Novel biodegradable polymeric and composite structures to be used as biomedical implants and tissue engineering scaffolds

Understanding the structure-property relationship is essential for the further development and rational design of new materials. Generally, the properties of materials depend on their processing history, where the processing variables manipulate the microstructure, and hence control the mechanical properties. For biomedical applications, the mismatch between the mechanical properties of a device made out of biodegradable polymer and the tissue intended to be regenerated may compromise the clinical success of the tissue engineering construct. The processing – structure –property relationships were established with poly(L-lactic acid) / PLLA and starch based materials using conventional injection molding. Moreover, the toughness of PLLA was augmented with the induction of a non-conventional melt based processing technique. Porous three-dimensional scaffolds combined with donor cells and growth factors have been employed to conduct and accelerate tissue regeneration. To understand the effect of porous morphology on mechanical properties of porous scaffolds, a comprehensive study was carried out to establish the structure – viscoelastic properties relationships of porous constructs in relevant physiologically conditions. Miscible polymer blends offer a route to tailor properties that may be desirable from both the constituent polymers. Here, we used polymer blends to develop porous structures by dissolving one of the constituent polymers. PLLA and poly(ethylene oxide) / PEO blend is miscible in the molten state and phase separates in the solid state, and PLLA is a hydrophobic polymer, whereas PEO is water soluble polymer. The internal surface of a three-dimensional construct can be easily textured using such kind of hydrophobic- hydrophilic miscible polymer blend, which is otherwise a complicated task. Moreover, the interconnectivity, an important requirement of the porous 3D constructs could be enhanced with the increased fraction of PEO. With 50 / 50 % PLLA and PEO composition, the blend is biphasic containing a homogeneous PLLA/PEO phase and a PEO-rich phase. Such partially miscible polymer blend has a very broad interface and offers an advantage to process at the high shear rates of convention thermoplastic processing techniques. We have demonstrated that alternate layers of two phases of a partially miscible polymer blend can be structured using conventional injection molding technique, followed by swelling and leaching of water soluble PEO creates the continuous porous lamellar scaffolds. An integrated, porous bi-layered scaffold was developed for osteochondral tissue engineering where the layer for the bone region was made out of PLLA and hydroxyapatite, and the cartilage-layer was composed of a PLLA and starch blend with controllable pore size and porosities. Bioactivity tests demonstrated that the bone-layer could induce the formation of a calcium-phosphate layer in-vitro, whereas the cartilage-layer does not exhibit the ability for calcification. A number of factors like the material, surface chemistry, polymer/bioactive ceramics compositions play decisive roles in the precipitation of calcium phosphate from simulated body fluid (SBF). The surface of a porous three-dimensional PLLA / bioactive glass composite scaffolds can alter the composition and morphology of inorganic phase, thus offering a very powerful tool for the design of novel materials. The textured surface of PLLA / bioactive glass was able to preferentially induce the nucleation and growth of octacalcium phosphate as compared with smooth surfaces that precipitate the typical apatite upon immersion in SBF.

Name thesis:degree_name

Tese de Doutoramento Ciência e Tecnologia de Materiais - Biomateriais.

Year dc:date.issued

2008

Author dc:creator

• Ghosh, Satyabrata

Advisors dc:contributor.advisor

• Mano, J. F.
• Reis, R. L.
• Viana, J. C.

Statement dc:rights

• restrictedAccess

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/1822/7776

OAI record oai:identifier

http://repositorium.sdum.uminho.pt/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Arepositorium.uminho.pt%3A1822%2F7776