urethane/calcium carbonate composite porous scaffolds for bone tissue engineering

porowate biomateria³y w ortopedii

Poly( ε-caprolactone)

urethane/calcium carbonate composite porous scaffolds for bone tissue engineering

Joanna Ryszkowska*

Key words: biomedical composite, polymer-bioceramics composites, poly(ε-caporolactone) urethanes, orthopedic applications, porous scaffolds, bone tissue engineering

Porowate pod³o¿a z kompozytu poli( ε- -kaprolaktono)uretanu i wêglanu wapnia przydatne w in¿ynierii tkanki kostnej

Porowate biomateria³y pe³ni¹ wa¿n¹ rolê w zastêpowaniu i regeneracji koœci. Wiele rodzajów porowatych polimerów, ceramiki i kompozytów cera- mika–polimer jest wykorzystywanych w ortopedii. Poli(ε-kaprolaktono)diol jest czêsto u¿ywany jako segment giêtki w syntezie poliuretanów (PUR), jest on biokompatybilny, powoli rozk³ada siê w wyniku procesów degradacji hydroli- tycznej i enzymatycznej. Ten poliol i alifatyczny izocyjanian zosta³y u¿yte do wytworzenia porowatych rusztowañ do zastosowañ ortopedycznych. Rusztowa- nia takie cechuje wysoka elastycznoœæ i dobra biokompatybilnoœæ, ale czêsto proces ich degradacji okazuje siê zbyt powolny i bioaktywnoœæ za niska. Sposo- bem na wyeliminowanie tego problemu jest zastosowanie kompozytów z biode- gradowalnych polimerów i bioaktywnej ceramiki. W przedstawionej pracy me- tod¹ koagulacji polimeru z roztworu w po³¹czeniu z wymywaniem soli wytwo- rzono dwa typy porowatych rusztowañ. Pierwszy typ kompozytów z PUR i wêg- lanu wapnia uzyskano in situ podczas polimeryzacji, drugi w trakcie procesu kszta³towania porów. Poli(ε-kaprolaktono)uretan i kompozyty PUR/wêglan wapnia by³y syntezowane bez u¿ycia rozpuszczalników i katalizatorów. Doda- tek do poliuretanu w trakcie polimeryzacji 5% mas. aragonitu lub kalcytu pro- wadzi³ do wzrostu sztywnoœci otrzymanych pianek.

S³owa kluczowe: kompozyty biomedyczne, kompozyty polimerowo-bio- ceramiczne, poli(ε-kaprolaktono)uretany, ortopedia, rusztowania porowate, in¿ynieria tkanki kostnej

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* Warsaw University of Tech- nology, Faculty of Materials Science & Engineering, War- saw, Poland

porowate biomateria³y w ortopedii

1. Introduction

Since 1963, when the first works were published concerning the usage of porous inert biomaterials, there has been a growing demand for new porous materials for medical applications [1].The therapy of damaged or lost tissues and organs include tissue or organ trans- plantation, surgical reconstruction, drug therapy, syn- thetic prostheses, and medical devices. Porous biomate- rials have proved to be important for bone replacement and regeneration [2]. Many porous polymers [3-5], po- rous ceramics [6-9] and porous polymer – bioceramic composites [10-20] have been prepared for orthopedic applications. These materials with clinical applications constitute an interesting field of research and develop- ment in the production of useful materials for implant fabrication. Different types of polymers: degradable (PCL, PLA) and nondegradable (PE, PMMA) are used as a matrix for composites [2, 10, 21].

Bioceramic materials used for bone regeneration as a filler in composites, can be classified in two groups:

bioinert and bioactive. Bioinert ceramics have almost no influence in the surrounding living tissue. Bioactive ce- ramics, by contrast, are capable of bonding with living osseous tissues and their finest example would be Bio- glass^®, sintered hydroxyapatite and glass ceramic [10].

To serve as a scaffold for bone tissue engineering, the material must be biocompatibile, mechanically inte- grable, osteoconductive, and have a macroporous struc- ture 10].

Polyurethanes (PURs) remain one of the most popular groups of biomaterials applied for medical de- vices [22, 23]. Their popularity has been sustained as a direct result of their segmented block copolymeric character, which endows them with a wide range of versatility in terms of tailoring their physical properties.

These polymers can be fabricated from various groups of substrates, due to this it is possible to obtain degrad- able and nondegradable polymers. Potential applica- tions of such biodegradable elastomers may be in car- diovascular implants, repair of articular cartilage, adhe- sion barriers and artificial skin. Biodegradable polyure- thane elastomers are expected to be suited for any appli- cation requiring the use of flexible elastic material, such as soft [24-28] and hard [28, 29] tissue engineering.

Generally, polyurethanes are made by a reaction a polyol with a diisocyanates followed by a chain exten- tion with a diol. Commonly used polyurethanes are based on aromatic isocyanates. These, however, lack biocompatibility due to toxic degradation products originating from the aromatic hard segment [30-33].

Therefore, aliphatic diisocyanates are preferred over conventional aromatic diisocyanates, essential for cell growth and differentiation [34].

Poly(ε-caprolactone) is commonly used as a soft segment in polyurethanes [35], known to be biocompa- tible, slowly hydrolytically and enzymatically degrad- able [36]. An aliphatic isocyanate and a poly(ε-capro- lactone) diol was used for fabrication of polyurethanes

to prepare porous scaffolds [37, 38]. Scaffolds made from these polyurethanes were highly elastic, with good biocompatibility, however the process of degrada- tion was too slow and bioactivity was too low. Bioacti- vity of polyurethane-based scaffolds was low, which is why they were coated with Bioglass^® particles [39].

Another way of minimizing the problems of porous polyurethanes scaffolds could be the usage of a biode- gradable polymer/bioactive ceramic composite.

Poly(ε-caprolactone) urethane elastomers (PUR) are formed from liquid components during two step prepolymer process [37, 38]. Often in the synthesis of poly(ester)urethanes based on aliphatic diisocyanates, performed via bulk polymerization, the use of catalyst is essential, if full physical properties are to be deve- loped. Without using catalysts polyurethanes could be prepared via solution polymerization, but the residue of catalyst and solvent could have an influence on the biocompatibility of polyurethanes [28, 29, 35].

Calcium carbonate has been recognized as a bone filling material and its good osteoconductivity has been approved in recent studies [40].

In the present work, two types of foam scaffolds were fabricated by the salt leaching/polymer coagula- tion method. The first type was made from PUR/cal- cium carbonate composite obtained in a polymerization process, the second type from PUR and calcium car- bonate mixed during the process of creating pores.

Poly(ε-caprolactone) urethane and the PUR/calcium carbonate composites were synthesized without the use of solvents and catalysts.

2. Materials and methods

2.1. Materials

The following reactants were used in the syntheses of polyurethanes: 4,4’-dicyclohexylmethane diisocya- nate (HMDI), polycaprolactone diol (PCL diol) with molecular weight 530, purchased from Aldrich Chemi- cal Co. (Germany). Polyol was dehydrated during mix- ing under vacuum for two hours at a 120^oC. Ethylene glycol (EG) (POCH, Gliwice) was dried under a mo- lecular sieve. The other chemicals were used as re- ceived. 1-methyl-2-pyrrolidone was supplied by Fluka, Germany and NaCl salt (crystal size ≤ 420 µm) was used as a pore former. As a filler two types of calcium carbonate: aragonite and calcite were used. Calcite (POCH, Gliwice) was obtained through grinding syn- thetic calcite, specific surface area of calcite was equal 2.12 m²/g and the diameter particle size of calcite pow- der was < 100 µm. Aragonite was obtained through precipitation of water solution of Na₂CO₃with a pre- sence of nucleus of crystallization with a dripping CaCl₂solution method in hot temperature, specific sur- face area of aragonite was equal 1.21 m²/g and the diameter particle size of calcite powder was < 100 µm.

Both fillers were prepared in the Institute of Glass and Ceramics, Warsaw.

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porowate biomateria³y w ortopedii

2.2. Synthesis of polyurethanes, composites and foams

Segmented polyurethanes with molar ratio of HMDI/PCL diol/EG 2:1:1 and a constant isocyanate index 1.00 were synthesized in moulds by the pre-poly- mer method. Soft segment based on a poly(ε-caprolac- tone) diol and hard segments of HMDI and EG were composed. These polymers contain about 52 wt % of the hard segment. Into the dewatered in a 120^oC PCL diols the HMDI was added. The reaction was carried out at a 60^oC for one hour, then EG was added and mixed for 15 minutes. The reaction was kept at a tem- perature 110^oC for 8 h.

Polyurethane/CaCO₃composites were prepared by in-situ polymerisation. Synthesis was performed with a prepolymer method. PCL diol and calcium carbonate was mixed under a vacuum for two hours at a tempera- ture 100^oC, afterwards the synthesis process proceeded In the same way as for PUR. The filler was added to the chosen polyurethane matrix in 5 wt % respectively to the whole weight of the polymer. Poly(ε-caprolactone) urethane and the composites were synthesized without the use of solvents and catalysts.

2.3. Foams preparation

Two types of porous scaffolds based on poly(ε-ca- prolactone) urethane were fabricated by the salt leach- ing/polymer coagulation method. Composites with ara- gonite or calcite for Type 1 scaffolds were prepared by in situ polymerization method, then were ground at li- quid nitrogen temperature and dissolved in 1-methyl-2- -pyrrolidone. The NaCl crystals were fractionated into two size ranges:≤ 6 µm, and 300-420 µm, and incorpo- rated into the polyurethane solution (15 wt %). The mass ratio of polymer solution to NaCl was 1:1. The polymer/salt/solvent mixture was poured into a mould (6 mm diameter) and immersed in distilled water for two days, where precipitation of the polymer and leach- ing of salt particles occurred simultaneously. Water was changed several times in order to increase salt leaching and solvent removing. The obtained porous composites was dried under vacuum.

The polyurethanes for Type 2 scaffolds were ground at liquid nitrogen temperature and dissolved in 1-methyl-2-pyrrolidone. Than fractioned NaCl crystals and aragonite or calcite were incorporated into the polyurethane solution (15 wt %). The mass ratio of polymer to aragonite or calcite was 100:5 and polymer solution to NaCl was 1:1. Afterwards the preparation process of this type of scaffold proceeded in the same way as for Type 1.

The foams preparation was described by Bil et al [39].

2.4. Characterization and in vitro studies

Fourier transform infrared (FTIR) spectroscopy was recorded with a Nicolet 6700 spectrometer (Thermo Electron Corporation). The microstructure of polyure- thanes was investigated on microsections surfaces. The samples were microtomed using a glass knife with a mi- crotome Leica RM 2165 with a system LN 21.

Thermal characteristics were performed using a differential scanning calorimeter (DSC Q1000, TA In- struments) an instrument equipped with a liquid nitro- gen cooling unit. The samples scanned from –80^oC to 200^oC, at a heating rate 10^oC/min, during the experi- ment, samples were purged with nitrogen gas.

Dynamic mechanical analysis (DMA) were carried out with a compressive mode DMA Q800 TA Instru- ments apparatus. The measurements were performed at a 1 Hz frequency, a 15 µm amplitude and a heating rate of 3^o/min from 20 to 120^oC. Compression tests were performed on a disc shaped specimen with diameter of 3 mm and thickness 4 mm.

The structure of the foams before and after immer- sion in SBF were characterized by a scanning electron microscopy (SEM – Hitachi 2600). SEM observations were performed after coating the samples with a thin film of carbon.

EDS and SEM analysis were used to verify if hy- droxyapatite (HA) had formed on the surface of the sam- ples treated in SBF. In vitro studies were carried out in concentrated simulated body fluid (1.0 SBF), which is a modified simulated body fluid with ion concentrations 1.0 times those of standard SBF, which contains ion con- centrations nearly equal to those of human blood plasma [41]. Incubation of samples in 1.0 SBF was carried out at controlled temperature of 37^oC. 1.0 SBF was prepared by dissolving the reagents NaCl, NaHCO₃, KCl, K₂HPO₄·

·3H₂O, MgCl₂·6H₂O, CaCl₂·2H₂O, and Na₂SO₄ into distilled water. The solution was buffered to pH 7.25 at 37^oC with tris(hydroxy-methyl)aminomethane and hy- drochloric acid. Composite foams were dipped in 10 ml 1.0 SBF for time periods of 5 and 90 days. Prismatic specimens of nominally the same dimensions were used for these experiments. The solution was changed after 45 days. After the right time periods samples were extracted from the solution, rinsed gently with distilled water and left to dry at 37^oC to stable mass.

The weight loss of composites during immersion in SBF was calculated as:

∆m= (m_t– m₀)/m₀× 100%

where m_o and m_t were the weights of the specimen before and after degradation, respectively, after t days of immersion in SBF.

3. Results and discussion

3.1. Properties and microstruc- ture of foams

FTIR spectroscopy was used to investigate the de- gree of hard and soft segment interaction in polyure-

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porowate biomateria³y w ortopedii

thanes and composites with aragonite and calcite ob- tained in two different procedures. FTIR spectra of in- vestigated PUR and composites showed characteristic bands of urethane groups at 3320–3330 cm^-1 (N–H groups stretching), 1700–1725 cm^-1(NHCOO stretch- ing), 1530–1533 cm^-1(C–N stretching, combined with N–H out of plan bending) (Fig. 1 and 2).

The absence of absorbance at 2267 cm^-1indicated a lack of unreacted isocyanate groups [22, 23]. Two

main spectral regions are the source of information about hard and soft segment of polyurethanes interac- tion: N–H and C=O absorption bands. A strong band, assigned to the free N–H stretching vibration, is present at 3325 cm^-1in all investigated PURs and composites [22]. The band in region 1680–1740 cm^-1 is due to a free and hydrogen bonded urethane carbonyl (CO) but in researched materials it was no possible to esti- mate the level of absorbance of characteristic absorp-

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Figure 2. FTIR – ATR spectra of the surface of polyurethane (1), composite PUR/calcite Type 1 (2) and Type 2 (3) scaffolds.

Rys. 2. Widma FTIR – ATR powierzchni materia³u rusztowañ: poliuretanów (1), kompozytów PUR/kalcyt typu 1 (2) i typu 2 (3)

Figure 1. FTIR – ATR spectra of the surface of polyurethane (1), composite PUR/aragonite Type 1 (2) and Type 2 (3) scaffolds.

Rys. 1. Widma FTIR – ATR powierzchni materia³u rusztowañ: poliuretanów (1), kompozytów PUR/aragonit typu 1 (2) i typu 2 (3)

porowate biomateria³y w ortopedii

tion bands connected with a free and hydrogen bonded urethane carbonyl, and as result is was not possible to estimate the degree of phase separation [42].

Characteristic absorption bands of the calcium car- bonate were observed at 2512cm^-1, 1447 cm^-1, 1160 cm^-1, 874 cm^-1, 851 cm^-1and 712 cm^-1. These bands were not observed on the spectra of the surface compo- sites with aragonite and calcite.

Fig. 3 shown the thermal properties of PUR and composite with aragonite, as obtained in a first DSC heating scan. Table 1 reports the glass transition tem- perature (T_g). DSC results show that the T_gof PURs is higher than the T_gof composites. We can assume that aragonite has an influence on the polymerization of composites Type 1. Particles of aragonite make phase separation in PUR more difficult. T_gof PUR/aragonite composites Type 1 is higher than Type 2. After fabrica- tion of foams Type 2 from solvent of PUR and arago- nite the interactions between macro particles are weaker and T_gof this PUR is lower.

The evaluation of storage modulus (E’) has been studied by DMA, an example curves of E’ are presented in Fig 4. Storage modulus was specified at 37^oC and compared in Table 1. For PUR aragonite composite Type 1 modulus is the highest. E’ for PUR and compo- sites PUR/aragonite Type 2 is much lower. Introduction of 5% aragonite into PUR during polymerization causes a significant increase of the foams stiffness.

Table 1. Thermal and thermomechanical properties of the polyurethanes and composites PUR/aragonite Tabela 1. W³aœciwoœci termiczne i termomechaniczne PUR i kompozytów PUR/aragonit

Sample code Tg (^oC) E’ at 37^oC

PUR 37.3 0.7 MPa

Composite PUR/aragonite Type 1 29.3 14.3 MPa Composite PUR/aragonite Type 2 26.7 0.3 MPa

7

1.

2.

3.

0.1 1 10 100

StorageModulus(MPa)

30 35 40 45 50

Temperature (°C)

1 2 3

Universal V4.1D TA Instruments

Figure 4. Storage modules of polyurethane (1), composite PUR/aragonite Type 1 (2) and Type 2 (3) scaffolds.

Ry s. 4. Sk³adowa rzeczy- wista modu³u zespolonego materia³ów rusztowañ: poli- uretanów (1), kompozytów PUR/aragonit typu 1 (2) i typu 2 (3)

Figure 3. DSC trace for poly- urethane (1), composite PUR/aragonite Type 1 (2) and Type 2 (3) scaffolds; the curves are separated.

Rys. 3. Termogramy DSC poliuretanów (1), kompozy- tów PUR/aragonit typu 1 (2) i typu 2 (3); krzywe zosta³y rozsuniête

porowate biomateria³y w ortopedii

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Figure 5. Structure of (1) polyurethane scaffold, (2) composite PUR/aragonite scaffold Type 1, (3) composite PUR/calcite Type 1 scaffold, (4) composite PUR/aragonite scaffold Type 2, (5) composite PUR/calcite Type 2 scaffold, before immersion in SBF at different magnifications

Rys. 5. Struktura pod³o¿y z: poliuretanów (1), kompozytów PUR/aragonit typu 1 (2) i PUR/kalcyt typu 1 (3), kompozytów PUR/aragonit typu 2 (4) i PUR/kalcyt typu 2 (5), przed ekspozycj¹ w SBF w ró¿nych powiêkszeniach

porowate biomateria³y w ortopedii

The microstructure or polyurethane and compo- sites scaffolds are illustrated in Figure 5. The salt leach- ing/polymer or composite coagulation method allows us to obtain scaffolds with an open and interconnected porous structure. The macropore size of polyurethane scaffolds is 400 µm (Fig.1a). In the picture at a higher magnification the micropourous structure of the pores walls was observed, the micropore size is about 8 µm (Fig. 5-1b). Foams from composites PUR/aragonite Type 1 has open pores, size 180 µm (Fig. 5-2a) and micropores size is about 10 µm, but there are much less interconnected macropores (Fig. 5-2b). Pore structure of PUR/calcite composites Type 1 scaffolds is similar to polyurethane foams, but open macropore have irregular structure and size is equal 250 µm (Fig. 5-3a); inter- connected micropores size is about 6 µm (Fig. 5-3b).

Scaffolds of Type 2 composites contain much less mi- cropores connecting the macropores (Fig. 5-4b, 5-5b).

The sizes of macropores in both types of composites are about 30 µm bigger than pores of Type 1 composites (Fig. 5-4a, 5-5a).

3.2. In vitro studies in SBF

In vitro studies in simulated body fluid were carried out in order to investigate how two types calcium car-

bonate filler influence the biodegradation process of polyurethane foams and improve the biocompatibility of the polymer and composites.

The biodegradation process was analyzed using thermal analysis DSC. Assessment of the changes oc- curring in the materials were monitored on the grounds of T_g changes of these materials. The results of the analyses are gathered on (Fig. 6). T_gof polyurethane does not change for 30 days in SBF only after 90 days the drop of T_gwas sharp. T_gof both composites rose systematically which indicates changes in the rigidity of these materials. The reason for these changes could be changes in chemical structure of these composites, changes on the surface can have a similar influence, for example emerging layers of sediment.

The weight loss studies showed that mass after 30 and 90 days in SBF of all investigated materials changes slightly within 1% of their mass (Fig. 7). These results indicate that together with a loss of composite mass the amount of sediment on the surface of these materials rose. The surface morphology of PUR and composites scaffolds was observed by SEM. The re- sults of these observation are presented in Fig. 8. We observed that pores in scaffolds are bigger after 30 days in SBF than pores of the same foams after 90 days in SBF.

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25 27 29 31 33 35 37 39

0 20 40 60 80 100

Immersion time in SBF, days

Glasstemperature,o C 1

2

3

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

30 90

Immersion time in SBF, days

Weightloss,%

1

1 2a

3a 2a

3a

3b 3b

2b

2b Figure 7. Weight loss of poly-

u re t h a n e ( 1 ) , c o m p osi t e PUR/aragonite Type 1 (2a) and Type 2 (2b); composite PUR/calcite Type 1 (3a) and Type 2 (3b) scaffolds.

Rys. 7. Ubytek masy pod³o¿y wykonanych z: poliuretanów (1), kompozytów PUR/arago- nit typu 1 (2a) i typu 2 (2b);

kompozytów PUR kalcyt typu 1 (3a) i typu 2 (3b) po ekspo- zycji w SBF

Figure 6. Tg of polyurethane (1), composite PUR/arago- nite Type 1 (2) and composite PUR/calcite Type 1 (3) scaf- folds after immersion in SBF.

Rys. 6. Temperatura zeszkle- nia: poliuretanów (1), kom- pozytów PUR/aragonit typu 1 (2) i kompozytów PUR/kalcyt typu 1 (3) po ekspozycji w SBF

porowate biomateria³y w ortopedii

In Fig. 9 we compare the changes of macropores in the observed scaffold. The size of the foam macropores from Type 2 composites did not change. Also the changes of micropore sizes were analyzed (Fig. 10). Their size and amount drops together with the immersion time in SBF.

On the surfaces of polyurethane scaffolds and com- posites Type 1 scaffolds we observed an occurrence of spherical particles. Their structure is shown in Fig. 11. The images of these particle show it is hydroxyapatite (HA).

The chemical composition of the layer was iden- tified by EDS analysis. Calcium and phosphorus, as predominant elements in the EDS spectrum, confirm the presence of HA on the surface of polyurethane (Fig. 12), composite PUR/aragonite Type 1 (Fig. 13) and composite PUR /calcite Type 1 scaffolds (Fig.

14). On the surfaces of composites Type 2 we did not observe a layer of spherical particles of HA (Fig. 15, 16).

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Figure 8. Surface of polyurethane (1a) after 30 days and (1b) 90 days of immersion in SBF; composite PUR/ara- gonite: (2a) after 30 days and (2b) 90 days of immersion in SBF; composite PUR/calcite: (3a) after 30 days and (3b) 90 days of immersion in SBF scaffolds.

Rys. 8. Struktura pod³o¿y wykonanych z: poliuretanów – po 30 dniach (1a) i 90 dniach (1b); kompozytów PUR/ara- gonit typu 1 – po 30 dniach (2a) i 90 dniach (2b); kompozytów PUR/kalcyt typu 1 – po 30 dniach (3a) i 90 dniach (3b) ekspozycji w SBF

0 100 200 300 400 500 600

0 30 90

Immersion time in SBF, days

Porediameter,um

1

1 1

2a

3a3b 3a3b 3a

2b 2b

2a 2a

Figure 9. Macropore diameter of polyurethane (1a) after 30 days and (1b) 90 days of immersion in SBF; composite PUR/aragonite:

(2a) after 30 days and (2b) 90 days of immersion in SBF; com- posite PUR/calcite: (3a) after 30 days and (3b) 90 days of immer- sion in SBF scaffolds.

Rys. 9. Zmiana œrednicy makro- porów pod³o¿y wykonanych z:

poliuretanów – po 30 dniach (1a) i 90 dniach (1b); kom- pozytów PUR/aragonit typu 1 – po 30 dniach (2a) i po 90 dniach (2b); kompozytów PUR/kalcyt typu 1 – po 30 dniach (3a) i 90 dniach (3b) ekspozycji w SBF

porowate biomateria³y w ortopedii

4. Conclusion

Bioactive and bioresorbable composites were de- veloped based on polyurethane and calcium carbonate.

The results indicate the important role of the com- posites preparation process in the formation of micro- pores. The composites preparation process has an influ- ence on the internal structure of the foams (SEM).

A structure of foams from composites, in which fillers

11

0 2 4 6 8 10 12

0 30 90

Im

Porediameter,µm

mersion time in SBF, days 1

1 2a

3a

3a 3a

2b 2a 3b 2b

3b 2a

Figure 10. Micropore diameter of polyurethane (1a) after 30 days and (1b) 90 days of immersion in SBF; composite PUR/aragonite:

(2a) after 30 days and (2b) 90 days of immersion in SBF; com- posite PUR/calcite: (3a) after 30 days and (3b) 90 days of immer- sion in SBF scaffolds.

Rys. 10. Zmiana œrednicy mikro- porów pod³o¿y wykonanych z:

poliuretanów – po 30 dniach (1a) i 90 dniach (1b); kompozytów PUR/aragonit typu 1 – po 30 dniach (2a) i po 90 dniach (2b);

kompozytów PUR/kalcyt typu 1 – po 30 dniach (3a) i 90 dniach (3b) ekspozycji w SBF

Figure 11. Surface of (1) PUR, (2) composite PUR/aragonite and (3) composite PUR/calcite scaffold Type 1 after 90 days of immersion in SBF at different magnifications

Rys. 11. Struktura – przedstawiona w ró¿nych powiêkszeniach – pod³o¿y z: poliuretanów (1), kompozytów PUR/aragonit typu 1 (2) i kompozytów PUR/kalcyt typu 1(3), po ekspozycji przez 90 dni w SBF

porowate biomateria³y w ortopedii

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Figure 12. Surface and EDS analysis of PUR scaffold after 90 days of immersion in SBF

Rys. 12. Struktura powierzchni i wynik analizy EDS rusztowania z PUR po 90 dniach ekspozycji w SBF

Figure 13. Surface and EDS analysis of composite PUR/aragonite scaffold Type 1 after 90 days of immersion in SBF

Rys. 13. Struktura powierzchni i wynik analizy EDS rusztowania z PUR/aragonit typu 1 po 90 dniach ekspozycji w SBF

Figure 14. Surface and EDS analysis of composite PUR/calcite scaffold Type 1 after 90days of immersion in SBF Rys. 14. Struktura powierzchni i wynik analizy EDS rusztowania z PUR/kalcyt typu 1 po 90 dniach ekspozycji w SBF

porowate biomateria³y w ortopedii

were connected with matrix, is different than those with chemical bonds (Type 1) and different if there were only physical interactions (Type 2). Rigidity also differs between the foams from composite Type 1 and compo- site Type 2. Rigidity of the foams prepared by in situ was higher than in other materials. A layer of HA did not occur on the surface of Type 2 composites.

The in vitro studies in SBF indicated that calcium carbonate filler imparted high bioactivity to the poly- urethane scaffolds by promoting the formation of a car- bonate hydroxyapatite layer on their surface. Result of in vitro studies show that composites with calcium car- bonate should simplify the process of born forming in vivo conditions.

Acknowledgements:

The authors thank Dr Zbigniew Jaegermann from Institute of Glass and Ceramics for supplying us arago-

nite and calcite. This scientific work was funded from the finances for education in the years 2006-2008 as research project No. R1301901.

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Figure 16. Surface and EDS analysis of composite PUR/calcite scaffold Type 2 after 90 days of immersion in SBF Rys. 16. Struktura powierzchni i wynik analizy EDS rusztowania z PUR/kalcyt typu 2 po 90 dniach ekspozycji w SBF

Figure 15. Surface and EDS analysis of composite PUR/aragonite scaffold Type 2 after 90 days of immersion in SBF

Rys. 15. Struktura powierzchni i wynik analizy EDS rusztowania z PUR/aragonit typu 2 po 90 dniach ekspozycji w SBF

porowate biomateria³y w ortopedii

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