Polymer Nanofilm Coatings - Report Example

Polymer Nanofilm Coatings Introduction Na chnology forms part of the most promising areas of biomedicine; especially with regards to interrogation of nature at length scale of DNA, proteins, and other biological molecules (Lee 30). This paper reviews nano-film biomaterials, which are functional and thin nanoscopic films based on polymers that act as biocompatible interfaces. In addition, there are strategies towards films that have independent mechanical rigidity and controllable bioactivity. Nanofilm coatings that are used in medical devices are made up of tri-block or di-block co-polymers. These nanofilms find use in various areas such as therapeutic agents by offering amphiphillic support. In this case, they are useful in forming active substrates for medical and biological applications. Polymer nanofilm coatings are generally applied in pharmaceutical and medical fields. Especially, this invention is related to pharmaceutical and medical products that possess biocompatible nanofilms for therapeutic uses. The patent for polymer nanofilm coatings makes several claims (Lee 31). For instance, the product is an implantable medical device that has three surfaces layered nanofilm structures. The device referred to also has one or more therapeutic agents, while at least one of the agents is not protein in nature. It is also selected from agents and inhibitors like thrombolytic agents and thrombin agents. In addition, the medical device has a co-polymer with one layer measuring between one and ten nano-meters in thickness, while the device also has an electrode. Background Science Biomaterials can be defined, as non-viable materials for use in medical devices to form interactions with other biological systems. One of the most challenging factors in bio-materials science is the control of cellular responses. Various material properties are regarded as being influential to cells in contact, including mechanical rigidity, topography, and hydrophobicity (Yasuda et al. 677). Additionally, the cells could be reactive with the material’s bio-active elements. In an ideal situation, these properties are tunable independently such that optimal materials can be designed with the aim of achieving a cellular response. Practically, mechanical rigidity and bioactivity are two properties that are hard to de-couple. For instance, examples from nanofilm biomaterials created through the LbL method controls rigidity via chemically cross-linking the network of polymers after assembly, while conference of bioactivity is done via surface adsorbed or film-embedded bio-molecules. When film bio-activation is preceded by cross-linking, the embedded bio-molecules could be rendered inaccessible to the cells they are in contact with, whereas when bio-activation is followed by cross-linking, bio-molecular loadings is limited at the surface of the film (Chow & Cheng 35). Thus, for the current approach to making polymer nanofilm coatings, bioactivity and mechanical rigidity of the coating are strongly and usually inversely coupled. Figure 1 Schematic for Nanofilm formation through Surface Cross-linking Strategy (A&B) and Nano-particle Templating Strategy (C&D) (Phelps et al. 1126) Thus, it was important to develop an approach to nanofilm coatings with bioactivity and mechanical rigidity that as tunable independently. One of the strategies to this was surface cross-linking, in which formation of cross-links was confined to the polymer film’s surface region in order not to interfere with species that are bioactive in the interior of the film (Yasuda 129). Nano-particle templating was another strategy used, here, the nanofilm was created alongside spherical latex nano-particles with cross-linking chemically, to improve rigidity of the film and imbue it with porous morphology, while removing nano-particles through dissolution. In this case, the idea revolved around the creation of a polymer nanofilm by hardening the polymer portion using standard methods of cross-linking followed by filling pore spaces with bioactive species (Johal 55). Both of these activities were done to extents that could be controlled independently. In using each of these strategies, there were key questions regarding how much the film would be penetrated by various macromolecular particles and species. Using the cross-linking method, the polymer, is bound to cross-linking agents so that it adsorbs to the film but does not penetrate it, allowing for the formation of cross-links with polymers that were already adsorbed to the surface of the film (Yang et al. 611). In this case, the most essential question was whether the formation of cross-links happened before penetration of the polymer nanofilm. Through the use of polymers labelled with fluorescent material and con-focal microscopy using laser scanning, it was verified that there was the formation of a layer with true surface cross-linking. With regards to nano-particle templating, the space in the pores is to be filled by species with bio-activity, although filling of the pores needed the species to go through the film into the interior regions. By utilizing laser scanning con-focal microscopy, it was possible to establish that the bioactive particles or species did penetrate the porous nanofilm, although this did not occur using a control film lacking in pores. Using the known concentration of bulk bioactive species, concentration of a bioactive material such as albumin within the nanofilm could be approximated to about ten percent or 0.1 mg/l of the mass film (Kato et al. 824). A question arose as to whether these strategies affected the properties of the nanofilm beyond bioactivity and mechanical rigidity. Analyzing the topography of the surface using AFM indicated that nano-particle templated films and standard cross-linked film possessed almost identical values of surface roughness at 10 nm and 7 nm respectively, as well as similar distribution of domain sizes in the order of twenty to fifty nm (Wu et al. 69). However, it is still possible to impart subtle structural differences via the process of templating, which contributed to potentially eventual response of the cells. With regards to the extent to which nano-particle templated and surface cross-linked nanofilms enhanced initial response of the cell, the researchers considered interactions of the film with MC3T3-E1 cells in their pre-osteoblastic phase (Malvadkar et al. 1025). Results showed that the amount of cells adhering to the surface cross-linked films were intermediate compared to that between fully cross-linked films and non-cross-linked films. In addition, it was also shown that cell spreading on porous nano-particle templated films were comparable to cell spreading on non-porous fully-cross-linked film, while it was greater than a cell spreading on non-cross linked, native films. Context of the Patent Several products are similar to polymer nanofilm coatings and could act as competition for the product. One of them is the amphiphillic co-polymer planar membrane, which could co-polymers of ABA nature, in which either A or B is hydrophilic, while the other part is hydrophobic (Wittmer et al. 4085). For this product, cross-linking is possible through various methods, such as polymerization from end-to-end of co-polymers that possess terminal groups that are unsaturated. Membrane proteins and other similar molecules can be co-opted into the membrane, enabling the transport of selected components. Vascular grafts utilizing coatings of amphiphillic block co-polymers are also products similar to the nanofilm coatings. A surface coated with amphiphillic co-polymers includes both hydrophilic and hydrophobic polymer chains. This can serve as a transporter for a wide drug range, including those already in use and others being considered or likely to be used in inhibiting stenosis (Moss 121). The drugs are released at rates that are controllable via varying the polymer chain length, cross-linking degree, or the ratio. Polymer coatings for pharmaceutical, as well as, medical devices are provided. Here, the surfaces are activated through formation of covalent bonds to metal surfaces using silane derivatives, binding lactone polymers covalently to this derivative via polymerization by in-situ opening of rings, and depositing one or more polyester layers on bonded lactones (Wittmer 56). It is possible deposit agents with bio-activity with polyester layers, in which the coated surfaces can be utilized in pharmaceutical and medical devices, such as stents. Hemo-compatible and bio-compatible polymer compositions are also similar in action to the polymer nanofilm coatings. Specifically, they are designed for the control of bio-active agent release from in vivo medical devices. Their application also provides vascular stents that have coatings for controlled release. Other embodiments of this invention involve peptide drug and co-polymer coated stents. Analyte sensors are also similar in activity to nanofilm coatings. They are generally related to membranes used with devices for implantation, especially for the detection of concentrations of analyte in biological samples (Phelps 28). Specifically, this invention is related to hydrophilic silicone polymerized membranes, as well as, to implantable devices that include this membrane. Micro-porous coatings are also similar to the polymer nanofilm coating. They are made of micro-porous glassy, metallic, or ceramic coatings on medical and pharmaceutical devices, comprising of bioactive agents for controlled agent release of various agents (Van Tassel 529). Finally, multilayered coatings for active agent elution control are also used similarly to the nanofilm coatings and involve application of coatings for elution control to substrates. This invention can also involve deposition of coating solutions to substrates in order to form base layers. This invention also could include the selection of solvent concentrations desired based on desired rates of elution. This technique is also worthwhile in the removal of solvents from base layers to attain the desired solvent concentration, while depositing parylene layers on the base layer (Phelps et al. 1126). This product could also include pharmaceutical and medical devices that include porous layers, base layers, and substrates. Parylene can be included in the base layer, while active agents in polymeric matrices are also included in the base layer. Weaknesses of the Patent Current strategies aimed at making nanofilm coatings are based on grafted polymers and release of agents. In the latter approach, antibiotics and other agents are embedded in materials prior to release via material degradation and/or diffusion. Although this is effective in various cases, it does have some weaknesses (Tretinnikov 65). For illustration, it is challenging to control the rate of release of various substrates through the polymer nanofilm coating. In addition, these materials could be potentially toxic to human cells, while the agents embedded in the material could be eventually depleted. Furthermore, there is a possibility that, where polymer nanofilm coatings are used for controlled release of antibiotics, resistance to the antibiotics could develop. With regards to the former approach, polymer nanofilm coatings are composed of quaternary, highly charged amine groups that are grafted chemically to the surface of the material with the objective of providing a more permanent effect. However, the chemistry used during grafting could be rather intricate, as well as inapplicable to specific materials. Long-term graft stability is also a challenge for this method (Pritchard et al. 857). While this invention included studies into the use of natural polymers in engineering of tissues, combination of natural polymers as coatings is not practical. One vital element of using polymer nanofilm coatings in tissue engineering is the synthetic or natural formation of scaffolding devices (Subbiah et al. 550). If natural materials are to be used, they are normally made up of gelatine, chitosan, fibrin, collagen, and other extra-cellular matrix species. However, materials derived naturally have specific limitations. Because they originate from animal and human tissue, they tend to be batch sensitive and expensive. In addition, materials derived naturally are yet to be discovered that have the ability for diverse and multiple signals. While there has been progress in this field, these materials still come with inferior control over mechanical properties and scaffold structure in comparison to more synthetic materials (Rudra et al. 1304). However, these synthetic materials also offer unique challenges compared to naturally sourced materials when used in polymer nanofilm coatings (Silva et al. 186). The most important goal in the use of synthetic materials is the final creation of materials that, over a period of time, will be degraded so as to enable the biological system to go back finally to its original state sans the system retaining any synthetic material. There are only three FDA approved synthetic polymers, which are naturally degradable, including PLA, PGA, and PDS. These materials also come with their specific limitations and drawbacks when used in polymer nanofilm coatings for tissue engineering (Silva et al. 186). While they do offer the best control over the rate of degradation, mechanical properties, and microstructure, they do not have molecules for recognition of cells. Conclusion Nanotechnology, via matching of vital bio-molecular and material length scales, has made critical contributions to the field of bio-medicine. This paper summarizes the current work in the area of thin polymer based nanofilm coating biomaterials, which have a thickness of approximately ten to one hundred nanometres. In this case, the nanofilms are controlled independently for mechanical rigidity and bioactivity, which are either achieved through nano-particle templating or surface cross-linking. While there are other inventions that offer similar practical use, such as amphiphillic co-polymer planar membranes and hemo-compatible and bio-compatible polymer compositions, polymer nanofilms offer great promise in the biological material interface world, in spite of weaknesses like controlling rates of substrate release. Works Cited Chow, Pierstorff. & Cheng, Ho. "Copolymeric Nanofilm Platform for Controlled and Localized Therapeutic Delivery." Acs Nano. 2.1 (2008): 33-40. Print. 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