A rapid and facile approach to predictably control integration between two materials with divergent properties is introduced. Programmed integration between photopolymerizable soft and stiff hydrogels is investigated due to their promise in applications such as tissue engineering where heterogeneous properties are often desired. The spatial control afforded by grayscale 3D printing is leveraged to define regions at the interface that permit diffusive transport of a second material in‐filled into the 3D printed part. The printing parameters (i.e., effective exposure dose) for the resin are correlated directly to mesh size to achieve controlled diffusion. Applying this information to grayscale exposures leads to a range of distances over which integration is achieved with high fidelity. A prescribed finite distance of integration between soft and stiff hydrogels leads to a 33% increase in strain to failure under tensile testing and eliminates failure at the interface. The feasibility of this approach is demonstrated in a layer‐by‐layer 3D printed part fabricated by stereolithography, which is subsequently infilled with a soft hydrogel containing osteoblastic cells. In summary, this approach holds promise for applications where integration of multiple materials and living cells is needed by allowing precise control over integration and reducing mechanical failure at contrasting material interfaces.
Local, micromechanical environment is known to influence cellular function in heterogeneous hydrogels, and knowledge gained in micromechanics will facilitate the improved design of biomaterials for tissue regeneration. In this study, a system comprising microstructured resilin‐like polypeptide (RLP)–poly(ethylene glycol) (PEG) hydrogels is utilized. The micromechanical properties of RLP‐PEG hydrogels are evaluated with oscillatory shear rheometry, compression dynamic mechanic analysis, small‐strain microindentation, and large‐strain indentation and puncture over a range of different deformation length scales. The measured elastic moduli are consistent with volume averaging models, indicating that volume fraction, not domain size, plays a dominant role in determining the low strain mechanical response. Large‐strain indentation under a confocal microscope enables the visualization of the microstructured hydrogel micromechanical deformation, emphasizing the translation, rotation, and deformation of RLP‐rich domains. The fracture initiation energy results demonstrate that failure of the composite hydrogels is controlled by the RLP‐rich phase, and their independence with domain size suggested that failure initiation is controlled by multiple domains within the strained volume. This approach and findings provide new quantitative insight into the micromechanical response of soft hydrogel composites and highlight the opportunities in employing these methods to understand the physical origins of mechanical properties of soft synthetic and biological materials.
more » « less- NSF-PAR ID:
- 10458045
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Macromolecular Bioscience
- Volume:
- 20
- Issue:
- 5
- ISSN:
- 1616-5187
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract 3D bioprinting is a promising technology to fabricate custom geometries for tissue engineering. However, most bioprintable hydrogels are weak and fragile, difficult to handle, and cannot mimic the mechanical behaviors of the native soft elastic tissues. A visible light crosslinked, single‐network, elastic, and biocompatible hydrogel system based on an acrylate triblock copolymer of poly(ethylene glycol) PEG and polycaprolactone (PCL) (PEG‐PCL‐DA) is developed. To enable its application in the bioprinting of soft tissues, the hydrogel system is modified on its printability and biodegradability. Furthermore, it is hypothesized that this elastic material can better transmit pulsatile forces to cells, leading to enhanced cellular response under mechanical stimulation. This central hypothesis is tested using vascular conduits with smooth muscle cells (SMCs) cultured under pulsatile forces in a custom‐made bioreactor. The results show that vascular conduits made of PEG‐PCL‐DA hydrogel faithfully recapitulate the rapid stretch and recoil under the pulsatile pressure from 1 to 3 Hz frequency, which induces a contractile SMC phenotype, consistently upregulating the core contractile transcription factors. In summary, this work demonstrates the potential of elastic hydrogel for 3D bioprinting of soft tissues by fine‐tuning the printability, and biodegradability, while possessing robust elastic properties suitable for manual handling and biomechanical stimulation.
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Abstract Background Hydrogels are one of the most ubiquitous polymeric materials. Among them gelatin, agarose and polyacrylamide-based formulations have been effectively utilized in a variety of biomedical and defense-related applications including ultrasound-based therapies and soft tissue injury investigations stemming from ballistic and blast exposures. Interestingly, while in most cases accurate prediction of the mechanical response of these surrogate gels requires knowledge of the underlying finite deformation, high-strain rate material properties, it is these properties that have remained scarce in the literature.
Objective Building on our prior works using Inertial Microcavitation Rheometry (IMR), here we present a comprehensive list of the high-strain rate (> 10
$$^3$$ Methods We analyze existing experimental gelatin IMR datasets and compare the results with prior data on polyacrylamide.
Results We show that a Neo-Hookean Kelvin-Voigt (NHKV) model can suitably simulate the high-rate material response of dynamic, physically crosslinked hydrogels like gelatin, while the introduction of a strain-stiffening parameter through the use of the quadratic Kelvin-Voigt (qKV) model was necessary to appropriately model chemically crosslinked hydrogels such as polyacrylamide due to the nature of the static,covalent bonds that comprise their structure.
Conclusions In this brief we show that knowledge of the type of underlying polymer structure, including its bond mobility, can directly inform the appropriate finite deformation, time-dependent viscoelastic material model for commonly employed tissue surrogate hydrogels undergoing high strain rate loading within the ballistic and blast regimes.
