Mechanical characterization of pore-graded bioactive glass scaffolds produced by robocasting

Since the discovery of 45S5 Bioglass® by Larry Hench, bioactive glasses have been widely studied as bone substitute materials and, in more recent years, have also shown great promise for producing three-dimensional scaffolds. The development of additive manufacturing techniques and their application in bone tissue engineering allows the design and fabrication of complex structures with controlled porosity. However, achieving strong and mechanically-reliable bioactive glass scaffolds is still a great challenge. Furthermore, there is a relative paucity of studies reporting an exhaustive assessment of other mechanical properties than compressive strength of glass-derived scaffolds. This research work aimed at determining key mechanical properties of silicate SiO2-Na2O-K2OMgO-CaO-P2O5 glass scaffolds fabricated by robocasting and exhibiting a porosity gradient. When tested in compression, these scaffolds had a strength of 6 MPa, a Young’s modulus around 340 MPa, a fracture energy of 93 kJ/m3 and a Weibull modulus of 3, which provides a quantification of the scaffold reliability and reproducibility. Robocasting was a suitable manufacturing method to obtain structures with favorable porosity and mechanical properties comparable to those of the human cancellous bone, which is fundamental regarding osteointegration of bone implants.

Bioactive glass-based materials with hierarchical porosity for medical applications: Review of recent advances

Bioactive glasses have been traditionally used in the clinical practice to fill and restore osseous defects due to their unique ability to bond to host bone and stimulate new bone growth. In the last decade, a new set of bioactive glasses characterized by a highly ordered mesoporous texture has been developed and studied as a smart platform for the controlled release of biomolecules, in situ therapy and regenerative applications. This review points out the great potential carried by hierarchical bioactive glass scaffolds that exhibit pore scales from the meso- to the macro-range, and their impact in the broad field of tissue engineering, including the emerging applications in contact with soft tissues and diagnostics. Recent advances in the preparation methods of these multiscale constructs (e.g. mono- or multi-phase scaffolds, fibrous meshes, coated systems, porous nanospheres, and composites) are examined, along with their strengths and weaknesses. A bright future is expected for hierarchical systems based on biocompatible mesoporous materials as they can provide a unique set of functionalities, including enhanced bioactivity, local release of ions and drugs to elicit specific therapeutic effects (improved osteogenesis and angiogenesis, antibacterial properties), and implant/drug tracking, which were unthinkable when research on bioactive glasses began.

STATEMENT OF SIGNIFICANCE

The advent of mesoporous bioactive glasses led to the birth of a new class of multifunctional biomaterials that have been proposed as smart platforms for local drug release and bone regeneration. Furthermore, mesoporous materials have been recently employed in the development of hierarchical macro-mesoporous scaffolds, composites and implantable systems. This reviews summarizes the latest applications of these multiscale biomaterials in tissue engineering, including the emerging applications in contact with soft tissues and diagnostics. The preparation methods, current uses and potential of these constructs and systems are examined and critically discussed to provide a useful, up-to-date contribution to the scientists working in the field.

Bioceramics in ophthalmology

The benefits of ceramics in biomedical applications have been universally appreciated as they exhibit an extraordinarily broad set of physico-chemical, mechanical and biological properties which can be properly tailored by acting on their composition, porosity and surface texture to increase their versatility and suitability for targeted healthcare applications. Bioceramics have traditionally been used for the repair of hard tissues, such as bone and teeth, mainly due to their suitable strength for load-bearing applications, wear resistance (especially alumina, zirconia and composites thereof) and, in some cases, bone-bonding ability (calcium orthophosphates and bioactive glasses). Bioceramics have been also applied in other medical areas, like ophthalmic surgery; although their use in such a context has been scientifically documented since the late 1700s, the potential and importance of ceramic ocular implants still seem to be underestimated and an exhaustive, critical assessment is currently lacking in the relevant literature. The present review aims to fill this gap by giving a comprehensive picture of the ceramic-based materials and implants that are currently used in ophthalmology and pointing out the strengths and weaknesses of the existing devices. A prospect for future research is also provided, highlighting the potential of new, smart bioceramics able to carry specific added values which could have a significant impact on the treatment of ocular diseases.

Simultaneous electrospinning and electrospraying: a straightforward approach for fabricating hierarchically structured composite membranes

We present here for the first time a simple method for micropatterning nonwoven composite membranes. The approach is based on the simultaneous electrospraying of microparticles and electrospinning of nanofibers from different polymer solution feeds (polyethylene glycol and poly(D,L-lactide)) on a common support. The mechanism of self-organization between fibers and particles into hierarchical honeycomb-like structures, as well as the evolution of the later as a function of the thickness of the composite, is investigated. We demonstrate that aggregates of particles, leading to a nonuniform distribution of the electrostatic field near the collector, are necessary to form the self-organized composite. Furthermore, it is shown that the specific dimensions of the generated patterns can be controlled by tuning the flow rate of electrospraying. The obtained composite mat exhibits a multilevel porous structure, with pore sizes ranging from few up to several hundreds of micrometers. Finally, it is shown that the microparticles can be selectively leached, allowing the production of a monocomponent membrane and retaining the hierarchical organization of the nanofibers suitable for biomedical and filtration applications.

Influence of surface treatment and biomimetic hydroxyapatite coating on the mechanical properties of hydroxyapatite/poly(L-lactic acid) fibers

Poly(L-lactic acid) (PLLA) micro-fibers have been coated with hydroxyapatite (HA) using a quick biomimetic method to form a precursor for bone repair composites. To increase the coating content within a coating time as short as 1–2.5 h, PLLA fibers have been treated by soaking in NaOH or NaOCl solutions at mild conditions. Although different surface hydrolysis and coating methods have been used to prepare bioceramic/polymer composites, it is for the first time that the influences of the surface treatment and HA coating process on the mechanical properties of the polymer and HA/polymer composite fibers were investigated systemically.

Optimization of composition, structure and mechanical strength of bioactive 3-D glass-ceramic scaffolds for bone substitution

Fabrication of 3-D highly porous, bioactive, and mechanically competent scaffolds represents a significant challenge of bone tissue engineering. In this work, Bioglass®-derived glass-ceramic scaffolds actually fulfilling this complex set of requirements were successfully produced through the sponge replication method. Scaffold processing parameters and sintering treatment were carefully designed in order to obtain final porous bodies with pore content (porosity above 70 %vol), trabecular architecture and mechanical properties (compressive strength up to 3 MPa) analogous to those of the cancellous bone. Influence of the Bioglass® particles size on the structural and mechanical features of the sintered scaffolds was considered and discussed. Relationship between porosity and mechanical strength was investigated and modeled. Three-dimensional architecture, porosity, mechanical strength and in vitro bioactivity of the optimized Bioglass®-derived scaffolds were also compared to those of CEL2-based glass-ceramic scaffolds (CEL2 is an experimental bioactive glass originally developed by the authors at Politecnico di Torino) fabricated by the same processing technique, in an attempt at understanding the role of different bioactive glass composition on the major features of scaffolds prepared by the same method.

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.

Emerging techniques in stratified designs and continuous gradients for tissue engineering of interfaces

Interfacial tissue engineering is an emerging branch of regenerative medicine, where engineers are faced with developing methods for the repair of one or many functional tissue systems simultaneously. Early and recent solutions for complex tissue formation have utilized stratified designs, where scaffold formulations are segregated into two or more layers, with discrete changes in physical or chemical properties, mimicking a corresponding number of interfacing tissue types. This method has brought forth promising results, along with a myriad of regenerative techniques. The latest designs, however, are employing "continuous gradients" in properties, where there is no discrete segregation between scaffold layers. This review compares the methods and applications of recent stratified approaches to emerging continuously graded methods.