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, 14 (6), 643-51

Size- And Shape-Dependent Foreign Body Immune Response to Materials Implanted in Rodents and Non-Human Primates


Size- And Shape-Dependent Foreign Body Immune Response to Materials Implanted in Rodents and Non-Human Primates

Omid Veiseh et al. Nat Mater.


The efficacy of implanted biomedical devices is often compromised by host recognition and subsequent foreign body responses. Here, we demonstrate the role of the geometry of implanted materials on their biocompatibility in vivo. In rodent and non-human primate animal models, implanted spheres 1.5 mm and above in diameter across a broad spectrum of materials, including hydrogels, ceramics, metals and plastics, significantly abrogated foreign body reactions and fibrosis when compared with smaller spheres. We also show that for encapsulated rat pancreatic islet cells transplanted into streptozotocin-treated diabetic C57BL/6 mice, islets prepared in 1.5-mm alginate capsules were able to restore blood-glucose control for up to 180 days, a period more than five times longer than for transplanted grafts encapsulated within conventionally sized 0.5-mm alginate capsules. Our findings suggest that the in vivo biocompatibility of biomedical devices can be significantly improved simply by tuning their spherical dimensions.

Conflict of interest statement

Competing Financial Interests

The authors declare no competing financial interests.


Figure 1
Figure 1. Increasing alginate sphere size results in reduced cellular deposition and fibrosis formation on the spheres
SLG20 alginate spheres (0.5 ml in volume) of 8 different sizes (0.3, 0.4, 0.5, 0.6, 0.7, 1, 1.5, and 1.9 mm) were implanted into the intraperitoneal space of C57BL/6 mice, where they were retained for 14 days and analyzed for degree of fibrosis upon retrieval. Dark field phase contrast images obtained from retrieved spheres reveal a significant decrease in level of cellular overgrowth with increase in sphere size (a); scale bar = 2mm). Z-stacked confocal images of retrieved spheres immunofluorescence stained with DAPI (highlighting cellular nuclei), phalloidin (Highlighting F-actin), and α-Smooth Muscle Actin (α-SMA, Myofibroblast cells) (b); Scale bar = 300μm). q-PCR based expression analysis of fibrotic markers α-SMA (c), Collagen 1a1 (d, Col1a1), and Collagen 1a2 (e, Col1a2) directly on the 8 various sized (0.3, 0.4, 0.5, 0.7, 0.9, 1, 1.5, 1.9 mm) spheres plotted normalized to relative expression levels on 300 μm sized spheres. Semi-quantitative western blot analysis of analysis of α-SMA expression in cell overgrowth from on microspheres (1–5 labeling of bands corresponds to individual mice) (f). Plot of analyzed band intensities from western blot images shown in f (g). Error bars, mean ± SEM. N = 5 mice per treatment. All experiments were performed at least three times. qPCR and western blot statistical analysis: one-way ANOVA with Bonferroni multiple comparison correction *: p < 0.05, **: p < 0.001, and ***: p < 0.0001.
Figure 2
Figure 2. Increasing the spherical diameter of a variety of materials including, hydrogels, ceramics, metals, and plastics results in reduced foreign body responses
Bright-field images obtained from retrieved medium (0.5 mm) and large (1.5–2 mm) sized versions of SLG20 alginate, LF10/60 alginate (endotoxin containing), glass, and polystyrene 14 days post intraperitoneal implant into C57BL/6 mice (a); Scale bar = 2 mm. Panel of representative immunofluorescence Z-stacked confocal images of materials stained for cell nuclei (DAPI, blue), macrophages (CD68, green) and fibrosis-associated activated myofibroblasts (α-SMA, red) (b); scale bar = 300 μm. Flow analysis, using specific markers for responding host macrophage (c) neutrophils (d); Mock = surgery and PBS only injection, SLG = SLG20 alginate, LF = LF10/60 alginate (endotoxin containing), PCL = polycaprolactone, and PS= polystyrene. Elispot multiplexed based cytokine array profiling of inflammatory cytokine protein production in response to implanted materials (e); SL = SLG20 alginate, LF = LF10/60 alginate (endotoxin containing), ST= stainless steel, GL = glass PC = polcaprolactone, and PS= polystyrene. Error bars, mean ± SEM. N = 5 mice per treatment. All experiments were performed at least three times. FACS size comparisons were performed by unpaired, two-tailed t-test *: p < 0.05, **: p < 0.001, and ***: p < 0.0001.
Figure 3
Figure 3. Comparing the size and shape dependence effects of fibrosis formation on to alginate hydrogels implanted in the subcutaneous dorsal region of non-human primates
Large 1.5 mm-sized spheres of SLG20 hydrogels implanted subcutaneously in the dorsal region of cynomolgus macaques resist fibrosis, while small spheres (0.5 mm sized) and cylinders (4 mm in diameter and 2 mm in height) become fibrotic. After 14 days, biopsy punches were used to excise implanted materials/peripheral host tissue; upon incision we observed that the large SLG20 alginate spheres were not embedded in host tissue and freely dissociated from the implant site (a). The retrieved large SLG20 hydrogels visually appear to be transparent and void of cellular deposition (b), which was also confirmed using H&E stained histological analysis (c); Scale bar = 500 μm. H&E and Masson’s Trichrome stained histological sections of excised tissue at 14 days (d, Scale bar = 500 μm), and 28 days (e, Scale bar = 500 μm) post-implantation with SLG20 alginate hydrogels formed into large spheres (1.5 mm in diameter), medium sized spheres (0.5 mm in diameter) or cylinders (4 mm in diameter and 1 mm in height), and as well a control saline alone injection (* in images demarks implanted materials). N = 2 for saline and discs; N = 4 for both 0.5 and 1.5 mm sphere groups. These experiments were performed once.
Figure 4
Figure 4. Comparison of 0.5 mm and 1.5 mm alginate capsules encapsulating rat islets (500 IE’s) in curing STZ-induced C57BL/6 diabetic mice
Live/dead staining confirming viability of islet cells post-encapsulation for large 1.5 mm as well as standard 0.5 mm capsules (a); Scale bar = 1000 μm. Blood glucose curves showing prolonged normoglycemia with large 1.5 mm diameter hydrogel alginate capsules, but only short-lived success with standard 0.5 mm diameter capsules (b). In vivo Glucose Tolerance Test (iv GTT) of healthy mice and diabetic mice 7 days post-transplantation with rat islets encapsulated in standard (0.5 mm) or large sized capsules (1.5 mm) shows no significant delays in BG correction as a function of capsule geometry (c). Kaplan-Meier plot showing fraction of cured STZ-C57BL/6 mice after being transplanted with either 0.5 mm or 1.5 mm diameter capsules, containing 500 IE’s of primary rat islets (d). Representative dark field phase contrast images of retrieved 0.5 mm or 1.5 mm alginate islet-containing capsules 6 months after transplantation show higher levels of cellular overgrowth on 0.5 mm capsules (e); Scale bar = 2000 μm. Confocal imaging panel showing nuclear DAPI (left), Newport green (islet marker, center), and overlay with bright field images of visible capsules (right) (f); Scale bar = 300 μm. Rat PDX-1 and host alpha smooth muscle actin expression from capsules retrieved from STZ treated mice 175 days post-transplant. As a reference, β-actin expression levels are also shown (g). qPCR analysis of rat islet marker Pdx1 expression in retrieved 0.5 or 1.5 mm alginate capsules (h). Error bars, mean ± SEM. N = 5 mice per treatment. All experiments were performed at least two or three times. qPCR statistical analysis: one-way ANOVA with Bonferroni multiple comparison correction *: p < 0.0001.
Figure 5
Figure 5. Kinetic profiling of host response to SLG20 alginate microspheres of 0.5 and 1.5 mm sizes in diameter
Flow analysis, using specific markers for responding host innate immune myeloid (a), neutrophil (b), and macrophage cells (c) at 1, 4, 7, 14, and 28 days post-implantation. In vivo intravital imaging of macrophage behavior and accumulation at 1, 4, or 7 days post-implantation (d). NanoString-based analysis for expression of macrophage phenotype markers analyzed from deposited cell RNA extracts at 1, 4, and 7 days post-implant, presented on a base 2 logarithmic scale (e). Error bars, mean ± SEM. For FACS analysis N = 5 mice per treatment, for intravital imaging: N = 3 mice per treatment, for Nanostring analysis N = 4 per treatment. FACS and intravital imaging experiments were performed twice and nanostring analysis was performed once. FACS size comparisons were performed by unpaired, two-tailed t-test *: p < 0.05, **: p < 0.001, and ***: p < 0.0001. For nanostring statistical analyses see supplemental methods.

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