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Hydrogel-Semiconductor Hybrids: Blurring the Line Between Biology and Technology

November 22, 2024

Hydrogels are materials that mimic the softness and flexibility of biological tissues, making them invaluable in medicine for tasks like wound healing and drug delivery. Semiconductors, on the other hand, power the electronics that define our modern world, offering functionalities like sensing, amplification, and light-based modulation. Bringing these two materials together could transform the way we design devices for biomedical use, but this combination has been difficult to achieve—until now.

Researchers have developed a process called solvent affinity–induced assembly that embeds a hydrophobic semiconducting polymer into a hydrogel without compromising its softness or stretchiness. This innovation allows the creation of a hybrid material that behaves like biological tissue while also carrying out advanced electronic functions. The process starts by mixing a semiconducting polymer called p(g2T-T) with a hydrogel-forming monomer, acrylic acid, in a solvent known as dimethyl sulfoxide (DMSO). Ultraviolet (UV) light is used to cross-link the mixture into a stable double-network structure, and the DMSO is then replaced with water. This crucial solvent exchange step transforms the material into a soft, water-filled hydrogel while preserving the semiconductor’s electronic properties.

The resulting material exhibits a modulus, or stiffness, as low as 81 kilopascals, similar to biological tissues, and can stretch up to 150% without breaking. Despite its softness, it maintains high charge-carrier mobility, a measure of how efficiently it conducts electricity, comparable to that of rigid semiconductors. The hydrogel’s porous structure further enhances its performance by promoting molecular interactions with surrounding fluids, which improves its ability to sense and respond to biochemical signals.

This breakthrough has significant implications for medicine and technology. Because the hybrid material matches the mechanical properties of living tissues, it reduces the likelihood of immune responses when used in the body. Its combination of biocompatibility and electronic functionality enables a range of possibilities, such as real-time biosensing to detect subtle changes in the body, like shifts in pH or glucose levels. It also has potential for light-based therapies, delivering precise stimulation to tissues or nerves through photomodulation. Furthermore, its softness and stretchability make it ideal for wearable or implantable devices that conform to the surface of organs or skin without causing discomfort or damage.

By merging the tissue-like properties of hydrogels with the advanced electronic capabilities of semiconductors, this innovation represents a major step forward in bioelectronics. The ability to create soft, biocompatible materials with integrated electronic functionality opens up new possibilities for smarter, more adaptable medical devices. From diagnostic tools to therapeutic implants, this hydrogel-semiconductor hybrid is poised to reshape the landscape of biomedicine.

As research continues, this hybrid material could become a cornerstone of next-generation bioelectronics, paving the way for seamless integration between biology and technology.

Reference:
Dai, Y., Wai, S., Li, P., Shan, N., Cao, Z., Li, Y., Wang, Y., Liu, Y., Liu, W., Tang, K., Liu, Y., Hua, M., Li, S., Li, N., Chatterji, S., Fry, H. C., Lee, S., Zhang, C., Weires, M., Sutyak, S., … Wang, S. (2024). Soft hydrogel semiconductors with augmented biointeractive functions. Science (New York, N.Y.), 386(6720), 431–439. https://doi.org/10.1126/science.adp9314

 

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  Timothy Durham was convicted of rape when a test showed his DNA genotype matched the DNA recovered from the crime scene. Eye witnesses testified that Durham was in a different state at the time of the incident, but he wasn’t exonerated from his 3000 year sentence until follow up DNA analysis showed that the preliminary forensic analysis used in the trial was misinterpreted (Thomas et al.). DNA testing serves an invaluable part in our criminal justice system, but it comes with complications and bias that can lead to wrongful convictions and misinformed juries.  

Background:

Forensic genetics aims to identify the origin of a biological sample. It can be traced back to Karl Landsteiner who discovered human ABO blood groups. With blood groups, suspects could be eliminated based on their blood type. For example, if a suspect had type A blood and there was type B blood left at the scene by the perpetrator, the investigators could rule out the suspect. Unfortunately, the reverse didn’t work. If the suspect and perpetrator both had the same blood type, it can’t be concluded that the suspect was guilty. Blood identifiers evolved into 8 distinct categories which improved the ability to eliminate suspects, but could only conclude that (if the system matched) it might be the perpetrator or this person might be related to the perpetrator (Jobling and Gill). The field evolved in the 1980s with the discovery of Minisatellites, lines of repetitive DNA that don’t encode proteins. Minisatellite patterns in DNA create what we know today as the DNA fingerprint, and it has a much higher accuracy rate than previous methods (Augustyn et al.). Around the same time, a breakthrough for victims of sexual assault was discovered. In the case of assault, bodily fluids of both the victim and the assaulter can get mixed. A process called differential lysis was created which could selectively increase the concentration of sperm in a fluid sample thereby allowing for accurate DNA testing (Jobling and Gill). Forensics evolved to use single-locus probe testing after several years because of its ease of interpretation. It looked at specific minisatellites that had high variability between subjects. This was the first DNA-based method to be used in a criminal investigation. Two murder homicides from several years apart were connected using DNA evidence. The evidence was then used to exonerate an innocent man, and the guilty party was found when he tried to evade mandatory DNA testing for all men in the small town. His guilt was then reinforced when the DNA profiles matched, and he gave a confession (Jobling and Gill). Finding DNA at a crime scene doesn’t guarantee that you’ll find a murderer. There are issues with non-pure samples and limited samples that make DNA work difficult, and accreditation of facilities and new techniques and take time (Jobling and Gill).  

Subjectivity of DNA Interpretation:

In a 2009 publication, the National Academy of Science discusses the possibility for subjective influence in lab based forensics. The interpretation bias happens in complex cases where, for example, there could be a mixture of DNA. A study published in 2011 looked specifically at this issue. A gang rape happened in Georgia, and the mixture in DNA from the case was used to prosecute one suspect after another suspect took a plea bargain to testify against him. With DNA mixtures, there are three possible conclusions: suspect excluded, suspect cannot be excluded, and inconclusive. If the suspect is excluded, it means that there’s little to no possibility that his DNA is part of the sample. If the suspect cannot be excluded, it means that there’s a possibility that his DNA is part of the sample. In the trial, the DNA examiners who knew the context of the case concluded that the suspect being prosecuted could not be excluded. The 2011 study gave the DNA evidence from this case and the DNA profiles of the suspects to 17 forensic examiners. These examiners had no context of the case, and they all worked independently. Of the 17, only 1 came to the same conclusion (suspect cannot be excluded) as the examiners who knew the context of the case. Twelve of the 17 concluded that the suspect who was prosecuted and convicted had no relation to the DNA found in the sample. Not only does this show that subjectivity occurs due to the context of the case, but the 17 examiners came up with different findings based on their past experiences meaning that not all DNA analysis is objective. Some organizations like the Scientific Working Group on DNA Analysis Methods say that quantitative statistical evidence should be presented with every categorical conclusion, but the US doesn’t require this (Dror and Hampikian).

False Positives:

There are two categories that cause wrongful identification in a DNA report: coincidental matches and false positives. Coincidental matches are DNA matches between two unrelated people. The probability of these matches is about 1 to 500,000 for white individuals and about 1 to 350,000 for black individuals. This small probability of coincidental matches makes people feel confident in DNA evidence. False positives, on the other hand, are matches between DNA and test DNA that result from issues in the forensics lab. There have been multiple cases of forensics labs accidentally switching victim and suspected rapist DNA which lead to convictions that were later overturned when the lab realized the error. There are also cases of misreading or misunderstanding a sample. In a case from 1993, a man was convicted of rape because someone interpreted a mixed sample of victim and perpetrator DNA as an individual sample. The conviction was again overturned. To prevent false convictions, retesting DNA is allowed, but it’s not an efficient solution. Many people are pushing for statistical information on the probability of false positives, so that the jurors can make accurate judgements based on DNA evidence (Thomas et al.).  

Conclusion:

DNA analysis is a useful tool for the criminal justice system, but subjectivity can be an issue in forensic testing. To combat wrongful convictions, there are organizations like The Innocence Project who use DNA testing to free the innocent, but reformed forensic testing standards should be put in place to prevent subjectivity and to ensure juries are correctly informed during trials. https://www.innocenceproject.org/    

Citation:

Augustyn , Adam, et al. “DNA Finerprinting.” Encyclopedia Britannica , 26 Apr. 2018, www.britannica.com/science/DNA-fingerprinting#ref153186. Dror, Itiel E., and Greg Hampikian. “Subjectivity and Bias in Forensic DNA Mixture Interpretation.” Science & Justice, vol. 51, no. 4, 2011, pp. 204–208., doi:10.1016/j.scijus.2011.08.004. Jobling, Mark A., and Peter Gill. “Encoded Evidence: DNA in Forensic Analysis.” Nature Reviews: Genetics, vol. 5, no. 10, Oct. 2004, pp. 739–751., doi:10.1038/nrg1455. Thompson, William C, et al. “How the Probability of a False Positive Affects the Value of DNA Evidence.” Journal of Forensic Sciences, vol. 48, no. 1, Jan. 2003, pp. 1–8., doi:10.1520/jfs2001171.