Review of bioactive glass: from Hench to hybrids.

45S5 Bioglass-derived glass-ceramic scaffolds for bone tissue engineering.

Unperturbed dimensions of stereoregular polymers.- Reinforcement of rubber by carbon black.- Transformations of phenolic antioxidants and the role of their products in the long-term properties of polyolefins.

Properties of polymers

Small-scale soft continuum robots capable of active steering and navigation in a remotely controllable manner hold great promise in diverse areas, particularly in medical applications. Existing continuum robots, however, are often limited to millimeter or centimeter scales due to miniaturization challenges inherent in conventional actuation mechanisms, such as pulling mechanical wires, inflating pneumatic or hydraulic chambers, or embedding rigid magnets for manipulation. In addition, the friction experienced by the continuum robots during navigation poses another challenge for their applications. Here, we present a submillimeter-scale, self-lubricating soft continuum robot with omnidirectional steering and navigating capabilities based on magnetic actuation, which are enabled by programming ferromagnetic domains in its soft body while growing hydrogel skin on its surface. The robot's body, composed of a homogeneous continuum of a soft polymer matrix with uniformly dispersed ferromagnetic microparticles, can be miniaturized below a few hundreds of micrometers in diameter, and the hydrogel skin reduces the friction by more than 10 times. We demonstrate the capability of navigating through complex and constrained environments, such as a tortuous cerebrovascular phantom with multiple aneurysms. We further demonstrate additional functionalities, such as steerable laser delivery through a functional core incorporated in the robot's body. Given their compact, self-contained actuation and intuitive manipulation, our ferromagnetic soft continuum robots may open avenues to minimally invasive robotic surgery for previously inaccessible lesions, thereby addressing challenges and unmet needs in healthcare.

Ferromagnetic soft continuum robots

During the resorbable-polymer-boom of the 1970s and 1980s, polycaprolactone (PCL) was used in the biomaterials field and a number of drug-delivery devices. Its popularity was soon superseded by faster resorbable polymers which had fewer perceived disadvantages associated with long term degradation (up to 3-4 years) and intracellular resorption pathways; consequently, PCL was almost forgotten for most of two decades. Recently, a resurgence of interest has propelled PCL back into the biomaterials-arena. The superior rheological and viscoelastic properties over many of its aliphatic polyester counterparts renders PCL easy to manufacture and manipulate into a large range of implants and devices. Coupled with relatively inexpensive production routes and FDA approval, this provides a promising platform for the production of longer-term degradable implants which may be manipulated physically, chemically and biologically to possess tailorable degradation kinetics to suit a specific anatomical site. This review will discuss the application of PCL as a biomaterial over the last two decades focusing on the advantages which have propagated its return into the spotlight with a particular focus on medical devices, drug delivery and tissue engineering.

The return of a forgotten polymer : Polycaprolactone in the 21st century

Glasses having a chemical composition between 1Na2O–2CaO–3SiO2 (1N2C3S) and 1.5Na2O–1.5CaO–3SiO2, containing 0, 2, 4 and 6 wt% P2O5, were crystallized to several volume percent through thermal treatments in the range 550–700 °C. These glasses and glass-ceramics were exposed to a simulated body fluid solution (SBF-K9 which is close to human plasma) for several time periods. Fourier transform infrared spectroscopy (FTIR) was used to determine the rate of hydroxy carbonate apatite (HCA) formation. Crystallization decreased the kinetics but did not inhibit the development of a HCA layer, even in fully crystallized ceramics. The onset time for crystallization of HCA varied from 8 h for a glass containing 6% P2O5 to 35 h for a fully crystallized 1.07Na2O–2CaO–3SiO2 ceramic. The HCA layer formation of these compositions in `in vitro' tests is much faster than in commercial bioactive materials such as synthetic hydroxyapatite ceramic, A/W glass-ceramic, Ceravital and Bioverit, for which the onset time usually takes at least seven days. FTIR and inductive coupled plasma studies confirmed the formation of an apatite layer which indicates bioactivity in the 1N2C3S crystal phase. X-ray diffraction experiments show that the phosphorus ions are kept in solid solution in the crystal phase. An apatite-like compound only appeared when the specimens were submitted to very long additional thermal treatments. The bioactivity of commercial materials is based on the apatite crystal phase, while the high level of bioactivity of this new generation of glass-ceramics is attained due to the combination of two mechanisms acting simultaneously; a non-phosphate bioactive crystal phase (1N2C3S) and the phosphorus ions in solid solution which are easily released from the structure, promoting a faster HCA layer formation similar to 45S5 Bioglass®.

Highly bioactive P2O5–Na2O–CaO–SiO2 glass-ceramics

One of the strategies to improve the mechanical performance of bioactive glasses for load-bearing implant devices has been the development of glass-ceramic materials. The present study aimed to evaluate the effect of a highly bioactive, fully-crystallized glass-ceramic (Biosilicate) of the system P(2)O(5)-Na(2)O-CaO-SiO(2) on various key parameters of in vitro osteogenesis. Surface characterization was carried out by scanning electron microscopy and Fourier transform infrared spectroscopy. Osteogenic cells were obtained by enzymatic digestion of newborn rat calvarial bone and by growing on Biosilicate discs and on control bioactive glass surfaces (Biosilicate) parent glass and Bioglass(R) 45S5) for periods of up to 17 days. All materials developed an apatite layer in simulated body fluid for 24h. Additionally, as early as 12 h under culture conditions and in the absence of cells, all surfaces developed a layer of silica-gel that was gradually covered by amorphous calcium phosphate deposits, which remained amorphous up to 72 h. During the proliferative phase of osteogenic cultures, the majority of cells exhibited disassembly of the actin cytoskeleton, whereas reassembly of actin stress fibers took place only in areas of cell multilayering by day 5. Although no significant differences were detected in terms of total protein content and alkaline phosphatase activity at days 11 and 17, Biosilicate supported significantly larger areas of calcified matrix at day 17. The results indicate that full crystallization of bioactive glasses in a range of compositions of the system P(2)O(5)-Na(2)O-CaO-SiO(2) may promote enhancement of in vitro bone-like tissue formation in an osteogenic cell culture system.

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In vitro osteogenesis on a highly bioactive glass‐ceramic (Biosilicate®)

In this review we critically analyze 28 theses and dissertations and over 30 scientific papers that tested Biosilicate®, a highly bioactive glass-ceramic, in a number of applications throughout the past 20 years. Biosilicate® presents a combination of positive features for bone tissue regeneration: it is highly bioactive, osteoconductive, osteoinductive, non-cytotoxic, non-genotoxic and has antibacterial properties. In addition, in the monolithic form, it is quite strong and tough. Its in vitro bioactivity is similar to that of the gold standard Bioglass 45S5. Biosilicate® has shown to be a very versatile, multipurpose biomaterial. It can be applied in powder, monolithic and 3D scaffold forms that could be easily machined during surgical procedures. This material has been successfully tested in a number of in vitro, in vivo and clinical studies, and several trials are ongoing. Biosilicate® is indeed a great option for a wide range of tissue engineering applications.

Biosilicate® — A multipurpose, highly bioactive glass-ceramic. In vitro, in vivo and clinical trials

Compositional and microstructural design of highly bioactive P2O5-Na2O-CaO-SiO2 glass-ceramics

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Oscar Peitl

Papers

Highly bioactive P2O5–Na2O–CaO–SiO2 glass-ceramics

In vitro osteogenesis on a highly bioactive glass‐ceramic (Biosilicate®)

Biosilicate® — A multipurpose, highly bioactive glass-ceramic. In vitro, in vivo and clinical trials

Compositional and microstructural design of highly bioactive P2O5-Na2O-CaO-SiO2 glass-ceramics

Gel-derived SiO2–CaO–Na2O–P2O5 bioactive powders: Synthesis and in vitro bioactivity