A Denver cardiologist accused of drugging and sexually assaulting women he met through dating apps was arraigned on more than 50 felony counts on Friday.

Dr. Stephen Matthews, 35, a board-certified cardiologist and internal medicine physician, pleaded not guilty to 51 counts, including sexual assault and drugging, online court records show.

Matthews was first arrested in March on three counts of sexual assault after a woman alleged he drugged and sexually assaulted her. Since then, 12 more alleged victims have come forward, according to the Denver District Attorney's Office.

In the initial case, a woman told police she met Matthews on Hinge and blacked out while on a date with him in January and couldn't remember having any sexual interaction with him, according to an arrest warrant affidavit. Matthews told police they had consensual sex after consuming several mimosas, then she fell ill, the affidavit said.

Douglas Cohen, one of Matthews' attorneys, told CBS News Colorado in April that Matthews was innocent and claimed there was a "failure to fully investigate" the case.

"The accuser's story simply does not add up. Police omitted from their arrest affidavit many details that contradict her claim of no consent," Cohen told the station. "The government also had no forensic medical evidence to prove the accuser was too impaired to consent. We will defend him to the fullest."

Matthews was released from custody on a $50,000 bond for the March arrest. Following media reports on his arrest in that case, more women reported being drugged and/or sexually assaulted by Matthews, police said. He was arrested again in May after nine more women came forward, with most meeting him on Hinge or Tinder as far back as 2019, according to the arrest warrant.

Several of the women reported feeling ill while on dates with Matthews at his home and then blacking out, according to the affidavit. One reported her next memory was crawling across his bedroom floor naked and "yelling at him asking what he did," the affidavit said. Another woman told police she became ill while on a date at a restaurant with Matthews and was not sexually assaulted but believed he drugged her, the affidavit said.

ABC News did not immediately receive a response from Matthews' attorneys to a message seeking comment on the latest allegations.

Matthews is being held on a $5 million bond at a Denver jail. He is scheduled to next appear in court on Dec. 28 for a motions hearing, online court records show.

The arraignment comes after a judge ruled earlier this month there was enough evidence for Matthews to stand trial in the case.

Stephen Burg with the Burg Simpson law firm, which is representing some of the women in civil court, told Denver ABC affiliate KMGH they plan to file a lawsuit once the criminal proceedings are over, alleging that Matthews was never removed from the dating apps despite being reported for sexual assault. They plan to name the Match Group, the parent company of Hinge and Tinder, as a defendant, he told the station.

"Generally, I would just say that he was reported early on in the process and was on the dating apps for years after being reported as a rapist," Burg told KMGH.

A Match Group spokesperson said what has been reported "is horrible and has no place on our platforms or anywhere."

"At Match Group, we are committed to help keep our community safe and we continuously work to improve our systems to help prevent bad actors from accessing our platform," the spokesperson said in a statement. "Our teams use a combination of automated tools and human moderation to help remove bad actors proactively."

The spokesperson added they are fully cooperating with law enforcement and "will continue to provide any information to them that would be helpful for their investigation."