Synergistic effects of BMP-2, BMP-6 or BMP-7 with human plasma fibronectin onto hydroxyapatite coatings: A comparative study

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.

Engineered dual affinity protein fragments to bind collagen and capture growth factors

Collagen type I lacks affinity for growth factors (GFs) and yet it is clinically used to deliver bone morphogenic protein 2 (BMP-2), a potent osteogenic growth factor. To mitigate this lack of affinity, supra-physiological concentrations of BMP-2 are loaded in collagen sponges leading to uncontrolled BMP-2 leakage out of the material. This has led to important adverse side effects such as carcinogenesis. Here, we design recombinant dual affinity protein fragments, produced in E. Coli, which contain two regions, one that spontaneously binds to collagen and a second one that binds BMP-2. By adding the fragment to collagen sponges, BMP-2 is sequestered enabling solid phase presentation of BMP-2. We demonstrate osteogenesis in vivo with ultra-low doses of BMP-2. Our protein technology enhances the biological activity of collagen without using complex chemistries or changing the manufacturing of the base material and so opens a pathway to clinical translation.

Cellular Response to Bone Morphogenetic Proteins-2 and -7 Covalently Bound to Photocrosslinked Heparin-Diazoresin Multilayer

Despite the plethora of research that exists on recombinant human bone morphogenetic protein-2 and -7 (rhBMP-2 and rhBMP-7) and has been clinically approved, there is still a need to gain information that would allow for their more rational use in bone implantology. The clinical application of supra-physiological dosages of these superactive molecules causes many serious adverse effects. At the cellular level, they play a role in osteogenesis and cellular adhesion, migration, and proliferation around the implant. Therefore, in this work, we investigated the role of the covalent binding of rhBMP-2 and rhBMP-7 separately and in combination with ultrathin multilayers composed of heparin and diazoresin in stem cells. In the first step, we optimized the protein deposition conditions via quartz crystal microbalance (QCM). Then, atomic force microscopy (AFM) and enzyme-linked immunosorbent assay (ELISA) were used to analyze protein-substrate interactions. The effect of the protein binding on the initial cell adhesion, migration, and short-term expression of osteogenesis markers was tested. In the presence of both proteins, cell flattening and adhesion became more prominent, resulting in limited motility. However, the early osteogenic marker expression significantly increased compared to the single protein systems. The presence of single proteins resulted in the elongation of cells, which promoted their migration activity.

Craniofacial therapy: advanced local therapies from nano-engineered titanium implants to treat craniofacial conditions

Nano-engineering-based tissue regeneration and local therapeutic delivery strategies show significant potential to reduce the health and economic burden associated with craniofacial defects, including traumas and tumours. Critical to the success of such nano-engineered non-resorbable craniofacial implants include load-bearing functioning and survival in complex local trauma conditions. Further, race to invade between multiple cells and pathogens is an important criterion that dictates the fate of the implant. In this pioneering review, we compare the therapeutic efficacy of nano-engineered titanium-based craniofacial implants towards maximised local therapy addressing bone formation/resorption, soft-tissue integration, bacterial infection and cancers/tumours. We present the various strategies to engineer titanium-based craniofacial implants in the macro-, micro- and nano-scales, using topographical, chemical, electrochemical, biological and therapeutic modifications. A particular focus is electrochemically anodised titanium implants with controlled nanotopographies that enable tailored and enhanced bioactivity and local therapeutic release. Next, we review the clinical translation challenges associated with such implants. This review will inform the readers of the latest developments and challenges related to therapeutic nano-engineered craniofacial implants.

Icariin Has a Synergistic Effect on the Osteoinductivity of Bone Morphogenetic Protein 2 at Ectopic Sites

OBJECTIVE

Establishing biocompatible, biodegradable, osteoconductive, and osteoinductive bone materials remains a challenging subject in the research of bone healing and bone regeneration. Previously, we demonstrated the osteogenic and osteoconductive effects of biomimetic calcium phosphate (BioCaP) incorporating with Icariin and/or bone morphogenetic protein 2 (BMP-2) at orthotopic sites.

METHODS

By implanting the BioCaP granules incorporated Icariin and/or BMP-2 into the dorsal subcutaneous pockets of adult male Sprague-Dawley (S-D) rats (6-7 weeks old), we investigated the osteoinductive efficacy of the samples. Micro-computed tomography(micro-CT) observations and histological slices were used to verify the osteoinduction of this system on the 2^nd and 5^th week. Statistical significances was evaluated using Turkey's post hoc test of one-way analysis of variance.

RESULTS

The osteoinduction of the BioCaP incorporated with BMP-2 or both agents was confirmed as expected. BioCaP with Icariin alone could not generate bone formation at an ectopic sites. Nevertheless, co-administration of Icariin increased bone mineral density (BMD; p < 0.01) (628mg HA/cm³ vs 570mg HA/cm³ ) and completely changed the distribution of newly formed bone when compared with the granules with BMP-2 alone, even though there was no significant difference in the volume of newly formed bone. In contrast, the BioCaP with both agents (37.86%) had significantly fewer remaining materials than the other groups by the end of the fifth week (53.22%, 53.62% and 48.22%) (p < 0.01).

CONCLUSION

The co-administration of Icariin and BMP-2 increased BMD changed the distribution of newly formed bone, and reduced the amount of remaining materials. Therefore, Icariin can stimulate BMP-2 when incorporated into BioCaP granules at ectopic sites, which makes it useful for bone tissue engineering.

Pushing the Natural Frontier: Progress on the Integration of Biomaterial Cues toward Combinatorial Biofabrication and Tissue Engineering

The engineering of fully functional, biological-like tissues requires biomaterials to direct cellular events to a near-native, 3D niche extent. Natural biomaterials are generally seen as a safe option for cell support, but their biocompatibility and biodegradability can be just as limited as their bioactive/biomimetic performance. Furthermore, integrating different biomaterial cues and their final impact on cellular behavior is a complex equation where the outcome might be very different from the sum of individual parts. This review critically analyses recent progress on biomaterial-induced cellular responses, from simple adhesion to more complex stem cell differentiation, looking at the ever-growing possibilities of natural materials modification. Starting with a discussion on native material formulation and the inclusion of cell-instructive cues, the roles of shape and mechanical stimuli, the susceptibility to cellular remodeling, and the often-overlooked impact of cellular density and cell-cell interactions within constructs, are delved into. Along the way, synergistic and antagonistic combinations reported in vitro and in vivo are singled out, identifying needs and current lessons on the development of natural biomaterial libraries to solve the cell-material puzzle efficiently. This review brings together knowledge from different fields envisioning next-generation, combinatorial biomaterial development toward complex tissue engineering.

Statistic Copolymers Working as Growth Factor-Binding Mimics of Fibronectin

Growth factors (GFs) play important roles in biological system and are widely used in tissue regeneration. However, their application is greatly hindered by short in vivo lifetime of GFs. GFs are bound to fibronectin dynamically in the extracellular matrix, which inspired the authors to mimic the GF binding domain of fibronectin and design GF-binding amphiphilic copolymers bearing positive charges. The optimal amino acid polymer can bind to a variety of representative GFs, such as bone morphogenetic protein-2 (BMP-2) and TGF-β1 from the transforming growth factor-β superfamily, PDGF-AA and PDGF-BB from the platelet-derived growth factor family, FGF-10 and FGF-21 from the fibroblast growth factor family, epidermal growth factor from the EGF family and hepatocyte growth factor from the plasminogen-related growth factor family, with binding affinities up to the nanomolar level. 3D scaffolds immobilized with the optimal copolymer enable sustained release of loaded BMP-2 without burst release and significantly enhances the in vivo function of BMP-2 for bone formation. This strategy opens new avenues in designing GF-binding copolymers as synthetic mimics of fibronectin for diverse applications.

Biodegradable macromers for implant bulk and surface engineering

Macromers, polymeric molecules with at least two functional groups for cross-polymerization, are interesting materials to tailor mechanical, biochemical and degradative bulk and surface properties of implants for tissue regeneration. In this review we focus on macromers with at least one biodegradable building block. Manifold design options, such as choice of polymeric block(s), optional core molecule and reactive groups, as well as cross-co-polymerization with suitable anchor or linker molecules, allow the adaptation of macromer-based biomaterials towards specific application requirements in both hard and soft tissue regeneration. Implants can be manufactured from macromers using additive manufacturing as well as molding and templating approaches. This review summarizes and discusses the overall concept of biodegradable macromers and recent approaches for macromer processing into implants as well as techniques for surface modification directed towards bone regeneration. These aspects are reviewed including a focus on the authors' contributions to the field through research within the collaborative research project Transregio 67.

The Role of Growth Factors in Bioactive Coatings

With increasing obesity and an ageing population, health complications are also on the rise, such as the need to replace a joint with an artificial one. In both humans and animals, the integration of the implant is crucial, and bioactive coatings play an important role in bone tissue engineering. Since bone tissue engineering is about designing an implant that maximally mimics natural bone and is accepted by the tissue, the search for optimal materials and therapeutic agents and their concentrations is increasing. The incorporation of growth factors (GFs) in a bioactive coating represents a novel approach in bone tissue engineering, in which osteoinduction is enhanced in order to create the optimal conditions for the bone healing process, which crucially affects implant fixation. For the application of GFs in coatings and their implementation in clinical practice, factors such as the choice of one or more GFs, their concentration, the coating material, the method of incorporation, and the implant material must be considered to achieve the desired controlled release. Therefore, the avoidance of revision surgery also depends on the success of the design of the most appropriate bioactive coating. This overview considers the integration of the most common GFs that have been investigated in in vitro and in vivo studies, as well as in human clinical trials, with the aim of applying them in bioactive coatings. An overview of the main therapeutic agents that can stimulate cells to express the GFs necessary for bone tissue development is also provided. The main objective is to present the advantages and disadvantages of the GFs that have shown promise for inclusion in bioactive coatings according to the results of numerous studies.

Bone Morphogenetic Protein 7 Expression in Alveolar Bone Addition With Autologous Blood, Lyophilized Bone and Atelocollagen

BACKGROUND/AIM

The biomaterials used in guided bone regeneration have undergone significant diversification in recent years. This study aimed to evaluate alveolar bone addition and bone morphogenetic protein 7 (BMP7) expression using an improved autologous and xenogeneic biomaterial.

MATERIALS AND METHODS

Chronic marginal periodontitis was induced in sheep; the intervention group received bone addition as periodontal therapy, using a composite system with lyophilized bovine bone enriched with atelocollagen type 1, platelet-rich plasma and advanced platelet-rich fibrin (A-PRF). Six weeks after the intervention, the dentoalveolar structures were evaluated using hematoxylin-eosin and immunohistochemical staining, to evaluate bone addition and BMP7 expression.

RESULTS

The untreated sheep showed inflammation, periodontal ligament destruction, remnants of calculus and bacterial plaque as well as foreign bodies in the desmodontal space, without sings of repair. In the treated sheep, fibroblasts/fibrosis, cartilage and/or new bone, cellular cementum and desmodontium, along with remnants of biomaterial with various degrees of cellularity were observed. In the untreated group, the presence of BMP7 was found in osteoblasts and osteocytes while in the treated group, it was mainly found in the biomaterial remnants, while immunohistochemical staining was less intense in the newly formed osteo-periodontal tissues. Quantitative analysis using the Mann-Whitney U-test showed highly statistically significant differences between the two groups, demonstrating the efficiency of this composite system.

CONCLUSION

The current composite system meets all the necessary conditions for promising guided alveolar bone regeneration.

Fabricating a novel HLC-hBMP2 fusion protein for the treatment of bone defects

Treating serious bone trauma with an osteo-inductive agent such as bone morphogenetic proteins (BMPs) has been considered as an optimized option when delivered via a collagen sponge (CS). Previous works have shown that the BMP concentration and release rate from approved CS carriers is difficult to control with precision. Here we presented the fabrication of a recombinant fusion protein from recombinant human-like collagen (HLC) and human BMP-2 (hBMP2). The fusion protein preserved the characteristic of HLC allowing the recombinant protein to be expressed in Yeast (such as Pichia pastoris GS115) and purified rapidly and easily with mass production after methanol induction. It also kept the stable properties of HLC and hBMP2 in the body fluid environment with good biocompatibility and no cytotoxicity. Moreover, the recombinant fusion protein fabricated a vertical through-hole structure with improved mechanical properties, and thus facilitated migration of bone marrow mesenchymal stem cells (MSCs) into the fusion materials. Furthermore, the fusion protein degraded and released hBMP-2 in vivo allowing osteoinductive activity and the enhancement of utilization rate and the precise control of the hBMP2 release. This fusion protein when applied to cranial defects in rats was osteoinductively active and improved bone repairing enhancing the repairing rate 3.5- fold and 4.2- fold when compared to the HLC alone and the control, respectively. There were no visible inflammatory reactions, infections or extrusions around the implantation sites observed. Our data strongly suggests that this novel recombinant fusion protein could be more beneficial in the treatment of bone defects than the simple superposition of the hBMP2/collagen sponge.

The Body's Cellular and Molecular Response to Protein-Coated Medical Device Implants: A Review Focused on Fibronectin and BMP Proteins

Recent years have seen a marked rise in implantation into the body of a great variety of devices: hip, knee, and shoulder replacements, pacemakers, meshes, glucose sensors, and many others. Cochlear and retinal implants are being developed to restore hearing and sight. After surgery to implant a device, adjacent cells interact with the implant and release molecular signals that result in attraction, infiltration of the tissue, and attachment to the implant of various cell types including monocytes, macrophages, and platelets. These cells release additional signaling molecules (chemokines and cytokines) that recruit tissue repair cells to the device site. Some implants fail and require additional revision surgery that is traumatic for the patient and expensive for the payer. This review examines the literature for evidence to support the possibility that fibronectins and BMPs could be coated on the implants as part of the manufacturing process so that the proteins could be released into the tissue surrounding the implant and improve the rate of successful implantation.

Controlled Delivery of Growth Factor by Hierarchical Nanostructured Core-Shell Nanofibers for the Efficient Repair of Critical-Sized Rat Calvarial Defect

Electrospun nanofibers have received much attention as bone tissue-engineered scaffolds for their capacity to mimic the structure of natural extracellular matrix (ECM). Most studies have reproduced nanofibers with smooth surface for tissue engineering. This is quite different from the triple-helical nanotopography of natural collagen nanofibrils. In this study, hierarchical nanostructures were coated on the surface of drug-loaded core-shell nanofibers to mimic natural collagen nanofibrils. The nanoshish-kebab (SK) structure was decorated regularly on the surface of the nanofibers, and the inner-loaded bone morphogenetic protein 2 (BMP2) exhibited a gentle release pattern, similar to a zero-order release pattern in kinetics. The in vitro study also showed that the SK structure could accelerate cell proliferation, attachment, and osteogenic differentiation. Four groups of scaffolds were implanted in vivo to repair critical-sized rat calvarial defects: (1) PCL/PVA (control); (2) SK-PCL/PVA; (3) PCL/PVA-BMP2; and (4) SK-PCL/PVA-BMP2. Much more bone was formed in the SK-PCL/PVA group (24.57 ± 3.81%) than in the control group (1.21 ± 0.23%). The BMP2-loaded core-shell nanofibers with nanopatterned structure (SK-PCL/PVA-BMP2) displayed the best repair efficacy (76.38 ± 4.13%), followed by the PCL/PVA-BMP2 group (39.86 ± 5.74%). It was believed that the hierarchical nanostructured core-shell nanofibers could promote osteogeneration and that the SK structure showed synergistic ability with nanofiber-loaded BMP2 in vivo for bone regeneration. Thus, this BMP2-loaded core-shell nanofiber scaffold with hierarchical nanostructure holds great potential for bone tissue engineering applications.

Dual delivery of platelet-derived growth factor and bone morphogenetic factor-6 on titanium surface to enhance the early period of implant osseointegration

OBJECTIVE

To test the surface properties and in vitro effects of a new sequential release system on MC3T3-E1 cells for improved osseointegration.

BACKGROUND

BMP6-loaded anodized titanium coated with PDGF containing silk fibroin (SF) may improve osseointegration.

METHODS

Titanium surfaces were electrochemically anodized, and SF layer was covered via electrospinning. Five experimental groups (unanodized Ti (Ti), anodized Ti (AnTi), anodized + BMP6-loaded Ti (AnTi-BMP6), anodized + BMP6 loaded + silk fibroin-coated Ti (AnTi-BMP6-SF), and anodized + BMP6-loaded + silk fibroin with PDGF-coated Ti (AnTi-BMP6-PDGF-SF)) were tested. After SEM characterization, contact angle analysis, and FTIR analysis, the amount of released PDGF and BMP6 was detected using ELISA. Cell proliferation (XTT), mineralization, and gene expression (RUNX2 and ALPL) were also evaluated.

RESULTS

After successful anodization and loading of PDGF and BMP6, contact angle measurements showed hydrophobicity for TiO₂ and hydrophilicity for protein-adsorbed surfaces. In FTIR, protein-containing surfaces exhibited amide-I, amide-II, and amide-III bands at 1600 cm^-1 -1700 cm^-1 , 1520 cm^-1 -1540 cm^-1 , and 1220 cm^-1 -1300 cm^-1 spectrum levels with a significant peak in BMP6- and/or SF-loaded groups at 1100 cm^-1 . PDGF release and BMP6 release were delayed, and relatively slower release was detected in SF-coated surfaces. Higher MC3T3-E1 proliferation and mineralization and lower gene expression of RUNX2 and ALPL were detected in AnTi-BMP6-PDGF-SF toward day 28.

CONCLUSION

The new system revealed a high potential for an improved early osseointegration period by means of a better factor release curve and contribution to the osteoblastic cell proliferation, mineralization, and associated gene expression.

Bone morphogenetic proteins 2, 6, and 9 differentially regulate the osteogenic differentiation of immortalized preodontoblasts

Our study attempted to compare the efficacies of bone morphogenetic protein (BMP) 2, 6, and 9 in inducing osteogenic differentiation of preodontoblasts (PDBs). We immortalized PDBs by introducing a reversible SV40 T antigen-based immortalization system. Cell proliferation capability was examined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay. The effects of BMP2, 6, and 9 on the osteogenic differentiation of immortalized preodontoblasts (iPDBs) were measured by alkaline phosphatase (ALP) activity assays and alizarin red S staining. The expression of osteogenic markers was evaluated by semiquantitative real-time polymerase chain reaction analysis. To assess ectopic bone formation, rat-derived iPDBs were transfected in culture with adenoviral vectors designated Ad-BMP2, 6, and 9 and subcutaneously or intramuscularly injected into mice. Several BMPs retained endogenous expression in PDBs and regulated the mRNA expression of mineralized tissue-associated proteins. ALP activity and mineralized nodule formation were significantly increased in the Ad-BMP9-transfected group relative to the control group. In addition, the most significant hard tissue formation was in this group. The results indicated that BMP signaling was involved in the osteogenic differentiation of iPDBs. BMP9 could be an efficacious accelerant of the osteogenic differentiation of iPDBs.

Surface Texturization of Breast Implants Impacts Extracellular Matrix and Inflammatory Gene Expression in Asymptomatic Capsules

BACKGROUND

Texturing processes have been designed to improve biocompatibility and mechanical anchoring of breast implants. However, a high degree of texturing has been associated with severe abnormalities. In this study, the authors aimed to determine whether implant surface topography could also affect physiology of asymptomatic capsules.

METHODS

The authors collected topographic measurements from 17 different breast implant devices by interferometry and radiographic microtomography. Morphologic structures were analyzed statistically to obtain a robust breast implant surface classification. The authors obtained three topographic categories of textured implants (i.e., "peak and valleys," "open cavities," and "semiopened cavities") based on the cross-sectional aspects. The authors simultaneously collected 31 Baker grade I capsules, sorted them according to the new classification, established their molecular profile, and examined the tissue organization.

RESULTS

Each of the categories showed distinct expression patterns of genes associated with the extracellular matrix (Timp and Mmp members) and inflammatory response (Saa1, Tnsf11, and Il8), despite originating from healthy capsules. In addition, slight variations were observed in the organization of capsular tissues at the histologic level.

CONCLUSIONS

The authors combined a novel surface implant classification system and gene profiling analysis to show that implant surface topography is a bioactive cue that can trigger gene expression changes in surrounding tissue, even in Baker grade I capsules. The authors' new classification system avoids confusion regarding the word "texture," and could be transposed to implant ranges of every manufacturer. This new classification could prove useful in studies on potential links between specific texturizations and the incidence of certain breast-implant associated complications.

Multifunctional Biomaterials: Combining Material Modification Strategies for Engineering of Cell-Contacting Surfaces

In the human body, cells in a tissue are exposed to signals derived from their specific extracellular matrix (ECM), such as architectural structure, mechanical properties, and chemical composition (proteins, growth factors). Research on biomaterials in tissue engineering and regenerative medicine aims to recreate such stimuli using engineered materials to induce a specific response of cells at the interface. Although traditional biomaterials design has been mostly limited to varying individual signals, increasing interest has arisen on combining several features in recent years to improve the mimicry of extracellular matrix properties. Tremendous progress in combinatorial surface modification exploiting, for example, topographical features or variations in mechanics combined with biochemical cues has enabled the identification of their key regulatory characteristics on various cell fate decisions. Gradients especially facilitated such research by enabling the investigation of combined continuous changes of different signals. Despite unravelling important synergies for cellular responses, challenges arise in terms of fabrication and characterization of multifunctional engineered materials. This review summarizes recent work on combinatorial surface modifications that aim to control biological responses. Modification and characterization methods for enhanced control over multifunctional material properties are highlighted and discussed. Thereby, this review deepens the understanding and knowledge of biomimetic combinatorial material modification, their challenges but especially their potential.

Biomimetic Coatings Obtained by Combinatorial Laser Technologies

The modification of implant devices with biocompatible coatings has become necessary as a consequence of premature loosening of prosthesis. This is caused mainly by chronic inflammation or allergies that are triggered by implant wear, production of abrasion particles, and/or release of metallic ions from the implantable device surface. Specific to the implant tissue destination, it could require coatings with specific features in order to provide optimal osseointegration. Pulsed laser deposition (PLD) became a well-known physical vapor deposition technology that has been successfully applied to a large variety of biocompatible inorganic coatings for biomedical prosthetic applications. Matrix assisted pulsed laser evaporation (MAPLE) is a PLD-derived technology used for depositions of thin organic material coatings. In an attempt to surpass solvent related difficulties, when different solvents are used for blending various organic materials, combinatorial MAPLE was proposed to grow thin hybrid coatings, assembled in a gradient of composition. We review herein the evolution of the laser technological process and capabilities of growing thin bio-coatings with emphasis on blended or multilayered biomimetic combinations. These can be used either as implant surfaces with enhanced bioactivity for accelerating orthopedic integration and tissue regeneration or combinatorial bio-platforms for cancer research.

Recent advances in the implant-based drug delivery in otorhinolaryngology

The surgical implant is an interdisciplinary therapeutic modality that offers unique advantages in the daily practice of otorhinolaryngology. Some well-known examples include cochlear implants, bone-anchored hearing aids, sinus stents, and tracheostomy tubes. Neuroprotective, osteogenic, anti-inflammatory, and antimicrobial effects are among their established or pursued functions. Implant-based drug delivery affords an efficient and potent approach to enhancing these therapeutic functions. Recent innovations have infiltrated all four elements of a drug-eluting implant. The purpose of this pre-clinical, biotechnology-oriented review is to discuss these developments in terms of the implant biomaterial, loaded medication, delivery pattern, and system fabrication. Cell-mediated neurotrophin release, fabrication of a hydroxyapatite-supported system, biodegradable polymer-based implants, and multiclass and multidrug delivery are some representative advancements. The ultimate goal here is to bridge the gap between biotechnology advances and clinical needs. The review is concluded with a perspective regarding the future opportunities and challenges in this popular and rapidly developing subject of research. STATEMENT OF SIGNIFICANCE: Surgical implants and local drug delivery are representative modern modalities of surgical treatment and medical treatment, respectively. Their synergy offers unique therapeutic advantages, such as minimal systemic side effects, proximity-related high efficiency, and potential absorbability. The applications of implant-based drug delivery have infiltrated otorhinolaryngology and head & neck surgery, which is well known for its related tissue diversity and surgical complexity. Examples discussed here include cochlear implants, bone-anchored hearing aids, sinus stents, and airway tubes. This timely review focuses primarily on the four fundamental components of an implant-based drug delivery system, namely implant biomaterial, loaded medication, delivery pattern, and system fabrication. A particular emphasis is placed upon the in vitro cellular and in vivo animal studies that demonstrate pre-clinical potentials.

Biomimetic Nanostructures with Compositional Gradient Grown by Combinatorial Matrix-Assisted Pulsed Laser Evaporation for Tissue Engineering

There is permanent progress with the fabrication of smart bioactive surfaces that could govern tissue regeneration. Thin coatings of two or more materials with compositional gradient allow the construction of arrays with different chemical and physical features on a solid substrate. With such intelligent bio-platforms, cells can be exposed to a tissue-like biomimetic micro-environment with precise characteristics that directs cells fate towards specific phenotypes. We have introduced combinatorial matrix-assisted pulsed laser evaporation (C-MAPLE) as an alternative approach for the fabrication in a single-step process of either organic or inorganic thin and nanostructured coatings with variable composition. A continuous reciprocal gradient of two biomolecules can be achieved by C-MAPLE with discrete areas exhibiting physicochemical specificity that modulates intracellular signaling events. Herein, we present a review of the current combinatorial laser strategies and methods for fabricating thin organic and inorganic films with compositional gradient with emphasis on the surface influence on cell responsiveness. In particular, the specific biological potential of surface functionalization with thin coatings of biopolymers, proteins and drugs will be discussed. Laser deposition combinatorial processes are considered an emerging unconventional technology that can be widely applied to produce composite multilayers and micro-patterns for faster cell colonization and tissue engineering.

Bone Morphogenetic Protein-2 Signaling in the Osteogenic Differentiation of Human Bone Marrow Mesenchymal Stem Cells Induced by Pulsed Electromagnetic Fields

Pulsed electromagnetic fields (PEMFs) are clinically used with beneficial effects in the treatment of bone fracture healing. This is due to PEMF ability to favor the osteogenic differentiation of mesenchymal stem cells (MSCs). Previous studies suggest that PEMFs enhance the osteogenic activity of bone morphogenetic protein-2 (BMP2) which is used in various therapeutic interventions. This study investigated the molecular events associated to the synergistic activity of PEMFs and BMP2 on osteogenic differentiation. To this aim, human MSCs (hMSCs) were exposed to PEMFs (75 Hz, 1.5 mT) in combination with BMP2, upon detection of the minimal dose able to induce differentiation. Changes in the expression of BMP signaling pathway genes including receptors and ligands, as well as in the phosphorylation of BMP downstream signaling proteins, such as SMAD1/5/8 and MAPK, were analyzed. Results showed the synergistic activity of PEMFs and BMP2 on osteogenic differentiation transcription factors and markers. The PEMF effects were associated to the increase in BMP2, BMP6, and BMP type I receptor gene expression, as well as SMAD1/5/8 and p38 MAPK activation. These results increase knowledge concerning the molecular events involved in PEMF stimulation showing that PEMFs favor hMSCs osteogenic differentiation by the modulation of BMP signaling components.

Copresentation of BMP-6 and RGD Ligands Enhances Cell Adhesion and BMP-Mediated Signaling

We report on the covalent immobilization of bone morphogenetic protein 6 (BMP-6) and its co-presentation with integrin ligands on a nanopatterned platform to study cell adhesion and signaling responses which regulate the transdifferentiation of myoblasts into osteogenic cells. To immobilize BMP-6, the heterobifunctional linker MU-NHS is coupled to amine residues of the growth factor; this prevents its internalization while ensuring that its biological activity is maintained. Additionally, to allow cells to adhere to such platform and study signaling events arising from the contact to the surface, we used click-chemistry to immobilize cyclic-RGD carrying an azido group reacting with PEG-alkyne spacers via copper-catalyzed 1,3-dipolar cycloaddition. We show that the copresentation of BMP-6 and RGD favors focal adhesion formation and promotes Smad 1/5/8 phosphorylation. When presented in low amounts, BMP-6 added to culture media of cells adhering to the RGD ligands is less effective than BMP-6 immobilized on the surfaces in inducing Smad complex activation and in inhibiting myotube formation. Our results suggest that a local control of ligand density and cell signaling is crucial for modulating cell response.

Effect of Hydroxyapatite Nanorods on the Fate of Human Adipose-Derived Stem Cells Assessed In Situ at the Single Cell Level with a High-Throughput, Real-Time Microfluidic Chip

The fate of stem cells at the single cell level with limited communication with other cells is still unknown due to the lack of an efficient tool for highly accurate molecular detection. Moreover, the conditional sensitivity of biological experiments requires a sufficient number of parallel experiments to support a conclusion. In this work, a microfluidic single cell chip is designed for use with a protein chip to investigate the effect of hydroxyapatite (HAp) on the osteogenic differentiation of human adipose-derived stem cells (hADSCs) in situ at the single cell level. By successfully detecting secretory proteins in situ, it is found that the HAp nanorods enhance osteogenic differentiation at the single cell level. In the chip, the single cell seeding approach confirms the osteogenic differentiation of the hADSCs, which endocytoses HAp, by reducing the influence of the factors secreted by neighboring differentiating cells. Most importantly, more than 7000 microchambers provide a sufficient number of parallel experiments for statistical analysis, which ensure a high level of repeatability of the HAp nanorod-induced osteogenic differentiation. The microfluidic chip comprising single cell culture microchambers with in situ detection capability is a promising tool for research on cell behavior or cell fate at the single cell level.

Newly Designed Human-Like Collagen to Maximize Sensitive Release of BMP-2 for Remarkable Repairing of Bone Defects

Designing the “ideal” hydrogel/matrix which can load bone morphogenetic protein-2 (BMP-2) in a low dose and with a sustained release is the key for its successful therapeutic application to enhance osteogenesis. The current use of natural collagen sponges as hydrogel/matrix is limited due to the collagen matrix showing weak mechanical strength and unmanageable biodegradability. Furthermore, the efficiency and safe dose usage of the BMP-2 has never been seriously considered other than purely chasing the lowest dose usage and extended-release time. In this paper, we customized a novel enzymatically cross-linked recombinant human-like collagen (HLC) sponge with low immunogenicity, little risk from hidden viruses, and easy production. We obtained a unique vertical pore structure and the porosity of the HLC, which are beneficial for Mesenchymal stem cells (MSCs) migration into the HLC sponge and angiopoiesis. This HLC sponge loading with low dose BMP-2 (1 µg) possessed high mechanical strength along with a burst and a sustained release profile. These merits overcome previous limitations of HLC in bone repair and are safer and more sensitive than commercial collagens. For the first time, we identified that a 5 µg dose of BMP-2 can bring about the side effect of bone overgrowth through this sensitive delivery system. Osteoinduction of the HLC-BMP sponges was proved by an in vivo mouse ectopic bone model and a rat cranial defect repair model. The method and the HLC-BMP sponge have the potential to release other growth factors and aid other tissue regeneration. Additionally, the ability to mass-produce HLC in our study overcomes the current supply shortage, which limits bone repair in the clinic.

Dental Implant Bioactive Surface Modifiers: An Update

Objectives:

Main purpose of this review was to present an update on various coating materials utilized in improving the surface chemistry of the dental implants.

Methods:

Literature search was carried out in various on-line databases such as PubMed, Medline, Google scholar, EBSCO, Wiley Science Library, and Saudi Digital Library using appropriate keywords (dental implant surface coatings, dental implant surface modifiers, and dental surface coatings).

Results:

Total of 569 studies were retrieved. All the relevant studies among them were reviewed and compiled.

Conclusion:

Current implant surface's biomimetic coatings offer many benefits compared to the traditional plasma sprayed coatings. Further incorporation of biomimetic coatings with various material has lead improvement in mechanical and biological properties of implants.

Effect of magnesium particle fraction on osteoinduction of hydroxyapatite sphere-based scaffolds

HAs-30Mg (incorporation of 30% Mg into HA sphere-based scaffolds) induced the optimum new bone formation.

Cisplatin-Loaded Graphene Oxide/Chitosan/Hydroxyapatite Composite as a Promising Tool for Osteosarcoma-Affected Bone Regeneration

Presently, tissue engineering approaches have been focused toward finding new potential scaffolds with osteoconductivity on bone-disease-affected cells. This work focused on the cisplatin (CDDP)-loaded graphene oxide (GO)/hydroxyapatite (HAP)/chitosan (CS) composite for enhancing the growth of osteoblast cells and prevent the development of osteosarcoma cells. The prepared composites were characterized for the confirmation of composite formation using Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction techniques. A flowerlike morphology was observed for the GO/HAP/CS-3/CDDP composite. UV-vis spectroscopy was used to observe the controlled release of CDDP from the GO/HAP/CS-3/CDDP composite, and 67.34% of CDDP was released from the composite over a time period of 10 days. The GO/HAP/CS-3/CDDP nanocomposites showed higher viability in comparison with GO/HAP/CS-3 on MG63 osteoblast-like cells and higher cytotoxicity against cancer cells (A549). The synthesized composite was found to show enhanced proliferative, adhesive, and osteoinductive effects on the alkaline phosphatase activity of osteoblast-like cells. Our results suggested that the CDDP-loaded GO/HAP/CS-3 nanocomposite has an immense prospective as a bone tissue replacement in the bone-cancer-affected tissues.

Catechin-conjugated mesoporous hydroxyapatite nanoparticle: A novel nano-antioxidant with enhanced osteogenic property

Hydroxyapatite is the main component of mineral phase of bone which is widely employed for coating metal implants and scaffold materials in synthetic bone grafts owing to its osteoinductive property. In order to improve the bioactivity of hydroxyapatite, mesoporous hydroxyapatite nanoparticles (MHAP) were synthesized and chemically functionalized with 3-aminopropyltriethoxysilane. The amine-functionalized nanoparticles were conjugated with a natural antioxidant, catechin (Cat), through a stable amide linkage. The true structure of the bioconstruct was confirmed by calculating condensed Fukui indices. The functionalized-hydroxyapatite nanoparticles (Cat@MHAP) showed an outstanding antioxidant activity, having reactivity toward hydroxyl and superoxide radicals larger than that of free catechin. To explore the bone cell responses to this material, multilayer nanoparticle films were prepared by MHAP and Cat@MHAP on a glass substrate. Afterward, the short- and long-term responses of cultured mesenchymal stem cells (MSCs), osteosarcoma cells (Saos-2), and doxorubicin-resistant cells (RSaos-2/Dox) on the surface of the prepared films were investigated. Both the MSCs and bone tumor cells selectively adhered onto Cat@MHAP surface as compared with glass and MHAP at initial culture time. Moreover, it was found that Cat@MHAP decreases the proliferation of Saos-2 and RSaos-2/Dox cells in a time-dependent manner, while it supports the growth of MSCs, indicating the ability of Cat@MHAP to distinguish tumor cells from normal ones. Further, Cat@MHAP promotes the osteogenic differentiation in both the MSCs and tumor cells, accompanied by the attenuation of intracellular ROS. From these results, Cat@MHAP is a novel "nano-antioxidant," which could be considered as a promising biomaterial in treating bone defects, particularly after surgery in osteosarcoma patients.

Engineered Coatings for Titanium Implants To Present Ultralow Doses of BMP-7

The ongoing research to improve the clinical outcome of titanium implants has resulted in the implemetation of multiple approches to deliver osteogenic growth factors accelerating and sustaining osseointegration. Here we show the presentation of human bone morphogenetic protein 7 (BMP-7) adsorbed to titanium discs coated with poly(ethyl acrylate) (PEA). We have previously shown that PEA promotes fibronectin organization into nanonetworks exposing integrin- and growth-factor-binding domains, allowing a synergistic interaction at the integrin/growth factor receptor level. Here, titanium discs were coated with PEA and fibronectin and then decorated with ng/mL doses of BMP-7. Human mesenchymal stem cells were used to investigate cellular responses on these functionalized microenvironments. Cell adhesion, proliferation, and mineralization, as well as osteogenic markers expression (osteopontin and osteocalcin) revealed the ability of the system to be more potent in osteodifferentiation of the mesenchymal cells than combinations of titanium and BMP-7 in absence of PEA coatings. This work represents a novel strategy to improve the biological activity of titanium implants with BMP-7.

Bone Tissue Engineering Strategies in Co-Delivery of Bone Morphogenetic Protein-2 and Biochemical Signaling Factors

Administration of bone morphogenetic protein-2 (BMP-2), which is commercially approved by the food and drug administration to damaged bone sites has been investigated for the purpose of bone tissue regeneration. BMP-2 can promote osteoblastic differentiation of mesenchymal stem cells as well as regeneration of bone formation in early phase. This review highlights various factors such as vitamin D, dexamethasone, platelet-derived growth factor, placental growth factor, BMP-7, and NEL-like protein-1 that enhance and stimulate angiogenesis, cell differentiation, and bone regeneration. These biochemical signals and growth factors (GFs) accelerate bone repair and remodeling either synergistically or individually. Delivery systems and scaffolds are used for sustained release of these cargo molecules and support at damaged bone sites. Compared with direct administration of BMP-2, current studies have demonstrated that a combination of multiple GFs and/or therapeutic chemical factors with delivery platforms synergistically facilitates bone regeneration. Therefore, in the future, multiple combinations of various GFs, chemicals, and materials could provide patients and surgeons with non-invasive treatment options without secondary surgery and pain. To the end, this review summarizes the biological functions and synergistic effects of dual administration modalities involving BMP-2 as well as recent developments in bone tissue engineering applications.

Bilayered BMP2 Eluting Coatings on Graphene Foam by Electrophoretic Deposition: Electroresponsive BMP2 Release and Enhancement of Osteogenic Differentiation

Recent development of three-dimensional graphene foam (GF) with conductive and interconnected macroporous structure is attracting particular attention as platforms for tissue engineering. However, widespread application of GF as bone scaffolds is restricted due to its poor mechanical property and inert surface character. To overcome these drawbacks, in this study, a bilayered biopolymer coating was designed and successfully deposited covering the entire surface area of GF skeleton. A poly(lactic-co-glycolic acid) layer was first dip-coated to strengthen the GF substrate, followed by the electrophoretic codeposition of a hybrid layer, consisting of chitosan and BMP2, to functionalize GF with the ability to recruit and induce osteogenic differentiation of hMSC. Our data indicated that the mechanical property of GF was significantly increased without compromising the macroporous structure. Importantly, the immobilized BMP2 exhibited sustained and electroresponsive release profiles with rapid response to the electric field exerted on GF, which is beneficial to balancing BMP2 dose in a physiological environment. Moreover, the osteogenic differentiation of hMSC was significantly improved on the functionalized GF. Taking advantage of the unique macrostructure from GF as well as the superior mechanical properties and BMP2 release profile supported by the deposited coatings, it is therefore expected that the developed GF could be a promising alternative as innovative bone-forming favorable scaffolds.