Non-crystalline composite tissue engineering scaffolds using boron-containing bioactive glass and poly(d,l-lactic acid) coatings

Performance comparison of PLA- and PLGA-coated porous bioceramic scaffolds: Mechanical, biodegradability, bioactivity, delivery and biocompatibility assessments

Bioceramics, particularly calcium phosphates, bioactive glasses, and crystalline silicates, are a principal group of biomaterials employed for the regeneration of damaged tissues and therapeutic delivery. The development of ceramic tissue engineering scaffolds with an appropriate combination of mechanical and biological properties is still one of the key challenges in this field. In this regard, the deposition of polymeric coatings on the scaffolds is a simple and effective approach to reinforce their functions. Among different polymers, the influences of biodegradable aliphatic polyester coatings, especially polylactic acid (PLA) and poly(lactic-co-glycolic acid) (PLGA), over the performance of the scaffolds have been investigated in numerous research. This review paper provides a comprehensive comparison of PLA- and PLGA-coated bioceramic scaffolds which are mainly employed in bone tissue engineering. It is concluded that both the polymers enhance the mechanical behaviors of the scaffolds, but control their biodegradability, bioactivity, and delivery kinetics, where PLA acts almost more influentially than PLGA in comparison. However, the response of biocompatibility to this surface treatment is condition-dependent and requires case-by-case experiments to be determined accurately.

Dissolution of Amorphous S53P4 Glass Scaffolds in Dynamic In Vitro Conditions

The silicate-based bioactive glass S53P4 is clinically used in bone regenerative applications in granule form. However, utilization of the glass in scaffold form has been limited by the high tendency of the glass to crystallize during sintering. Here, careful optimization of sintering parameters enabled the manufacture of porous amorphous S53P4 scaffolds with a strength high enough for surgical procedures in bone applications (5 MPa). Sintering was conducted in a laboratory furnace for times ranging from 25 to 300 min at 630 °C, i.e., narrowly below the commencement of the crystallization. The phase composition of the scaffolds was verified with XRD, and the ion release was tested in vitro and compared with granules in continuous flow of Tris buffer and simulated body fluid (SBF). The amorphous, porous S53P4 scaffolds present the possibility of using the glass composition in a wider range of applications.

Scaffold-free biofabrication of adipocyte structures with magnetic levitation

Tissue engineering research aims to repair the form and/or function of impaired tissues. Tissue engineering studies mostly rely on scaffold-based techniques. However, these techniques have certain challenges, such as the selection of proper scaffold material, including mechanical properties, sterilization, and fabrication processes. As an alternative, we propose a novel scaffold-free adipose tissue biofabrication technique based on magnetic levitation. In this study, a label-free magnetic levitation technique was used to form three-dimensional (3D) scaffold-free adipocyte structures with various fabrication strategies in a microcapillary-based setup. Adipogenic-differentiated 7F2 cells and growth D1 ORL UVA stem cells were used as model cells. The morphological properties of the 3D structures of single and cocultured cells were analyzed. The developed procedure leads to the formation of different patterns of single and cocultured adipocytes without a scaffold. Our results indicated that adipocytes formed loose structures while growth cells were tightly packed during 3D culture in the magnetic levitation platform. This system has potential for ex vivo modeling of adipose tissue for drug testing and transplantation applications for cell therapy in soft tissue damage. Also, it will be possible to extend this technique to other cell and tissue types.

Cellulose acetate-gelatin-coated boron-bioactive glass biocomposite scaffolds for bone tissue engineering

In this study, we aimed to prepare and characterize porous scaffolds composed of pure and boron oxide (B₂O₃)-doped bioactive glass (BG) that were infiltrated by cellulose acetate-gelatin (CA-GE) polymer solution for bone tissue engineering applications. Composite scaffolds were cross-linked with glutaraldehyde after polymer coating to protect the structural integrity of the polymeric-coated scaffolds. The impact of B₂O₃ incorporation into BG-polymer porous scaffolds on the cross-sectional morphology, porosity, mechanical properties, degradation and bioactivity of the scaffolds was investigated. Human dental pulp stem cells (hDPSCs) were enzymatically isolated and used for cell culture studies. According to scanning electron microscope analysis, the porous structure of the scaffolds was preserved after polymer coating. After polymer infiltration, the porosity of the scaffolds decreased from 64.2% to 59.35% for pure BG scaffolds and from 67.3% to 58.9% for B₂O₃-doped scaffolds. Meanwhile, their compressive strengths increased from 0.13 to 0.57 MPa and from 0.20 to 0.82 MPa, respectively. After polymer infiltration, 7% B₂O₃-incorporated BG scaffolds had higher weight loss and Ca-P layer deposition than pure BG scaffolds, after 14 d of incubation in simulated body fluid at 37 °C. Higher attachment and proliferation of hDPSCs were observed on 7% B₂O₃-BG-CA/GE scaffolds. In addition, the alkaline phosphatase activity of the cells was about 1.25-fold higher in this group than that observed on BG-CA/GE scaffolds after 14 d of incubation in osteogenic medium, while their intracellular calcium amounts were 1.7-fold higher than observed on BG-CA/GE after 7 d of incubation in osteogenic medium. Our results suggested that porous cellulose acetate-gelatin-coated boron-BG scaffolds hold promise for bone tissue engineering applications.

Bioactive Glasses and Glass-Ceramics for Healthcare Applications in Bone Regeneration and Tissue Engineering

The discovery of bioactive glasses (BGs) in the late 1960s by Larry Hench et al. was driven by the need for implant materials with an ability to bond to living tissues, which were intended to replace inert metal and plastic implants that were not well tolerated by the body. Among a number of tested compositions, the one that later became designated by the well-known trademark of 45S5 Bioglass® excelled in its ability to bond to bone and soft tissues. Bonding to living tissues was mediated through the formation of an interfacial bone-like hydroxyapatite layer when the bioglass was put in contact with biological fluids in vivo. This feature represented a remarkable milestone, and has inspired many other investigations aiming at further exploring the in vitro and in vivo performances of this and other related BG compositions. This paradigmatic example of a target-oriented research is certainly one of the most valuable contributions that one can learn from Larry Hench. Such a goal-oriented approach needs to be continuously stimulated, aiming at finding out better performing materials to overcome the limitations of the existing ones, including the 45S5 Bioglass®. Its well-known that its main limitations include: (i) the high pH environment that is created by its high sodium content could turn it cytotoxic; (ii) and the poor sintering ability makes the fabrication of porous three-dimensional (3D) scaffolds difficult. All of these relevant features strongly depend on a number of interrelated factors that need to be well compromised. The selected chemical composition strongly determines the glass structure, the biocompatibility, the degradation rate, and the ease of processing (scaffolds fabrication and sintering). This manuscript presents a first general appraisal of the scientific output in the interrelated areas of bioactive glasses and glass-ceramics, scaffolds, implant coatings, and tissue engineering. Then, it gives an overview of the critical issues that need to be considered when developing bioactive glasses for healthcare applications. The aim is to provide knowledge-based tools towards guiding young researchers in the design of new bioactive glass compositions, taking into account the desired functional properties.

Strength, toughness, and reliability of a porous glass/biopolymer composite scaffold

Development of bioactive glass and ceramic scaffolds intended for the reconstruction of large segmental bone defects remains a challenge for materials science due to the complexities involved in clinical implantation, bone-implant reaction, implant degradation and the multiple loading modes the implants subjected to. A comprehensive evaluation of the mechanical properties of inorganic scaffolds and exploration of new ways to toughen brittle constructs are critical prior to their successful application in loaded sites. A simple and widely adopted approach involves the coating of an inorganic scaffold with a polymeric material. In this work, a systematic evaluation of the influence of a biopolymer, polycaprolactone (PCL), coating on the mechanical performance of bioactive glass scaffolds was carried out. Results from this work indicate that a biopolymer PCL coating was more effective in increasing the compressive strength and reliability of the glass scaffold under compression, but less effective in improving its flexural strength or fracture toughness. This is the first report that reveals the limited successfulness of a polymer coating in improving the toughness of strong scaffolds, suggesting that new and novel ways of toughening inorganic scaffolds should be future research directions for scaffolds applied in loaded sites. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1209-1217, 2018.

[Research and application progress of bioactive glass in bone repair]

Objective

To review the research and application progress of bioactive glass in bone repair.

Methods

The recently published literature concerning bioactive glass in bone repair was reviewed and summarized.

Results

Bioactive glass can classified different types, such as bioactive glass particulate, bioactive glass scaffold, bioactive glass coating, injectable bioactive glass cement, and bioactive glass delivery system. Bioactive glass has been well studied in the field of bone repair due to its excellent biological properties. Also, the remarkable progress has been made in various aspects.

Conclusion

Bioactive glass is a reliable material of bone repair and will play an even more important role in the future.

Microwave-induced production of boron-doped HAp (B-HAp) and B-HAp coated composite scaffolds

The aim of the present study is to produce boron (B) doped hydroxyapatite (B-HAp), which has an osteoinductive property, and investigate in-vitro osteogenesis potential of B-HAp coated chitosan (B-HAp/Ch) scaffolds. At first, B-HAp was produced by the interaction of ions within the concentrated synthetic body fluid containing boron (B-SBF) with microwave energy. Boron incorporation into HAp structure was performed by the substitution of borate ions with phosphate and hydroxyl ions. Experiments were carried out with different microwave powers and exposure times, and optimum conditions for the production of B-HAp were determined. B-HAp precipitated from B-SBF by 600W microwave power has 1.15±0.11% (w/w) B, 1.40 (w/w) Ca/P ratio, 4.30±0.07% (w/w) carbonate content, 30±4nm rod-like morphology and bone-like amorphous structure. Then, chitosan scaffolds that were prepared by freeze-drying were coated with B-HAp by performing microwave-assisted precipitation in the presence of scaffolds to improve their bioactivities and mechanical properties. The formation of apatite layer and the penetration of apatites into the pores were observed by scanning electron microscopy (SEM). Fourier Transform Infrared spectroscopy (ATR-FTIR) and X-ray diffraction (XRD) analysis also confirmed the presence of B-HAp layer. As control, hydroxyapatite coated chitosan scaffolds (HAp/Ch) produced at the same conditions were used. The results of cell culture studies indicated that B releasing from scaffolds enhances proliferation and osteoblastic differentiation of MC3T3-E1 cells. This work emphasized the importance of the use of B within the scaffolds for enhancing in-vitro bone tissue engineering applications.

Magnetic nanocomposites of boron and vitamin C

Magnetic nanocomposites of boron and vitamin C for potential targeted delivery/therapy applications are reported here.

Toughening and functionalization of bioactive ceramic and glass bone scaffolds by biopolymer coatings and infiltration: a review of the last 5 years

Inorganic scaffolds with high interconnected porosity based on bioactive glasses and ceramics are prime candidates for applications in bone tissue engineering. These materials however exhibit relatively low fracture strength and high brittleness. A simple and effective approach to improve the toughness is to combine the basic scaffold structure with polymer coatings or through the formation of interpenetrating polymer-bioactive ceramic microstructures. The polymeric phase can additionally serve as a carrier for growth factors and therapeutic drugs, thus adding biological functionalities. The present paper reviews the state-of-the art in the field of polymer coated and infiltrated bioactive inorganic scaffolds. Based on the notable combination of bioactivity, improved mechanical properties and drug or growth factor delivery capability, this scaffold type is a candidate for bone and osteochondral regeneration strategies. Remaining challenges for the improvement of the materials are discussed and opportunities to broaden the application potential of this scaffold type are also highlighted.

Scaffold-based regeneration of skeletal tissues to meet clinical challenges

The management and reconstruction of damaged or diseased skeletal tissues have remained a significant global healthcare challenge. The limited efficacy of conventional treatment strategies for large bone, cartilage and osteochondral defects has inspired the development of scaffold-based tissue engineering solutions, with the aim of achieving complete biological and functional restoration of the affected tissue in the presence of a supporting matrix. Nevertheless, significant regulatory hurdles have rendered the clinical translation of novel scaffold designs to be an inefficient process, mainly due to the difficulties of arriving at a simple, reproducible and effective solution that does not rely on the incorporation of cells and/or bioactive molecules. In the context of the current clinical situation and recent research advances, this review will discuss scaffold-based strategies for the regeneration of skeletal tissues, with focus on the contribution of bioactive ceramic scaffolds and silk fibroin, and combinations thereof, towards the development of clinically viable solutions.

Toward Strong and Tough Glass and Ceramic Scaffolds for Bone Repair

The need for implants to repair large bone defects is driving the development of porous synthetic scaffolds with the requisite mechanical strength and toughness in vivo. Recent developments in the use of design principles and novel fabrication technologies are paving the way to create synthetic scaffolds with promising potential for reconstituting bone in load-bearing sites. This article reviews the state of the art in the design and fabrication of bioactive glass and ceramic scaffolds that have improved mechanical properties for structural bone repair. Scaffolds with anisotropic and periodic structures can be prepared with compressive strengths comparable to human cortical bone (100-150 MPa), while scaffolds with an isotropic structure typically have strengths in the range of trabecular bone (2-12 MPa). However, the mechanical response of bioactive glass and ceramic scaffolds in multiple loading modes such as flexure and torsion - as well as their mechanical reliability, fracture toughness, and fatigue resistance - has received little attention. Inspired by the designs of natural materials such as cortical bone and nacre, glass-ceramic and inorganic/polymer composite scaffolds created with extrinsic toughening mechanisms are showing potential for both high strength and mechanical reliability. Future research should include improved designs that provide strong scaffolds with microstructures conducive to bone ingrowth, and evaluation of these scaffolds in large animal models for eventual translation into clinical applications.

Bone formation controlled by biologically relevant inorganic ions: role and controlled delivery from phosphate-based glasses

The role of metal ions in the body and particularly in the formation, regulation and maintenance of bone is only just starting to be unravelled. The role of some ions, such as zinc, is more clearly understood due to its central importance in proteins. However, a whole spectrum of other ions is known to affect bone formation but the exact mechanism is unclear as the effects can be complex, multifactorial and also subtle. Furthermore, a significant number of studies utilise single doses in cell culture medium, whereas the continual, sustained release of an ion may initiate and mediate a completely different response. We have reviewed the role of the most significant ions that are known to play a role in bone formation, namely calcium, zinc, strontium, magnesium, boron, titanium and also phosphate anions as well as copper and its role in angiogenesis, an important process interlinked with osteogenesis. This review will also examine how delivery systems may offer an alternative way of providing sustained release of these ions which may effect and potentiate a more appropriate and rapid tissue response.

Copper-releasing, boron-containing bioactive glass-based scaffolds coated with alginate for bone tissue engineering

The aim of this study was to synthesize and characterize new boron-containing bioactive glass-based scaffolds coated with alginate cross-linked with copper ions. A recently developed bioactive glass powder with nominal composition (wt.%) 65 SiO2, 15 CaO, 18.4 Na2O, 0.1 MgO and 1.5 B2O3 was fabricated as porous scaffolds by the foam replica method. Scaffolds were alginate coated by dipping them in alginate solution. Scanning electron microscopy investigations indicated that the alginate effectively attached on the surface of the three-dimensional scaffolds leading to a homogeneous coating. It was confirmed that the scaffold structure remained amorphous after the sintering process and that the alginate coating improved the scaffold bioactivity and mechanical properties. Copper release studies showed that the alginate-coated scaffolds allowed controlled release of copper ions. The novel copper-releasing composite scaffolds represent promising candidates for bone regeneration.

Bioactive glass scaffolds for bone tissue engineering: state of the art and future perspectives

The repair and regeneration of large bone defects resulting from disease or trauma remains a significant clinical challenge. Bioactive glass has appealing characteristics as a scaffold material for bone tissue engineering, but the application of glass scaffolds for the repair of load-bearing bone defects is often limited by their low mechanical strength and fracture toughness. This paper provides an overview of recent developments in the fabrication and mechanical properties of bioactive glass scaffolds. The review reveals the fact that mechanical strength is not a real limiting factor in the use of bioactive glass scaffolds for bone repair, an observation not often recognized by most researchers and clinicians. Scaffolds with compressive strengths comparable to those of trabecular and cortical bones have been produced by a variety of methods. The current limitations of bioactive glass scaffolds include their low fracture toughness (low resistance to fracture) and limited mechanical reliability, which have so far received little attention. Future research directions should include the development of strong and tough bioactive glass scaffolds, and their evaluation in unloaded and load-bearing bone defects in animal models.

Hydrogels in spinal cord injury repair strategies

Nowadays there are at present no efficient therapies for spinal cord injury (SCI), and new approaches have to be proposed. Recently, a new regenerative medicine strategy has been suggested using smart biomaterials able to carry and deliver cells and/or drugs in the damaged spinal cord. Among the wide field of emerging materials, research has been focused on hydrogels, three-dimensional polymeric networks able to swell and absorb a large amount of water. The present paper intends to give an overview of a wide range of natural, synthetic, and composite hydrogels with particular efforts for the ones studied in the last five years. Here, different hydrogel applications are underlined, together with their different nature, in order to have a clearer view of what is happening in one of the most sparkling fields of regenerative medicine.

Bioactive composites for bone tissue engineering

One of the major challenges for bone tissue engineering is the production of a suitable scaffold material. In this review the currently available composite material options are considered and the methods of production and assessing the scaffolds are also discussed. The production routes range from the use of porogens to produce the porosity through to controlled deposition methods. The testing regimes include mechanical testing of the produced materials through to in vivo testing of the scaffolds. While the ideal scaffold material has not yet been produced, progress is being made.

Bioactive glass-based scaffolds for bone tissue engineering

Originally developed to fill and restore bone defects, bioactive glasses are currently also being intensively investigated for bone tissue engineering applications. In this chapter, we review and discuss current knowledge on porous bone tissue engineering scaffolds made from bioactive silicate glasses. A brief historical review and the fundamental requirements in the field of bone tissue engineering scaffolds will be presented, followed by a detailed overview of recent developments in bioactive glass-based scaffolds. In addition, the effects of ionic dissolution products of bioactive glasses on osteogenesis and angiogenic properties of scaffolds are briefly addressed. Finally, promising areas of future research and requirements for the advancement of the field are highlighted and discussed.

Bioactive Glass and Glass-Ceramic Scaffolds for Bone Tissue Engineering

Traditionally, bioactive glasses have been used to fill and restore bone defects. More recently, this category of biomaterials has become an emerging research field for bone tissue engineering applications. Here, we review and discuss current knowledge on porous bone tissue engineering scaffolds on the basis of melt-derived bioactive silicate glass compositions and relevant composite structures. Starting with an excerpt on the history of bioactive glasses, as well as on fundamental requirements for bone tissue engineering scaffolds, a detailed overview on recent developments of bioactive glass and glass-ceramic scaffolds will be given, including a summary of common fabrication methods and a discussion on the microstructural-mechanical properties of scaffolds in relation to human bone (structure-property and structure-function relationship). In addition, ion release effects of bioactive glasses concerning osteogenic and angiogenic responses are addressed. Finally, areas of future research are highlighted in this review.