The use of immobilized osteogenic growth peptide on gradient substrates synthesized via click chemistry to enhance MC3T3-E1 osteoblast proliferation

Supramolecular Peptide Nanofiber Hydrogels for Bone Tissue Engineering: From Multihierarchical Fabrications to Comprehensive Applications

Bone tissue engineering is becoming an ideal strategy to replace autologous bone grafts for surgical bone repair, but the multihierarchical complexity of natural bone is still difficult to emulate due to the lack of suitable biomaterials. Supramolecular peptide nanofiber hydrogels (SPNHs) are emerging biomaterials because of their inherent biocompatibility, satisfied biodegradability, high purity, facile functionalization, and tunable mechanical properties. This review initially focuses on the multihierarchical fabrications by SPNHs to emulate natural bony extracellular matrix. Structurally, supramolecular peptides based on distinctive building blocks can assemble into nanofiber hydrogels, which can be used as nanomorphology-mimetic scaffolds for tissue engineering. Biochemically, bioactive motifs and bioactive factors can be covalently tethered or physically absorbed to SPNHs to endow various functions depending on physiological and pharmacological requirements. Mechanically, four strategies are summarized to optimize the biophysical microenvironment of SPNHs for bone regeneration. Furthermore, comprehensive applications about SPNHs for bone tissue engineering are reviewed. The biomaterials can be directly used in the form of injectable hydrogels or composite nanoscaffolds, or they can be used to construct engineered bone grafts by bioprinting or bioreactors. Finally, continuing challenges and outlook are discussed.

Instant hydrogelation encapsulates drugs onto implants intraoperatively against osteoarticular tuberculosis

Osteoarticular Tuberculosis (TB) is a challenging issue because of its chronicity and recurrence. Many drug delivery systems (DDSs) have been developed for general chemotherapy. Herein, we take advantage of instant hydrogelation to in situ encapsulate drugs onto implants intraoperatively, optimizing the drug release profile against osteoarticular TB. First-line chemodrugs, i.e. rifampicin (RFP) and isoniazid (INH) are firstly loaded on tricalcium phosphate (TCP). Then, the encapsulating hydrogel is fabricated by dipping in chitosan (CS) and β-glycerophosphate (β-GP) solution and heating at 80 °C for 40 min. The hydrogel encapsulation inhibits explosive drug release initially, but maintains long-term drug release (INH, 158 days; RFP, 53 days) in vitro. Therefore, this technique could inhibit bone destruction and inflammation from TB effectively in vivo, better than our previous ex situ prepared DDSs. The encapsulating technology, i.e. instant hydrogelation of drug-loaded implants, shows potential for regulating the type and ratio of drugs, elastic and viscous modulus of the hydrogel according to the state of illness intraoperatively for optimal drug release.

Click-functionalized hydrogel design for mechanobiology investigations

The advancement of click-functionalized hydrogels in recent years has coincided with rapid growth in the fields of mechanobiology, tissue engineering, and regenerative medicine. Click chemistries represent a group of reactions that possess high reactivity and specificity, are cytocompatible, and generally proceed under physiologic conditions. Most notably, the high level of tunability afforded by these reactions enables the design of user-controlled and tissue-mimicking hydrogels in which the influence of important physical and biochemical cues on normal and aberrant cellular behaviors can be independently assessed. Several critical tissue properties, including stiffness, viscoelasticity, and biomolecule presentation, are known to regulate cell mechanobiology in the context of development, wound repair, and disease. However, many questions still remain about how the individual and combined effects of these instructive properties regulate the cellular and molecular mechanisms governing physiologic and pathologic processes. In this review, we discuss several click chemistries that have been adopted to design dynamic and instructive hydrogels for mechanobiology investigations. We also chart a path forward for how click hydrogels can help reveal important insights about complex tissue microenvironments.

High-Throughput Methods in the Discovery and Study of Biomaterials and Materiobiology

The complex interaction of cells with biomaterials (i.e., materiobiology) plays an increasingly pivotal role in the development of novel implants, biomedical devices, and tissue engineering scaffolds to treat diseases, aid in the restoration of bodily functions, construct healthy tissues, or regenerate diseased ones. However, the conventional approaches are incapable of screening the huge amount of potential material parameter combinations to identify the optimal cell responses and involve a combination of serendipity and many series of trial-and-error experiments. For advanced tissue engineering and regenerative medicine, highly efficient and complex bioanalysis platforms are expected to explore the complex interaction of cells with biomaterials using combinatorial approaches that offer desired complex microenvironments during healing, development, and homeostasis. In this review, we first introduce materiobiology and its high-throughput screening (HTS). Then we present an in-depth of the recent progress of 2D/3D HTS platforms (i.e., gradient and microarray) in the principle, preparation, screening for materiobiology, and combination with other advanced technologies. The Compendium for Biomaterial Transcriptomics and high content imaging, computational simulations, and their translation toward commercial and clinical uses are highlighted. In the final section, current challenges and future perspectives are discussed. High-throughput experimentation within the field of materiobiology enables the elucidation of the relationships between biomaterial properties and biological behavior and thereby serves as a potential tool for accelerating the development of high-performance biomaterials.

Osteogenic Peptides and Attachment Methods Determine Tissue Regeneration in Modified Bone Graft Substitutes

The inclusion of biofunctional molecules with synthetic bone graft substitutes has the potential to enhance tissue regeneration during treatment of traumatic bone injuries. The clinical use of growth factors has though been associated with complications, some serious. The use of smaller, active peptides has the potential to overcome these problems and provide a cost-effective, safe route for the manufacture of enhanced bone graft substitutes. This review considers the design of peptide-enhanced bone graft substitutes, and how peptide selection and attachment method determine clinical efficacy. It was determined that covalent attachment may reduce the known risks associated with growth factor-loaded bone graft substitutes, providing a predictable tissue response and greater clinical efficacy. Peptide choice was found to be critical, but even within recognised families of biologically active peptides, the configurations that appeared to most closely mimic the biological molecules involved in natural bone healing processes were most potent. It was concluded that rational, evidence-based design of peptide-enhanced bone graft substitutes offers a pathway to clinical maturity in this highly promising field.

Proteins, peptides and peptidomimetics as active agents in implant surface functionalization

The recent impact of implants on improving the human life quality has been enormous. During the past two decades we witnessed major advancements in both material and structural development of implants. They were driven mainly by the increasing patients' demand and the need to address the major issues that come along with the initially underestimated complexity of the bone-implant interface. While both, the materials and design of implants reached a certain, balanced state, recent years brought a shift in focus towards the bone-implant interface as the weakest link in the increasing implant long-term usability. As a result, several approaches were developed. They aimed at influencing and enhancing the implant osseointegration and its proper behavior when under load and stress. With this review, we would like to discuss the recent advancements in the field of implant surface modifications, emphasizing the importance of chemical methods, focusing on proteins, peptides and peptidomimetics as promising agents for titanium surface coatings.

Gelatin Templated Polypeptide Co-Cross-Linked Hydrogel for Bone Regeneration

Polypeptides with short chains of amino acid monomers have been widely applied in the clinic because of their various biological functions. However, the easily-inactivated characteristics and burst releasing of the peptides limit their application in vivo. Here, a novel osteogenic polypeptide hydrogel (GelMA-c-OGP) is created by co-cross-linking template photo-cross-linked gelatin (GelMA) with photo-cross-linkable osteogenic growth peptides (OGP) using ultraviolet radiation. GelMA enables the formation of hydrogel with photo-cross-linkable OGP with good mechanical properties and also promotes bone regeneration. GelMA-c-OGP hydrogel accelerates the bone formation procedure of osteogenic precursor cells by significantly enhancing the expression of osteogenic-related genes BMP-2, OCN, and OPN, and increasing the precipitation of calcium salts in osteoblasts. Similarly, GelMA-c-OGP hydrogel promotes bone regeneration in vivo. Furthermore, it is observed that more collagen fibers connect cortical bones in the GelMA-c-OGP implanted group than the control group by hematoxylin-eosin and immunohistochemical staining of Collagen I and TGF-β. The co-cross-linked OGP polypeptide converts from liquid to solid hydrogel with transient UV light in situ, which also can strengthen the mechanical property of the defect bone and avoid burst osteogenic peptide, releasing during the bone defect healing period. Overall, this hydrogel delivering system has a significant impact on bone defect healing compared with traditional methods.

Enhancing Schwann cell migration using concentration gradients of laminin-derived peptides

Neuroregeneration following peripheral nerve injury is largely mediated by Schwann cells (SC), the principal glial cell that supports neurons in the peripheral nervous system. Axonal regeneration in vivo is limited by the extent of SC migration into the gap between the proximal and distal nerve, however, little is known regarding the principal driving forces for SC migration. Engineered microenvironments, such as molecular and protein gradients, play a role in the migration of many cell types, including cancer cells and fibroblasts. However, haptotactic strategies have not been applied widely to SC. Herein, a series of tethered laminin-derived peptides were analyzed for their influence on SC adhesion, proliferation, and alignment. Concentration gradient substrates were fabricated using a controlled vapor deposition method, followed by covalent peptide attachment via a thiol-ene reaction, and characterized by X-ray photoelectron spectroscopy (XPS) and MALDI-MS imaging. While tethered RGD peptides supported SC adhesion and proliferation, concentration gradients of RGD had little influence on biased SC directional migration. In contrast, YIGSR promoted less SC attachment than RGD, yet YIGSR peptide gradients directed migration with a strong bias to the concentration profile. With YIGSR peptide, overall speed increased with the steepness of the peptide concentration profile. YIGSR gradients had no haptotactic effect on rat dermal fibroblast migration, in contrast to fibroblast migration on RGD gradients. The response of SC to these tethered peptide gradients will guide the development of translationally relevant constructs designed to facilitate endogenous SC infiltration into defects for nerve regeneration.

Functionalization of titanium substrate with multifunctional peptide OGP-NAC for the regulation of osteoimmunology

The immune response to an orthopedic implant is closely related to the nearby bone metabolism balance. To modify titanium (Ti) substrates and accordingly regulate the balance between osteoclast activation and osteoblast differentiation, a multifunctional peptide OGP-NAC was synthesized via conjugating an osteogenic growth peptide (OGP) with N-acetylcysteine (NAC). Then, the synthesized peptide was employed to functionalize Ti substrates and the response of both osteoblasts and osteoclasts was investigated in vitro. The results showed that OGP-NAC was successfully prepared and immobilized onto Ti substrate surfaces. Thereafter, studies on introducing RAW 264.7 cells (one kind of monocyte macrophage responsible for immune responses) to osteoclasts demonstrated that the peptide modified Ti surface could inhibit RAW 264.7 cells from secreting important inflammatory cytokines (TNF-α and IL-1β), and suppress the activation of MAPK, NF-κB and NFAT c1, which are important transcription factors for osteoclastogenesis. Meanwhile, the modified surface promoted osteoblast spreading, proliferation and differentiation. The study offers a feasible strategy to mediate the balance between osteoclast activation and osteoblast differentiation, having great potential for improving osseointegration of an orthopedic implant.

Bacteriophage-based biomaterials for tissue regeneration

Bacteriophage, also called phage, is a human-safe bacteria-specific virus. It is a monodisperse biological nanostructure made of proteins (forming the outside surface) and nucleic acids (encased in the protein capsid). Among different types of phages, filamentous phages have received great attention in tissue regeneration research due to their unique nanofiber-like morphology. They can be produced in an error-free format, self-assemble into ordered scaffolds, display multiple signaling peptides site-specifically, and serve as a platform for identifying novel signaling or homing peptides. They can direct stem cell differentiation into specific cell types when they are organized into proper patterns or display suitable peptides. These unusual features have allowed scientists to employ them to regenerate a variety of tissues, including bone, nerves, cartilage, skin, and heart. This review will summarize the progress in the field of phage-based tissue regeneration and the future directions in this field.

Polydopamine-modified poly(l-lactic acid) nanofiber scaffolds immobilized with an osteogenic growth peptide for bone tissue regeneration

It is highly desirable for bone tissue engineering scaffolds to have significant osteogenic properties and capability to improve cell growth and thus enhance bone regeneration. In this study, a poly(l-lactic acid) (PLLA) nanofiber scaffold-immobilized osteogenic growth peptide (OGP) was prepared via polydopamine (PDA) coating. X-ray photoelectron spectroscopy (XPS), contact angle measurement, and scanning electron microscopy (SEM) were used to determine the OGP immobilization, hydrophilicity and surface roughness of the samples. The SEM and fluorescence images demonstrate that the PLLA nanofiber scaffolds immobilized with the OGP have excellent cytocompatibility in terms of cell adhesion and proliferation. The ALP activity and the Runx2 and OPN expression results indicated that the PLLA nanofiber scaffolds immobilized with OGP significantly enhanced the osteogenic differentiation and calcium mineralization of hMSCs in vitro. A rat model of critical skull bone defect was selected to evaluate the bone formation capacity of the scaffolds. Micro CT analysis and histological results demonstrated that the PLLA scaffolds immobilized with OGP significantly promoted bone regeneration in critical-sized bone defects. This study verifies that the PLLA scaffold-immobilized OGP has significant potential in bone tissue engineering.

Polydopamine-modified PLLA nanofiber scaffolds immobilized with osteogenic growth peptide were designed and prepared for promoting bone formation.

Aspartic and Glutamic Acid Templated Peptides Conjugation on Plasma Modified Nanofibers for Osteogenic Differentiation of Human Mesenchymal Stem Cells: A Comparative Study

Optimization of nanofiber (NF) surface properties is critical to achieve an adequate cellular response. Here, the impact of conjugation of biomimetic aspartic acid (ASP) and glutamic acid (GLU) templated peptides with poly(lactic-co-glycolic acid) (PLGA) electrospun NF on osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hMSCs) was evaluated. Cold atmospheric plasma (CAP) was used to functionalize the NF surface and thus to mediate the conjugation. The influence of the CAP treatment following with peptide conjugation to the NF surface was assessed using water contact angle measurements, Fourier-Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). The effect of CAP treatment on morphology of NF was also checked using Scanning Electron Microscopy (SEM). Both the hydrophilicity of NF and the number of the carboxyl (-COOH) groups on the surface increased with respect to CAP treatment. Results demonstrated that CAP treatment significantly enhanced peptide conjugation on the surface of NF. Osteogenic differentiation results indicated that conjugating of biomimetic ASP templated peptides sharply increased alkaline phosphatase (ALP) activity, calcium content, and expression of key osteogenic markers of collagen type I (Col-I), osteocalcin (OC), and osteopontin (OP) compared to GLU conjugated (GLU-pNF) and CAP treated NF (pNF). It was further depicted that ASP sequences are the major fragments that influence the mineralization and osteogenic differentiation in non-collagenous proteins of bone extracellular matrix.

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.

Upregulation of osteogenesis of mesenchymal stem cells with virus-based thin films

A major aim of tissue engineering is to develop biomimetic scaffolding materials that can guide the proliferation, self-renewal and differentiation of multipotent stem cells into specific lineages. Cellular functions can be controlled by the interactions between cells and biomaterials. Therefore, the surface chemistry and topography of support materials play a pivotal role in modulating cell behaviors at many stages of cell growth and development. Due to their highly ordered structure and programmable surface chemistries, which provide unique topography as biomaterials, viral nanoparticles have been utilized as building blocks for targeted cell growth and differentiation. This review article discusses the fabrication of two-dimensional virus-based thin film on substrates and highlights the study of the effect of chemical and physical cues introduced by plant virus nanoparticle thin films on the promotion of osteogenic differentiation of BMSCs.

Growth Factor Delivery Systems for Tissue Engineering and Regenerative Medicine

Growth factors (GFs) are often a key component in tissue engineering and regenerative medicine approaches. In order to fully exploit the therapeutic potential of GFs, GF delivery vehicles have to meet a number of key design criteria such as providing localized delivery and mimicking the dynamic native GF expression levels and patterns. The use of biomaterials as delivery systems is the most successful strategy for controlled delivery and has been translated into different commercially available systems. However, the risk of side effects remains an issue, which is mainly attributed to insufficient control over the release profile. This book chapter reviews the current strategies, chemistries, materials and delivery vehicles employed to overcome the current limitations associated with GF therapies.

Nanostructured interfacial self-assembled peptide-polymer membranes for enhanced mineralization and cell adhesion

Soft interfacial materials, such as self-assembled polymer membranes, are gaining increasing interest as biomaterials since they can provide selective barriers and/or controlled affinity interactions important to regulate cellular processes. Herein, we report the design and fabrication of multiscale structured membranes integrating selective molecular functionalities for potential applications in bone regeneration. The membranes were obtained by interfacial self-assembly of miscible aqueous solutions of hyaluronan and multi-domain peptides (MDPs) incorporating distinct biochemical motifs, including mineralizing (EE), integrin-binding (RGDS) and osteogenic (YGFGG) peptide sequences. Circular dichroism and Fourier transform infrared spectroscopy analyses of the MDPs revealed a predominant β-sheet conformation, while transmission electron microscopy (TEM) showed the formation of fibre-like nanostructures with different lengths. Scanning electron microscopy (SEM) of the membranes showed an anisotropic structure and surfaces with different nanotopographies, reflecting the morphological differences observed under TEM. All the membranes were able to promote the deposition of a calcium-phosphate mineral on their surface when incubated in a mineralizing solution. The ability of the MDPs, coated on coverslips or presented within the membranes, to support cell adhesion was investigated using primary adult periosteum-derived cells (PDCs) under serum-free conditions. Cells on the membranes lacking RGDS remained round, while in the presence of RGDS they appear to be more elongated and anchored to the membrane. These observations were confirmed by SEM analysis that showed cells attached to the membrane and exhibiting an extended morphology with close interactions with the membrane surface. We anticipate that these molecularly designed interfacial membranes can both provide relevant biochemical signals and structural biomimetic components for stem cell growth and differentiation and ultimately promote bone regeneration.

Stimulus-response click chemistry based aptamer-functionalized mesoporous silica nanoparticles for fluorescence detection of thrombin

In most aptamer based stimulus response mesoporous silica nanoparticles (MSN) systems, the aptamer is modified on the MSN via electrostatic interaction, however leakage might exist after a certain time in the system and hence the stability is not good. In this study, the pores of MSN were capped by aptamer through click chemistry reaction for the first time and the system was then employed to develop a fluorescence biosensor. Specifically, the aptamer of the target (thrombin in this study) was hybridized with its complementary DNA (which was initially modified with alkyne at the terminal) to form a double strand DNA (dsDNA) firstly, and then this dsDNA was modified on N₃ modified MSN via Cu(I) catalyzed alkyne-azide cycloaddition reaction. The guest molecules (fluorescein) were blocked in the pores of the MSN with high efficiency and nearly no leakage was detected. Upon the introduction of thrombin, thrombin specifically recognized its aptamer, so aptamer released from the MSN; and the single strand DNA(ssDNA) left could not cap the pores of the MSN efficiently and hence caused the releasing of fluorescein into the solution. The enhanced fluorescence intensity of the system has a good linear relationship with the thrombin concentration in the range of 50-1000ngmL^-1 with a detection limit of 28.46ngmL^-1. The proposed biosensor has been successfully applied to detect thrombin in serum samples with high selectivity. The same strategy can be applied to develop biosensors for different targets by changing the adopted aptamer.

Isolation and Characterization of Lactoferrin Peptides with Stimulatory Effect on Osteoblast Proliferation

Lactoferrin is reported to be a potential food protein with osteogenic activity. However, the activity of lactoferrin peptides is questionable. In the present study, we isolated and characterized peptides from lactoferrin with stimulatory effect on osteoblast proliferation. Peptides from the lactoferrin pepsin hydrolysate were purified using cation-exchange and gel-filtration chromatography. Effects of different hydrolysates and peptides on the proliferation of osteoblast MC3T3-E1 cells were compared by MTT assay. Results showed that fraction P5-a from Superdex Peptide 10/300 GL gel chromatography showed better activity. Tricine-sodium dodecyl sulfate polyacrylamide gel electrophoresis and high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry confirmed that two peptides components of P5-a corresponded to fractions of 20-78 and 191-277 amino acids in Bos taurus lactoferrin molecule (GI: 221706349). These results will provide some theoretical and practical data for the preparation and application of osteogenic peptides in functional food industry.

Harnessing cAMP signaling in musculoskeletal regenerative engineering

This paper reviews the most recent findings in the search for small molecule cyclic AMP analogues regarding their potential use in musculoskeletal regenerative engineering.

Fabrication and characterization of chitosan/OGP coated porous poly(ε-caprolactone) scaffold for bone tissue engineering

As one of the stimulators on bone formation, osteogenic growth peptide (OGP) improves both proliferation and differentiation of the bone cells in vitro and in vivo. The aim of this work was the preparation of three dimensional porous poly(ε-caprolactone) (PCL) scaffold with high porosity, well interpore connectivity, and then its surface was modified by using chitosan (CS)/OGP coating for application in bone regeneration. In present study, the properties of porous PCL and CS/OGP coated PCL scaffold, including the microstructure, water absorption, porosity, hydrophilicity, mechanical properties, and biocompatibility in vitro were investigated. Results showed that the PCL and CS/OGP-PCL scaffold with an interconnected network structure have a porosity of more than 91.5, 80.8%, respectively. The CS/OGP-PCL scaffold exhibited better hydrophilicity and mechanical properties than that of uncoated PCL scaffold. Moreover, the results of cell culture test showed that CS/OGP coating could stimulate the proliferation and growth of osteoblast cells on CS/OGP-PCL scaffold. These finding suggested that the surface modification could be a effective method on enhancing cell adhesion to synthetic polymer-based scaffolds in tissue engineering application and the developed porous CS/OGP-PCL scaffold should be considered as alternative biomaterials for bone regeneration.

Peptides for bone tissue engineering

Molecular signals in the form of growth factors are the main modulators of cell behavior. However, the use of growth factors in tissue engineering has several drawbacks, including their costs, difficult production, immunogenicity and short half-life. Furthermore, many of them are pleiotropic and, since a single growth factor can have different active domains, their effect is not always fully controllable. A very interesting alternative that has recently emerged is the use of biomimetic peptides. Sequences derived from the active domains of soluble or extracellular matrix proteins can be used to functionalize the biomaterials used as scaffolds for new tissue growth to either direct the attachment of cells or to be released as soluble ligands. Since these short peptides can be easily designed and cost-effectively synthesized in vitro, their use has opened up a world of new opportunities to obtain cheaper and more effective implants for regenerative medicine strategies. In this extensive review we will go through many of the most important peptides with potential interest for bone tissue engineering, not limiting to those that only mediate cell adhesion or induce the osteogenic differentiation of progenitor cells, but also focusing on those that direct angiogenesis because of its close relation with bone formation.

Two-Dimensional Magnesium Phosphate Nanosheets Form Highly Thixotropic Gels That Up-Regulate Bone Formation

Hydrogels composed of two-dimensional (2D) nanomaterials have become an important alternative to replace traditional inorganic scaffolds for tissue engineering. Here, we describe a novel nanocrystalline material with 2D morphology that was synthesized by tuning the crystallization of the sodium-magnesium-phosphate system. We discovered that the sodium ion can regulate the precipitation of magnesium phosphate by interacting with the crystal's surface causing a preferential crystal growth that results in 2D morphology. The 2D nanomaterial gave rise to a physical hydrogel that presented extreme thixotropy, injectability, biocompatibility, bioresorption, and long-term stability. The nanocrystalline material was characterized in vitro and in vivo and we discovered that it presented unique biological properties. Magnesium phosphate nanosheets accelerated bone healing and osseointegration by enhancing collagen formation, osteoblasts differentiation, and osteoclasts proliferation through up-regulation of COL1A1, RunX2, ALP, OCN, and OPN. In summary, the 2D magnesium phosphate nanosheets could bring a paradigm shift in the field of minimally invasive orthopedic and craniofacial interventions because it is the only material available that can be injected through high gauge needles into bone defects in order to accelerate bone healing and osseointegration.

Targeted delivery as key for the success of small osteoinductive molecules

Molecules such as growth factors, peptides and small molecules can guide cellular behavior and are thus important for tissue engineering. They are rapidly emerging as promising compounds for the regeneration of tissues of the musculoskeletal system. Growth factors have disadvantages such as high cost, short half-life, supraphysiological amounts needed, etc. Therefore, small molecules may be an alternative. These molecules have been discovered using high throughput screening. Small osteoinductive molecules exhibit several advantages over growth factors owing to their small sizes, such as high stability and non-immunogenicity. These molecules may stimulate directly signaling pathways that are important for osteogenesis. However, systemic application doesn't induce osteogenesis in most cases. Therefore, local administration is needed. This may be achieved by using a bone graft material providing additional osteoconductive properties. These graft materials can also act by themselves as a delivery matrix for targeted and local delivery. Furthermore, vascularization is necessary in the process of osteogenesis. Many of the small molecules are also capable of promoting vascularization of the tissue to be regenerated. Thus, in this review, special attention is given to molecules that are capable of inducing both angiogenesis and osteogenesis simultaneously. Finally, more recent preclinical and clinical uses in bone regeneration of those molecules are described, highlighting the needs for the clinical translation of these promising compounds.

Multifunctional and Spatially Controlled Bioconjugation to Melt Coextruded Nanofibers

Polymeric fibers have drawn recent interest for uses in biomedical technologies that span drug delivery, regenerative medicine, and wound-healing patches, amongst others. We have recently reported a new class of fibrous biomaterials fabricated using coextrusion and a photochemical modification procedure to introduce functional groups onto the fibers. In this report, we extend our methodology to control surface modification density, describe methods to synthesize multifunctional fibers, and provide methods to spatially control functional group modification. Several different functional fibers are reported for bioconjugation, including propargyl, alkene, alkoxyamine, and ketone modified fibers. The modification scheme allows for control over surface density and provides a handle for downstream functionalization with appropriate bioconjugation chemistries. Through the use of multiple orthogonal chemistries, fiber chemistry could be differentially controlled to append multiple modifications. Spatial control on the fiber surface was also realized, leading to reverse gradients of small molecule dyes. One application is demonstrated for pH-responsive drug delivery of an anti-cancer therapeutics. Finally, the introduction of orthogonal chemical modifications onto these fibers allowed for modification with multiple cell-responsive peptides providing a substrate for osteoblast differentiation.

Enhanced Schwann cell attachment and alignment using one-pot "dual click" GRGDS and YIGSR derivatized nanofibers

Using metal-free click chemistry and oxime condensation methodologies, GRGDS and YIGSR peptides were coupled to random and aligned degradable nanofiber networks postelectrospinning in a one-pot reaction. The bound peptides are bioactive, as demonstrated by Schwann cell attachment and proliferation, and the inclusion of YIGSR with GRGDS alters the expression of the receptor for YIGSR. Additionally, aligned nanofibers act as a potential guidance cue by increasing the aspect ratio and aligning the actin filaments, which suggest that peptide-functionalized scaffolds would be useful to direct SCs for peripheral nerve regeneration.

Smart nanoprobes for the detection of alkaline phosphatase activity during osteoblast differentiation

Gold nanoparticle-conjugated fluorescent hydroxyapatite (AuFHAp) was developed as a smart nanoprobe for measuring alkaline phosphatase (ALP) activity.

Untangling the effects of peptide sequences and nanotopographies in a biomimetic niche for directed differentiation of iPSCs by assemblies of genetically engineered viral nanofibers

Here we report the design of a unique matrix, assembled from engineered M13 phage bionanofibers with specific cues of nanotopographies and versatile signal peptides to simulate native niche for directing the fate of induced pluripotent stem cells (iPSCs). By independently varying the peptide sequences and nanotopographies, we find that the resident iPSCs on the phage matrix are first differentiated into mesenchymal progenitor cells (MPCs), which are further differentiated into osteoblasts in the absence of osteogenic supplements due to the elongation induced by phage nanofibers. The phage-based matrix represents not only a biomimetic stem cell niche enabling independently varying biochemical and biophysical cues in one system but also a substrate for generating a safe and efficient cell source for tissue engineering.

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.

Growth factor conjugation: strategies and applications

Growth factors, first known for their essential role in the initiation of mitosis, are required for a variety of cellular processes and their localized delivery is considered as a rational approach in their therapeutic application to assure a safe and effective treatment while avoiding unwanted adverse effects. Noncovalent immobilization of growth factors as well as their covalent conjugation is amongst the most common strategies for localized delivery of growth factors. Today, immobilized and covalently conjugated growth factors are considered as a promising drug design and are widely used for protein reformulation and material design to cover the unwanted characteristics of growth factors as well as improving their functions. Selection of a suitable conjugation technique depends on the substrate chemistry and the availability of functional reactive groups in the structure of growth factor, the position of reactive groups in growth factor molecules and its relation with the receptor binding area, and the intention of creating either patterned or unpatterned conjugation. Various approaches for growth factor reformulation have been reported. This review provides an overview on chemical conjugation of growth factors and covers the relevant studies accomplished for bioconjugation of growth factors and their related application.