Accelerated de novo formation of bone is a highly desirable aim of implants targeting musculoskeletal injuries. To date, this has primarily been addressed by biologic factors. However, there is an unmet need for robust, highly reproducible yet economic alternative strategies that strongly induce an osteogenic cell response. Here, we present a surface engineering method of translating bioactive nanopatterns from polymeric in vitro studies to clinically relevant material for orthopedics: three-dimensional, large area metal. We use a titanium-based sol–gel whereby metal implants can be engineered to induce osteoinduction both in vitro and in vivo. We show that controlled disordered nanotopographies presented as pillars with 15–25 nm height and 100 nm diameter on titanium dioxide effectively induce osteogenesis when seeded with STRO-1-enriched human skeletal stem cells in vivo subcutaneous implantation in mice. After 28 days, samples were retrieved, which showed a 20-fold increase in osteogenic gene induction of nanopatterned substrates, indicating that the sol–gel nanopatterning method offers a promising route for translation to future clinical orthopedic implants.

No abstract

Polydimethylsiloxane (PDMS) is used by many for nanoimprint applications due to its affordability, ease of preparation, mechanical flexibility, compatibility with imprint resists and transparency to UV light. However PDMS is notoriously flexible, tacky and permeable to air. Here fluorinated ethylene-propylene (FEP) is considered as a viable and versatile alternative material for nanoimprint stamps. FEP possesses many of the desirable nanoimprint attributes associated with PDMS but crucially also features a range of complementary characteristics, including an order of magnitude more mechanical strength allowing it to handle higher loads than PDMS, an intrinsically non-stick surface and is compatible with oxygen sensitive resists. Unlike elastomeric polymers, FEP is glassy so patterning may be realised via hot embossing. Not only is this a facile and rapid means of physical structuring but it also facilitates combinatorial patterning, providing a versatility beyond that of traditional casting materials. Due to the intrinsically slow creep of FEP both micro- and nanopatterning are successfully performed sequentially. Feature sizes from 45 nm were successfully realised via the hot-embossing method. To further demonstrate the potential of the material, a modified computer numerical control machine is used. It is capable of photo-, nanoimprint- and laser lithography in conjunction with patterned FEP foils. The tool is used to perform pattern transfer into a developmental nanoimprint resist from Micro Resist Technology, mr-NIL210 XP, and Nano SU-8 3005 negative tone photo resist from MicroChem. Ultimately three-tier lithography is performed in unison and advantageous step-and-repeat performance is achieved with fabricated FEP imprint stamps as they demould more compliantly and resist pressure and contamination better than PDMS.

In order to directly imprint features into a hard metal such as titanium, an imprinting stamp composed of material of greater hardness is required. Diamond is the hardest known material, so is an obvious choice for the production of direct‐imprint stamps. Diamond also benefits from a low surface energy, chemical inertness, high resistance to wear and is easily cleaned of contaminants, further favouring it as a stamp material of choice. Chemical vapour deposited ultra‐nanocrystalline diamond (UNCD) provides similar mechanical properties to bulk single crystal diamond and can be deposited across large surface areas. This work examines the use of UNCD as a stamp medium for the transfer of nanoscale features into commercially pure titanium (cpTi) substrates. Development of an efficient and viable method for nanopatterning large, non‐planar cpTi surfaces is highly desirable to control cell adhesion on the surface of bio‐implants. The fabrication of UNCD nanoimprint stamps is detailed and the ability of UNCD to imprint cpTi is illustrated. A square‐ordered matrix of 200 nm diameter pillars over a quarter mm square area are shown to be imprinted with the depth quantified against load (kg). The limitations of the technology are also discussed.