Collagen/Beta-Tricalcium Phosphate Based Synthetic Bone Grafts via Dehydrothermal Processing

Direct inkjet writing type 1 bovine collagen/β-tricalcium phosphate scaffolds for bone regeneration

Bone tissue has the capacity to regenerate under healthy conditions, but complex cases like critically sized defects hinder natural bone regeneration, necessitating surgery, and use of a grafting material for rehabilitation. The field of bone tissue engineering (BTE) has pioneered ways to address such issues utilizing different biomaterials to create a platform for cell migration and tissue formation, leading to improved bone reconstruction. One such approach involves 3D-printed patient-specific scaffolds designed to aid in regeneration of boney defects. This study aimed to develop and characterize 3D printed scaffolds composed of type I collagen augmented with β-tricalcium phosphate (COL/β-TCP). A custom-built direct inkjet write (DIW) printer was used to fabricate β-TCP, COL, and COL/β-TCP scaffolds using synthesized colloidal gels. After chemical crosslinking, the scaffolds were lyophilized and subjected to several characterization techniques, including light microscopy, scanning electron microscopy, and x-ray diffraction to evaluate morphological and chemical properties. In vitro evaluation was performed using human osteoprogenitor cells to assess cytotoxicity and proliferative capacity of the different scaffold types. Characterization results confirmed the presence of β-TCP in the 3D printed COL/β-TCP scaffolds, which exhibited crystals that were attributed to β-TCP due to the presence of calcium and phosphorus, detected through energy dispersive x-ray spectroscopy. In vitro studies showed that the COL/β-TCP scaffolds yielded more favorable results in terms of cell viability and proliferation compared to β-TCP and COL scaffolds. The novel COL/β-TCP scaffold constructs hold promise for improving BTE applications and may offer a superior environment for bone regeneration compared with conventional COL and β-TCP scaffolds.

Osteogenic Differentiation of Canine Adipose Derived Mesenchymal Stem Cells on B-TCP and B-TCP/Collagen Biomaterials

Mesenchymal stem cells are adult stem cells that have the ability to differentiate into osteogenic, chondrogenic, adipogenic and myogenic lineages. In the field of orthopedics and traumatology, mesenchymal stem cells in combination with biomaterials are used especially for the treatment of bone fractures and diseases in both humans and animals. The purpose of this study is to promote growth, proliferation and osteogenic differentiation of mesenchymal stem cells that were isolated from the adipose tissue of canines on B-TCP (Beta-tricalcium phosphate) and B-TCP/Collagen biomaterials. MTT analysis was performed to test the cell adhesion and proliferation on B-TCP and B-TCP/Collagen biomaterials that were used to mimic the extracellular matrix of three-dimensional bone tissue. Scanning electron microscope analysis was performed to show general surface characters of B-TCP and B-TCP /Collagen biomaterials. The osteoinductive capacities of the B-TCP and B-TCP/Collagen biomaterials were determined by alkaline phosphatase and Von Kossa stainings, and RT-PCR analysis. The ALP activity of the B-TCP/Col containing material was significantly higher than the B-TCP on the first days. In terms of gene expression, there were no significant differences except 14th-day SPARC gene expression. The results of Von Kossa staining indicate that B-TCP/Col has above the desired level degradation capacity. As a result of this research, although it is advantageous in terms of alkaline phosphatase activity and osteogenic gene expression compared to B-TCP material, it is thought that B-TCP/Collagen biomaterial should be developed for use in bone tissue engineering due to its high degradation property.

A Comprehensive Review on Collagen Type I Development of Biomaterials for Tissue Engineering: From Biosynthesis to Bioscaffold

Collagen is the most abundant structural protein found in humans and mammals, particularly in the extracellular matrix (ECM). Its primary function is to hold the body together. The collagen superfamily of proteins includes over 20 types that have been identified. Yet, collagen type I is the major component in many tissues and can be extracted as a natural biomaterial for various medical and biological purposes. Collagen has multiple advantageous characteristics, including varied sources, biocompatibility, sustainability, low immunogenicity, porosity, and biodegradability. As such, collagen-type-I-based bioscaffolds have been widely used in tissue engineering. Biomaterials based on collagen type I can also be modified to improve their functions, such as by crosslinking to strengthen the mechanical property or adding biochemical factors to enhance their biological activity. This review discusses the complexities of collagen type I structure, biosynthesis, sources for collagen derivatives, methods of isolation and purification, physicochemical characteristics, and the current development of collagen-type-I-based scaffolds in tissue engineering applications. The advancement of additional novel tissue engineered bioproducts with refined techniques and continuous biomaterial augmentation is facilitated by understanding the conventional design and application of biomaterials based on collagen type I.

In Vivo Bone Tissue Engineering Strategies: Advances and Prospects

Reconstruction of critical-sized bone defects remains a tremendous challenge for surgeons worldwide. Despite the variety of surgical techniques, current clinical strategies for bone defect repair demonstrate significant limitations and drawbacks, including donor-site morbidity, poor anatomical match, insufficient bone volume, bone graft resorption, and rejection. Bone tissue engineering (BTE) has emerged as a novel approach to guided bone tissue regeneration. BTE focuses on in vitro manipulations with seed cells, growth factors and bioactive scaffolds using bioreactors. The successful clinical translation of BTE requires overcoming a number of significant challenges. Currently, insufficient vascularization is the critical limitation for viability of the bone tissue-engineered construct. Furthermore, efficacy and safety of the scaffolds cell-seeding and exogenous growth factors administration are still controversial. The in vivo bioreactor principle (IVB) is an exceptionally promising concept for the in vivo bone tissue regeneration in a predictable patient-specific manner. This concept is based on the self-regenerative capacity of the human body, and combines flap prefabrication and axial vascularization strategies. Multiple experimental studies on in vivo BTE strategies presented in this review demonstrate the efficacy of this approach. Routine clinical application of the in vivo bioreactor principle is the future direction of BTE; however, it requires further investigation for overcoming some significant limitations.

Effectively improved 3-dimensional structural stability of atelocollagen-gelatin sponge biomaterial by heat treatment

Atelocollagen-gelatin (ACG) sponge was fabricated from atelocollagen and gelatin by lyophilization without introducing toxic substances. This study aimed to investigate the effects of heat treatment on the 3-dimensional structural stability of ACG sponge biomaterial. ACG sponge samples were fabricated and heat treated at 125^oC for 12 h in the vacuum. The results revealed that heat treatment did not affect porosity, pore size and mechanical compressive strength. Heat-treated ACG sponge showed decreased absorbance and peak shift of amid I (C=O) stretches, slightly higher water uptake degree and significantly decreased in vitro degradation rate. Moreover, heat-treated ACG sponge maintained good 3-dimensional surface morphology and porous microstructure throughout 7 days, while non-heat-treated ACG sponge collapsed in less than 24 h. The human mesenchymal stromal cells (hMSCs) were shown to adhere and grow well on heat-treated ACG sponges. These results indicate that heat treatment is effective and safe to stabilize 3-dimensional ACG sponge biomaterial for tissue engineering.

Fabrication and characterization of PHEMA–gelatin scaffold enriched with graphene oxide for bone tissue engineering

Background

Growing investigations demonstrate that graphene oxide (GO) has an undeniable impact on repairing damaged bone tissue. Moreover, it has been stated in the literatures that poly(2-hydroxyethyl methacrylate) (PHEMA) and gelatin could provide a biocompatible structure.

Methods

In this research, we fabricated a scaffold using freeze-drying method comprised of PHEMA and gelatin, combined with GO. The validation of the successful fabrication of the scaffolds was performed utilizing Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction assay (XRD). The microstructure of the scaffolds was observed using scanning electron microscopy (SEM). The structural properties of the scaffolds including mechanical strength, hydrophilicity, electrical conductivity, and degradation rate were also evaluated. Human bone marrow‐derived mesenchymal stem cells (hBM-MSCs) were used to evaluate the cytotoxicity of the prepared scaffolds. The osteogenic potential of the GO-containing scaffolds was studied by measuring the alkaline phosphatase (ALP) activity after 7, 14, and 21 days cell culturing.

Results

SEM assay showed a porous interconnected scaffold with approximate pore size of 50–300 μm, appropriate for bone regeneration. The increase in GO concentration from 0.25 to 0.75% w/v exhibited a significant improvement in scaffolds compressive modulus from 9.03 ± 0.36 to 42.82 ± 1.63 MPa. Conventional four-probe analysis confirmed the electrical conductivity of the scaffolds in the semiconductor range. The degradation rate of the samples appeared to be in compliance with bone healing process. The scaffolds exhibited no cytotoxicity using MTT assay against hBM-MSCs. ALP analysis indicated that the PHEMA–Gel–GO scaffolds could efficiently cause the differentiation of hBM-MSCs into osteoblasts after 21 days, even without the addition of the osteogenic differentiation medium.

Conclusion

Based on the results of this research, it can be stated that the PHEMA–Gel–GO composition is a promising platform for bone tissue engineering.

Integrated printed BDNF/collagen/chitosan scaffolds with low temperature extrusion 3D printer accelerated neural regeneration after spinal cord injury

Recent studies have shown that 3D printed scaffolds integrated with growth factors can guide the growth of neurites and promote axon regeneration at the injury site. However, heat, organic solvents or cross-linking agents used in conventional 3D printing reduce the biological activity of growth factors. Low temperature 3D printing can incorporate growth factors into the scaffold and maintain their biological activity. In this study, we developed a collagen/chitosan scaffold integrated with brain-derived neurotrophic factor (3D-CC-BDNF) by low temperature extrusion 3D printing as a new type of artificial controlled release system, which could prolong the release of BDNF for the treatment of spinal cord injury (SCI). Eight weeks after the implantation of scaffolds in the transected lesion of T10 of the spinal cord, 3D-CC-BDNF significantly ameliorate locomotor function of the rats. Consistent with the recovery of locomotor function, 3D-CC-BDNF treatment could fill the gap, facilitate nerve fiber regeneration, accelerate the establishment of synaptic connections and enhance remyelination at the injury site.

In Vivo Assessment of Synthetic and Biological-Derived Calcium Phosphate-Based Coatings Fabricated by Pulsed Laser Deposition: A Review

The aim of this review is to present the state-of-the art achievements reported in the last two decades in the field of pulsed laser deposition (PLD) of biocompatible calcium phosphate (CaP)-based coatings for medical implants, with an emphasis on their in vivo biological performances. There are studies in the dedicated literature on the in vivo testing of CaP-based coatings (especially hydroxyapatite, HA) synthesized by many physical vapor deposition methods, but only a few of them addressed the PLD technique. Therefore, a brief description of the PLD technique, along with some information on the currently used substrates for the synthesis of CaP-based structures, and a short presentation of the advantages of using various animal and human implant models will be provided. For an in-depth in vivo assessment of both synthetic and biological-derived CaP-based PLD coatings, a special attention will be dedicated to the results obtained by standardized and micro-radiographies, (micro) computed tomography and histomorphometry, tomodensitometry, histology, scanning and transmission electron microscopies, and mechanical testing. One main specific result of the in vivo analyzed studies is related to the demonstrated superior osseointegration characteristics of the metallic (generally Ti) implants functionalized with CaP-based coatings when compared to simple (control) Ti ones, which are considered as the “gold standard” for implantological applications. Thus, all such important in vivo outcomes were gathered, compiled and thoroughly discussed both to clearly understand the current status of this research domain, and to be able to advance perspectives of these synthetic and biological-derived CaP coatings for future clinical applications.

Effect of Dehydrothermal Treatment on the Mechanical Properties and Biocompatibility of Plaster of Paris–CaCO3 Hydrogel Loaded With Cinnamaldehyde for Biomedical Purposes

CaCO3 hydrogel incorporation into Plaster of Paris (POP) formulations decreased the resorption rate of the POP after implantation in the body. Although an inflammatory process is required as part of wound healing, the accumulation and activation of inflammatory cells in the POP–hydrogel CaCO3 implant area needs to be controlled. Therefore, cinnamaldehyde, as an anti-inflammatory agent with a unique α, β-unsaturated aldehyde, was incorporated into the CaCO3 hydrogel. During the incorporation, both the lipophilic and hydrophilic sides of the cinnamaldehyde molecule can influence the physical and mechanical properties of the CaCO3 hydrogel, in which mechanical properties of a tissue engineering scaffold are important to fine tune cellular activity during implantation. On the other hand, as a 3-dimensional polymeric structure, crosslinking is needed for the CaCO3 hydrogel to stabilize and increase its molecular weight for better mechanical strength, and more resistance to heat, wear, and solvent attack. For that purpose, dehydrothermal treatment (DHT) was applied to the crosslink hydrogel system as a favorable crosslinking method to avoid the use of a chemical agent. In this study, 3 groups of hydrogels of CaCO3, namely DHT crosslinked, loaded with cinnamaldehyde, and loaded with cinnamaldehyde followed by DHT crosslinking were developed before being combined with POP in 50 wt%. To evaluate the effect of DHT to the final POP-cinnamaldehyde-loaded CaCO3 hydrogel properties and biocompatibility, scanning electron microscopy, contact angle, surface roughness, hardness, diametral tensile strength, and in vivo biocompatibility studies were conducted. It was observed that cinnamaldehyde with DHT treatment improved the POP–hydrogel CaCO3 properties and had good biocompatibility. Thus, POP-cinnamaldehyde-loaded CaCO3 hydrogel can be a promising bone substitute containing an anti-inflammatory agent.

Synthesis and characterization of collagen/calcium phosphate scaffolds incorporating antibacterial agent for bone tissue engineering application

In the present study, we developed a novel niosomal nanocarrier embedded into a collagen/β- tricalcium phosphate (Col/β-TCP) scaffold for the local delivery of thymol as a natural anti-bacterial reagent. The niosomal Col/β-TCP (N-Col/β-TCP) scaffolds with different weight ratios of β-TCP to Col were prepared by freeze-drying. The antimicrobial activities of the prepared samples against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were assessed by agar diffusion method. The release profile of niosomal thymol from the optimized composite scaffolds showed a sustained profile where 66% of the loaded thymol was released over 30 days. The compressive modulus of niosome added scaffolds with an equal ratio of β-TCP and Col was calculated as 972±1.3KPa. This scaffold showed significantly higher values of cell viability (as evaluated by an MTT assay) against L929 fibroblasts than a scaffold without niosomal thymol after 24 and 72 h. Among synthesized samples, Col/β-TCP1 showed the greatest effectiveness of anti-bacterial activity toward Gram-positive and Gram-negative bacteria with higher activity against Gram-positive ones. The results of this study highlight the potential of niosomal-thymol loaded Col/β-TCP1 scaffold as an anti-bacterial bone substitute for possible osteomyelitis treatment.

Synthesis of Conductive Carbon Aerogels Decorated with β-Tricalcium Phosphate Nanocrystallites

There has been substantial interest in research aimed at conductive carbon-based supports since the discovery that the electrical stimulus can have dramatic effect on cell behavior. Among these carbon-aerogels decorated with biocompatible polymers were suggested as future materials for tissue engineering. However, high reaction temperatures required for the synthesis of the aerogels tend to impair the stability of the polymeric networks. Herein, we report a synthetic route towards carbon-aerogel scaffolds decorated with biocompatible ceramic nanoparticles of tricalcium phosphate. The composites can be prepared at temperature as high as 1100 °C without significant effect on the morphology of the composite which is comparable with the original aerogel framework. Although the conductivity of the composites tends to decrease with the increasing ceramic content the measured conductivity values are similar to those previously reported on polymer-functionalized carbon-aerogels. The cell culture study revealed that the developed constructs support cell proliferation and provide good cell attachment suggesting them as potentially good candidates for tissue-engineering applications.

Comparative evaluation of the physicochemical properties of nano-hydroxyapatite/collagen and natural bone ceramic/collagen scaffolds and their osteogenesis-promoting effect on MC3T3-E1 cells

The use of various types of calcium phosphate has been reported in the preparation of repairing materials for bone defects. However, the physicochemical and biological properties among them might be vastly different. In this study, we prepared two types of calcium phosphates, nano-hydroxyapatite (nHA) and natural bone ceramic (NBC), into 3D scaffolds by mixing with type I collagen (CoL), resulting in the nHA/CoL and NBC/CoL scaffolds. We then evaluated and compared the physicochemical and biological properties of these two calcium phosphates and their composite scaffold with CoL. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD) and compressive tests were used to, respectively, characterize the morphology, composition, distribution and the effect of nHA and NBC to collagen. Next, we examined the biological properties of the scaffolds using cytotoxicity testing, flow cytometry, immunofluorescence staining, biocompatibility testing, CCK-8 assays and RT-PCR. The results reflected that the Ca2+ released from nHA and NBC could bind chemically with collagen and affect its physicochemical properties, including the infrared absorption spectrum and compression modulus, among others. Furthermore, the two kinds of scaffolds could promote the expression of osteo-relative genes, but showed different gene induction properties. In short, NBC/CoL could promote the expression of early osteogenic genes, while nHA/CoL could upregulate late osteogenic genes. Conclusively, these two composite scaffolds could provide MC3T3-E1 cells with a biomimetic surface for adhesion, proliferation and the formation of mineralized extracellular matrices. Moreover, nHA/CoL and NBC/CoL had different effects on the period and extent of MC3T3-E1 cell mineralization.

Composite Based on Biphasic Calcium Phosphate (HA/β-TCP) and Nanocellulose from the Açaí Tegument

The use of lignocellulosic remnants of the açaí agro-business will benefit the environment with a precursor material for biomedical applications. Nanocellulose (NC) allows the biomimetic growth of biphasic ceramics on its surface, with characteristics compatible with bone tissue, including bioactive properties and biocompatibility. In this study, the composites were obtained from açaí tegument (Euterpe Oleracea Mart.) NC using acid hydrolysis. The characterization performed by scanning electron microscopy showed the characteristic crystals of hydroxyapatite (HA) and calcium triphosphate (β-TCP) based on the results of X-ray diffraction, with the peak at 22°, showing the NC nucleation of HA and peak at 17° showing tricalcium phosphate (β-TCP). Fourier transform infrared spectroscopy confirmed the presence of O-H at 3400 cm⁻¹ and C-H at 2900 cm⁻¹, which is characteristic of cellulose; peaks were also observed at 1609 cm⁻¹, verifying the reduction in lignin content. Groups PO₄⁻³ at approximately 1070 cm⁻¹, P-OH at 910–1040 cm⁻¹, and HCO₃⁻ at 2450 cm⁻¹ confirmed the formation of HA and β-TCP. The zeta potential had a range of −11 ± 23.8 mV related to particle size, which had a range of 164.2 × 10⁻⁹–4748 × 10⁻⁹ m.

Development of a bioactive porous collagen/β-tricalcium phosphate bone graft assisting rapid vascularization for bone tissue engineering applications

We developed collagen (COL) and collagen/beta tricalcium phosphate (COL/β-TCP) scaffolds with a β-TCP/collagen weight ratio of 4 by freeze-drying. Mouse bone marrow-derived mesenchymal stem cells (BMMSCs) were cultured on these scaffolds for 14 days. Samples were characterized by physicochemical analyses and their biological properties such as cell viability and alkaline phosphatase (ALP) activity was, also, examined. Additionally, the vascularization potential of the prepared scaffolds was tested subcutaneously in Wistar rats. We observed a microporous structure with large porosity (∼95-98%) and appropriate pore size (120-200 µm). The COL/β-TCP scaffolds had a much higher compressive modulus (970 ± 1.20 KPa) than pure COL (0.8 ± 1.82 KPa). In vitro model of apatite formation was established by immersing the composite scaffold in simulated body fluid for 7 days. An ALP assay revealed that porous COL/β-TCP can effectively activate the differentiation of BMMSCs into osteoblasts. The composite scaffolds also promoted vascularization with good integration with the surrounding tissue. Thus, introduction of β-TCP powder into the porous collagen matrix effectively improved the mechanical and biological properties of the collagen scaffolds, making them potential bone substitutes for enhanced bone regeneration in orthopedic and dental applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 73-85, 2018.

RUNX1 Plays an Important Role in Mediating BMP9-Induced Osteogenic Differentiation of Mesenchymal Stem Cells Line C3H10T1/2, Murine Multi-Lineage Cells Lines C2C12 and MEFs

As one of the least studied bone morphogenetic proteins (BMPs), BMP9 is highly capable of promoting osteogenic differentiation. However, the underlying mechanism involved remains largely unknown. Recent studies have demonstrated that RUNX1 (runt-related transcription factor 1) is essential in osteoblast/chondrocyte maturation. In this study, we investigated the function of RUNX1 in BMP9-induced osteogenic of murine mesenchymal stem cell line (C3H10T1/2) and murine multi-lineage cell lines (C2C12 and MEFs). Our data showed that BMP9 promoted the endogenous expression of RUNX1 in C3H10T1/2, C2C12 and MEFs. Moreover, RUNX1 was probably a direct target of BMP9/Smad signaling. BMP9-induced osteogenic differentiation was enhanced by overexpression of RUNX1, whereas inhibited by knockdown RUNX1 in C3H10T1/2, C2C12 and MEFs. Further mechanism studies demonstrated that RUNX1 might affect BMP9-induced phosphorylation of Smad1/5/8, but not the phosphorylation of p38 and ERK1/2.Our results suggest that RUNX1 may be an essential modulator in BMP9- induced osteogenic differentiation of MSCs (Mesenchymal stem cells).

Calcium Phosphate Bioceramics: A Review of Their History, Structure, Properties, Coating Technologies and Biomedical Applications

Calcium phosphate (CaP) bioceramics are widely used in the field of bone regeneration, both in orthopedics and in dentistry, due to their good biocompatibility, osseointegration and osteoconduction. The aim of this article is to review the history, structure, properties and clinical applications of these materials, whether they are in the form of bone cements, paste, scaffolds, or coatings. Major analytical techniques for characterization of CaPs, in vitro and in vivo tests, and the requirements of the US Food and Drug Administration (FDA) and international standards from CaP coatings on orthopedic and dental endosseous implants, are also summarized, along with the possible effect of sterilization on these materials. CaP coating technologies are summarized, with a focus on electrochemical processes. Theories on the formation of transient precursor phases in biomineralization, the dissolution and reprecipitation as bone of CaPs are discussed. A wide variety of CaPs are presented, from the individual phases to nano-CaP, biphasic and triphasic CaP formulations, composite CaP coatings and cements, functionally graded materials (FGMs), and antibacterial CaPs. We conclude by foreseeing the future of CaPs.

Hybrid Aorta Constructs via In Situ Crosslinking of Poly(glycerol-sebacate) Elastomer Within a Decellularized Matrix

Decellularization of tissues and organs has high potential to obtain unique conformation and composition as native tissue structure but may result in weakened tissue mechanical strength. In this study, poly(glycerol-sebacate) (PGS) elastomers were combined with decellularized aorta fragments to investigate the changes in mechanical properties. PGS prepolymer was synthesized via microwave irradiation and then in situ crosslinked within the decellularized aorta extracellular matrix (ECM). Tensile strength (σ) values were found comparable as 0.44 ± 0.10 MPa and 0.57 ± 0.18 MPa for native and hybrid aorta samples, respectively, while elongation at break (ɛ) values were 261% ± 17%, 7.5% ± 0.57%, and 22.18% ± 2.48% for wet control (native), decellularized dried aortae, and hybrid matrices, showing elastic contribution. Young's modulus data indicate that there was a threefold decrease in stiffness compared to decellularized samples once PGS is introduced into the ECM structure. Scanning electron microscopy (SEM) analysis of hybrid grafts revealed that the construct preserves porosity in medial layer of the vessel. Biocompatibility analyses showed no cytotoxic effects on human abdominal aorta smooth muscle cells. Cell studies showed 98% activity in hybrid graft extracts. As a control, collagen coating of the hybrid grafts was performed in the recellularization stage. SEM analysis of recellularized hybrid grafts revealed that cells were attached to the surface of the hybrid graft and proliferated during the 14 days of culture in both groups. This study shows that introducing an elastomer into the native ECM structure following decellularization process can be a useful approach for the preparation of mechanically enhanced composites for soft tissues.

Bi-layered constructs of poly(glycerol-sebacate)-β-tricalcium phosphate for bone-soft tissue interface applications

This study aims to establish a facile protocol for the preparation of a bi-layered poly(glycerol-sebacate) (PGS)/β-tricalcium phosphate (β-TCP) construct and to investigate its potential for bone-soft tissue engineering applications. The layered structure was prepared by distributing the ceramic particles within a prepolymer synthesized in a microwave reactor followed by a cross-linking of the final construct in vacuum (<10mbar). The vacuum stage led to the separation of cross-linked elastomer (top) and ceramic (bottom) phases. Results showed that addition of β-TCP particles to the elastomer matrix after the polymerization led to an increase in compression strength (up to 14±2.3MPa). Tensile strength (σ), Young's modulus (E), and elongation at break (%) values were calculated as 0.29±0.03MPa and 0.21±0.03; 0.38±0.02 and 1.95±0.4; and 240±50% and 24±2% for PGS and PGS/β-TCP bi-layered constructs, respectively. Morphology was characterized by using Scanning Electron Microscopy (SEM) and micro-computed tomography (μ-CT). Tomography data revealed an open porosity of 35% for the construct, mostly contributed from the ceramic phase since the elastomer side has no pore. Homogeneous β-TCP distribution within the elastomeric structure was observed. Cell culture studies confirmed biocompatibility with poor elastomer-side and good bone-side cell attachment. In a further study to investigate the osteogenic properties, the construct were loaded with BMP-2 and/or TGF-β1. The PGS/β-TCP bi-layered constructs with improved mechanical and biological properties have the potential to be used in bone-soft tissue interface applications where soft tissue penetration is a problem.

Bioinspired Collagen-Apatite Nanocomposites for Bone Regeneration

INTRODUCTION

Natural bone has a complex hierarchical nanostructure composed of well-organized collagen fibrils embedded with apatite crystallites. Bone tissue engineering requires scaffolds with structural properties and functionality similar to the natural bone. Inspired by bone, a collagen-apatite (Col-Ap) nanocomposite was fabricated with bonelike subfibrillar nanostructures using a modified bottom-up biomimetic approach and has a potential role in the healing of large bone defects in unresolved apical periodontitis.

METHODS

The bone regeneration potential of the Col-Ap nanocomposite was investigated by comparing it with inorganic beta-tricalcium phosphate and organic pure collagen using a critical-sized rodent mandibular defect model. Micro-computed tomographic imaging and histologic staining were used to evaluate new bone formation in vivo.

RESULTS

When compared with the beta-tricalcium phosphate and collagen scaffolds, the Col-Ap nanocomposite scaffold exhibited superior regeneration properties characterized by profuse deposition of new bony structures and vascularization at the defect center. Immunohistochemistry showed that the transcription factor osterix and vascular endothelial growth factor receptor 1 were highly expressed in the Col-Ap group. The results indicate that the Col-Ap nanocomposite activates more bone-forming cells and stimulates more vascular tissue ingrowth. Furthermore, the Col-Ap nanocomposite induces extracellular matrix secretion and mineralization of rat bone marrow stem cells. The increased expression of transforming growth factor beta 1 may contribute to the formation of a mineralized extracellular matrix.

CONCLUSIONS

The present study lays the foundation for the development of Col-Ap nanocomposite-based bone grafts for future clinical applications in bone regeneration of large periapical lesions after apical curettage or apicoectomy.

A Comparative Evaluation of the Mechanical Properties of Two Calcium Phosphate/Collagen Composite Materials and Their Osteogenic Effects on Adipose-Derived Stem Cells

Adipose-derived stem cells (ADSCs) are ideal seed cells for use in bone tissue engineering and they have many advantages over other stem cells. In this study, two kinds of calcium phosphate/collagen composite scaffolds were prepared and their effects on the proliferation and osteogenic differentiation of ADSCs were investigated. The hydroxyapatite/β-tricalcium phosphate (HA/β-TCP) composite scaffolds (HTPSs), which have an additional β-tricalcium phosphate, resulted in better proliferation of ADSCs and showed osteogenesis-promoting effects. Therefore, such composite scaffolds, in combination with ADSCs or on their own, would be promising for use in bone regeneration and potential clinical therapy for bone defects.

Application of Collagen Scaffold in Tissue Engineering: Recent Advances and New Perspectives

Collagen is the main structural protein of most hard and soft tissues in animals and the human body, which plays an important role in maintaining the biological and structural integrity of the extracellular matrix (ECM) and provides physical support to tissues. Collagen can be extracted and purified from a variety of sources and offers low immunogenicity, a porous structure, good permeability, biocompatibility and biodegradability. Collagen scaffolds have been widely used in tissue engineering due to these excellent properties. However, the poor mechanical property of collagen scaffolds limits their applications to some extent. To overcome this shortcoming, collagen scaffolds can be cross-linked by chemical or physical methods or modified with natural/synthetic polymers or inorganic materials. Biochemical factors can also be introduced to the scaffold to further improve its biological activity. This review will summarize the structure and biological characteristics of collagen and introduce the preparation methods and modification strategies of collagen scaffolds. The typical application of a collagen scaffold in tissue engineering (including nerve, bone, cartilage, tendon, ligament, blood vessel and skin) will be further provided. The prospects and challenges about their future research and application will also be pointed out.