The study is designed to evaluate the safety, efficacy, and pharmacokinetics (PK) of three ascending doses of AMT-143 to determine the appropriate dose of AMT-143 for the management of postsurgical pain following inguinal hernia repair. Healthy male and female participants 18 years of age scheduled for open inguinal hernia repair surgery will be enrolled. Participants will all receive general anesthesia. The open inguinal hernia repair will be performed by a participating surgeon and the study medication will be administered by the surgeon prior to wound closure. AMT-143 is provided as a hydrogel containing 385 mg/mL ropivacaine (on a ropivacaine HCl equivalence basis). AMT-143 hydrogel will be provided as pre-filled syringes for administration via instillation into the surgical site after surgery and prior to suture. This will be a randomized, single blind, placebo and active controlled, dose escalation study performed at one clinical site to determine optimal doses of AMT-143. The study will consist of 30 participants, 10 per dose. Participants will receive AMT-143, or saline placebo, or ropivacaine 1% solution. Participants will be blinded to treatment. All assessments up to 4 h will be performed in the hospital clinic setting. Post discharge follow-up for the study will be handled on an outpatient basis and will be conducted by a home nurse up to Day 21. The participant will return to the clinical site for a final End of Study visit on Day 28.