**1. Introduction**

200 Polyurethane

38, 453-8.

134-9.

Suppl 2, B11-9.

*Biomater,* 6, 125-8.

*Int,* 22, 47-50.

289-93.

*Proc Inst Mech Eng H,* 222, 1175-83.

*Orthop Assoc,* 8, 254-60; discussion 260.

milling operations. *J Biomech,* 39, 33-9.

*Musculoskeletal Surgery,* 93, 9-13.

Shin, H. C. & Yoon, Y. S. (2006) Bone temperature estimation during orthopaedic round bur

Shuler, T. E., Boone, D. C., Gruen, G. S. & Peitzman, A. B. (1995) Percutaneous iliosacral screw fixation: early treatment for unstable posterior pelvic ring disruptions. *J Trauma,*

Silber, J. S., Anderson, D. G., Daffner, S. D., Brislin, B. T., Leland, J. M., Hilibrand, A. S., Vaccaro, A. R. & Albert, T. J. (2003) Donor site morbidity after anterior iliac crest bone harvest for single-level anterior cervical discectomy and fusion. *Spine (Phila Pa 1976),* 28,

Simoes, J. A., Vaz, M. A., Blatcher, S. & Taylor, M. (2000) Influence of head constraint and muscle forces on the strain distribution within the intact femur. *Med Eng Phys,* 22, 453-9. Spagnolo, R., Bonalumi, M., Pace, F. & Capitani, D. (2009) Minimal-invasive posterior approach in the treatment of the posterior wall fractures of the acetabulum.

Stˆlken, J. S. & Kinney, J. H. (2003) On the importance of geometric nonlinearity in finite-

Stoffel, K., Dieter, U., Stachowiak, G., Gachter, A. & Kuster, M. S. (2003) Biomechanical testing of the LCP--how can stability in locked internal fixators be controlled? *Injury,* 34

Szivek, J. A., Thomas, M. & Benjamin, J. B. (1993) Characterization of a synthetic foam as a

Szivek, J. A., Thompson, J. D. & Benjamin, J. B. (1995) Characterization of three formulations of a synthetic foam as models for a range of human cancellous bone types. *J Appl* 

Thompson, M. S., McCarthy, I. D., Lidgren, L. & Ryd, L. (2003) Compressive and shear properties of commercially available polyurethane foams. *J Biomech Eng,* 125, 732-4. Tile, M., Helfet, D. L. & Kellam, J. F. (Eds.) (2003) *Fractures of the pelvis and acetabulum,* 

Trnka, H. J., Nyska, M., Parks, B. G. & Myerson, M. S. (2001) Dorsiflexion contracture after the Weil osteotomy: results of cadaver study and three-dimensional analysis. *Foot Ankle* 

Wehner, T., Penzkofer, R., Augat, P., Claes, L. & Simon, U. (2010) Improvement of the shear fixation stability of intramedullary nailing. *Clin Biomech (Bristol, Avon),* 26, 147-51. Zdero, R., Olsen, M., Bougherara, H. & Schemitsch, E. H. (2008) Cancellous bone screw purchase: a comparison of synthetic femurs, human femurs, and finite element analysis.

Zdero, R., Rose, S., Schemitsch, E. H. & Papini, M. (2007) Cortical screw pullout strength and effective shear stress in synthetic third generation composite femurs. *J Biomech Eng,* 129,

Zoys, G. N., Mcganity, P. L., Lanctot, D. R., Athanasiou, K. A. & Heckman, J. D. (1999) Biomechanical evaluation of fixation of posterior acetabular wall fractures. *J South* 

element simulations of trabecular bone failure. *Bone,* 33, 494-504.

model for human cancellous bone. *J Appl Biomater,* 4, 269-72.

Philadelphia, PA USA, Lippincott Williams & Wilkins.

Polyurethanes (PUs) are one of the most "pluripotent" synthetic polymer classes used in medical applications. Due to their structural versatility, they have been widely discussed as materials appropriate for biomedical applications (Abd El-Rehim & El-Amaouty, 2004; Guelcher et. al., 2007; Guelcher, 2008; Kavlock et. al, 2007; J.S. Lee et. al., 2001; Lelah & Cooper, 1987; Siepe et. al., 2007). Up to now, new PUs have been synthesized that possess good mechanical properties. Most of them are considered biocompatible on account of *in vitro* cytotoxicity evaluation.

However, it is well known that structural and mechanical adaptability of PUs is not always accompanied by cell and tissue biocompatibility. Therefore, numerous data in the literature are focused on biocompatibilization or functionalization of PUs (Yao, 2008; Sartori, 2008, Huang & Xu, 2010). Some promising methods for the improvement of biological response of PUs are conjugation, blending or coating with natural polymers. Thus, polysaccharides as chitosan, cellulose and their derivatives (Raschip, 2009; Zia, 2009; Zuo, 2009), proteins and glycoproteins as collagen, fibrin, fibronectin (R. Chen et. al., 2010; Sartori et. al., 2008), proteoglycans and glycosaminoglycans (Gong et. al., 2010) and other molecules (Hwang & Meyerhoff, 2008; Hsu et. al., 2004; Makala et. al., 2006; Song et. al., 2005; Verma & Marsden, 2005) are employed successfully for PUs modification. Owing its specific properties, hydroxypropylcellulose (HPC) is already used as binder, thickener, lubricating material (artificial tears) and emulsion stabilizer in pharmaceutical and food industry. Moreover, HPC may provide interactions through its hydroxyl radicals, being an excellent compound for copolymerization in scaffolds for tissue engineering and in drug delivery systems (Berthier et. al., 2011; D. Chen & Sun, 2000; Gutowska et. al., 2001; Raschip et. al., 2009;

© 2012 Butnaru et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Butnaru et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Valenta & Auner, 2004). In previous studies we found that when added to PU structure, HPC improves hydrophilicity and mechanical properties of PUs by increasing the elasticity of the resulted materials (Macocinschi et. al., 2009).

Biocompatibility and Biological Performance

of the Improved Polyurethane Membranes for Medical Applications 203

Briefly, isocyanate terminated urethane prepolymers were first synthesized by the polyaddition reactions between 4',4'-diphenylmethane diisocyanate (MDI) and macrodiols in N,N-dimethylformamide (DMF) as solvent. Poly(ethylene adipate)diol (PEGA, Mn = 2000 g/mol), polytetrahydrofuran (PTHF, Mn = 2000 g/mol) or poly(propylene)glycol (PPG, Mn = 2000 g/mol) were used as macrodiols. The urethane prepolymers were treated in a subsequent step with ethylene glycol (EG) as chain extender. Finally, HPC (average weight molecular weight Mw = 95 000 g/mol) was added to PU solutions to obtain the following compositions for all PU/HPC samples: macrodiol/MDI/EG/HPC = 52.24 /36.57/7.27/3.92 (weight ratios). As the molar ratio between isocyanate groups in MDI and the sum of hydroxylic groups in macrodiol and EG was 1.02, the excess of isocyanate groups linked to PU prepolymers were available to bind a part of HPC chains. Membranes with about 1 mm thickness were prepared by pouring PU/HPC DMF solutions in distilled water, at 40 oC. The formed films were then

dried under vacuum for several days and kept in distilled water for solvent removing.

respectively**.** 

**2.2. ζ potential determination** 

conductivity (Luxbacher, 2006)

**2.3. Wettability** 

To half of PUs with PEGA macrodiol in the soft segment no HPC was added to obtain PU-PEGA reference sample. HPC containing samples based on PEGA, PTHF and PPG macrodiols were codified as PU-PEGA/HPC; PU-PTHF/HPC and PU-PPG/HPC,

ζ potential of the PU membranes was measured by streaming potential method using a commercial electrokinetic analyzer SurPASS, (Anton Paar GmbH, Graz, Austria). For each sample, ζ potential has been measured in 0.1 M NaCl solution at physiological 7.4 pH value, a 300 mbar electrolyte pressure and a 80 ml/min flow rate. For statistical reasons, four streaming potentials were measured. The mean value of these data was used for potential calculation by Fairbrother–Mastin equation, considering also the effect of surface

*Wettability* of the PU membranes was determined by measuring the surface contact angle and water uptake. For surface contact angle, uniform drops of the tested liquid (doubledistilled water) with a volume of 2 μl were deposited on the film surface and the contact angles were measured after 30 s, using a video-based optical contact angle measuring device equipped with a Hamilton syringe in a temperature-controlled environmental chamber. All measurements were performed at room temperature of 25 C. Repeated measurements of a given contact angle were all within the range of ± 3 degrees. *Water uptake* was calculated as

Material extraction in a simulated biological microenvironment was done for long period of time (over 2 months) in Hank's Balanced Salt Solution (HBSS) without Ca2+ and Mg2+, with

the ratio between fully hydrated and dried sample weights.

**2.4. Material extraction in a simulated biological microenvironment** 

Considering the reviewed concept of biocompatibility as "the ability to exist in contact with tissues of the human body without causing an unacceptable degree of harm to the body" (Williams, 2008), our interdisciplinary work was focused on the synthesis of PU-based materials with improved ability to long-time functional integration. PU/HPC membranes were prepared by blending method. HPC was chosen due to its physical-chemical properties, its demonstrated biocompatibility and accessibility. The aim of the chapter is to highlight the most important criteria, able to predict the behaviour of material-tissue interfaces and the long-term material-tissue integration, in order to select most suitable compositions and morphologies for specific medical application. Thus, surface zeta (ζ) potential, wettability (as contact angle measurement and water uptake), pH modification after long time hydration and autoclaving, protein adsorption at protein physiological concentration and some relevant elements of bulk and surface morphology are treated as screening criteria for suitable membrane choice in the first part of the chapter. Biological performance evaluation, such as oxidative stress action, thrombogenicity and *in vivo* behaviour of PU/HPC membranes are further discussed.
