Hydrogels provide a solution-mimicking environment for the interaction with living systems that make them desirable for various biomedical and technological applications. Because relevant biological processes in living tissues occur at the biomolecular scale, hydrogel nanopatterning can be leveraged to attain novel material properties and functionalities. However, the fabrication of high aspect ratio (HAR) nanostructures in hydrogels capable of self-standing in aqueous environments, with fine control of the size and shape distribution, remains challenging. Here, we report the synthesis of nanostructures with a HAR in bacterial cellulose (BC) hydrogel via directed plasma nanosynthesis using argon ions. The nanostructures in BC are reproducible, stable to sterilization, and liquid immersion. Using in-situ surface characterization and semiempirical modeling, we discovered that pattern formation was linked to the formation of graphitelike clusters composed of a mixture of C-C and C=C bonds. Moreover, our model predicts that reactive species at the onset of the argon irradiation accelerate the bond breaking of weak bonds, contributing to the formation of an amorphous carbon layer and nanopattern growth.

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Stress shielding and osseointegration are two main challenges in bone regeneration, which have been targeted successfully by chemical and physical surface modification methods. Direct irradiation synthesis (DIS) is an energetic ion irradiation method that generates self‐organized nanopatterns conformal to the surface of materials with complex geometries (e.g., pores on a material surface). This work exposes porous titanium samples to energetic argon ions generating nanopatterning between and inside pores. The unique porous architected titanium (Ti) structure is achieved by mixing Ti powder with given amounts of spacer NaCl particles (vol % equal to 30%, 40%, 50%, 60%, and 70%), compacted and sintered, and combined with DIS to generate a porous Ti with bone‐like mechanical properties and hierarchical topography to enhance Ti osseointegration. The porosity percentages range between 25% and 30% using 30 vol % NaCl space‐holder (SH) volume percentages to porosity rates of 63%–68% with SH volume of 70 vol % NaCl. Stable and reproducible nanopatterning on the flat surface between pores, inside pits, and along the internal pore walls are achieved, for the first time on any porous biomaterial. Nanoscale features were observed in the form of nanowalls and nanopeaks of lengths between 100 and 500 nm, thicknesses of 35‐nm and heights between 100 and 200 nm on average. Bulk mechanical properties that mimic bone‐like structures were observed along with increased wettability (by reducing contact values). Nano features were cell biocompatible and enhanced in vitro pre‐osteoblast differentiation and mineralization. Higher alkaline phosphatase levels and increased calcium deposits were observed on irradiated 50 vol % NaCl samples at 7 and 14 days. After 24 h, nanopatterned porous samples decreased the number of attached macrophages and the formation of foreign body giant cells, confirming nanoscale tunability of M1–M2 immuno‐activation with enhanced osseointegration.

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