Characterization of a hybrid bone substitute composed of polylactic acid tetrapod chips and hydroxyapatite powder

Poly(L-lactic acid) scaffold with oriented micro-valley surface and superior properties fabricated by solid-state drawing for blood-contact biomaterials

Most biomaterials composed of biodegradable polymers will contact either accidentally or consistently with blood and this commonly requires both good  mechanical strength and blood compatibility. Despite this demand, current processing methods still make it difficult and complex to simultaneously improve the two properties. To overcome present limitations, the aim of this work is to develop a solid-state drawing which is a novel method for blood-contact biomaterials that can simultaneously improve the two essential factors of mechanical strength and blood compatibility, as well as induce a micro-patterned surface. Solid-state drawn (SSD) poly(L-lactic acid) (PLLA) film significantly maximally increased tensile strength and elastic modulus about ninefold and sixfold, respectively, compared to undrawn film. Furthermore, it was determined that SSD-PLLA film had highly developed molecular orientation, higher crystallinity and surface hydrophobicity. Additionally, the SSD method could greatly reduce roughness of the surface and induce the formation of aligned valleys, forming microstructures on the film surface. The topographical cue delayed hydrolytic degradation and prevented damage on the surface by NaOH of alkali compounds are compared with undrawn film. In energy-dispersive x-ray spectroscopy analysis, the surface of SSD film treated by NaOH was not detected on any ions whereas undrawn film held foreign ions on surface defects. The hemolysis rate of SSD film was considerably decreased with an increase of draw ratio up to 0.2% maximally and SSD film has shown greatly lower platelet adhesion compared to undrawn film in blood-compatibility analysis. Interestingly, one-directional alignment of micro-valley structure on SSD film could promote initial adhesion of human umbilical vein endothelial cells (HUVEC) compared with undrawn film and guide the direction of HUVEC. In conclusion, the newly designed SSD method has shown potential for developing blood-contact biomaterials simply due to great mechanical properties, blood compatibility and an aligned micro-patterned surface.

Covalently cross-linked hydroxyapatite–citric acid–based biomimetic polymeric composites for bone applications

Composite materials based on bioceramics and polymers offer excellent opportunities in the quest for developing optimal bone grafts for bone tissue engineering. Herein, we have functionalized nano hydroxyapatite with citric acid and subsequently cross-linked with poly(propylene fumarate) and poly(ethylene glycol) to afford a composite with better interfacial bonding properties. This study involved two biomimetic composites, 3CP-VP and 5CP-VP, prepared by varying the concentration of hydroxyapatite. Uniform homogenous distribution of hydroxyapatite was identified through Raman spectral imaging in both the composite matrices. The compressive moduli of the biomimetic composites after 4-week immersion in phosphate-buffered saline ranged between 100 and 300 MPa, which falls well within the accepted values reported for human trabecular bone. Moreover, biodegradation studies revealed only an average weight loss of 10%–17% during the 7-week time period. Furthermore, apatite mineralization was evaluated using scanning electron microscopy and energy dispersive X-ray analysis, and contact angle measurements revealed hydrophobic surfaces with preferential adsorption to albumin. More importantly, blood compatibility studies demonstrated no significant hemolysis and no visible red blood cell aggregation, while cytotoxicity evaluation via direct contact, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, and live–dead assays on human osteoblast sarcoma cell line exhibited good biocompatibility with negligible cytotoxicity. In addition, in vitro drug release studies with gentamycin-loaded composites demonstrated a controlled and sustained release profile with about 35% of drug released over a period of 2 weeks. These findings show that these composites could be developed into stand-alone bone substitutes for bone tissue engineering coupled with drug delivery applications.