Construction of multilayered molecular reservoirs on a titanium alloy implant for combinational drug delivery to promote osseointegration in osteoporotic conditions

A sugary solution: Harnessing polysaccharide-based materials for osteoporosis treatment

Osteoporosis, a prevalent skeletal disorder characterized by diminished bone density, compromised microstructure, and heightened fracture susceptibility, poses a growing public health concern exacerbated by aging demographics. Polysaccharides-based materials, derived from a diverse range of sources, exhibit exceptional biocompatibility. They possess a structure similar to the extracellular matrix, which can enhance cell adhesion in vivo, and demonstrate superior biological activity compared to artificial materials. This study delved into an in-depth examination of the various biomaterials and polysaccharide families associated with the treatment of osteoporosis. This article elucidates the benefits and attributes of polysaccharide-based materials in contrast to current clinical treatment modalities, delineating how these materials address prevalent challenges in the clinical management of osteoporosis. An overview of the prospective applications of polysaccharide-based materials in the future is also provided, as well as outlines the challenges that should be addressed prior to the clinical implementation of such materials.

Recent advances in layer-by-layer assembly scaffolds for co-delivery of bioactive molecules for bone regeneration: an updated review

Orthopedic implants have faced challenges in treating bone defects due to various factors, including inadequate osseointegration, oxidative stress, bacterial infection, immunological rejection, and poor individualized treatment. These challenges profoundly affect both the results of treatment and patients' daily lives. There is great promise for the layer-by-layer (LbL) assembly method in tissue engineering. The method primarily relies on electrostatic attraction and entails the consecutive deposition of electrolyte complexes with opposite charges onto a substrate, leading to the formation of homogeneous single layers that can be quickly deposited to produce nanolayer films. LbL has attracted considerable interest as a coating technology because of its ease of production, cost-effectiveness, and capability to apply diverse biomaterial coatings without compromising the primary bio-functional properties of the substrate materials. This review will look into the fundamentals and evolution of LbL in orthopedics, provide an analysis of the chemical strategy used to prepare bone implants with LbL and introduce the application of LbL bone implants in orthopedics over recent years. Among the many potential uses of LbL, such as the implementation of sustained-release and programmed drug delivery, which in turn promotes the osseointegration and the development of new blood vessels, as well as antibacterial, antioxidant, and other similar applications. In addition, we offer a thorough examination of cell behavior and biomaterial interaction to facilitate the advancement of next-generation LbL films for tissue engineering.

Synthetic nanointerfacial bioengineering of Ti implants: on-demand regulation of implant-bone interactions for enhancing osseointegration

Titanium and its alloys are the most commonly used biometals for developing orthopedic implants to treat various forms of bone fractures and defects, but their clinical performance is still challenged by the unfavorable mechanical and biological interactions at the implant-tissue interface, which substantially impede bone healing at the defects and reduce the quality of regenerated bones. Moreover, the impaired osteogenesis capacity of patients under certain pathological conditions such as diabetes and osteoporosis may further impair the osseointegration of Ti-based implants and increase the risk of treatment failure. To address these issues, various modification strategies have been developed to regulate the implant-bone interactions for improving bone growth and remodeling in situ. In this review, we provide a comprehensive analysis on the state-of-the-art synthetic nanointerfacial bioengineering strategies for designing Ti-based biofunctional orthopedic implants, with special emphasis on the contributions to (1) promotion of new bone formation and binding at the implant-bone interface, (2) bacterial elimination for preventing peri-implant infection and (3) overcoming osseointegration resistance induced by degenerative bone diseases. Furthermore, a perspective is included to discuss the challenges and potential opportunities for the interfacial engineering of Ti implants in a translational perspective. Overall, it is envisioned that the insights in this review may guide future research in the area of biometallic orthopedic implants for improving bone repair with enhanced efficacy and safety.

Application of advanced surface modification techniques in titanium-based implants: latest strategies for enhanced antibacterial properties and osseointegration

Titanium-based implants, renowned for their excellent mechanical properties, corrosion resistance, and biocompatibility, have found widespread application as premier implant materials in the medical field. However, as bioinert materials, they often face challenges such as implant failure caused by bacterial infections and inadequate osseointegration post-implantation. Thus, to address these issues, researchers have developed various surface modification techniques to enhance the surface properties and bioactivity of titanium-based implants. This review aims to outline several key surface modification methods for titanium-based implants, including acid etching, sol-gel method, chemical vapor deposition, electrochemical techniques, layer-by-layer self-assembly, and chemical grafting. It briefly summarizes the advantages, limitations, and potential applications of these technologies, presenting readers with a comprehensive perspective on the latest advances and trends in the surface modification of titanium-based implants.

Drug Delivery and Therapy Strategies for Osteoporosis Intervention

With the advent of the aging society, osteoporosis (OP) risk increases yearly. Currently, the clinical usage of anti-OP drugs is challenged by recurrent side effects and poor patient compliance, regardless of oral, intravenous, or subcutaneous administration. Properly using a drug delivery system or formulation strategy can achieve targeted drug delivery to the bone, diminish side effects, improve bioavailability, and prolong the in vivo residence time, thus effectively curing osteoporosis. This review expounds on the pathogenesis of OP and the clinical medicaments used for OP intervention, proposes the design approach for anti-OP drug delivery, emphatically discusses emerging novel anti-OP drug delivery systems, and enumerates anti-OP preparations under clinical investigation. Our findings may contribute to engineering anti-OP drug delivery and OP-targeting therapy.

Progress in Surface Modification of Titanium Implants by Hydrogel Coatings

Although titanium and titanium alloys have become the preferred materials for various medical implants, surface modification technology still needs to be strengthened in order to adapt to the complex physiological environment of the human body. Compared with physical or chemical modification methods, biochemical modification, such as the introduction of functional hydrogel coating on implants, can fix biomolecules such as proteins, peptides, growth factors, polysaccharides, or nucleotides on the surface of the implants, so that they can directly participate in biological processes; regulate cell adhesion, proliferation, migration, and differentiation; and improve the biological activity on the surface of the implants. This review begins with a look at common substrate materials for hydrogel coatings on implant surfaces, including natural polymers such as collagen, gelatin, chitosan, and alginate, and synthetic materials such as polyvinyl alcohol, polyacrylamide, polyethylene glycol, and polyacrylic acid. Then, the common construction methods of hydrogel coating (electrochemical method, sol-gel method and layer-by-layer self-assembly method) are introduced. Finally, five aspects of the enhancement effect of hydrogel coating on the surface bioactivity of titanium and titanium alloy implants are described: osseointegration, angiogenesis, macrophage polarization, antibacterial effects, and drug delivery. In this paper, we also summarize the latest research progress and point out the future research direction. After searching, no previous relevant literature reporting this information was found.

Biopolymeric Coatings for Local Release of Therapeutics from Biomedical Implants

The deployment of structures that enable localized release of bioactive molecules can result in more efficacious treatment of disease and better integration of implantable bionic devices. The strategic design of a biopolymeric coating can be used to engineer the optimal release profile depending on the task at hand. As illustrative examples, here advances in delivery of drugs from bone, brain, ocular, and cardiovascular implants are reviewed. These areas are focused to highlight that both hard and soft tissue implants can benefit from controlled localized delivery. The composition of biopolymers used to achieve appropriate delivery to the selected tissue types, and their corresponding outcomes are brought to the fore. To conclude, key factors in designing drug-loaded biopolymeric coatings for biomedical implants are highlighted.

Recent Advancements in Metallic Drug-Eluting Implants

Over the past decade, metallic drug-eluting implants have gained significance in orthopedic and dental applications for controlled drug release, specifically for preventing infection associated with implants. Recent studies showed that metallic implants loaded with drugs were substituted for conventional bare metal implants to achieve sustained and controlled drug release, resulting in a desired local therapeutic concentration. A number of secondary features can be provided by the incorporated active molecules, including the promotion of osteoconduction and angiogenesis, the inhibition of bacterial invasion, and the modulation of host body reaction. This paper reviews recent trends in the development of the metallic drug-eluting implants with various drug delivery systems in the past three years. There are various types of drug-eluting implants that have been developed to meet this purpose, depending on the drug or agents that have been loaded on them. These include anti-inflammatory drugs, antibiotics agents, growth factors, and anti-resorptive drugs.

Gene-activated titanium implants for gene delivery to enhance osseointegration

Osseointegration is the direct and intimate contact between mineralized tissue and titanium implant at the bone-implant interface. Early establishment and stable maintenance of osseointegration is the key to long-term implant success. However, in patients with compromised conditions such as osteoporosis and patients beginning early load-bearing activities such as walking, lower osseointegration around titanium implants is often observed, which might result in implant early failure. Gene-activated implants show an exciting prospect of combining gene delivery and biomedical implants to solve the problems of poor osseointegration formation, overcoming the shortcomings of protein therapy, including rapid degradation and overdose adverse effects. The conception of gene-activated titanium implants is based on "gene-activated matrix" (GAM), which means scaffolds using non-viral vectors for in situ gene delivery to achieve a long-term and efficient transfection of target cells. Current preclinical studies in animal models have shown that plasmid DNA (pDNA), microRNA (miRNA), and small interference RNA (siRNA) functionalized titanium implants can enhance osseointegration with safety and efficiency, leading to the expectation of applying this technique in dental and orthopedic clinical scenarios. This review aims to comprehensively summarize fabrication strategies, current applications, and futural outlooks of gene-activated implants, emphasizing nucleic acid targets, non-viral vectors, implant surface modification techniques, nucleic acid/vector complexes loading strategies.

Titanium Implant Surface Effects on Adherent Macrophage Phenotype: A Systematic Review

Immunomodulatory biomaterials have the potential to stimulate an immune response able to promote constructive and functional tissue remodeling responses as opposed to persistent inflammation and scar tissue formation. As such, the controlled activation of macrophages and modulation of their phenotype through implant surface modification has emerged as a key therapeutic strategy.

METHODS

Online databases were searched for in vitro studies between January 1991 and June 2020 which examined the effect of titanium implant surface topography on the adherent macrophage phenotype at either the gene or protein level.

RESULTS

Thirty-nine studies were subsequently included for review. Although there was significant heterogeneity between studies, treatment of titanium surfaces increased the surface roughness or hydrophilicity, and hence increased macrophage attachment but decreased cell spreading. Physical coating of the titanium surface also tended to promote the formation of cell clusters. Titanium and titanium-zirconium alloy with a micro- or nano-scale rough topography combined with a hydrophilic surface chemistry were the most effective surfaces for inducing an anti-inflammatory phenotype in adherent macrophages, as indicated by significant changes in cytokine gene expression and or cytokine secretion profiles.

CONCLUSIONS

The published data support the hypothesis that incorporation of specific topographical and physiochemical surface modifications to titanium can modulate the phenotypic response of adherent macrophages.

Aspirin/PLGA coated 3D-printed Ti-6Al-4V alloy modulate macrophage polarization to enhance osteoblast differentiation and osseointegration

Although titanium (Ti) and Ti-based alloy have been widely used as dental and orthopedic implant materials, its bioinertness hindered the rapid osseointegration. Therefore, it is recommended to acquire ideal topographic and chemical characteristics through surface modification methods. 3D printing is a delicate manufacture technique which possesses superior controllability and reproducibility. While aspirin serve as a well-established non-steroidal anti-inflammatory agent. Recently, the importance of immune system in regulating bone dynamics has attracted increasing attention. We herein superimposed the aspirin/poly (lactic-co-glycolic acid) (ASP/PLGA) coating on the 3D-printed Ti-6Al-4V surface with uniform micro-structure to establish the Ti64-M-ASP/PLGA substrate. Scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and contact angle test confirmed the successful fabrication of the Ti64-M-ASP/PLGA substrate, with increased wettability and sustained release pattern of ASP. Compared with the Ti64 base material, the Ti64-M-ASP/PLGA substrate showed enhanced M2 and depressed M1 genes and proteins expressions in macrophages. The novel Ti64-M-ASP/PLGA substrate also displayed enhanced osteoblast proliferation, adhesion, extracellular mineralization ability and osteogenic gene expressions when cultured with macrophage conditioned medium in vitro. Furthermore, rat femora implantation model was used for in vivo evaluation. After 4 weeks of implantation, push out test, micro-computed tomography (micro-CT) and histological analyses all confirmed the superior osseointegration capabilities of the Ti64-M-ASP/PLGA implant than the other groups. Our study revealed the synergistic role played by 3D-printed micro topography and immunoregulatory drug aspirin in promoting osteogenesis in vitro and accelerating osseointegration in vivo, thus providing a promising method for better modifying the implant surface. Graphical abstract.

Hormone and implant osseointegration: Elaboration of the relationship among function, preclinical, and clinical practice

As clusters of peptides or steroids capable of high-efficiency information transmission, hormones have been substantiated to coordinate metabolism, growth, development, and other physiological processes, especially in bone physiology and repair metabolism. In recent years, the application of hormones for implant osseointegration has become a research hotspot. Herein, we provide a comprehensive overview of the relevant reports on endogenous hormones and their corresponding supplementary preparations to explore the association between hormones and the prognosis of implants. We also discuss the effects and mechanisms of insulin, parathyroid hormone, melatonin, vitamin D, and growth hormone on osseointegration at the molecular and body levels to provide a foothold and guide future research on the systemic conditions that affect the implantation process and expand the relative contraindications of the implant, and the pre-and post-operative precautions. This review shows that systemic hormones can regulate the osseointegration of oral implants through endogenous or exogenous drug-delivery methods.

Construction of Local Drug Delivery System on Titanium-Based Implants to Improve Osseointegration

Titanium and its alloys are the most widely applied orthopedic and dental implant materials due to their high biocompatibility, superior corrosion resistance, and outstanding mechanical properties. However, the lack of superior osseointegration remains the main obstacle to successful implantation. Previous traditional surface modification methods of titanium-based implants cannot fully meet the clinical needs of osseointegration. The construction of local drug delivery systems (e.g., antimicrobial drug delivery systems, anti-bone resorption drug delivery systems, etc.) on titanium-based implants has been proved to be an effective strategy to improve osseointegration. Meanwhile, these drug delivery systems can also be combined with traditional surface modification methods, such as anodic oxidation, acid etching, surface coating technology, etc., to achieve desirable and enhanced osseointegration. In this paper, we review the research progress of different local drug delivery systems using titanium-based implants and provide a theoretical basis for further research on drug delivery systems to promote bone–implant integration in the future.

Bioactive Coatings on Titanium: A Review on Hydroxylation, Self-Assembled Monolayers (SAMs) and Surface Modification Strategies

Titanium (Ti) and its alloys have been demonstrated over the last decades to play an important role as inert materials in the field of orthopedic and dental implants. Nevertheless, with the widespread use of Ti, implant-associated rejection issues have arisen. To overcome these problems, antibacterial properties, fast and adequate osseointegration and long-term stability are essential features. Indeed, surface modification is currently presented as a versatile strategy for developing Ti coatings with all these challenging requirements and achieve a successful performance of the implant. Numerous approaches have been investigated to obtain stable and well-organized Ti coatings that promote the tailoring of surface chemical functionalization regardless of the geometry and shape of the implant. However, among all the approaches available in the literature to functionalize the Ti surface, a promising strategy is the combination of surface pre-activation treatments typically followed by the development of intermediate anchoring layers (self-assembled monolayers, SAMs) that serve as the supporting linkage of a final active layer. Therefore, this paper aims to review the latest approaches in the biomedical area to obtain bioactive coatings onto Ti surfaces with a special focus on (i) the most employed methods for Ti surface hydroxylation, (ii) SAMs-mediated active coatings development, and (iii) the latest advances in active agent immobilization and polymeric coatings for controlled release on Ti surfaces.

Recent advances in chitosan-based layer-by-layer biomaterials and their biomedical applications

In recent years, chitosan-based biomaterials have been continually and extensively researched by using layer-by-layer (LBL) assembly, due to their potentials in biomedicine. Various chitosan-based LBL materials have been newly developed and applied in different areas along with the development of technologies. This work reviews the recent advances of chitosan-based biomaterials produced by LBL assembly. Driving forces of LBL, for example electrostatic interactions, hydrogen bond as well as Schiff base linkage have been discussed. Various forms of chitosan-based LBL materials such as films/coatings, capsules and fibers have been reviewed. The applications of these biomaterials in the field of antimicrobial applications, drug delivery, wound dressings and tissue engineering have been comprehensively reviewed.

Spatiotemporally controlled calcitonin delivery: Long-term and targeted therapy of skeletal diseases

Bone is a connective tissue that support the entire body and protect the internal organs. However, there are great challenges on curing intractable skeletal diseases such as hypercalcemia, osteoporosis and osteoarthritis. To address these issues, calcitonin (CT) therapy is an effective treatment alternative to regulate calcium metabolism and suppress inflammation response, which are closely related to skeletal diseases. Traditional calcitonin formulation requires frequent administration due to the low bioavailability resulting from the short half-life and abundant calcitonin receptors distributed through the whole body. Therefore, long-term and targeted calcitonin delivery systems (LCDS and TCDS) have been widely explored as the popular strategies to overcome the intrinsic limitations of calcitonin and improve the functions of calcium management and inflammation inhibition in recent years. In this review, we first explain the physiological effects of calcitonin on bone remodeling: (i) inhibitory effects on osteoclasts and (ii) facilitated effects on osteoblasts. Then we summarized four strategies for spatiotemporally controlled delivery of calcitonin: micro-/nanomedicine (e.g. inorganic micro-/nanomedicine, polymeric micro-/nanomedicine and supramolecular assemblies), hydrogels (especially thermosensitive hydrogels), prodrug (PEGylation and targeting design) and hybrid biomaterials. Subsequently, we discussed the application of LCDS and TCDS in treating hypercalcemia, osteoporosis, and arthritis. Understanding and analyzing these advanced calcitonin delivery applications are essential for future development of calcitonin therapies toward skeletal diseases with superior efficacy in clinic.

Enamel matrix derivative (EMD) enhances the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs)

To investigate the EMD's capacity in BMSCs osteogenic differentiation. In vivo and in vitro, BMSCs were treated with EMD, scanning electron microscopy, and Alizarin Red staining were used to detect the changes in the osteogenic ability of BMSCs, and the proliferation ability of BMSCs was evaluated by CCK8. In addition, by adding xav939, a typical inhibitor of Wnt/β-catenin signaling pathway, the regulatory function of Wnt/β-catenin signaling was clarified. The results showed that EMD promote cell proliferation and 25 μg/ml EMD had the most significant effect. Cells inducing osteogenesis for 2 and 3 even 4 weeks, the cell staining is deeper in EMD treated group than that of the control (P < 0.05) by alizarin Red staining, suggesting more mineralization of BMSCs. In vivo implanting the titanium plate wrapped with 25 μg/ml EMD treated-BMSC film into nude mice for 8 weeks, more nodules were formed on the surface of the titanium plate than that the control (P < 0.05). HE showed that there is a little blue-violet immature bone-like tissue block. Besides, the expression of RUNX Family Transcription Factor 2 (Runx2), Osterix, Osteocalcin (OCN), collagen I (COLI), alkaline phosphatase (ALP) and β-catenin were inhibited in xav939 group (P < 0.05); Inversely, all were activated in EMD group (P < 0.05). In conclusion, EMD promoted the proliferation and osteogenic differentiation of BMSCs. EMD's function on BMSCs might be associated with the Wnt/β-catenin signaling pathway.

Properties improvement of titanium alloys scaffolds in bone tissue engineering: a literature review

Owing to their excellent biocompatibility and corrosion-resistant properties, titanium (Ti) (and its alloy) are essential artificial substitute biomaterials for orthopedics. However, flaws, such as weak osteogenic induction ability and higher Young's modulus, have been observed during clinical application. As a result, short- and long-term postoperative follow-up has found that several complications have occurred. For decades, scientists have exerted efforts to compensate for these deficiencies. Different modification methods have been investigated, including changing alloy contents, surface structure transformation, three-dimensional (3D) structure transformation, coating, and surface functionalization technologies. The cell-surface interaction effect and imitation of the natural 3D bone structure are the two main mechanisms of these improved methods. In recent years, significant progress has been made in materials science research methods, including thorough research of titanium alloys of different compositions, precise surface pattern control technology, controllable 3D structure construction technology, improvement of coating technologies, and novel concepts of surface functionalization. These improvements facilitate the possibility for further research in the field of bone tissue engineering. Although the underlying mechanism is still not fully understood, these studies still have some implications for clinical practice. Therefore, for the direction of further research, it is beneficial to summarize these studies according to the basal method used. This literature review aimed to classify these technologies, thereby providing beginners with a preliminary understanding of the field.

Multifunctional natural polymer-based metallic implant surface modifications

High energy traumas could cause critical damage to bone, which will require permanent implants to recover while functionally integrating with the host bone. Critical sized bone defects necessitate the use of bioactive metallic implants. Because of bioinertness, various methods involving surface modifications such as surface treatments, the development of novel alloys, bioceramic/bioglass coatings, and biofunctional molecule grafting have been utilized to effectively integrate metallic implants with a living bone. However, the applications of these methods demonstrated a need for an interphase layer improving bone-making to overcome two major risk factors: aseptic loosening and peri-implantitis. To accomplish a biologically functional bridge with the host to prevent loosening, regenerative cues, osteoimmunomodulatory modifications, and electrochemically resistant layers against corrosion appeared as imperative reinforcements. In addition, interphases carrying antibacterial cargo were proven to be successful against peri-implantitis. In the literature, metallic implant coatings employing natural polymers as the main matrix were presented as bioactive interphases, enabling rapid, robust, and functional osseointegration with the host bone. However, a comprehensive review of natural polymer coatings, bridging and grafting on metallic implants, and their activities has not been reported. In this review, state-of-the-art studies on multifunctional natural polymer-based implant coatings effectively utilized as a bone tissue engineering (BTE) modality are depicted. Protein-based, polysaccharide-based coatings and their combinations to achieve better osseointegration via the formation of an extracellular matrix-like (ECM-like) interphase with gap filling and corrosion resistance abilities are discussed in detail. The hypotheses and results of these studies are examined and criticized, and the potential future prospects of multifunctional coatings are also proposed as final remarks.

Nanointeraction: The profound influence of nanostructured and nano-drug delivery biomedical implant surfaces on cell behavior

Nanostructured surfaces feature promising biological properties on biomaterials attracting large interest at basic research, implant industry development, and bioengineering applications. Thou, nanoscale interactions at a molecular and cellular level are not yet completely understood and its biological and clinical implications need to be further elucidated. As follows, the aim of this comprehensive review was to evaluate nanostructured surfaces at biomedical implants focusing on surface development, nanostructuration, and nanoengineered drug delivery systems that can induce specific cell interactions in all relevant aspects of biological, reparative, anti-bacterial, anti-inflammatory and clinical processes. The methods and the physio-chemical properties involved in nanotopography performance, the main cellular characteristics involved at surface/cell interaction, and a summary of results and outlooks reported in studies applying nanostructured surfaces and nano-drug delivery systems is presented. The future prospects and commercial translation of this developing field, particularly concerning multifunctional nanostructured surfaces and its clinical implications are further discussed. At a cellular level, nanostructured biomedical implant surfaces can enhance osteogenesis by targeting osteoblasts, osteocytes, and mesenchymal cells, stimulate fibroblast/epithelial cells proliferation and adherence, inhibit bacterial cell proliferation and biofilm accumulation, and act as immune-modulating surfaces targeting macrophages and reducing pro-inflammatory cytokine expression. Moreover, several methodological options to create drug-delivery systems on metallic implant surfaces are available, however, the clinical translation is yet incomplete. The efficiency of which nanostructured/nano-delivery surfaces may target specific cell interactions and favor clinical outcomes needs to be further elucidated in pre-clinical and clinical studies, along with engineering solutions for commercial translation and approval of controlling agencies.