Polylactide bioabsorbable polymers for guided tissue regeneration

Poly-L-lactide scaffolds with super pores obtained by freeze-extraction method

A nonplanar polylactide scaffold to be used in tissue engineering was obtained by freeze-extraction method. Properties of the scaffold were modified by adding Eudragit® E100. The impact of the modification on morphology, porosity and pore size, mass absorbability, mechanical properties was determined. Scanning electron microscopy (SEM), hydrostatic weighing test, static compression test was used to this end. The chemical composition of the scaffold was defined based on infrared spectroscopy (FTIR) and energy-dispersive X-ray spectroscopy (EDX). Biocompatibility was confirmed by quantitative tests and microscopic observation. The obtained results show that the obtained scaffolds may be applied as a carrier of hydrophilic cellular growth factors for more efficient tissue regeneration.

A Resorbable Biomaterial Shaped as a Tubular Chamber and Containing Stem Cells: A Pilot Study on Artificial Bone Regeneration

In a previous study, we showed how healing of non-union defects in rabbit radii can be achieved by means of a tubular resorbable chamber, in comparison with untreated defects. In the present study, we placed bone marrow stem cells inside the chamber. Bone marrow was obtained by percutaneous aspiration from the iliac crest in 9 adult New Zealand rabbits. Stem cells were separated by the centrifugation technique. In the same animals, a defect of 10 mm was created in both radii. On the left side, the defect was treated with the poly-DL-Lactide chamber, in which a suspension of autologous cells was injected; on the right side, only autologous cells were used. Radiological and histomorphometric data were compared within this study as well as with the results of our previous study. At 3, 6 and 9 months, there was no healing on the right side. On the left side, progressive bone formation with reunion of the stumps was observed in the chamber. We conclude that stem cells can accelerate bone healing when contained in the tubular chamber.

Polyurethane/Polylactide-Blend Films Doped with Zinc Ions for the Growth and Expansion of Human Olfactory Ensheathing Cells (OECs) and Adipose-Derived Mesenchymal Stromal Stem Cells (ASCs) for Regenerative Medicine Applications

Polymeric biomaterials based on polyurethane and polylactide blends are promising candidates for regenerative medicine applications as biocompatible, bioresorbable carriers. In current research we showed that 80/20 polyurethane/polylactide blends (PU/PLDL) with confirmed biological properties in vitro may be further improved by the addition of ZnO nanoparticles for the delivery of bioactive zinc oxide for cells. The PU/PLDL blends were doped with different concentrations of ZnO (0.001%, 0.01%, 0.05%) and undertaken for in vitro biological evaluation using human adipose stromal stem cells (ASCs) and olfactory ensheathing cells (OECs). The addition of 0.001% of ZnO to the biomaterials positively influenced the morphology, proliferation, and phenotype of cells cultured on the scaffolds. Moreover, the analysis of oxidative stress markers revealed that 0.001% of ZnO added to the material decreased the stress level in both cell lines. In addition, the levels of neural-specific genes were upregulated in OECs when cultured on sample 0.001 ZnO, while the apoptosis-related genes were downregulated in OECs and ASCs in the same group. Therefore, we showed that PU/PLDL blends doped with 0.001% of ZnO exert beneficial influence on ASCs and OECs in vitro and they may be considered for future applications in the field of regenerative medicine.

Tissue engineering approaches for bone repair: concepts and evidence

Over the last decades, the medical world has advanced dramatically in the understanding of fracture repair. The three components needed for fracture healing are osteoconduction, osteoinduction and osteogenesis. With newly designed scaffolds, ex vivo produced growth factors and isolated stem cells, most of the challenges of critical size bone defects have been resolved in vitro, and in some cases in animal models as well. However, there are still challenges needed to be overcome before these technologies can be fully converted from the bench to the bedside. These technological and biological advancements need to be converted to mass production of affordable products that can be used in every part of the world. Vascularity, full substation of scaffolds by native bone, and bio-safety are the three most critical steps to be challenged before reaching the clinical setting.

From Hippocrates to tissue engineering: surgical strategies in wound treatment

The history of wound treatment has been virtually the history of surgery for many centuries and also is a history of alliance and conflicts between the physician and nature. The Hippocratic statement about natura medicatrix has been well known since antiquity, but often was neglected. Suppuration was considered a necessary event in the healing process and was elicited by the surgeons with traumatic and painful procedures. The concept of simplicity in treating the wounds was suggested by Teodorico Borgognone and Henry de Mondeville in 13th century and was confirmed only three centuries later by the works of Ambroise Paré and Cesare Magati. The history of wound management has been characterized by empiricism since the 18th century, but it took a physiopathological direction during the 19th century when Virchow investigated tissue reaction to injuries, and Lister introduced antiseptic procedures in surgery. By establishing the basis for a biological method to treat wounds, the seeds were sown to enhance the pathways involved in tissue repair, also with the support of new strategies and technology.

In vitro evaluation of various bioabsorbable and nonresorbable barrier membranes for guided tissue regeneration

BACKGROUND

Different types of bioabsorbable and nonresorbable membranes have been widely used for guided tissue regeneration (GTR) with its ultimate goal of regenerating lost periodontal structures. The purpose of the present study was to evaluate the biological effects of various bioabsorbable and nonresorbable membranes in cultures of primary human gingival fibroblasts (HGF), periodontal ligament fibroblasts (PDLF) and human osteoblast-like (HOB) cells in vitro.

METHODS

Three commercially available collagen membranes [TutoDent (TD), Resodont (RD) and BioGide (BG)] as well as three nonresorbable polytetrafluoroethylene (PTFE) membranes [ACE (AC), Cytoplast (CT) and TefGen-FD (TG)] were tested. Cells plated on culture dishes (CD) served as positive controls. The effect of the barrier membranes on HGF, PDLF as well as HOB cells was assessed by the Alamar Blue fluorometric proliferation assay after 1, 2.5, 4, 24 and 48 h time periods. The structural and morphological properties of the membranes were evaluated by scanning electron microscopy (SEM).

RESULTS

The results showed that of the six barriers tested, TD and RD demonstrated the highest rate of HGF proliferation at both earlier (1 h) and later (48 h) time periods (P < 0.001) compared to all other tested barriers and CD. Similarly, TD, RD and BG had significantly higher numbers of cells at all time periods when compared with the positive control in PDLF culture (P < or = 0.001). In HOB cell culture, the highest rate of cell proliferation was also calculated for TD at all time periods (P < 0.001). SEM observations demonstrated a microporous structure of all collagen membranes, with a compact top surface and a porous bottom surface, whereas the nonresorbable PTFE membranes demonstrated a homogenous structure with a symmetric dense skin layer.

CONCLUSION

Results from the present study suggested that GTR membrane materials, per se, may influence cell proliferation in the process of periodontal tissue/bone regeneration. Among the six membranes examined, the bioabsorbable membranes demonstrated to be more suitable to stimulate cellular proliferation compared to nonresorbable PTFE membranes.

The role of evaluation methods in the assessment of peripheral nerve regeneration through synthetic conduits: a systematic review

Object

A number of evaluation methods that are currently used to compare peripheral nerve regeneration with alternative repair methods and to judge the outcome of a new paradigm were hypothesized to lack resolving power. This would too often lead to the conclusion that the outcome of a new paradigm could not be discerned from the outcome of the current gold standard, the autograft. As a consequence, the new paradigm would incorrectly be judged as successful.

Methods

An overview of the methods that were used to evaluate peripheral nerve regeneration after grafting of the rat sciatic nerve was prepared. All articles that were published between January 1975 and December 2004 and concerned grafting of the rat sciatic nerve (minimum graft length 5 mm) and in which the experimental method was compared with an untreated or another grafted nerve were included. The author scored the presence of statistically significant differences between paradigms.

Results

Evaluation of nerve fiber count, nerve fiber density, N-ratio, nerve histological success ratio, compound muscle action potential, muscle weight, and muscle tetanic force are methods that were demonstrated to have resolving power.

Conclusions

A number of evaluation methods are not suitable to demonstrate a significant difference between experimental paradigms in peripheral nerve regeneration. It is preferable to apply a combination of evaluation methods with resolving power to evaluate nerve regeneration properly.

Repairing Periodontal Bone Defect with In Vivo Tissue Engineering Bone

The purpose of this study was to develop a feasible approach for repairing periodontal bone defects with the in vivo tissue engineering bone incorporated with bioabsorbable PLA membrane and to provide evidences for the clinical application. Osteoinductive HA/β-TCP sintered at 1100°C were implanted in the femur medial muscles in the hind legs of three dogs. Four weeks after implantation, the in vivo tissue engineering (TE) bone was explanted. Meanwhile, artificial periodontal bone defects of 8mm×6mm were performed on the buccal side of 4th premolar and 1st molar of mandible bilaterally, with the exposure of dental roots. The defects were treated as follows: (1) in vivo TE bone and PLA membrane; (2) HA/β-TCP ceramics and PLA membrane; (3) PLA membrane only; (4) empty control. At the 2, 4, 8 weeks post-transplantation, the dogs were sacrificed. The specimen were harvested and evaluated by gross inspection, dental radiography, SPECT (99mTC-MDP) and histological observation by MPIA2500. The results showed that more mature osseointegration was found in the group 1. We presumed that the in vivo TE bone graft could enhance the reparation of periodontal bone defects.

Bioabsorbable scaffold for in situ bone regeneration

A non-porous poly-DL-lactide tubular chamber filled by demineralised bone matrix (DBM) and bone marrow stromal cells (BMSC) in combination, was evaluated as a scaffold for guided bone regeneration (GBR) in an experimental model using the rabbit radius. The tubular chamber had an internal diameter of 4.7 mm, a wall thickness of 0.4 mm and a length of 18 mm. Autologous BMSC were obtained, under general anaesthesia from rabbit iliac crest and isolated by centrifugation technique. Allogenic DBM was obtained from cortico-cancellous bone of rabbits. In general anaesthesia, a 10-mm defect was bilaterally created in the radii of 10 rabbits. On the right side (experimental side) the defect was bridged with the chamber filled with both BMSC and DBM. On the left side (control side) the defect was treated by positioning DBM and BMSC between the two stumps. At an experimental time of 4 months histology and histomorphometry demonstrated that the presence of a tubular chamber significantly improved bone regrowth in the defect The mean thickness of newly-formed bone inside the chamber was about 56.7+/-3.74% of the normal radial cortex, in comparison with 46.7+/-10.7% when DBM and BMSC without the chamber were placed in the defect, P<0.05). These results confirmed the effectiveness of the chamber as a container for factors promoting bone regeneration.

Biocompatibility of Poly-DL-lactic acid (PDLLA) for Lung Tissue Engineering

This study explores the possibility of growing lung cells on poly-DL-lactic acid (PDLLA) scaffolds, with a view to in future engineer pulmonary tissue for human implantation. As a first step in this process, the ability of PDLLA to maintain the growth of lung epithelium is tested using a robust cell line. Poly-DL-lactic acid has been investigated in two forms, as planar discs and as 3-D foams, and it has been demonstrated that PDLLA is not only nontoxic to pneumocytes but it also actively supports their growth. The initial findings suggest that the material is an appropriate matrix for engineering of distal lung tissue.

Guided bone regeneration in the treatment of segmental diaphyseal defects: a comparison between resorbable and non-resorbable membranes

This study compares non-absorbable, ethyl cellulose (EC) membranes and absorbable, chitosan (CH) membranes in a rabbit model. Bone regeneration, evaluated by radiological and pathological parameters, was seen in both groups. In the EC group the process was faster but was followed by a sharp decrease, whereas in the CH group it was slower and continuous.

Instrumented transforaminal lumbar interbody fusion with bioresorbable polymer implants and iliac crest autograft

STUDY DESIGN

Twenty-seven patients underwent instrumented transforaminal lumbar interbody fusion (TLIF) procedures using bioresorbable implants as interbody spacers. The greater than 2-year clinical and radiographic results of this series are presented along with as a review of relevant preclinical and preliminary clinical studies of bioresorbables.

OBJECTIVE

To determine the clinical suitability of bioresorbable implants used as interbody spacers in spinal fusion surgery applications, particularly in the TLIF procedure.

SUMMARY OF BACKGROUND DATA

Bioresorbable technology has been in clinical use by surgeons of a variety of specialties for over 35 years. The use of bioresorbable implants in spine surgery, however, has only been widely investigated in the last several years. The use of slowly degrading bioresorbable implants has the potential for load sharing during fusion when used for interbody applications, retaining imaging quality after fusion, obviating later implant removal, providing biologic barriers as well as other various applications. Animal studies and early clinical series with the use of these materials for a variety of indications have been encouraging.

METHODS

This study evaluates the use of bioresorbable polymer spacers manufactured with a 70:30 copolymer of poly-L-lactide and D,L-lactide as interbody spacers in 27 of 31 patients with 2 years or more follow-up who underwent instrumented TLIF for primarily degenerative indications.

RESULTS

At a mean of 31.9 months follow-up, 25 patients (92.6%) were judged to have solid fusions and 22 patients (81.5%) had good to excellent results. Three patients (11.1%) experienced complications, none of which were directly or indirectly attributable to the use of the bioresorbable polymer implant. Only one implant in 1 patient (3.7%) demonstrated mechanical failure on insertion, and that patient exhibited no clinical sequelae.

CONCLUSIONS

Bioresorbable implants have significant potential for use in spine surgery. This potential is realized in this first published clinical series using bioresorbable implants as interbody spacers with a minimum follow-up of 2 years, significantly exceeding the biologic "life expectancy" (12-18 months) of the implant material. Both the clinical and radiographic results of this study support the use of interbody devices manufactured from bioresorbable polymers for structural interbody support in the TLIF procedure.

Prosthetic devices shaped as tubular chambers for the treatment of large diaphyseal defects by guided bone regeneration

Guided tissue regeneration is based on the hypothesis that the different tissues have unequal abilities to penetrate a wounded area during the healing process. The use of a device acting as a chamber allows the growth of a particular tissue and prevents the ingrowth of other tissues which impair the healing process. At the same time the chamber protects and maintains in situ the intrinsic growth factors so that they may perform their specific activity. Guided tissue regeneration currently plays a well-recognized role mostly in dentistry and peripheral nerve surgery but interesting perspectives have also opened up in orthopedics. Considering the possibility of using guided bone regeneration in the repair of diaphyseal bone defects, this updated survey highlights some critical points and pathways related to the state-of-the-art of this promising procedure, focusing particularly on the properties of the material to make the tubular chamber, the use of osteopromotive factors and the most appropriate animal model to be used for the experimental evaluation.

PELA microspheres loaded H. pylori lysates and their mucosal immune response

AIM: To prepare poly (D,L-lactide)-polyethylene glycol copolymer (PELA) microspheres loaded H.pylori lysates or Cystografin and observe their targeting in gastrointestinal mucous membrane or analyze the mucosal immune responses by oral administration.

METHODS: PELA microspheres loaded H.pylori lysates or Cystografin were prepared by double emulsion evaporation method. Their distribution in gastrointestinal mucous membrane was observed by CT.Balb/c mice orally immunized in mucosal immune responses, whose antibody production in salivary and gut washing and antibody secreting cells in Peyer’s patches (PP) were estimated by ELISA and ELISPOT, respectively. The microspheres’ physical properties, such as particle size, protein level and morphology were investigated.

RESULTS: All prepared microspheres were found to have a smooth surface morphology from 3.20-4.05 μm in diameter and high encapsulation efficiency from 74.9%-82.2%. No significant correlation in their physical properties was shown, depending on their molecular weight at the similar composition ratio. Immunization with all types of PELA-Hp microspheres elevated the saliva sIgA level at week 3 by approximately 3-4 times that with soluble antigen, which was greatly enhanced after boosting. At one week after last immunization with all types of PELA-Hp microspheres (week 8), the specific sIgA-ASCs, IgG-ASCs and sIgA in salivary rose obviously. In intestinal Peyer’s patches, the specific sIgA-ASCs were 5.92-6.98 × 10⁴/mL cell and IgG-ASCs were 3.47-4.02 × 10⁴/mL cell, about 5-9 times higher than those with soluble antigen (P < 0.01). ASCs in intestine were more than those in stomach and the majority of the ASCs were sIgA-ASCs. The sIgA in gut washing fluid was 1.62-1.85 OD, about 3-6 times tthat of those with soluble antigen. There were significant differences of the ASCs and sIgA in gut washing fluid as compared with those of PBS and MS-0 (P < 0.05). There appeared to be good correlation between sIgA level in gut washing fluid and sIgA-ASCs in intestinal Peyer’s patches.

CONCLUSION: PELA microspheres may be used as vehicle to delivery antigen and adjuvant in designing oral vaccination.

Resorbable posterolateral graft containment in a rabbit spinal fusion model

OBJECT

The authors studied the effect of a resorbable graft containment device in a rabbit posterolateral lumbar spinal fusion model.

METHODS

Twenty rabbits were divided into four groups: autologous bone graft (ABG), ABG with the MacroPore containment device (ABG + MP), demineralized bone matrix (DBM), and DBM with the containment device (DBM + MP). Fusion mass was assessed at 6 weeks with high-resolution radiography and volumetric computerized tomography. The graft containment device was associated with alteration of the fusion mass structure and significant enhancement of fusion mass volume (ABG versus ABG + MP, p = 0.027; DBM versus DBM + MP, p = 0.043).

CONCLUSIONS

A bioabsorbable protective graft containment device successfully enhanced posterolateral spinal fusion mass volume.

Resorbable posterolateral graft containment in a rabbit spinal fusion model

The effect of a resorbable graft containment device was evaluated in a rabbit posterolateral lumbar spinal fusion model. Twenty rabbits were divided into four groups: autogenous bone graft (ABG), ABG with the MacroPore containment device (MacroPore Biosurgery Inc, San Diego, Calif) (ABG+MP), demineralized bone matrix (DBM), and DBM with the containment device (DBM+MP). Fusion mass was assessed at 6 weeks with high resolution radiographs and volumetric computed tomography (CT). The graft containment device was associated with alteration of the fusion mass structure and significant enhancement of fusion mass volume (ABG versus ABG+MP, P=.027; DBM versus DBM+MP, P=.043). A bioabsorbable, protective graft containment device successfully enhanced posterolateral spinal fusion mass volume.

Enhanced guided bone regeneration with a resorbable chamber containing demineralized bone matrix

BACKGROUND

The effectiveness of a nonporous poly-DL-lactide tubular chamber in guiding bone regeneration through a long bone defect had already been assessed in an experimental model using the rabbit radius. The injection of bone marrow stem cells into the chamber had proven to enhance bone regeneration.

METHODS

The present study reports on the development of the above research project in a subsequent stage. Demineralized bone matrix (DBM) obtained by milling New Zealand rabbit femoral and tibial diaphyses was placed into a tubular chamber. A 10-mm defect was bilaterally created in the radii of 10 rabbits. On the left side (chamber side) the defect was treated by means of a poly-DL-lactide chamber filled with DBM, whereas DBM alone was used on the right side (control).

RESULTS

Controls were performed at 3 and 6 months by radiographs and histomorphometry and demonstrated better bone growth on the chamber side versus the control side. A comparison with the results previously obtained by stem cell injection into the chamber revealed significant acceleration of bone regrowth in the first 3 months because of the addition of DBM to the chamber. However, no significant difference was found between the two sides after 6 months.

CONCLUSION

These results have confirmed the effectiveness of the chamber as a container for the factors promoting bone regeneration, probably because the osteogenetic activity is maintained in situ.

In vitro comparison of bioabsorbable and non-resorbable membranes in bone regeneration

BACKGROUND

Barrier membranes are used to prevent down-growth of the oral mucosa along the root surface and to allow alveolar bone regeneration in guided tissue regeneration. Several studies have demonstrated bone regenerates in the presence of bioabsorbable and non-resorbable membranes, but no studies have compared multiple bioabsorbable barriers to one another and to non-resorbable barriers. This study evaluated the in vitro influence of bioabsorbable and non-resorbable membranes on specific parameters of human osteoblast activity.

METHODS

Human osteoblasts were cultured on bioabsorbable membranes made of collagen, hyaluronic acid, and poly DL-lactide, and the most common non-resorbable membrane which is made of expanded polytetrafluoroethylene (ePTFE). The osteoblasts were cultured in vitro for 24 hours on barrier membranes in the presence of 3H-thymidine and 3H-proline to study cell proliferation and collagen synthesis. Transforming growth factor-beta1 (TGF-beta1) secretion was evaluated in conditioned media using an ELISA kit.

RESULTS

The results showed that collagen and poly DL-lactide stimulated DNA synthesis more than ePTFE and hyaluronic acid. All bioabsorbable membranes significantly increased collagen synthesis and alkaline phosphatase activity. Collagen and hyaluronic acid increased secretion of TGF-beta1, a growth factor involved in bone remodeling.

CONCLUSIONS

These data suggest bioabsorbable membranes, particularly collagen and hyaluronic acid, may promote bone regeneration through their activity on osteoblasts.

Approaches permitting and enhancing motoneuron regeneration after spinal cord, ventral root, plexus and peripheral nerve injuries

The motoneuron has a strong ability to regenerate after injury. However, the problems of nerve cell survival after a proximal axotomy, difficulty in axonal elongation after intraspinal lesion and the lack of target specificity during nerve fibre regrowth interfere with a good functional restitution. Current research has addressed these impediments. New approaches for the management of complicated as well as intraspinal lesions and peripheral nerve trunk injuries are described.