NOVELTY - A biofuel cell device (100), comprises: substrate (101); anode (102) including catalyst (107) to facilitate conversion of fuel in biological fluid (BF) to a product in an oxidative process that releases electrons captured at the anode, thereby extracting energy from the fuel; cathode (103) placed on substrate adjacent to anode and separated from it by a spacing region (109), where cathode is formed of a material that is electrically conductive and capable of reducing oxygenated substance in BF to a second product in a chemical reduction process, where second product gains electrons.    USE - As biofuel cell device, preferably epidermal biofuel cell device used in biofuel cell system (claimed), which are used in variety of industries, e.g. biomedical, healthcare, fitness/athletics and energy industries such as remote power systems; in wastewater treatment, implantable biomedical devices.    ADVANTAGE - The implementation of the printed biofuel cells can lower the cost of healthcare and alleviate the burden on the healthcare provider. The devices include biofuel cells that provide low-cost, paper-thin power sources that can sustain implantable/body-worn medical devices, such as bionic implants and bioelectronics. The fabrication methods produce the robust, high-power output, and inexpensive biofuel cells capable of processing a wide variety of biofuels. The biofuel cell devices are capable of energy extraction from various biofuels that can include glucose and alcohol (in whole blood), lactate (in perspiration), and uric acid and urea (in urine). Additionally, the biofuel cell devices can also be implemented as remote power systems that can significantly lower the costs involved with energy generation. The biofuel cell devices and systems are especially well-suited to meet the requirements of field-deployable power generation. By using thick-film and roll-to-roll fabrication methodologies, very high power-to-weight ratios are achieved, making the biofuel cells extremely appealing for body-worn applications. Unlike conventional fuel cells which must function at high temperatures to operate efficiently, the present biofuel cells are amenable to operation at ambient temperatures, thus minimizing thermal signatures. Due to its direct-conversion architecture, the biofuel cells are devoid of moving parts, hence underscoring its durability and zero acoustic footprint, which, along with its lack of a heat signature, can help conceal its presence. The biofuel cells are comprised of biocompatible materials and are completely recyclable, unlike conventional fuel cell devices as well as most batteries and photovoltaic systems.    DETAILED DESCRIPTION - A biofuel cell device (d1) (100), comprises: a substrate (101); an anode (102) formed on the substrate of an electrically conductive material, the anode including a catalyst (107) to facilitate the conversion of a fuel substance in a biological fluid to a first product in an oxidative process that releases electrons captured at the anode, thereby extracting energy from the fuel substance; a cathode (103) configured on the substrate adjacent to the anode and separated from the anode by a spacing region (109), the cathode formed of a material that is electrically conductive and capable of reducing an oxygenated substance in the biological fluid to a second product in a chemical reduction process in which the second product gains electrons; and a load (105) configured of at least one electrical circuit element electrically coupled between the anode and the cathode via electrical interconnects (104) to obtain the extracted energy as electrical energy. INDEPENDENT CLAIMS are included for the following:    (1) a biofuel cell device (d2);    (2) a biofuel cell system (S1);    (3) fabricating (m1) a biofuel cell involving: depositing an electrically conductive ink on a substrate to form an anode electrode and a cathode electrode adjacent to and separated from one another, the depositing including printing the ink on a stencil placed over the substrate, the stencil including a patterned region configured in a design of the anode and the cathode to allow transfer of the ink on the substrate, and the stencil inhibiting transfer of the ink in areas outside the patterned region; and curing the electrically conductive ink to produce a biofuel cell device;    (4) an epidermal biofuel cell device (d3);    (5) fabricating (m2) an epidermal biofuel cell device.    DESCRIPTION OF DRAWING(S) - The figure shows a block diagram of biofuel cell device.    Biofuel cell device (100)    Substrate (101)    Anode (102)    Cathode (103)    Electrical interconnects (104)    Load (105)    Catalyst (107)    Spacing region (109)