Controlled release of bone morphogenetic protein (BMP)-2 from nanocomplex incorporated on hydroxyapatite-formed titanium surface

Growth factor-functionalized titanium implants for enhanced bone regeneration: A review

Titanium and titanium alloys are widely favored materials for orthopedic implants due to their exceptional mechanical properties and biological inertness. The additional benefit of sustained local release of bioactive substances further promotes bone tissue formation, thereby augmenting the osseointegration capacity of titanium implants and attracting increasing attention in bone tissue engineering. Among these bioactive substances, growth factors have shown remarkable osteogenic and angiogenic induction capabilities. Consequently, researchers have developed various physical, chemical, and biological loading techniques to incorporate growth factors into titanium implants, ensuring controlled release kinetics. In contrast to conventional treatment modalities, the localized release of growth factors from functionalized titanium implants not only enhances osseointegration but also reduces the risk of complications. This review provides a comprehensive examination of the types and mechanisms of growth factors, along with a detailed exploration of the methodologies used to load growth factors onto the surface of titanium implants. Moreover, it highlights recent advancements in the application of growth factors to the surface of titanium implants (Scheme 1). Finally, the review discusses current limitations and future prospects for growth factor-functionalized titanium implants. In summary, this paper presents cutting-edge design strategies aimed at enhancing the bone regenerative capacity of growth factor-functionalized titanium implants-a significant advancement in the field of enhanced bone regeneration.

Development and Characterization of Heparin-Containing Hydrogel/3D-Printed Scaffold Composites for Craniofacial Reconstruction

Regeneration of cartilage and bone tissues remains challenging in tissue engineering due to their complex structures, and the need for both mechanical support and delivery of biological repair stimuli. Therefore, the goal of this study was to develop a composite scaffold platform for anatomic chondral and osteochondral repair using heparin-based hydrogels to deliver small molecules within 3D-printed porous scaffolds that provide structure, stiffness, and controlled biologic delivery. We designed a mold-injection system to combine hydrolytically degradable hydrogels and 3D-printed scaffolds that could be employed rapidly (< 30 min) in operating room settings (~23 °C). Micro-CT analysis demonstrated the effectiveness of our injection system through homogeneously distributed hydrogel within the pores of the scaffolds. Hydrogels and composite scaffolds exhibited efficient loading (~94%) of a small positively charged heparin-binding molecule (crystal violet) with sustained release over 14 days and showed high viability of encapsulated porcine chondrocytes over 7 days. Compression testing demonstrated nonlinear viscoelastic behavior where tangent stiffness decreased with scaffold porosity (porous scaffold tangent stiffness: 70%: 4.9 MPa, 80%: 1.5 MPa, and 90%: 0.20 MPa) but relaxation was not affected. Lower-porosity scaffolds (70%) showed stiffness similar to lower ranges of trabecular bone (4-8 MPa) while higher-porosity scaffolds (80% and 90%) showed stiffness similar to auricular cartilage (0.16-2 MPa). Ultimately, this rapid composite scaffold fabrication method may be employed in the operating room and utilized to control biologic delivery within load-bearing scaffolds.

Hydroxyapatite: A journey from biomaterials to advanced functional materials

Hydroxyapatite (HAp), a well-known biomaterial, has witnessed a remarkable evolution over the years, transforming from a simple biocompatible substance to an advanced functional material with a wide range of applications. This abstract provides an overview of the significant advancements in the field of HAp and its journey towards becoming a multifunctional material. Initially recognized for its exceptional biocompatibility and bioactivity, HAp gained prominence in the field of bone tissue engineering and dental applications. Its ability to integrate with surrounding tissues, promote cellular adhesion, and facilitate osseointegration made it an ideal candidate for various biomedical implants and coatings. As the understanding of HAp grew, researchers explored its potential beyond traditional biomaterial applications. With advances in material synthesis and engineering, HAp began to exhibit unique properties that extended its utility to other disciplines. Researchers successfully tailored the composition, morphology, and surface characteristics of HAp, leading to enhanced mechanical strength, controlled drug release capabilities, and improved biodegradability. These modifications enabled the utilization of HAp in drug delivery systems, biosensors, tissue engineering scaffolds, and regenerative medicine applications. Moreover, the exceptional biomineralization properties of HAp allowed for the incorporation of functional ions and molecules during synthesis, leading to the development of bioactive coatings and composites with specific therapeutic functionalities. These functionalized HAp materials have demonstrated promising results in antimicrobial coatings, controlled release systems for growth factors and therapeutic agents, and even as catalysts in chemical reactions. In recent years, HAp nanoparticles and nanostructured materials have emerged as a focal point of research due to their unique physicochemical properties and potential for targeted drug delivery, imaging, and theranostic applications. The ability to manipulate the size, shape, and surface chemistry of HAp at the nanoscale has paved the way for innovative approaches in personalized medicine and regenerative therapies. This abstract highlights the exceptional evolution of HAp, from a traditional biomaterial to an advanced functional material. The exploration of novel synthesis methods, surface modifications, and nanoengineering techniques has expanded the horizon of HAp applications, enabling its integration into diverse fields ranging from biomedicine to catalysis. Additionally, this manuscript discusses the emerging prospects of HAp-based materials in photocatalysis, sensing, and energy storage, showcasing its potential as an advanced functional material beyond the realm of biomedical applications. As research in this field progresses, the future holds tremendous potential for HAp-based materials to revolutionize medical treatments and contribute to the advancement of science and technology.

Can Graphene Pave the Way to Successful Periodontal and Dental Prosthetic Treatments? A Narrative Review

Graphene, as a promising material, holds the potential to significantly enhance the field of dental practices. Incorporating graphene into dental materials imparts enhanced strength and durability, while graphene-based nanocomposites offer the prospect of innovative solutions such as antimicrobial dental implants or scaffolds. Ongoing research into graphene-based dental adhesives and composites also suggests their capacity to improve the quality and reliability of dental restorations. This narrative review aims to provide an up-to-date overview of the application of graphene derivatives in the dental domain, with a particular focus on their application in prosthodontics and periodontics. It is important to acknowledge that further research and development are imperative to fully explore the potential of graphene and ensure its safe use in dental practices.

Osteoconductive, Osteogenic, and Antipathogenic Plasma Electrolytic Oxidation Coatings on Titanium Implants with BMP-2

We report a one-pot plasma electrolytic oxidation (PEO) strategy for forming a multi-element oxide layer on the titanium surface using complex electrolytes containing Na2HPO4, Ca(OH)2, (NH2)2CO, Na2SiO3, CuSO4, and KOH compounds. For even better bone implant ingrowth, PEO coatings were additionally loaded with bone morphogenetic protein-2 (BMP-2). The samples were tested in vivo in a mouse craniotomy model. Tests for bactericidal and fungicidal activity were carried out using clinically isolated multi-drug-resistant Escherichia coli (E. coli) K261, E. coli U20, methicillin-resistant Staphylococcus aureus (S. aureus) CSA154 bacterial strains, and Neurospora crassa (N. crassa) and Candida albicans (C. albicans) D2528/20 fungi. The PEO-Cu coating effectively inactivated both Gram-positive and Gram-negative bacteria at low concentrations of Cu2+ ions: minimal bactericidal concentration for E. coli and N. crassa (99.9999%) and minimal inhibitory concentration (99.0%) for S. aureus were 5 ppm. For all studied bacterial and fungal strains, PEO-Cu coating completely prevented the formation of bacterial and fungal biofilms. PEO and PEO-Cu coatings demonstrated bone remodeling and moderate osteoconductivity in vivo, while BMP-2 significantly enhanced osteoconduction and osteogenesis. The obtained results are encouraging and indicate that Ti-based materials with PEO coatings loaded with BMP-2 can be widely used in customized medicine as implants for orthopedics and cranio-maxillofacial surgery.

The Osteogenesis Mechanisms of Dental Alveolar Bone Socket Post Induction with Hydroxyapatite Bovine Tooth Graft: An Animal Experimental in Rattus norvegicus Strain Wistar

OBJECTIVES

 Surgical endodontics (hemisection) commonly involves the alveolar bone socket and the periradicular tissue. In today's era, optimizing the bone healing process is updated by using bone graft induction. This study explores the mechanisms of bone healing of the alveolar bone socket post-dental extraction of Wistar rats after administration of a bovine tooth graft (hydroxyapatite bovine tooth graft [HAp-BTG]).

MATERIALS AND METHODS

 Fifty Wistar rats were randomly selected into two groups, control and treatment, and into five subgroups on days 3, 7, 14, 21, and 28. The postextraction socket was filled with polyethylene glycol (PEG) as the control and PEG + HAp-BTG as the treatment group. On days 3, 7, 14, 21, and 28, Wistar rats were sacrificed, mandibles were taken, paraffin blocks were made, cut 4 µm thick, and made into glass preparations for microscopic examination. The variable analysis was performed by staining hematoxylin-eosin for osteoblasts (OBs) and osteoclasts (OCs) and immunohistochemistry for runt-related transcription factor 2 (RUNX2), osterix (OSX), osteocalcin (OCN), bone morphogenic protein (BMP) 2. We analyzed the expressed cell count per microscope field.

RESULTS

 In general, the number of cell expressions in the treatment group was significantly higher and faster, except for significantly lower OC. The high variables peak occurred on day 14 for RUNX2 and OCN, on day 7 for OSX, while OB significantly increased on day 21 and remained until day 28. The decrease of OC cells occurred on day 7 and remained low until 28 days. BMP2 was first dominantly induced by HAp-BTG, then the others.

CONCLUSION

 HAp-BTG can induce higher and faster bone healing biomarkers. BMP2 is the dominant first impacted. On the 28th day, it did not significantly express the suppression of OC by OB, which entered the bone formation and remodeling step.

Dopamine/DOPAC-assisted immobilization of bone morphogenetic protein-2 loaded Heparin/PEI nanogels onto three-dimentional printed calcium phosphate ceramics for enhanced osteoinductivity and osteogenicity

Nowadays, the three-dimensional (3D) printed calcium phosphate (CaP) ceramics have well-designed geometric structure, but suffer from relative weak osteoinductivity. Surface modification by incorporating bone morphogenetic protein-2 (BMP2) onto scaffolds is considered as an efficient approach to improve their bioactivity. However, high dose and uncontrolled burst release of BMP2 may cause undesired side effect. In the present study, porous BCP ceramics with inverse face-centred cube structure prepared by digital light processing (DLP)-based 3D printing technique were used as the substrates. BMP2 proteins were loaded in the self-assembled Heparin/PEI nanogels (NP/BMP2), and then immobilized onto BCP substrates through the intermediate mussel-derived bioactive dopamine and dihydroxyphenylacetic acid (DA/DOPAC) coating layers to construct functional BCP/layer/NP/BMP2 scaffolds. Our results showed that Heparin/PEI nanogel was a potent delivery system for BMP2, and BCP/layer/NP/BMP2 scaffolds exhibited the high loading capacity, controlled release rate, and sustained local delivery of BMP2. In vitro cell experiments with bone marrow stromal cells (BMSCs) found that BCP/layer/NP/BMP2 could promote cell proliferation, facilitate cell spreading, accelerate cell migration, up-regulate expression of osteogenic genes, and improve synthesis of osteoblast-related proteins. Moreover, the murine intramuscular implantation model suggested that BCP/layer/NP/BMP2 had a superior osteoinductive capacity, and the rat femoral condyle defect repair model showed that BCP/layer/NP/BMP2 could enhance in situ bone repair and regeneration. These findings demonstrate that the incorporation of BMP2 loaded Heparin/PEI nanogels to 3D printed scaffolds holds great promise in fabricating bone graft with a superior biological performance for orthopedic application.

Advanced PLGA hybrid scaffold with a bioactive PDRN/BMP2 nanocomplex for angiogenesis and bone regeneration using human fetal MSCs

Biodegradable polymers have been used with various systems for tissue engineering. Among them, poly(lactic-co-glycolic) acid (PLGA) has been widely used as a biomaterial for bone regeneration because of its great biocompatibility and biodegradability properties. However, there remain substantial cruxes that the by-products of PLGA result in an acidic environment at the implanting site, and the polymer has a weak mechanical property. In our previous study, magnesium hydroxide (MH) and bone extracellular matrix are combined with a PLGA scaffold (PME) to improve anti-inflammation and mechanical properties and osteoconductivity. In the present study, the development of a bioactive nanocomplex (NC) formed along with polydeoxyribonucleotide and bone morphogenetic protein 2 (BMP2) provides synergistic abilities in angiogenesis and bone regeneration. This PME hybrid scaffold immobilized with NC (PME/NC) achieves outstanding performance in anti-inflammation, angiogenesis, and osteogenesis. Such an advanced PME/NC scaffold suggests an integrated bone graft substitute for bone regeneration.

Modification of Titanium Implant and Titanium Dioxide for Bone Tissue Engineering

Bone tissue engineering using titanium (Ti) implant and titanium dioxide (TiO₂) with their modification is gaining increasing attention. Ti has been adopted as an implant material in dental and orthopedic fields due to its superior properties. However, it still requires modification in order to achieve robust osteointegration between the Ti implant and surrounding bone. To modify the Ti implant, numerous methods have been introduced to fabricate porous implant surfaces with a variety of coating materials. Among these, plasma spraying of hydroxyapatite (HA) has been the most commonly used with commercial success. Meanwhile, TiO₂ nanotubes have been actively studied as the coating material for implants, and promising results have been reported about improving osteogenic activity around implants recently. Also porous three-dimensional constructs based on TiO₂ have been proposed as scaffolding material with high biocompatibility and osteoconductivity in large bone defects. However, the use of the TiO₂ scaffolds in load-bearing environment is somewhat limited. In order to optimize the TiO₂ scaffolds, studies have tried to combine various materials with TiO₂ scaffolds including drug, mesenchymal stem cells, Al₂O₃-SiO₂ solid and HA. This article will shortly introduce the properties of Ti and Ti-based implants with their modification, and review the progress of bone tissue engineering using the TiO₂ nanotubes and scaffolds.

Regenerative Models for the Integration and Regeneration of Head Skeletal Tissues

Disease of, or trauma to, the human jaw account for thousands of reconstructive surgeries performed every year. One of the most popular and successful treatment options in this context involves the transplantation of bone tissue from a different anatomical region into the affected jaw. Although, this method has been largely successful, the integration of the new bone into the existing bone is often imperfect, and the integration of the host soft tissues with the transplanted bone can be inconsistent, resulting in impaired function. Unlike humans, several vertebrate species, including fish and amphibians, demonstrate remarkable regenerative capabilities in response to jaw injury. Therefore, with the objective of identifying biological targets to promote and engineer improved outcomes in the context of jaw reconstructive surgery, we explore, compare and contrast the natural mechanisms of endogenous jaw and limb repair and regeneration in regenerative model organisms. We focus on the role of different cell types as they contribute to the regenerating structure; how mature cells acquire plasticity in vivo; the role of positional information in pattern formation and tissue integration, and limitations to endogenous regenerative and repair mechanisms.

Comparative analysis of bone regeneration behavior using recombinant human BMP-2 versus plasmid DNA of BMP-2

Bone regeneration and the osteoinductive capacity of implants are challenging issues in clinical medicine. Currently, recombinant growth factors and nonviral gene transfer are the most frequently investigated methods for bone growth enhancement, although the more favorable method remains unclear. There is a lack of knowledge in literature about the in vivo comparison of these methods for bone regeneration. BMP-2, which is the most commonly used growth factor for osteogenesis, was applied at its most efficient dose as a recombinant growth factor (rhBMP-2) and as a growth-factor-encoding copolymer protected gene vector (pBMP-2) in a critical size bone defect (CSD) model to determine the most suitable method for bone regeneration. CSDs were induced bilaterally in 32 Sprague-Dawley rats. RhBMP-2 (62.5 μg) or pBMP-2 (2.5 μg) was embedded in poly(d,l-)lactide-coated titanium discs. Survival times were set at 14, 28, 56, and 112 days. After euthanasia, samples were analyzed via micro-computed tomography, polychrome sequential fluorescent labeling, and immunohistochemistry. Whereas defects in both groups were bridged with new bone after 56 days, rhBMP-2 initially induced ectopic new bone formation that was later remodeled in an unorganized hypodense manner. In contrast, pBMP-2 led to slower but steady bone regeneration with physiological tissue morphology, as confirmed by high osteoblast activity shown by osteocalcin staining. CD68 and TRAP staining verified high osteoclast activity for the rhBMP-2 group. pBMP-2 successfully induced locally controlled physiological bone regeneration, whereas rhBMP-2 triggered rapid and ectopic but insufficient bone formation. Thus, nonviral gene transfer appears to be more favorable for clinical applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 163-173, 2019.

Evaluation of BMP-2 Enhances the Osteoblast Differentiation of Human Amnion Mesenchymal Stem Cells Seeded on Nano-Hydroxyapatite/Collagen/Poly(l-Lactide)

Background: The aim of this study is to evaluate the effects of recombinant human bone morphogenetic protein 2 (rhBMP-2), human amnion mesenchymal stem cells (hAMSCs), and nanohydroxyapatite/collagen/poly(l-lactide) (nHAC/PLA) in tissue engineering to provide potential approaches for periodontal bone regeneration. Methods: hAMSCs were isolated from discarded amniotic membrane samples and cultured in vitro. Alkaline phosphatase (ALP) staining and alizarin red staining were performed to evaluate the osteoblast (OB) differentiation ability of hAMSCs. Three groups were divided: the experimental group (cells transfected with pcDNA3.1-rhBMP-2), the blank group (cells without gene transfection), and the control group (cells transfected with empty plasmid). RT-PCR and western blot were used to examine whether rhBMP-2 has been successfully expressed. 3-(4,5)-dimethylthiahiazol(-z-y1)-3,5-di-phenytetrazo-liumromide assay (MTT) was done to detect the effect of rhBMP-2 on hAMSCs seeded on nHAC/PLA. ALP activity, mineral formation assay, calcium, phosphate and osteocalcin (OCN) content, and OCN and RUNX2 expression of hAMSCs were detected to evaluate osteogenic differentiation capability of rhBMP-2 on hAMSCs seeded on nHAC/PLA. Results: hAMSCs exhibited intense ALP staining, obvious calcium deposition, and mineralization nodules, and rhBMP-2 were highly expressed in the experimental group. The proliferation of the hAMSCs with rhBMP-2 on nHAC/PLA was significantly higher than the cells without rhBMP-2, and the cells all increased in a time-dependent manner. rhBMP-2 significantly increased the OCN and phosphate content, mineral formation, ALP activity, osteogenic biomarkers OCN, and Runx2, and decreased calcium content in hAMSCs seeded on the nHAC/PLA scaffold. Conclusions: This finding demonstrated that hAMSCs has an ideal OB differentiation ability. rhBMP-2 facilitates the proliferation and osteogenesis of hAMSCs. The nHAC/PLA could act as a good scaffold for hAMSCs seeding, proliferation, and osteogenic differentiation. The application of rhBMP-2, nHAC/PLA, and hAMSCs in tissue engineering may offer promising possibilities for periodontal bone regeneration.

Sustained Release of BMP-2 from Porous Particles with Leaf-Stacked Structure for Bone Regeneration

Sustained release of bioactive molecules from delivery systems is a common strategy for ensuring their prolonged bioactivity and for minimizing safety issues. However, residual toxic reagents, the use of harsh organic solvents, and complex fabrication procedures in conventional delivery systems are considered enormous impediments toward clinical use. Herein, we describe bone morphogenetic protein-2 (BMP-2)-immobilized porous polycaprolactone particles with unique leaf-stacked structures (LSS particles) prepared using clinically feasible materials and procedures. The BMP-2 immobilized in these LSS particles is continuously released up to 36 days to provide an appropriate environment for osteogenic differentiation of human periosteum-derived cells and new bone formation. Thus, the leaf-stacked structures of these LSS particles provide a simple but clinically applicable platform for effectively delivering a variety of bioactive molecules, such as growth factors, hormones, cytokines, peptides, etc.

Biomaterials for the Delivery of Growth Factors and Other Therapeutic Agents in Tissue Engineering Approaches to Bone Regeneration

Bone fracture followed by delayed or non-union typically requires bone graft intervention. Autologous bone grafts remain the clinical "gold standard". Recently, synthetic bone grafts such as Medtronic's Infuse Bone Graft have opened the possibility to pharmacological and tissue engineering strategies to bone repair following fracture. This clinically-available strategy uses an absorbable collagen sponge as a carrier material for recombinant human bone morphogenetic protein 2 (rhBMP-2) and a similar strategy has been employed by Stryker with BMP-7, also known as osteogenic protein-1 (OP-1). A key advantage to this approach is its "off-the-shelf" nature, but there are clear drawbacks to these products such as edema, inflammation, and ectopic bone growth. While there are clinical challenges associated with a lack of controlled release of rhBMP-2 and OP-1, these are among the first clinical examples to wed understanding of biological principles with biochemical production of proteins and pharmacological principles to promote tissue regeneration (known as regenerative pharmacology). After considering the clinical challenges with such synthetic bone grafts, this review considers the various biomaterial carriers under investigation to promote bone regeneration. This is followed by a survey of the literature where various pharmacological approaches and molecular targets are considered as future strategies to promote more rapid and mature bone regeneration. From the review, it should be clear that pharmacological understanding is a key aspect to developing these strategies.

Graphene-Based Nanomaterials for Tissue Engineering in the Dental Field

The world of dentistry is approaching graphene-based nanomaterials as substitutes for tissue engineering. Apart from its exceptional mechanical strength, electrical conductivity and thermal stability, graphene and its derivatives can be functionalized with several bioactive molecules. They can also be incorporated into different scaffolds used in regenerative dentistry, generating nanocomposites with improved characteristics. This review presents the state of the art of graphene-based nanomaterial applications in the dental field. We first discuss the interactions between cells and graphene, summarizing the available in vitro and in vivo studies concerning graphene biocompatibility and cytotoxicity. We then highlight the role of graphene-based nanomaterials in stem cell control, in terms of adhesion, proliferation and differentiation. Particular attention will be given to stem cells of dental origin, such as those isolated from dental pulp, periodontal ligament or dental follicle. The review then discusses the interactions between graphene-based nanomaterials with cells of the immune system; we also focus on the antibacterial activity of graphene nanomaterials. In the last section, we offer our perspectives on the various opportunities facing the use of graphene and its derivatives in associations with titanium dental implants, membranes for bone regeneration, resins, cements and adhesives as well as for tooth-whitening procedures.

Localization and promotion of recombinant human bone morphogenetic protein-2 bioactivity on extracellular matrix mimetic chondroitin sulfate-functionalized calcium phosphate cement scaffolds

Localization of recombinant human bone morphogenetic protein-2 (rhBMP-2) with continuous and effective osteogenic stimulation is still a great challenge in the field of bone regeneration. To achieve this aim, rhBMP-2 was tethered on chondroitin sulfate (CS)-functionalized calcium phosphate cement (CPC) scaffolds through specific noncovalent interactions. CS, one of the core glycosaminoglycans, was covalently conjugated onto CPC scaffolds with the assistance of polydopamine (PDA) and further immobilized rhBMP-2 in a biomimetic form. The CPC-PDA-CS scaffolds not only controlled the release kinetics and presentation state of rhBMP-2 but also effectively increased the expression levels of bone morphogenetic protein receptors (BMPRs) and enhanced the recognitions of the remaining rhBMP-2 to BMPRs. Strikingly, the rhBMP-2-loaded CPC-PDA-CS significantly promoted the cellular surface translocation of BMPRs (especially BMPR-IA). In vivo studies demonstrated that, compared with the rhBMP-2 upon CPC and CPC-PDA, the rhBMP-2 upon CPC-PDA-CS exhibited sustained release and induced high quality and more ectopic bone formation. Collectively, these results suggest that rhBMP-2 can be localized within CS-functionalized CPC scaffolds and exert continuous, long-term, and effective osteogenic stimulation. Thus, this work could provide new avenues in mimicking bone extracellular matrix microenvironment and localizing growth factor activity for enhanced bone regeneration.

STATEMENT OF SIGNIFICANCE

A bioinspired chondroitin sulfate (CS)-functionalized calcium phosphate cement (CPC) platform was developed to tether recombinant human bone morphogenetic protein-2 (rhBMP-2), which could exhibit continuous, long-term, and effective osteogenic stimulation in bone tissue engineering. Compared with rhBMP-2-loaded CPC, the rhBMP-2-loaded CPC-polydopamine-CS scaffolds induced higher expression of bone morphogenetic protein receptors (BMPRs), greater cellular surface translocation of bone morphogenetic protein receptor-IA, higher binding affinity of BMPRs/rhBMP-2, and thus higher activation of the drosophila gene mothers against decapentaplegic protein-1/5/8 (Smad1/5/8) and extracellular-regulated protein kinases-1/2 (ERK1/2) signaling. This work can provide new guidelines for the design of BMP-2-based bioactive materials for bone regeneration.

Applications of Metals for Bone Regeneration

The regeneration of bone tissue is the main purpose of most therapies in dental medicine. For bone regeneration, calcium phosphate (CaP)-based substitute materials based on natural (allo- and xenografts) and synthetic origins (alloplastic materials) are applied for guiding the regeneration processes. The optimal bone substitute has to act as a substrate for bone ingrowth into a defect, as well as resorb in the time frame needed for complete regeneration up to the condition of restitution ad integrum. In this context, the modes of action of CaP-based substitute materials have been frequently investigated, where it has been shown that such materials strongly influence regenerative processes such as osteoblast growth or differentiation and also osteoclastic resorption due to different physicochemical properties of the materials. However, the material characteristics needed for the required ratio between new bone tissue formation and material degradation has not been found, until now. The addition of different substances such as collagen or growth factors and also of different cell types has already been tested but did not allow for sufficient or prompt application. Moreover, metals or metal ions are used differently as a basis or as supplement for different materials in the field of bone regeneration. Moreover, it has already been shown that different metal ions are integral components of bone tissue, playing functional roles in the physiological cellular environment as well as in the course of bone healing. The present review focuses on frequently used metals as integral parts of materials designed for bone regeneration, with the aim to provide an overview of currently existing knowledge about the effects of metals in the field of bone regeneration.

Multivalent ion-based in situ gelling polysaccharide hydrogel as an injectable bone graft

We prepared in situ gelling alginate (ALG)/hyaluronic acid (HA) hydrogels with a controllable gelation rate using CaSO₄ as a crosslinking agent and Na₂HPO₄ as a crosslinking retardation agent. The ALG/HA hydrogels provided sustained release of bone morphogenetic protein-2 (BMP-2) immobilized in the hydrogels over 5 weeks. The BMP-2-immobilized ALG/HA hydrogels with different ALG/HA ratios were investigated for their in vitro osteogenic differentiation behavior of human bone marrow stem cells (hBMSCs) and in vivo bone regeneration behavior using an animal model (mandibular defect model of miniature pigs). Our findings from cell culture and animal study demonstrated that the osteogenic differentiation of hBMSCs was improved with increasing HA composition in the hydrogel. The hBMSCs/BMP-2-immobilized ALG/HA hydrogel allowed greatly enhanced osteogenic differentiation of hBMSCs (in vitro) and bone regeneration (in vivo) compared with the ALG/HA hydrogel itself and single hBMSCs- or BMP-2-immobilized hydrogel groups.

Application of Materials as Medical Devices with Localized Drug Delivery Capabilities for Enhanced Wound Repair

The plentiful assortment of natural and synthetic materials can be leveraged to accommodate diverse wound types, as well as different stages of the healing process. An ideal material is envisioned to promote tissue repair with minimal inconvenience for patients. Traditional materials employed in the clinical setting often invoke secondary complications, such as infection, pain, foreign body reaction, and chronic inflammation. This review surveys the repertoire of surgical sutures, wound dressings, surgical glues, orthopedic fixation devices and bone fillers with drug eluting capabilities. It highlights the various techniques developed to effectively incorporate drugs into the selected material or blend of materials for both soft and hard tissue repair. The mechanical and chemical attributes of the resultant materials are also discussed, along with their biological outcomes in vitro and/or in vivo. Perspectives and challenges regarding future research endeavors are also delineated for next-generation wound repair materials.

Effects of rhBMP-2 gene transfection to periodontal ligament cells on osteogenesis

The present study aims to investigate the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the osteogenesis of periodontal ligament (PDL) cells. The expression vector of rhBMP-2 (pcDNA3.1-rhBMP-2) was established. PDL cells were obtained through the enzymatic digestion and tissue explant methods and verified by immunohistochemistry. Cells were classified into experimental (cells transfected with pcDNA3.1/rhBMP-2-EGFP), blank (cells with no transfection) and control group (cells transfected with empty plasmid). rhBMP-2 expression was assessed via Western blotting analysis. The mineralization ability, alkaline phosphatase (ALP) activity and level of related osteogenic biomarkers were detected to evaluate the osteogenic characteristics of PDL cells. The rhBMP-2 expression vector (pcDNA3.1-rhBMP-2) was successfully established. Primary PDL cells displayed a star or long, spindle shape. The cultured cells were long, spindle-shaped, had a plump cell body and homogeneous cytoplasm and the ellipse nucleus contained two or three nucleoli. Cells displayed a radial, sheaf-like or eddy-like arrangement after adherence growth. Immunohistochemical staining confirmed that cells originated from mesenchymal opposed to epithelium. The experimental group exhibited an enhanced mineralization ability, higher ALP activity and increased expression of rhBMP-2 and osteogenic biomarkers (Runx2, collagen type I and osteocalcin) than the blank and control group. The present study demonstrated that rhBMP-2 transfection enhances the osteogenesis of PDL cells and provides a possibility for the application of rhBMP-2 expression products in dental disease treatment.

Strontium doping promotes bioactivity of rhBMP-2 upon calcium phosphate cement via elevated recognition and expression of BMPR-IA

Preserving and improving osteogenic activity of bone morphogenetic protein-2 (BMP-2) upon implants remains one of the key limitations in bone regeneration. With calcium phosphate cement (CPC) as model, we have developed a series of strontium (Sr)-doped CPC (SCPC) to address this issue. The effects of fixed Sr on the bioactivity of recombinant human BMP-2 (rhBMP-2) as well as the underlying mechanism were investigated. The results suggested that the rhBMP-2-induced osteogenic activity was significantly promoted upon SCPCs, especially with a low amount of fixed Sr (SrCO₃ content <10wt%). Further studies demonstrated that the Sr-induced enhancement of bioactivity of rhBMP-2 was related to an elevated recognition of bone morphogenetic protein receptor-IA (BMPR-IA) to rhBMP-2 and an increased expression of BMPR-IA in C2C12 model cells. As a result, the activations of BMP-induced signaling pathways were different in C2C12 cells incubated upon CPC/rhBMP-2 and SCPCs/rhBMP-2. These findings explicitly decipher the mechanism of SCPCs promoting osteogenic bioactivity of rhBMP-2 and signify the promising application of the SCPCs/rhBMP-2 matrix in bone regeneration implants.

Synergistic effects of fibronectin and bone morphogenetic protein on the bioactivity of titanium metal

To improve the biological properties of bioactive titanium metal, recombinant human bone morphogenetic protein 2(rhBMP-2) and fibronectin (Fn) were adsorbed on its surface solely or contiguously to modify the anodic oxidized titanium (AO-Ti), acid-alkali-treated titanium (AA-Ti), and polished titanium (P-Ti). It is found that the different bioactive titanium surface structures had great influence on protein adsorption. The adsorption amounts of BMP adsorbed solely and Fn/BMP adsorbed contiguously were AA-Ti > P-Ti > AO-Ti, and that for Fn adsorbed solely was AA-Ti ≈ P-Ti > AO-Ti. The conformation of proteins was changed remarkably after the adsorption. For BMP, the α-helix decreased on AA-Ti and stabilized on P-Ti and AO-Ti. For Fn, the β-sheet on PT-Ti and AA-Ti increased significantly. For Fn/BMP, the percentage of β-sheet on AA-Ti increased, and that of α-helix on all samples was stable. MSCs showed greater adhesion and spreading on Fn/BMP groups. MTT and Elisa tests showed that the synergistic effects of proteins made the cells proliferate and differentiate faster. It indicated both the surface structure and the synergistic effects of proteins could influence the biological properties of titanium metals. It provides research foundation for improving the biological properties of bioactive titanium metals by simultaneous application of several proteins. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2485-2498, 2017.

Development and characterization of heparin-immobilized polycaprolactone nanofibrous scaffolds for tissue engineering using gamma-irradiation

Polycaprolactone (PCL) has been considered a useful material for orthopedic devices and osseous implants because of its biocompatibility and bone-forming activity.

Tethering of rhBMP-2 upon calcium phosphate cement via alendronate/heparin for localized, sustained and enhanced osteoactivity

rhBMP-2 was tethered on surface of calcium phosphate cement via alendronate–heparin. This novel delivery system can concurrently satisfy high bioactive immobilization and sustainable release of rhBMP-2, and consequently induce rapid bone regeneration.

Engineering a favourable osteogenic microenvironment by heparin mediated hybrid coating assembly and rhBMP-2 loading

(1) HApNPs are conferred with negative charges by surface modification with heparin. (2) Heparinized HApNPs and polycation CS are assembled to form a hybrid coating. (3) RhBMP-2 is introduced into the coating via the intermolecular binding with heparin.

Improved rhBMP-2 function on MBG incorporated TiO2 nanorod films

In the process of biomaterials mediated bone regeneration, rhBMP-2 delivery at efficient dose in sustained kinetics is crucial for promoting cell osteogenic differentiation. Meanwhile, surface morphology of the biomaterials could regulate cellular responses as well as strengthen the rhBMP-2 interaction with cells for better bone induction. Herein, TiO₂ nanorod films with varied mesoporous bioactive glass (MBG) incorporation amount were designed to strengthen the efficacy of rhBMP-2, basing on optimized loading/release behaviors and surface nanostructure cooperatively. The MBG incorporation improved rhBMP-2 loading amount and regulated its release behavior. Consequently, the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) on the incorporated films was extremely enhanced, and the incorporated nanorod film with 200nm MBG thickness exhibited the best osteoinduction effect. However, MBG film and the incorporated nanorod film had the same loading amount of rhBMP-2, the latter showed a much higher expression of 7-day osteogenic differentiation index than the former, which could be attributed to the synergistic effect of optimized rhBMP-2 release behavior and surface morphology. The MBG incorporated TiO₂ nanorod films here presents a promising strategy for enhancing osteoinduction through optimized rhBMP-2 release behavior.

The modulation of stem cell behaviors by functionalized nanoceramic coatings on Ti-based implants

Nanoceramic coating on the surface of Ti-based metallic implants is a clinical potential option in orthopedic surgery. Stem cells have been found to have osteogenic capabilities. It is necessary to study the influences of functionalized nanoceramic coatings on the differentiation and proliferation of stem cells in vitro or in vivo. In this paper, we summarized the recent advance on the modulation of stem cells behaviors through controlling the properties of nanoceramic coatings, including surface chemistry, surface roughness and microporosity. In addition, mechanotransduction pathways have also been discussed to reveal the interaction mechanisms between the stem cells and ceramic coatings on Ti-based metals. In the final part, the osteoinduction and osteoconduction of ceramic coating have been also presented when it was used as carrier of BMPs in new bone formation.

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The effects of basic physical properties like roughness, topography and porous stucture of ceramic coatings on the stem cells behaviors on Ti-based alloys have been reviewed together.

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The chemical way to modulate the cell behaviors is also discussed in this review paper; and the related mechanotransduction pathways have been described in this paper.

Growth-Factor Nanocapsules That Enable Tunable Controlled Release for Bone Regeneration

Growth factors are of great potential in regenerative medicine. However, their clinical applications are largely limited by the short in vivo half-lives and the narrow therapeutic window. Thus, a robust controlled release system remains an unmet medical need for growth-factor-based therapies. In this research, a nanoscale controlled release system (degradable protein nanocapsule) is established via in situ polymerization on growth factor. The release rate can be finely tuned by engineering the surface polymer composition. Improved therapeutic outcomes can be achieved with growth factor nanocapsules, as illustrated in spinal cord fusion mediated by bone morphogenetic protein-2 nanocapsules.

Enhanced osteogenesis on biofunctionalized poly(ɛ-caprolactone)/poly(m-anthranilic acid) nanofibers

Biofunctionalized nanofibers with a desired biological function can be used as a tissue engineering scaffold due to their small fiber diameters and porous structure. In the present study, poly(ɛ-caprolactone)/poly(m-anthranilic acid) nanofibers were biofunctionalized with covalent immobilization of bone morphogenetic protein-2 (BMP-2) through 1-ethyl-3-(dimethyl-aminopropyl) carbodiimide hydrochloride/N-hydroxysuccinimide activation. Fourier transform infrared analysis of the nanofiber surfaces confirmed the successful immobilization. The amount of immobilized BMP-2 was determined with bicinchoninic acid protein assay. The nanofibers before and after BMP-2 immobilization were non-cytotoxic and enhanced the attachment and proliferation of Saos-2 cells. Biofunctionalization of nanofibers with BMP-2 promoted in vitro osteogenic activity. The alkaline phosphatase activity and calcium mineralizatio of cells after 14 days of in vitro culture were enhanced on nanofibers with immobilized BMP-2.

Self-assembled Biodegradable Nanoparticles and Polysaccharides as Biomimetic ECM Nanostructures for the Synergistic effect of RGD and BMP-2 on Bone Formation

Producing biomimetic extracellular matrix (ECM) is an effective approach to improve biocompatibility of medical devices. In this study, biomimetic ECM nanostructures are constructed through layer-by-layer self-assembling positively charged chitosan (Chi), negatively charged oxidized sodium alginate (OAlg), and positively charged bovine serum albumin (BSA)-based nanoparticles. The BSA-based nanoparticles in the self-assembled films not only result in porous nanostructures similar to natural ECM, but also preserve the activity and realize the sustained release of Bone morphogenetic protein-2 (BMP-2). The results of bone marrow stem cells (BMSCs) culture demonstrate that the penta-peptide glycine-arginine-glycine-aspartate-serine (GRGDS) grafted Chi/OAlg films favor cell adhesion and proliferation. GRGDS and BMP-2 in biomimetic ECM nanostructures synergistically promote BMSC functions and new bone formation. The RGD and BMP incorporated biomimetic ECM coatings could be applied on a variety of biomedical devices to improve the bioactivity and biocompatibility.

Development of Porous Beads to Provide Regulated BMP-2 Stimulation for Varying Durations: In Vitro and In Vivo Studies for Bone Regeneration

It is commonly accepted that the sustained release of bone morphogenetic protein-2 (BMP-2) can enhance bone regeneration and minimize its safety issues. However, little is known regarding the appropriate duration of BMP-2 stimulation for sufficient osteogenic differentiation and new bone formation because of the short half-life of BMP-2 in the physiological environment and the lack of a well-defined delivery matrix that can regulate the release period of BMP-2. In this study, we prepared porous poly(lactic-co-glycolic acid) (PLGA) beads with different surface pore sizes that can regulate the release period of BMP-2 (i.e., 7, 17, and 30 days) while providing the BMP-2 concentration required for bone regeneration. Our findings in both in vitro cell culture and in vivo animal studies using these BMP-2-loaded beads demonstrate that release of BMP-2 within 7 days affects only the initial differentiation of human periosteum-derived cells (hPDCs) and does not significantly enhance their subsequent differentiation into mature functional cells. However, extending the duration of BMP-2 stimulation over 17 days can provide a suitable environment for osteogenic differentiation of hPDCs and new bone formation.

Regulating the osteogenic function of rhBMP 2 by different titanium surface properties

Bone morphogenetic protein 2 (BMP-2) is important for regulating the osteogenic differentiation of mesenchymal stem cells and the response of bone tissue. It adsorbs on the surface of biomedical implants immediately and plays a role of mediator between the materials surfaces and the host cells. Studies usually connect the material surface properties and the new bone formation directly. However, interaction between the adsorbed BMP-2 on the implant surface and the cells in the tissue is the key to explaining the osteogenic properties of the material. So, in this article, we investigated the conformational and functional changes induced by the surface modified titanium metals. We found that the α-helix and β-sheet structure of rhBMP-2 can be well maintained on the anodic oxidation treated titanium surface. The osteogenic function of rhBMP-2 can sustain for a relatively long time even though there is less amount adhere to the surface compared with that on the acid alkali treated titanium. Surface properties, especially the morphology enable a larger amount of rhBMP-2 to adsorb to the surface of the acid alkali treated titanium, but the conformation of the protein is severely influenced. The percentage of α-helix structure is also significantly decreased so that the efficacy of rhBMP-2 is only maintained in the early time. This study indicated that different surface modification of the surface could regulate the structure of rhBMP-2 and then further influence its osteogenic function. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1882-1893, 2016.

Surface Functionalization of Titanium Alloy with miR-29b Nanocapsules To Enhance Bone Regeneration

Titanium and its alloys have been widely used over the past 3 decades as implants for healing bone defects. Nevertheless, the bioinert property of titanium alloy limits its clinical application and surface modification method is frequently performed to improve the biological and chemical properties. Recently, the delivery of microRNA with osteogenesis capability has been recognized as a promising tool to enhance bone regeneration of implants. Here, we developed a biodegradable coating to modify the titanium surface in order to enhance osteogenic bioactivity. The previous developed nanocapsules were used as the building blocks, and then a bioactive titanium coating was designed to entrap the miR-29b nanocapsules. This coating was not only favorable for cell adhesion and growth but also provided sufficient microRNA transfection efficacy and osteoinductive potential, resulting in a significant enhancement of bone regeneration on the surface of bioinert titanium alloy.

A review on carrier systems for bone morphogenetic protein-2

Bone morphogenetic protein-2 (BMP-2) has unique bone regeneration property. The powerful osteoinductive nature makes it considered as second line of therapy in nonunion bone defect. A large number of carriers and delivery systems made up of different materials have been investigated for controlled and sustained release of BMP-2. The delivery systems are in the form of hydrogel, microsphere, nanoparticles, and fibers. The carriers used for the delivery are made up of metals, ceramics, polymers, and composites. Implantation of these protein-loaded carrier leads to cell adhesion, degradation which eventually releases the drug/protein at site specific. But, problems like ectopic growth, lesser protein delivery, inactivation of the protein are reported in the available carrier systems. Therefore, it is need of an hour to modify the available carrier systems as well as explore other biomaterials with desired properties. In this review, all the reported carrier systems made of metals, ceramics, polymers, composites are evaluated in terms of their processing conditions, loading capacity and release pattern of BMP-2. Along with these biomaterials, the attempts of protein modification by adding some functional group to BMP-2 or extracting functional peptides from the protein to achieve the desired effect, is also evaluated. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 904-925, 2017.

Spatiotemporal release of BMP-2 and VEGF enhances osteogenic and vasculogenic differentiation of human mesenchymal stem cells and endothelial colony-forming cells co-encapsulated in a patterned hydrogel

Reconstruction of large bone defects is limited by insufficient vascularization and slow bone regeneration. The objective of this work was to investigate the effect of spatial and temporal release of recombinant human bone morphogenetic protein-2 (BMP2) and vascular endothelial growth factor (VEGF) on the extent of osteogenic and vasculogenic differentiation of human mesenchymal stem cells (hMSCs) and endothelial colony-forming cells (ECFCs) encapsulated in a patterned hydrogel. Nanogels (NGs) based on polyethylene glycol (PEG) macromers chain-extended with short lactide (L) and glycolide (G) segments were used for grafting and timed-release of BMP2 and VEGF. NGs with 12kDa PEG molecular weight (MW), 24 LG segment length, and 60/40L/G ratio (P12-II, NG(10)) released the grafted VEGF in 10days. NGs with 8kDa PEG MW, 26 LG segment length, and 60/40L/G ratio (P8-I, NG(21)) released the grafted BMP2 in 21days. hMSCs and NG-BMP2 were encapsulated in a patterned matrix based on acrylate-functionalized lactide-chain-extended star polyethylene glycol (SPELA) hydrogel and microchannel patterns filled with a suspension of hMSCs+ECFCs and NG-VEGF in a crosslinked gelatin methacryloyl (GelMA) hydrogel. Groups included patterned constructs without BMP2/VEGF (None), with directly added BMP2/VEGF, and NG-BMP2/NG-VEGF. Based on the results, timed-release of VEGF in the microchannels in 10days from NG(10) and BMP2 in the matrix in 21days from NG(21) resulted in highest extent of osteogenic and vasculogenic differentiation of the encapsulated hMSCs and ECFCs compared to direct addition of VEGF and BMP2. Further, timed-release of VEGF from NG(10) in hMSC+ECFC encapsulating microchannels and BMP2 from NG(21) in hMSC encapsulating matrix sharply increased bFGF expression in the patterned constructs. The results suggest that mineralization and vascularization are coupled by localized secretion of paracrine signaling factors by the differentiating hMSCs and ECFCs.

When 1+1>2: Nanostructured composites for hard tissue engineering applications

Multicomponent, synergistic and multifunctional nanostructures have taken over the spotlight in the realm of biomedical nanotechnologies. The most prospective materials for bone regeneration today are almost exclusively composites comprising two or more components that compensate for the shortcomings of each one of them alone. This is quite natural in view of the fact that all hard tissues in the human body, except perhaps the tooth enamel, are composite nanostructures. This review article highlights some of the most prospective breakthroughs made in this research direction, with the hard tissues in main focus being those comprising bone, tooth cementum, dentin and enamel. The major obstacles to creating collagen/apatite composites modeled after the structure of bone are mentioned, including the immunogenicity of xenogeneic collagen and continuously failing attempts to replicate the biomineralization process in vitro. Composites comprising a polymeric component and calcium phosphate are discussed in light of their ability to emulate the soft/hard composite structure of bone. Hard tissue engineering composites created using hard material components other than calcium phosphates, including silica, metals and several types of nanotubes, are also discoursed on, alongside additional components deliverable using these materials, such as cells, growth factors, peptides, antibiotics, antiresorptive and anabolic agents, pharmacokinetic conjugates and various cell-specific targeting moieties. It is concluded that a variety of hard tissue structures in the body necessitates a similar variety of biomaterials for their regeneration. The ongoing development of nanocomposites for bone restoration will result in smart, theranostic materials, capable of acting therapeutically in direct feedback with the outcome of in situ disease monitoring at the cellular and subcellular scales. Progress in this research direction is expected to take us to the next generation of biomaterials, designed with the purpose of fulfilling Daedalus' dream - not restoring the tissues, but rather augmenting them.

Electrochemically assisted deposition of hydroxyapatite on Ti6Al4V substrates covered by CVD diamond films - Coating characterization and first cell biological results

Although titanium and its alloys are widely used as implant material for orthopedic and dental applications they show only limited corrosion stability and osseointegration in different cases. The aim of the presented research was to develop and characterize a novel surface modification system from a thin diamond base layer and a hydroxyapatite (HAp) top coating deposited on the alloy Ti6Al4V widely used for implants in contact with bone. This coating system is expected to improve both the long-term corrosion behavior and the biocompatibility and bioactivity of respective surfaces. The diamond base films were obtained by Microwave Plasma Assisted Chemical Vapor Deposition (MW-PACVD); the HAp coatings were formed in aqueous solutions by electrochemically assisted deposition (ECAD) at varying polarization parameters. Scanning electron microscopy (SEM), Raman microscopy, and electrical conductivity measurements were applied to characterize the generated surface states; the calcium phosphate coatings were additionally chemically analyzed for their composition. The biological properties of the coating system were assessed using hMSC cells analyzing for cell adhesion, proliferation, and osteogenic differentiation. Varying MW-PACVD process conditions resulted in composite coatings containing microcrystalline diamond (MCD/Ti-C), nanocrystalline diamond (NCD), and boron-doped nanocrystalline diamond (B-NCD) with the NCD coatings being dense and homogeneous and the B-NCD coatings showing increased electrical conductivity. The ECAD process resulted in calcium phosphate coatings from stoichiometric and non-stoichiometric HAp. The deposition of HAp on the B-NCD films run at lower cathodic potentials and resulted both in the highest coating mass and the most homogenous appearance. Initial cell biological investigations showed an improved cell adhesion in the order B-NCD>HAp/B-NCD>uncoated substrate. Cell proliferation was improved for both investigated coatings whereas ALP expression was highest for the uncoated substrate.

Calcium phosphate nanocoatings and nanocomposites, part I: recent developments and advancements in tissue engineering and bioimaging

A number of materials have been applied as implant coatings and as tissue regeneration materials. Calcium phosphate holds a special consideration, due to its chemical similarity to human bone and, most importantly, its dissolution characteristics, which allow for bone growth and regeneration. The applications of molecular and nanoscale-based biological materials have been and will continue to play an ever increasing role in enhancing and improving the osseointegration of dental and orthopedic implants. More recently, extensive research efforts have been focused on the development and applications of fluorescent nanoparticles and nanocoatings for in vivo imaging and diagnostics as well as devising methods of adding luminescent or fluorescent capabilities to enhance the in vivo functionality of calcium phosphate-based biomedical materials.

Effects of Immobilized BMP-2 and Nanofiber Morphology on In Vitro Osteogenic Differentiation of hMSCs and In Vivo Collagen Assembly of Regenerated Bone

Engineering bone tissue is particularly challenging because of the distinctive structural features of bone within a complex biochemical environment. In the present study, we fabricated poly(L-lactic acid) (PLLA) electrospun nanofibers with random and aligned morphology immobilized with bone morphogenic protein-2 (BMP-2) and investigated how these signals modulate (1) in vitro osteogenic differentiation of human mesenchymal stem cells (hMSCs) and (2) in vivo bone growth rate, mechanical properties, and collagen assembly of newly formed bone. The orientation of adherent cells followed the underlying nanofiber morphology; however, nanofiber alignment did not show any difference in alkaline phosphate activity or in calcium mineralization of hMSCs after 14 days of in vitro culture in osteogenic differentiation media. In vivo bone regeneration was significantly higher in the nanofiber implanted groups (approximately 65-79%) as compared to the defect-only group (11.8 ± 0.2%), while no significant difference in bone regeneration was observed between random and aligned groups. However, nanoindentation studies of regenerated bone revealed Young's modulus and contact hardness with anisotropic feature for aligned group as compared to random group. More importantly, structural analysis of collagen at de novo bone showed the ability of nanofiber morphology to guide collagen deposition. SEM and TEM images revealed regular, highly ordered collagen assemblies on aligned nanofibers as compared to random fibers, which showed irregular, randomly organized collagen deposition. Taken together, we conclude that nanofibers in the presence of osteoinductive signals are a potent tool for bone regeneration, and nanofiber alignment can be used for engineering bone tissues with structurally assembled collagen fibers with defined direction.

Bone Regeneration Using Bone Morphogenetic Proteins and Various Biomaterial Carriers

Trauma and disease frequently result in fractures or critical sized bone defects and their management at times necessitates bone grafting. The process of bone healing or regeneration involves intricate network of molecules including bone morphogenetic proteins (BMPs). BMPs belong to a larger superfamily of proteins and are very promising and intensively studied for in the enhancement of bone healing. More than 20 types of BMPs have been identified but only a subset of BMPs can induce de novo bone formation. Many research groups have shown that BMPs can induce differentiation of mesenchymal stem cells and stem cells into osteogenic cells which are capable of producing bone. This review introduces BMPs and discusses current advances in preclinical and clinical application of utilizing various biomaterial carriers for local delivery of BMPs to enhance bone regeneration.

Polysaccharide nanoparticles for protein and Peptide delivery: exploring less-known materials

Finding adequate carriers for protein and peptide delivery has become an urgent need, owing to the growing number of macromolecules identified as having therapeutic potential. Nanoparticles have emerged in the field as very promising vehicles and much work has been directed to testing the capacity of different materials to compose the matrix of these carriers. Natural materials and, specifically, polysaccharides have been taking the forefront of the challenge, because of several favoring properties that include the higher propensity to exhibit biodegradability and biocompatibility, and also the high structural flexibility. The majority of works found in the literature regarding polysaccharide nanoparticles uses very popular materials like chitosan or hyaluronic acid. This review is aimed at describing and exploring the potential of polysaccharides that are not so well known or that are less explored. For those, the main properties will be described, together with an overview of the reported applications as nanoparticle matrix materials.

Bone Morphogenetic Protein-2 Adsorption onto Poly-ɛ-caprolactone Better Preserves Bioactivity In Vitro and Produces More Bone In Vivo than Conjugation Under Clinically Relevant Loading Scenarios

BACKGROUND

One strategy to reconstruct large bone defects is to prefabricate a vascularized flap by implanting a biomaterial scaffold with associated biologics into the latissimus dorsi and then transplanting this construct to the defect site after a maturation period. This strategy, similar to all clinically and regulatory feasible biologic approaches to surgical reconstruction, requires the ability to quickly (<1 h within an operating room) and efficiently bind biologics to scaffolds. It also requires the ability to localize biologic delivery. In this study, we investigated the efficacy of binding bone morphogenetic protein-2 (BMP2) to poly-ɛ-caprolactone (PCL) using adsorption and conjugation as a function of time.

METHODS

BMP2 was adsorbed (Ads) or conjugated (Conj) to PCL scaffolds with the same three-dimensional printed architecture while altering exposure time (0.5, 1, 5, and 16 h), temperature (4°C, 23°C), and BMP2 concentration (1.4, 5, 20, and 65 μg/mL). The in vitro release was quantified, and C2C12 cell alkaline phosphatase (ALP) expression was used to confirm bioactivity. Scaffolds with either 65 or 20 μg/mL Ads or Conj BMP2 for 1 h at 23°C were implanted subcutaneously in mice to evaluate in vivo bone regeneration. Micro-computed tomography, compression testing, and histology were performed to characterize bone regeneration.

RESULTS

After 1 h exposure to 65 μg/mL BMP2 at 23°C, Conj and Ads resulted in 12.83 ± 1.78 and 10.78 ± 1.49 μg BMP2 attached, respectively. Adsorption resulted in a positive ALP response and had a small burst release; whereas conjugation provided a sustained release with negligible ALP production, indicating that the conjugated BMP2 may not be bioavailable. Adsorbed 65 μg/mL BMP2 solution resulted in the greatest regenerated bone volume (15.0 ± 3.0 mm³), elastic modulus (20.1 ± 3.0 MPa), and %bone ingrowth in the scaffold interior (17.2% ± 5.4%) when compared with conjugation.

CONCLUSION

Adsorption may be optimal for the clinical application of prefabricating bone flaps due to BMP2 binding in a short exposure time, retained BMP2 bioactivity, and bone growth adhering to scaffold geometry and into pores with healthy marrow development.

Biodegradable chitosan nanoparticle coatings on titanium for the delivery of BMP-2

A simple method for the functionalization of a common implant material (Ti6Al4V) with biodegradable, drug loaded chitosan-tripolyphosphate (CS-TPP) nanoparticles is developed in order to enhance the osseointegration of endoprostheses after revision operations. The chitosan used has a tailored degree of acetylation which allows for a fast biodegradation by lysozyme. The degradability of chitosan is proven via viscometry. Characteristics and degradation of nanoparticles formed with TPP are analyzed using dynamic light scattering. The particle degradation via lysozyme displays a decrease in particle diameter of 40% after 4 days. Drug loading and release is investigated for the nanoparticles with bone morphogenetic protein 2 (BMP-2), using ELISA and the BRE luciferase test for quantification and bioactivity evaluation. Furthermore, nanoparticle coatings on titanium substrates are created via spray-coating and analyzed by ellipsometry, scanning electron microscopy and X-ray photoelectron spectroscopy. Drug loaded nanoparticle coatings with biologically active BMP-2 are obtained in vitro within this work. Additionally, an in vivo study in mice indicates the dose dependent induction of ectopic bone growth through CS-TPP-BMP-2 nanoparticles. These results show that biodegradable CS-TPP coatings can be utilized to present biologically active BMP-2 on common implant materials like Ti6Al4V.

The bifunctional regulation of interconnected Zn-incorporated ZrO2 nanoarrays in antibiosis and osteogenesis

Bifunctional regulation in antibiosis and osteogenesis is obtained using well-organized Zn-incorporated ZrO₂ nanoarrays with interconnected internal space.