of human bone, which not only has spectral bactericidal properties, but also has no cytotoxicity. The purpose of this study is to provide a theoretical basis for the surface modification of porous tantalum and to determine the best surface modification method. The surface structure of the sample was characterized by x-ray diffractometer, x-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope, and the Zn-doped Ta2O5nanorods are characterized by antibacterial test, MTT test, ICP and other methods. The sample has good antibacterial properties and no cytotoxicity. The results of this study have potential implications for the development of new and improved biomedical materials.

Porous metal implants: processing, properties, and challenges

Porous and functionally graded materials have seen extensive applications in modern biomedical devices-allowing for improved site-specific performance; their appreciable mechanical, corrosive, and biocompatible properties are highly sought after for lightweight and high-strength load-bearing orthopedic and dental implants. Examples of such porous materials are metals, ceramics, and polymers. Although, easy to manufacture and lightweight, porous polymers do not inherently exhibit the required mechanical strength for hard tissue repair or replacement. Alternatively, porous ceramics are brittle and do not possess the required fatigue resistance. On the other hand, porous biocompatible metals have shown tailorable strength, fatigue resistance, and toughness. Thereby, a significant interest in investigating the manufacturing challenges of porous metals has taken place in recent years. Past research has shown that once the advantages of porous metallic structures in the orthopedic implant industry have been realized, their biological and biomechanical compatibility-with the host bone-has been followed up with extensive methodical research. Various manufacturing methods for porous or functionally graded metals are discussed and compared in this review, specifically, how the manufacturing process influences microstructure, graded composition, porosity, biocompatibility, and mechanical properties. Most of the studies discussed in this review are related to porous structures for bone implant applications; however, the understanding of these investigations may also be extended to other devices beyond the biomedical field.

Preparation, modification, and clinical application of porous tantalum scaffolds

Porous tantalum (Ta) implants have been developed and clinically applied as high-quality implant biomaterials in the orthopedics field because of their excellent corrosion resistance, biocompatibility, osteointegration, and bone conductivity. Porous Ta allows fine bone ingrowth and new bone formation through the inner space because of its high porosity and interconnected pore structure. It contributes to rapid bone integration and long-term stability of osseointegrated implants. Porous Ta has excellent wetting properties and high surface energy, which facilitate the adhesion, proliferation, and mineralization of osteoblasts. Moreover, porous Ta is superior to classical metallic materials in avoiding the stress shielding effect, minimizing the loss of marginal bone, and improving primary stability because of its low elastic modulus and high friction coefficient. Accordingly, the excellent biological and mechanical properties of porous Ta are primarily responsible for its rising clinical translation trend. Over the past 2 decades, advanced fabrication strategies such as emerging manufacturing technologies, surface modification techniques, and patient-oriented designs have remarkably influenced the microstructural characteristic, bioactive performance, and clinical indications of porous Ta scaffolds. The present review offers an overview of the fabrication methods, modification techniques, and orthopedic applications of porous Ta implants.

Fabrication of Porous Tantalum with Low Elastic Modulus and Tunable Pore Size for Bone Repair

Porous tantalum (Ta) is a potential bone substitute due to its excellent biocompatibility and desirable mechanical properties. In this work, a series of porous Ta materials with interconnected micropores and varying pore sizes from 23 to 210 μm were fabricated using spark plasma sintering. The porous structure was formed by thermal decomposition of ammonium bicarbonate powder premixed in the Ta powder. The pore size and porosity were controlled by the categorized particle size of ammonium bicarbonate. The porous Ta has elastic moduli in the range of 2.1-3.2 GPa and compressive yield strength in the range of 23-34 MPa, which are close to those of human bone. In vitro, as-fabricated porous Ta demonstrates excellent biocompatibility by supporting adhesion and proliferation of preosteoblasts. In vivo studies also validate its bone repair capability after implantation in a rat femur defect model. The study demonstrates a facile strategy to fabricate porous Ta with controllable pore size for bone repair.

Advances in surface modification of tantalum and porous tantalum for rapid osseointegration: A thematic review

After bone defects reach a certain size, the body can no longer repair them. Tantalum, including its porous form, has attracted increasing attention due to good bioactivity, biocompatibility, and biomechanical properties. After a metal material is implanted into the body as a medical intervention, a series of interactions occurs between the material’s surface and the microenvironment. The interaction between cells and the surface of the implant mainly depends on the surface morphology and chemical composition of the implant’s surface. In this context, appropriate modification of the surface of tantalum can guide the biological behavior of cells, promote the potential of materials, and facilitate bone integration. Substantial progress has been made in tantalum surface modification technologies, especially nano-modification technology. This paper systematically reviews the progress in research on tantalum surface modification for the first time, including physicochemical properties, biological performance, and surface modification technologies of tantalum and porous tantalum.

Influence of porous tantalum scaffold pore size on osteogenesis and osteointegration: A comprehensive study based on 3D-printing technology

The emerging role of porous tantalum (Ta) scaffold for bone tissue engineering is noticed due to its outstanding biological properties. However, it is controversial which pore size and porosity are more conducive for bone defect repair. In the present work, porous tantalum scaffolds with pore sizes of 100-200, 200-400, 400-600 and 600-800 μm and corresponding porosities of 25%, 55%, 75%, and 85% were constructed, using computer aided design and 3D printing technologies, then comprehensively studied by in vitro and in vivo studies. We found that Ta scaffold with pore size of 400-600 μm showed stronger ability in facilitating cell adhesion, proliferation, and osteogenic differentiation in vitro. In vivo tests identified that porous tantalum scaffolds with pore size of 400-600 μm showed better performance of bone ingrowth and integration. In mechanism, computational fluid dynamics analysis proved porous tantalum scaffolds with pore size of 400-600 μm hold appropriate permeability and surface area, which facilitated cell adhesion and proliferation. Our results strongly indicate that pore size and porosity are essential for further applications of porous tantalum scaffolds, and porous tantalum scaffolds with pore size 400-600 μm are conducive to osteogenesis and osseointegration. These findings provide new evidence for further application of porous tantalum scaffolds for bone defect repair.

Tantalum and its derivatives in orthopedic and dental implants: Osteogenesis and antibacterial properties

Implant-associated infections and aseptic loosening are some of the main reasons for implant failure. Therefore, there is an urgent need to improve the osseointegration and antibacterial capabilities of implant materials. In recent years, a large number of breakthroughs in the biological application of tantalum and its derivatives have been achieved. Owing to their corrosion resistance, biocompatibility, osseointegration ability, and antibacterial properties, they have shown considerable potential in orthopedic and dental implant applications. In this review, we provide the latest progress and achievements in the research on osseointegration and antibacterial properties of tantalum as well as its derivatives, and summarize the surface modification methods to enhance their osseointegration and antibacterial properties.

Osteogenic potential of the growth factors and bioactive molecules in bone regeneration

The growing need for treatment of the impaired bone tissue has resulted in the quest for the improvement of bone tissue regeneration strategies. Bone tissue engineering is trying to create bio-inspired systems with a coordinated combination of the cells, scaffolds, and bioactive factors to repair the damaged bone tissue. The scaffold provides a supportive matrix for cell growth, migration, and differentiation and also, acts as a delivery system for bioactive factors. Bioactive factors including a large group of cytokines, growth factors (GFs), peptides, and hormonal signals that regulate cellular behaviors. These factors stimulate osteogenic differentiation and proliferation of cells by activating the signaling cascades related to ossification and angiogenesis. GFs and bioactive peptides are significant parts of the bone tissue engineering systems. Besides, the use of the osteogenic potential of hormonal signals has been an attractive topic, particularly in osteoporosis-related bone defects. Due to the unstable nature of protein factors and non-specific effects of hormones, the engineering of scaffolds to the controlled delivery of these bioactive molecules has paramount importance. This review updates the growth factors, engineered peptides, and hormones that are used in bone tissue engineering systems. Also, discusses how these bioactive molecules may be linked to accelerating bone regeneration.

3D-printed porous tantalum: recent application in various drug delivery systems to repair hard tissue defects

INTRODUCTION

The treatment of hard tissue defects, especially those of bone and cartilage, induced by infections or tumors remains challenging. Traditional methods, including debridement with systematic chemotherapy, have shortcomings owing to their inability to eliminate infections and high systematic toxicity.

AREA COVERED

This review comprehensively summarizes and discusses the current applications of 3D-printed porous tantalum (3D-P-p-Ta), a novel drug delivery strategy, in drug delivery systems to repair hard tissue defects, as well as the limitations of existing data and potential future research directions.

EXPERT OPINION

Drug delivery systems have advanced medical treatments, with the advantages of high local drug concentration, long drug-release period, and minimal systematic toxicity. Due to its excellent biocompatibility, ideal mechanical property, and anti-corrosion ability, porous tantalum is one of the most preferable loading scaffolds. 3D printing allows for freedom of design and facilitates the production of regular porous implants with high repeatability. There are several reports on the application of 3D-P-p-Ta in drug delivery systems for the management of infection- or tumor-associated bone defects, yet, to the best of our knowledge, no reviews have summarized the current research progress.

Porous Tantalum and Titanium in Orthopedics: A Review

Porous metal is metal with special porous structures, which can offer high biocompatibility and low Young's modulus to satisfy the need for orthopedic applications. Titanium and tantalum are the most widely used porous metals in orthopedics due to their excellent biomechanical properties and biocompatibility. Porous titanium and tantalum have been studied and applied for a long history until now. Here in this review, various manufacturing methods of titanium and tantalum porous metals are introduced. Application of these porous metals in different parts of the body are summarized, and strengths and weaknesses of these porous metal implants in clinical practice are discussed frankly for future improvement from the viewpoint of orthopedic surgeons. Then according to the requirements from clinics, progress in research for clinical use is illustrated in four aspects. Various creative designs of microporous and functionally gradient structure, surface modification, and functional compound systems of porous metal are exhibited as reference for future research. Finally, the directions of orthopedic porous metal development were proposed from the clinical view based on the rapid progress of additive manufacturing. Controllable design of both macroscopic anatomical bionic shape and microscopic functional bionic gradient porous metal, which could meet the rigorous mechanical demand of bone reconstruction, should be developed as the focus. The modification of a porous metal surface and construction of a functional porous metal compound system, empowering stronger cell proliferation and antimicrobial and antineoplastic property to the porous metal implant, also should be taken into consideration.

Application of combined porous tantalum scaffolds loaded with bone morphogenetic protein 7 to repair of osteochondral defect in rabbits<sup/>

PURPOSE

Porous tantalum (PT) has been widely used in orthopaedic applications for low modulus of elasticity, excellent biocompatibility, and the microstructures similar to cancellous bone. In order to improve the biological activity of PT, biologically active factors can be combined with the material. The purpose of this study was to investigate if bone morphogenetic protein 7 (BMP-7) modifications could enhance the repairing of cartilage of PT in osteochondral defect in medial femoral condyle of rabbits.

METHODS

A cylindrical osteochondral defect model was created on the animal medial femoral condyle of and filled as follows: PT modified with BMP-7 for MPT group, non-modified PT for the PT group, while no implants were used for the blank group. The regenerated osteochondral tissue was assessed and analyzed by histological observations at four, eight and 16 weeks post-operation and evaluated in an independent and blinded manner by five different observers using a histological score. Osteochondral and subchondral bone defect repair was assessed by micro-CT scan at 16 weeks post-operation, while the biomechanical test was performed at 16 weeks post-operation.

RESULTS

Briefly, higher overall histological score was observed in the MPT group compared to PT group. Furthermore, more new osteochondral tissue and bone formed at the interface and inside the inner pores of scaffolds of the MPT group compared to PT group. Additionally, the micro-CT data suggested that the new bone volume fractions and the quantity and quality of trabecular bone, as well as the maximum release force of the bone, were higher in the MPT group compared to PT group.

CONCLUSIONS

We demonstrated that the applied modified PT with BMP-7 promotes excellent subchondral bone regeneration and may serve as a novel approach for osteochondral defects repair.