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Stock-based Compensation (Tables)

3 Months Ended

12 Months Ended

Mar. 31, 2024

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock Option Activity

A summary of activity for the three months ended March 31, 2024 is as follows:

		Options				Weighted Average Exercise Price				Weighted Average Remaining Contractual Term (years)				Aggregate Intrinsic Value
Balance as of December 31, 2023			140,109			$	37.48				8.07
Granted			163,025			$	2.03
Cancelled/forfeited			(1	)		$	289,125
Balance as of March 31, 2024			303,133			$	17.46				8.94			$	7,600
Vested and expected to vest at March 31, 2024			278,083			$	18.64				8.87			$	6,800
Exercisable at March 31, 2024			84,908			$	50.13				7.37			$	500

A summary of activity for the year ended December 31, 2023 is as follows:

		Options				Weighted Average Exercise Price				Weighted Average Remaining Contractual Term (years)				Aggregate Intrinsic Value
Balance as of December 31, 2022			78,334			$	68.16				8.00
Granted			68,422				5.00
Cancelled/forfeited			(6,647	)			283.76
Balance as of December 31, 2023			140,109			$	37.48				8.07			$	7,000
Vested and expected to vest at December 31, 2023			133,810			$	38.62				8.02			$	—
Exercisable at December 31, 2023			72,843			$	60.17				7.41			$	6,000

Weighted-average Assumptions

The fair value of each option awarded during the years ended December 31, 2023 and 2022 was estimated on the date of grant using the Black-Scholes-Merton option valuation model based on the following weighted-average assumptions:

		December 31, 2023				December 31, 2022
Expected term			6.0 years				6.0 years
Risk-free interest rate			4.06	%			2.83	%
Expected volatility			127.0	%			123.4	%
Dividends			0	%			0	%
Resulting fair value		$	4.47			$	7.05

Summary of Share-Based Compensation Recognized

The following table summarizes share-based compensation recognized during the years ended December 31, 2023 and 2022 in the statement of operations:

		2023				2022
Research and development		$	66			$	87
General and administrative			503				519
Total share-based compensation		$	569			$	606

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Tabular disclosure of cost recognized for award under share-based payment arrangement by plan. Includes, but is not limited to, related tax benefit.

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-Name Accounting Standards Codification
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Tabular disclosure of activity for award under share-based payment arrangement. Includes, but is not limited to, outstanding award at beginning and end of year, granted, exercised, forfeited, and weighted-average grant date fair value.

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Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions.

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