Load-bearing bioactive hybrid materials

Diplomityön tavoitteena oli tutkia kolmiulotteisten kuormaa kantavien bioaktiivisten hybridimateriaalien valmistusta ortopedisiin sovelluksiin. Sovelluskohteeksi valittiin välilevyimplantti spinaalifuusioon. Kuormaa kantavana komponenttina materiaalissa toimi EBM -menetelmällä valmistettu titaaniseosverkko (TiAl6V4), kun taas bioaktiivisena komponenttina toimi joko pankkiluumurska tai biohajoavan polymeerin ja bioaktiivisen lasin muodostama komposiitti. Polymeeri huokoistettiin solujen sisään kasvun mahdollistamiseksi. Tutkimuksessa valmistettiin huokoisia polymeerirakenteita termoplastisesta sekä valosilloittuvasta poly(ε-kaprolaktonista). Termoplastisesta polymeeristä valmistettiin huokoisia rakenteita kolmella eri tavalla: kylmäkuivaamalla, kylmäuutolla sekä kastamismenetelmällä. Kylmäuutetuiden näytteiden huokoisuusrakenne selvitettiin μCT-kuvantamisella sekä pyyhkäisyelektronimikroskoopilla, jolloin selvisi, että huokoisuus on yhtenäistä ja huokoisuus oli 66-76 %. Huokoskoko on kuitenkin todennäköisesti liian pieni solujen sisään kasvulle. Polymeerin valosilloitusta varten syntetisoitiin metakryloitua ε-kaprolaktoni oligomeeriä, minkä jälkeen se sekoitettiin bioaktiivisen lasin sekä huokoisuuden aikaan saavan suolan kanssa. Titaaniverkko upotettiin massaan ja polymeeri valosilloitettiin. Työssä määritettiin valosilloitettujen polymeerinäytteiden sekä hohkaluunäytteiden puristuslujuus. Titaaniseosverkkojen puristuslujuus (8 MPa) sekä puristusmoduuli (0.2 GPa) olivat samaa suuruusluokkaa hohkaluun kirjallisuusarvojen kanssa (2-22 MPa ja 0.2-1.9 GPa). Puristuslujuusarvojen perusteella hybridimateriaali on mahdollisesti sopiva haluttuun sovelluskohteeseen selkärangassa, jossa on hohkaluuta. Kortikaaliluun sovelluksiin materiaali ei kuitenkaan sovellu, sillä kortikaaliluulla on huomattavasti korkeammat puristuslujuuden arvot kirjallisuudessa (100-230 MPa).The aim of this thesis was to study the preparation of three dimensional load-bearing bioactive hybrid materials for orthopedic applications. The application area is interbody cage in spinal fusion. The load-bearing component in the material is electron beam melting (EBM) manufactured titanium alloy (TiAl6V4) mesh, whereas the bioactive component was either crushed bone graft or composite made of biodegradable polymer and bioactive glass (BAG). Polymers were made porous to allow bone ingrowth. In this study, porous structures were made of thermoplastic and photocrosslinkable polycaprolactone (PCL). Three methods were used to prepare porous structures of thermoplastic PCL: freeze drying, freeze extraction and dipping. Porous structure of freeze extraction samples was determined using micro computed tomography (μCT) and scanning electron microscope. Pores were interconnected and porosity was 66-76 %. However, the pore size was probably too small for cell ingrowth. For photocorsslinking of PCL, methacrylated PCL oligomer was synthetized and mixed with BAG and porogen agent salt. Titanium alloy mesh was immersed in the mixture and the polymer was photocrosslinked. Compression strength at break was determined for photocrosslinked samples and trabecular bone samples. Compression strength at break (8 MPa) and compressive modulus (0.2 GPa) for titanium meshes were close to literature values of trabecular bone (2-22 MPa and 0.2-1.9 GPa, respectively). Therefore, the hybrid material is probably suitable for interbody cage fusion, because vertebrae are trabecular bone. However, cortical bone has much higher compression strength values at literature (100-230 MPa). Therefore the materials cannot be used in cortical bone applications

Resorboituvat polyesterit ja -eetterit; rakenteet, kontrolloitu vapautuminen ja regeneraatio

The public defense on 10th June 2020 at 12:00 will be available via remote technology. Link: https://aalto.zoom.us/j/69610780620 Zoom Quick Guide: https://www.aalto.fi/en/services/zoom-quick-guide Electronic online display version of the doctoral thesis is available by email by request from [email protected] polymers are widely used in tissue regeneration and controlled drug delivery due to their excellent modification possibilities. The aims of this thesis are to synthetize hydrolytically-degradable polymers, study the effect of polymer composition and structure on drug release and prepare controlled 3D-structures for the purpose of nerve and bone regenerative scaffolds. In this thesis, both thermoplastic and photo-crosslinkable polyesters and –ethers were synthetized. Thermoplastic polyesters were modified by adjusting the monomer ratio and incorporating poly(ethylene glycol) (PEG) to the molecular structure to tailor the degradation rate and hydrophilicity of the polymers. The polymers were used to prepare interconnected, porous structures via supercritical carbon dioxide foaming. Photo-crosslinkable polycaprolactone (PCL) -macromers were synthetized and pre-designed structures with high accuracy were built via 3D-fabrication method stereolithography (SLA). Furthermore, anhydride-modified, photo-crosslinkable PCL and PEG -macromers were synthetized and used in preparation of pH-sensitive networks. The application areas of the polymers are in controlled drug delivery and tissue regeneration. Thermoplastic polyester foams were used to release bone growth inducing active agents. One of the polymer/active agent combinations resulted in near zero-order drug release, which is favored in drug releasing applications. pH-sensitive networks were used to study the release of model drugs. In vitro drug release studies showed that the polymers have potential as pH sensitive, colon-targeted drug delivery devices for macromolecules. SLA was used to build drug releasing PCL-structures with defined porosities and surface to volume ratios. Porous structures released the model drug with a burst, whereas solid samples had a slower drug release rate. PCL-based nerve guidance channels were also prepared via SLA. The channels were filled with cryogel and they exhibited excellent nerve regeneration in vivo. In conclusion, polymers were modified to suit the specific needs of each application. The degradation rate of polymers was tailored and they were modified to be more hydrophilic, photo-crosslinkable or pH-sensitive.Resorboituvia polymeerejä käytetään laajasti kudosteknologiassa ja kontrolloidussa lääkeaineannostelussa, sillä niitä voidaan muokata erilaisiin käyttökohteisiin. Tämän väitöskirjan tavoitteena oli valmistaa hydrolyyttisesti hajoavia polyestereitä ja -eettereitä, tutkia polymeerin kemiallisen koostumuksen ja kappaleen rakenteen vaikutusta lääkeainevapautukseen sekä valmistaa kontrolloituja 3D-rakenteita luu- ja hermoregeneraatioon. Tässä väitöskirjassa syntetisoitiin termoplastisia ja valosilloittuvia polyestereitä ja -eettereitä. Erilaisia termoplastisia polyestereitä valmistettiin monomeerien suhdetta säätämällä sekä liittämällä kemialliseen rakenteeseen polyeteeniglykolia (PEG) hajoamisnopeuden ja hydrofiilisyyden muokkaamiseksi. Polymeerejä käytettiin läpihuokoisten rakenteiden valmistukseen ylikriittisellä hiilidioksidihuokostuksella. 3D-valmistumenenelmä stereolitografialla (SLA) valmistettiin valosilloittuvasta polykaprolaktoni (PCL) -makromeeristä rakenteita tietokoneavusteisesti suunniteltujen mallien pohjalta. Lisäksi valosilloitettujen PCL ja PEG-makromeerien kemiallista rakennetta muokattiin anhdydridillä, jolloin voitiin valmistaa pH-sensitiivisiä verkkorakentetia. Kehitettyjen polymeerien sovelluskohteita ovat kontrolloitu lääkeaineannostelu sekä kudosten regeneraation tukeminen. Termoplastista polyesterirakenteista vapautettiin luun kasvua indusoivia aktiiviaineita. Yksi polymeerin ja aktiiviaineen yhdistelmä saavutti tasainen vapautusnopeuden, mikä on usein tavoitteena lääkeainetta kontrolloidusti vapauttavissa sovelluksissa. pH-sensitiivisten verkkorakenteiden soveltuvuutta lääkeainevapautukseen tutkittiin kahden malliaineen avulla. In vitro kokeet osoittivat, että polymeereillä on potentiaalia pH-sensitiivisinä, paksusuoleenkohdennettuina lääkeaineannostelumateriaaleina. SLA:lla puolestaan valmistettiin PCL-rakenteita, joilla oli suunnitellut huokosrakenteet sekä pinta-alan ja tilavuuden suhde. Huokoiset rakenteet vapauttivat lääkeaineen nopeasti, kun taas umpinaiset kappaleet vapauttivat malliaineen hitaammin. SLA:lla valmistettiin myös putkimaisia PCL-rakenteita, jotka täytettiin kryogeelillä. Valmistetut rakenteet osoittivat eläinkokeissa erinomaista hermoregeneraatiota. Yhteenvetona nämä tutkimukset osoittavat, että polymeerien ominaisuuksia voitiin muokata erilaisiin käyttötarkoituksiin. Polymeerien hajoamisnopeutta voitiin säätää ja lisäksi valmistettiin hydrofiilisempiä, valosilloittuvia ja pH-sensitiivisiä polymeerejä

Photo-crosslinked anhydride-modified polyester and –ethers for pH-sensitive drug release

Photo-crosslinkable polymers have a great potential for the delivery of sensitive drugs. They allow preparation of drug releasing devices by photo-crosslinking, thus avoiding high processing temperatures. In this study, the hydrolysis behavior and drug release of three different photo-crosslinkable poly(ether anhydride)s and one poly(ester anhydride) were investigated. Three-arm poly(ethylene glycol) or polycaprolactone was reacted with succinic anhydride to obtain carboxylated macromers, and further functionalized with methacrylic anhydride to form methacrylated marcromers with anhydride linkages. The synthetized macromers were used to prepare photo-crosslinked matrices with different hydrolytic degradation times for active agent release purposes. The hydrolysis was clearly pH-sensitive: polymer networks degraded slowly in acidic conditions, and degradation rate increased as the pH shifted towards basic conditions. Drug release was studied with two water-soluble model drugs lidocaine (234 mol/g) and vitamin B12 (1355 g/mol). Vitamin B12 was released mainly due to polymer network degradation, whereas smaller molecule lidocaine was released also through diffusion and swelling of polymer network. Only a small amount of vitamin B12 was released in acidic conditions (pH 1.3 and pH 2.1). These polymers have potential in colon targeted drug delivery as the polymer could protect sensitive drugs from acidic conditions in the stomach, and the drug would be released as the conditions change closer to neutral pH in the intestine.Peer reviewe

Drug-releasing Biopolymeric Structures Manufactured via Stereolithography

Additive manufacturing (AM) techniques, such as stereolithography (SLA), enable the preparation of designed complex structures. AM has gained interest especially in the tissue engineering field due to the possibility to manufacture patient specific implants. However, AM could be useful also in controlled drug release applications, since the size and shape of the device, pore architecture and surface to volume ratio can be accurately designed. In this study, SLA was used to prepare polycaprolactone scaffold structures containing the model drug lidocaine. The release of lidocaine was studied and the influence of porosity and surface to volume ratio of structures to the drug release was analyzed. Porous samples released lidocaine faster compared to solid ones, whereas the degree of porosity and surface to volume ratio did not have a clear effect on the drug release profile.Peer reviewe

Hydrolysis and drug release from poly(ethylene glycol)-modified lactone polymers with open porosity

The ability to release active agents from a porous scaffold structure in situ enables the simultaneous structural support for the cells proliferating and differentiating towards tissue as well as the stimulation of tissue regeneration. Due to the great potentiality of such approach, drug-releasing scaffolds were fabricated from hydrolytically degradable polymers. Three copolymers of poly(ethylene glycol), ɛ-caprolactone, L- and D,L-lactide were synthesized and blended with bone-growth inducing active agents, dexamethasone (DM) and 2-phospho-L-ascorbic acid trisodium salt (AS). Porous scaffolds were prepared by means of super-critical carbon dioxide foaming. In the final scaffold structures, the particle size, location and the water solubility of the drug affected the release kinetics. As the large and water soluble AS particles were more exposed to the buffer solution compared to small DM particles, the AS release was burst-like whereas DM showed a long-term release. The material structure had a significant effect on the release kinetics as the porous scaffolds released active agents faster compared to the solid cylinders. Furthermore, this study showed the strong effect of polymer degradation and wettability on the release, which were more determinative than the pore architecture.Peer reviewe

Biomimetic Photocurable Three-Dimensional Printed Nerve Guidance Channels with Aligned Cryomatrix Lumen for Peripheral Nerve Regeneration

Repair and regeneration of critically injured peripheral nerves is one of the most challenging reconstructive surgeries. Currently available and FDA approved nerve guidance channels (NGCs) are suitable for small gap injuries, and their biological performance is inferior to that of autografts. Development of biomimetic NGCs with clinically relevant geometrical and biological characteristics such as topographical, biochemical, and haptotactic cues could offer better regeneration of the long-gap complex nerve injuries. Here, in this study, we present the development and preclinical analysis of three-dimensional (3D) printed aligned cryomatrix-filled NGCs along with nerve growth factor (NGF) (aCG + NGF) for peripheral nerve regeneration. We demonstrated the application of these aCG + NGF NGCs in the enhanced and successful regeneration of a critically injured rat sciatic nerve in comparison to random cryogel-filled NGCs, multichannel and clinically preferred hollow conduits, and the gold standard autografts. Our results indicated similar effect of the aCG + NGF NGCs viz-a-viz that of the autografts, and they not only enhanced the overall regenerated nerve physiology but could also mimic the cellular aspects of regeneration. This study emphasizes the paradigm that these biomimetic 3D printed NGCs will lead to a better functional regenerative outcome under clinical settings.Peer reviewe

Chemical compatibility of fused filament fabrication-based 3-D printed components with solutions commonly used in semiconductor wet processing

3-D printing shows great potential in laboratories for making customized labware and reaction vessels. In addition, affordable fused filament fabrication (FFF)-based 3-D printing has successfully produced high-quality and affordable scientific equipment, focusing on tools without strict chemical compatibility limitations. As the additives and colorants used in 3-D printing filaments are proprietary, their compatibility with common chemicals is unknown, which has prevented their widespread use in laboratory chemical processing. In this study, the compatibility of ten widely available FFF plastics with solvents, acids, bases and solutions used in the wet processing of semiconductor materials is explored. The results provide data on materials unavailable in the literature and the chemical properties of 3-D printable plastics that were, are in line with literature. Overall, many 3-D printable plastics are compatible with concentrated solutions. Polypropylene emerged as a promising 3-D printable material for semiconductor processing due to its tolerance of strongly oxidizing acids, such as nitric and sulfuric acids. In addition, 3-D printed custom tools were demonstrated for a range of wet processing applications. The results show that 3-D printed plastics are potential materials for bespoke chemically resistant labware at less than 10% of the cost of such purchased tools. However, further studies are required to ascertain if such materials are fully compatible with clean room processing.Peer reviewe

Chemical compatibility of fused filament fabrication-based 3-D printed components with solutions commonly used in semiconductor wet processing

3-D printing shows great potential in laboratories for making customized labware and reaction vessels. In addition, affordable fused filament fabrication (FFF)-based 3-D printing has successfully produced high-quality and affordable scientific equipment, focusing on tools without strict chemical compatibility limitations. As the additives and colorants used in 3-D printing filaments are proprietary, their compatibility with common chemicals is unknown, which has prevented their widespread use in laboratory chemical processing. In this study, the compatibility of ten widely available FFF plastics with solvents, acids, bases and solutions used in the wet processing of semiconductor materials is explored. The results provide data on materials unavailable in the literature and the chemical properties of 3-D printable plastics that were, are in line with literature. Overall, many 3-D printable plastics are compatible with concentrated solutions. Polypropylene emerged as a promising 3-D printable material for semiconductor processing due to its tolerance of strongly oxidizing acids, such as nitric and sulfuric acids. In addition, 3-D printed custom tools were demonstrated for a range of wet processing applications. The results show that 3-D printed plastics are potential materials for bespoke chemically resistant labware at less than 10% of the cost of such purchased tools. However, further studies are required to ascertain if such materials are fully compatible with clean room processing