Volume 647

Tying knots in surgical sutures requires precise amounts of force — too little force and the sutured wound will gape and leak, too much and the wound will bloat and blood flow becomes restricted. Robots can help, but their complex sensing systems are hampered in operations with limited space, such as minimally invasive surgeries. In this week’s issue, Tiefeng Li and colleagues analyse the force mechanics of the simple slipknot and reveal that it can be used to transmit force mechanically to close wounds consistently without the need for electronics. The researchers found that topologically designed slipknots can deliver force with 95.4% consistency. They used this to design a system they call a ‘sliputure’ in which a slipknot is added to the surgical thread alongside the normal surgical knot. The surgeon ties the surgical knot on the wound as usual, but then pulls the slipknot until it opens, which transmits the appropriate amount of mechanical force to close the surgical knot to the correct pressure. In tests, the team found that the sliputure approach improved the knot precision of inexperienced surgeons by 121%, and also aided blood supply and tissue healing after surgery.

The cover features a close-up of the eastern green mamba (Dendroaspis angusticeps), one of many highly venomous snake species found in sub-Saharan Africa. Bites from venomous snakes are a major health problem in the region, causing thousands of deaths and serious injuries every year. But current antivenoms, although effective, are problematic — they tend to be expensive, can cause adverse reactions and have limited efficacy against many venoms. In this week’s issue, Andreas Laustsen and colleagues present an engineered antivenom that shows promise in treating a wide variety of snake venoms. The antivenom is based on small antibodies called nanobodies. By inoculating llamas and alpacas with the venom from 18 African snake species, including mambas, cobras and rinkhals, the researchers were able to identify eight nanobodies that targeted the key toxins in the various venoms. Combining these nanobodies, the team created an antivenom that in mice offered protection against the venoms from 17 of the 18 snakes tested.

One of the features that sets mammals apart from other vertebrates is their jaw — most jawed vertebrates have several bones in their lower jaw, but mammals have just one. The evolution of this jaw structure has long been used as a marker to separate mammals from other vertebrates. In this week’s issue, Fangyuan Mao and colleagues reveal fresh details about the evolution of the mammalian jaw joint. The researchers used micro-computed tomography to examine the skulls of two mammal predecessors — the newly described Polistodon chuannanensis (pictured in an artist’s impression on the cover) and the new species Camurocondylus lufengensis. The Polistodon skull is about 160 million years old and has a previously unknown arrangement of the jaw bone. Camurocondylus is older, dating from the Early Jurassic epoch around 200 million years ago, and again displays a novel jaw shape. Together, the team argues, these diverse jaw joints indicate that the evolutionary path to the mammalian jaw was one of independent innovations in response to ecological pressures.

Our ability to process information into complex emotions, behaviours and decisions relies on the rich diversity of cell types that make up the human brain. Uncovering the molecular and cellular events that take place during brain development could reveal not only the mechanisms that give rise to this diversity but also shed light on how this process might go awry in neurodevelopmental disorders such as autism and schizophrenia. In this week’s issue, the BRAIN Initiative Cell Atlas Network (BICAN) builds on its previous work creating atlases of cell types in the adult mouse, non-human primate (NHP) and human brains to present cell-type atlases of the developing human, mouse and NHP brains. Across a suite of papers, nine of which are published in Nature, the researchers uncover the complex programs through which cell types emerge during brain development in humans and animals, revealing both the shared and unique features of the human brain. The latest work, along with future research directions, is summed up in a Perspective article by Tomasz Nowakowski and colleagues.