Structural, mechanical and swelling characteristics of 3D scaffolds from chitosan-agarose blends

This study aimed to explore the correlation between mechanical and structural properties of chitosan-agarose blend (Ch-Agrs) scaffolds. Porosity of Ch-Agrs scaffolds was constant at 93%, whilst pore sizes varied between 150 and 550 μm. Pore sizes of the blend scaffolds (150 - 300 μm) were significantly smaller than for either agarose or chitosan scaffolds alone (ca. 500 μm). Ch50-Agrs50 blend scaffold showed the highest compressive modulus and strength values (4.5 ± 0.4 and 0.35 ± 0.03 MPa) due to reduction in the pore size. The presence of agarose improved the stability of the blends in aqueous media. The increase in compressive properties and residual weight after the TGA test, combined with the reduction in the swelling percentage of the blend scaffolds suggested an interaction between chitosan and agarose via hydrogen bonding which was confirmed using FTIR analysis. All wet blend scaffolds exhibited instant recovery after full compression. This study shows the potential of Ch-Agrs scaffolds for repairing soft tissue

Phosphate glass fibres and their composites

An overview of the research conducted utilising phosphate glass fibres (PGFs), their manufacturing processes and utilisation potential for biomedical applications is presented in this chapter. Phosphate glasses of varying compositions in the form of fibrous structures alone and as fibrous reinforcements within composites are discussed. This chapter also highlights the methodologies used for the manufacture of these resorbable glass fibres and their composites. The advantages of using bioresorbable fibres in terms of their mechanical, dissolution, ion release, and in vitro and in vivo biocompatibility properties for the replacement, augmentation, guidance and growth of both hard and soft tissue in repair applications are also presented

Wet and dry flexural high cycle fatigue behaviour of fully bioresorbable glass fibre composites: in-situ polymerisation versus laminate stacking

Fully bioresorbable phosphate based glass fibre reinforced polycaprolactone (PCL/PGF) composites are potentially excellent candidates to address current issues experienced with use of metal implants for hard tissue repair, such as stress shielding effects. It is therefore essential to investigate these materials under representative loading cases and to understand their fatigue behaviour (wet and dry) in order to predict their lifetime in service and their likely mechanisms of failure. This paper investigated the dry and wet flexural fatigue behaviour of PCL/PGF composites with 35% and 50% fibre volume fraction (Vf). Significantly longer flexural fatigue life (p < 0.0001) and superior fatigue damage resistance were observed for In-situ Polymerised (ISP) composites as compared to the Laminate Stacking (LS) composites in both dry and wet conditions, indicating that the ISP promoted considerably stronger interfacial bonding than the LS. Immersion in fluid (wet) during the flexural fatigue tests resulted in significant reduction (p < 0.0001) in the composites fatigue life, earlier onset of fatigue damage and faster damage propagation. Regardless of testing conditions, increasing fibre content led to shorter fatigue life for the PCL/PGF composites. Meanwhile, immersion in degradation media caused softening of both LS and ISP composites during the fatigue tests, which led to a more ductile failure mode. Among all the composites that were investigated, ISP35 (35% Vf) composites maintained at least 50% of their initial stiffness at the end of fatigue tests in both conditions, which is comparable to the flexural properties of human cortical bones. Consequently, ISP composites with 35% Vf maintained at least 50% of its flexural properties after the fatigue failure, which the mechanical retentions were well matched with the properties of human cortical bones

Flexible and transparent films produced from cellulose nanowhisker reinforced agarose

Transparent and flexible nanocomposite films with a range of Agarose to Cellulose Nano-Whisker (CNW) ratios were produced using never-dried CNWs. The incorporation of never-dried CNWs within Agarose played an important role in the surface roughness (Ra 7–15 nm) and light transparency of the films (from 84 to 90%). Surface induced crystallisation of Agarose by CNWs was also found with increasing percentage of crystallinity (up to 79%) for the nanocomposite films, where CNW acted as nucleating sites. The enhanced tensile strength (ca. 30% increase) and modulus (ca. 90% increase) properties of the nanocomposite films compared to the control Agarose film indicated the effectiveness of the nanowhiskers incorporation. The storage modulus of the nanocomposite films increased also to be tripled Agarose alone as the CNWs content reached 43%. The swelling kinetics of the nanocomposites revealed that addition of CNWs reduced the long-term swelling capacity and swelling rate of the nanocomposite

Developing alkaline titanate surfaces for medical applications

Improving the surface of medical implants by plasma spraying of a hydroxyapatite coating can be of critical importance to their longevity and the patient’s convalescence. However, residual stresses, cracking, undesired crystallisation and delamination of the coating compromise the implants lifetime. A promising alternative surface application is an alkali-chemical treatment to generate bioactive surfaces, such as sodium and calcium titanate and their derivatives. Such surfaces obviate the need for high temperatures and resulting micro-crack formation and potentially improve the bioactive and bone integration properties through their nanoporous structures. Also, metallic ions such as silver, gallium and copper can be substituted into the titanate structure with the potential to reduce or eliminate the infections. This review examines the formation and mechanisms of bioactive/antibacterial alkaline titanate surfaces, their successes and limitations, and explores the future development of implant interfaces via multifunctional titanate surfaces on Ti-based alloys and on alternative substrate materials

Performance of multiphase scaffolds for bone repair based on two-photon polymerized poly(d,l-lactide-co-ɛ-caprolactone), recombinamers hydrogel and nano-HA

Multiphase hybrids were fabricated from poly(d,l-lactide-co-ɛ-caprolactone) (PLCL) copolymer scaffolds impregnated with silk-elastin-like recombinamers (SELRs) hydrogel containing 2 wt% hydroxyapatite nanoparticles (nHA). The PLCL scaffolds, triply-periodic minimal surface geometry, were manufactured using two-photon stereolithography. In vitro degradation studies were conducted on PLCL scaffolds in inflamed tissue mimic media (pH ~ 4.5–6.5) or phosphate buffered saline (PBS) at 37 °C. Compression test revealed instant shape recovery of PLCL scaffolds after compression to 70% strain, ideal for arthroscopic delivery. Degradation of these scaffolds was accelerated in acidic media, where mass loss and compressive properties at day 56 were about 2–6 times lower than the scaffolds degraded in PBS. No significant difference was seen in the compressive properties between PLCL scaffolds and the hybrids due to the order of magnitude difference between the hydrogels and the PLCL scaffolds. Moreover, degradation properties of the hybrids did not significantly change by inclusion of SELR+/−nHA nanocomposite hydrogels. The hybrids lost approximately 40% and 84% of their initial weight and mechanical properties, respectively after 112 days of degradation. Cytotoxicity assessment revealed no cytotoxic effects of PLCL or PLCL-SELR+/−2%nHA scaffolds on bone marrow-derived human Mesenchymal Stem Cells. These findings highlight the potential of these hybrid constructs for bone and cartilage repair

Computational mechanical characterization of geometrically transformed Schwarz P lattice tissue scaffolds fabricated via two photon polymerization (2PP)

Schwarz P unit cell-based tissue scaffolds comprised of poly(D,L-lactide-co-caprolactone)(PLCL) fabricated via the additive manufacturing technique, two-photon polymerisation (2PP) were found to undergo geometrical transformations from the original input design. A Schwarz P unit cell surface geometry CAD model was reconstructed to take into account the geometrical transformations through CAD modeling techniques using measurements obtained from an image-based averaging technique before its implementation for micromechanical analysis. Effective modulus results obtained from computational mechanical characterization via micromechanical analysis of the reconstructed unit cell assigned with the same material model making up the fabricated scaffolds demonstrated excellent agreement with a small margin of error at 6.94% from the experimental mean modulus (0.69 0.29MPa). The possible sources for the occurrence of geometrical transformations are discussed in this paper. The interrelationships between different dimensional parameters making up the Schwarz P architecture and resulting effective modulus are also assessed and discussed. With the ability to accommodate the geometrical transformations, maintain efficiency in terms of time and computational resources, micromechanical analysis has the potential to be implemented in tissue scaffolds with a periodic microstructure as well as other structures outside the field of tissue engineering in general

Glass microparticle‐ versus microsphere‐filled experimental dental adhesives

This study aimed to formulate antibacterial dental adhesives. Phosphate‐substituted methacrylate adhesives were modified with 0–20 wt % copper‐doped glass microparticles. Two shapes of microparticles were used: regular shaped (microspheres) and irregular shaped (microparticles). The morphology/composition, roughness, monomer conversion (DC%), thermogravimetric analysis, and antibacterial action against S. mutans and P. aeruginosa and ion release were investigated. The results showed that microspheres produced adhesives with a relatively smoother surface than microparticles did. The DC% of adhesives increased with increasing glass filler content. Filled adhesives showed polymer decomposition at ~315 °C and glass melting at 600–1000 °C. The weight loss percent of adhesives decreased with increasing weight percent of fillers. Glass microparticles at 0–20 wt % significantly increased the antibacterial action of adhesives against both bacteria. Glass microspheres at 0–5 wt % significantly increased the antibacterial action of adhesives against both bacteria. Only 20 wt % microparticle‐filled adhesive showed an inhibition zone similar to tobramycin (positive control). Microparticle‐filled adhesives (with >5 wt % filler) significantly reduced S. mutans more than their microsphere counterparts. Microsphere‐filled adhesives (with ≤5 wt % filler) significantly reduced P. aeruginosa more than their microparticle counterparts. Microsphere‐filled adhesives showed higher Cu release than their microparticle counterparts. Accordingly, phosphate‐substituted methacrylate filled with glass could be used as an antibacterial adhesive

Developing highly nanoporous titanate structures via wet chemical conversion of DC magnetron sputtered titanium thin films

© 2020 The Authors Titanate structures have been widely investigated as biomedical component surfaces due to their bioactive, osteoinductive and antibacterial properties. However, these surfaces are limited to Ti and its alloys, due to the nature of the chemical conversion employed. The authors present a new method for generating nanoporous titanate structures on alternative biomaterial surfaces, such as other metals/alloys, ceramics and polymers, to produce bioactive and/or antibacterial properties in a simple yet effective way. Wet chemical (NaOH; 5 M; 60 °C; 24 h) conversion of DC magnetron sputtered Ti surfaces on 316L stainless steel were investigated to explore effects of microstructure on sodium titanate conversion. It was found that the more equiaxed thin films (B/300) generated the thickest titanate structures (ca. 1.6 μm), which disagreed with the proposed hypothesis of columnar structures allowing greater NaOH ingress. All film parameters tested ultimately generated titanate structures, as confirmed via EDX, SEM, XPS, XRD, FTIR and Raman analyses. Additionally, the more columnar structures (NB/NH & B/NH) had a greater quantity of Na (ca. 26 at.%) in the top portion of the films, as confirmed via XPS, however, on average the Na content was consistent across the films (ca. 5–9 at.%). Film adhesion for the more columnar structures (ca. 42 MPa), even on polished substrates, were close to that of the FDA requirement for plasma-sprayed HA coatings (ca. 50 MPa). This study demonstrates the potential of these surfaces to be applied onto a wide variety of material types, even polymeric materials, due to the lower processing temperatures utilised, with the vision to generate bioactive and/or antibacterial properties on a plethora of bioinert materials

Production of High Silicon-Doped Hydroxyapatite Thin Film Coatings via Magnetron Sputtering: Deposition, Characterisation, and In Vitro Biocompatibility

In recent years, it has been found that small weight percent additions of silicon to HA can be used to enhance the initial response between bone tissue and HA. A large amount of research has been concerned with bulk materials, however, only recently has the attention moved to the use of these doped materials as coatings. This paper focusses on the development of a co-RF and pulsed DC magnetron sputtering methodology to produce a high percentage Si containing HA (SiHA) thin films (from1.8 to 13.4 wt. %; one of the highest recorded in the literature to date). As deposited thin films were found to be amorphous, but crystallised at different annealing temperatures employed, dependent on silicon content, which also lowered surface energy profiles destabilising the films. X-ray photoelectron spectroscopy (XPS) was used to explore the structure of silicon within the films which were found to be in a polymeric (SiO2; Q4) state. However, after annealing, the films transformed to a SiO44- Q0, state, indicating that silicon had substituted into the HA lattice at higher concentrations than previously reported. A loss of hydroxyl groups and the maintenance of a single-phase HA crystal structure further provided evidence for silicon substitution. Furthermore, a human osteoblast cell (HOB) model was used to explore the in vitro cellular response. The cells appeared to prefer the HA surfaces compared to SiHA surfaces, which was thought to be due to the higher solubility of SiHA surfaces inhibiting protein mediated cell attachment. The extent of this effect was found to be dependent on film crystallinity and silicon content