International Journal of Biological Sciences. International Journal of Medical Sciences. Journal of Bone and Joint Infection. Global reach, higher impact. Theranostics ; single teltow Hydrogels based on gelatin have evolved as promising multifunctional biomaterials. Gelatin is crosslinked with lysine diisocyanate ethyl ester LDI and the molar ratio of gelatin and LDI in the starting material mixture determines elastic properties of the resulting hydrogel.
Degradation and biomaterial-tissue-interaction were investigated in vivo MRI, optical imaging, PET and ex vivo single teltow, histology, serum analysis. Multimodal imaging revealed that the number of covalent net points correlates well with degradation time, which allows for targeted modification of hydrogels based on properties of single teltow tissue to be replaced.
Importantly, the degradation time was also dependent on the number of implants per animal. Despite local mechanisms of tissue remodeling no adverse tissue single teltow could be observed neither locally single teltow systemically.
Finally, this preclinical investigation in immunocompetent mice clearly demonstrated a complete restoration of the original healthy tissue. Autoradiography ex vivo, Biomaterials, Computed tomography, Magnetic resonance imaging, Optical imaging, Positron emission tomography.
In recent years, hydrogel-based biomaterials have evolved as highly versatile and promising tools for clinical [ 1 ] and research [ 2 ] applications. Different hydrogels are produced depending on the specific need, such as soft tissue replacement, organ patches, or drug delivery systems.
Hydrogels with different physical properties can also be designed and implanted in non-self-healing critical size defects, temporarily replacing the extracellular matrix ECMand assisting the healing process for example in bony structures [ 3 ]. The material of choice should be degraded in rates suitable for the envisioned application, allowing optimal ingrowth of cells and supporting the wound healing process.
Tailoring the physicochemical properties of polymers at the start of their single teltow as well as during their degradation may be reached by the formation of polymer single teltow. For this purpose, biopolymers derived from ECM are attractive materials, as they are degradable, offer sites for cell adhesion, and are generally highly biocompatible [ single teltow ].
Current clinical applications for soft tissue replacement focus mainly single teltow the use of collagen or differentially single teltow collagen [ 5 ]. However, immunogenic responses single teltow collagen-based implants have been reported [ 6 ].
In addition, cross-linking agents needed for network formation may show toxic side effects [ 7 ] during material degradation processes [ 8 ], which could induce adverse tissue reactions, such as strong inflammatory and immunogenic responses, thereby adversely affecting the healing process and successful tissue restoration [ 910 ]. Previous research has shown that gelatin, which is the partial thermally and chemically degraded product of collagen, possesses lower immunogenicity than collagen [ 11 ], and can be stabilized through the single teltow of covalent net points [ 12 ].
Gelatin as highly biocompatible, biodegradable, low immunogenic, and low-cost material is therefore highly attractive for single teltow clinical applications e. The use of gelatin-based hydrogels stabilized through reaction with lysine diisocyanate ethyl ester LDI [ 14 ] has already yielded promising in vitro results in the interaction with mesenchymal stem cells [ 15 ] and arterial endothelial cells [ 16 ].
First results from a pilot animal experiment using an immunocompetent nude mouse SKH1 model further revealed single teltow high degree of biocompatibility together with a specific degradation single teltow of the cross-linked gelatin over 35 days. This has been demonstrated single teltow histological Masson Goldner staining and immunohistochemical cyclooxygenase-2 staining single teltow of sections from explants of hydrogels with surrounding tissue ex vivo [ 16 ].
For a better understanding of intra-individual physiological processes as well as potential long lasting and late effects, it is necessary to employ in vivo imaging techniques depicting the degradation of the implant, biomaterial-tissue-interactions, and systemic reactions in a quantitative manner, and to correlate these findings with ex vivo techniques showing local cellular behavior.
Thereby, multimodal and single teltow techniques contribute to a better understanding of the biological response to the hydrogels and will provide selection criteria for potential therapeutic applications. This single teltow small animal multimodal and multiscale imaging study in SKH1 mice conducted in single teltow and ex vivo aimed at detailed elucidation of hydrogel degradation, tissue response, integration, and systemic response at different time points 1, 7, 14, 21, 35 days up to 84 days post subcutaneous implantation of two hydrogels with different numbers of covalent and physical net points.
Animal experiments were performed in accordance with the guidelines of the German Regulations for Animal Welfare. The protocol was approved by the local Ethical Committee for Animal Experiments reference number The implantation procedure was done as described previously [ 16 ].
SKH1 mice age weeks, weight g were implanted subcutaneously s. Subcutaneous skin pockets were formed posterior to incision using surgical scissors. Sham-operated animals followed the same procedure except for the actual hydrogel implantation. Relaxation time was 38 ms. Of single teltow, no MRI contrast agents were used. For single teltow purpose, hydrogels together with surrounding tissue were surgically removed at different time points representing different material sizes for both single teltow. Staining was single teltow in 0.
In vivo luminescence and fluorescence imaging. For luminescence and fluorescence measurements the small animal optical imaging device in vivo Xtreme Bruker was used.
The detection of reactive oxygen species was performed using the click to see more probe L Wako Chemicals. Animals were injected intraperitoneally click at this page. In parallel, the same amount of 0. Exposure time for fluorescence images was 1 s. For the acquisition and quantification of click Bruker Molecular Imaging software version 7.
For luminescence images, net luminescence intensity was determined. To minimize quantification of unspecific auto-fluorescence, fluorescence images of MMP activity measurements were first divided by the reference channel. Subsequently, net fluorescence intensity was quantified. Single teltow small animal positron emission tomography PET after i. Emission data were collected continuously for 60 min.
The data were decay, scatter, and attenuation X-ray corrected. The frames were reconstructed by maximum a posteriori MAP method with 4 iterations and 6 subsets. Standardized uptake values SUVs were calculated over the ROI as single teltow ratio of activity concentration at time t and injected dose at time of injection t 0 divided by body weight. Following PET single teltow 60 min p. Serum sample preparation and analysis.
At selected time points, whole blood samples were collected by heart puncture of 4 anesthetized mice for each group and allowed to clot for 30 min at room temperature. The supernatant was transferred into a single teltow tube and snap frozen in liquid nitrogen single teltow. For histological analysis 3 animals single teltow group were sacrificed at the selected time points. The hydrogels were surgically removed including the surrounding tissue.
For cryosectioning samples were cut through the middle of the remaining hydrogel piece. Samples were embedded in 7. Specific tissue response was visualized using immunohistochemical staining for different cell markers, which are single teltow in Table 1.
Except for VEGFR-2 staining, where a fluorescent secondary antibody Alexa-Fluor was used, biotinylated secondary antibodies were used. Images were acquired using AxioImager. A1 and the appropriate software package AxioVision Carl Zeiss. Fluorescent images were acquired using a laser scanning confocal microscope IX83, Olympus and the appropriate software FluoView Olympus. To this end, the color threshold plugin was used.
RGB values were set for cell nuclei and for immunohistochemically positively stained areas. The positively stained area was divided by area of cell nuclei for AEC staining or by number of cell nuclei for fluorescent staining. Single teltow the measurement of capsule thickness AxioVision Carl Zeiss software single teltow used. Capsule thickness was measured for sections of three different animals per time point. For each section 5 points on each capsule-side the skin- and muscle-side around the implant were measured.
Single teltow data single teltow expressed as means and standard deviations. For correlation between datasets Pearson single teltow coefficient was calculated. To determine the volume of implanted gelatin-based hydrogels, magnetic resonance imaging MRI with a specifically designed T2 weighted measuring sequence was performed.
Hydrogel implantation and visualization. Confocal microscopy images reveal different surface structures of the different hydrogels upper right panel. Implantation workflow is single teltow in the lower panel.
First mice skin is disinfected, second incision and skin pocket is formed, third pre-swollen hydrogel is implanted, fourth just click for source is closed by the use of spray-plaster.
After drawing a volume of interest around the material red sphere and applying a threshold middle panel the volume of the hydrogels could be calculated. Ex vivo cryosections revealed similar sizes for the hydrogels compared to the sizes at the MRI images at the different time points Fig. To determine whether the volume measured by MRI represents the actual volume of the hydrogel, spectral MRI analysis was performed to distinguish free water molecules from non-covalently single teltow water and fatty acid chemical environment protons [ 17 ] Fig.
Spectra of both materials showed only one prominent peak, assigned to the free water signal. Therefore, protons measured within the hydrogel are in single teltow environment of free water, which single teltow in accordance with the situation in a swollen hydrogel [ 3132 ]. Due to similar densities of the gelatin-based hydrogels compared to the surrounding tissue the material could not be visualized and, therefore, not be quantified directly using small animal CT measurements in vivo.
Consequently, volume of implanted hydrogels was initially quantified at different time points after implantation using MRI. The implanted material see more well as the surrounding tissue was surgically removed and explants were further processed for phosphotungstic acid PTA staining.
PTA binds to fibrin, collagen, and other proteins that are ubiquitously present in connective tissues single teltow all organs, allowing analysis of soft tissue using CT ex vivo [ 3334 ]. Therefore, we hypothesized that PTA would also stain the hydrogels, or more precisely the remaining covalently cross-linked gelatin-LDI scaffolds.
Supporting this just click for source, the original implants and, single teltow to progress of degradation, their remains could be clearly visualized and quantified using CT after PTA staining Fig.
This factor is explained by dehydration of hydrogels during the staining procedure. Taken together, the combination of PTA-CT and MRI led to the conclusion that our proposed MRI volume analysis method is indeed reliable for studying size and degradation behavior of implanted gelatin-based hydrogels in vivo.
Successful establishment of the MRI quantification method allowed for assessment of the volumes of implanted hydrogels over the whole degradation period. Importantly, a difference in degradation rates between animals bearing one implant single-implanted or two implants double-implanted was observed.
Important mechanisms for degradation single teltow the gelatin-based hydrogels are hydrolysis and enzymatic degradation [ 16 ].
To investigate to which extent enzymatic degradation plays a role in vivoand to detect potential differences between the two hydrogel-species, MMP activity measurements were link in vivo. In vitro experiments investigating the direct contact between endothelial cells HAECmacrophages activated THP-1 and the hydrogels showed no elevation of MMP levels in the cell culture supernatant [ 16 ].
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