Micromachining technology and biomedical engineering

Biological and Mechanical Effects of Micro-Nanostructured Titanium Surface on an Osteoblastic Cell Line In vitro and Osteointegration In vivo

Hybrid micro-nanostructure implant surface was produced on titanium (Ti) surface by acid etching and anodic oxidation to improve the biological and mechanical properties. The biological properties of the micro-nanostructure were investigated by simulated body fluid (SBF) soaking test and MC3T3-E1 cell co-culture experiment. The cell proliferation, spreading, and bone sialoprotein (BSP) gene expression were examined by MTT, SEM, and reverse transcription-polymerase chain reaction (RT-PCR), respectively. In addition, the mechanical properties were evaluated by instrumented nanoindentation test and friction-wear test. Furthermore, the effect of the micro-nanostructure surface on implant osteointegration was examined by in vivo experiment. The results showed that the formation of bone-like apatite was accelerated on the micro-nanostructured Ti surface after immersion in simulated body fluid, and the proliferation, spreading, and BSP gene expression of the MC3T3-E1 cells were also upregulated on the modified surface. The micro-nanostructured Ti surface displayed decreased friction coefficient, stiffness value, and Young's modulus which were much closer to those of the cortical bone, compared to the polished Ti surface. This suggested much better mechanical match to the surrounding bone tissue of the micro-nanostructured Ti surface. Furthermore, the in vivo animal experiment showed that after implantation in the rat femora, the micro-nanostructure surface displayed higher bonding strength between bone tissues and implant; hematoxylin and eosin (H&E) staining suggested that much compact osteoid tissue was observed at the interface of Micro-nano-Ti-bone than polished Ti-bone interface after implantation. Based on these results mentioned above, it was concluded that the improved biological and mechanical properties of the micro-nanostructure endowed Ti surface with good biocompatibility and better osteointegration, implying the enlarged application of the micro-nanostructure surface Ti implants in future.

Microfabricated nanochannel implantable drug delivery devices: trends, limitations and possibilities

This is a review of the application of microfabrication technologies, borrowed from the semiconductor industry, to drug delivery implants incorporating structures in the nanometer dimension. In the futuristic ideal, these systems would involve the implantation of precisely microfabricated drug delivery systems with nanopores, nanochannels and/or nanoreservoirs fabricated from silicon, coupled with electronic sensing and actuator systems, for the precise, timed and/or targeted delivery of drugs. After more than a decade in conceptualisation and experimentation, four systems that have commercial potential are discussed: i) implantable microchips with on-demand microdosage for one or more therapeutic agents under internal control or external control using a wireless link; ii) nanopore pumps, implantable titanium pumps, consisting of a drug reservoir with a nanopore-release membrane, capable of delivering potent small or macromolecules at constant serum levels for sustained periods of time; iii) nanocages, microfabricated nanopore immunoisolation chambers for cellular implants, capable of natural feedback-controlled delivery of proteins and peptides; and iv) nanobuckets, micromachined silicon porous particles with drug-loading capacity and targeting ligands for localised delivery. Each of the systems, along with future trends in microfabrication manufacturing, limitations and possibilities, are discussed.