Tissue response and in vivo degradation of selected polyhydroxyacids: polylactides (PLA), poly(3-hydroxybutyrate) (PHB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/VA)

Biocompatibilities and biodegradation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s produced by a model metabolic reaction-based system

Background

This study evaluated the biocompatibilities of random and putative block poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s (PHBVs) produced by a metabolic reaction-based system. The produced PHBVs were fractionated, and the copolymer sequence distributions were analyzed using ¹H and ¹³C NMR spectroscopy. The thermal properties were analyzed using differential scanning calorimetry (DSC). Mechanical tests were conducted using a universal testing machine. The in vitro cytotoxicities of films composed of random PHBVs and putative block PHBVs were investigated against three types of mammalian cells. The surfaces of the copolymer films and the morphologies of the cells were qualitatively monitored using scanning electron microscopy (SEM) and atomic force microscopy (AFM).

Results

Films composed of poly(3-hydroxybutyrate) (PHB), random PHBVs, putative block PHBVs, polystyrene and polyvinylchloride were prepared and characterized. The diad and triad sequence distributions indicated that the PHBVs produced via the fed-batch cultivation using two different feed systems resulted in two types of copolymers: random PHBVs and putative block PHBVs. The monomer compositions and sequence distributions strongly affected the thermal and mechanical properties. The mechanical integrity and characteristics of the film surfaces changed with the HV content. Notably, the random PHBVs possessed different mechanical properties than the putative block PHBVs. The biocompatibilities of these films were evaluated in vitro against three types of mammalian cells: L292 mouse connective tissue, human dermal fibroblast and Saos-2 human osteosarcoma cells. None of the PHBV films exhibited cytotoxic responses to the three types of mammalian cells. Erosion of the PHA film surfaces was observed by scanning electron microscopy and atomic force microscopy. The production of transforming growth factor-β-1 and interleukin-8 was also examined with regards to the usefulness of PHB and PHBV as biomaterials for regenerative tissue. The production of IL-8, which is induced by PHB and PHBVs, may be used to improve and enhance the wound-healing process because of deficiencies of IL-8 in the wound area, particularly in problematic wounds.

Conclusion

Taken together, the results support the use of PHB and the random and putative block PHBVs produced in this study as potential biomaterials in tissue engineering applications for connective tissue, bone and dermal fibroblast reconstruction.

Interrelationship between bone substitution materials and skeletal muscle tissue

Bone density and quantity are primary conditions for the insertion and stability of dental implants. In cases of a lack of adequate maxillary or mandibulary bone, bone augmentation will be necessary. The use of synthetic bioactive bone substitution materials is of increasing importance as alternatives to autogenously bone grafts. It is well known that bone can influence muscle function and muscle function can influence bone structures. Muscles have a considerable potential of adaptation and muscle tissue surrounding an inserted implant or bone surrogate can integrate changes in mechanical load of the muscle and hereupon induce signaling cascades with protein synthesis and arrangement of the cytoskeleton. The Musculus latissimus dorsi is very often used for the analyses of the in vivo biocompatibility of newly designed biomaterials. Beside macroscopically and histologically examination, biocompatibility can be assessed by analyses of the biomaterial influence of gene expression. This review discusses changes in the fiber type distribution, myosin heavy chain isoform composition, histological appearance and vascularization of the skeletal muscle after implantation of bone substitution materials. Especially, the effects of bone surrogates should be described at the molecular-biological and cellular level.

Poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) scaffolds coated with PhaP-RGD fusion protein promotes the proliferation and chondrogenic differentiation of human umbilical cord mesenchymal stem cells in vitro

Human umbilical cord blood-derived mesenchymal stem cells (hUC-MSCs) have been widely used in tissue engineering. The aim of this study is to evaluate the ability of poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) scaffolds coated with polyhydroxyalkanoate binding protein fused with arginyl-glycyl-aspartic acid (PhaP-RGD) to promote the proliferation and chondrogenic differentiation of hUC-MSCs seeded on them. The PhaP-RGD fusion protein was expressed by Escherichia coli. PHBHHx films were coated with PhaP-RGD fusion protein and the physiochemical properties were examined. hUC-MSCs were seeded on PHBHHx films with or without PhaP-RGD precoating and tested for changes in morphology, viability, and chondrogenic differentiation. We found that PhaP-RGD-coated PHBHHx films had similar surface morphology to uncoated PHBHHx. The water contact angle of the coated PHBHHx surface was lower than that of the uncoated surface (10.63° vs. 98.69°). At 7 and 14 days after seeding, the PhaP-RGD-coated PHBHHx group showed greater numbers of viable cells compared to the uncoated PHBHHx group. The expression levels of aggrecan and collagen II were enhanced in the PhaP-RGD-coated PHBHHx group relative to the uncoated PHBHHx group. Histological analysis using toluidine blue staining showed elevated formation of proteoglycan producing chondrocytes in the PhaP-RGD-coated PHBHHx group. Additionally, the synthesis of proteoglycan and collagen was significantly enhanced within the PhaP-RGD constructs. Taken together, PhaP-RGD coating promotes the proliferation and chondrogenic differentiation of hUC-MSCs seeded on PHBHHx films. PhaP-RGD-coated PHBHHx may be a useful scaffold for cartilage tissue engineering.

Evaluation of local cancellous bone amelioration by poly-L-DL-lactide copolymers to improve primary stability of dental implants: a biomechanical study in sheep

OBJECTIVES

The aim of this study was to evaluate the clinical performance of local cancellous bone amelioration by a 70:30 poly-(L-lactide-co-D,L-Lacide) copolymer with two different implant designs on primary stability and after 4 and 12 weeks of healing time.

MATERIAL AND METHODS

In six sheep, n = 36 implants (TH) with a conditioned, sandblasted, thermal acid-etched micro-rough surface and n = 36 implants (NB) with a highly crystalline and phosphate-enriched anodized titanium oxide surface were placed in the pelvic bone. Using an ultrasound-based process named Constant Amelioration Process (CAP), half of peri-implant trabecular bone structures were locally tested with 70:30 poly-(L-lactide-co-D,L-Lacide) copolymer in both implant groups, TH and NB. The CAP technology employs ultrasonic energy to liquefy 70:30 poly-(L-lactide-co-D,L-Lacide) which enters the inter-trabecular space, leading to local reinforcement of the cancellous bone structure after solidification of the copolymer. The CAP test group was compared with reference implants placed with the conventional site preparation according to the manufacturers' description. Primary stability was assessed by the measurement of torque-in values and implant stability quotient (ISQ; n = 18 per group). Secondary stability was analyzed by biomechanical removal torque testing after 4 and 12 weeks (n = 9 per group).

RESULTS

Insertion torque value (23.3 N cm ± 13.6) of reference TH implants demonstrated a statistically significant (P = 0.00) difference in comparison with test TH implants (41.9 N cm ± 19.5). Reference NB implants revealed a statistically significant (P = 0.03) lower insertion torque value (23.7 N cm ± 13.5) than test NB implants (39.7 N cm ± 18.6). ISQ values increased for all implants from initial implant placement until sacrifice at 12 weeks. Reference TH implants tended to result in an increase in torque values from 4 weeks (181.9 N cm ± 22.8) to 12 weeks (225.7 N cm ± 47.4). This trend could be also proven for implants of test sites (4 week: 176.8 N cm ± 24.1; 12 week: 201.5 N cm ± 53.4). For reference, NB implants a non-significant increase in removal torque values from 4 weeks (146. 7 N cm ± 18.0) to 12 weeks (170.2 N cm ± 40.4) was observed. Removal torque values of test NB implants did not increase from 4 weeks (153.3 N cm ± 21.5) to 12 weeks (146.1 N cm ± 37.5).

CONCLUSION

Biomechanical data proved significantly enhanced primary stability of dental implants after local amelioration without long-term sequelae and irrespective of implant design. After 4- and 12-week healing time, removal torque of locally test implants was as high as for control implants, and osseointegration was therefore not influenced by the CAP process. No correlation between ISQ values and torque values was found.

Dermal fillers: facts and controversies

Dermal fillers have been used for decades in soft tissue augmentation. Currently, filler implementation is among the most common minimally invasive procedures for rejuvenation and body sculpturing. There is a broad variety of filler materials and products. Despite immense experience, a number of controversies in this topic exist. Some of these controversies are addressed in this review, for example, who should perform filler injections, the difference between permanent and nonpermanent fillers, the off-label use of liquid silicone, and the role of pain reduction. Implementation of guidelines and restriction of filler use by trained physicians can improve safety for patients.

Hierarchically structured nerve guidance channels based on poly-3-hydroxybutyrate enhance oriented axonal outgrowth

Traumatic peripheral nerve lesions can cause local anesthesia, paralysis and loss of autonomic control. Reconstruction using engineered nerve guidance conduits (NGCs) is rarely successful due to the sub-optimal characteristics of the conduits. To address the demands of clinical practice, we developed a hierarchically structured NGC from slowly resorbing poly(3-hydroxybutyric acid) (P3HB). The NGC consists of a permeable single-lumen tube and melt-spun fibrillar lumen fillers. Permeable tubes were constructed from P3HB/poly(ɛ-caprolactone) (PCL) blends or poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid) (P(3HB-co-4HB)). Polyvinylpyrrolidone was used as a porogen in solvent-free thermoplastic processing, followed by selective polymer leaching. All tested material compositions showed hydrolytic degradation after 16weeks in phosphate buffered saline, whereas P3HB/PCL tubes maintained mechanical strength compared to (P(3HB-co-4HB)). The porous scaffolds allowed diffusion of large molecules (∼70kDa). In vitro studies demonstrated that mouse fibroblasts survived and proliferated inside closed porous tubes. An in vitro model of axonal regeneration using dorsal root ganglia and sympathetic cervical ganglia demonstrated that the NGCs successfully supported neuron survival and neurite outgrowth. The introduction of fibrillar lumen fillers promoted oriented neurite growth and coating with extracellular matrix proteins further increased ganglia attachment and cell migration. In this study we show that P3HB-based NGCs scaffolds have potential in long gap peripheral nerve repair strategies.

Knitted polylactide 96/4 L/D structures and scaffolds for tissue engineering: shelf life, in vitro and in vivo studies

This study covers the whole production cycle, from biodegradable polymer processing to an in vivo tissue engineered construct. Six different biodegradable polylactide 96/4 L/D single jersey knits were manufactured using either four or eight multifilament fiber batches. The properties of those were studied in vitro for 42 weeks and in 0- to 3-year shelf life studies. Three types (Ø 12, 15 and 19 mm) of cylindrical scaffolds were manufactured from the knit, and the properties of those were studied in vitro for 48 weeks. For the Ø 15 mm scaffold type, mechanical properties were also studied in a one-year in vivo experiment. The scaffolds were implanted in the rat subcutis. All the scaffolds were γ-irradiated prior to the studies. In vitro, all the knits lost 99% of their mechanical strength in 30 weeks. In the three-year follow up of shelf life properties, there was no decrease in the mechanical properties due to the storage time and only a 12% decrease in molecular weight. The in vitro and in vivo scaffolds lost their mechanical properties after 1 week. In the case of the in vivo samples, the mechanical properties were restored again, stepwise, by the presence of growing/maturing tissue between weeks 3 and 12. Faster degradation was observed with in vitro scaffolds compared to in vivo scaffolds during the one-year follow up.

Evaluation of PHBHHx and PHBV/PLA fibers used as medical sutures

Two types of fibers were prepared by using bio-based materials: a mono-filament made from poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) and a multi-filament made from poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polylactic acid (PLA) blend. The two fibers were evaluated for mechanical properties, biocompatibility and degradability for the potential application as medical sutures. The PHBHHx fiber showed remarkable biocompatibility by H.E. Stainning, with very little impact to the surrounding tissues. The degradation of the fiber was observed by SEM after implantation for 36 weeks, and the major degradation product was detected after 96 weeks. Consistently, the PHBHHx fiber maintained more than half of the mechanical properties after 96 weeks. The other fiber was prepared by twisting PHBV/PLA blend strands to a bunch, and showed high biocompatibility and relatively high degradability. The bunched structure loosed after 36 weeks of implantation. These low-cost and easily prepared fibers have great potential in medical applications, since they could avoid the formation of fibrous capsule, reduce the size of scar, and degrade into non-toxic and even beneficial products.

In vitro and in vivo bioactivity assessment of a polylactic acid/hydroxyapatite composite for bone regeneration

Synthetic bone graft substitutes based on composites consisting of a polymer and a calcium-phosphate (CaP) ceramic are developed with the aim to satisfy both mechanical and bioactivity requirements for successful bone regeneration. In the present study, we have employed extrusion to produce a composite consisting of 50 wt.% poly(D,L-lactic acid) (PLA) and 50 wt.% nano-sized hydroxyapatite (HA) powder, achieving homogeneous distribution of the ceramic within the polymeric phase. In vitro, in both a simulated physiological saline (SPS) and a simulated body fluid (SBF), a greater weight loss was observed for PLA/HA than for PLA particles upon 12-week immersion. Furthermore, in SPS, a continuous release of calcium and phosphate from the composite was measured, whereas in SBF, decrease of the amount of the two ions in the solution was observed both for PLA and PLA/HA accompanied with the formation of a CaP layer on the surface. In vitro characterization of the composite bioactivity was performed by culturing human mesenchymal stromal cells (hMSCs) and assessing proliferation and osteogenic differentiation, with PLA as a control. Both PLA/HA composite and PLA control were shown to support hMSCs proliferation over a period of two weeks. In addition, the composite significantly enhanced alkaline phosphatase (ALP) activity of hMSCs in osteogenic medium as compared with the polymer control. A novel implant design was employed to develop implants from dense, extruded materials, suitable for testing osteoinductivity in vivo. In a preliminary study in dogs, PLA/HA composite implants induced heterotopic bone formation upon 12-week intramuscular implantation in all animals, in contrast to PLA control, which was not osteoinductive. Unlike in vitro, a more pronounced degradation of PLA was observed in vivo as compared with PLA/HA composite.

Biomedical applications of polyhydroxyalkanoates, an overview of animal testing andin vivoresponses

Polyhydroxyalkanoates (PHAs) have been established as biodegradable polymers since the second half of the twentieth century. Altering monomer composition of PHAs allows the development of polymers with favorable mechanical properties, biocompatibility and desirable degradation rates, under specific physiological conditions. Hence, the medical applications of PHAs have been explored extensively in recent years. PHAs have been used to develop devices, including sutures, nerve repair devices, repair patches, slings, cardiovascular patches, orthopedic pins, adhesion barriers, stents, guided tissue repair/regeneration devices, articular cartilage repair devices, nerve guides, tendon repair devices, bone-marrow scaffolds, tissue engineered cardiovascular devices and wound dressings. So far, various tests on animal models have shown polymers, from the PHA family, to be compatible with a range of tissues. Often, pyrogenic contaminants copurified with PHAs limit their pharmacological application rather than the monomeric composition of the PHAs and thus the purity of the PHA material is critical. This review summarizes the animal testing, tissue response, in vivo molecular stability and challenges of using PHAs for medical applications. In future, PHAs may become the materials of choice for various medical applications.

Application of Biodegradable Polyhydroxyalkanoates as Surgical Films for Ventral Hernia Repair in Mice

The cytotoxicity and biosafety of poly-(3-hydroxybutyrate) (P3HB) and poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HBV) films were investigated in vitro using 3T3 fibroblast cells and in vivo through subcutaneous implantation of the film in mice. The in vitro test revealed that endotoxin-free P3HB and P3HBV films allowed cell attachment and growth. Film-soaked conditional media showed no significant inhibitory or cytotoxic effects on cell proliferation. The in vivo absorption test showed that both the P3HB and P3HBV films slowly degraded and that P3HB had a slower degradation rate than that of P3HBV. Applying a P3HB film in hernia repair demonstrated a favorable outcome: the film was able to correct the abdominal ventral hernia by inducing connective tissue and fat ingrowth and exhibited an extremely slow rate of degradation. Furthermore, the P3HB film demonstrated the advantage of lower intestinal adhesion to the ventral hernia site compared with the P3HBV and PP commercial films.

Permeability of Porous Poly(3-hydroxybutyrate) Barriers of Single and Bilayer Type for Implant Applications

Poly(3-hydroxybutyrate) (PHB) is a polyester which shows excellent biocompatibility and a PHB material is therefore considered suitable for many biomedical applications. A highly porous PHB material may be designed to facilitate the transport of small molecules and body fluids or serve as a biocompatible temporary barrier. In this study, PHB films with varying degree of porosity and pore interconnectivity were made by solvent casting using water-in-oil emulsion templates of varying composition. The morphology was characterized by SEM and the water permeability of the films was determined. The results show that an increased water content of the template emulsion resulted in a film with increased porosity. A fine tuning of the film morphology of the casted films was achieved by varying the salt content of the water phase of the template emulsion. The porosity of these films was roughly the same but the water permeability varied between23·10-13and1486·10-13 m2/s. It was concluded that the major determinant of the water permeability through these films is the pore interconnectivity. Furthermore, we report on the formation and water permeability of bilayer PHB films consisting of a porous layer combined with a dense backing layer.

Poly(4-hydroxybutyrate) (P4HB) production in recombinant Escherichia coli: P4HB synthesis is uncoupled with cell growth

BACKGROUND

Poly(4-hydroxybutyrate) (P4HB), belonging to the family of bacterial polyhydroxyalkanoates (PHAs), is a strong, flexible and absorbable material which has a large variety of medical applications like tissue engineering and drug delivery. For efficient production of P4HB recombinant Escherichia coli has been employed. It was previously found that the P4HB synthesis is co-related with the cell growth. In this study, we aimed to investigate the physiology of P4HB synthesis, and to reduce the total production cost by using cheap and widely available xylose as the growth substrate and sodium 4-hydroxybutyrate (Na-4HB) as the precursor for P4HB synthesis.

RESULTS

Six different E. coli strains which are able to utilize xylose as carbon source were compared for their ability to accumulate P4HB. E. coli JM109 was found to be the best strain regarding the specific growth rate and the P4HB content. The effect of growth conditions such as temperature and physiological stage of Na-4HB addition on P4HB synthesis was also studied in E. coli JM109 recombinant in batch culture. Under the tested conditions, a cellular P4HB content in the range of 58 to 70% (w w(-1)) and P4HB concentrations in the range of 2.76 to 4.33 g L(-1) were obtained with a conversion yield (Y(P4HB/Na-4HB)) of 92% w w(-1) in single stage batch cultures. Interestingly, three phases were identified during P4HB production: the "growth phase", in which the cells grew exponentially, the "accumulation phase", in which the exponential cell growth stopped while P4HB was accumulated exponentially, and the "stagnation phase", in which the P4HB accumulation stopped and the total biomass remained constant.

CONCLUSIONS

P4HB synthesis was found to be separated from the cell growth, i.e. P4HB synthesis mainly took place after the end of the exponential cell growth. High conversion rate and P4HB contents from xylose and precursor were achieved here by simple batch culture, which was only possible previously through fed-batch high cell density cultures with glucose.

Tissue engineering in the vasculature

Tissue engineering holds great promise to address complications and limitations encountered with the use of traditional prosthetic materials, such as thrombogenicity, infection, and future degeneration which represent the major morbidity and mortality after device implant surgery. The general concept of tissue engineering consists of three main components: a scaffold material, a cell type for seeding the scaffold, and biochemical, physio-chemical signaling and remodeling process. This remodeling process is guided by cell signals derived from both seeded cells and host inflammatory cells that infiltrate the scaffold and deposit extracellular matrix, forming the neotissue. Vascular tissue engineering is at the forefront in the translation of this technology to clinical practice, as tissue engineered vascular grafts (TEVGs) have now been successfully implanted in children with congenital heart disease. In this report, we review the history, advances, and state of the art in TEVGs.

Preconditioned 70S30C bioactive glass foams promote osteogenesis in vivo

Bioactive glass scaffolds (70S30C; 70% SiO2 and 30% CaO) produced by a sol-gel foaming process are thought to be suitable matrices for bone tissue regeneration. Previous in vitro data showed bone matrix production and active remodelling in the presence of osteogenic cells. Here we report their ability to act as scaffolds for in vivo bone regeneration in a rat tibial defect model, but only when preconditioned. Pretreatment methods (dry, pre-wetted or preconditioned without blood) for the 70S30C scaffolds were compared against commercial synthetic bone grafts (NovaBone® and Actifuse®). Poor bone ingrowth was found for both dry and wetted sol-gel foams, associated with rapid increase in pH within the scaffolds. Bone ingrowth was quantified through histology and novel micro-CT image analysis. The percentage bone ingrowth into dry, wetted and preconditioned 70S30C scaffolds at 11 weeks were 10±1%, 21±2% and 39±4%, respectively. Only the preconditioned sample showed above 60% material-bone contact, which was similar to that in NovaBone and Actifuse. Unlike the commercial products, preconditioned 70S30C scaffolds degraded and were replaced with new bone. The results suggest that bioactive glass compositions should be redesigned if sol-gel scaffolds are to be used without preconditioning to avoid excess calcium release.

Current status of surgery in dermatology

An article titled "Current issues in dermatologic office-based surgery" was published in the JAAD in October 1999 (volume 41, issue 4, pp. 624-634). The article was developed by the Joint American Academy of Dermatology/American Society for Dermatologic Surgery Liaison Committee. A number of subjects were addressed in the article including surgical training program requirements for dermatology residents and selected advances in dermatologic surgery that had been pioneered by dermatologists. The article concluded with sections on credentialing, privileging, and accreditation of office-based surgical facilities. Much has changed since 1999, including more stringent requirements for surgical training during dermatology residency, and the establishment of 57 accredited Procedural Dermatology Fellowship Training Programs. All of these changes have been overseen and approved by the Residency Review Committee for Dermatology and the Accreditation Committee for Graduate Medical Education. The fertile academic environment of academic training programs with interaction between established dermatologic surgeons and fellows, as well as the inquisitive nature of many of our colleagues, has led to the numerous major advances in dermatologic surgery, which are described herein.

Influence of the molecular weight of poly(lactide-co-glycolide) on the in vivo cartilage repair by a construct of poly(lactide-co-glycolide)/fibrin gel/mesenchymal stem cells/transforming growth factor-β1

The poly(lactide-co-glycolide) (PLGA, LA/GA 75/25) sponges with different weight average molecular weights (Mw 52, 122, and 177 kDa) were fabricated and were used to build the constructs of PLGA/fibrin gel/mesenchymal stem cells (MSCs)/transforming growth factor-β1 (TGF-β1). The PLGA 177 with the highest Mw (177 kDa) had the fastest degradation rate at the initial stage, whereas the PLGA 122 had the moderate degradation rate and smallest mass loss. After implantation in rabbit knees for 12 weeks, the full-thickness defects (both cartilage and subchondral bone were destroyed with a diameter and depth of 4 mm) repaired by the PLGA 122 group had formed a hyaline cartilage-like tissue with abundant glycosaminoglycans on the top layer and subchondral bone on the bottom layer. The group also achieved the best macroscopic (11.3 ± 0.8) and histological scoring (Wakitani, 0.5 ± 0.6). To unveil the mechanism of the cartilage repair outcome and the PLGA degradation behaviors, the chondrogenesis-related genes, inflammatory cytokines, and matrix metalloproteinase (MMP) activity were analyzed by quantitative reverse transcription-polymerase chain reaction at week 1, 3, and 6 postsurgery. At each time point, the regenerated tissues by the PLGA 122 group had the highest mRNA expression of SOX9 and collagen type II, but the smallest mRNA expression of interleukin-1β and tumor necrosis factor α, and MMP-13 and MMP-3. In summary, as a scaffolding matrix, the PLGA with different Mw shows a huge difference in cartilage regeneration in vivo. The one with a moderate Mw (122 kDa) causes the weakest inflammatory response and results in the best cartilage regeneration.

Current treatment methods for combination antiretroviral therapy-induced lipoatrophy of the face

Summary

Combination antiretroviral therapy (CART) reduces the mortality and morbidity in HIV-infected patients. However, facial lipoatrophy (FLA) is one of the well-known side-effects of this treatment and subsequently imposes major problems for HIV-infected patients. In the last decade, ample experience has been obtained with both local therapeutic options as well as possible systemic treatment options. Soft tissue fillers are a relatively simple and efficient treatment option for FLA. Especially, the biodegradable semi-permanent fillers combine a good effect with durability and an acceptable safety profile. The best way to prevent or restrict the development of FLA remains the exclusion of thymidine analogue nucleoside reverse-transcriptase inhibitors from the CART schedule.

A novel approach to structural facial volume replacement

Improved understanding of the anatomy and physiology of the aging face has laid the foundation for adopting an earlier and more comprehensive approach to facial rejuvenation, shifting the focus from individual wrinkle treatment and lift procedures to a holistic paradigm that considers the entire face and its structural framework. This article presents an overview of a comprehensive method to address facial aging. The key components to the reported strategy for improving facial cosmesis include, in addition to augmentation of volume loss, protection with sunscreens and antioxidants; promotion of epidermal cell turnover with techniques such as superficial chemical peels; microlaser peels and microdermabrasion; collagen stimulation and remodeling via light, ultrasound, or radiofrequency (RF)-based methods; and muscle control with botulinum toxin. For the treatment of wrinkles and for the augmentation of pan-facial dermal lipoatrophy, several types of fillers and volumizers including hyaluronic acid (HA), autologous fat, and calcium hydroxylapatite (CaHA) or injectable poly-L-lactic acid (PLLA) are available. A novel bimodal, trivector technique to restore structural facial volume loss that combines supraperiosteal depot injections of volume-depleted fat pads and dermal/subcutaneous injections for panfacial lipoatrophy with PLLA is presented. The combination of treatments with fillers; toxins; light-, sound-, and RF-based technologies; and surgical procedures may help to forestall the facial aging process and provide more natural results than are possible with any of these techniques alone.

LEVEL OF EVIDENCE V

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Application of poly-L-lactic acid nanosheet as a material for wound dressing

The authors evaluated the efficacy of an ultrathin nanosheet consisting of poly-L-lactic acid (75 nm thick) as a wound dressing material. A full-thickness skin defect was made on the backs of mice and overlapped with or without the poly-L-lactic acid nanosheet. Wound healing was more rapidly improved by overlapping with the nanosheet, especially in the early healing period (at 4 to 6 days). The remaining wound area in the treatment group was significantly smaller at 4 days than in the control group. Histologically, a clear layer was observed over the granulation layer by the nanosheet therapy at 4 days. Thus, overlapping therapy with the poly-L-lactic acid nanosheet accelerated wound healing and formed a clear layer just above the granulation tissue. The poly-L-lactic acid nanosheet may have potential as a novel wound dressing to promote wound healing.

Techniques for the optimization of facial and nonfacial volumization with injectable poly-l-lactic acid

With the recognition of the key role of volume loss in the facial aging process, injectable dermal fillers and volumizers have become increasingly important treatment options for recontouring and rejuvenating the aging face. While replacement fillers effectively correct individual lines and wrinkles, volumizing agents that replace collagen provide a longer-lasting, volume-based alternative. Poly-L-lactic acid (PLLA) has been shown to increase dermal thickness and volume for up to 2 years and beyond. Although early clinical use of this agent in patients with HIV-associated facial lipoatrophy was associated with a significant rate of nodule or papule formation, subsequent experience has helped define the proper reconstitution volumes and injection techniques for optimizing results and minimizing nodule/papule formation. While injectable PLLA has been used successfully for rejuvenation of most facial areas, increasing experience suggests that it is a versatile agent capable of providing aesthetic enhancement in multiple areas of the body, including the dorsum of the hands, the décolleté, the neck, the buttocks, the medial ankles, and acne scars. Although the current published experience in these areas is limited, further studies and clinical use of injectable PLLA will clarify the potential of this agent as a minimally invasive alternative and/or adjunct to surgery for restoring volume loss in multiple anatomic areas.

LEVEL OF EVIDENCE V

This journal requires that authors assign a level of evidence to each article.

Degradation of P(3HB) and P(3HB-co-3HV) in biological media

The biodegradability of oriented fibers made of polyhydroxybutyrate (P(3HB)) and its co-polymer with beta-hydroxyvalerate (P(3HB-co-3HV)) was investigated in buffer solutions and in biological media in vitro and in vivo. The fibers of both polymer types demonstrated resistance to hydrolytic degradation in buffer solutions at 38 degrees C and pH from 4.5 to 7.0 (for up to 180 days). It has been found that the biodegradation of the fibers in vitro in blood and serum and in vivo is accompanied by weight losses and minor changes in the microstructure with no significant losses in the tensile strength over a long time (up to 180 days). The biodegradation rate of the less crystalline co-polymer P(3HB-co-3HV) fibers was 1.4-2.0-times higher than that of the homopolymer P(3HB). It has also been shown that the degradation of the fibers in vivo is influenced both by tissue fluid enzymes and cells (macrophages and foreign-body giant cells). The fibers were eroded on the surface only with no gross defects and no dramatic effects on their mechanical performance.

Optimizing Injectable Poly-L-Lactic Acid Administration for Soft Tissue Augmentation: The Rationale for Three Treatment Sessions

BACKGROUND

The availability and variety of different injectable modalities has led to a dramatic increase in soft tissue augmentation procedures in recent years. Injectable poly-L-lactic acid (PLLA) is a synthetic, biodegradable polymer device approved in the United States for use in immunocompetent patients as a single regimen of up to four treatment sessions for correction of shallow to deep nasolabial fold contour deficiencies and other facial wrinkles. Injectable PLLA is also approved for restoration and/or correction of signs of facial fat loss (lipoatrophy) in individuals with HIV.

METHODS

The present article provides an overview of previous studies with injectable PLLA, and specifically focuses on the number of recommended treatment sessions and intervals between treatment sessions. The authors also provide two case studies to support their recommendations for an average of three treatment sessions.

RESULTS

Although the specific mechanisms remain hypothetical, injections of PLLA are believed to cause a cascade of cellular events that lead to collagen repair and subsequent restoration of facial volume. Because the development of a response to injectable PLLA is gradual and its duration of effect is long lasting, sufficient time between treatment sessions should be allocated to avoid overcorrection.

CONCLUSION

Studies of injectable PLLA support the hypothesized mode of operation, and the experience and clinical recommendations of the authors that suggest that three treatment sessions are an optimal regimen for use of injectable PLLA in the majority of patients.

Orthopedic implant of a polyhydroxybutyrate (PHB) and hydroxyapatite composite in cats

The purpose of this study was to evaluate the tissue response to a 70% polyhydroxybutyrate and 30% hydroxyapatite composite in the form of a bone implant, placed intracortically in the distal metaphyseal of the right femur, and subcutaneous implants in cats. Samples of the composite were implanted subcutaneously in the dorsolumbar region and the distal metaphyseal region of the right femur of the animals. The study used 12 neutered adult mixed breed cats, weighing an average of 3.5kg. The cats were randomly divided into three groups: GI, GII and GIII, according to the length of the assessment period. The assessments of their subcutaneous and bone tissues were performed at 15, 30 and 45 days and at 30, 60 and 90 days, respectively. The subcutaneous and bone reactions to the composites were characterized by granulomatous inflammation with a predominance of macrophages and giant cells. The results showed that the composites triggered a chronic local inflammatory response, despite their clinical acceptance.