Note 6 - Common Stock and Convertible Preferred Stock (Details Textual)								1 Months Ended	12 Months Ended
	Jun. 01, 2018 USD ($) $ / shares shares	Apr. 16, 2018 $ / shares shares	Mar. 14, 2018 USD ($) $ / shares shares	Mar. 27, 2017 $ / shares shares	Mar. 08, 2017 $ / shares shares	Aug. 01, 2016 $ / shares shares	May 15, 2015 $ / shares shares	Apr. 30, 2018 shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Nov. 30, 2021 shares	Oct. 31, 2021 shares	Mar. 12, 2018 USD ($)	Feb. 13, 2015 $ / shares shares	Jun. 26, 2014 $ / shares shares
Common Stock, Shares Authorized (in shares)		8,224,000							300,000,000	8,484,000
Common Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares									$ 0.0001	$ 0.001
Common Stock, Voting Rights, Vote Per Share									1
Dividends, Common Stock, Total | $									$ 0
Proceeds from Issuance of Common Stock | $									$ 8,382,826	$ 0
Preferred Stock, Convertible, Conversion Ratio									1
Preferred Stock, Automatic Conversion, Common Stock Price Per Share in Offering (in dollars per share) | $ / shares									$ 10.00
Preferred Stock, Automatic Conversion, Minimum Net Proceeds in Offering | $									$ 37,500,000
Number of Members of the Board Elected by Preferred Stockholders									3
Number of Members of the Board									7
Number of Members of the Board Elected by Common and Preferred Stockholders									2
Preferred Stock, Shares Authorized (in shares)		5,042,000							10,000,000	5,042,000
Preferred Stock, Shares Issued, Total (in shares)									0	4,852,414
Note Payable Maturing December 2023 [Member]
Debt Instrument, Face Amount | $			$ 1,000,000										$ 1,000,000
Debt Instrument, Interest Rate, Stated Percentage			8.00%							8.00%			8.00%
Note Payable Maturing May 2022 [Member]
Debt Instrument, Face Amount | $	$ 1,000,000
Debt Instrument, Interest Rate, Stated Percentage	12.00%									12.00%
Series D Preferred Stock Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares				$ 2.57
Class of Warrant or Right, Issued During Period (in shares)				58,366
Series E Preferred Stock Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)	194,553
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares	$ 2.57
Class of Warrant or Right, Issued During Period (in shares)	38,911							77,821
Option to Purchase Series B Preferred Stock [Member]
Option Indexed to Issuer's Equity, Shares (in shares)							350,000
Option Indexed to Issuer's Equity, Percentage of Shares Purchased							33.33%
Option to Award Series E Preferred Stock Warrants [Member]
Option Indexed to Issuer's Equity, Shares (in shares)			38,911
Option Indexed to Issuer's Equity, Strike Price (in dollars per share) | $ / shares			$ 2.57
Series A, A-2, and C Preferred Stock [Member]
Number of Members of the Board Elected by Preferred Stockholders									2
Series B, D and E Preferred Stock [Member]
Number of Members of the Board Elected by Preferred Stockholders									1
Series A Preferred Stock [Member]
Preferred Stock, Shares Authorized (in shares)															1,050,000
Preferred Stock, Shares Issued, Total (in shares)															1,042,853
Shares Issued, Price Per Share (in dollars per share) | $ / shares															$ 1.00
Series A-2 Preferred Stock [Member]
Preferred Stock, Shares Authorized (in shares)														420,000
Preferred Stock, Shares Issued, Total (in shares)														412,735
Shares Issued, Price Per Share (in dollars per share) | $ / shares														$ 1.21
Series B Preferred Stock [Member]
Shares Issued, Price Per Share (in dollars per share) | $ / shares							$ 1.43
Stock Issued During Period, Shares, New Issues (in shares)							1,049,997
Series C Preferred Stock [Member]
Shares Issued, Price Per Share (in dollars per share) | $ / shares						$ 2.07
Stock Issued During Period, Shares, New Issues (in shares)						483,092
Series D Preferred Stock [Member]
Shares Issued, Price Per Share (in dollars per share) | $ / shares					$ 2.57
Stock Issued During Period, Shares, New Issues (in shares)					692,292
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)					1
Series E Preferred Stock [Member]
Shares Issued, Price Per Share (in dollars per share) | $ / shares		$ 2.57
Stock Issued During Period, Shares, New Issues (in shares)		703,989
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)		1
Nonemployees [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)											148,480	183,100
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares									$ 2.00
Private Placement Offering [Member]
Sale of Stock, Number of Shares Issued in Transaction (in shares)									33,147,192
Sale of Stock, Price Per Share (in dollars per share) | $ / shares									$ 2.00
Proceeds from Issuance of Common Stock | $									$ 11,500,000
Payments of Stock Issuance Costs | $									$ 2,100,000
Stock Issued During Period, Shares, New Issues (in shares)									1,294,000