Loading of BMP-2-related peptide onto three-dimensional nano-hydroxyapatite scaffolds accelerates mineralization in critical-sized cranial bone defects

The Impact of Nano-Hydroxyapatite Scaffold Enrichment on Bone Regeneration In Vivo-A Systematic Review

OBJECTIVES

In order to ensure improved and accelerated bone regeneration, nano-hydroxyapatite scaffolds are often enriched with different bioactive components to further accelerate and improve bone healing. In this review, we critically examined whether the enrichment of nHAp/polymer scaffolds with growth factors, hormones, polypeptides, microRNAs and exosomes improved new bone formation in vivo.

MATERIALS AND METHODS

Out of 2989 articles obtained from the literature search, 106 papers were read in full, and only 12 articles met the inclusion criteria for this review.

RESULTS

Several bioactive components were reported to stimulate accelerated bone regeneration in a variety of bone defect models, showing better results than bone grafting with nHAp scaffolds alone.

CONCLUSIONS

The results indicated that composite materials based on nHAp are excellent candidates as bone substitutes, while nHAp scaffold enrichment further accelerates bone regeneration. The standardization of animal models should be provided in order to clearly define the most significant parameters of in vivo studies. Only in this way can the adequate comparison of findings from different in vivo studies be possible, further advancing our knowledge on bone regeneration and enabling its translation to clinical settings.

Harnessing the Potential of PLGA Nanoparticles for Enhanced Bone Regeneration

Recently, nanotechnologies have become increasingly prominent in the field of bone tissue engineering (BTE), offering substantial potential to advance the field forward. These advancements manifest in two primary ways: the localized application of nanoengineered materials to enhance bone regeneration and their use as nanovehicles for delivering bioactive compounds. Despite significant progress in the development of bone substitutes over the past few decades, it is worth noting that the quest to identify the optimal biomaterial for bone regeneration remains a subject of intense debate. Ever since its initial discovery, poly(lactic-co-glycolic acid) (PLGA) has found widespread use in BTE due to its favorable biocompatibility and customizable biodegradability. This review provides an overview of contemporary advancements in the development of bone regeneration materials using PLGA polymers. The review covers some of the properties of PLGA, with a special focus on modifications of these properties towards bone regeneration. Furthermore, we delve into the techniques for synthesizing PLGA nanoparticles (NPs), the diverse forms in which these NPs can be fabricated, and the bioactive molecules that exhibit therapeutic potential for promoting bone regeneration. Additionally, we addressed some of the current concerns regarding the safety of PLGA NPs and PLGA-based products available on the market. Finally, we briefly discussed some of the current challenges and proposed some strategies to functionally enhance the fabrication of PLGA NPs towards BTE. We envisage that the utilization of PLGA NP holds significant potential as a potent tool in advancing therapies for intractable bone diseases.

Neuro-bone tissue engineering: emerging mechanisms, potential strategies, and current challenges

The skeleton is a highly innervated organ in which nerve fibers interact with various skeletal cells. Peripheral nerve endings release neurogenic factors and sense skeletal signals, which mediate bone metabolism and skeletal pain. In recent years, bone tissue engineering has increasingly focused on the effects of the nervous system on bone regeneration. Simultaneous regeneration of bone and nerves through the use of materials or by the enhancement of endogenous neurogenic repair signals has been proven to promote functional bone regeneration. Additionally, emerging information on the mechanisms of skeletal interoception and the central nervous system regulation of bone homeostasis provide an opportunity for advancing biomaterials. However, comprehensive reviews of this topic are lacking. Therefore, this review provides an overview of the relationship between nerves and bone regeneration, focusing on tissue engineering applications. We discuss novel regulatory mechanisms and explore innovative approaches based on nerve-bone interactions for bone regeneration. Finally, the challenges and future prospects of this field are briefly discussed.

Biocompatibility and antibacterial activity of MgO/Ca3(PO4)2 composite ceramic scaffold based on vat photopolymerization technology

Recent advancements in medical technology and increased interdisciplinary research have facilitated the development of the field of medical engineering. Specifically, in bone repair, researchers and potential users have placed greater demands on orthopedic implants regarding their biocompatibility, degradation rates, antibacterial properties, and other aspects. In response, our team developed composite ceramic samples using degradable materials calcium phosphate and magnesium oxide through the vat photopolymerization (VP) technique. The calcium phosphate content in each sample was, respectively, 80 %, 60 %, 40 %, and 20 %. To explore the relationship between the biocompatibility, antibacterial activity, and MgO content of the samples, we cultured them with osteoblasts (MC3T3-E1), Escherichia coli (a gram-negative bacterium), and Staphylococcus aureus (a gram-positive bacterium). Our results demonstrate that as the MgO content of the sample increases, its biocompatibility improves but its antibacterial activity decreases. Regarding the composite material samples, the 20 % calcium phosphate content group exhibited the best biocompatibility. However, after 0.5 h of co-cultivation, the antibacterial rates of all groups except the 20 % calcium phosphate content group co-cultured with S. aureus exceed 80 %. Furthermore, after 3 h, the antibacterial rates against E. coli exceed 95 % in all groups. This is because higher levels of MgO correspond to lower pH values and Mg2+ concentrations in the cell and bacterial culture solutions, which ultimately promote cell and bacterial proliferation. This elevates the biocompatibility of the samples, albeit at the expense of their antimicrobial efficacy. Thus, modulating the MgO content in the composite ceramic samples provides a strategy to develop gradient composite scaffolds for better control of their biocompatibility and antibacterial performance during different stages of bone regeneration.

MY-1-Loaded Nano-Hydroxyapatite Accelerated Bone Regeneration by Increasing Type III Collagen Deposition in Early-Stage ECM via a Hsp47-Dependent Mechanism

The extracellular matrix (ECM) plays a crucial part in regulating stem cell function through its distinctive mechanical and chemical effect. Therefore, it is worth studying how to activate the driving force of osteoblast cells by dynamic changing of ECM and accelerate the bone regeneration. In this research, a novel peptide MY-1 is designed and synthesized. To achieve its sustained releasing, the nano-hydroxyapatite (nHA) is chosen as the carrier of MY-1 by mixed adsorption. The results reveal that the sustainable releasing of MY-1 regulates the synthesis and secretion of ECM from rat bone marrow mesenchymal stem cells (rBMSCs), which promotes the cell migration and osteogenic differentiation in the early stage of bone regeneration. Further analyses demonstrate that MY-1 increases the expression and nuclear translocation of β-catenin, and then upregulates the level of heat shock protein 47 (Hsp47), thereby accelerating the synthesis and secretion of type III collagen (Col III) at the early stage. Finally, the promoted rapid transformation of Col III to Col I at late stage benefits the bone regeneration. Hence, this study can provide a theoretical basis for the local application of MY-1 in bone regeneration.

Sintering densification mechanism and mechanical properties of the 3D-printed high-melting-point-difference magnesium oxide/calcium phosphate composite bio-ceramic scaffold

Over the past few years, biodegradable ceramic scaffolds have gained significant attention in the field of bone repair. Calcium phosphate (Ca3(PO4)2)- and magnesium oxide (MgO)-based ceramics are biocompatible, osteogenic, and biodegradable, making them attractive for potential applications. However, the mechanical properties of Ca3(PO4)2 are limited. We developed a magnesium oxide/calcium phosphate composite bio-ceramic scaffold characterized by a high melting point difference, using vat photopolymerization (VP) technology to address this issue. The primary goal was to fabricate high-strength ceramic scaffolds using biodegradable materials. In this study, we investigated ceramic scaffolds with varying MgO contents and sintering temperatures. We also discussed the co-sintering densification mechanism of high and low melting-point materials associated with composite ceramic scaffolds. During sintering, a liquid phase was generated, which filled up the pores generated during the vaporization of additives (such as resin) under the influence of capillary force. This led to an increase in the extent of ceramic densification realized. Moreover, we found ceramic scaffolds with 80 wt% MgO exhibited the best mechanical performance. This kind of composite scaffold performed better than pure MgO scaffold. The results reported herein highlight that high-density composite ceramic scaffolds can be potentially used in the field of bone repair.

Optimizing Delivery of Therapeutic Growth Factors for Bone and Cartilage Regeneration

Bone- and cartilage-related diseases, such as osteoporosis and osteoarthritis, affect millions of people worldwide, impairing their quality of life and increasing mortality. Osteoporosis significantly increases the bone fracture risk of the spine, hip, and wrist. For successful fracture treatment and to facilitate proper healing in the most complicated cases, one of the most promising methods is to deliver a therapeutic protein to accelerate bone regeneration. Similarly, in the setting of osteoarthritis, where degraded cartilage does not regenerate, therapeutic proteins hold great promise to promote new cartilage formation. For both osteoporosis and osteoarthritis treatments, targeted delivery of therapeutic growth factors, with the aid of hydrogels, to bone and cartilage is a key to advance the field of regenerative medicine. In this review article, we propose five important aspects of therapeutic growth factor delivery for bone and cartilage regeneration: (1) protection of protein growth factors from physical and enzymatic degradation, (2) targeted growth factor delivery, (3) controlling GF release kinetics, (4) long-term stability of regenerated tissues, and (5) osteoimmunomodulatory effects of therapeutic growth factors and carriers/scaffolds.

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.

Nano-Hydroxyapatite Composite Scaffolds Loaded with Bioactive Factors and Drugs for Bone Tissue Engineering

Nano-hydroxyapatite (n-HAp) is similar to human bone mineral in structure and biochemistry and is, therefore, widely used as bone biomaterial and a drug carrier. Further, n-HAp composite scaffolds have a great potential role in bone regeneration. Loading bioactive factors and drugs onto n-HAp composites has emerged as a promising strategy for bone defect repair in bone tissue engineering. With local delivery of bioactive agents and drugs, biological materials may be provided with the biological activity they lack to improve bone regeneration. This review summarizes classification of n-HAp composites, application of n-HAp composite scaffolds loaded with bioactive factors and drugs in bone tissue engineering and the drug loading methods of n-HAp composite scaffolds, and the research direction of n-HAp composite scaffolds in the future is prospected.

Frontiers of Hydroxyapatite Composites in Bionic Bone Tissue Engineering

Bone defects caused by various factors may cause morphological and functional disorders that can seriously affect patient's quality of life. Autologous bone grafting is morbid, involves numerous complications, and provides limited volume at donor site. Hence, tissue-engineered bone is a better alternative for repair of bone defects and for promoting a patient's functional recovery. Besides good biocompatibility, scaffolding materials represented by hydroxyapatite (HA) composites in tissue-engineered bone also have strong ability to guide bone regeneration. The development of manufacturing technology and advances in material science have made HA composite scaffolding more closely related to the composition and mechanical properties of natural bone. The surface morphology and pore diameter of the scaffold material are more important for cell proliferation, differentiation, and nutrient exchange. The degradation rate of the composite scaffold should match the rate of osteogenesis, and the loading of cells/cytokine is beneficial to promote the formation of new bone. In conclusion, there is no doubt that a breakthrough has been made in composition, mechanical properties, and degradation of HA composites. Biomimetic tissue-engineered bone based on vascularization and innervation show a promising future.

Treatment of Traumatic Cartilage Defects of Rabbit Knee Joint by Adipose Derived Stem Cells Combined with Kartogenin Hydroxyapatite Nano-Microsphere Complex

Kartogenin (KGN) can effectively promote the differentiation of adipose derived stem cells (ADSCs) into chondrocytes. With the help of three-dimensional slow-release technology, nano-microspheres are generated and used for cartilage repair. First, KGN solution was prepared, which was dissolved in distilled water, and NaOH solution, HEPES buffer, sodium chloride particles, and hydroxyapatite (HA) solution were added to prepare KGN-HA gel solution containing KGN. ADSCs were isolated from the posterior iliac of four-week-old New Zealand rabbits. After 0.5 mL of rabbit second-generation ADSCs suspension was taken, 2 mL KGN-HA gel solution was added, and they were mixed well to obtain ADSCs/KGN-HA gel. After drying treatment, ADSCs/KGN-HA nanospheres were precipitated. In the experiment, the minimum inhibitory concentration (MIC) of Staphylococcus aureus (MIC) > 2 μg/mL in each group of KGN-HA gel solution was reached within 30 days. Group K3 had the highest KGN encapsulation rate and the largest cumulative release. The biological activity of ADSCs was good in the ADSCs/KGN-HA nanoparticle solution. After two weeks of incubation, the nanospheres were positive for type II collagen staining/toluidine blue staining, that was, chondrocyte phenotype. The rabbit knee articular cartilage defect model was established. The defect part was filled with ADSCs/KGN-HA gel, which was similar in color to the surrounding tissues. The two sides of the tissue section and the surrounding cartilage tissue healed well, and no carrier material remained. Moreover, the cells were round, with cartilage lacuna formed around them, and after the simple periosteum was covered and repaired, the surface was sunken. The cell structure changed, and the healing with the surroundings was poor. In summary, under the slow release of KGN, ADSCs/KGN-HA nanospheres made ADSCs maintain a good biological form, which grew and proliferated normally. The ADSCs/KGN-HA nanoparticles cultured in vitro had a good repair effect on the animal model of articular cartilage defects.

Polypeptides IGF-1C and P24 synergistically promote osteogenic differentiation of bone marrow mesenchymal stem cells in vitro through the p38 and JNK signaling pathways

OBJECTIVES

Insulin-like growth factor-1 (IGF-1) and bone morphogenetic protein 2 (BMP-2) both promote osteogenesis of bone marrow mesenchymal stem cells (BMSCs). IGF-1C, the C domain peptide of IGF-1, and P24, a BMP-2-derived peptide, both have similar biological activities as their parent growth factors. This study aimed to investigate the effects and mechanisms of polypeptides IGF-1C and P24 on the osteogenic differentiation of BMSCs.

METHODS

The optimum concentrations of IGF-IC and P24 were explored. The effects of the two polypeptides on BMSC proliferation and osteogenic differentiation were examined using a CCK-8 assay, flow cytometry, alkaline phosphatase (ALP) staining, ALP activity assay, alizarin red S staining, qPCR, and Western blotting. In addition, specific pathway inhibitors were utilized to explore whether the p38 and JNK pathways were involved in this process.

RESULTS

The optimal concentration of both polypeptides was 50 μg/ml. IGF-1C and P24 synergistically promoted BMSC proliferation, increased ALP activity and calcified nodule formation, upregulated the mRNA and protein levels of Osx, Runx2, Ocn, Opn, and Col1a1, and improved the phosphorylation levels of p38 and JNK proteins. Inhibition of the pathways significantly reduced p38 and JNK activation and blocked Runx2 expression while inhibiting ALP activity and calcified nodule formation.

CONCLUSIONS

These findings suggest that IGF-1C and P24 synergistically promote the osteogenesis of BMSCs through activation of the p38 and JNK signaling pathways.

In situ bone regeneration with sequential delivery of aptamer and BMP2 from an ECM-based scaffold fabricated by cryogenic free-form extrusion

In situ tissue engineering is a powerful strategy for the treatment of bone defects. It could overcome the limitations of traditional bone tissue engineering, which typically involves extensive cell expansion steps, low cell survival rates upon transplantation, and a risk of immuno-rejection. Here, a porous scaffold polycaprolactone (PCL)/decellularized small intestine submucosa (SIS) was fabricated via cryogenic free-form extrusion, followed by surface modification with aptamer and PlGF-2123-144*-fused BMP2 (pBMP2). The two bioactive molecules were delivered sequentially. The aptamer Apt19s, which exhibited binding affinity to bone marrow-derived mesenchymal stem cells (BMSCs), was quickly released, facilitating the mobilization and recruitment of host BMSCs. BMP2 fused with a PlGF-2123-144 peptide, which showed "super-affinity" to the ECM matrix, was released in a slow and sustained manner, inducing BMSC osteogenic differentiation. In vitro results showed that the sequential release of PCL/SIS-pBMP2-Apt19s promoted cell migration, proliferation, alkaline phosphatase activity, and mRNA expression of osteogenesis-related genes. The in vivo results demonstrated that the sequential release system of PCL/SIS-pBMP2-Apt19s evidently increased bone formation in rat calvarial critical-sized defects compared to the sequential release system of PCL/SIS-BMP2-Apt19s. Thus, the novel delivery system shows potential as an ideal alternative for achieving cell-free scaffold-based bone regeneration in situ.

Controlled delivery of bone morphogenic protein-2-related peptide from mineralised extracellular matrix-based scaffold induces bone regeneration

Ideal bone tissue engineering scaffolds composed of extracellular matrix (ECM) require excellent osteoconductive ability to imitate the bone environment. We developed a mineralised tissue-derived ECM-modified true bone ceramic (TBC) scaffold for the delivery of aspartic acid-modified bone morphogenic protein-2 (BMP-2) peptide (P28) and assessed its osteogenic capacity. Decellularized ECM from porcine small intestinal submucosa (SIS) was coated onto the surface of TBC, followed by mineralisation modification (mSIS/TBC). P28 was subsequently immobilised onto the scaffolds in the absence of a crosslinker. The alkaline phosphatase activity and other osteogenic differentiation marker results showed that osteogenesis of the P28/mSIS/TBC scaffolds was significantly greater than that of the TBC and mSIS/TBC groups. In addition, to examine the osteoconductive capability of this system in vivo, we established a rat calvarial bone defect model and evaluated the new bone area and new blood vessel density. Histological observation showed that P28/mSIS/TBC exhibited favourable bone regeneration efficacy. This study proposes the use of mSIS/TBC loaded with P28 as a promising osteogenic scaffold for bone tissue engineering applications.

Bioactive Sr2+/Fe3+co-substituted hydroxyapatite in cryogenically 3D printed porous scaffolds for bone tissue engineering

Developing multi-doped bioceramics that possess biological multifunctionality is becoming increasingly attractive and promising for bone tissue engineering. In this view innovative Sr²⁺/Fe³⁺co-substituted nano-hydroxyapatite with gradient doping concentrations fixed at 10 mol% has been deliberately designed previously. Herein, to evaluate their therapeutic potentials for bone healing, novel gradient SrFeHA/PCL scaffolds are fabricated by extrusion cryogenic 3D printing technology with subsequent lyophilization. The obtained scaffolds exhibit desired 3D interconnected porous structure and rough microsurface, along with appreciable release of bioactive Sr²⁺/Fe³⁺from SrFeHA components. These favorable physicochemical properties render printed scaffolds realizing effective biological applications bothin vitroandin vivo, particularly the moderate co-substituted Sr7.5Fe2.5HA and Sr5Fe5HA groups exhibit remarkably enhanced bioactivity that not only promotes the functions of MC3T3 osteoblasts and HUVECs directly, but also energetically manipulates favorable macrophages activation to concurrently facilitate osteogenesis/angiogenesis. Moreover,in vivosubcutaneous implantation and cranial defects repair outcomes further confirm their superior capacity to dictate immune reaction, implants vascularization andin situbone regeneration, mainly dependent on the synergetic effects of released Sr²⁺/Fe³⁺. Accordingly, for the first time, present study highlights the great potential of Sr7.5Fe2.5HA and Sr5Fe5HA for ameliorating bone regeneration process by coupling of immunomodulation with enhanced angio- and osteogenesis and hence may provide a new promising alternative for future bone tissue engineering.

Osteogenic potential of the growth factors and bioactive molecules in bone regeneration

The growing need for treatment of the impaired bone tissue has resulted in the quest for the improvement of bone tissue regeneration strategies. Bone tissue engineering is trying to create bio-inspired systems with a coordinated combination of the cells, scaffolds, and bioactive factors to repair the damaged bone tissue. The scaffold provides a supportive matrix for cell growth, migration, and differentiation and also, acts as a delivery system for bioactive factors. Bioactive factors including a large group of cytokines, growth factors (GFs), peptides, and hormonal signals that regulate cellular behaviors. These factors stimulate osteogenic differentiation and proliferation of cells by activating the signaling cascades related to ossification and angiogenesis. GFs and bioactive peptides are significant parts of the bone tissue engineering systems. Besides, the use of the osteogenic potential of hormonal signals has been an attractive topic, particularly in osteoporosis-related bone defects. Due to the unstable nature of protein factors and non-specific effects of hormones, the engineering of scaffolds to the controlled delivery of these bioactive molecules has paramount importance. This review updates the growth factors, engineered peptides, and hormones that are used in bone tissue engineering systems. Also, discusses how these bioactive molecules may be linked to accelerating bone regeneration.

Creation of Bony Microenvironment with Extracellular Matrix Doped-Bioactive Ceramics to Enhance Osteoblast Behavior and Delivery of Aspartic Acid-Modified BMP-2 Peptides

Introduction

Decellularized matrix from porcine small intestinal submucosa (SIS) endows scaffolds with an ECM-like surface, which enhances stem cell self-renewal, proliferation, and differentiation. Mesoporous bioactive glass (MBG) is extensively recognized as an excellent bio-ceramic for fabricating bone grafts.

Materials and Methods

In the current study, SIS was doped on an MBG scaffold (MBG/SIS) using polyurethane foam templating and polydopamine chemistry method. To mimic the bony environment of a natural bone matrix, an ECM-inspired delivery system was constructed by coupling the BMP2-related peptide P28 to a heparinized MBG/SIS scaffold (MBG/SIS-H-P28). The release of P28 from MBG/SIS-H-P28 and its effects on the proliferation, viability, and osteogenic differentiation of bone marrow stromal stem cells were investigated in vitro and in vivo.

Results

Our research indicated that the novel tissue-derived ECM scaffold MBG/SIS has a hierarchical and interconnected porous architecture, and superior biomechanical properties. MBG/SIS-H-P28 released P28 in a controlled manner, with the long-term release time of 40 d. The results of in vitro experiments showed improvements in cell proliferation, cell viability, alkaline phosphatase activity, and mRNA expression levels of osteogenesis-related genes (Runx-2, OCN, OPN, and ALP) compared to those of MBG/SIS or MBG/SIS-P28 and MBG/SIS-H-P28. The in vivo results demonstrated that MBG/SIS-H-P28 scaffolds evidently increased bone formation in rat calvarial critical-sized defect compared to that in controls.

Conclusion

MBG/SIS-H-P28 scaffolds show potential as ideal platforms for delivery of P28 and for providing a bony environment for bone regeneration.

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.

Nanostructured Biomaterials for Bone Regeneration

This review article addresses the various aspects of nano-biomaterials used in or being pursued for the purpose of promoting bone regeneration. In the last decade, significant growth in the fields of polymer sciences, nanotechnology, and biotechnology has resulted in the development of new nano-biomaterials. These are extensively explored as drug delivery carriers and as implantable devices. At the interface of nanomaterials and biological systems, the organic and synthetic worlds have merged over the past two decades, forming a new scientific field incorporating nano-material design for biological applications. For this field to evolve, there is a need to understand the dynamic forces and molecular components that shape these interactions and influence function, while also considering safety. While there is still much to learn about the bio-physicochemical interactions at the interface, we are at a point where pockets of accumulated knowledge can provide a conceptual framework to guide further exploration and inform future product development. This review is intended as a resource for academics, scientists, and physicians working in the field of orthopedics and bone repair.

Hydroxyapatite Particles—Directing the Cellular Activity in Bone Regeneration Processes: An Up-To-Date Review

Tissue engineering has evolved quickly over the years and provided three generations of scaffolds for bone tissue applications. Numerous materials have been used to induce the desired effect at cellular levels. Mechano-transduction is a phenomenon which is now gaining the attention and focus of tissue engineering researchers. The idea of controlling the cellular fate and inducing a proper response of the human body in contact with different tissue-engineered systems is now under investigation. Moreover, in order to avoid the appearance of on-site infections and the need for a second surgery, scaffolds with dual functionality are now being developed. Hydroxyapatite (HA) is an intensively studied material in this field and various combinations are under examination for the development of such scaffolds. Various techniques were exploited over the years for HA scaffold production, in order to obtain the most accurate matrix which can mimic the native bone tissue and restore its function. Biomimetic scaffolds aim to direct the cellular fate by imitating the natural structure of the bone tissue in terms of porosity, topography, composition, and surface properties. HA particles are exploited in bone tissue engineering in many forms, such as pure or composite scaffolds or reinforcement agents. In this regard, the aim of this review is to offer a current state of art about the use and synthesis of hydroxyapatite particles and their interaction with the physiological media under certain circumstances.

Preparation of BMP-2/chitosan/hydroxyapatite antibacterial bio-composite coatings on titanium surfaces for bone tissue engineering

In this paper, petaling hydroxyapatite (HA)/TiO₂ composite coatings were firstly prepared on titanium (Ti) surface by one-step micro-arc oxidation (MAO), and then pure chitosan (CS) and bone morphogenic protein-2 (BMP-2)-encapsulated CS coatings were respectively loaded on the HA/TiO₂ surfaces by dip-coating method to endow Ti with good antibacterial and biological properties. The bonding strength between coatings was studied by scratch method. The degradability of CS, BMP-2 release behavior, bioactivity, biocompatibility and antibacterial activity of the obtained (BMP-2)/CS/HA/TiO₂ coatings were examined by in vitro tests. The results showed that, the thicker the HA layer, the larger the loaded BMP-2 and CS amount, resulting in better bonding strength between coatings, antibacterial activity and biocompatibility. In addition, with the increase of CS concentration, more CS was loaded on HA coatings, which benefited the increase of CS degrading amount, the prolonged CS degradation time and BMP-2 release time, resulting in improved antibacterial and biological property. All CS/HA/TiO₂ coatings accelerated cell adhesion, spreading and proliferation, and promoted HA formation in simulated body fluids (SBF). After loading BMP-2 in CS, the BMP-2 can significantly improve cell adhesion, spreading and proliferation, and the loaded amount can also be controlled by the concentration of BMP-2 solution. The present study indicates that, by controlling the thickness of HA layers and concentrations of CS and BMP-2 solutions, the Ti implant material with excellent biological and antibacterial properties can be achieved.

Adsorption and release kinetics of growth factors on barrier membranes for guided tissue/bone regeneration: A systematic review

OBJECTIVES

Guided bone / tissue regeneration (GBR/GTR) procedures are necessary to improve conditions for implant placement. These techniques in turn can be enhanced by using growth factors (GFs) such as bone morphogenetic protein (BMP-2) and platelet-derived growth factor (PDGF) to accelerate regeneration. The aim of the present systematic review was to evaluate the GF loading and release kinetics of barrier membranes.

STUDY DESIGN

A total of 138 articles were screened in PubMed databases, and 31 meeting the inclusion criteria were included in the present systematic review.

RESULTS

All the articles evaluated bio-resorbable membranes, especially collagen or polymer-based membranes. In most studies, the retention and release kinetics of osteogenic GFs such as BMP-2 and PDGF were widely investigated. Growth factors were incorporated to the membranes by soaking and incubating the membranes in GF solution, followed by lyophilization, or mixing in the polymers before evaporation. Adsorption onto the membranes depended upon the membrane materials and additional reagents such as heparin, cross-linkers and GF concentration. Interestingly, most studies showed two phases of GF release from the membranes: a first phase comprising a burst release (about 1 day), followed by a second phase characterized by slower release. Furthermore, all the studies demonstrated the controlled release of sufficient concentrations of GFs from the membranes for bioactivities.

CONCLUSIONS

The adsorption and release kinetics varied among the different materials, forms and GFs. The combination of membrane materials, GFs and manufacturing methods should be considered for optimizing GBR/GTR procedures.

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.

Biomimetic Composite Scaffold Containing Small Intestinal Submucosa and Mesoporous Bioactive Glass Exhibits High Osteogenic and Angiogenic Capacity

Biomaterials with excellent osteogenic and angiogenic activities are desirable to repair massive bone defects. Decellularized matrix from porcine small intestinal submucosa (SIS) has attracted particular attention for tissue regeneration because it has strong angiogenic effects and retains plentiful bioactive components. However, it has inferior osteoinductivity and osteoconductivity. In this study, we developed porous composite of SIS combined with mesoporous bioactive glass (SIS/MBG) with the goal of improving the mechanical and biological properties. SIS/MBG scaffolds showed uniform interconnected macropores (∼150 μm), high porosity (∼76%), and enhanced compressive strength (∼0.87 MPa). The proliferation and osteogenic gene expression (Runx2, ALP, Ocn, and Col-Iα) of rat bone marrow stromal cells (rBMSCs) as well as the proliferation, angiogenic gene expression (VEGF, bFGF, and KDR), and tube formation capacity of human umbilical vein endothelial cells (HUVECs) in SIS/MBG scaffolds were significantly upregulated compared with nonmesoporous bioactive glass (BG)-modified SIS (SIS/BG) and SIS-only scaffolds. Western blot analysis revealed that SIS/MBG induced rBMSCs to osteogenic differentiation through the activation of Wnt/β-Catenin signaling pathway, and SIS/MBG enhanced angiogenic activity of HUVEC through the activation of PI3k/Akt pathways. The in vivo results demonstrated that SIS/MBG scaffolds significantly enhanced new bone formation and neovascularization simultaneously in critical-sized rat calvarial defects as compared with SIS/BG and SIS. Collectively, the osteostimulative and angiostimulative biomimetic composite scaffold SIS/MBG represents an exciting biomaterial option for bone regeneration.

Guided osteoporotic bone regeneration with composite scaffolds of mineralized ECM/heparin membrane loaded with BMP2-related peptide

Introduction

At present, the treatment of osteoporotic defects poses a great challenge to clinicians, owing to the lower regeneration capacity of the osteoporotic bone as compared with the normal bone. The guided bone regeneration (GBR) technology provides a promising strategy to cure osteoporotic defects using bioactive membranes. The decellularized matrix from the small intestinal submucosa (SIS) has gained popularity for its natural microenvironment, which induces cell response.

Materials and methods

In this study, we developed heparinized mineralized SIS loaded with bone morphogenetic protein 2 (BMP2)-related peptide P28 (mSIS/P28) as a novel GBR membrane for guided osteoporotic bone regeneration. These mSIS/P28 membranes were obtained through the mineralization of SIS (mSIS), followed by P28 loading onto heparinized mSIS. The heparinized mSIS membrane was designed to improve the immobilization efficacy and facilitate controlled release of P28. P28 release from mSIS-heparin-P28 and its effects on the proliferation, viability, and osteogenic differentiation of bone marrow stromal stem cells from ovariectomized rats (rBMSCs-OVX) were investigated in vitro. Furthermore, a critical-sized OVX calvarial defect model was used to assess the bone regeneration capability of mSIS-heparin-P28 in vivo.

Results

In vitro results showed that P28 release from mSIS-heparin-P28 occurred in a controlled manner, with a long-term release time of 40 days. Moreover, mSIS-heparin-P28 promoted cell proliferation and viability, alkaline phosphatase activity, and mRNA expression of osteogenesis-related genes in rBMSCs-OVX without the addition of extra osteogenic components. In vivo experiments revealed that mSIS-heparin-P28 dramatically stimulated osteoporotic bone regeneration.

Conclusion

The heparinized mSIS loaded with P28 may serve as a potential GBR membrane for repairing osteoporotic defects.