1. Introduction

Understanding human soft tissue deformation is important for preventing and decreasing the tissue damage due to mechanical load by external products. Experimental data for material properties of living human tissue are limited. Moreover, tissue tolerance to loads seems depend on the individual-specific conditions including health [1].

To investigate the influence of tissue material representation in soft tissue strategy with a 2D generic multilayer model of the lower leg was introduced. Two material sets were applied, each representing skin, fat, vessels and bones separately while fascia and muscle tissues had either separate or combined material properties. External loads were applied by three different shapes of prosthetic sockets. The relative change between the two used material sets were considerable regarding the distribution and magnitudes of tissue’s stresses and strains as well as the contact pressures.

Soft tissue injuries, including contusions, strains, and sprains, are among the most prevalent injuries encountered in clinical, sports, and occupational settings. These injuries typically involve damage to muscles, tendons, ligaments, or connective tissue, often resulting from blunt trauma, excessive mechanical stress, or repetitive overuse. Soft tissue contusions, in particular, are characterized by localized damage to underlying tissues without disruption of the skin, leading to pain, swelling, and potential hematoma formation. Despite their high incidence, understanding the mechanisms underlying soft tissue injury and recovery remains complex, as these processes involve intricate interactions between cellular, molecular, and biomechanical factors [1,2,3,4].

Experimental models have played a pivotal role in advancing our knowledge of soft tissue injury pathogenesis, providing platforms to study inflammation, vascular damage, and tissue repair. These models are indispensable for evaluating the efficacy of therapeutic interventions, including anti-inflammatory drugs, regenerative therapies, and rehabilitation protocols [5,6,7]. However, the diversity of injury types and the multifaceted nature of soft tissue healing necessitate the use of various experimental approaches, ranging from in vivo animal studies to in vitro and computational models [8].

This review aims to provide a comprehensive analysis of experimental models used in soft tissue contusion and injury research. By exploring their design, strengths, and limitations, we seek to highlight the critical insights gained through these models and their translational relevance. Additionally, the review addresses emerging trends, such as the integration of 3D bioprinting and AI-enhanced simulations, and discusses the ethical challenges associated with experimental research. Through this synthesis, we aim to identify gaps in current methodologies and propose directions for future research to improve clinical outcomes for individuals with soft tissue injuries [9,10].

Moreover, the mechanisms of soft tissue behaviour and risk for damage when exposed to external loads are not yet fully understood. Several studies investigating specific biomechanical material properties in vivo have been performed over the years, but further investigations are still needed [9-12]. The multilayer configuration, diverse tissue structures and time dependence are challenging aspects of human soft tissues [9,10,13]. So far there is no established standard methodology for obtaining properties of individualspecific soft tissues [10,14]. Additionally, little reference data for soft tissue materials from living humans are available.

2. Purpose of the Research

The primary purpose of this research is to provide a comprehensive review of the experimental models utilized to study soft tissue contusions and injuries. By critically analyzing existing methodologies, this research aims to:

Ø Evaluate the Utility of Experimental Models: Examine the strengths, limitations, and translational potential of animal models, in vitro systems, and computational approaches used to simulate soft tissue injuries.

Ø Understand Pathophysiological Mechanisms: Explore how these models have contributed to elucidating the cellular, molecular, and biomechanical processes underlying soft tissue injury, including inflammation, vascular damage, and tissue repair.

Ø Assess Applications in Therapeutics and Rehabilitation: Highlight the role of experimental models in testing pharmacological agents, regenerative therapies, and physical rehabilitation techniques aimed at improving recovery outcomes.

Ø Identify Gaps and Ethical Challenges: Address limitations in current models, including their relevance to human conditions and ethical considerations associated with animal experimentation, and propose innovative solutions to overcome these barriers.

Ø Guide Future Research Directions: Offer insights into emerging technologies, such as 3D bioprinting and AI-driven simulations, to advance the field of soft tissue injury modeling and improve clinical translation.

By synthesizing current knowledge and identifying areas for improvement, this research seeks to advance the understanding of soft tissue injuries and foster the development of more effective diagnostic, therapeutic, and rehabilitative strategies.

3. Materials and Methods

To conduct this review, a systematic literature search was performed using electronic databases, including PubMed, Scopus, Web of Science, and Google Scholar. The following keywords were used: soft tissue injury, contusion models, experimental models, animal studies, in vitro systems, computational modeling, tissue repair, and inflammation. Articles published up to November 2024 were considered, with no restrictions on publication date.

Peer-reviewed articles describing experimental models of soft tissue injuries. Studies focusing on animal models, in vitro systems, and computational approaches. Research examining pathophysiological mechanisms or therapeutic interventions. Studies on non-soft tissue injuries (e.g., bone fractures, neurological damage). Articles lacking methodological details or primary experimental data. Non-English publications, unless translated versions were available.

Animal studies included in this review primarily involve rodent models (e.g., rats and mice), which are commonly used due to their anatomical and physiological similarities to humans. Large animal models, such as pigs, were also reviewed for their translational relevance. Injury induction methods assessed include: dropped weights or pneumatic impactors to simulate contusions, controlled mechanical force applied to soft tissues and use of freezing to induce localized tissue damage.

In vitro studies were reviewed for their ability to model cellular responses under controlled conditions. Materials used include: myoblasts, fibroblasts, and endothelial cells, simulating extracellular matrix properties, for studying vascular interactions and tissue stress, computational models were analyzed for their role in simulating soft tissue mechanics and predicting injury outcomes.

Techniques reviewed include: to model tissue deformation and stress distribution, predicting the effects of different forces on soft tissues.

Information was extracted on: model design and setup, injury induction methods and severity metrics, parameters measured (e.g., inflammatory markers, tissue repair rates), therapeutic and rehabilitative interventions evaluated.

For animal models, ethical approval details were documented where available, including adherence to the 3Rs principle (Replacement, Reduction, and Refinement). Alternatives to animal testing, such as advanced in vitro and computational models, were also emphasized.

This systematic approach ensured a robust analysis of current experimental models and their contributions to understanding soft tissue contusions and injuries.

4. Results and Discussion

Rodent models (rats, mice) were most commonly used due to their cost-effectiveness and ease of handling. Injury was typically induced using blunt trauma devices or controlled compression methods. Key findings included: acute inflammatory responses characterized by elevated cytokine levels (e.g., TNF-α, IL-6), evidence of vascular damage, muscle fiber degeneration, and subsequent repair processes, effectiveness of anti-inflammatory and regenerative therapies, such as mesenchymal stem cell (MSC) treatments.

Large animal models, such as pigs, provided more translationally relevant insights due to their anatomical similarity to humans but were less commonly used due to ethical and logistical challenges.

In Vitro Models:

Cell culture systems using fibroblasts, myoblasts, and endothelial cells offered detailed insights into cellular mechanisms, such as proliferation, migration, and extracellular matrix (ECM) remodeling.

Hydrogels and scaffolds allowed researchers to simulate 3D environments, revealing the importance of ECM composition in tissue repair.

Limitations included the lack of systemic factors, such as immune and vascular responses, that are present in vivo.

Computational Models:

Finite Element Analysis (FEA) and biomechanical simulations effectively predicted tissue deformation and stress under different trauma scenarios.

Computational models were particularly valuable in optimizing injury induction protocols and testing hypothetical therapeutic interventions before in vivo application.

Pharmacological Interventions:

Non-steroidal anti-inflammatory drugs (NSAIDs) and corticosteroids showed efficacy in reducing acute inflammation but were associated with delayed tissue regeneration in some studies.

MSC-based therapies enhanced tissue repair and reduced fibrosis, highlighting their potential in regenerative medicine.

Physical Rehabilitation:

Animal studies demonstrated the benefits of controlled mechanical loading and exercise in promoting tissue repair and functional recovery.

Timing and intensity of rehabilitation protocols were critical for optimal outcomes.

Limitations of Current Models

Animal Models: Despite their physiological relevance, interspecies differences limited the direct translation of findings to humans. Ethical concerns and logistical challenges further restricted their use.

In Vitro Models: Simplistic setups often failed to replicate the complexity of tissue responses in vivo.

Computational Models: While useful for predictive analysis, these models relied heavily on accurate input data, which could limit their applicability.

5. Discussion

Experimental models have been instrumental in advancing our understanding of soft tissue injury mechanisms and testing therapeutic strategies. Animal models remain the gold standard for studying systemic responses, while in vitro and computational models provide complementary insights into specific cellular and biomechanical aspects.

The integration of advanced technologies, such as 3D bioprinting and organ-on-a-chip systems, offers promising avenues to bridge the gap between in vitro and in vivo studies. These methods could provide more physiologically relevant environments while reducing reliance on animal testing.

Adopting the 3Rs principle is essential to address ethical concerns. Enhanced collaboration between researchers and regulatory bodies can foster the development of more refined models that balance scientific rigor with ethical responsibility.

Future Directions

Combining multiple model types (e.g., in vitro systems with computational simulations) for a more holistic approach.

Leveraging AI and machine learning to enhance predictive capabilities and optimize experimental designs.

Expanding the use of large animal models and human-relevant systems to improve translational outcomes.

This synthesis underscores the critical role of experimental models in soft tissue injury research while highlighting the need for continued innovation to overcome current limitations and drive clinical advancements.

6. Conclusions

Experimental models are fundamental tools in advancing our understanding of soft tissue contusions and injuries. They provide critical insights into the pathophysiological mechanisms, including inflammation, vascular damage, and tissue repair, and serve as platforms for evaluating therapeutic and rehabilitative interventions. Animal models remain the cornerstone of this research due to their systemic relevance, while in vitro systems and computational models offer complementary advantages in exploring cellular responses and biomechanical dynamics.

However, each model type presents limitations. Animal models face ethical and translational challenges, in vitro models often lack systemic complexity, and computational models are constrained by data accuracy and real-world applicability. Addressing these limitations requires innovative approaches, such as integrating 3D bioprinting, organ-on-a-chip technologies, and AI-driven predictive tools.

Future research should emphasize the development of more human-relevant models, interdisciplinary collaborations, and adherence to ethical principles. By leveraging emerging technologies and refining experimental methodologies, the field can enhance its translational impact, ultimately improving clinical outcomes for individuals suffering from soft tissue injuries.

This review highlights the critical role of experimental models in bridging the gap between basic research and clinical application, providing a roadmap for future advancements in the study and treatment of soft tissue injuries.