Polyanhydride degradation and erosion

It was the intention of this paper to give a survey on the degradation and erosion of polyanhydrides. Due to the multitude of polymers that have been synthesized in this class of material in recent years, it was not possible to discuss all polyanhydrides that have gained in significance based on their application. It was rather the intention to provide a broad picture on polyanhydride degradation and erosion based on the knowledge that we have from those polymers that have been intensively investigated. To reach this goal this review contains several sections. First, the foundation for an understanding of the nomenclature are laid by defining degradation and erosion which was deemed necessary because many different definitions exist in the current literature. Next, the properties of major classes of anhydrides are reviewed and the impact of geometry on degradation and erosion is discussed. A complicated issue is the control of drug release from degradable polymers. Therefore, the aspect of erosion-controlled release and drug stability inside polyanhydrides are discussed. Towards the end of the paper models are briefly reviewed that describe the erosion of polyanhydrides. Empirical models as well as Monte-Carlo-based approaches are described. Finally it is outlined how theoretical models can help to answer the question why polyanhydrides are surface eroding. A look at the microstructure and the results from these models lead to the conclusion that polyanhydrides are surface eroding due to their fast degradation. However they switch to bulk erosion once the device dimensions drop below a critical limit.     

Block Copolymer Cross-Linked Nanoassemblies Improve Particle Stability and Biocompatibility of Superparamagnetic Iron Oxide Nanoparticles

Purpose

To develop cross-linked nanoassemblies (CNAs) as carriers for superparamagnetic iron oxide nanoparticles (IONPs).

Methods

Ferric and ferrous ions were co-precipitated inside core-shell type nanoparticles prepared by cross-linking poly(ethylene glycol)-poly(aspartate) block copolymers to prepare CNAs entrapping Fe₃O₄ IONPs (CNA-IONPs). Particle stability and biocompatibility of CNA-IONPs were characterized in comparison to citrate-coated Fe₃O₄ IONPs (Citrate-IONPs).

Results

CNA-IONPs, approximately 30 nm in diameter, showed no precipitation in water, PBS, or a cell culture medium after 3 or 30 h, at 22, 37, and 43°C, and 1, 2.5, and 5 mg/mL, whereas Citrate-IONPs agglomerated rapidly (> 400 nm) in all aqueous media tested. No cytotoxicity was observed in a mouse brain endothelial-derived cell line (bEnd.3) exposed to CNA-IONPs up to 10 mg/mL for 30 h. Citrate-IONPs (> 0.05 mg/mL) reduced cell viability after 3 h. CNA-IONPs retained the superparamagnetic properties of entrapped IONPs, enhancing T2-weighted magnetic resonance images (MRI) at 0.02 mg/mL, and generating heat at a mild hyperthermic level (40?~?42°C) with an alternating magnetic field (AMF).

Conclusion

Compared to citric acid coating, CNAs with a cross-linked anionic core improved particle stability and biocompatibility of IONPs, which would be beneficial for future MRI and AMF-induced remote hyperthermia applications.     

Polyanhydride microsphere formulation by solvent extraction

A novel process based on solvent extraction was developed to produce drug-loaded polyanhydride microspheres for controlled-release applications. The technique consists of adding a chloroform solution of polyanhydride and drug into a stirred silicone oil phase containing suspended droplets of surfactant. No chemical reaction, heating, nor contact with water was required in this process. The microspheres produced were capable of releasing various dyes for prolonged periods of time.     

Polymer Chemistry Influences Monocytic Uptake of Polyanhydride Nanospheres

Purpose  To demonstrate that polyanhydride copolymer chemistry affects the uptake and intracellular compartmentalization of nanospheres by THP-1 human monocytic cells. Methods  Polyanhydride nanospheres were prepared by an anti-solvent nanoprecipitation technique. Morphology and particle diameter were confirmed via scanning election microscopy and quasi-elastic light scattering, respectively. The effects of varying polymer chemistry on nanosphere and fluorescently labeled protein uptake by THP-1 cells were monitored by laser scanning confocal microscopy. Results  Polyanhydride nanoparticles composed of poly(sebacic anhydride) (SA), and 20:80 and 50:50 copolymers of 1,6-bis-(p-carboxyphenoxy)hexane (CPH) anhydride and SA were fabricated with similar spherical morphology and particle diameter (200 to 800 nm). Exposure of the nanospheres to THP-1 monocytes showed that poly(SA) and 20:80 CPH:SA nanospheres were readily internalized whereas 50:50 CPH:SA nanospheres had limited uptake. The chemistries also differentially enhanced the uptake of a red fluorescent protein-labeled antigen. Conclusions  Nanosphere and antigen uptake by monocytes can be directly correlated to the chemistry of the nanosphere. These results demonstrate the importance of choosing polyanhydride chemistries that facilitate enhanced interactions with antigen presenting cells that are necessary in the initiation of efficacious immune responses.     

Polyanhydride Mierospheres that Display Near-Constant Release of Water-Soluble Model Drug Compounds

A new method to prepare polyanhydride microspheres capable of near-constant sustained release of low molecular weight, water-soluble molecules is presented. The polyanhydrides used were poly-(fatty acid dimer) (PFAD), poly(sebacic acid) (PSA), and their co-polymers [P(FAD-SA)]. Acid orange 63 (AO), acid red 8 (AR), and p-nitroaniline, were used as model release molecules. P(FAD-SA) microspheres containing the molecules with or without gelatin were prepared by a modified solvent evaporation method using a double emulsion. The microspheres were spherical with diameters of 50–125 µm and encapsulated more than 85% of the molecule, irrespective of the compound used. Near-zero-order degradation kinetics were observed for 5 days as judged by sebacic acid (SA) release. Microsphere degradation was pH sensitive, being enhanced at high pH, and became more stable in acidic conditions, irrespective of the incorporation of gelatin in the matrix. For the gelatin-free microspheres, a close correlation of SA release and AO release was observed (2% loading), suggesting a release mechanism that was controlled dominantly by degradation. However, the incorporation of gelatin into the microsphere significantly extended the periods of molecule release from P(FAD-SA) microspheres, although the degradation profile of the microspheres themselves was quite similar to that of gelatin-free microspheres. It is possible that an interaction between FAD monomers and gelatin molecules causes continued release, even after the polymer matrix completely degrades (even after complete degradation, FAD monomers remain because of their poor water solubility). Thermal analysis of polyanhydride microspheres at different degradation stages demonstrated that a crystalline structure was formed between gelatin and the FAD monomers produced with microsphere degradation. This gelatin effect on the extended period of drug release was not observed for microspheres prepared from other polyanhydrides: poly (sebacic acid) and its co-polymer of bis(p-carboxyphenoxy) propane and sebacic acid. It is therefore likely that the crystalline structure formed between gelatin and FAD monomers may function as a reservoir for water-soluble drugs, leading to an extended period of molecule release from the gelatin-loaded P(FAD-SA) microspheres.     

Preparation and Characterization of Carmustine Loaded Polyanhydride Wafers for Treating Brain Tumors

Pharmaceutical Research -     

Biocompatibility of haemoperfusion

To evaluate the influence of haemoperfusion on haemodynamics, complement system, leucocyte and thrombocyte concentration, a controlled study was performed in three groups of five dogs each. During the first 30 min of haemoperfusion with columns containing cellulose-coated activated charcoal, a significant decrease of mean aortic pressure, cardiac output and stroke volume was observed, while heart rate and total systemic resistance decreased. A comparable phenomenon, although to a much lesser extent, was observed during perfusion using columns containing polystyrene resin. Perfusion with columns containing cellulose-coated activated charcoal caused a significant decrease in total haemolytic complement, indicating activation of the complement system. A significant decrease in the leucocyte and thrombocyte concentration due to sequestration of granulocytes and thrombocytes in the columns was observed during the first 30 min of perfusion in both groups. Pulmonary leucostasis, without decrease of arterial oxygen tension, occurred during perfusion with columns containing cellulose-coated activated charcoal. Both the simultaneous occurrence and the transient character of the haemodynamic changes, complement activation and sequestration of granulocytes and thrombocytes in the perfusion column suggest a relationship between these various changes. The results stress the importance of close monitoring of the haemodynamic parameters of the intoxicated patient, particularly during the early phase of haemoperfusion.     

Polyanhydride implant for antibiotic delivery--from the bench to the clinic

A polyanhydride implant (Septacin) containing gentamicin sulfate was developed for sustained local delivery of the drug to the site of infection in the treatment of osteomyelitis. Laboratory-scale injection molding equipment was utilized to fabricate the implant for in vitro characterization. Molding conditions were optimized to produce implants with a skin-core structure which was found to be critical in preventing the initial cracking of the implant during in vitro drug release test in water. A manufacturing process consisting of twin-screw extrusion, pelletizing, and injection molding was developed. Polymer-drug pellets were characterized with respect to copolymer molecular weight and drug content uniformity. The implants were terminally sterilized by gamma-radiation which was found to cause increase in copolymer molecular weight as a result of polymer chain extension. The stability of Septacin was evaluated as a function of storage temperature and time. A marked decline in copolymer molecular weight occurred in samples stored above freezing temperatures and significantly slower drug-release profiles were also exhibited by these samples. In vivo drug release from Septacin in rats showed that the gentamicin plasma levels were extremely low, indicating the low systemic exposure to gentamicin. Furthermore, Septacin samples have demonstrated efficacy in the rat skin-abscess and horse-joint infection models. Results from a human in vivo study also showed high local drug concentrations at implantation sites while systemic exposure to the drug was minimal.     

Chemically Reducible Lipid Bilayer Coated Mesoporous Silica Nanoparticles Demonstrating Controlled Release and HeLa and Normal Mouse Liver Cell Biocompatibility and Cellular Internalization

A controlled release system composed of mesoporous silica nanoparticles with covalently bound dipalmitoyl moieties supporting phosphorylated lipids has been successfully synthesized and characterized. This MSN system demonstrates controlled release of fluorescein molecules under disulfide reducing conditions. Flow cytometry analyses confirm increased biocompatibility of the resulting lipid bilayer MSNs (LB-MSNs) from nonfunctional MSNs. Fluorescently labeled LB-MSNs are examined via confocal fluorescent microscopy ex vivo and were found to enter both normal and cancer cell lines. The LB-MSNs presented here have potential to be used as rapid and diverse functionalized, stable liposome analogues for drug delivery.     

The Relationship Between Structures and In Vitro Properties of a Polyanhydride Implant Containing Gentamicin Sulfate

Laboratory scale injection-molding equipment was utilized to fabricate an implant consisting of poly(FAD:SA 1:1) and 20% (w/w) gentamicin sulfate. Characterizations were performed to determine the molecular weight and glass transition temperature of poly(FAD:SA 1:1). A study was carried out to investigate the relationships between the in vitro performance, morphology, and micro-structures of the molded implants. It was found that implants produced with different structures exhibited different physical integrities in water, i.e., cracking or non-cracking. For the non-cracking implants, a skin–core structure formed by an oriented skin layer was observed under a polarized light microscope. The same morphology was not seen in the cracking implants. The crystal orientation in the skin layer of the non-cracking implants was further identified using a wide-angle x-ray diffraction method (WAXD). No crystal orientation could be found in the cracking implants by WAXD. Furthermore, studies were carried out to evaluate the in vitro drug release for implants showing different degrees of integrity in water. The in vitro drug release of the cracking implants was markedly faster than that of the non-cracking implants due to the pronounced initial drug-burst effect as a result of crack formation in the implants.     

Biocompatibility of hemodialysis using cuprophane membranes

In a controlled study of the influence of hemodialysis on hemodynamics, complement system, leucocyte- and thrombocyte concentration was studied in two groups of five non-uremic dogs each. During the initial 30 min of dialysis with the commonly used cuprophane membrane, a transient but significant decrease of the mean aortic pressure and cardiac output occurred while simultaneously heart rate and systemic vascular resistance decreased. Thrombocyte concentration decreased significantly during the initial 60 min of dialysis due to sequestration in the dialyzer. Transient leucopenia due to pulmonary leucostasis occurred without decrease of the arterial oxygen tension. The simultaneous occurrence and transient character of the hemodynamic changes, leucopenia and thrombocytopenia suggest a relationship between these phenomena. These results indicate that the biocompatibility of cuprophane dialysis membranes is of importance not only with regard to changes in the leucocyte- and thrombocyte-count but also with regard to hemodynamic changes.     

双层人工皮肤的生物相容性研究

目的 考察一种新型的皮肤替代物双层人工皮肤的生物相容性.方法 依据GB/T16886医疗器械生物学评价标准规定的细胞毒性、急性毒性试验、皮内刺激试验、致敏试验、亚慢性毒性试验、植入试验和遗传毒性试验方法,评价双层人工皮肤的生物相容性,以验证其安全性和有效性.结果 显示双层人工皮肤无急性毒性、无皮内刺激作用、无致敏作用,细胞毒性不超过1级;皮下植入后1周、4周和12周后,植入组织样品的炎症反应和纤维囊形成与对照无明显差别;遗传毒性采用鼠伤寒沙门氏菌回复突变试验（Ames试验）、体外哺乳动物细胞染色体畸变试验、哺乳动物细胞体外基因突变试验,结果均为阴性,说明双层人工皮肤无遗传毒性.结论 双层人工皮肤具有良好的生物相容性,没有观察到不良反应,符合临床使用要求.     

Morphological Characterization of Polyanhydride Biodegradable Implant Gliadel® During in Vitro and in Vivo Erosion Using Scanning Electron Microscopy

Purpose. The objectives of the current study are to characterize the distribution of the chemotherapeutic agent carmustine (BCNU) in spray dried polyanhydride microspheres and to describe the morphological changes that occur during the in vitro and in vivo erosion of the polyanhydride implant-GLIADEL^®, which consists of BCNU distributed in the copolymer matrix of poly(carboxyphenoxy propane:sebacic acid) in a 20:80 molar ratio (p(CPP:SA, 20:80)). Methods. Scanning electron microscopy (SEM) was used to visualize the morphological changes of the polymer during the manufacturing process and in vitro and in vivo erosion. Results. This study revealed that BCNU was homogeneously distributed within spray dried polyanhydride microspheres with no phase separation. The porosity of the wafer fabricated from spray dried polyanhydride microspheres gradually increased during erosion. During the initial period following wafer implantation in the brains of rats, erosion was mainly confined to the surface layer of the wafer with the majority of the wafer remaining intact. The eroding front gradually advanced from the surface to the interior of the wafer in a layerwise fashion, creating pores and connecting channel. Eventually both the interior and exterior of the wafers were eroded and the same porous structure was seen throughout the whole wafer. Conclusions. This study provides the first visual observation of the morphological changes of the GLIADEL^® wafer during erosion of the polyanhydride matrix and release of the drug substance BCNU. The observations in this study support the conclusion that BCNU release from a polyanhydride wafer is controlled both by diffusion of the drug and erosion of the polymer matrix.     

Biocompatibility Issues of Implantable Drug Delivery Systems

Pharmaceutical Research -     

Biocompatibility and bioabsorption of microfibrillar collagen hemostat in experimental animals

The effects of Microfibrillar Collagen Hemostat (MCH) and Gelfoam® after surgical implantation into incision sites of the liver, kidney, and brain were studied in beagle dogs, rabbitsm, and beagle dogs, respectively. The results of these experimental animal studies suggest that MCH is comparable to Gelfoam® with respect to biocompatability, rate of bioassimilation, and a lack for adverse systematic effects. The brain, liver, and kidney tissues responed comparably to MCH and Gelfoam® with a mild to moderate infiltration of macrophages and mononuclear cells. Most of the hemostatic compound had dissappeared from the incision sites by Day 28 and completely disappeared by Day 84. The tissue degree response was interpreted as a factor in the process of bioassmilation of the two hemostatic materials. Both hemostatic compounds contributed to adhesion formation in the experimental models. The incidence of adhesions was somewhat lower for MCH than for Gelfoam®, but both produced more adhesions than were found at the control sites. The adhesions were only to the adjacent structures and always localized to the surgical site. When MCH or Gelfoam® is used under conditions similar to those in the present experimental study, were tissue approximation is impaired, and where growth of granulation tissue is stimulated by the physical presence of the hemostatic compound, there is the possibility for increased incidence of adhesion formation. However, when an intraperitoneal absorbable hemostatic compound is desired, the present studies in experimental animals suggest that MCH will safe by exhibiting minimal tissue reaction.     

柠檬酸包埋的四氧化三铁纳米颗粒的安全性研究

目的对直径为15 nm的柠檬酸包埋的四氧化三铁纳米颗粒(下以Fe3O4-CA表示)进行安全性研究.方法将Fe3O4-CA以等体积不等浓度经口染毒,分别进行小鼠最大耐受量试验,小鼠骨髓细胞微核试验,小鼠精子畸形试验.结果小鼠灌胃最大耐受量大于600 mg*kg-1;小鼠骨髓细胞微核试验,各剂量组的微核率均低于0.2%;小鼠精子畸形试验中,Fe3O4-CA高剂量组小鼠精子畸形率高于3.8%(P＜0.05).结论在600 mg*kg-1范围内,Fe3O4-CA对小鼠体细胞无致突变性,而对小鼠雄性生殖细胞可能有致突变性.     

羧甲基壳聚糖在大鼠颅内组织相容性的初步观察

目的:探讨生物可降解缓释材料羧甲基壳聚糖(CMCS)在大鼠脑组织中的生物相容性,为开发其临床新用途奠定基础。方法:32只SD大鼠随机分为实验组和对照组,分别植入同面积的CMCS和明胶海绵。观察术后大鼠的行为改变和第3,7,14,30天的局部组织反应(HE染色)。结果:两组大鼠在实验期内均无明显行为改变,术后第3,7,14,30天的组织学观察表明CMCS为异物反应,与明胶海绵类似,无明显差异(P<0.05)。随时间推移,CMCS有不同程度降解。结论:CMCS具有良好的脑组织生物相容性,并可安全的降解,可作为颅内植入化疗缓释材料进一步开发。     

Nanoparticles for detection and diagnosis

Nanoparticle based platforms for identification of chemical and biological agents offer substantial benefits to biomedical and environmental science. These platforms benefit from the availability of a wide variety of core materials as well as the unique physical and chemical properties of these nanoscale materials. This review surveys some of the emerging approaches in the field of nanoparticle based detection systems, highlighting the nanoparticle based screening methods for metal ions, proteins, nucleic acids, and biologically relevant small molecules.