Nanoengineered Shape-Memory Hemostat

Abstract

Uncontrolled hemorrhage is the predominant cause of preventable combat deaths. Various biomaterials serve as hemostatic agents due to their procoagulant or absorptive activity. However, these biomaterials often lack expansion capabilities, which severely limits use in noncompressible wounds. This study combines a hemostatic nanocomposite with a shape-memory polymer foam to design a composite material with both hemostatic and physical expansion properties. This composite is fabricated in two formulations: a foam externally coated in a highly concentrated nanocomposite ("coated composite") and a foam containing a diluted nanocomposite infused throughout its pores ("infused composite"). Both formulations retain the shape-memory foam's expansion property. Further, the coated composite shows improved fluid uptake (>2-fold) versus infused composites or foam. The nanocomposite component dissociates from the foam under degradative conditions, with the foam remaining stable for 30 days. Hemostatic studies illustrate that the coated composite reduces the clotting time by ≈20%. Alternatively, the infused composite improves clotting over a larger distance (up to ≈2× distance from the composite). These results signify a modular hemostatic ability: the coated composite reduces clotting and improves fluid uptake, while the infused composite achieves diffuse clotting and maintains mechanical properties. Thus, these materials pose a strong potential for use in noncompressible wounds.

Keywords: expandable biomaterials; hemostats; nanocomposites; porous materials; wound healing.

Figure 1

Design and fabrication of a nanoengineered shape memory biomaterial. A) Schematic representation of coated and infused composite fabrication. The figure was produced using Biorender.com. B) Optimization of nanocomposite demonstrating infiltration of nanocomposite within foam's porous structure at various concentrations of nanosilicate (nSi) and gelatin (gel). Representative images are shown. N = 6; bars show mean ± standard error of the mean; Ordinary one‐way ANOVA with Tukey multiple comparison test, ****p < 0.0001 (GraphPad Prism 9, exact p values are provided in Table S1, Supporting Information). C) Light photographs and SEM images of nanocomposite (6% nSi 3% gelatin), foam, coated composite, and infused composite showing microporous structure of nanocomposite, macroporous structure of foam, and combined macro‐ and microporous structures of coated and infused composites. D) EDS analysis of foam, coated composite, and infused composite highlighting the presence of nanosilicates, indicated by the presence of Mg and Si ions. Representative images and spectra are shown. Abbreviations: nSi ‐ nanosilicate; gel ‐ gelatin.

Figure 2

Degradation characteristics and cytocompatibility of foam and composites. A) Schematic of nanocomposite (purple) dissolution and foam (gray) degradation. The figure was produced using Biorender.com. B) Accelerated oxidative degradation of foam, infused composites, and coated composites for up to 30 days. N = 4; points show mean ± standard deviation. C) Accelerated oxidative degradation of foam and coated composites up to 90 days. N = 4; points show mean ± standard deviation. D) Accelerated hydrolytic degradation of foam and coated composites for up to 90 days. N = 4; points show mean ± standard deviation. E) Initial and day 30 FTIR spectra for foam, infused composite, and coated composite with identification of peaks relevant to foam and composite structures. F) SEM images showing porous structure and surface degradation. Representative images are shown. G) FTIR spectra before and after E‐beam sterilization at 43.8 kGy showing maintenance of relevant peaks between non‐ and E‐beam sterilized samples. H) Cellular proliferation following treatment with media containing solutes leached from composite. Cellular proliferation was determined via Alamar Blue assay. N = 4; bars show mean ± standard error of the mean (two‐way ANOVA with Tukey post hoc test in GraphPad Prism 9.0. *p < 0.0332, **p < 0.0021, ***p < 0.0002, and ****p < 0.0001). Abbreviations: E‐beam ‐ electron‐beam; comp ‐ composite.

Figure 3

Expansion characterization of composites and foam. A) Expansion of foam, infused composite, and coated composite in deionized water (n = 5); points show mean ± standard error of the mean. Representative images of foam are shown. B) Expansion of foam, infused composite, and coated composite in PBS (n = 5); points show mean ± standard error of the mean. Representative images of the infused composite are shown. C) Expansion of foam, infused composite, and coated composite in citrated bovine blood plasma (n = 4); points show mean ± standard error of the mean. Representative images of the coated composite are shown. D) Radial expansion force when submerged in deionized water (n = 5); representative curve shown for visual clarity. E) Axial expansion force when submerged in PBS (n = 6); points shown are mean. Standard deviation is not shown for visual clarity. F) Comparison of axial expansion forces. Bar graphs show mean ± standard deviation (two‐way ANOVA with Tukey multiple comparisons test). G) Swelling ratio of foam, infused composite, and coated composite in PBS at 37 °C (n = 3); points show mean ± standard deviation (Ordinary one‐way ANOVA with Tukey multiple comparisons test) H) Raw (non‐normalized) fluid absorbed per sample type. Samples are all 1 cm cubes (n = 3); points show mean ± standard deviation (Ordinary one‐way ANOVA with Tukey multiple comparisons test). I) Expansion profile of coated composites before and after E‐beam sterilization at 43.8 kGy (n = 3); points show mean ± standard deviation. Statistical significance is indicated by *p < 0.0332, **p < 0.0021, ***p < 0.0002, ****p < 0.0001, GraphPad Prism 9.

Figure 4

Hemostatic properties of composites. A) Quantitative clotting time measurement via inversion test (n = 8); bars show mean ± standard deviation (ordinary one‐way ANOVA with Tukey multiple comparisons test, different letters indicate statistically significant differences of at least p < 0.0332, GraphPad Prism 9, exact p values are shown in Table S2, Supporting Information). B) Qualitative hemostatic assessment under static conditions for composites and component materials. Representative images are shown. C) Qualitative hemostatic assessment under static conditions with variable “cavity” volumes. Representative images are shown. D) Quantification of spread of clot formation (n = 5); bars show mean ± standard deviation (two‐way ANOVA with Tukey multiple comparisons test, different letters indicate statistically significant differences of at least p < 0.0332, GraphPad Prism 9, exact p values are shown in Table S3, Supporting Information).

Figure 5

Absorption of blood by expandable composite hemostat. A) Schematic of composite expansion and blood absorption. The figure was produced using Biorender.com. B) Time‐lapse snapshots of foam, infused composite, and coated composite when placed into pooled blood at 0 s (top) and 120 s (bottom). C) SEM images showing blood cell infiltration and formation of fibrin networks within foam and composites’ porous structures. Representative images are shown. D) Quantification of blood volume absorbed by foam, infused composite, and coated composite over a period of 10 min. Experiment conducted in two rounds: Round 1: n = 3 foam and n= 3 coated composites. Round 2: n = 3 foam and n = 3 infused composites. Points show mean ± standard deviation. Two‐way ANOVA with Tukey multiple comparisons test; no statistical significance was present between sample types at any given time point. Statistical analysis conducted in GraphPad Prism 9. Exact p values are shown in Table S4, Supporting Information. E) Visualization of blood volume absorbed and sample expansion over a period of 10 min. (Representative images for (D)).

Figure 6

Hemostat delivery and practical use. A) Schematic of hemostatic particle injector. The figure was produced using Biorender.com. Inset: compressed infused composite particles. B) Schematics and photographs of custom‐designed injector. Schematics were produced using SolidWorks (Dassault Systèmes, France). C) Average force required to inject composite hemostat particles. N = 5; bars show mean ± standard deviation. Line for 71 N indicates maximum force requirement desired. Ordinary one‐way ANOVA with Tukey multiple comparisons test, different letters indicate statistically significant differences of at least p < 0.0332. Statistical analysis conducted in GraphPad Prism 9. Exact p values are shown in Table S5, Supporting Information. D) Peak force required to inject composite hemostat particles. N = 5; bars show mean ± standard deviation. Line for 71 N indicates maximum force requirement desired. Ordinary one‐way ANOVA with Tukey multiple comparisons test, different letters indicate statistically significant differences of at least p < 0.0332. Statistical analysis conducted in GraphPad Prism 9. Exact p values are shown in Table S6, Supporting Information. E) Composite dimensions before and after injection. N = 10; bars show mean ± standard deviation. Individual points are omitted for visual clarity. Two‐way ANOVA with Sidak multiple comparisons test; no statistical significance was found between measurements taken before and after injection for any given dimension. Statistical analysis conducted in GraphPad Prism 9. Exact p values are shown in Table S7, Supporting Information. F) Cavity model of penetrating trauma with expansion of injected particles.