Americans are more knowledgeable this year in answering basic civics questions, according to the Annenberg Constitution Day Civics Survey, conducted annually by the Annenberg Public Policy Center (APPC) of the University of Pennsylvania.

More than two-thirds of U.S. adults (70%) are able to name all three branches of government – the executive, judicial, and legislative – significantly more than a year ago (65%). When asked which rights the First Amendment guarantees, 79% can name “freedom of speech,” an increase over 2024 (74%).

“People can’t cherish, safeguard, or exercise their constitutionally protected rights unless they know that they have them and understand how effective use of them sustains our system of government,” said APPC director Kathleen Hall Jamieson. “Civics education at home and in schools should be a high priority as a result.” 

Released for Constitution Day (Sept. 17^th), the nationally representative survey also finds that trust in the U.S. Supreme Court continues to deteriorate, with nearly 6 in 10 people (59%) voicing little or no trust the nation’s highest court is operating in their best interests.

Highlights

The 2025 Annenberg Constitution Day Civics Survey finds that:

• Over two-thirds of Americans (70%) can name all three branches of government.
• Asked what specific rights are guaranteed by the First Amendment, 79% say freedom of speech.
• Four in 10 U.S. adults (41%) have at least a moderate amount of trust the Supreme Court is operating in their best interests. There is a nearly 60-point gap between the parties – 75% of Republicans have at least a moderate amount of trust in the court but just 18% of Democrats do.
• There’s bipartisan support for several potential Supreme Court reforms, with over 80% favoring prohibiting justices from participating in cases in which they have “personal or financial interests.”

Annenberg Constitution Day Civics Survey

The nationally representative Annenberg Constitution Day Civics Survey, conducted for the Annenberg Public Policy Center by independent research company SSRS, draws on responses to Annenberg surveys of empaneled, nationally representative samples of U.S. adults during three periods. In March, respondents (n=1,363) were asked about attitudes toward the Supreme Court. In May-July, that same panel (n=1,334) was asked about proposed reforms to the court. In August, a different nationally representative panel (n=1,684) was asked about civics knowledge. All have a margin of sampling error of ± 3.5 percentage points at the 95% confidence level. For details, see the topline. See the full release online for additional information.

The branches of government and First Amendment

More than two-thirds of Americans (70%) can name all three branches of government, the highest in a few years. (The question has been asked since 2007 and annually since 2014, but a shift in survey methodology from phone to internet in 2023 means the recent figures are not directly comparable to the older ones.) In addition, 12% can name two branches, 6% can name one, and 13% cannot name any, no significant change from last year.

There is an upsurge in awareness of most of the five First Amendment rights, with 40% able to name most of the rights, up from 30% in 2024. When respondents are asked if they can name the specific rights guaranteed by the First Amendment:

• Nearly 4 out of 5 (79%) say freedom of speech, up significantly from 74% in 2024;
• Nearly half (48%) say freedom of religion, up from 39% in 2024;
• 36% say right of assembly, up from 27% in 2024;
• 34% say freedom of the press, statistically unchanged;
• 12% say the right to petition, statistically unchanged.

The 2025 increases in knowledge, during the first year of the second Trump administration, parallel a 2018 increase during the first Trump administration. In both cases, a torrent of executive actions and the resulting judicial cases and actions by Congress produced a rush of political news.

Political party affiliation did not appear to play a role in the increase in civics knowledge.

Eroding trust in the Supreme Court

In the past few years, a number of surveys have shown declining trust in the Supreme Court and a widening gap between the political parties in views on the court. The Annenberg survey finds that from 2019 to March 2025, the percentage of U.S. adults holding at least a moderate amount of trust in the court dropped from 68% to 41%.

“Trust has fallen sharply and become polarized,” said University of Pennsylvania political science professor Matt Levendusky, who directs APPC’s Institutions of Democracy division. “Even after previous controversial decisions, like Bush v. Gore, trust in the court rebounded. But in the years since Dobbs [in 2022], it has continued to erode.”

The survey finds a widening, nearly 60-point gap between the parties on trust in the Supreme Court. As of March 2025, 75% of Republicans and Republican-leaning respondents have at least a moderate amount of trust, up from 69% in May 2024, while just 18% of Democrats and Democratic-leaning respondents do, down from 29% in May 2024.  

“The court was once held in high esteem by Democrats and Republicans alike, but that is no longer the case,” Levendusky said. “If the court is just another political actor, then it loses its special place in our political system, with worrying long-term implications.”

Broad popular support for some Supreme Court reforms

Asked about potential measures to reform the Supreme Court, most Americans favor prohibiting participation of justices in cases in which they have personal or financial conflicts (83%); creating a formal ethics code for justices (78%); mandatory retirement age (72%); and term limits (69%). Under half favor other proposals – allowing the public to vote to overturn Supreme Court rulings on controversial issues (44%) and increasing the size of the court (31%).

How partisanship affects views of court reform

Bipartisan majorities favor four potential reforms to the Supreme Court, though there are partisan differences in the extent to which they favor them. The top potential reform supported by members of both parties is prohibiting justices from participating in cases in which they have personal or financial interests, backed by 86% of Democrats and 83% of Republicans. Notably, most survey respondents in both parties do not favor increasing the number of justices on the Supreme Court, an idea proposed by some Democrats and backed by 44% of Democrats, 15% of Republicans, and 33% of independents. One proposal – allowing the public to vote to overturn Supreme Court decisions on controversial issues – is supported by half of Democrats (50%), but just 38% of Republicans and 45% of independents.

Constitution Day

APPC releases its annual civics survey in advance of Constitution Day, which celebrates the signing of the Constitution on Sept. 17, 1787. APPC’s initiatives to enhance civics education include Annenberg Classroom, which offers free resources for teaching the Constitution, and the Civics Renewal Network, a coalition of 46 nonpartisan, nonprofit organizations dedicated to improving civics education by providing free, high-quality resources for teachers. New resources include the collaborative Constitution Day Hub website and the Annenberg Classroom film “Balancing State and Federal Power: The Constitution’s Commerce Clause.”

“Strengthening the citizenry’s knowledge of the U.S. Constitution remains paramount for the long-term health of the nation’s democracy. This year’s APPC Constitution Day Civics Survey points to some clear knowledge gains, but there is also evidence indicating that there is more work to be done,” said R. Lance Holbert, director of APPC’s Leonore Annenberg Institute for Civics.

The Annenberg Constitution Day Civics Survey was developed under the leadership of Levendusky, Jamieson, Holbert, research analyst Shawn Patterson Jr. and APPC’s managing director of survey research, Ken Winneg.

The Annenberg Public Policy Center was established in 1993 to educate the public and policy makers about communication’s role in advancing public understanding of political, science, and health issues at the local, state, and federal levels.

For decades, scientific consensus held that platelets—the small, disc-shaped cell fragments circulating in the blood—were the primary force behind clot contraction. Platelets tightly pull on strands of the protein fibrin, creating a dense mesh that stabilizes the clot and stops bleeding. Red blood cells, by contrast, were thought to be bystanders, essentially filling space within the clot without influencing its mechanics. However, new experimental data from the University of Pennsylvania team reveals that red blood cells are far from inert; instead, they contribute significant contractile forces, reshaping how we understand the fundamental mechanics of blood clot dynamics.

The team’s unexpected findings came from an experiment designed to test the assumption that clot contraction requires platelets. By creating blood clots entirely devoid of platelets, researchers anticipated no contraction would occur. To their surprise, the clots shrank in volume by more than 20%. This initial observation was rigorously verified by chemically inhibiting platelet activity in normal blood samples, yet clot contraction persisted robustly. These results unequivocally demonstrated that red blood cells themselves can drive clot compaction, revealing a platelet-independent mechanism that refines the conceptual framework of thrombus formation.

To explain this phenomenon, the researchers enlisted the expertise of Prashant Purohit, a mechanical engineer specializing in soft materials and bioengineering. Purohit’s mathematical modeling pointed to a process known as osmotic depletion as the primary force behind the red blood cell aggregation within clots. Osmotic depletion is a physical effect typically observed in colloidal mixtures—substances where microscopic particles cluster due to imbalances in surrounding molecular concentrations. In the context of blood clots, proteins suspended in the fluid environment create an osmotic pressure gradient that effectively pushes red blood cells closer together.

As a clot develops, a fibrin meshwork forms which captures red blood cells within its intricate protein lattice. When these cells become tightly packed, proteins in the blood plasma are forced out of the narrow spaces between them, increasing the protein concentration in the surrounding fluid. This concentration difference generates a pressure that “squeezes” the red blood cells further together. Rather than being mere placeholders, the red blood cells experience a powerful external force compelling them to contract the clot volume and mechanically reinforce the fibrin network. This compelling physical interaction ensures that the clot shrinks and strengthens even in the absence of platelets pulling the fibrin strands.

Beyond osmotic depletion, the team also considered another previously proposed mechanism—bridging. Bridging involves weak molecular attractions on the surfaces of red blood cells leading to adhesion and clustering. However, Purohit’s modeling and subsequent experiments revealed that this effect is considerably weaker and insufficient to account for the observed degree of clot contraction. Experiments using modified blood samples lacking the molecules responsible for bridging still exhibited substantial clot shrinkage, but when conditions suppressed osmotic depletion forces, contraction was minimal. This elegant combination of theory and practice affirms osmotic depletion as the dominant mechanism in platelet-independent clot compaction.

This newfound role of red blood cells has critical clinical implications. Disorders such as thrombocytopenia, characterized by dangerously low platelet counts, often lead to uncontrolled bleeding due to impaired clot formation. Understanding that red blood cells can compensate, at least partially, and contribute actively to clot contraction may reshape therapeutic approaches to such conditions. Additionally, the mechanics uncovered may shed light on how clots fragment and embolize, traveling through the bloodstream to obstruct critical vessels and cause strokes. Fine-tuning the knowledge of these mechanical forces opens possibilities for novel interventions aimed at preventing or mitigating thrombotic complications.

The interdisciplinary nature of this study—melding cell biology, biophysics, mechanical engineering, and clinical insight—illustrates the power of collaboration in biomedical innovation. Using sophisticated imaging, biochemical assays, and computational modeling, the researchers unraveled complex biomechanical interactions within the clot’s microenvironment, a process that had remained elusive since blood cells were first described centuries ago. This research highlights the dynamic and mechanical contributions of each cellular player beyond their traditionally assigned roles.

From a biophysical standpoint, the study extends our comprehension of how soft, viscoelastic materials behave under mechanical stress in physiological conditions. Blood clots represent an adaptive material paradigm where cellular and protein components integrate in a delicately balanced microarchitecture. The study’s findings emphasize that cellular biomechanics—not just biochemical signaling—is instrumental in the maintenance and regulation of hemostasis. Red blood cells’ ability to aggregate and generate compressive forces challenges existing models and indicates that clot maturation is a holistic, multi-component process.

The implications also extend to biomimetic engineering and the design of synthetic materials. By understanding the natural principles governing red blood cell aggregation and fibrin network stiffening, engineers may develop advanced materials that dynamically respond to mechanical forces, with potential applications in wound healing technologies or medical devices. This insight bridges fundamental science with translational research aimed at enhancing patient care through innovative material science.

While this study marks a significant milestone, the researchers acknowledge that many questions remain. How various pathological conditions alter red blood cell mechanical properties and osmotic interactions needs further exploration. Similarly, the interplay between red blood cells, platelets, fibrin, and other blood components under diverse physiological and pathological states warrants deeper investigation. Future research will likely investigate the modulation of osmotic depletion forces as therapeutic targets and the potential for controlling clot size and stability with precision medicine approaches.

In conclusion, the University of Pennsylvania team’s discovery that red blood cell aggregation contributes actively to blood clot contraction radically changes our understanding of hemostasis. This platelet-independent mechanism, driven by osmotic depletion forces, enriches the biological narrative of how clots form, mature, and stabilize. With far-reaching implications in clinical hematology, stroke prevention, and biomaterials science, this work exemplifies the profound insights gained when engineering principles illuminate biological phenomena, ushering a new era of multidisciplinary investigation into the life-saving mysteries of blood clotting.

Subject of Research: Cells

Article Title: Red blood cell aggregation within a blood clot causes platelet-independent clot shrinkage

News Publication Date: 22-Jul-2025

Web References:
https://doi.org/10.1182/bloodadvances.2024015533

References: Blood Advances, University of Pennsylvania study supported by NIH grants R01 HL148227, P01 HL146373, R01 HL148014, R01 HL159256, and American Heart Association 25POST1357254/2025

Image Credits: Rustem Litvinov

Keywords: red blood cells, blood clots, clot contraction, platelet-independent clotting, osmotic depletion, fibrin mesh, hemostasis, thrombocytopenia, embolism, stroke, biophysics, blood biomechanics