Regenerative medicine for skeletal muscle loss: a review of current tissue engineering approaches.

Skeletal muscle is capable of regeneration following minor damage, more significant volumetric muscle loss (VML) however results in permanent functional impairment. Current multimodal treatment methodologies yield variable functional recovery, with reconstructive surgical approaches restricted by limited donor tissue and significant donor morbidity. Tissue-engineered skeletal muscle constructs promise the potential to revolutionise the treatment of VML through the regeneration of functional skeletal muscle. Herein, we review the current status of tissue engineering approaches to VML; firstly the design of biocompatible tissue scaffolds, including recent developments with electroconductive materials. Secondly, we review the progenitor cell populations used to seed scaffolds and their relative merits. Thirdly we review in vitro methods of scaffold functional maturation including the use of three-dimensional bioprinting and bioreactors. Finally, we discuss the technical, regulatory and ethical barriers to clinical translation of this technology. Despite significant advances in areas, such as electroactive scaffolds and three-dimensional bioprinting, along with several promising in vivo studies, there remain multiple technical hurdles before translation into clinically impactful therapies can be achieved. Novel strategies for graft vascularisation, and in vitro functional maturation will be of particular importance in order to develop tissue-engineered constructs capable of significant clinical impact.

[Modern polyurethanes in cardiovascular surgery]. / Sovremennye poliuretany v serdechno-sosudistoi khirurgii.

Currently, there is great clinical demand for synthetic tissue-engineered cardiovascular prostheses with good long-term patency. Polyurethanes belong to the class of polymers with excellent bio- and hemocompatibility. They are known to possess good mechanical properties, but are prone to processes of degradation in conditions of functioning in living organisms. Attempts at solving this problem have resulted in the development of various new subclasses of polyurethanes such as thermoplastic polyether polyurethanes, polyurethanes with a silicone segment, polycarbonate polyurethanes and nanocomposite polyurethanes. This was accompanied and followed by offering a series of new technologies of production of implantable medical devices such as vascular grafts, heart valves and others. In the presented review, we discuss biological and mechanical properties of modern subclasses of polyurethanes, as well as modern methods of manufacturing implantable medical devices made of polyurethanes, especially small-diameter vascular prostheses.

Tissue engineering in urethral reconstruction.

Urethral strictures are one of the most common urological problems, yet the natural limitations of wound healing and the physiologic demands on the anatomic structures combine to also make urethral strictures one of the most challenging urological problems to manage. Proper wound healing demands well approximated edges because prolonged inflammation and granulation, required to close large, deep wounds, will result in excess collagen production, fibrosis, and the formation of a scar or, in the urethra, a stricture. Biomaterials have successfully been used to approximate the ECM of several different tissue types and can define a three dimensional space suitable for the formation of new tissues with both appropriate structure and appropriate function. Biomaterials can be broadly categorized as either synthetic polymers or tissue matrices, each with their advantages and limitations. Recent studies utilizing cell seeded natural biomaterials in urethral repair has yielded some promising results. However, advancements in the use of alternative sources of cells for matrix seeding and cell-seeded synthetic materials hold the possibility of even better results in the future.

The role of cements in dental lant success, Part I.

Peri-implant disease can be the result of residual excess cement. While there is no ideal implant restorative cement, the clinician must be aware that the material selection for implant restorations should not be based on properties which are more suited to restoration of the natural dentition. More appropriate criteria would be those unique to implants and the specific challenges these medical devices bring to the restorative dentist.

The development of carbohydrate polymer- and protein-based biomaterials and their role in environmental health and hygiene: A review.

Biological macromolecules have been significantly used in the medicine due to their certain therapeutic values. Macromolecules have been employed in medical filed in order to enhance, support, and substitute damaged tissues or any other biological function. In the past decade, the biomaterial field has developed considerably because of vast innovations in regenerative medicine, tissue engineering, etc. Different types of biological macromolecules such as natural protein and polysaccharide etc. and synthetic molecules such as metal based, polymer based, and ceramic based etc. have been discussed. These materials can be modified by coatings, fibres, machine parts, films, foams, and fabrics for utilization in biomedical products and other environmental applications. At present, the biological macromolecules can used in different areas like medicine, biology, physics, chemistry, tissue engineering, and materials science. These materials have been used to promote the healing of human tissues, medical implants, bio-sensors and drug delivery, etc. These materials also considered as environmentally sustainable as they are prepared in association with renewable natural resources and living organisms in contrast to non-renewable resources (petrochemicals). In addition, enhanced compatibility, durability and circular economy of biological materials make them highly attractive and innovative for current research.The present review paper summarizes a brief about biological macromolecules, their classification, methods of synthesis, and their role in biomedicine, dyes and herbal products.

Optimal suture materials for contaminated gastrointestinal surgery: does infection influence the decrease of the tensile strength of sutures?

PURPOSE: Suture materials are selected based on the following factors: absorbable/non-absorbable, monofilament/multifilament, duration with sufficiently high tensile strength, and the tissue to be sutured. Absorbable sutures are hydrolyzed in tissues. However, little is known about the influence of infection on the hydrolysis and decrease in the tensile strength. METHODS: Four kinds of sutures, i.e., non-absorbable multifilament silk, non-absorbable monofilament polypropylene (Prolene(®)), absorbable multifilament polyglactin 910 (Vicryl(®)), and absorbable monofilament polydioxanone (PDS(®)) were implanted in the back of rats. A suspension of Escherichia coli + Bacteroides fragilis or saline was injected subcutaneously into the contaminated and clean condition groups, respectively. The sutures were removed 1, 2, 4 or 8 weeks after the implantation. RESULTS: There was significantly more severe inflammation macroscopically for the silk sutures under the contaminated conditions (p = 0.03), however, no significant differences were observed among the other three sutures. All 4 kinds of sutures showed a reduction of the tensile strength over time. There were no significant differences in the magnitude of reduction between both the clean and contaminated conditions for any of the sutures. CONCLUSIONS: The reduction of the tensile strength with time did not differ significantly between sutures exposed to contaminated and clean conditions, even for the absorbable sutures.

Biomaterials and biologics in craniofacial reconstruction.

Complications related to surgery, including infection, wound dehiscence, and implant protrusion, are costly and may cause severe morbidity to patients. The choice of implants materials is critical for a successful outcome, particularly in craniofacial reconstructions. This review discusses the potential benefits and drawbacks of biologically active materials used for craniofacial bone repair as alternatives to inert implant prostheses.

Secondary rhinoplasty: management of the overresected dorsum.

Any discussion of grafting the dorsum in secondary rhinoplasty must take into account the different indications (aesthetic, augmentation, and structure) as well as recent changes in materials and techniques (fascia, diced cartilage). We have placed solid dorsal grafts with diced cartilage grafts either as an isolated diced cartilage graft in fascia graft or as the aesthetic dorsal contour layer of a composite reconstruction. The rational for this profound change in selection and indication of dorsal grafts for revising the overresected dorsum will become clear as the various alternative materials and techniques are analyzed. Currently, we only employ autogenous tissues.

Permanent soft tissue fillers.

As our youth-oriented society ages, interest in nonsurgical aesthetic techniques has generated a dramatic rise in the use of filling agents for facial rejuvenation. Backed by multiple published studies documenting safety and efficacy, soft tissue fillers are often viewed as treatments with minimal recovery time and limited risk of complications when compared with traditional surgical interventions. This has led to a genuine demand for fillers with similar safety profiles but ever increasing longevity in their aesthetic corrections. This review addresses many of the permanent soft tissue fillers that are commercially available worldwide as well as important concerns regarding their complications.

Future trends and new materials.

The variety of products available as injectable fillers and neuromodulators continues to increase. New products are soon to be introduced in the United States that will enable the clinician to treat a greater array of esthetic problems and concerns. In addition, existing materials are being modified to allow for less painful treatments and easier product handling.

Suturing: an update for the general dental practitioner.

UNLABELLED: Sutures are routinely used to achieve haemostasis and to approximate soft tissues after extractions, periodontal procedures, implant surgery and soft tissue biopsies. This paper provides the general dental practitioner with the knowledge and understanding of sutures to select the most appropriate for use. Common suturing techniques are also discussed. CLINICAL RELEVANCE: Suturing is an important aspect of dental practice, the selection of an appropriate suture and technique is integral to obtaining an optimal outcome.

[Bone substitutes: Classification and concerns]. / Les biomatériaux de substitution osseuse : classification et intérêt.

Autograft is considered as the "gold standard" for bone reconstruction. It provides osteoinductive factors, osteogenic cells, and appropriate osteoconductive scaffold. Donor site morbidity is the main limitation of autograft. Donor disease transmission limits the use of allograft. Synthetic bone substitutes still lack osteoinductive or osteogenic properties. Composite bone substitutes combining synthetic scaffold and biochemical substances initiating proliferation and cell differentiation, and possibly osteogenesis. Bone substitutes and grafts intended for clinical use are listed.

An introduction to bone tissue engineering.

Bone tissue has the capability to regenerate itself; however, defects of a critical size prevent the bone from regenerating and require additional support. To aid regeneration, bone scaffolds created out of autologous or allograft bone can be used, yet these produce problems such as fast degradation rates, reduced bioactivity, donor site morbidity or the risk of pathogen transmission. The development of bone tissue engineering has been used to create functional alternatives to regenerate bone. This can be achieved by producing bone tissue scaffolds that induce osteoconduction and integration, provide mechanical stability, and either integrate into the bone structure or degrade and are excreted by the body. A range of different biomaterials have been used to this end, each with their own advantages and disadvantages. This review will introduce the requirements of bone tissue engineering, beginning with the regeneration process of bone before exploring the requirements of bone tissue scaffolds. Aspects covered include the manufacturing process as well as the different materials used and the incorporation of bioactive molecules, growth factors and cells.

Host tissue interaction, fate, and risks of degradable and nondegradable gel fillers.

BACKGROUND: A constantly increasing number of gel fillers for aesthetic and reconstructive purposes have been introduced during the last 20 years. Most of the new ones are modified versions of the original collagen and hyaluronic acid gels. They have been reconstructed, often by adding cross-bindings to the polymer in order to obtain a more dense molecular structure, which will prolong degradation and filling effect of the gel. Other gel fillers contain particles of organic (poly-lactic acid) or inorganic (calcium hydroxylapatite) material, which have been used in human tissue for other purposes (degradable suture material and bone cement, respectively). The permanent fillers (silicone oil and polyacrylamide gel) have been used for many years, silicone mainly in the US and polyacrylamide gel in most countries outside the US and Canada. OBJECTIVE: Complications occur, and they appear to be more frequent with particulated fillers, polyacrylamide gel and silicone oil. However, these complications differ in nature and depend on the filler type used. METHODS AND MATERIALS: This overview presents the different gel filler types, how they interact with host tissue, and what can go wrong. The results and conclusion are based on experimental and clinical observations coupled with a search of the literature. RESULTS AND CONCLUSION: Complications following homogenous hydrogels are caused by infection with bacteria, which have been inserted into the gel during injection. If not treated with relevant antibiotics (but instead steroids or large doses of NSAIDs) the bacteria form a biofilm, which gives rise to a low-grade chronic infection that is resistant to antibiotics. Complications following particulated gels and silicone oil are not known, but bacteria in a biofilm and/or endotoxins released by these is a possibility which deserves further investigations, primarily by using the fluorescence in situ hybridization (FISH) technique.

Current strategies and applications of tissue engineering in dentistry--a review part 1.

UNLABELLED: A new direction in the field of vital pulp therapy is given by the introduction of tissue engineering as an emerging science. It aims to regenerate a functional tooth-tissue structure by the interplay of three basic key elements: stem cells, morphogens and scaffolds. It is a multidisciplinary approach that combines the principles of biology, medicine, and engineering to repair and/or regenerate a damaged tissue and/or organ. This two part article reviews and discusses the basic concept and strategies so far studied and researched for the engineering of basic dental tissues, to restore a functional tooth anatomy. This first part focuses on a detailed description of key elements used in tissue engineering and their applied clinical applications in dentistry. The second part will deal with the strategies that are being used and/or developed to regenerate the tooth tissues with the help of this scientific principle. CLINICAL RELEVANCE: The field of tissue engineering has recently shown promising results and a good prospect in dentistry for the development of the most ideal restorations to replace the lost tooth structure with a functional replacement.

Injectable fillers: an American perspective.

Since 1981, there has been a significant repertoire of United States Food and Drug Administrtion (FDA) approved fillers for both cosmetic rejuvenation and facial lipoatrophy. Currently available dermal fillers include bovine, human and porcine collagens, hyaluronic acids of animal and biosynthetic origin, poly-L-lactic acid, calcium hydroxylapatite, and polymethylmethacrylate. Many of these fillers were first available in Europe and Canada before their arrival in the United States (USA) and many of the complications known about these products have come from studies conducted both in the USA and abroad. Several of the fillers that are currently available abroad or are used in the USA off-label have been associated with significant complications. The authors review three of these fillers: liquid injectable silicone, DermaLive/DermaDeep, and Bio-Alcamid.

Regenerative Materials for Surgical Reconstruction: Current Spectrum of Materials and a Proposed Method for Classification.

Chronic wound management is an enormous economic strain and quality-of-life issue for patients. Current treatments are ineffective or expensive and invasive. Materials (native and artificial) can act as the basis to enhance wound repair but often fall short of complete healing. The therapeutic index of materials have often been enhanced by combining them with drug or biologic elution technologies. Combination of materials with living drugs (cells) presents a new paradigm for enhancing therapy. Cell material interaction and therapeutic output will depend on variables ascribed to the living drug as well as variables ascribed to the underlying matrix. In this article, we review medical matrices currently approved by the US Food and Drug Administration (FDA) that would likely be the first generation of materials to be used in this manner. Currently there are hundreds of different materials on the market. Identification of the right combinations would benefit from a classification scheme to group materials with similar composition or derivation. We provide a classification scheme and FDA documentation references that should provide researchers and clinicians a starting point for testing these materials in the laboratory and rapidly transitioning cell therapies to the bedside.

Biomaterials Evaluation: Conceptual Refinements and Practical Reforms.

Regarding the widespread and ever-increasing applications of biomaterials in different medical fields, their accurate assessment is of great importance. Hence the safety and efficacy of biomaterials is confirmed only through the evaluation process, the way it is done has direct effects on public health. Although every biomaterial undergoes rigorous premarket evaluation, the regulatory agencies receive a considerable number of complications and adverse event reports annually. The main factors that challenge the process of biomaterials evaluation are dissimilar regulations, asynchrony of biomaterials evaluation and biomaterials development, inherent biases of postmarketing data, and cost and timing issues. Several pieces of evidence indicate that current medical device regulations need to be improved so that they can be used more effectively in the evaluation of biomaterials. This article provides suggested conceptual refinements and practical reforms to increase the efficiency and effectiveness of the existing regulations. The main focus of the article is on strategies for evaluating biomaterials in US, and then in EU.

Permanent Implantable Medical Devices in Exotic Pet Medicine.

Medical devices are defined as implantable if they are intended to remain in the body after the procedure. In veterinary medicine, use of such devices is marginal but may find some indications. Use in exotic pet medicine is even more challenging due to size restriction and the limited data available. This review focuses on the esophageal and tracheal stent in the case of stricture, ureteral stent and subcutaneous ureteral bypass in the case of ureteral obstruction, permanent urinary diversion in the case of bladder atony, and pacemaker in the case of severe arrythmias. Comparative aspects are developed.

Non-hyaluronic acid fillers.

Fillers are numerous, and the products currently available have effects that may last from a few months to many years. These are used to treat facial wrinkles, and some of the new fillers exert a stimulatory effect, restoring volume in focal areas of the face by inducing collagen fibers. The dermasurgeon should thoroughly understand the indications and uses of these fillers to meet fully a patient's expectations. Some fillers are biodegradable (12-18 months), others slowly biodegradable (2-5 years), whereas others are permanent implants. The disadvantage of the traditional biodegradable fillers is their short duration (6-12 months). Over the past decade, semipermanent fillers (polylactic acid and ceramics) have been used: they do have a longer effect, but they might induce granulomas especially on the lips. Also, permanent fillers are traditionally linked to a higher incidence of granulomas and extrusions, although with the new formulations, the adverse events are decreased.