| Schedule of revenue recognition | 
    |  |  | Three
    Months Ended June 30, |  |  
    |  |  | 2020 |  |  | 2019 |  |  
    | Products: |  |  |  |  |  |  |  
    | Disposable
    products: |  |  |  |  |  |  |  |  |  
    | Functional
    neurosurgery |  | $ | 1,049,015 |  |  | $ | 1,690,122 |  |  
    | Biologics
    and drug delivery |  |  | 406,955 |  |  |  | 244,949 |  |  
    | Therapy |  |  | 21,300 |  |  |  | 17,830 |  |  
    | Capital
    equipment |  |  | 115,800 |  |  |  | 241,293 |  |  
    | Total
    product revenue |  |  | 1,593,070 |  |  |  | 2,194,194 |  |  
    | Services: |  |  |  |  |  |  |  |  |  
    | Capital
    equipment and other |  |  | 123,998 |  |  |  | 243,954 |  |  
    | Biologics
    and drug delivery |  |  | 760,714 |  |  |  | 168,250 |  |  
    | Total
    service revenue |  |  | 884,712 |  |  |  | 412,204 |  |  
    | Total
    revenue |  | $ | 2,477,782 |  |  | $ | 2,606,398 |  |    
    |  |  | Six Months Ended June 30, |  |  
    |  |  | 2020 |  |  | 2019 |  |  
    | Products: |  |  |  |  |  |  |  |  |  
    | Disposable products: |  |  |  |  |  |  |  |  |  
    | Functional neurosurgery |  | $ | 2,733,424 |  |  | $ | 3,294,767 |  |  
    | Biologics and drug delivery |  |  | 580,330 |  |  |  | 529,859 |  |  
    | Therapy |  |  | 78,800 |  |  |  | 17,830 |  |  
    | Capital equipment |  |  | 303,901 |  |  |  | 515,692 |  |  
    | Total product revenue |  |  | 3,696,455 |  |  |  | 4,358,148 |  |  
    | Services: |  |  |  |  |  |  |  |  |  
    | Capital equipment and other |  |  | 280,493 |  |  |  | 455,156 |  |  
    | Biologics and drug delivery |  |  | 1,616,428 |  |  |  | 265,611 |  |  
    | Total service revenue |  |  | 1,896,121 |  |  |  | 720,767 |  |  
    | Total revenue |  | $ | 5,593,376 |  |  | $ | 5,078,915 |  |  |