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Updated: Aug 29, 2026
Modeling Posthemorrhagic Hydrocephalus of Prematurity in Rats
Published on: March 28, 2025
Age-dependent changes in material properties of the brain and braincase of the rat
Amit Gefen1, Nurit Gefen, Qiliang Zhu
1Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Insights
Pediatric head injury biomechanics differ from adults. Immature rat brains are stiffer, while their braincases are more compliant, informing injury models.
Area of Science:
- Biomedical Engineering
- Pediatric Traumatology
- Computational Biology
Background:
- Head injury mechanisms in children differ from adults.
- Pediatric-specific material properties are needed for accurate biomechanical modeling of head injuries.
- Understanding age-related changes in brain and skull properties is crucial for pediatric head injury research.
Purpose of the Study:
- To determine age-specific material properties of the rat brain and braincase.
- To compare the biomechanical properties of immature and mature rat brains and braincases.
- To provide data for developing age-specific computational models of pediatric head injury.
Main Methods:
- Indentation tests were performed on rat brains at postnatal days (PND) 13, 17, 43, and 90 to measure shear moduli.
- Finite element modeling was used to estimate the effective elastic moduli of the braincase.
- Both in situ and in vitro measurements were conducted for brain tissue properties.
Main Results:
- Immature rat brains (PND 13-17) were significantly stiffer than mature brains (PND 43-90).
- The braincase's effective elastic modulus showed no significant age-dependent change, with increased rigidity attributed to skull thickness.
- Immature rat brains exhibited higher instantaneous (G(i)) and long-term (G(∞)) shear moduli compared to mature brains.
Conclusions:
- Immature rat brains are biomechanically stiffer than adult brains.
- The pediatric braincase becomes more rigid with age primarily due to increased skull thickness, not tissue stiffening.
- These findings are essential for developing age-specific experimental and computational models for pediatric head injury simulations.
Abstract:
Clinical and biomechanical evidence indicates that mechanisms and pathology of head injury in infants and young children may be different from those in adults. Biomechanical computer-based modeling, which can be used to provide insight into the thresholds for traumatic tissue injury, requires data on material properties of the brain, skull, and sutures that are specific for the pediatric population. In this study, brain material properties were determined for rats at postnatal days (PND) 13, 17, 43, and 90, and skull/suture composite (braincase) properties were determined at PND 13, 17, and 43. Controlled 1 mm indentation of a force probe into the brain was used to measure naive, non-preconditioned (NPC) and preconditioned (PC) instantaneous (G(i)) and long-term (G( infinity )) shear moduli of brain tissue both in situ and in vitro. Brains at 13 and 17 PND exhibited statistically indistinguishable shear moduli, as did brains at 43 and 90 PND. However, the immature (average of 13 and 17 PND) rat brain (G(i) = 3336 Pa NPC, 1754 Pa PC; G( infinity )= 786 Pa NPC, 626 Pa PC) was significantly stiffer (p < 0.05) than the mature (average of 43 and 90 PND) brains (G(i) = 1721 Pa NPC, 1232 Pa PC; G( infinity ) = 508 Pa NPC, 398 Pa PC). A "reverse engineering" finite element model approach, which simulated the indentation of the force probe into the intact braincase, was used to estimate the effective elastic moduli of the braincase. Although the skull of older rats was significantly thicker than that of the younger rats, there was no significant age-dependent change in the effective elastic modulus of the braincase (average value = 6.3 MPa). Thus, the increase in structural rigidity of the braincase with age (up to 43 PND) was due to an increase in skull thickness rather than stiffening of the tissue. These observations of a stiffer brain and more compliant braincase in the immature rat compared with the adult rat will aid in the development of age-specific experimental models and in computational head injury simulations. Specifically, these results will assist in the selection of forces to induce comparable mechanical stresses, strains and consequent injury profiles in brain tissues of immature and adult animals.
