Coating with a modular bone morphogenetic peptide promotes healing of a bone-implant gap in an ovine model

Tissue engineering innovations to enhance osseointegration in immediate dental implant loading: A narrative review

The demand for efficient and accelerated osseointegration in dental implantology has led to the exploration of innovative tissue engineering strategies. Immediate implant loading reduces treatment duration and necessitates robust osseointegration to ensure long-term implant success. This review article discusses the current studies of tissue engineering innovations for enhancing osseointegration in immediate dental implant loading in the recent decade. Keywords "tissue engineering," "osseointegration," "immediate implant loading," and related terms were systematically searched. The review highlights the potential of bioactive materials and growth factor delivery systems in promoting osteogenic activity and accelerating bone regeneration. The in vivo experiment demonstrates significantly improved osseointegration in the experimental group compared to traditional immediate loading techniques, as evidenced by histological analyses and biomechanical assessments. It is possible to revolutionize the treatment outcomes and patient satisfaction in dental implants by integrating bioactive materials and growth factors.

Biomedical applications of solid-binding peptides and proteins

Over the past decades, solid-binding peptides (SBPs) have found multiple applications in materials science. In non-covalent surface modification strategies, solid-binding peptides are a simple and versatile tool for the immobilization of biomolecules on a vast variety of solid surfaces. Especially in physiological environments, SBPs can increase the biocompatibility of hybrid materials and offer tunable properties for the display of biomolecules with minimal impact on their functionality. All these features make SBPs attractive for the manufacturing of bioinspired materials in diagnostic and therapeutic applications. In particular, biomedical applications such as drug delivery, biosensing, and regenerative therapies have benefited from the introduction of SBPs. Here, we review recent literature on the use of solid-binding peptides and solid-binding proteins in biomedical applications. We focus on applications where modulating the interactions between solid materials and biomolecules is crucial. In this review, we describe solid-binding peptides and proteins, providing background on sequence design and binding mechanism. We then discuss their application on materials relevant for biomedicine (calcium phosphates, silicates, ice crystals, metals, plastics, and graphene). Although the limited characterization of SBPs still represents a challenge for their design and widespread application, our review shows that SBP-mediated bioconjugation can be easily introduced into complex designs and on nanomaterials with very different surface chemistries.

Bone fixation techniques for managing joint disorders and injuries: A review study

The majority of surgical procedures treating joint disorders require a technique to realize a firm implant-to-tissue and/or a tissue-to-tissue fixation. Fixation methods have direct effects on survival, performance and integration of orthopedic implants This review paper gives an overview of novel fixation techniques that have been evaluated and optimized for orthopaedic joint implants and could be alternatives for traditional implant fixation techniques or inspirations for future design of joint implantation procedures.

METHOD

The articles were selected using the Scopus search engine. Key words referring to traditional fixation methods have been excluded to find potential innovative fixation techniques. In order to review the recent anchorage systems, only articles that been published during the period of 2010-2020 have been included.

RESULTS

A total of 57 studies were analyzed. The result revealed that three main fixation principles are being employed: using mechanical interlockings, employing adhesives, and performing tissue-bonding strategies.

CONCLUSION

The development of fixation techniques demonstrates a transformation from the general anchoring tools like K-wires toward application-specific designs. Several new methods have been designed and evaluated, which highlight encouraging results as described in this review. It seems that mechanical fixations provide the strongest anchorage. Employing (bio)-adhesives as fixation tool could revolutionize the field of orthopedic surgery. However, the adhesives must be improved and optimized to meet the requirements of an anchorage system. Long-term fixation might be formed by tissue ingrowth approaches which showed promising results. In most cases further clinical studies are required to explore their outputs in clinical applications.

Peptide-Enriched Silk Fibroin Sponge and Trabecular Titanium Composites to Enhance Bone Ingrowth of Prosthetic Implants in an Ovine Model of Bone Gaps

Osteoarthritis frequently requires arthroplasty. Cementless implants are widely used in clinics to replace damaged cartilage or missing bone tissue. In cementless arthroplasty, the risk of aseptic loosening strictly depends on implant stability and bone–implant interface, which are fundamental to guarantee the long-term success of the implant. Ameliorating the features of prosthetic materials, including their porosity and/or geometry, and identifying osteoconductive and/or osteoinductive coatings of implant surfaces are the main strategies to enhance the bone-implant contact surface area. Herein, the development of a novel composite consisting in the association of macro-porous trabecular titanium with silk fibroin (SF) sponges enriched with anionic fibroin-derived polypeptides is described. This composite is applied to improve early bone ingrowth into the implant mesh in a sheep model of bone defects. The composite enables to nucleate carbonated hydroxyapatite and accelerates the osteoblastic differentiation of resident cells, inducing an outward bone growth, a feature that can be particularly relevant when applying these implants in the case of poor osseointegration. Moreover, the osteoconductive properties of peptide-enriched SF sponges support an inward bone deposition from the native bone towards the implants. This technology can be exploited to improve the biological functionality of various prosthetic materials in terms of early bone fixation and prevention of aseptic loosening in prosthetic surgery.

Bilayered Scaffold Prepared from a Kartogenin-Loaded Hydrogel and BMP-2-Derived Peptide-Loaded Porous Nanofibrous Scaffold for Osteochondral Defect Repair

Recently, a bilayered scaffold with an anisotropic structure mimicking a native osteochondral tissue shows considerable potential for treating osteochondral defects. Herein, a bilayered scaffold consisting of biomimetic cartilage and a subchondral bone architecture was constructed for repairing osteochondral defect. A hydrogel prepared by the Schiff base reaction of gelatin, silk fibroin, and oxidized dextran was designed as the cartilage layer, while a nanofibrous scaffold with a macroporous structure prepared from the polymer blend of poly(l-lactic acid)/poly(lactic-co-glycolic acid)/poly(ε-caprolactone) using the dual phase separation technique served as a subchondral layer. The subchondral layer was then treated with polydopamine coating for osteogenic factor immobilization. To facilitate the chondrogenic and osteogenic differentiation of bone marrow mesenchymal stem cells on the bilayered scaffold, the cartilage-inducing drug kartogenin (KGN) and osteogenic-inducing factor bone morphogenetic protein 2-derived peptides (P24 peptides) were, respectively, loaded on the subchondral layer. Next, the in vitro release of KGN and P24 peptide from the corresponding layer was monitored, respectively, and the results showed that both the release time of KGN and P24 peptides would last for more than 28 days. The in vitro results indicated that the KGN-loaded cartilage layer and P24 peptides-loaded subchondral layer were capable of supporting cell proliferation, and induced the chondrogenic and osteogenic differentiation, respectively. Furthermore, the in vivo experiments suggested that the bilayered scaffold significantly accelerated the regeneration of the osteochondral tissue in the rabbit knee joint model. Consequently, this bilayered scaffold loaded with KGN and P24 peptides would be a promising candidate for repairing osteochondral defect.

Tissue engineered bone mimetics to study bone disorders ex vivo: Role of bioinspired materials

Recent advances in materials development and tissue engineering has resulted in a substantial number of bioinspired materials that recapitulate cardinal features of bone extracellular matrix (ECM) such as dynamic inorganic and organic environment(s), hierarchical organization, and topographical features. Bone mimicking materials, as defined by its self-explanatory term, are developed based on the current understandings of the natural bone ECM during development, remodeling, and fracture repair. Compared to conventional plastic cultures, biomaterials that resemble some aspects of the native environment could elicit a more natural molecular and cellular response relevant to the bone tissue. Although current bioinspired materials are mainly developed to assist tissue repair or engineer bone tissues, such materials could nevertheless be applied to model various skeletal diseases in vitro. This review summarizes the use of bioinspired materials for bone tissue engineering, and their potential to model diseases of bone development and remodeling ex vivo. We largely focus on biomaterials, designed to re-create different aspects of the chemical and physical cues of native bone ECM. Employing these bone-inspired materials and tissue engineered bone surrogates to study bone diseases has tremendous potential and will provide a closer portrayal of disease progression and maintenance, both at the cellular and tissue level. We also briefly touch upon the application of patient-derived stem cells and introduce emerging technologies such as organ-on-chip in disease modeling. Faithful recapitulation of disease pathologies will not only offer novel insights into diseases, but also lead to enabling technologies for drug discovery and new approaches for cell-based therapies.

The use of recombinant human bone morphogenetic protein-2 (rhBMP-2) in maxillofacial trauma

In recent years, recombinant human bone morphogenetic protein-2 (rhBMP-2) has been introduced as a therapeutic option in the treatment of several congenital and acquired craniofacial defects. Although there have been promising clinical results, the international literature still lacks complete guidelines, including limits and indications for the use of rhBMP-2. The possible indications for rhBMP-2 in patients undergoing facial trauma are discussed in this article.

Mineral binding peptides with enhanced binding stability in serum

Modular growth factor peptides that bind to calcium phosphate minerals via an osteocalcin-inspired sequence show significantly enhanced binding stability in serum.

Taking cues from the extracellular matrix to design bone-mimetic regenerative scaffolds

There is an ongoing need for effective materials that can replace autologous bone grafts in the clinical treatment of bone injuries and deficiencies. In recent years, research efforts have shifted away from a focus on inert biomaterials to favor scaffolds that mimic the biochemistry and structure of the native bone extracellular matrix (ECM). The expectation is that such scaffolds will integrate with host tissue and actively promote osseous healing. To further enhance the osteoinductivity of bone graft substitutes, ECM-mimetic scaffolds are being engineered with a range of growth factors (GFs). The technologies used to generate GF-modified scaffolds are often inspired by natural processes that regulate the association between endogenous ECMs and GFs. The purpose of this review is to summarize research centered on the development of regenerative scaffolds that replicate the fundamental collagen-hydroxyapatite structure of native bone ECM, and the functionalization of these scaffolds with GFs that stimulate critical events in osteogenesis.

Evaluating Length: The Use of Low-dose Biplanar Radiography (EOS) and Tantalum Bead Implantation

BACKGROUND

Low-dose biplanar radiography (EOS) is an appealing imaging modality for use in children given its low radiation and ease of use. The goal of this study was to determine the accuracy and reliability of EOS compared with CT scanogram for measurement of leg length and to assess interrater and intrarater reliability of measured interbead distances for EOS and CT scanogram after insertion of tantalum beads into lamb femurs.

METHODS

Tantalum beads (0.8 mm) were inserted into the cortex on both the medial and lateral sides of 10 skeletally immature lamb femurs. CT scanogram and EOS imaging were obtained. Measurements of total length and distance between bead pairs were recorded on anteroposterior and lateral views by 2 orthopaedic surgeons on 2 separate occasions. Pearson correlations were performed for statistical comparisons.

RESULTS

EOS measurements showed near-perfect correlation to those of CT scanogram (r>0.96, P<0.001). Intrarater reliability was excellent for all measurements with EOS (r>0.98, P<0.001) and CT scanogram (r>0.99, P<0.001) as was interrater reliability for EOS (r>0.98, P<0.001) and CT scanogram (r>0.99, P<0.001).

CONCLUSIONS

EOS is comparable with CT scanogram in the assessment of limb length and the distance between 2 radiopaque markers. Reliability was excellent for all measurements. The combination of EOS imaging and tantalum bead implantation may be an effective way to evaluate physeal growth following procedures such as epiphysiodesis and physeal bar resection.

LEVEL OF EVIDENCE

Level II—diagnostic

Biomaterial strategies for engineering implants for enhanced osseointegration and bone repair

Bone tissue has a remarkable ability to regenerate and heal itself. However, large bone defects and complex fractures still present a significant challenge to the medical community. Current treatments center on metal implants for structural and mechanical support and auto- or allo-grafts to substitute long bone defects. Metal implants are associated with several complications such as implant loosening and infections. Bone grafts suffer from donor site morbidity, reduced bioactivity, and risk of pathogen transmission. Surgical implants can be modified to provide vital biological cues, growth factors and cells in order to improve osseointegration and repair of bone defects. Here we review strategies and technologies to engineer metal surfaces to promote osseointegration with the host tissue. We also discuss strategies for modifying implants for cell adhesion and bone growth via integrin signaling and growth factor and cytokine delivery for bone defect repair.

Inhibition of osteoblast mineralization by phosphorylated phage-derived apatite-specific peptide

Functionalization of biomaterials with material- and cell-specific peptide sequences allows for better control of their surface properties and communication with the surrounding environment. Using a combinatorial phage display approach, we previously identified the peptide VTKHLNQISQSY (VTK) with specific affinity to biomimetic apatite. Phosphorylation of the serine residues of the peptide (pVTK) caused a significant increase in binding to apatite, as well as a dose-dependent inhibition of osteoblast mineralization. In this study, we investigated the mechanisms behind pVTK mediated inhibition of mineralization using MC3T3 cells and testing the hypothesis that mineralization is inhibited via alteration of the Enpp1-TNAP-Ank axis. Inhibition of mineralization was not due to disruption of collagen deposition or calcium chelation by the negatively charged pVTK. The timing of peptide administration was important in inhibiting mineralization - pVTK had a greater effect at later stages of osteogenic differentiation (days 7-12 of culture corresponding to matrix maturation and mineralization), and could prevent progression of mineralization once it had started. pVTK treatment resulted in a significant decrease in ectonucleotide pyrophosphatase/phosphodiesterase 1 (Enpp1) enzyme activity and gene expression. The expression of ankylosis protein (Ank), osteopontin (OPN) and Pit-1 genes was also significantly reduced with peptide treatment, while tissue non-specific alkaline phosphatase (TNAP), bone sialoprotein (BSP), and Runx2 gene expression was significantly higher. The ability of pVTK to inhibit mineralization can potentially be translated into therapeutics against pathological calcification seen in cardiovascular disease, osteoarthritis or craniosynostosis, or be used to prevent failure of biomaterials due to calcification, such as bioprosthetic heart valves.

Coated Sutures

The addition of specific proteins or growth factors onto sutures would provide a direct application of exogenous factors to promote tissue repair. The higher levels of growth factors and cytokines may optimize the healing environment and promote tissue recovery. Despite this proposed benefit, the current orthopedic literature on the use of coated sutures is limited. Although several of the published studies investigating healing improvement by coated sutures have shown promising results, these data are only based on in vitro or small animal experiments. Recent meta-analyses have reported positive effects of triclosan-coated antimicrobial sutures in regards to reduction of surgical site complications. However, biologically coated sutures are not yet widely accepted due to several unanswered questions (concentration, release kinematics, tissue reactions, etc.) in addition to the high costs of such products. Further studies are needed to demonstrate the efficacy of coated sutures in orthopedic surgery.

BMP-2 Derived Peptide and Dexamethasone Incorporated Mesoporous Silica Nanoparticles for Enhanced Osteogenic Differentiation of Bone Mesenchymal Stem Cells

Bone morphogenetic protein-2 (BMP-2), a growth factor that induces osteoblast differentiation and promotes bone regeneration, has been extensively investigated in bone tissue engineering. The peptides of bioactive domains, corresponding to residues 73-92 of BMP-2 become an alternative to reduce adverse side effects caused by the use of high doses of BMP-2 protein. In this study, BMP-2 peptide functionalized mesoporous silica nanoparticles (MSNs-pep) were synthesized by covalently grafting BMP-2 peptide on the surface of nanoparticles via an aminosilane linker, and dexamethasone (DEX) was then loaded into the channel of MSNs to construct nanoparticulate osteogenic delivery systems (DEX@MSNs-pep). The in vitro cell viability of MSNs-pep was tested with bone mesenchymal stem cells (BMSCs) exposure to different particle concentrations, revealing that the functionalized MSNs had better cytocompatibility than their bare counterparts, and the cellular uptake efficiency of MSNs-pep was remarkably larger than that of bare MSNs. The in vitro results also show that the MSNs-pep promoted osteogenic differentiation of BMSCs in terms of the levels of alkaline phosphatase (ALP) activity, calcium deposition, and expression of bone-related protein. Moreover, the osteogenic differentiation of BMSCs can be further enhanced by incorporating of DEX into MSNs-pep. After intramuscular implantation in rats for 3 weeks, the computed tomography (CT) images and histological examination indicate that this nanoparticulate osteogenic delivery system induces effective osteoblast differentiation and bone regeneration in vivo. Collectively, the BMP-2 peptide and DEX incorporated MSNs can act synergistically to enhance osteogenic differentiation of BMSCs, which have potential applications in bone tissue engineering.

In silico Mechano-Chemical Model of Bone Healing for the Regeneration of Critical Defects: The Effect of BMP-2

The healing of bone defects is a challenge for both tissue engineering and modern orthopaedics. This problem has been addressed through the study of scaffold constructs combined with mechanoregulatory theories, disregarding the influence of chemical factors and their respective delivery devices. Of the chemical factors involved in the bone healing process, bone morphogenetic protein-2 (BMP-2) has been identified as one of the most powerful osteoinductive proteins. The aim of this work is to develop and validate a mechano-chemical regulatory model to study the effect of BMP-2 on the healing of large bone defects in silico. We first collected a range of quantitative experimental data from the literature concerning the effects of BMP-2 on cellular activity, specifically proliferation, migration, differentiation, maturation and extracellular matrix production. These data were then used to define a model governed by mechano-chemical stimuli to simulate the healing of large bone defects under the following conditions: natural healing, an empty hydrogel implanted in the defect and a hydrogel soaked with BMP-2 implanted in the defect. For the latter condition, successful defect healing was predicted, in agreement with previous in vivo experiments. Further in vivo comparisons showed the potential of the model, which accurately predicted bone tissue formation during healing, bone tissue distribution across the defect and the quantity of bone inside the defect. The proposed mechano-chemical model also estimated the effect of BMP-2 on cells and the evolution of healing in large bone defects. This novel in silico tool provides valuable insight for bone tissue regeneration strategies.

How does the pathophysiological context influence delivery of bone growth factors?

"Orthobiologics" represents an important category of therapeutics for the regeneration of bone defects caused by injuries or diseases, and bone growth factors are a particularly rapidly growing sub-category. Clinical application of bone growth factors has accelerated in the last two decades with the introduction of BMPs into clinical bone repair. Optimal use of growth factor-mediated treatments heavily relies on controlled delivery, which can substantially influence the local growth factor dose, release kinetics, and biological activity. The characteristics of the surrounding environment, or "context", during delivery can dictate growth factor loading efficiency, release and biological activity. This review discusses the influence of the surrounding environment on therapeutic delivery of bone growth factors. We specifically focus on pathophysiological components, including soluble components and cells, and how they can actively influence the therapeutic delivery and perhaps efficacy of bone growth factors.

Effects of BMP-12-releasing sutures on Achilles tendon healing

Tendon healing is a complex coordinated event orchestrated by numerous biologically active proteins. Unfortunately, tendons have limited regenerative potential and as a result, repair may be protracted months to years. Current treatment strategies do not offer localized delivery of biologically active proteins, which may result in reduced therapeutic efficacy. Surgical sutures coated with nanostructured minerals may provide a potentially universal tool to efficiently incorporate and deliver biologically active proteins directly to the wound. Additionally, previous reports indicated that treatment with bone morphogenetic protein-12 (BMP-12) improved tendon healing. Based on this information, we hypothesized that mineral-coated surgical sutures may be an effective platform for localized BMP-12 delivery to an injured tendon. The objective of this study was, therefore, to elucidate the healing effects of mineral-coated sutures releasing BMP-12 using a rat Achilles healing model. The effects of BMP-12-releasing sutures were also compared with standard BMP-12 delivery methods, including delivery of BMP-12 through collagen sponge or direct injection. Rat Achilles tendons were unilaterally transected and repaired using BMP-12-releasing suture (0, 0.15, 1.5, or 3.0 μg), collagen sponge (0 or 1.5 μg BMP-12), or direct injection (0 or 1.5 μg). By 14 days postinjury, repair with BMP-12-releasing sutures reduced the appearance of adhesions to the tendon and decreased total cell numbers. BMP-12 released from sutures and collagen sponge also tended to improve collagen organization when compared with BMP-12 delivered through injection. Based on these results, the release of a protein from sutures was able to elicit a biological response. Furthermore, BMP-12-releasing sutures modulated tendon healing, and the delivery method dictated the response of the healing tissue to BMP-12.

Bioactive surface modification of metal oxides via catechol-bearing modular peptides: multivalent-binding, surface retention, and peptide bioactivity

A series of multivalent dendrons containing a bioactive osteogenic growth peptide (OGP) domain and surface-binding catechol domains were obtained through solid phase synthesis, and their binding affinity to hydroxyapatite, TiO2, ZrO2, CeO2, Fe3O4 and gold was characterized using a quartz crystal microbalance with dissipation (QCM-d). Using the distinct difference in binding affinity of the bioconjugate to the metal oxides, TiO2-coated glass slides were selectively patterned with bioactive peptides. Cell culture studies demonstrated the bioavailability of the OGP and that OGP remained on the surface for at least 2 weeks under in vitro cell culture conditions. Bone sialoprotein (BSP) and osteocalcein (OCN) markers were upregulated 3-fold and 60-fold, respectively, relative to controls at 21 days. Similarly, 3-fold more calcium was deposited using the OGP tethered dendron compared to TiO2. These catechol-bearing dendrons provide a fast and efficient method to functionalize a wide range of inorganic materials with bioactive peptides and have the potential to be used in coating orthopaedic implants and fixation devices.

Stable biofunctionalization of hydroxyapatite (HA) surfaces by HA-binding/osteogenic modular peptides for inducing osteogenic differentiation of mesenchymal stem cells

Hydroxyapatite (HA), the principal component of bone mineral, shows osteoconductive properties when employed for coating metal implants as well as scaffold materials in synthetic bone grafts. With the goal of providing this material with osteoinductive capabilities to promote faster bone regeneration, we show an easy approach to functionalize HA implant surfaces and enrich them with osteoinductive properties by the use of HA-binding modular peptides. The modular peptides are designed as a combination of two domains, an HA-binding peptide motif and an osteogenic peptide motif derived from the osteogenic growth peptide (OGP) or bone morphometric protein 7 (BMP-7). To identify the best HA-binding peptide, several nature-inspired peptides derived from natural bone extracellular matrix proteins (bone sialoprotein, osteonectin, osteocalcin, and salivarin statherin) were compared for HA-binding activity, revealing concentration-dependent and incubation-time-dependent behaviours. We discovered that a Poly-E heptamer (E7) is the best HA-binding peptide, and thus combined it with a second osteogenic peptidic domain to create an osteoinductive modular peptide. After binding/release characterization, we found that the addition of the second osteogenic peptide domain did not change the binding profile of the modular peptides and caused only a slight change in their release kinetics. Mesenchymal stem cells (MSCs) were cultured on the HA substrates functionalized with modular peptides, and cell adhesion, proliferation, and differentiation in a basal medium (i.e., without any osteogenic supplements) were investigated. Gene expression data clearly showed that MSCs were committed to differentiate into osteoblasts in the presence of the modular peptides. HA discs functionalized with the E7 BMP-7 modular peptide showed the best capability in inducing the osteogenic differentiation of MSCs among all modular peptides studied. The modular peptides can easily be used to functionalize the HA implants through its constituent HA-binding motif, leaving the osteogenic peptide motif protruding from the surface for inducing osteogenesis. Our work opens up a new approach to the formulation of new bioactive HA coatings and implants for bone and dental repair.

Chitosan-based scaffolds for bone tissue engineering

Bone defects requiring grafts to promote healing are frequently occurring and costly problems in health care. Chitosan, a biodegradable, naturally occurring polymer, has drawn considerable attention in recent years as scaffolding material in tissue engineering and regenerative medicine. Chitosan is especially attractive as a bone scaffold material because it supports the attachment and proliferation of osteoblast cells as well as formation of mineralized bone matrix. In this review, we discuss the fundamentals of bone tissue engineering and the unique properties of chitosan as a scaffolding material to treat bone defects for hard tissue regeneration. We present the common methods for fabrication and characterization of chitosan scaffolds, and discuss the influence of material preparation and addition of polymeric or ceramic components or biomolecules on chitosan scaffold properties such as mechanical strength, structural integrity, and functional bone regeneration. Finally, we highlight recent advances in development of chitosan-based scaffolds with enhanced bone regeneration capability.

Controlled multiple growth factor delivery from bone tissue engineering scaffolds via designed affinity

It is known that angiogenesis plays an important role in bone regeneration and that release of angiogenic and osteogenic growth factors can enhance bone formation. Multiple growth factors play key roles in processes that lead to tissue formation/regeneration during natural tissue development and repair. Therefore, treatments aiming to mimic tissue regeneration can benefit from multiple growth factor release, and there remains a need for simple clinically relevant approaches for dual growth factor release. We hypothesized that mineral coatings could be used as a platform for controlled incorporation and release of multiple growth factors. Specifically, mineral-coated scaffolds were "dip coated" in multiple growth factor solutions, and growth factor binding and release were dictated by the growth factor-mineral binding affinity. Beta tricalcium phosphate (β-TCP) scaffolds were fabricated using indirect solid-free form fabrication techniques and coated with a thin conformal mineral layer. Mineral-coated β-TCP scaffolds were sequentially dipped in recombinant human vascular endothelial growth factor (rhVEGF) and a modular bone morphogenetic peptide, a mineral-binding version of bone morphogenetic protein 2 (BMP2), solutions to allow for the incorporation of each growth factor. The dual release profile showed sustained release of both growth factors for over more than 60 days. Scaffolds releasing either rhVEGF alone or the combination of growth factors showed an increase in blood vessel ingrowth in a dose-dependent manner in a sheep intramuscular implantation model. This approach demonstrates a "modular design" approach, in which a controllable biologics carrier is integrated into a structural scaffold as a thin surface coating.

Valency-dependent affinity of bioactive hydroxyapatite-binding dendrons

Hydroxyapatite (HA)-coated surfaces are used widely as stationary phase for protein and enzyme purification, coatings for dental and orthopedic implants, and composite materials for tissue engineering substrates. More advanced applications are envisioned, but progress has been slowed by the limited ability to controllably functionalize the surface of HA with biomolecules in a translationally relevant manner. Herein we report the synthesis and characterization of a series of multivalent, HA-binding peptide bioconjugates with variable valency and tether length which afford the ability to precisely tune the desired binding behavior. The respective binding affinities of the multivalent constructs to HA surface were characterized by quartz crystal microbalance with dissipation monitoring (QCM-D) techniques, and the relationship between dendron structure and binding affinity was revealed. Tetravalent constructs of HA-binding peptides show a 100-fold enhancement in binding affinity compared to HA-binding peptide sequences reported previously. Both biotin and bone morphogenic protein-2 (BMP-2) derivative peptide were successfully linked to the focal point as initial demonstrations.

High affinity binding of an engineered, modular peptide to bone tissue

Bone grafting procedures have become common due in part to a global trend of population aging. Native bone graft is a popular choice when compared to various synthetic bone graft substitutes, owing to superior biological activity. Nonetheless, the insufficient ability of bone allograft to induce new bone formation and the insufficient remodeling of native bone grafts call for osteoinductive factors during bone repair, exemplified by recombinant human bone morphogenetic protein 2 (rhBMP2). We previously developed a modular bone morphogenetic peptide (mBMP) to address complications associated with the clinical use of rhBMP2 as a bone graft substitute. The mBMP is designed to strongly bind to hydroxyapatite, the main inorganic component of bone and teeth, and to provide pro-osteogenic properties analogous to rhBMP2. Our previous in vivo animal studies showed that mBMP bound to hydroxyapatite-coated orthopedic implants with high affinity and stimulated new bone formation. In this study, we demonstrate specific binding of mBMP to native bone grafts. The results show that mBMP binds with high affinity to both cortical and trabecular bones, and that the binding is dependent on the mBMP concentration and incubation time. Importantly, efficient mBMP binding is also achieved in an ex vivo bone bioreactor where bone tissue is maintained viable for several weeks. In addition, mBMP binding can be localized with spatial control on native bone tissue via simple methods, such as dip-coating, spotting, and direct writing. Taken together with the pro-osteogenic activity of mBMP established in previous bone repair models, these results suggest that mBMP may promote bone healing when coated on native bone grafts in a clinically compatible manner.