In the U.S., 30% of adults suffer joint pain, most commonly in the knee, which severely limits mobility and is often attributed to injury of cartilage and underlying bone in the joint. Current treatment methods such as microfracture result in less resilient fibrocartilage with eventual failure; autografting can cause donor site morbidity and poor integration. To overcome drawbacks in treatment, tissue engineers can design cell-instructive biomimetic scaffolds using biocompatible materials as alternate therapies for osteochondral defects. Nanofibrous poly (L-lactic acid) (PLLA) scaffolds of uniform, spherical, interconnected and well-defined pore sizes that are fabricated using a thermally-induced phase separation and sugar porogen template method create an extracellular matrix-like environment which facilitates cell adhesion and proliferation. Herein we report that chondrogenesis and endochondral ossification of rabbit and human bone marrow stromal cells (BMSCs) can be controlled by scaffold pore architecture, particularly pore size. Small-pore scaffolds support enhanced chondrogenic differentiation in vitro and cartilage formation in vivo compared to large-pore scaffolds. Endochondral ossification is prevented in scaffolds with very small pore sizes; pore interconnectivity is critical to promote capillary ingrowth for mature bone formation. These results provide a novel strategy to control tissue regenerative processes by tunable architecture of macroporous nanofibrous scaffolds.

We developed a straightforward, fast, and versatile technique to fabricate mineralized nanofibrous polymer scaffolds for bone regeneration in this work. Nanofibrous poly(l-lactic acid) scaffolds were fabricated using both electrospinning and phase separation techniques. An electrodeposition process was designed to deposit calcium phosphate on the nanofibrous scaffolds. Such scaffolds contain a high quality mineral coating on the fiber surface with tunable surface topography and chemical composition by varying the processing parameters, which can mimic the composition and structure of natural bone extracellular matrix and provide a more biocompatible interface for bone regeneration.

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Hopeite coating on metals by the phosphate chemical conversion (PCC) method has received more attention for its potential biomedical use. It is difficult to get a PCC phosphate coating due to the presence of a passive oxide layer on the surface of titanium. In this research, we report on effects of ultrasonic irradiation (UI) on formation, crystal size, microstructure, and corrosion resistance of the PCC coatings on Ti. It is shown that both coatings formed with and without UI are composed of hopeite (Zn 3 (PO 4 ) 2 •4H 2 O) with similar crystal shape. FE-SEM observation demonstrates that UI can significantly decrease crystal size from 50−100 to 5−20 μm within a duration time of 30−60 min. Short period PCC treatment of 5 min shows that UI can enhance the formation of coating with the increase of nucleation rate. And the nucleation rate with UI of 250 W is significantly higher than that of 50 W. The electrochemical analysis reveals that the corrosion resistance of the coatings can also be improved by ultrasonic irradiation treatment. Human fibroblast cell culture studies indicate that the cells attach and spread well on the surface of PCC coatings, which is indicative of the fact that the coatings have excellent biocompatibility and bioactivity.

Nanocomposite coatings obtained by the controlled addition of inorganic nanoparticles into the treatment baths not only improve the corrosion resistance and mechanical properties, but also enhance the functional properties.

Zinc (Zn) alloys provide a new generation for orthopedic applications due to their essential physiological effects and promising degradation properties. However, excessive release of Zn ions (Zn2+) during degradation and the severe inflammatory microenvironment are not conducive to osseointegration, which is determined by the characteristics of the implant surface. Therefore, it is essential to modulate the release rate of Zn alloys by surface modification technology and endow them with anti‐inflammatory and osteogenic effects. In this study, two kinds of phosphate chemical conversion (PCC) coatings with different compositions and morphological structures are prepared, namely Zn–P (with disk‐like crystals) and Ca–Zn–P (with lamellar crystals). Although all the PCC‐coated Zn implants have low cytotoxicity, Ca–Zn–P show better osteoimmunomodulation effects in several aspects: the induction of the M2‐phenotype macrophage polarization and thus promotion of osteogenesis in vitro; the regulation of the bone immune microenvironment which is conducive to tissue regeneration and osseointegration in vivo; and the release of ions (through PI3K/AKT and Wnt signaling pathways) and the morphological structures (through RhoGTPase signaling pathways) act as possible mechanisms of M2 polarization. The Ca–Zn–P coating can be considered to provide new insights into bone immunomodulation and osseointegration.