Rapid synthesis of degradable polyols based on esters and thioethers for use in polyurethanes

Abstract

A degradable polyurethane (PUr) having degradation rates useful for hemostatic dressings for controlling bleeding in traumatic wounds. Degradable PUrs may be synthesized from degradable monomers based on hydrolytically labile esters and oxidatively labile thioethers using rapid click-chemistry reactions. Monomers may include trimethylolpropane tris(3-mercaptopropionate) (TMPMP), dipentaerythritol hexakis(3-mercaptopropionate) (DPEHMP), dipentaerythritol hexakis(3-mercaptopropionate) (DPEHMP) or 2,2'-(ethylenedioxy) diethanethiol reacted with hydroxyethyl acrylate, 3-buten-1-ol, 3-methyl-3-buten-1-ol, or 3-buten-2-ol. Synthesis of these monomers is rapid and has no byproducts or toxic catalysts that require removal, enabling polyol synthesis and immediate use in further polymerization

Description

TITLERAPID SYNTHESIS OF DEGRADABLE POLYOLS BASED ON ESTERS AND THIOETHERS FOR USE IN POLYURETHANESBACKGROUND1. FIELD OF THE INVENTION

[0001] The present disclosure relates to the polyol monomers and, more particularly, to the rapid synthesis of novel polyol monomers with degradable ester and thioether linkages to provide degradable polymers.2. DESCRIPTION OF THE RELATED ART

[0002] One and a half million people die every year from uncontrolled bleeding in traumatic wounds, such as gunshot wounds. Although gauze and tourniquets have remained the gold standard of treatment for such wounds, they have major limitations. Gauze and tourniquets are only effective for wounds that can be compressed, such as extremity injuries to limbs; they cannot be used for non-compressible bleeds (e.g., injuries to the neck or torso), which make up more than 90% of military-related trauma deaths. Additionally, gauze must eventually be removed from the wound, and 100% of gauze-treated wounds experience rebleeding upon removal. Similarly, XStat, an alternative commercial treatment option, is only approved for use up to four hours and requires a 22-fold increase in time to remove compared to gauze. Removal of XStat within this time frame is not always possible in prolonged field care scenarios, posing a major safety concern for patients. Even if these patients can seek proper medical care within a safe time frame, non-degradable dressings must be fully removed before surgery

[0003] Polyurethanes are widely employed in biomedical applications, including aneurysm treatment, wound dressings, coatings, and hemostatic dressings. Polyurethane (PUr) shape memory polymer foams have the potential to act as both a hemostatic dressing to stop uncontrolled bleeding in traumatic wounds and a scaffold to facilitate tissue regeneration. For this application, polyurethane foams should be left to degrade in the wound as it heals. However, previously developed PUr foams have too slow of a degradation rate to be clinically relevant for wound healing applications.

[0004] PUrs have been modified and functionalized with other synthetic (e.g., polyester polyols, polyethers, polycarbonates, or polycaprolactones) or bioactive (gelatin, chitosan, or hydroxyapatite) monomers to make biodegradable PUrs. Previously synthesized PUr with hydrolytically labile ester linkages had -30% mass remaining at 12 weeks in a rat subcutaneous implant model, missing the target of 100% mass loss in <3 months. Thus,previous attempts to incorporate degradable ester linkages into polyurethanes have resulted in slowly degrading scaffolds due to the hydrophobicity of the polyurethane network that prevents water access to the hydrolytically-labile ester groups. Additionally, previous approaches to degradable polyol synthesis require long time frames (1-2 days) for synthesis and difficult purification strategies. Accordingly, there is a need in the art for an approach that can provide polyurethane shape memory polymers that have enhanced degradation susceptibility and are easily synthesized.BRIEF SUMMARY OF THE INVENTION

[0005] The present invention provides an approach for easily synthesizing polyurethanes that incorporate degradable ester and thioester linkages for enhanced degradation susceptibility. The present invention includes a library of degradable polyols containing esters and thioethers for use in PUr foam fabrication. Notably, the degradable linkages were synthesized using a simple, rapid, solvent-free click-chemistry reaction from readily available reactants. This process resulted in monomers with essentially 100% yield with no need for purification that were ready to use during PUr synthesis within a matter of minutes after fabrication. For example, the present invention may employ a thioether adjacent to the ester linkages, which can be oxidized to enhance degradation susceptibility. The thioether also accelerates hydrolysis of the ester linkages, and this degradation susceptibility of the monomer can be tuned by altering the space between the ester and thiol groups.

[0006] In one embodiment, the present invention may be a degradable composition comprising a polythiol monomer having a thioether coupled to an ester by no more than two methylene groups. The polythiol monomer may comprise any reactant with two to four free thiol groups reacted with any other reactant with a terminal vinyl group and a terminal hydroxyl group. These monomers may comprise trimethylolpropane tris(3- mercaptopropionate) reacted with hydroxyethyl acrylate, 3-buten-l-ol, 3-methyl-3-buten-l- ol, or 3-buten-2-ol. Alternatively, these monomers may comprise trimethylolpropane tris(thioglycolate) reacted with hydroxyethyl acrylate, 3-buten-l-ol, 3-methyl-3-buten-l-ol, or 3-buten-2-ol, or dipentaerythritol hexakis(3 -mercaptopropionate) reacted with hydroxyethyl acrylate, 3-buten-l-ol, 3-methyl-3-buten-l-ol, or 3-buten-2-ol. Alternatively, these monomers may comprise 2,2'-(ethylenedioxy) diethanethiol reacted with hydroxyethyl acrylate. The polythiol monomer may then be polymerized along with an isocyanate to form a PUr having the desired degradation characteristics.

[0007] In another embodiment, the present invention may be a method of forming a degradable composition comprising the step reacting a thiol with hydroxyethyl acrylate, 3-buten-l-ol, 3-methyl-3-buten-l-ol, or 3-buten-2-ol to form a polythiol monomer having a sulfide group adjacent to an ester. The method may further comprise the step of polymerizing the polythiol monomer with an isocyanate to form a polyurethane. The thiol may be selected from the group consisting of trimethylolpropane tris(3 -mercaptopropionate), dipentaerythritol hexakis(3-mercaptopropionate), or 2,2'-(ethylenedioxy)diethanethiol. The isocyanate may be hexamethylene diisocyanate, isophorene diisocyanate, toluyene diisocyanate, methylene diisocyanate, or trimethylhexamethylene diisocyanate.

[0008] The present invention provides for a quick (6 minute) synthesis of the monomers with no byproducts or toxic catalysts that require removal, enabling polyol synthesis and immediate use in further polymerization. The rapid synthesis and high yield of the monomers of the present invention may highly benefit the polyurethane industry, allowing for the quick and easy production of PUrs with tunable degradation rates for use in implantable biomedical device applications. The design of a biodegradable PUr has vast potential to improve outcomes for traumatic wounds by enabling tissue regeneration after placement, ultimately reducing traumatic wound morbidity and mortality for millions of patients each year.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0009] The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:

[0010] FIG. 1 is a schematic of polythiol synthesis (scheme 1) and polyurethane synthesis (scheme 2). The resulting polythiols in scheme 1 are named based on number of arms (trithiol [T] or hexathiol [H]) and the number of methylene groups between the sulfide and ester(s) (1 and / or 2). Scheme 2a shows the general reaction for polyurethanes, and scheme 2b shows the specific monomers used during synthesis. HE A: hydroxyethyl acrylate, DPEHMP: dipentaerythritol Hexakis(3-mercaptopropionate), LAP: lithium phenyl (2,4,6- trimethylbenzoyl) phosphinate, TEA: triethylamine, TMPMP: trimethylolpropane tris(3 - mercaptopropionate), TMPTTG: trimethylolpropane Tris(thioglycolate), HDI: hexamethylene diisocyanate, HPED: N,N,N',N'-tetrakis-(2-hydroxy- propyl)- ethylenediamine, and TEtA: triethanolamine.

[0011] FIG. 2 is FTIR spectra of the polythiol synthesis reactions for a) the singleester monomers and b) the two-ester monomers. Consumption of the thiol peak confirms complete functionalization with the hydroxyl end groups.

[0012] FIG. 3 is a series of charts of PUr foam material properties, a) SEM micrographs of foam pore structure and a representative PUr foam. Scale bar (1000 pm) applies to all SEM images, b) Average pore sizes of each foam formulation, c) Glass transition temperature of each foam formulation, d) Foam swelling ratios after 24 h in 37°C water. The compressive modulus of e) dry and f) wet foam samples, n = 3, mean ± standard deviation displayed. *p<0.05 relative to control foam.

[0013] FIG. 4 is a series of graphs of foam degradation over 12 weeks in vitro. Mass loss in 3% H2O2 for a) single-ester foams and b) two-ester foams. Mass loss in 0.1 M NaOH for c) single-ester foams and d) two-ester foams, n = 3, mean ± standard deviation displayed.

[0014] FIG. 5 is a series of images of erosion profiles and changes in pore morphology throughout degradation, a) Erosion profdes for each foam at day 0, days 28, 56, and 84 in 3% H2O2, and days 29, 50, and 84 in 0.1 M NaOH. Scale bar applies to all images, b) SEM micrographs of pore structure for each foam at day 0, days 28, 56, and 84 in 3% H2O2, and days 29, 50, and 84 in 0.1 M NaOH. Scale bar applies to all images.

[0015] FIG. 6 is a series of graphs of FTIR spectra for each foam formulation at days 0 and 84 in both degradation media (3% H2O2 and 0.1 M NaOH). Changes in peaks corresponding to tertiary amine oxidation, sulfide oxidation, urethane oxidation, and ester hydrolysis, respectively, are indicated.

[0016] FIG. 7 is a series of graphs of changes in foam a) swelling ratios b) wet compressive moduli c) dry density and d) glass transition temperature throughout degradation in 3% H2O2 and 0.1 M NaOH. A and C: n = 3, mean ± standard deviation displayed. *p<0.05 relative to day 0. B and D: n = 1.

[0017] FIG. 8 is a series of graphs of foam safety and blood-material interactions, a) Degradation byproduct cytocompatibility at 24, 48, and 72 h at 1X-32X dilutions, b) Hemolysis of each foam, QCCG, and positive (PBS) and negative (DI water) controls after 1 h incubation in Na-citrated whole porcine blood, c) Prothrombin concentrations after 1 h incubation in Na-citrated whole porcine blood, d) Weight percent of blood absorption after 1 h incubation in Na-citrated whole porcine blood, e) SEM micrographs of platelet interactions on foams after 1 h incubation in Na-citrated whole porcine blood. Scale bar applies to all images. QCCG: QuikClot Combat Gauze (clinical control), n = 3, mean ± standard deviation displayed. *p<0.05 relative to control foam.DETAILED DESCRIPTION OF THE INVENTION

[0018] Referring to the figures, wherein like numerals refer to like parts throughout, the present invention is an approach for forming polyurethanes with degradable linkages sothat degradation more closely matches the rate of traumatic would healing. More specifically, to increase the degradation rate, monomers containing esters and sulfides were synthesized using a solvent- free, click chemistry reaction by reacting ester-containing polythiols, such as trimethylolpropane tris(3 -mercaptopropionate) (TMPMP), dipentaerythritol hexakis(3- mercaptopropionate) (DPEHMP) and dipentaerythritol hexakis(3 -mercaptopropionate) (DPEHMP), with reactants that contain one vinyl group and one hydroxyl group, such as 3- buten-l-ol or 2-hydroxyethyl acrylate (HEA), using lithium phenyl-2,4,6- trimethylbenzoylphosphinate (LAP) photoinitiator and UV light. The reaction of the present invention yielded sulfide-containing monomers with hydroxyl end groups that can react with isocyanates to produce PUr foams having the desired material characteristics. The present invention thus provides a platform of biodegradable PUr foams for use in traumatic wound healing.

[0019] EXAMPLE

[0020] Materials

[0021] N,N,N',N'-tetrakis-(2-hydroxy- propyl)-ethylenediamine (HP ED), triethanolamine (TEtA), hexamethylene diisocyanate (HD I), dibutyltin dilaurate (DBTDL), trimethylolpropane tris(thioglycolate) (TMPTTG), and triethylamine (TEA) were purchased from Fisher Scientific (Waltham, MA) and used as received. Trimethylolpropane tris(3- mercaptopropionate) (TMPMP), dipentaerythritol hexakis(3 -mercaptopropionate) (DPEHMP), 3-buten-l-ol, 2-hydroxyethyl acrylate (HEA), lithium phenyl-2, 4,6- trimethylbenzoylphosphinate (LAP) photoinitiator, and l,4-diazabicyclo[2.2.2]octane (DABCO 33 LV) were purchased from Sigma Aldrich (St. Louis, MO) and used as received. Hydrogen peroxide (H2O2, certified ACS, 30%), sodium hydroxide (NaOH), and ethanol (reagent alcohol) were purchased from Fisher Scientific (Waltham, MA). Vorasurf DC 198 surfactant was provided by DOW (Midland, MI).

[0022] Synthesis of Polythiols

[0023] TMPMP, TMPTTG, and DPEHMP were reacted with 3-buten-l-ol or HEA using click chemistry to yield polythiols with free hydroxyl (OH) end groups. Figure 1 (scheme 1) shows the reaction scheme for each of the resulting polythiols, identified by the number of arms (trithiol [T] or hexathiol [H]) and how many methylene groups are present between the ester(s) and sulfide moieties (1 or 2), since both characteristics directly relate to their expected degradation rate. One mol of TMPMP, TMPTTG, or DPEHMP was combined with 3, 3, or 6 mols of 3-buten-l-ol, respectively, to react the free thiols with the vinyl group. LAP photoinitiator was added to each monomer mix at 0.01 wt% via mixing in a high-speedmixer (Flacktek, Inc., Landrum, SC) at 3500 rpm for 30 seconds. The monomer mixes were then placed in a UV light box (365 nm) for 6 minutes. A Nicolet i70 attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectrometer (Fischer Scientific, Waltham, MA) was used to monitor reaction progression at 0, 3, and 6 minutes (absorbance measured at 4 cm'1resolution and presented as an average of 16 scans). Successful formation of the thioether was indicated by the disappearance of the thiol and vinyl peaks at 2540 cm'1and 1640 cm'1, respectively, and the formation of the thioether peak at 1230 cm'1(Figure 2a).!H nuclear magnetic resonance (NMR, Bruker Avance III HD 400 MHz) was used to confirm the final trithiol and hexathiol products. Each spectrum was collected in CDCh at 298 K using the TMS / solvent signal as an internal reference. 1HNMR (CDC13; ppm): T-2: 0.91 (t, - CH2C / L, 3H), 1.32 (q, -C / LCH3, 2H), 1.50 (tt, -SCH2C / LCH2CH2OH, 6H), 1.73 (tt, - SCH2CH2C / / 2CH2OH, 6H), 2.60 (t, -COC / L-, 6H), 2.76 (t, -CH2CH2-, 12H), 3.67 (t, - C / LOH, 6H), and 4.06 (s, -C / LOCO-, 6H). T-l: 1.06 (t, -CH2CH3, 5H), 1.62 (q, - SCH2C / / 2C / / 2CH2OH, 12H), 2.60 (tt, -CH2SCH2-, 6H), 3.17 (tt, -COC / LS-, 6H), 3.59 (t, - C / LOH, 6H), and 4.06 (s, -C / LOCO-, 6H). H-2: 1.70 (tt, -SCH2CLLC / LCH2OH, 24H), 2.62 (tt, -COC / L-, 12H), 2.78 (t, -CL SCL -, 24H), 3.45 (s, -CH2OCH2-, 4H), 3.65 (t, -C / LOH, 12H), and 4.12 (s, -C / LOCO-, 12H).

[0024] Similarly, 1 mol of TMPMP, TMPTTG, or DPEHMP was mixed with 3, 3, or 6 mols of HEA, respectively, and 1 wt% TEA at 3500 rpm for 30 seconds to form monomers with two ester linkages. This reaction occurred immediately upon mixing. ATR-FTIR and NMR were performed on the final product. Successful formation of the thioether was indicated through ATR-FTIR by the disappearance of the thiol and vinyl peaks at 2540 cm'1and 1620 cm'1, respectively, and the formation of the thioether peak at 1100 cm'1(Figure 2b). 1HNMR (CDC13; ppm): T-2, 2: 0.85 (t, -CH2C / L, 3H), 1.46 (q, -C / / 2CH3-, 2H), 2.60 (dt- C / / 2CH2SCH2CH2C / L-, 12H), 2.76 (t, -CH2CH2-, 12H), 3.74 (t, -C / LOH, 6H), 4.00 (s, - C / LOCO-, 6H), and 4.18 (t, -COOC / L-, 6H). T-l, 2: 0.87 (t, -CH2C / L, 3H), 1.46 (q, - C / LCH3, 2H), 2.62 (t, -SCH2C / LCO-, 6H), 2.86 (t, -SC / LCH2CO-, 6H), 3.23 (s, -COC / LS-, 6H), 3.76 (t, -C / LOH, 6H), 4.06 (s, -C / LOCO-, 6H), and 4.18 (t, -COOC / L-, 6H). H-2, 2: 2.60 (t, -CH2CH2SCH2CH2CH2-, 24H), 2.74 (t, -CH2CH2-, 24H), 3.37 (s, -CH2QCH2-, 4H), 3.76 (t, -C / LOH, 12H), 4.08 (s, -C / LOCO-, 12H), and 4.18 (t, -COOC / L-, 12H).

[0025] Foam synthesis

[0026] The overall PUr foam reaction scheme is shown in Figure 1 (scheme 2). The resulting trithiols (T) and hexathiol (H) were incorporated during PUr foam synthesis at 15 or 30 mol% of the total hydroxyl molecular equivalents, resulting in 13 different foamformulations, including the control foam. Sample ID descriptions are outlined in Table 1. First, an NCO premix was made inside of a controlled atmosphere glovebox (Labconco, Inc., Kansas City, MO) by combining 100% of the NCO mol equivalents (HD I) with a 0.35 mol ratio of the total OH equivalents (HPED with either TEtA (control) or one of the newly synthesized polythiol monomers). The premix was then speed-mixed at 3500 rpm for 30 s and placed in a 50°C oven to react for 48 h. After 48 h, an OH mix was made by combining the remaining 0.65 OH mol equivalents (HPED with either TEtA or one of the polythiols) with deionized (DI) water, DBTDL, and DABCO. This mixture was again combined at 3500 rpm for 30 s. Then, the NCO premix was removed from the oven, cooled to room temperature, and the surfactant was added and combined at 3500 rpm for 30 s. Lastly, the NCO premix and OH mix were combined at 1800 rpm for 10 s, quickly poured into a cylindrical mold, and allowed to foam in a 50°C oven for 5 minutes. The added wt% of each reactive foaming component is summarized in Table 2. The surfactant was added at 7.3 wt% for all foam formulations. All foams were washed with DI water and 70% ethanol to remove catalysts and surfactant before characterization and analysis.

[0027] Spectroscopic analysis

[0028] To confirm the incorporation of the degradable polythiols into each foam, the surface chemistry was characterized using ATR-FTIR spectroscopy. Small foam pieces (~2 mg) were scanned at a resolution of 4 cm'1. Spectra of the samples were generated using OMNIC software and presented as absorbance vs. wavelength over an average of 16 scans. Successful incorporation of the polythiols into each foam was indicated by a C=O stretch and an O-C-C stretch from the ester at 1700 cm'1and 1100 cm'1, respectively.

[0029] Foam pore analysis

[0030] Foam samples (~1 cm3, n=6) were cut from the top, middle, and bottom of each foam along parallel and perpendicular directions relative to the foam-rise direction during foam synthesis. Samples were then coated in gold for 45 s using a high vacuum sputter coater (Denton Vacuum, Moorestown, NJ). A JEOL JSM 5600 or JEOL JSM-IT100 scanning electron microscope (SEM, JEOL USA, Peabody, MA) was used to image pore morphology at 10 kV and 25X magnification. ImageJ was used to quantify pore size (average taken from at least 6 pores in at least 3 images) from the SEM micrographs.

[0031] Density

[0032] The volume of cylindrical foam samples (n=3, ~1 cm length, 8 mm diameter) was calculated from the length and an average of 3 diameter measurements along the length. Their mass was obtained, and density was calculated for the foams in their expanded, open- porous shape. To determine their density while crimped, the same foam samples were heated to 70°C for 15 minutes, crimped radially in a manual crimper (Blockwise Engineering, Tempe, AZ), and then cooled to room temperature. Then, the crimped volume was determined, and the crimped foam density was calculated based on the mass.

[0033] Swelling ratio

[0034] Cylindrical foam samples (n=3, ~1 cm length, 8 mm diameter) were prepared with a biopsy punch, and their dry mass (Wa) was measured. Then, the foam samples were submerged in DI water for 24 h. After 24 h, the samples were gently patted with Kimwipes to remove excess water, and the swollen mass was measured (Ws). Swelling ratio (SR) was calculated as

[0036] Thermal analysis

[0037] Samples (n=3, 3-5 mg) were prepared in T-zero aluminum pans. A Q200 or DSC 250 differential scanning calorimeter (DSC, TA instruments, New Castle, DE) was used to measure the glass transition temperature (Tg). Samples were equilibrated at -40°C, heated to 120°C at 10°C / min, held isothermally for 2 minutes, cooled to -40°C at 10°C / min, then heated to 120°C at 10°C / min. The half-height of the endothermic transition in the second heating cycle was used to determine the Tg.

[0038] Mechanical testing

[0039] Compressive modulus of both dry and wet samples was tested. For dry compressive modulus, cylindrical samples (8 mm diameter, 4 mm thickness, n=3) were prepared. For each test, the direction of loading was set to ‘compression’, the control rate was set to -1 mm / min, and the end limit was set to 24 N. Samples were placed on the lower platen, the upper platen was lowered until it was just touching the sample, the position and force were zeroed, and then the run began. The runs stopped when the end limit was reached or before the upper clamp could contact the bottom clamp. The stress (kPa) and strain (mm) were calculated from the results of each run. A stress versus strain curve was plotted, and the compressive modulus was determined from the slope of the linear region between 0.02 and 0.1 strain. The compressive modulus of wet (plasticized) samples was determined by first soaking the samples in DI water at 50 °C for 20 minutes. After 20 minutes, samples wereremoved from the water, gently patted to remove excess water, and mechanical testing was performed as described above.

[0040] Real-time’ oxidative degradation

[0041] Sacrificial samples (8 mm diameter, 1 mm length, n=3 per each sample ID) were prepared for a 12-week degradation study in 3% H2O2 with samples analyzed at 10 time points (weeks 2, 4, and 5-12). The samples were kept in separate scintillation vials containing 10 mL of the degradation media and stored in an incubator at 37 °C while shaking at 100 rpm. Media was changed 2X / week. At each time point, the sacrificial samples were removed from media, dried overnight in a vacuum oven at room temperature, and then weighed.Images were taken of each sample to monitor bulk versus surface erosion profiles, and the density of each sample was calculated from mass, length, and diameter measurements. Changes in foam pore structure, chemistry, and thermal properties due to degradation were characterized using SEM, FTIR, and DSC, respectively, as described above. At weeks 4, 8, and 12, changes in hydrophilicity (i.e., swelling ratio) and mechanical properties were analyzed. Samples were weighed directly from media (wet, swollen weight) to calculate the swelling ratio. Then, a cross-section was cut from the wet sample, and the wet compressive modulus was measured following the procedure above. Then, those foams were dried for the remaining analyses listed above.

[0042] Accelerated hydrolytic degradation

[0043] Samples (8 mm diameter, 1 mm length, n=3 per each sample ID) were prepared for a degradation study in 0.1M NaOH with sacrificial samples prepared for 10 time points. Samples were first sacrificed every 5 days (days 5, 10, and 15). Then, samples were sacrificed every week (days 22, 29, 36, 43, and 50), and then at days 64 and 84, with media changed 2X / week. Samples were again incubated in vials with 10 mL of media at 37 °C shaking at 100 rpm. Sample analysis was performed as described above for the ‘real-time’ analysis, with swelling ratio and compressive modulus measured directly from wet samples at days 29, 50, and 84.

[0044] Cytocompatibility

[0045] Dulbecco’s modified Eagle’s medium (DMEM, high glucose GlutaMAX) supplemented with 10% heat- inactivated fetal bovine serum (FBS) and 1% penicillin-streptomycin (P / S, Gibco) was used to culture NIH / 3T3 Swiss mouse fibroblasts (ATCC-CCL92, passages 10-15) at 37°C / 5% CO2. Cell morphology and even cell distribution was confirmed using a Zeiss Axiovert inverted microscope (Zeiss, Baden- Wurttemberg, Germany). When the cells reached -100% confluency, the culture media wasremoved, and cells were washed with sterile phosphate-buffered saline (PBS). The cells were trypsinized and then seeded in a 24-well tissue-culture polystyrene plate at 10,000 cells / well. Cell viability was determined using a LIVE / DEAD™ viability / cyto toxicity kit (Invitrogen, Thermo Fisher Scientific). After 24 h of culture, sterile foam samples (~1 mm thick, 6 mm diameter) were added to the pre-seeded 24-well plates. After 24 hours, the foam samples were removed and the live / dead stain was prepared based on manufacturer recommendations (1 pL calcein-AM and 4 pL ethidium homodimer- 1 in 2 mL DPBS). Then, 200 pL of the stain was added to each well. A positive (cytocompatible) control was prepared with no foam sample, and a negative (cytotoxic) control had cells in 30% H2O2. The well plate was protected from light and the stain was allowed to incubate for 20 minutes before cells were imaged using a Leica DM4000 B inverted fluorescent microscope (Leica Microsystems,Wetzlar, Germany). ImageJ was used to quantify the number of live and dead cells, and cell viability was calculated as: . > >

[0046] 100

[0047] Degradation byproduct cytocompatibility

[0048] Cytocompatibility of the degradation byproducts was conducted as performed by Herting et al. Briefly, foam samples (n=3) were cut and weighed to have the same mass (200 mg), and then incubated in 10 ml of 30% H2O2 at 70°C until complete degradation occurred. Once fully degraded, the solutions were diluted to 2% H2O2, and 1500 U / ml of bovine liver catalase was added to neutralize the solutions for 7 days at 37°C. A 2% H2O2 solution treated with catalase was used as a control. A ferric thiocyanate kit (Chemetrics) was used to confirm complete neutralization; if the solutions were not neutralized, they were filtered with a 0.22 pm syringe filter and treated with catalase for another 7 days. This process was repeated as needed. The fdtered byproduct extracts were then tested with a Pierce Coomassie Plus Protein Assay (ThermoFisher Scientific, Waltham, MA) to ensure the concentration of any remaining catalase was below 0.227 mg / mL (based on experimentally obtained IC30 value by Herting et al.). The extracts were re-filtered as needed until the concentrations were low enough to proceed with cytocompatibility analysis.

[0049] 3T3 cells were cultured, seeded onto 24-well plates at 10,000 cells / well, and incubated (37°C / 5% CO2) as described above. After 24 h, media was removed from each well, and 300 pL of fresh media was added plus 300 pL of the sterilized byproduct extracts in serial dilutions (IX, 2X, 4X, 8X, 16X, and 32X; diluted in the same culture media). After 24, 48, and 72 h, the solutions were removed and 600 pL of 10% alamar blue (resazurin) wasadded to each sample and control well (positive: cells; negative: no cells) and incubated at 37°C for 2 h. Then, the solutions from each well were transferred to a 96-well solid black polystyrene plate (n=3, 150 pL). A microplate reader (BioTek Synergy 2, Agilent Technologies, Winooski, VT) was used to measure fluorescence (excitation: 530 / 25; emission: 590 / 35; gain: top 50%). Cell viability was calculated as: . > _ [0050 100

[0051] Blood-material interactions

[0052] Hemolysis

[0053] A hemolysis assay was performed as an initial measure of hemocompatibility to ensure that the foams would not rupture red blood cells or have an adverse effect on blood interactions. Foam samples (n=3, 10 mg) and QuikClot Combat Gauze (QCCG, clinical control) were incubated in 5 mL IX PBS for 5 hours at 37°C in a 15 mL centrifuge tube. Controls included tubes (n=3) containing 5 mL of IX PBS (positive, non-hemolytic) or DI water (negative, hemolytic). Whole porcine pig blood anticoagulated with Na-Citrate (Lampire Biological Laboratories, Everett, PA, USA) was removed from refrigerated storage and allowed to come to room temperature. Then, 0.1 mL of blood was added to each tube and incubated at 37°C for 1 h. After 1 h, the tubes were centrifuged at 1000 rpm for 10 min, and 0.2 mL of the supernatant (n=3 per sample / tube) was added to a 96-well plate. The optical absorbance was measured with a plate reader (BioTek Synergy 2, Agilent Technologies, Winooski, VT) at 545 nm. Percent hemolysis was calculated as:

[0054] 100

[0055] Prothrombin generation

[0056] To test whether the degradable foam formulations impact the clotting behavior compared to the control PUr foam, a Pig Prothrombin ELISA kit (Abeam, Cambridge, United Kingdom) was used. Foam samples (n=3) and QuikClot Combat Gauze (QCCG, positive control) were cut into 5 mg samples and placed in a 96-well plate. Prothrombin standards were prepared according to the manufacturer’s guidelines. Foam samples were incubated in platelet-poor plasma (PPP, 100X dilution) anticoagulated with Na-Citrate (Lampire Biological Laboratories, Everett, PA, USA) for 1 h at 37°C. After 1 h, the samples were transferred to the ELISA microplate and incubated for 2 h at room temperature. The plate was then washed with buffer and treated with IX Biotinylated Prothrombin Antibody for 1 h. The plate was rewashed and treated with IX Streptavidin-Peroxidase Conjugate for 30 min. The plate was washed and treated with chromogen substrate for 10 min in ambient light, and thenthe stop solution was added. The absorbance of each sample well was determined using a microplate reader (BioTek Synergy 2, Agilent Technologies, Winooski, VT) at 450 nm. A standard curve of optical density at 450 nm vs. prothrombin concentration (0 to 400 ng / mL) was plotted from the prothrombin standards and fit to a logarithmic curve. The prothrombin concentration of each sample was calculated from the curve.

[0057] Blood absorption

[0058] Dry foam samples and QCCG (n=3, ~1 cm3) were weighed (Wd), placed in a 24-well plate, and incubated in 2 mL Na-citrated whole porcine blood at 37°C. Samples were weighed after 1 h to determine the amount of blood absorbed (Wb). Blood absorption was calculated as:

[0059] 100

[0060] Platelet interactions

[0061] Foam samples and QCCG (n=3, ~0.5 cm3) were incubated in Na-citrated whole porcine blood for 1 h at 37°C. After 1 h, the samples were gently rinsed with PBS to remove non-attached cells and then fixed in 2.5% glutaraldehyde (Electron Microscopy Sciences, Hatfield, PA, USA) for 24 h at 4°C. Following fixation, the samples were dehydrated in increasing ethanol concentrations (50%, 70%, 95%, and 100%; 30 min each) and dried overnight in a vacuum oven at room temperature. The dried samples were sputter- coated with Au at 45 mA for 60 s, and imaged using SEM (JEOL JSM-IT100, Peabody, MA) at 1000X magnification and 10 kV.

[0062] Statistical analysis

[0063] Measurements are presented as mean ± standard deviations. A student’s t-test was performed in Microsoft Excel with two-tailed distribution and two-sample unequal variance. If p < 0.05, differences were considered statistically significant.

[0064] RESULTS

[0065] Structural properties

[0066] Incorporation of the degradable polythiols did not impact the overall pore structure of the PUr foams (Figure 3a). Pores were uniform in all foams, indicating pore stability during the gas foaming process. Higher ester-containing formulations, like 30H-2 and 30H-2,2, had greater pore openness, whereas all other formulations had closed-cell pores. This result is consistent with previous work, where incorporating esters into the backbone of PUr foams increased pore interconnectivity. Pore sizes averaged from -800-1200 pm, with no statistically significant differences between the new formulations and the control PUr (950± 200 gm, Figure 3b). Foam densities were low (<0.08 g / cm3) for all formulations, demonstrating that the degradable polythiols can be incorporated into low-density foams (Table 3). Furthermore, many formulations — primarily those containing 15% polythiols — had significantly decreased foam density, corresponding with their generally larger pore sizes compared to both the control and their corollary 30% foam formulations.

[0067] Hydrophilicity

[0068] Incorporation of the degradable monomers into the PUr foams significantly increased foam hydrophobicity, as demonstrated by lower swelling ratios among the degradable foams (Figure 3c). HPED and TEtA in the control PUr have hydrophilic tertiary amine groups that the degradable polythiols lack, allowing for greater swelling. Furthermore, the thioethers are hydrophobic, and the esters are considered hydroneutral, contributing to an overall decrease in hydrophilicity.

[0069] Thermal properties

[0070] The incorporation of the degradable polythiols into PUr foams significantly reduced the glass transition temperature (Tg) compared to that of the control PUr (56 ± 2°C, Figure 3d). This result was expected because of an increase in the free volume of the polymer network due to the longer branches of the T-l, T-2, H-2, T-1,2, T-2,2, and H-2,2 monomers relative to HPED and TEtA. The control PUr foam has higher crosslink density because the HPED and TEtA crosslinks are closer together, inhibiting free rotation of bonds. The 15% foam formulations with smaller content of longer chain polyols had higher Tg’s than their corollary 30% foams, but they were still significantly below that of the control.

[0071] Mechanical properties

[0072] The 15% formulations were generally stiffer than their corollary 30% foam, as demonstrated by higher compressive modulus among dry samples (Figure 3e). This trend corresponds to their higher crosslink density from higher HPED wt% and shorter monomer chains. The 15T-2 and 15H-2 foams had more comparable modulus to the control (178 ± 67 kPa), at 226 ± 63 kPa and 267 ± 48 kPa, respectively. The other formulations were significantly lower, with compressive moduli ranging from 2-22 kPa. There were smaller differences among the compressive modulus of foams in their wet, plasticized state (Figure 3f). The 15T-1, 15T-1,2, 15T-2,2, and 15H-2,2 had significantly lower wet compressive moduli compared to the control, but no other differences were significant. The wet compressive modulus is most relevant to in vivo conditions, as these foams would be employed in the presence of water in blood and tissue. Tissue engineering scaffolds require a comparable modulus to the surrounding tissue; all foams have a wet compressive modulus comparable to that of liver, which among healthy individuals falls within the range of 2-9 kPa.

[0073] Degradation analysis

[0074] Mass loss and erosion

[0075] All of the degradable foam formulations had increased mass loss over 12 weeks compared to the control PUr (Figure 4). In ‘real-time’ oxidative media (3% H2O2), the fastest degrading foams, 30T-l,2, 30T-2,2, and 30H-2,2, had 8 ± 8%, 13 ± 9%, and 6 ± 5% mass remaining, respectively (Figure 4b). Notably, these foams contained an ester on either side of the sulfide moiety. In contrast, the 30T-2 formulation had 41% mass remaining and was the fastest degrading formulation among foams with one ester near the sulfide. The two- ester formulations generally underwent more consistent linear mass loss than the single-ester foams: control (R2= 0.807,) 15T-1 (R2= 0.833), 30T-1 (R2= 0.878), 15T-2 (R2= 0.955), 30T-2 (R2= 0.846), 15H-2 (R2= 0.963), 30H-2 (R2= 0.948), 15T-1,2 (R2= 0.897), 30T-l,2 (R2= 0.919), 15T-2,2 (R2= 0.974), 30T-2,2 (R2= 0.921), 15H-2,2 (R2= 0.932), and 30H-2,2 (R2= 0.973).

[0076] In accelerated hydrolytic media (0.1 M NaOH), the same foams (30T-l,2, 30T-2,2, and 30H-2,2) had 52%, 56%, and 52% mass remaining at 12 weeks, with significant mass loss between weeks 1 and 2, after which mass loss plateaued (Figure 4d). This trend is consistent with that of our previous ester-containing PUr formulations, which exhibited 20% mass loss within the first two weeks and thereafter remained relatively stable. All foam formulations underwent surface erosion (Figure 5 a), which is preferred over bulk erosion to maintain foam structural integrity throughout degradation. Furthermore, surface erosionallows for easy tuning of the starting foam mass to achieve complete degradation within 8-12 weeks, which can be determined from foam mass loss rates in Table 4.

[0077] Pore morphology

[0078] The control PUr had the least pore collapse, corresponding with the least amount of degradation. There is some pore strut breakage at day 56 in 3% H2O2, but no noticeable breakage to the control foam was observed in 0.1 M NaOH (Figure 5b), corresponding with the lack of hydro lytically-labile groups in its backbone. In comparison, the degradable PUr foams had significant strut breakage and pore collapse at day 28 in both 3% H2O2 and 0.1 M NaOH. All images were taken at the same magnification (25X), demonstrating the significant reduction in foam pore size over time. In some instances, the foams became extremely tacky, causing them to stick to themselves during the drying process without the ability to re-expand upon heating. This stickiness could be due to an increase in hydrophilicity and hydrogen bonding and is seen through the apparent loss of pores in 30T-1 (Day 84 in 0.1 M NaOH), 30T-2 (Day 84 in both 3% H2O2 and 0.1 M NaOH) and both 30T- 2,2 and 30H-2,2 (Day 56 and Day 84 in 3% H2O2).

[0079] Spectroscopic analysis

[0080] A reduction in the tertiary amine peak (HPED and TEtA for control; HPED for all other formulations) around 1050 cm'1, and a shift in the urethane peak from -1677 cm'1to 1690 cm'1, demonstrate oxidative degradation in all foam formulations in 3% H2O2 (Figure 6), consistent with previous work. All formulations except the control had a peak form at -900 cm'1in 3% H2O2, due to the formation of a sulfoxide or sulfone from sulfideoxidation. Similarly, all formulations except the control had a peak form around 1615 cm'1in 3% H2O2 due to the formation of carboxylic acids (C=O and C-O-H) during ester hydrolysis. This peak was only notable in 0.1 M NaOH among the 30% foam formulations (vs. 15% foams containing fewer esters), emphasizing the role of sulfide oxidation in facilitating ester hydrolysis.

[0081] Changes in foam hydrophilicity, density, and compressive modulus

[0082] Control foam swelling ratios remained relatively constant throughout degradation, while the degradable foams generally had an increase in swelling ratio, particularly in 0.1 M NaOH. This increase in swelling ratio reflects an increase in hydrophilicity (Figure 7a). The hydrophobic thioethers become more hydrophilic through oxidation as the thioether breaks down into more polar sulfones and sulfoxides with a greater affinity for water. Similarly, the hydrolysis of esters increases hydrophilicity because the ester breaks down into polar carboxylic acids and alcohols that can more readily interact with water.

[0083] Figure 7b shows the foam densities after sample drying. Although the dry density is not biologically relevant, the increase in foam densities throughout degradation reflects the increase in foam hydrophilicity. The samples became extremely tacky throughout degradation, causing the foams to stick to themselves upon drying without the ability to reexpand, as was seen in the SEM micrographs of pore morphology (Figure 5b). This tackiness could potentially be beneficial for cell and tissue adherence to the PUr foams, as cells tend to preferentially attach to more hydrophilic surfaces.

[0084] All foams had a substantial decrease in compressive modulus in both 3% H2O2 and 0.1 M NaOH (Figure 7c). A decrease in mechanical stiffness corresponds with the physical breakdown of each foam, including surface erosion of foam pores and the collapse of pore struts that increase the free volume of foam samples and reduce their density in the wet state. Throughout degradation, the compressive moduli of each foam drops below that of liver (2-9 kPa), but these materials could potentially still provide structural support for tissue repair throughout degradation.

[0085] Thermal Analysis

[0086] Foam thermal properties changed significantly throughout degradation. In 3% H2O2, the degradable foams generally had an increase in glass transition temperature (Tg) at the start of degradation, as seen by the higher Tg’s at day 28 (Figure 7d). This increase in Tg is most likely an indicator of oxidation induced crosslinking, which would correspond with the formation of a peak at -1090 cm'1in the 3% H2O2 FTIR spectra (Figure 6).

[0041] As thefoams degrade more, their Tg decreases, as indicated by a drop in Tg at day 56 and a further drop at day 84. These decreases in Tg correspond with a decrease in foam crosslink density, increasing the mobility of the polymer chains. The control foam demonstrated no signs of crosslinking, but its Tg similarly decreased with oxidative degradation as its crosslink density reduced upon oxidation of the tertiary amines.

[0087] In 0.1 M NaOH, the control foam Tg remained the same, which was expected due to its lack of hydrolytically labile groups. All of the degradable foams had an increase in Tg from day 0 to day 29, after which the Tg’s remained relatively constant across days 50 and 84. This initial change corresponds with the time in which these foams had significant mass loss in 0.1 M NaOH (Figure 4), after which mass loss generally plateaued. Despite the increase in Tg, there was no clear indication of crosslinking in the FTIR spectra in 0.1 M NaOH (Figure 6). The increase in Tg may instead be an effect of hydrogen bonding, as suggested by Nakamura et al.; they saw a linear increase in the Tg of their polymers as hydrolysis increased. In 0.1 M NaOH, the foams’ esters are hydrolyzed into carboxylic acids, which can hydrogen bond with one another, increasing Tg.

[0088] Cell and blood-material interactions

[0089] Foam Safety

[0090] Cell viability was greater than 95% in the presence of all foam formulations after direct cell contact for 24 h, meeting the ISO 10993 biocompatibility standard of >75% viability for biomedical devices (Table 5). To evaluate the safety of the foam degradation byproducts, cells were exposed to solutions of the fully degraded foams for 24, 48, and 72 h (Figure 8a). At 24 h, all foams had >95% cell viability at IX dilution. At 48 and 72 h, viability dropped to -70% and 55%, respectively. However, the non-diluted solutions represent an unlikely scenario in vivo where cells would be exposed to 100% of the degradation byproducts at one time. At 2X and 4X dilutions, cell viability is at or greater than 100% at 72 h, which is more representative of in vivo occurrences. Namely, as the foams degrade over time, their byproducts will be cleared from the body, so cells will only be exposed to a small percentage of the byproducts at any given time, presenting no concerns of cytotoxicity. Similarly, all foam formulations are hemocompatible, with hemolysis below 1% (Figure 8b), ensuring that red blood cells will not be damaged when in contact with the foams.

[0091] Clotting Behavior

[0092] Changes in foam chemistry are expected to impact biological interactions, as properties like hydrophilicity and charge can impact protein adsorption to a material. The degradable foams are more hydrophobic than the control PUr, and the esters introduce new dipole-dipole bonding sites. Thus, clotting behavior was characterized to determine the effects of chemistry changes on blood / material interactions. The degradable foam formulations generate comparable concentrations of prothrombin relative to the control PUr and the QCCG clinical control, with no statistically significant differences (Figure 8c). Blood absorption was comparable among the 15% foam formulations and the control, but there were statistically significant decreases in blood absorption among most of the 30% formulations (Figure 8d), which corresponds with an increase in hydrophobicity and swelling (Figure 3c). SEM micrographs of platelet morphology show that the degradable foam formulations have increased platelet interactions, with greater platelet attachment, activation, and aggregation (Figure 8e). The control foam has fewer platelets attached, and the aggregates are smaller. Platelet activation can be seen most prominently among the 15T-2,2 and 30T-2,2 foams, where the platelets have protrusions on their surface, a morphological indicator of activation. Furthermore, fibrin deposition can be seen on the 15T-1 and 30T-1 foams, as indicated by the fibrous networks across platelets. Large aggregates are observed on the 15H-2, 30H-2, 30T- 1,2, 30T-2,2, 15H-2,2, and 30H-2,2 foams, suggestive of a ‘platelet plug’ and clot formation. Notably, the degradable foams have comparable platelet aggregates to that of QCCG, which contains kaolin, a hemostatic agent known to accelerate clotting; this result demonstrates that pore structure and foam chemistry alone are effective at initiating clotting without the need for other hemostatic additives.

[0093] DISCUSSION

[0094] Foam synthesis and characterization

[0095] The primary advantage of this PUr system is the easy-to-synthesize degradable polythiols. The starting reactants are miscible with one another and do not require solvents for dissolution. Additionally, the catalyst / photoinitiator makes up a very small wt% of the total reaction components, allowing them to be easily washed out after PUr foam crosslinking to minimize potential effects on cytotoxicity. The polythiols are made within minutes and require no purification, allowing their immediate use in foam fabrication. The starting reactants are also readily available, which in combination with the rapid synthesis, could facilitate the large-scale production of these foams for commercialization.

[0096] The significant drop in Tgafter polythiol incorporation compared to that of the control PUr may be important depending on the intended application. Our control PUr foam is a shape memory polymer, capable of maintaining a low-profile, secondary shape after programming above its dry Tg(~55°C); it will then rapidly expand and return to its primary, open-porous shape when plasticized in water at 37°C. The low Tgof the degradable foams removes the ability for these foams to remain fixed in a secondary shape. That said, a shape memory polymer-based dressing is not necessary for effective hemostasis. The low density of these foams allows them to be tightly packed in a delivery device for ease of storage, and they will rapidly expand when delivered to a bleeding wound. If a higher Tgis required for a particular application, the 15% foam formulations with higher Tg’s that are comparable to that of the control could be employed, with a tradeoff of slower degradation rates as compared with those of the 30% foam formulations. Other diisocyanates could potentially be used to increase Tg, such as trimethylhexamethylene diisocyanate (TMHDI). TMHDI has bulky methyl groups that increase the energy required to rotate bonds about the backbone; however, the increase in Tgis relatively small, and the added hydrophobic methyl groups could slow down the rate of degradation.

[0097] Degradation

[0098] In previous work, the same foam samples were used repeatedly throughout the study. That is, foams were repeatedly dried at set time points, weighed to determine mass loss, and then returned to degradation media. This method of studying degradation accelerates the degradation process because of foam breakdown due to the mechanical forces of repeatedly drying each sample. This present invention uses an improved method for studying degradation in vitro, in which sacrificial samples are prepared for each time point, allowing us to predict in vivo degradation rates more accurately.

[0099] The primary degradation mechanism of the control PUr is through oxidation of the tertiary amine groups. However, this oxidation occurs relatively slowly, hence the needfor incorporating additional oxidatively and hydrolytically labile groups. In vivo, reactive oxygen species (ROS) are released from macrophages in the blood. ROS are highly reactive, most commonly present as a superoxide anion (02*-), hydrogen peroxide (H2O2), or a hydroxyl radical (*0H). The unstable radicals will readily react with the free electrons on thioethers, oxidizing the sulfide into a sulfone or sulfoxide. Oxidation of the sulfide groups facilitates the hydrolysis of adjacent esters into carboxylic acids, which occurs in vivo through water present in blood and tissue, helping to speed up overall degradation rates.

[0100] The fastest degrading foams in 3% H2O2 (30T-l,2, 30T-2,2, and 30H-2,2) show that the number of esters has the greatest effect on degradation. All of these foams had an ester on both sides of the sulfide, as opposed to the formulations with a single ester near the sulfide. Additionally, in these foams, the degradable polythiols made up 30% of the total OH mol equivalents, as opposed to the slower degrading 15% formulations with less ester content. Finally, within these three fastest degrading formulations, the 30H-2,2 foam had the lowest mass remaining (6%), compared to 30T-2,2 (13%), showing that increasing ester content with the use of hexathiol monomers further increases degradation compared to the trithiol monomers. The proximity of the sulfide and ester moieties had a smaller but noticeable effect on degradation as well when comparing the 30T-l,2 foam mass loss (8%) to the 30T-2,2, foam (13%). These studies provide a toolbox for tuning degradable monomers within more hydrophobic materials to achieve desired degradation profiles. This information complements previous work on hydrogels with ester and thiol groups.

[0101] After achieving hemostasis, these foams could be left in the wound to degrade during healing to serve as scaffolds for tissue regeneration. Here, the degradable foams primarily underwent surface erosion, which is ideal for maintaining structural integrity throughout degradation. This property allows the foams to degrade from the outside in, providing room for new, healthy tissue while maintaining bulk properties for longer time frames. In addition to their degradation rate and erosion profiles, these foams all have moduli comparable to that of liver tissue in their wet, plasticized state at the start of degradation. Tissue scaffolds should have comparable moduli to the surrounding tissue to properly facilitate tissue repair. One potential hindrance to tissue repair is the large pore size of these foams. The ideal pore size for cells to attach and spread is typically in the range of 50-300 pm for soft tissues like liver, cartilage, cardiac tissue, and skeletal muscle. The degradable foams have pore sizes ranging from -900-1200 pm across foams, but the pores start to collapse and become smaller over degradation, which is when new tissue would migrate in.

[0102] Biological interactions

[0103] During the coagulation cascade, prothrombin is activated and then cleaved by Factor Xa to form thrombin, an enzyme that induces platelet aggregation and converts fibrinogen to fibrin. Fibrin then polymerizes, which traps red blood cells and forms a clot around the platelet aggregates. The degradable foams all had comparable prothrombin formation with no statistically significant differences compared to the control PUr. Despite this result, the degradable foams demonstrated an increase in platelet interactions. The degradable foams are more hydrophobic than the control PUr due to the additional sulfide groups, which may increase fibrinogen adsorption and subsequent platelet attachment. The physical process of platelet aggregation is an important accompaniment to the series of chemical reactions that occur to stop bleeding in the coagulation cascade. An increase in platelet attachment, activation, and aggregation can result in a temporary plug to more quickly stop blood loss. Our previous work incorporating esters into PUr foams increased foam hydrophilicity; the previously developed degradable monomers contained hydrophilic tertiary amine groups, which negatively affected blood-material interactions. Namely, the previously developed degradable foams had lower platelet attachment and longer times to induce a stable clot compared to the control PUr. The primary goal of these PUr foams is to control bleeding in traumatic wounds, so incorporating degradable linkages should not hinder their ability to initiate clotting. Notably, the degradable foams in this work demonstrated an increase in clotting capability compared to the control PUr, which could improve their efficacy as a hemostatic dressing.

[0104] CONCLUSIONS

[0105] The simple, solvent-free, rapid click chemistry synthesis of the degradable polythiols allows for ease of fabricating biodegradable PUr foams that can be scaled up for commercial production. Introducing sulfide and ester moieties into the PUr foam network significantly increased foam degradation rates in vitro in ‘real-time’ oxidative degradation media (3% H2O2), with the fastest degrading foams (30T-l,2, 30T-2,2, and 30H-2,2) demonstrating that the number of esters has the greatest effect on degradation. The linear mass loss and surface erosion of the foams lend to easily tailoring the foam starting mass to match the target endpoint for 100% degradation. The degradable foams are highly biocompatible, hemocompatible, and have nontoxic degradation byproducts. Furthermore, the increase in foam hydrophobicity from the incorporation of the esters and sulfides improves platelet interactions, which could aid in controlling bleeding. Overall, the biodegradable PUr foam hemostatic dressings of the present invention could significantly improve bleeding control in traumatic wounds and enable tissue regeneration to promote healing.

Claims

CLAIMSWhat is claimed is:

1. A degradable composition, comprising a polythiol monomer having a thioether coupled to an ester by no more than two methylene groups.

2. The degradable composition of claim 1, wherein the polythiol monomer comprises trimethylolpropane tris(3 -mercaptopropionate) reacted with hydroxyethyl acrylate, 3-buten-l-ol, 3-methyl-3-buten-l-ol, or 3-buten-2-ol.

3. The degradable composition of claim 1, wherein the polythiol monomer comprises trimethylolpropane tris(thioglycolate) reacted with hydroxyethyl acrylate, 3-buten- l-ol, 3-methyl-3-buten-l-ol, or 3-buten-2-ol.

4. The degradable composition of claim 1, wherein the polythiol monomer comprises dipentaerythritol hexakis(3 -mercaptopropionate) reacted with hydroxyethyl acrylate, 3-buten-l-ol, 3-methyl-3-buten-l-ol, or 3-buten-2-ol.

5. The degradable composition of claim 1, wherein the polythiol monomer comprises 2,2'-(ethylenedioxy) diethanethiol reacted with hydroxyethyl acrylate.

6. The degradable composition of claim 1, wherein the polythiol monomer is polymerized along with an isocyanate to form a polyurethane.

7. A method of forming a degradable composition, comprising the step of forming a polythiol monomer having a sulfide group adjacent to an ester.

8. The method of claim 7, wherein the step of forming the polythiol monomer comprises the step of reacting a thiol with a compound selected from the group consisting of hydroxyethyl acrylate, 3-buten-l-ol, 3-methyl-3-buten-l-ol, and 3-buten-2-ol to form the polythiol monomer having the sulfide group adjacent to the ester.

9. The method of claim 8, further comprising the step of polymerizing the polythiol monomer with an isocyanate to form a polyurethane.

10. The method of claim 8, wherein the thiol is selected from the group consisting of trimethylolpropane tris(3 -mercaptopropionate), dipentaerythritol hexakis(3- mercaptopropionate), dipentaerythritol hexakis(3-mercaptopropionate), and 2,2'- (ethylenedioxy) diethanethiol.

11. The method claims 10, wherein the thiol is reacted with hydroxyethyl acrylate, 3-buten-l-ol, 3-methyl-3-buten-l-ol, or 3-buten-2-ol.

12. The method of claim 11, wherein the isocyanate is selected from the group consisting of hexamethylene diisocyanate, isophorene diisocyanate, toluyene diisocyanate, methylene diisocyanate, and trimethylhexamethylene diisocyanate.

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