Biocompatibility of poly(etherurethane urea) containing dehydroepiandrosterone

Biostability and biological performance of a PDMS-based polyurethane for controlled drug release

Polymers have been used to deliver therapeutic agents in a range of medical devices with drug eluting stents being the most widespread current application. Although polymers enable controlled release of a therapeutic agent, the polymeric surface has been reported to provide suboptimal biocompatibility and haemocompatibility and it has been suggested that currently used polymers may be at least partly responsible for the late adverse events observed in intravascular stent systems. In this study, the biostability and biological performance of a siloxane-based polyurethane elastomer (E2A) demonstrating excellent long-term biostability in the unloaded state was investigated following incorporation of a therapeutic agent. After implantation in an ovine model for 6 months, samples were assessed using SEM and ATR-FTIR to determine changes in the surface chemical structure and morphology of the materials and tensile testing was used to examine changes in bulk characteristics. Biological response was assessed using in vitro cytotoxicity testing and histological analysis. Results indicated that incorporation of 25mg/g dexamethasone acetate (DexA) into the siloxane-based polyurethane resulted in no significant difference in the biostability and biocompatibility of the material. Some level of cytotoxic potential was exhibited which was believed to result from residual DexA leaching from samples during the extraction process. These findings suggest that E2A is a potential candidate for a delivery vehicle of therapeutic agents in implantable drug delivery applications.

Biostability and biocompatibility of poly(ether)urethane containing gold or silver nanoparticles in a porcine model

Nanocomposites from polyether-type waterborne polyurethane (PU) incorporated with different amounts of gold nanoparticles (17.4-65 ppm) or silver nanoparticles (30.2-113 ppm) were prepared. Specifically, the nanocomposite containing 43.5 ppm of gold or 30.2 ppm of silver was previously found to possess the best thermal and mechanical properties. The enhanced biostability of the nanocomposite at the specific nanoparticle content was also observed in subcutaneous rats. The latter was probably related to the free radical scavenging ability of the nanocomposite shown in vitro. In this study, the in vivo biostability of the full series of these nanocomposites was assessed by porcine subcutaneous implantation for 19 days followed by microscopic examination and chemical characterization using attenuated total reflectance-infrared spectroscopy (ATR-IR). The nanocomposite at 43.5 ppm of gold ("PU-Au 43.5 ppm") and that at 30.2 ppm of silver ("PU-Ag 30.2 ppm") exhibited superior biostability in pigs to those at higher or lower nanoparticle contents. In particular, evidence of oxidative chain scission and crosslinking of the surface was presented by ATR-IR spectra in the explanted PU and nanocomposites other than PU-Au 43.5 ppm and PU-Ag 30.2 ppm. The extent of biodegradation and that of foreign body reactions were highly associated in these nanocomposites, both of which showing negative correlation with the free radical scavenging ability. The interdependency among antioxidation/biostability/biocompatibility of PU was demonstrated in this porcine model.

Novel Biopolymers as Implant Matrix for the Deliveryof Ciprofloxacin: Biocompatibility, Degradation, and In Vitro Antibiotic Release

The purpose of this study was to investigate the in vitro-in vivo degradation and tissue compatibility of three novel biopolymers viz. polymerized rosin (PR), glycerol ester of polymerized rosin (GPR) and pentaerythritol ester of polymerized rosin (PPR) and study their potential as implant matrix for the delivery of ciprofloxacin hydrochloride. Free films of polymers were used for in vitro degradation in PBS (pH 7.4) and in vivo in rat subcutaneous model. Sample weight loss, molecular weight decline, and morphological changes were analyzed after periodic intervals (30, 60, and 90 days) to monitor the degradation profile. Biocompatibility was evaluated by examination of the inflammatory tissue response to the implanted films on postoperative days 7, 14, 21, and 28. Furthermore, direct compression of dry blends of various polymer matrices with 20%, 30%, and 40% w/w drug loading was performed to investigate their potential for implant systems. The implants were characterized in terms of porosity and ciprofloxacin release. Biopolymer films showed slow rate of degradation, in vivo rate being faster on comparative basis. Heterogeneous bulk degradation was evident with the esterified products showing faster rates than PR. Morphologically all the films were stiff and intact with no significant difference in their appearance. The percent weight remaining in vivo was 90.70 +/- 6.2, 85.59 +/- 5.8, and 75.56 +/- 4.8 for PR, GPR, and PPR films respectively. Initial rapid drop in Mw was demonstrated with nearly 20.0% and 30.0% decline within 30 days followed by a steady decline to nearly 40.0% and 50.0% within 90 days following in vitro and in vivo degradation respectively. Biocompatibility demonstrated by acute and subacute tissue reactions showed minimal inflammatory reactions with prominent fibrous encapsulation and absence of necrosis demonstrating good tissue compatibility to the extent evaluated. All implants showed erosion and increase in porosity that affected the drug release. Increase in drug loading significantly altered the ciprofloxacin release in extended dissolution studies. PPR produced drug release >90% over a period of 90 days promising its utility in implant systems. The results demonstrated the utility of novel film forming biopolymers as implant matrix for controlled/sustained drug delivery with excellent biocompatibility characteristics.

Surface modification of poly(ether urethane urea) with modified dehydroepiandrosterone for improvedin vivo biostability

In this study, a fatty acid urethane derivative of dehydroepiandrosterone (DHEA) was synthesized and evaluated as a polyurethane additive to increase long-term biostability. The modification was hypothesized to reduce the water solubility of the DHEA and physically anchor the additive in the polyurethane during implantation. Polyurethane film weight loss in water as a function of time was studied to determine the polymer retention of the modified DHEA. The polyurethane film with unmodified DHEA had significant weight loss in the first day (10%) that was previously correlated to rapid leaching of the additive. The polyurethane film with modified DHEA had significantly less weight loss at all time points indicating improved polymer retention. The effect of the modified DHEA additive on the biostability of a poly(ether urethane urea) was examined after 5 weeks of subcutaneous implantation in Sprague-Dawley rats. Optical micrographs and infrared analysis of the specimens indicated that the modified DHEA bloomed to the surface of the film forming a crystalline surface layer approximately 10-15 microns thick. After explantation, this surface layer was intact without measurable differences in surface chemistry as monitored by attenuated total reflectance-Fourier transform infrared spectroscopy. There was no evidence of degradation of the polyurethane underneath the modified DHEA surface layer as compared with the polyurethane control. We have concluded that the modified DHEA self-assembled into a protective surface coating that inhibited degradation of the polyurethane. The roughness of the modified DHEA surface layer prevented adherent cell analysis to determine if the additive retained the ability to down-regulate macrophage activity. Subsequent studies will investigate the ability of surface-modifying additives to modulate cellular respiratory bursts in addition to the formation of an impermeable barrier. This bimodal approach to improving biostability holds great promise in the field of polyurethane biomaterials.

In vivo biocompatibility and biodegradation of poly(ethylene carbonate)

Biodegradation and biocompatibility of poly(ethylene carbonate) (PEC) was examined using an in vivo cage implant system. Exudate analysis showed that PEC and PEC degradation products were biocompatible and induced minimal inflammatory and wound healing responses. Adherent foreign body giant cells (FBGCs) caused pitting on the PEC surface, which led to extensive degradation over time. Data obtained from molecular weight and examination of film cross-sections in the scanning electron microscope (SEM) indicated that PEC underwent surface erosion with no change to the remaining bulk. Attenuated total reflectance infrared (ATR-FTIR) spectroscopy was used to characterize the chemical degradation. Superoxide anion released from inflammatory cells appeared to initiate an "unzipping" mechanism of degradation by deprotonation of PEC hydroxyl end groups. The resulting alkoxide ion participated in a concerted mechanism involving water and the carbonate carbonyl, leading to elimination of ethylene glycol. Carbonate ions decomposed further with release of carbon dioxide to regenerate alkoxide ion.

Biodegradation and in vivo biocompatibility of rosin: a natural film-forming polymer

The specific aim of the present study was to investigate the biodegradation and biocompatibility characteristics of rosin, a natural film-forming polymer. Both in vitro as well as in vivo methods were used for assessment of the same. The in vitro degradation of rosin films was followed in pH 7.4 phosphate buffered saline at 37 degrees C and in vivo by subdermal implantation in rats for up to 90 days. Initial biocompatibility was followed on postoperative days 7, 14, 21, and 28 by histological observations of the surrounding tissues around the implanted films. Poly (DL-lactic-co-glycolic acid) (PLGA) (50:50) was used as reference material for biocompatibility. Rate and extent of degradation were followed in terms of dry film weight loss, molecular weight (MW) decline, and surface morphological changes. Although the rate of in vitro degradation was slow, rosin-free films showed complete degradation between 60 and 90 days following subdermal implantation in rats. The films degraded following different rates, in vitro and in vivo, but the mechanism followed was primarily bulk degradation. Rosin films demonstrated inflammatory reactions similar to PLGA, indicative of good biocompatibility. Good biocompatibility comparable to PLGA is demonstrated by the absence of necrosis or abscess formation in the surrounding tissues. The study provides valuable insight, which may lead to new applications of rosin in the field of drug delivery.

Study of the biodegradation and in vivo biocompatibility of novel biomaterials

The degradation of two rosin-based biomaterials, the glycerol ester of maleic rosin (GMR) and the pentaerythritol ester of maleic rosin (PMR), was examined in vitro in phosphate-buffered saline at pH 7.4 and in vivo in a subcutaneous rat model. Free films of the two biomaterials with mean thickness 0.4+/-0.02 mm were used for the study. The initial biocompatibility was followed by microscopic examination of the inflammatory tissue response to the implanted films. Sample weight loss and molecular weight decline of the free films was used to monitor the degradation quantitatively, while surface morphological changes were analysed for qualitative estimation. Biocompatibility response was followed on post-operative days 7, 14, 21 and 28 and compared with those of poly(DL-lactic-co-glycolic acid) (PLGA) (50:50) films. Both biomaterials showed slow in vitro degradation when compared with the in vivo rate. The mechanism followed was, however, bulk degradation of the films. The penta-esterified form of maleic rosin was observed to degrade more rapidly than glycerol esterified maleic rosin. The acute and subacute inflammatory reactions were characterized by fibrosis at the end of 28 days. The biomaterials showed reasonable tissue tolerance to the extent evaluated. There was a total absence of tissue necrosis or abscess formation for all implanted films. The response, although not identical to that of PLGA, is reasonable, promising new drug delivery applications for rosin biomaterials.

Cytotoxic reaction and TNF-alpha response of macrophages to polyurethane particles

Their unique mechanical and biological properties make polyurethanes (PUs) ideal materials for many implantable devices. However, uncertain long-term biostability in the human physiological environment limits their extensive clinical applications. Chronic inflammatory response associated with macrophage activation has been suggested as a prime factor; although the mechanism of macrophage activation in response to biomaterial surfaces and debris is still unknown. The overall objective of this work was to study the response of macrophages to PU materials in vitro by measuring cell viability and activity. The studies were carried out using phagocytozable-size PU particles from three types of commercially-available PUs: Pellethane 2363 80ABA (PL); Tecothane TT2065 (TC65); and Tecothane TT2085 (TC85). These polymers posess the same generic composition but differ in the length of hard and soft segments, as revealed by the FTIR and NMR studies. The results showed that PU particles affected both viability and activity of J774 macrophages. The percentage of mortality ranged from 1 to 15% with 10-100 microg ml(-1) of particles after 24 and 48 h incubation. These three types of particles induced different mortality on the macrophages. Specifically, the mortality with PL particles was 1-4% (p > 0.05), while the mortality with TC85 particles was 2-10% (p < 0.05) and 4-15% with TC65 (p < 0.05). Conversely, these particles also affected cell proliferation. Cell numbers increased by 132 and 167% after 24 and 48 h incubation, respectively, without particles, whereas the cell numbers increased only 46 and 78% with TC65, 66 and 105% with TC85, and 67 and 110% with PL in the presence of 100 microg ml(-1) of particles for the respective incubation times. PU particles also increased TNF-alpha release from macrophage. After having been incubated for 24 h with 100 microg ml(-1) particles of TC65, TC85, and PL, macrophages release TNF-alpha 7.4, 5.2, and 4.1 times more than the control. In conclusion, PU particles had cytotoxic effects on J774 macrophage at high concentrations. The order of macrophage response for three types of particles was TC65 > TC85 > PL. PU particles' effect on macrophage viability and activity depends on the concentration of particles and their chemical composition, especially on the ratio of hard to soft segments.

In vitro modulation of macrophage phenotype and inhibition of polymer degradation by dexamethasone in a human macrophage/Fe/stress system

A new in vitro accelerated biological model, the macrophage-FeCl2-stress system was used for the evaluation of dexamethasone (DEX)-polymer formulations. This model combines the effects of cells (macrophages), transition metal ions (Fe2+), and polymer stress to promote material biodegradation. The cell and material effects of DEX, either in solution or incorporated into a polyetherurethane matrix (DEX/PEU), were monitored. Cell morphology and hydroperoxide formation in the polymer during cell culturing were characterized. After a subsequent treatment with FeCl2 the development of environmental stress cracking in the polymer was evaluated. We attempted to duplicate the biodegradation of PEU in terms of environmental stress cracking (ESC). Our results support the direct involvement of macrophages in polyetherurethane oxidation, probably by inducing hydroperoxide formation in the polymer structure. Under the influence of stress or strain, polymers with sufficient hydroperoxides degrade in the presence of Fe2+ metal ions in a manner that closely resembles the stress cracking that is observed in vivo. By contrast, polymers treated with either agents that inhibit cell activation and/or the oxidative burst, or with cells with no oxidative burst did not show signs of the biodegradative process. We demonstrated a reduction in hydroperoxide formation and no later ESC development in macrophage-cultured PEU in the presence of DEX in solution or in DEX-loaded PEU. We believe the prevention of initial polymer oxidation by reducing the cell's potential to produce oxidative stress at the tissue-biomaterial interface can directly inhibit the ESC degradation of chronically implanted polymers. The in vitro macrophage-Fe-stress system is a valuable tool for reliable assessment and cost-effective evaluation of biomaterials.