Micro-Porous PLLA Scaffolds for Orthopedic Surgical Fixation Devices

Anterior cruciate ligament (ACL) reconstructive surgery is a major health concern world-wide because of a large aging population and increased occurrence of sport-related injuries. Tissue engineering is a rapidly growing interdisciplinary field that offers a promising new approach for ACL repair. The aim of this project is to explore novel “smart” surgical fixation devices that not only secure a graft in place without strength failure, but also incorporate and release bioactive materials, intended to promote bone tissue growth. In order to facilitate bioactive reagent release, biopolymeric scaffolds with continuous micro-porous structure were developed. The morphology of the porous structures in the poly-L-lactic acid (PLLA) matrix reflects the differential influence of the concentration of sacrificial material (PS-polystyrene), phase separation levels of the immiscible polymers (PLLA and PS), and melt-blending conditions (Fig. 1) [1]. During removal of the sacrificial material, the chemical solvent might introduce some chemical reactant into the scaffolds. In order to assess the feasibility of using the micro-porous structures for medical applications, 7F2 osteoblasts were cultured on these scaffolds for 7 days. The attachment and proliferation of 7F2 cells on all scaffolds were assessed by fluorescent nuclear staining with Hoechst 33258 and phalloidin. The morphology of 7F2 osteoblasts on solid PLLA and PLLA/HA with 40% porous structure scaffolds till the 7 days pos-seeding was observed under confocal microscopy (Fig. 2A and B). The results showed that removal of the sacrificial material does not influence cell growth and the composites are biocompatible. Besides in vitro cytotoxicity test, in vivo test of all the micro-porous structural scaffolds was performed through rat subcutaneous surgery. Histological analysis (H&E staining) of the porous PLLA/HA with 40% pores retrieved from rat subcutaneous tissue 4 weeks postimplantation show that cells start to grow inside the porous scaffold (Fig. 3A). The morphology of surrounding extracellular matrix (ECM) growing on the scaffolds was observed under SEM. Figure 3B shows soft tissue attached onto PLLA/HA porous scaffold after 1 month post implantation time point, which indicates the good biocompatibility of the scaffolds. Based on these data we predict that these scaffolds will be suitable for inducing and sustaining bone tissue regeneration, and will be feasible for ACL repair.

The Study on PLLA-Nanodiamond Composites for Surgical Fixation Devices

Biopolymers have a great potential in biomedical engineering, having been used as scaffolds for hard and soft tissues, such as bone and blood vessels for many years. More recently biopolymers have also found applications in surgical fixation devices. Compared with conventional metal fixation devices, bone grafts and organ substitutes, biopolymer products have advantages of no long-term implant palpability or temperature sensitivity, predictable degradation to provide progressive bone loading and no stress shielding, all of which leads to a better bone healing, reduced patient trauma and cost, elimination of second surgery for implant removal, and fewer complications from infections. However lack of initial fixation strength and bioactivity are two major concerns which limited more widespread applications of biopolymers in orthopedic surgery. Nanodiamond is attractive for its use in reinforcement of composite materials due to their outstanding mechanical, chemical and biological properties. Nanotechnology shows us many innovations and it is generally accepted view that many could be further developed and applied in tissue engineering. In this work, we conduct poly(L-lactic acid) (PLLA) and octadecylamine functionalized nanodiamond (ND-ODA) composite research to optimize the polymer/ND interface, thus to reinforce the mechanical strength. Composites comprising PLLA matrix with embedded ND-ODA were prepared by mixing PLLA/chloroform solution with chloroform suspension of nanodiamonds at concentrations of 0–10 by weight percent. The dispersion of ND-ODA was observed by transmission electron microscopy (TEM). TEM micrographs show that ND-ODA can disperse uniformly in PLLA till 10% wt. Nanoindentation result shows the mechanical strength of ND-ODA/PLLA composites improving following increasing the concentration of ND-ODA in composites. The noncytotoxicity of ND-ODA was demonstrated on 7F2 Osteoblasts. To test the usefulness of ND-ODA/PLLA composites as scaffolds for supporting cell growth, 7F2 Osteoblasts were cultured on scaffolds for 6 days. The attachment and proliferation of 7F2 on all scaffolds were assessed by fluorescent nuclear staining with Hoechst 33258 and Alamar BlueTM assay. The results showed that the adding ND-ODA does small influence cell growth, which indicates the composites have good biocompatibility. The morphology of 7F2 cells growing on all ND-ODA/PLLA composite scaffolds was determined by SEM, which confirms the Osteoblasts spread on the scaffolds. All these results combined suggest that ND-ODA/PLLA might provide a novel composite suitable for surgical fixation devices.

The Co-Continuous Micro-Porous PLLA Scaffolds and Their Application for ACL Reconstruction

Anterior cruciate ligament (ACL) reconstructive surgery is a major health concern world-wide because of a large aging population and increased occurrence of sport-related damage. Tissue engineering is a rapidly growing interdisciplinary field that offers a promising new approach for ACL repair. In order to overcome the shortages of current existing surgical fixation devices, we are combining gradient cellular structure (GCS) injection molding technique and biomedical engineering to develop novel surgical fixation devices (screw, anchor, plate, pin, staple, etc.) that not only incorporate bioactive materials such as growth factors, healing drugs and cells, but have natural bone GCS structure, intended to mimic the natural bone and promote bone tissue growth and eventually eliminate the defects associated with existing surgical fixation devices. In this work, a series of novel poly-L-lactic acid (PLLA) scaffolds with micro-porous structure were prepared by injection molding an immiscible polymer blend, with spatially controlled thermal conditioning to adjust the phase size from core to surface. The produced scaffolds were observed under SEM, which shows a co-continuous structure was created successfully through our method. The biocompatibility and the feasibility of produced micro-porous structural PLLA and PLLA/HA scaffolds as a matrix supporting cell growth tested by culturing murine osteoblasts cell line (7F2) for up to 9 days were assessed by Alamar Blue™ assay, which showed that the manufacturing process had no negative effects on cell proliferation. The cell attachment, spreading, migration and proliferation to confluence were assessed by fluorescent nuclear staining with Hoechst 33258. In order to evaluate the functional and cell biological applicability of the micro-porous structural PLLA scaffolds, a subcutaneous biodegradation test was performed through rat model for 1 week and 1 month time period, respectively. Our results showed that the micro-porous structural PLLA scaffolds are non-toxic, and they showed a mild foreign body reaction and complete fibrous encapsulation after implantation. Well created interconnected porous structure and biocompatibility suggest great potential of the micro-porous PLLA scaffolds in application for ACL reconstruction.