Biomedical subjects

A Lendlein

Publications and source records attributed to A Lendlein.

14 recordsLinked to original sources

PubMed2006

Polymeric triple-shape materials.

Shape-memory polymers represent a promising class of materials that can move from one shape to another in response to a stimulus such as heat. Thus far, these systems are dual-shape materials. Here, we report a triple-shape polymer able to change from a first shape (A) to a second shape (B) and from there to a third shape (C). Shapes B and C are recalled by subsequent temperature increases. Whereas shapes A and B are fixed by physical cross-links, shape C is defined by covalent cross-links established during network formation. The triple-shape effect is a general concept that requires the application of a two-step programming process to suitable polymers and can be realized for various polymer networks whose molecular structure allows formation of at least two separated domains providing pronounced physical cross-links. These domains can act as the switches, which are used in the two-step programming process for temporarily fixing shapes A and B. It is demonstrated that different combinations of shapes A and B for a polymer network in a given shape C can be obtained by adjusting specific parameters of the programming process. Dual-shape materials have already found various applications. However, as later discussed and illustrated by two examples, the ability to induce two shape changes that are not limited to be unidirectional rather than one could potentially offer unique opportunities, such as in medical devices or fasteners.

Journal Article↗

PubMed2006

Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers.

In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temperature, T(switch). If polymers cannot be warmed up by heat transfer using a hot liquid or gaseous medium, noncontact triggering will be required. In this article, the magnetically induced shape-memory effect of composites from magnetic nanoparticles and thermoplastic shape-memory polymers is introduced. A polyetherurethane (TFX) and a biodegradable multiblock copolymer (PDC) with poly(p-dioxanone) as hard segment and poly(epsilon-caprolactone) as soft segment were investigated as matrix component. Nanoparticles consisting of an iron(III)oxide core in a silica matrix could be processed into both polymers. A homogeneous particle distribution in TFX could be shown. Compounds have suitable elastic and thermal properties for the shape-memory functionalization. Temporary shapes of TFX compounds were obtained by elongating at increased temperature and subsequent cooling under constant stress. Cold-drawing of PDC compounds at 25 degrees C resulted in temporary fixation of the mechanical deformation by 50-60%. The shape-memory effect of both composite systems could be induced by inductive heating in an alternating magnetic field (f = 258 kHz; H = 30 kA x m(-1)). The maximum temperatures achievable by inductive heating in a specific magnetic field depend on sample geometry and nanoparticle content. Shape recovery rates of composites resulting from magnetic triggering are comparable to those obtained by increasing the environmental temperature.

Journal Article↗

PubMed2005

Dynamics of beta1-integrins in living fibroblasts--effect of substratum wettability.

The dynamics of integrin receptors mobility was studied in living human fibroblasts using fluorescence-labeled beta(1)-integrin monoclonal antibodies. Time-lapse image series were obtained by confocal laser scanning microscopy when cells were adhering on model hydrophilic (clean glass) and hydrophobic (octadecyl-silanized; i.e., ODS) surfaces coated with fibronectin. Direct measurements showed approximately twice-higher velocity of integrins on glass compared to ODS, and these velocities varied in different zones of the cells. A kinetic model and algorithm for quantification of images was developed, and the analysis identified three receptor populations on glass: immobilized (82.76% of all), slow (4.16%), and fast (13.08%), while, on ODS, only two were identified: immobilized (83.36%) and fast (16.64%). Fast integrins in the peripheral zone of cells have maximal velocities of 0.353 +/- 0.02 mum/min (n = 48, four cells) on hydrophilic and 0.218 +/- 0.02 mum/min (n = 30, three cells) on hydrophobic substrata. The slow population has a velocity of 0.114 mum/min (n = 48, four cells). Further analyses show that these velocities also differ significantly in the peripheral and middle zones of cells in a substrate-dependent fashion. A well-defined circular motion of receptors around the cell center expressed mainly on hydrophobic substrata was monitored and quantified as well.

Algorithms↗

PubMed2005

On the tissue compatibility of poly(ether imide) membranes: an in vitro study on their interaction with human dermal fibroblasts and keratinocytes.

Recently we have developed a novel type of membrane based on poly(ether imide) (PEI) which is considered for biomedical application. To improve its physical and biological performance it was modified by blending with poly(benzimidazole) (PBI). In the present study both membranes were characterized in terms of their physicochemical properties and in vitro tissue compatibility using human dermal fibroblasts and keratinocytes. The modified membrane (PEI*) was more hydrophilic, less porous and had an increased surface (zeta) potential. We further found that blending with PBI tends to promote cell contact, at least initially, as indicated by the improved overall cell morphology, adhesion and spreading of fibroblasts, and the development of focal adhesion complexes. The effects of fibronectin (FN) and serum coating were also beneficial when compared to pure PEI and tissue culture polystyrene (TCP), which correlates to a higher adsorption of both FN and vitronectin detected by ELISA. However, a clear tendency for homotypic cellular interaction particularly of keratinocytes was obtained in contact with membranes, which was much stronger pronounced on PEI*. Although the initial adhesion was greater on PEI*, a surprising decrease in cell growth was observed at later stages of incubation, which may be explained with the membrane-promoted cellular aggregation leading to an easier detachment from the substratum. Thus, membranes based on blends of PEI with PBI could provide a tissue compatible scaffold with lowered adhesive properties, which might be a useful tool for the transfer of cells, for example, to in vitro engineered tissue constructs.

Actins↗

PubMed2005

[Cell proliferation and cellular activity of primary cell cultures of the oral cavity after cell seeding on the surface of a degradable, thermoplastic block copolymer].

Using standard cell biological and biochemical methods we were able to test the ability of a degradable, thermoplastic block copolymer to support the adhesion, proliferation, and the cellular activity of primary cell cultures of the oral cavity in vitro. The delicate balance between a group of endogenous enzymes, Matrix Metalloproteinases (MMPs), and their inhibitors (Tissue Inhibitor of MMPs, TIMPs) have a decisive function in the remodeling of the extracellular matrix during processes like wound healing or the integration of biomaterials in surrounding tissues after implantation. Recently developed, biodegradable thermoplastic elastomers with shape-memory properties may be the key to develop new therapeutical options in head and neck surgery. Primary cell cultures of the oral cavity of Sprague-Dawley rats were seeded on the surface of a thermoplastic block copolymer and on a polystyrene surface as control. Conditioned media of the primary cells were analyzed for MMPs and TIMPs after different periods of cell growth. The MMP and TIMP expression was analysed by zymography and a radiometric enzyme assay. No statistically significant differences in the appearance and the kinetic of MMP-1, MMP-2, MMP-9 and TIMPs were detected between cells grown on the polymer surface compared to the control. An appropriate understanding of the molecular processes that regulate cellular growth and integration of a biomaterial in surrounding tissue is the requirement for an optimal adaptation of biodegradable, polymeric biomaterials to the physiological, anatomical, and surgical conditions in vivo to develop new therapeutic options in otolaryngology and head and neck surgery.

Absorbable Implants↗

PubMed2005

Shape-memory polymers as stimuli-sensitive implant materials.

Shape-memory polymers are stimuli-responsive materials. Upon exposure to an external stimulus, e.g. an increase in temperature, they have the capability of changing their shape. The shape-memory effect results from the polymer's structure and morphology in combination with a certain processing and programming technology. Stimuli-sensitive implant materials have a high potential for applications in minimally invasive surgery. A group of biodegradable implant materials with shape-memory has been developed for applications in biomedicine. These implant materials are not a single polymer but polymer systems that allow the variation of different macroscopic properties over a wide range by only small changes in the chemical structure. In this way, it is possible to implement a variety of different applications with tailor-made polymers of the same family. Two different types of degradable shape-memory polymer systems, covalently cross-linked polymer networks and thermoplastic elastomers, are presented and examples are given for each case.

Absorbable Implants↗

PubMed2005

Expression of MMPs and TIMPs in primary epithelial cell cultures of the upper aerodigestive tract seeded on the surface of a novel polymeric biomaterial.

INTRODUCTION: Using standard cell biological and biochemical experimental approaches we were able to test the ability of a particular polymer construct to support the adhesion, proliferation, and the cellular acitivity of pharyngeal cells. The delicate balance between Matrix Metalloproteinases (MMPs) and their endogenous inhibitors (Tissue Inhibitor of MMPs, TIMPs) have a decisive function in the remodeling of the extracellular matrix during cellular ingrowth. Novel polymeric biomaterials may be useful to develop new therapeutic options in head and neck surgery. METHODS: Primary cell cultures of the pharynx of Sprague-Dawley rats were seeded on the surface of a thermoplastic multi-block copolymer and on a polystyrene surface as control. Conditioned media of the primary cells was analyzed for MMPs and TIMPs. The MMP and TIMP expression was analysed by zymography and a radiometric enzyme assay. RESULTS: No statistically significant differences in the levels of MMP-1, MMP-2, MMP-9 and TIMPs were detected between cells grown on the novel polymer surface versus control. CONCLUSION: An appropriate understanding of the molecular machinery that regulates gene expression and cellular growth in tissue engineered constructs is the requirement for an optimal adaptation of biodegradable biomaterials to develop new therapeutic options in otolaryngology and head and neck surgery.

Animals↗

PubMed2005

Smart implant materials.

The combination of stimuli-sensitive implant materials and minimally invasive surgery techniques is expected to give rise to numerous applications. Biodegradable thermoplastic elastomers are presented here as an example of a group of biodegradable implant materials with shape-memory properties. Their capabilities and use in a smart suture are described.

Absorbable Implants↗

PubMed2004

The influence of the chemical composition of cell culture material on the growth and antibody production of hybridoma cells.

The multiplication and antibody production of murine hybridoma cells cultured on five different polymer membranes were tested and compared with conventional tissue culture polystyrene (TCPS). Membranes were prepared from polyacrylonitrile (PAN) and acrylonitrile copolymerized with N-vinylpyrrolidone (NVP20, NVP30), Na-methallylsulfonate (NaMAS) and N-(3-amino-propyl-methacrylamide-hydrochloride) (APMA). Cell number and antibody concentration were quantified as criteria for viability and productivity. Adhesion of hybridoma cells was characterized by vital and scanning electron microscopy. The results suggest that a strong adhesion of cells, observed on APMA and TCPS, increased cell growth but reduced monoclonal antibody production. In contrast membranes with lowered adhesivity such as NVP20 provided favourable conditions for monoclonal antibody production. In addition it was shown that this membrane also possessed a minor fouling as indicated by the low decrease of water flux across the membrane after protein adsorption. It was concluded that NVP20 could be a suitable material for the development of hollow fibre membranes for bioreactors.

Animals↗

PubMed2004

Biomaterial-microvasculature interaction on polymers after implantation in mice.

Biomaterial research is expected to forward new materials to be used as, e.g., implant materials or as scaffolds for tissue engineering. It is central for such a scaffold material to create the track on which those cells can inhabitate the scaffold needed to rebuild functional tissue substitutes. For the biointegration of the implant with the native cellular tissue this must be able to grow on the material surface. For the elimination of the degradation products and the adeqaute transport of nutrients/gases within the newly formed tissue the angiogenesis of new blood vessels is thought to play an important role. In the present study, a new biomaterial, a non-porous polymeric AB-network based on oligo (epsilon-hydroxycaproat) and oligobutylacrylat, was implanted in animals. Male NMRI mice were implanted subcutaneously for one week to nine weeks. Immediately after the explantation, the probes were examined histologically. Already one week after implantation, there was a strong tissue-integration of the polymer. Importantly, blood vessels appeared at the polymer surface. At nine weeks after implantation the tissue integration was stronger than after one week and blood vessels were still observed in the periimplant tissue. The mechanism of the early integration of the polymer is not clear. The relationship between the new periimplant vessels and the integration of the polymer has to be studied.

Animals↗

PubMed2003

In vitro cytotoxicity testing of AB-polymer networks based on oligo(epsilon-caprolactone) segments after different sterilization techniques.

Recently developed versatile biodegradable polymeric biomaterial offer new therapeutic options in numerous medical fields. Biocompatibility is a crucial requirement for the biomedical application of biomaterials, including the sterilization of these materials with the use of accepted protocols. Ethylene-oxide (EO) and low-temperature plasma (LTP) sterilization are frequently used low-temperature sterilization technologies for heat-sensitive materials. The agarose diffusion assay is a recommended cell-screening test to assess the cytotoxicity of biomaterials in vitro. The sensitivity of the agarose assay can be increased by using a modified computer-based image-analysis system. The influence of EO and LTP sterilization on the cytotoxicity of a versatile polymer system of shape-memory polymer networks based on oligo (epsilon-caprolactone) dimethacrylate and n-butyl acrylate was investigated. Statistically significant differences in the rate of cell lysis after EO and LTP sterilization of the polymer samples were detected by using this modified quantification system. The influence of the different sterilization techniques on the cytotoxicity of the polymeric material, as well as the clinical relevance of the described differences, are discussed.

Animals↗

PubMed2003

The importance of angiogenesis in the interaction between polymeric biomaterials and surrounding tissue.

The uncomplicated outcome of surgical interventions after biomedical application of biomaterials depends on successful wound healing. Wound healing is a highly complex process compossed of a number of overlapping phases, including inflammation, epithelialization, angiogenesis and matrix deposition. Inadequate angiogenesis limits the transport between the microvasculature and implanted biomaterials. The regulation of angiogenesis is based on numerous growth factors, proteolytic enzymes, extracellular matrix components, cell adhesion molecules, and vasoactive factors. Capillary endothelial cells were grown for different time periods (day 1, 3, 6, 9 and 12) on the surface of a recently developed biodegradable polymeric biomaterial. As control the cells were seeded on the gelatine coated polystyrene surface of commercially available cell cultures dishes. Endothelial cells became adherent and showed confluent cells layers during increasing time period on both surfaces. The total cell number of cells grown on the gelatine coated polystyrene surface was higher in comparison to the polymer surface. The chorioallantois membrane (CAM) assay was used as a sensitive assay to investigate the influence of angiogenesis in vivo. After 48 hours of exposure of the CAM to polymer samples no avascular zones, free of capillaries and/or thrombosis or hemorrhage were detectable. Considering the biofunctionality of our recently developed polymer in these experiments different surface modifications of the polymer are the topic of current investigation to support the biomaterial-microvasculature interactions in vivo.

Absorbable Implants↗

PubMed2002

[Detailed evaluation of the agarose diffusion test in biocompatibility study with a microscopic image analysis system. Effect of plasma sterilization on biocompatible of an improved photoset polymer].

In addition to sterilizability, biocompatibility is a further necessary property of biomaterials. The agarose diffusion test is an established standard in vitro procedure for investigating this property. The usual method of evaluating the agarose diffusion test, based on macroscopic determination of the size of the zone of decoloration, and microscopic assessment of cell lysis, limits the power of the test. To obtain more information on the impact of plasma sterilization on the biocompatibility of a new polymer, a high-resolution computer-aided morphometric image analysis system for the quantification of the agarose diffusion test at the cellular level has been developed. This was able to detect statistically significant differences in the cell lysis rate of plasma sterilized polymer specimens before and after 4 weeks of incubation in a physiological solution. The new method provides highly detailed information on the interaction of soluble material elements and cells. In addition to cell damage by potentially toxic elements, the sensitivity of the L929 fibroblasts used in the agarose diffusion test to mechanical stress also needs to be considered and verified by further investigations.

Animals↗

PubMed2001

AB-polymer networks based on oligo(epsilon-caprolactone) segments showing shape-memory properties.

Although shape-memory metal alloys have wide use in medicine and other areas, improved properties, particularly easy shaping, high shape stability, and adjustable transition temperature, are realizable only by polymer systems. In this paper, a polymer system of shape-memory polymer networks based on oligo(epsilon-caprolactone) dimethacrylate as crosslinker and n-butyl acrylate as comonomer was introduced. The influence of two structural parameters, the molecular weight of oligo(epsilon-caprolactone) dimethacrylate and the weight content of n-butyl acrylate, on macroscopic properties of polymer networks such as thermal and mechanical properties has been investigated. Tensile tests above and below melting temperature showed a decrease in the elastic modulus with increasing comonomer weight content. The crystallization behavior of the new materials has been investigated, and key parameters for the programming procedure of the temporary shape have been evaluated. Shape-memory properties have been quantified by thermocyclic experiments. All samples reached uniform deformation properties with recovery rates above 99% after 3 cycles. Whereas strain recovery increased with increasing n-butyl acrylate content, strain fixity decreased, reflecting the decreasing degree of crystallinity of the material.

Journal Article↗