Degradable polyester-based scaffolds are ideal for tissue engineering applications where long-term structural integrity and mechanical support are a requisite. However, their hydrophobic and unfunctionalized surfaces restrain their tissue-mimetic quality. Instead, hyaluronan (HA) hydrogels are able to act as cell-instructive materials with the ability to recapitulate native tissue, although HA is rapidly metabolized in vivo. Taking advantage of these distinctly diverse material properties, a degradable and concurrent hybrid hydrogel material was developed that combines the short-term tissue-relevant properties of bio-orthogonal crosslinked HA with the long-term structural and mechanical support of poly(L-lactide-co-trimethylene carbonate) (PLATMC) scaffolds. This method rendered the formulation of transparent, minimally swelling hydrogel compartments with a desirable cell-instructive “local” elastic modulus within the scaffold matrix without impeding key material properties of PLATMC. Long-term degradability over 180 days in vivo was realized by the integral PLATMC scaffold architecture obtained through either extrusion-based 3D printing or salt-particulate leaching. Intrinsic diffusion capacity within the hydrogel elicited unaffected degradation kinetics of PLATMC in vivo, despite its autocatalytic bulk degradation characteristics displayed when 3D-printed. The effect of the processing method on the material properties of PLATMC markedly extends to its in vivo degradation characteristics, and essential uniform degradation behavior can be advanced using salt-particulate leaching. Regardless of the scaffold fabrication method, the polymer exhibited a soft and flexible nature throughout the degradation period, governed by the rubbery state of the polymer. Our results demonstrate that the physicochemical properties of the hybrid hydrogel scaffold endow it with the potential to act as a cell instructive microenvironment while not affecting key material properties of PLATMC postprocessing. Importantly, the HA hydrogel does not adversely impact the degradation behavior of PLATMC, a vital aspect in the fabrication of tissue engineering constructs. The results presented herein open new avenues for the adoption of concurrent and well-defined tissue-relevant materials exhibiting the potential to recreate microenvironments for cell encapsulation and drug delivery in vivo while providing essential structural integrity and long-term degradability. 

Synthetic, degradable macromonomers have been developed to serve as ink for 3D printing technologies based on direct-ink-writing. The macromonomers are purposely designed to be cross-linkable under the radical mechanism, to impart hydrophilicity to the final material, and to have rheological properties matching the printer's requirements. The suitable viscosity enables the ink to be printed at room temperature, in absence of organic solvents, and to be cross-linked to manufacture soft 3D scaffolds that show no indirect cytotoxicity and have a hydration capacity of up to 100% their mass and a compressive modulus in the range of 0.4-2 MPa.

In soft tissue defects that arise due to trauma, tumor resections and complex burns, a significant loss in adipose tissue remains a considerable challenge due to the insufficient regenerative capacity of the tissue. This thesis focuses on assessing cell-material interactions between degradable 3D polymer scaffolds with different designs and adipose tissue-derived stem cells. This knowledge can be used to engineer 3D scaffolds with adequate physio-chemical and mechanical properties along with an appropriate design that augments adipose tissue regeneration.

Salt-leaching 3D scaffolds were fabricated from various medical-grade polyesters, and cellular behavior was evaluated by correlating the physical, chemical, and mechanical properties of the scaffolds. The results showed that the glass transition temperature modulated the mechanical properties of the scaffolds, affecting stem cell proliferation and adipogenic differentiation. The same sets of polymers were further used in melt extrusion-based 3D printer and printability was established for the fabrication of customized 3D scaffolds. Based on printability and cell-scaffolds interaction results, poly (L-lactide-co-trimethylene carbonate) was used to print 3D scaffolds in different soft and pliable designs that promoted adipogenic differentiation. To fabricate even softer, and more hydrophilic 3D scaffolds, poly (ɛ-caprolactone-co-p-dioxanone) and a unique scaffold design were utilized within the research group. The copolymer 3D scaffolds were further combined with knitted mesh and electrospun nanofibers to develop scaffolds with multilayer architecture, modular scaffolds. The in vitro results asserted that the modular scaffold enhanced cell-material interactions by almost five times of those observed for the scaffold alone. Therefore, it can be concluded that softness and pliability are crucial and an appropriate scaffold design with adequate mechanical support is required for enhancing cell-material interaction. The in vitro results asserted that the modular scaffold enhanced cell-material interactions by almost five times of those observed for the scaffold alone. Therefore, it can be concluded that softness and pliability are crucial and an appropriate scaffold design with adequate mechanical support is required for enhancing cell-material interaction. The in vitro results asserted that the modular scaffold enhanced cell-material interactions by almost five times of those observed for the scaffold alone. Therefore, it can be concluded that softness and pliability are crucial and an appropriate scaffold design with adequate mechanical support is required for enhancing cell-material interaction.

I mjukvävnadsdefekter som uppstår på grund av trauma, tumörresektioner och komplexa brännskador förblir en signifikant förlust av fettvävnad en utmaning på grund av vävnadens otillräckliga regenereringskapacitet. Denna avhandlingen fokuserar på att förstå interaktionerna mellan polymerer och celler, mellan nedbrytbara 3D-polymermatriser med olika design och stamceller som härrör från fettvävnad. Resultaten ger kunskap för att kunna skapa 3D-matriser med lämpliga fysikalisk-kemiska och mekaniska egenskaper som tillsammans med en lämplig design ger möjlighet för fettvävnadsregenerering.

Saltlakade 3D-matriser tillverkades av polyestrar av medicinsk kvalitet, cellernas beteende utvärderades för att korrelera matrisens fysiska, kemiska och mekaniska egenskaper. Resultaten visade att glasomvandlingstemperaturen påverkade matrisens mekaniska egenskaper, vilket i sin tur påverkade stamcellsförökning och den adipogena differentieringen. Samma uppsättning polymerer användes i en extruderbaserad 3D-skrivare för att tillverka 3D-matriser. Baserat på hur polymererna påverkades av 3D-skrivaren och resultat från interaktionerna mellan celler och polymerer valdes poly(L-laktid-sam-trimetylenkarbonat) för att skriva ut mjuka och böjbara 3D-matriser samt främja adipogen differentiering.För att tillverka ännu mjukare, böjliga och mer hydrofila 3D-matriser syntetiserades en ny polymer inom forskargruppen, poly(ɛ-kaprolakton-sam-p-dioxanon), och en unik matrisdesign togs fram. 3D-matrisen kombinerades vidare med stickade nät och elektrospunna nanofibrer för att utveckla multilagermatriser, modulmatriser. In vitro-resultaten visade att modulmatrisen förbättrade cell-materialinteraktionen nästan fem gånger i jämförelse med endast 3D-matrisen. Slutsatsen är att matrisens mjukhet och böjlighet är avgörande och att en anpassad matrisdesign med lämpligt mekaniskt stöd krävs för att förbättra cell-materialinteraktionen. 

Aliphatic polyesters are the synthetic polymers most commonly used in the development of resorbable medical implants / devices. Various three-dimensional (3D) scaffolds have been fabricated from these polymers and used in adipose tissue engineering. However, their systematic evaluation altogether lacks, which makes it difficult to select a suitable degradable polymer to design 3D resorbable implants and / or devices able to effectively mimic the properties of adipose tissue. Additionally, the impact of sterilization methods on the medical devices, if any, must be taken into account. We evaluate and compare five different medical-grade resorbable polyesters with l-lactide content ranging from 50 to 100 mol% and exhibiting different physiochemical properties depending on the comonomer (d-lactide, ε-caprolactone, glycolide, and trimethylene carbonate). The salt-leaching technique was used to prepare 3D microporous scaffolds. A comprehensive assessment of the physical, chemical, and mechanical properties of the scaffolds was carried out in PBS at 37 ° C. The cell-material interactions and the ability of the scaffolds to promote adipogenesis of human adipose tissue-derived stem cells were assessed in vitro. The diverse physical and mechanical properties of the scaffolds, due to the different composition of the copolymers, influenced human adipose tissue-derived stem cells proliferation and differentiation. Scaffolds made from polymers which were above their glass transition temperature and with low degree of crystallinity showed better proliferation and adipogenic differentiation of stem cells. The effect of sterilization techniques (electron beam and ethylene oxide) on the polymer properties was also evaluated. Results showed that scaffolds sterilized with the ethylene oxide method better retained their physical and chemical properties. Overall, the presented research provides (i) a detailed understanding to select a degradable polymer that has relevant properties to augment adipose tissue regeneration and can be further used to fabricate medical devices / implants; (ii) directions to prefer a sterilization method that does not change polymer properties. the presented research provides (i) a detailed understanding to select a degradable polymer that has relevant properties to augment adipose tissue regeneration and can be further used to fabricate medical devices / implants; (ii) directions to prefer a sterilization method that does not change polymer properties. the presented research provides (i) a detailed understanding to select a degradable polymer that has relevant properties to augment adipose tissue regeneration and can be further used to fabricate medical devices / implants; (ii) directions to prefer a sterilization method that does not change polymer properties.

We present a solution to regenerate adipose tissue using degradable, soft, pliable 3D-printed scaffolds made of a medical-grade copolymer coated with polydopamine. The problem today is that while printing, the medical grade copolyesters degrade and the scaffolds become very stiff and brittle, being not optimal for adipose tissue defects. Herein, we have used high molar mass poly(L-lactide-co-trimethylene carbonate) (PLATMC) to engineer scaffolds using a direct extrusion-based 3D printer, the 3D Bioplotter (R). Our approach was first focused on how the printing influences the polymer and scaffold's mechanical properties, then on exploring different printing designs and, in the end, on assessing surface functionalization. Finite element analysis revealed that scaffold's mechanical properties vary according to the gradual degradation of the polymer as a consequence of the molar mass decrease during printing. Considering this, we defined optimal printing parameters to minimize material's degradation and printed scaffolds with different designs. We subsequently functionalized one scaffold design with polydopamine coating and conducted in vitro cell studies. Results showed that polydopamine augmented stem cell proliferation and adipogenic differentiation owing to increased surface hydrophilicity. Thus, the present research show that the medical grade PLATMC based scaffolds are a potential candidate towards the development of implantable, resorbable, medical devices for adipose tissue regeneration.

The advancement of 3D printing technologies in the fabrication of degradable scaffolds for tissue engineering includes, from the standpoint of the polymer chemists, an urgent need to develop new materials that can be used as ink and are suitable for medical applications. Here, we demonstrate that a copolymer of epsilon-caprolactone (CL) with low amounts of p-dioxanone (DX) (15 mol %) is a degradable and printable material that suits the requirements of melt extrusion 3D printing technologies, including negligible degradation during thermal processing. It is therefore a potential candidate for soft tissue regeneration. The semicrystalline CL/DX copolymer is processed at a lower temperature than a commercial polycaprolactone (PCL), shaped as a filament for melt extrusion 3D printing and as porous and pliable scaffolds with a gradient design. Scaffolds have Young's modulus in the range of 60-80 MPa, values suitable for provision of structural support for damaged soft tissue such as breast tissue. SEM and confocal microscope indicate that the CL/DX copolymer scaffolds support adipose stem cell attachment, spreading, and proliferation.

Various 3D printing techniques currently use degradable polymers such as aliphatic polyesters to create well-defined scaffolds. Even though degradable polymers are influenced by the printing process, and this subsequently affects the mechanical properties and degradation profile, degradation of the polymer during the process is not often considered. Degradable scaffolds are today printed and cell-material interactions evaluated without considering the fact that the polymer change while printing the scaffold. Our methodology herein was to vary the printing parameters such as temperature, pressure, and speed to define the relationship between printability, polymer microstructure, composition, degradation profile during the process, and rheological behavior. We used high molecular weight medical-grade (co)polymers, poly(L-lactide-co-epsilon-caprolactone) (PCLA), poly(L-lactide-co-glycolide) (PLGA), and poly(D,L-lactide-co-glycolide) (PDLGA), with L-lactide content ranging from 25 to 100 mol %, for printing in an extrusion-based printer (3D Bioplotter). Optical microscopy confirmed that the polymers were printable at high resolution and good speed, until a certain degree of degradation. The results show also that printability can not be claimed just by optimizing printing parameters and highlight the importance of a careful analysis of how the polymer's structure and properties vary during printing. The polymers thermally decomposed from the first processing minute and caused a decrease in the average block length of the lactide blocks in the copolymers and generated lower crystallinity. Poly(L-lactide) (PLLA) and PCLA are printable at a higher molecular weight, less degradation before printing was possible, compared to PLGA and PDLGA, a result explained by the higher complex viscosity and more elastic polymeric melt of the copolymer containing glycolide (GA) and lactide (LA). In more detail, copolymers comprised of LA and epsilon-caprolactone (CL) formed lower molecular weight compounds over the course of printing, while the PLGA copolymer was more susceptible to intermolecular transesterification reactions, which do not affect the overall molecular weight, but cause changes in the copolymer microstructure. This results in a longer printing time for PLGA than PLLA and PCLA.