Tissue engineering
John Dudley Langdon, Mohan Francis Patel, Robert Andrew Ord, Peter Brennan in Operative Oral and Maxillofacial Surgery, 2017
The underlying hard tissues offer the framework for overlying facial aesthetics, as defects in osseous and cartilaginous tissues are visibly portrayed through the soft tissues. Classically, significant morbidity and deformity is traded in a distant donor area for reconstruction of craniofacial structures. Allogeneic grafts are available; however, in order to achieve minimal immunologic response, all cellular tissues are removed reducing the potential for reliable integration. Lastly, alloplastic materials are at risk for foreign body reaction, with significant inflammation and increased risk of infection. Tissue-engineered scaffolds have been created to capitalize on a patient’s innate healing response while adding specific factors at the local site to attempt to improve hard tissue regeneration. Tissue engineering has explored a number of materials for creation of scaffolds including polymers, ceramics and composites. Polymers (polylactic acid, polyglycolic acid, polycaprolactone, polypropylene fumarate) have variable properties and offer reliable biodegradation. More permanent ceramics (hydroxyapetite, tricalcium phosphate) can be used alone, but are frequently combined with polymers in composite grafts. Composites can also include biofactors such as purified concentrated growth factors, transduced cells with various viral vectors, and autogenous bone marrow cells.
Animal Selections in Orthopaedic Research
Yuehuei H. An, Richard J. Friedman in Animal Models in Orthopaedic Research, 2020
For example, in the development of a new bioabsorbable material, measurements of its mechanical strength and degradation rate in a saline environment must be tested. Its biocompatibility in cell culture must also be assessed (Figure 1). After these in vitro studies, the material cannot immediately be tested in humans because it may have undetected toxic effects in human tissues. In the past, some products containing polylactide acid (PLA) and polyglycolic acid (PGA) have caused tissue lysis in human subjects leading to aseptic abscesses. Will the new absorbable material cause a similar problem? This question has to be answered before clinical trials are undertaken. Therefore, an animal model (using lower level animals such as rats) can be used to test the biocompatibility and degradation rate of the material, in vivo. Tests such as these are normally accomplished by subcutaneous and intraosseous implantation. If the experiment does not reveal any significant toxic effects, a second animal model (using higher level animals such as rabbits) can be used to evaluate the potential applications of the material, such as fixation of fractures or osteotomies or repair of ligaments or cartilage defects. At the same time, the process of material degradation and replacement by host tissues could investigated. If the material functions well enough for fracture fixation or ligament repair in all animal models, then consideration may be given to a cautious, well controlled human trial (Figure 1).1
Vaccine Adjuvants in Immunotoxicology
Mesut Karahan in Synthetic Peptide Vaccine Models, 2021
Nanoparticles are manufactured using albumin, collagen, starch, chitosan, and dextran out of natural polymers and polymethylmethacrylate, polyesters, polyanhydrides, and polyamides among synthetic polymers (Li et al. 2014). There are biodegradable or non-biodegradable polymers. Non-biodegradable polymers may cause unexpected effects by accumulation in the body. In the vaccine studies, the characteristics such as toxic effects of the polymer on the organism, antigen release speed capacity, stability status under storage conditions, and stability in the in vivo conditions should be taken into account in making a decision for an ideal polymer carrier system (Skwarczynski and Toth 2011, 2016). The comprehensive toxicity tests for several synthetic polymers such as polyesters, polylactic acid (PLA), polyglycolic acid, and their copolymers poly(lactic-co-glycolic acid) (PLGA) have been carried out and they are FDA-approved for use in humans (Li et al. 2014; Cordeiro and Alonso 2016). The most commonly used biodegradable polymers are PLA, PLGA, polyglutamic acid (PGA), polycaprolactone (PCL), and polyhydroxybutyrate. PLGA is the most frequently used polymer in the nanoparticle studies (Li et al. 2014). Skwarczynski and Toth (2011) have reported in their study that MUC-1 peptide vaccine assembled into PLGA nanoparticle carrier system accompanied with adjuvant MPLA created immune response by inducing T cells. However, it has been noted in the same article that need for use of adjuvant in the PLGA-based systems still continues (Skwarczynski and Toth 2011).
Cell homing strategy as a promising approach to the vitality of pulp-dentin complexes in endodontic therapy: focus on potential biomaterials
Published in Expert Opinion on Biological Therapy, 2022
Elaheh Dalir Abdolahinia, Zahra Safari, Sayed Soroush Sadat Kachouei, Ramin Zabeti Jahromi, Nastaran Atashkar, Amirreza Karbalaeihasanesfahani, Mahdieh Alipour, Nastaran Hashemzadeh, Simin Sharifi, Solmaz Maleki Dizaj
One of the essential aspects of tissue engineering is the use of biodegradable scaffolds [18]. For tissue engineering, a variety of synthetic or natural polymers and calcium phosphate-based materials have been used. Polyglycolic acid (PGA) was employed as a scaffold in the first work on dental tissue engineering [19]. In addition, collagen sponge scaffolds and collagen gels have recently been found to be effective for tooth regeneration [16,20]. Thus, scaffolds promote cell recruitment, proliferation, and differentiation and serve as a vehicle for bioactive or targeted cells [6,21,22]. These functions may contribute to their capacity to stimulate the revitalization of tooth regeneration. However, there are various alternative scaffold materials available, and knowledge of their effects on tooth regeneration is currently limited [23].
Risk factors for recurrent bleeding from acute hemorrhagic rectal ulcer
Published in Scandinavian Journal of Gastroenterology, 2018
Naoyuki Nishimura, Motowo Mizuno, Yuichi Shimodate, Akira Doi, Hirokazu Mouri, Kazuhiro Matsueda
We found also that although bleeding from AHRU usually ceased spontaneously or with hemostatic treatment, recurrent bleeding was common (30%). Similar or higher rates have been reported by others (24–50%) [3,5,9]. Various methods of endoscopic hemostasis have been used in the treatment of bleeding from AHRU: argon plasma coagulation, forceps coagulation, clipping, hypertonic saline-epinephrine injection, and band ligation [3,5,7]. In the present study, all these methods, plus forceps coagulation, were used singly or in combination, and hemostasis was achieved in most patients. As in previous studies [3,9], we found no significant difference among hemostatic methods used in the rate of recurrent bleeding from AHRU. Second-look colonoscopy has been reported effective for reducing recurrent bleeding from AHRU [9]. In a recent case report, the polyglycolic acid sheet was applied in the attempted promotion of ulcer healing and prevention of recurrent bleeding [12]. The optimal procedure for prevention of recurrent bleeding from AHRU has not been established.
Fascicular turnover flap in the reconstruction of facial nerve defects: an experimental study in rats
Published in Journal of Plastic Surgery and Hand Surgery, 2019
Miyuki Uehara, Wu Wei Min, Moriaki Satoh, Fumiaki Shimizu
In cases of facial nerve gap repair, autologous nerve grafts are recognized as the only clinically effective choice [1–3]. Recently, Mackinnon et al. reported the utility of acellular nerve allograft, and this procedure is now widely used [13]. There have also been a number of studies regarding artificial nerve development, and various products are currently widely used in different countries [4–7,14]. Many biodegradable polymers, including polylactic acid (PLA), polyglycolic acid (PGA) and polylactic-co-glycolic acid (PLGA), have been reported [4–7,14]. However, these kinds of acellular compounds seem to have limited indications for nerve gap reconstruction. Indeed, a long nerve gap (more than 3 cm) is difficult to reconstruct without cell components [13].
Related Knowledge Centers
- Copolymer
- Hydrolysis
- Polyester
- Polymer
- Lactic Acid
- Thermoplastic
- Aliphatic Compound
- Glycolic Acid
- Caprolactone
- Trimethylene Carbonate