This Injectable Gel Could One Day Rebuild Muscle, Skin, and Fat

Car crashes, battle wounds, and surgeries can leave people with gaping holes in soft tissue that are often too large for their bodies to repair. Now, researchers have developed a nanofiber-reinforced injectable gel that can rebuild missing muscle and connective tissues by serving as a scaffold and recruiting the body’s wound-healing cells. So far,...
A new injectable gel could help repair damaged soft tissues.

Car crashes, battle wounds, and surgeries can leave people with gaping holes in soft tissue that are often too large for their bodies to repair. Now, researchers have developed a nanofiber-reinforced injectable gel that can rebuild missing muscle and connective tissues by serving as a scaffold and recruiting the body’s wound-healing cells. So far, the team has tested the material only in rats and rabbits. But if it performs as well in humans, it could give reconstructive surgeons a fast and easy way to help patients regenerate lost tissues without scarring or deformity.

“Soft tissue losses are a ubiquitous problem in clinical medicine,” says Sashank Reddy, a reconstructive surgeon at the Johns Hopkins University School of Medicine in Baltimore, Maryland. Surgeons can transplant tissue from another body region to the injury site. But that involves trauma for patients and tissue loss from another part of the body. Surgeons can also insert synthetic implants. But immune cells typically just wall off those implants, leaving behind thick, fibrous scars.

Then there are gellike fillers. When injuries are small—on the order of fingertip-size—surgeons often inject a gel made from hyaluronic acid (HA) that immune cells called macrophages can infiltrate. As they burrow inside and encounter HA molecules, macrophages typically send out signals that recruit blood vessel–forming cells and other cells that help repair the damage. But with larger gaps in tissue, HA gels are typically too squishy to hold their shape. Researchers have tried to fortify gels by linking gel molecules. But to make gels strong and tough enough to behave like tissue, researchers must add so many links that they create a stiff 3D mesh. But its pores are too small for macrophages and other cells to penetrate. “It changes the biology,” says Jennifer Elisseeff, a biomedical engineer at Johns Hopkins who was not part of Reddy’s team. As a result, the macrophages release signals that lead to scar tissue.

Get more great content like this delivered right to you!

Country * Afghanistan Aland Islands Albania Algeria Andorra Angola Anguilla Antarctica Antigua and Barbuda Argentina Armenia Aruba Australia Austria Azerbaijan Bahamas Bahrain Bangladesh Barbados Belarus Belgium Belize Benin Bermuda Bhutan Bolivia, Plurinational State of Bonaire, Sint Eustatius and Saba Bosnia and Herzegovina Botswana Bouvet Island Brazil British Indian Ocean Territory Brunei Darussalam Bulgaria Burkina Faso Burundi Cambodia Cameroon Canada Cape Verde Cayman Islands Central African Republic Chad Chile China Christmas Island Cocos (Keeling) Islands Colombia Comoros Congo Congo, the Democratic Republic of the Cook Islands Costa Rica Cote d’Ivoire Croatia Cuba Curaçao Cyprus Czech Republic Denmark Djibouti Dominica Dominican Republic Ecuador Egypt El Salvador Equatorial Guinea Eritrea Estonia Ethiopia Falkland Islands (Malvinas) Faroe Islands Fiji Finland France French Guiana French Polynesia French Southern Territories Gabon Gambia Georgia Germany Ghana Gibraltar Greece Greenland Grenada Guadeloupe Guatemala Guernsey Guinea Guinea-Bissau Guyana Haiti Heard Island and McDonald Islands Holy See (Vatican City State) Honduras Hungary Iceland India Indonesia Iran, Islamic Republic of Iraq Ireland Isle of Man Israel Italy Jamaica Japan Jersey Jordan Kazakhstan Kenya Kiribati Korea, Democratic People’s Republic of Korea, Republic of Kuwait Kyrgyzstan Lao People’s Democratic Republic Latvia Lebanon Lesotho Liberia Libyan Arab Jamahiriya Liechtenstein Lithuania Luxembourg Macao Macedonia, the former Yugoslav Republic of Madagascar Malawi Malaysia Maldives Mali Malta Martinique Mauritania Mauritius Mayotte Mexico Moldova, Republic of Monaco Mongolia Montenegro Montserrat Morocco Mozambique Myanmar Namibia Nauru Nepal Netherlands New Caledonia New Zealand Nicaragua Niger Nigeria Niue Norfolk Island Norway Oman Pakistan Palestine Panama Papua New Guinea Paraguay Peru Philippines Pitcairn Poland Portugal Qatar Reunion Romania Russian Federation Rwanda Saint Barthélemy Saint Helena, Ascension and Tristan da Cunha Saint Kitts and Nevis Saint Lucia Saint Martin (French part) Saint Pierre and Miquelon Saint Vincent and the Grenadines Samoa San Marino Sao Tome and Principe Saudi Arabia Senegal Serbia Seychelles Sierra Leone Singapore Sint Maarten (Dutch part) Slovakia Slovenia Solomon Islands Somalia South Africa South Georgia and the South Sandwich Islands South Sudan Spain Sri Lanka Sudan Suriname Svalbard and Jan Mayen Swaziland Sweden Switzerland Syrian Arab Republic Taiwan Tajikistan Tanzania, United Republic of Thailand Timor-Leste Togo Tokelau Tonga Trinidad and Tobago Tunisia Turkey Turkmenistan Turks and Caicos Islands Tuvalu Uganda Ukraine United Arab Emirates United Kingdom United States Uruguay Uzbekistan Vanuatu Venezuela, Bolivarian Republic of Vietnam Virgin Islands, British Wallis and Futuna Western Sahara Yemen Zambia Zimbabwe

Required fields are indicated by an asterisk (*)

Now, Reddy and his colleagues have come up with a better way to reinforce HA gels. They first created nanofibers out of a biodegradable polymer used for decades in dissolvable sutures, called polycaprolactone. They then treated the fibers so that some would contain molecular linkers designed to bind to HA. An hourslong process formed bonds between the molecular linkers and the HA molecules, creating a gel that was as resilient as soft tissue. And, much as a bit of rebar reinforces concrete, the gel needed only a small volume of nanofibers to become rigid. That small amount meant the gel still had gaps large enough for cells to easily pass through. The resulting 3D mesh, says Reddy, has a striking resemblance to the body’s extracellular matrix, the natural scaffolding for healthy tissues.

To test their material, Reddy and his colleagues injected it into rabbits in which some fat had been surgically excised, before the material stiffened. Not only did the gel take the shape of the missing tissue as it firmed up, but after it did, macrophages readily infiltrated it and released signals that recruited blood vessel–forming cells, among others. The animals were able to rebuild chunks of tissue as large as 10 cubic centimeters, about the size of a human finger, researchers report today in Science Translational Medicine.

The new gel is “cutting edge, scientifically,” says Ali Khademhosseini, a bioengineer at the University of California, Los Angeles, who wasn’t involved in the research. He notes that, unlike other gels, this one does not include growth factors and other biological signaling molecules, instead relying on the body to supply its own. That simplicity could make it easier for the gel to pass muster with the U.S. Food and Drug Administration, Khademhosseini says.

The gel could also help repair soft tissues with specific functions, like heart muscle cells. Hai-Quan Mao, a biomaterials expert and member of the team from Johns Hopkins, says the researchers hope to seed the matrix with stem cells that form cardiac tissue, in order to help repair tissue damage after a heart attack. That’s still in the research phase; in the meantime, the researchers have already formed a company to commercialize the technology, called LifeSprout.